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Calcium carbonate fouling on double-pipe heat exchanger with different heat exchanging surfaces
Abstract
An experimental setup of double pipe heat exchanger fouling test rig was built to investigate the mineral scale deposition on different heat exchanger pipe surfaces. Progressive fouling deposition on different material surfaces under the similar solution conditions were observed and analyzed. Measurable data on the progressive build-up of scale deposits, deposition rate, as well as the composition and crystal morphology of the deposits were studied after each experimental run by analyzing the deposited scale on the test pipes. In this research the artificial calcium carbonate deposit on different material surfaces is considered as it is one of the major constituents of the most scales found in heat exchanging equipment. Fouling on different smooth test pipes were investigated in the centrally located larger concentric pipe heat exchanger. Uniform flow condition near the pipe surface was maintained by constant flow rate throughout the system. The calcium carbonate deposition rates on five different metal surfaces (Stainless steel 316, brass, copper, aluminium and carbon steel) were investigated. The results illustrated an upward trend for fouling rate with time on the tested specimens. The deposition on the surfaces showed a linear growth with the enhancement of thermal conductivity of the metals. However, deposition on carbon steel metal surfaces did not follow the typical linear trend of thermal conductivity over deposition as its surface was altered by corrosion effects. In addition, temperature, velocity, and concentration effects on fouling deposition were investigated on the SS316 metal surface. It is noted that the fouling deposition increases with the increase of temperature and concentration due to enhanced deposition potential whereas reduces due to the increase of velocity which enhances shear stress.
... Although nanofluids enhance radiative heat transfer and thermal conductivity, studies of nanoparticle stability in FPSWH are limited to considering that nanofluids are viable [41]. As state above, mitigating the impact of pipe fouling in nanofluid systems is essential to ensure optimal performance and efficiency, where coating and surface treatment strategies have been proposed to reduce fouling of nanofluid pipelines, [17,[54][55][56]. Thus, the long-term progress studies of thermal efficiency stability and the nanofluid thermophysical properties drift are crucial. ...
... Mitigating the impact of-pipe fouling in nanofluid systems is essential to ensure optimal performance and efficiency. Coating and surface treatment strategies have been proposed to reduce fouling of nanofluid pipelines, [17,54,55,137]. Fouling mitigation on heat exchanger surfaces is by adding water-based nanofluids with EDTA (ethylenediaminetetraacetic acid) treated MWCNTs, which involve adherent deposits of nanoparticles [54]. In addition, in heat exchangers, coatings based on titanium, silicon and polymers have shown fouling reduction by modifying the surface at the micro/nanoscale level [137]. ...
... Coating and surface treatment strategies have been proposed to reduce fouling of nanofluid pipelines, [17,54,55,137]. Fouling mitigation on heat exchanger surfaces is by adding water-based nanofluids with EDTA (ethylenediaminetetraacetic acid) treated MWCNTs, which involve adherent deposits of nanoparticles [54]. In addition, in heat exchangers, coatings based on titanium, silicon and polymers have shown fouling reduction by modifying the surface at the micro/nanoscale level [137]. ...
The nanofluids enhance the thermal performance of FPSC concerning conventional working fluids, improving their thermophysical properties to transfer heat. Nanofluid stability affects the long-term of FPSC's performance, and it plays a leading role in the certainty of successful projects. Most of the literature attends to the FPSC's performance over short periods versus expectations of 20-30 years. This review focusses on the thermal efficiency stability of solar water-nanofluid heaters by identifying the most common parameters and methods, as well as the nanoparticle characteristics effects, surfactant usage and fouling on the nanofluid lifetime in FPSC. Nanofluids improve thermal efficiency by 5-35% concerning conventional working fluids, reaching up to 0.85. Z-potential is an indicator to establish particle dispersion degree, which means, at the same time, the nanofluid usage time. The stability was improved by surfactant, preparation method, or nanoparticle content (0.2-0.3% volume base). Nanofluid fouling is common and significantly affects the thermal conductivity (≥11%). The widespread application of nanofluids waits for better nanoparticle dispersion over major' usage time, and stability improves at higher temperatures (>90 • C). When nanoparticle instability increases as working time goes by, its viscosity, friction forces and pressure drop also increase, so the pumping power requirement rises. In FPSC, the stability reports reach up to 2.5% of the heater's lifetime. However, stability reports reach up to 2.5% of the heater's lifetime. They must be increased by considering the most common parameters like Z-potential, preparation methods, nanoparticle characteristics, surfactant usage, and fouling to improve the certainty of successful nanofluids FPSC projects.
... The selection of a chemical cleaning technology for new equipment is relatively straightforward, as it is known in advance what type of contaminant needs to be removed [25]. However with equipment which is already in operation, the composition, structure, and thickness of the deposits can vary and depend on the operating conditions [26]. Contaminants can even be found which vary significantly from one place to another in the same equipment [27]. ...
... A chemical cleaning method has been developed in which material deposited inside thermal equipment is dissolved with the help of an innovative biodegradable preparation in which, in addition to the main decalcification component, there are corrosion inhibiting, antifoaming and antimicrobial components [26]. The growth of microorganisms on moist surfaces results in biofilm formation [27]. ...
... The growth of microorganisms on moist surfaces results in biofilm formation [27]. The effect of the uncontrolled growth of microorganisms on the surfaces of structural elements is the deposition of slime [26]. ...
... In both situations, surface deposition causes a reduction in heat transfer efficiency, increasing the power consumption and blockage of flowlines in heat transfer devices subjected to fouling [10,36,176,177]. It has been revealed that surface temperature, solution composition, flow rate and substrate nature play a role in the kinetics, adhesion and morphology of deposited scale [22,28,[178][179][180]. ...
... The solution chemistry such as salt concentration, dissolved CO2 concentration, the presence of additives, impurities and pH is also able to influence the fouling process [27,40,50,166]. Finally, surface properties like roughness, topography, surface energy and substrate metal could be utilised to accelerate or hinder the fouling process [162,178,210]. ...
... It has been found that the relationship is linear between the concentration of CaCO3 in water and scale precipitation potential, where the latter increases three times when the amount of CaCO3 increases from 100 mg.l -1 to 300 mg.l -1 [12]. Teng, et al. [178] studied the effects of water hardness on the formation of CaCO3 deposits. ...
Scale formation has long been a concern in domestic appliances such as electric boilers, steam irons, washing machines, dishwashers, coffee makers and potable water distribution systems in general. Potable water contains a variety of ions prone to precipitate over a range of concentrations depending on water quality and its geographic location. The kinetics and mechanisms of mineral scaling from potable water in the open and closed household systems have received no attention.
The present study aims to gain an understanding of the mechanisms and structure of inorganic fouling from potable water in household appliances conditions. Four experimental setups and methodologies were developed to achieve the work goals, namely boiling static setup, flow visualization rig, flow-evaporation scaling cell, and pressurised flow-evaporation scaling cell. The bulk precipitation in closed systems during pool boiling conditions was evaluated. Then, the surface deposition of inorganic minerals from potable water under the convective heat transfer was investigated. Finally, the effects of water evaporation were examined at various surface conditions, key operating conditions, and water ionic species.
The effects of solution temperature, surface material, surface roughness, evaporation area, water composition, heating and cooling rates on the bulk precipitation and surface deposition in closed systems were investigated using the boiling static setup. The solution temperature promotes the bulk precipitation and the polymorphic transformation from both calcite and vaterite to aragonite. The results also showed that the faster the cooling and heating rates the lower the scaling rate. However, CaCO3 formed in the cooling period was greater than in the heating period.
The inorganic scaling kinetics during the convective heat transfer were studied using a once-through flow visualisation setup through investigating the effects of surface temperature, material, roughness, flow rate and vapour bubbles. The study showed that all parameters, especially vapour bubbles, play a vital role in the scaling kinetics and scale morphology.
The influence of surface temperature, pressure, surface roughness and the ionic species on the fouling mechanism and structure was evaluated during the boiling convective heat transfer using the flow-evaporation scaling cell. The water species examined include sodium, chloride, magnesium, sulphate, total organic carbon (TOC) and zinc. The pressure significantly minimises the fouling resistance as well as the amount of the deposits. However, the impact of different ionic species varies from negligible to strong. Understanding the kinetics of surface deposition and bulk precipitation of inorganic minerals from potable water allows for better design and development of household appliances and systems.
... The experimental findings show that the fouling deposits in large quantities on material with higher thermal conductivity such as stainless steel, aluminum, brass, and copper. However, fouling on carbon steel metal failed to comply the linear trend due to corrosion effects [42]. Fouling on cooper tubes with different structures (smooth, superhydrophobic and liquid inner surfaces) was characterized leading to new theoretical and practical guidance [26,43]. ...
... In our study, the fouling properties resulting from the presence of multiple salts simulating a real cooling water. In contrast, the literature often focuses solely on the properties of CaCO 3 fouling [38,42,81]. This variation in fouling composition can lead to difference in thermal conductivity and densities (as seen in the Table.5). ...
In this paper, structural, chemical, and thermos-physical characteristics of fouling and tube materials for hybrid
cooling tower bundles in Concentrated Solar Power (CSP) facilities are addressed. Toward an in-depth understanding and a comparison of the fouling mechanism on galvanized steel and polymer tubes, results obtained
from the characterization studies and the experimental test correlations were used to calculate the sticking
probability (P) and deposit bond strength (ξ) based on the Kern-Seaton model. According to the data, the polymer
tube had three times higher the adhering probability of the galvanized steel tube with a value of PPf = 3.15*102
Ns/m2
, whereas the deposit bond strength was two times lower with a value of ξPf = 3.49*10− 8
. The results
revealed that when it comes to polymer tubes, the ones with a finer surface structure tend to attract foulants from
deluge water more readily. However, once foulants are attached to the heat transfer surface, it's simpler to be
removed. The substantial increase in kaolinite and gypsum phases can explain this occurrence. On the other
hand, galvanized tubes, exhibit the opposite behavior. It is anticipated that this constructive study will shed light
on performance-enhancing fouling mechanisms and offer a scientific basis for thermal engineers.
... In recent years, surface material and its morphology has enhanced the interest of researchers and is considered as one of the important influencers in crystallization fouling. Teng et al. [50] characterized the behaviour of various surface materials for the study of CaCO 3 crystallization fouling using double-pipe heat exchanger. The results illustrated the linear growth relationship among the rising thermal conductivity of studied surface and foulant deposition. ...
... They also performed the experiments on addition of Arabic gum as additive which produced similar results on fouling inhibition as shown in Fig. 14 [98]. Teng et al. studied CaCO 3 fouling mitigation with the addition of EDTA [99] and DTPA [50] treated MWCNT-based nanofluid and obtained encouraging results as presented in Fig. 15, EDTA and DPTA treated MWCNT reduced the deposition of CaCO 3 on heat exchanger surface. Longer induction period was produced due to the increase in additive concentration, the calcium ion adsorption by additive was improved. ...
A wide range of industrial processes (i.e., evaporation and condensation in desalination process, steam power plant, solar plant, etc.) involve heat transfer among the fluids. During the process of evaporative and cooling heat transfer, undesirable materials from the fluids accumulate on the surfaces, which critically reduces the performance of heat exchangers and creates one of the biggest challenges in energy transfer. Though the various studies on prediction and removal of fouling was conducted by numerous scientists, this problem is still unresolved in industrial process and is responsible for huge environmental damage and economic losses. This investigation provides a comprehensive overview of crystallization fouling in heat exchangers. Various factors affecting the deposition of crystallization foulaning such as fluid temperature, flow velocity, surface material and roughness, concentration and boiling are systematically reviewed. Accuracy and uncertainty of different equipment and experimental studies are discussed. In addition, fouling modelling is comprehensively discussed from earlier fundamental model to recent computational fluid dynamic and artificial neural networks model. Furthermore, mitigation of fouling with off-line and online approaches are chronologically discussed. Finally, an overview from environmental and economic prospective of fouling in heat exchangers are discussed. The future directions for crystallization fouling in heat exchangers are emphasized, which will support the researchers and industries to retard fouling and achieve economic benefits.
... 9 For instance, cooling water used in HE tends to deposit salts such as calcium sulfate and calcium carbonate onto the inner surface of condenser tubes, gradually reducing heat transfer performance, surface thermal conductivity, and condenser efficiency, with substantial economic consequences. 10 A higher rate of fluid velocity (Re > 12,000) causes reduced fouling deposition and significant foulant removal. 11 Several experimental studies reveal the direct dependence of fouling deposition on heat transfer surfaces to the foulant concentration in the fluid. ...
... 35 The cost function is formulated using two control objectives describing the tracking error (J e ) and change in input (J ΔU ) as in (9). The tracking error is quantified by using the squared difference between the reference/setpoint (T sp so ) and predicted HE behavior ( b T so ) for a finite duration indicated by the prediction horizon (p) as in (10). The change in tube side mass flow rate (m t ) from the nominal value (m SS t ) is determined over the finite control horizon (m) as in (11). ...
Fouling is an inevitable phenomenon that tends to change the dynamics of the heat exchanger (HE). An accurate prediction model describing these varying HE dynamics is demanded to implement model predictive control (MPC), which has been addressed in this work. A novel iterative quality weighted interpolation (IQWI) technique is proposed to determine the prediction model from the linear parametric varying (LPV) model. It uses a set of linear state‐space (SS) models, which have been identified from the input–output data of the industrial HE under various fouling conditions. The quality of the identified models is assessed using a fuzzy inference system (FIS) based on fit percentage and data quality. IQWI technique uses incremental thresholds for the model quality to iteratively generate interpolation curves. Each interpolation curve is capable of estimating the model parameters, which are fused using the distance weighted method to determine the optimal model parameters. The proposed technique is capable of improving the model accuracy by 24.43%. The use of a fouling‐based prediction model equips the MPC with accurate knowledge of HE dynamics, which enables it to provide efficient control. Experimental analysis under five different fouling conditions and comparative analysis with the existing controller indicates the efficiency of the proposed method.
... CaCl 2 and NaHCO 3 were used in proportionate amounts in distilled water to create a fouling solution that contained 300 mg/L of CaCO 3 [44]. The graphical presentation of CaCO 3 preparation from the reaction of CaCl 2 and NaHCO 3 in water is illustrated in Figure 5 [45]. ...
Fouling and corrosion mitigation in heat exchange equipment remains a significant challenge. Numerous research techniques have been developed to address this issue. Surface modification is an effective method for preventing fouling and corrosion. This work used electrodeposition and dip coating techniques to create a nickel–graphene/polytetrafluoroethylene (NGP) composite hydrophobic coating. The field emission scanning electron microscopy, contact angle analyzer, X-ray photoelectron spectroscopy, energy dispersive spectroscopy, and atomic force microscopy techniques were used to investigate the surface morphologies, wettability, binding energies, chemical compositions, and roughness, respectively. The water contact angle (WCA) of the NGP hydrophobic coating (147.1° ± 2.2°) was significantly higher than the WCA of carbon steel (76.8° ± 1.6°). Electrochemical impendence spectroscopy results showed that the NGP composite hydrophobic coating has improved anti-corrosion performance with a greater capacitive curve, a higher modulus of impedance value at low frequency, and increased charge transfer resistance. Furthermore, fouling testing at various temperatures exhibited the anti-fouling and anti-corrosion behavior of the NGP composite hydrophobic coating, suggesting possible uses in practical applications.
... These studies reveal that the interactions between inhibitors and calcite surfaces are pivotal to their anti-scaling properties (Dong et al., 2020;Li et al., 2022Li et al., , 2023Mohammed et al., 2022). Nevertheless, investigations into the deposition and surface interaction mechanisms of the initial scale layer under diverse conditions, including varying water chemistries, remain significantly limited (Chen et al., 2005;Teng et al., 2017). ...
... One paper found that crystal growth increases with surface temperature and decreases with increasing flow velocity [60]. The fouling rate increases with higher surface temperature [61,62], higher differential temperature [61,63], and lower flow rate [61,64,65]. Research showed that the wetting area of a falling film is reduced at low temperatures and flow rates due to film shrinkage, especially at the bottom of the heating surface [66]. ...
The reduction of the specific effluent discharge volumes of paper mills leads to concentrated process waters that are difficult to treat. Evaporation is an effective water reclamation technology; however, its feasibility largely depends on the fouling behavior of the calcium rich process water. A pilot plant study was conducted to investigate fouling of an evaporator processing the production water from a recycled containerboard mill. The evaporator was operated continuously for five weeks at an evaporation temperature of 55°C and a differential temperature of 5°C, and with a recovery rate of approximately 90%. The calcium ion concentration of the circulating liquor exceeded 7,000 mg/L with a pH of 6. Despite the high fouling potential of the circulating liquor, the heat transfer coefficient did not decline over the investigated trial. The absence of deposits on large areas of the heating surfaces demonstrate that the process water does not generally form deposits under the conditions that were investigated. Calcium sulfate deposits were only found in areas where there was inadequate coverage of liquid over the heating surfaces. The findings show that evaporators can be used to effectively close the water system of recycled containerboard mills without fouling impacting the energy efficiency. Application: This work demonstrates for the first time, in a long-duration pilot plant study, the successful use of evaporation to reclaim water from the process water of a recycle containerboard mill without negative impact on its energy balance. For this purpose, a custom-built low-temperature vacuum evaporator pilot plant was installed on-site at a paper mill to investigate operation, selective separation efficiency, and feasibility under relevant conditions.
... The accumulated sediments reduce the efficiency of equipment operation, as well as transmission capacities, which cause an increase in energy needed for pumping water. The fundamental factors associated with the formation of accretions can be [1][2][3]: • speed; the higher the speed the lower the chance of creating sediment, ...
... One example is dairy drinks. In the sterilization process in HE at a temperature >100 o C, different results were found, namely: (i) protein content was greater than mineral content and fat content was found to be the least (protein > mineral > fat) [1][2][3][4][5][6] and (ii) Mineral> protein> fat [7,8]. In the sterilization process in HE at a temperature of 100-140 o C also found different results, namely: (i) protein > mineral > fat [4,[9][10][11] and (ii) Mineral> protein> fat [9,12,13]. ...
Background: This research was motivated by the determination of the sanitation schedule in the heat exchanger area for some products (milk, avocado juice, and orange juice), as well as the inconsistency of the results of previous studies related to the chemical composition of the fouling layer. Objectives: a) to test the effect of raw material composition on the chemical composition of the fouling layer. b) to test microbial growth's effect on fouling's chemical composition (protein). Methods: mathematical derivation of the formation process of Resistant Dirt Factor (Rd) in the form of an Equation; ANOVA was used to test the effect of the dependent variable (protein) and predictor (microbial). Results: a) The composition of the raw material strongly influences the chemical composition of the fouling layer; b) There is a strong effect between microbial growth and protein content as a fouling composition (p<0.05). Conclusion: A strong influence between microbial growth and the composition of the fouling layer (protein) can close the research gap related to the inconsistency of previous research results (fouling layer composition), so there is no prolonged debate.
... Han et al. [26] showed that the operating factors had a significant effect on the morphology of the fouling, so that vaterite at the high flow rate (0.9 l/min) and low concentration of calcium chloride have a significant share of polymorphs formed, while increasing temperature has increased the share of aragonite polymorphs. Putranto et al. [27] stated that with increasing temperature from 27 °C to 50 °C, the crystalline phase of CaCO 3 changed from vaterite to aragonite, but Teng et al. [28] showed that the simultaneous presence of calcite and vaterite was observed on all tested metals, but no aragonite was found in the test conditions. Chen and Xiang [29] suggested that decreasing the [CO 3 ...
Several experiments have been performed to investigate the effects of operational parameters such as bulk temperature, heat flux, and fluid flow rate on calcium carbonate (CaCO3) fouling under single phase forced convection (FC) and two-phase subcooled flow boiling (SFB) conditions. Since no particle filtration was performed in the experimental loop, the presence of suspended particles in the solution caused the formation of particulate fouling along with crystallization fouling. The obtained combined crystallization and particulate fouling complicated the analysis of the effects of the parameters which has been rarely studied. Results show that contrary to previous findings, no induction period was observed, and the fouling curves had an asymptotic trend like the particulate fouling curves. On the other hand, contrary to other observations considered the effects of bubble formation on the crystallization fouling as the cause of fouling intensification, in the present study, bubbles mitigated fouling formation. In addition, although CaCO3 is a reverse solubility salt, it was observed that increasing heat flux decreased the amount of deposition. It is mainly due to the formation of more aragonite polymorphs at higher heat fluxes, which are more brittle and more easily removed by bubbles activity at high fluxes.
... It is said that the reason for this is that the accumulation is directly proportional to the increase in the thermal conductivity coefficient of the metal surfaces. The finding in SS316 metal is that the increase in the concentration with temperature increased the precipitation and since the shear stress linearly increased with the flow rate, it was also observed that the fouling decreased (Teng et al., 2017).In refineries where intense inorganic concentrations are followed, a thermo-hydraulic method was used to examine the fouling character in heat exchangers. As a result, it was stated in the study that it is an advanced model for the fouling problem and its diagnosis (Diaz-Bejarano et al., 2017).A common problem in environments with high particulate fouling in plate heat exchangers in aircrafts have been considered. ...
... It is said that the reason for this is that the accumulation is directly proportional to the increase in the thermal conductivity coefficient of the metal surfaces. The finding in SS316 metal is that the increase in the concentration with temperature increased the precipitation and since the shear stress linearly increased with the flow rate, it was also observed that the fouling decreased (Teng et al., 2017).In refineries where intense inorganic concentrations are followed, a thermo-hydraulic method was used to examine the fouling character in heat exchangers. As a result, it was stated in the study that it is an advanced model for the fouling problem and its diagnosis (Diaz-Bejarano et al., 2017).A common problem in environments with high particulate fouling in plate heat exchangers in aircrafts have been considered. ...
... Also, mitigating techniques, such as special coatings to inhibit nucleation or reduce adhesion strength, have received some attention over the years [9,10]. In that sense, experimental [11,12] and numerical studies [13,14] aimed at fundamentally understanding the fouling mechanisms and improving mitigation techniques for different scenarios. Also, studies focusing on fouling of flow systems with inserts (i.e., twisted tapes) were carried out [15], as well as the cleaning frequency of systems subjected to fouling [16]. ...
The occurrence of inorganic fouling (gypsum, CaSO4·2H2O) is investigated numerically by considering a 2-D, fully discrete and fully coupled multi-physics turbulence models. The novelty of the study is associated with the fact that all transfer rates, which are simultaneously evaluated, are determined based on calculated gradients and not based explicitly on wall correlations, as often done, especially for mass transfer. The fluid flow simulations consider two low-Re turbulence models (k-ω and SST k-ω), which are assisted by two models for the turbulent Prandtl number and three models for the turbulent Schmidt number. The implemented 2-D models are fully validated against classical laws of the wall for momentum, heat and mass transfer. After validation, the multi-physics results are compared with existing experimental fouling data and the commonly employed Kern-Seaton model. The results show that the proposed models are fully capable of predicting fouling. More specifically, the present 2-D results show that the relation between the deposition rate constant and temperature, through the Arrhenius equation, shows an R-squared agreement of 0.68, which can be considered good when compared with the agreement returned by the 0-D model (R²=0.18). Furthermore, the experimental deposition mass flux reported in the literature shows a better agreement with the presently proposed 2-D approach than the available 0-D model.
... Scale formation is a major concern in lots of engineering fields such as power generation, [1] oil and gas, [2] and desalination. [3] The blades of the steam turbines, the inner walls of the heat exchanger pipelines, and the heating surfaces of the distillation plates are often faced with the most severe scaling and corrosion under scaling. ...
Bionic self‐cleaning coatings have exhibited scaling inhibition for their low surface free energy. The key issue is focused on the long‐term anti‐scaling performance for the hydrophobicity failure after scaled. Inspired by “grass‐to‐stone” phenomenon, we reported a polymer coating (WCA = 120°, WSA = 14°) with the water contact angle of its 720 h‐scaled surface increased to 135°and scaling reduced by 90–95%. The nucleation and growth of CaCO3 at “coating‐crystal” interface are investigated, and a physical model for self‐healing film interface inhibiting scaling is innovatively proposed, as an important step toward designing long‐term anti‐scaling coating for engineering application. In the dynamic scaling condition, “Nano‐grass” like low surface tension molecules with –C–Si groups come out from the self‐cleaning coating surface at 80°C, and spontaneously migrate onto high surface tension CaCO3 surface by surface tension and capillary force, and form a “micro‐leaf” like hydrophobic self‐healing film, which is a process of self‐cleaning surface reconstruction to inhibit secondary nucleation and growth of CaCO3 crystals.
... All rights reserved. studies, Teng et al. [12] experimentally correlated the calcium carbonate deposition on several heat transfer surface material types and observed that the extent of foulant deposition is directly proportional to the thermal conductivity of the surface. For the effect of velocity on the fouling, several experiments have shown that the increase in velocity leads to lower fouling deposition, due to the increase amount of shear resulting in lower rate of deposition and relatively higher rate removal of deposition layer. ...
Several energy applications involve flow of untreated heat transfer fluids that contain trace amounts of mineral salts, such as calcium carbonate and calcium sulfate, which show reverse solubility with temperature. The gradual accretion of these salts onto the heat transfer surfaces causes fouling that degrades thermal performance over time. While fouling of bare surfaces has been extensively studied, fouling of nonwetting superhydrophobic or liquid-infused surfaces is less understood, especially under dynamic flow conditions. This study presents a systematic experimental analysis to elucidate dynamic flow fouling of calcium carbonate and calcium sulfate on smooth, superhydrophobic and liquid-infused surfaces in a generalized manner. Copper tubes with modified inner surface wettability are fabricated and subjected to forced convection at different flow rates and fouling salt concentrations. Fouling characteristics of the two salts on the different surfaces are examined through microstructural analysis, and quantified in terms of asymptotic fouling resistance that measures the total extent of fouling, and a threshold time, which correlates to the onset of significant fouling. Using Taguchi design of experiments, the study reports, for the first time, closed-form analytical relationships for the asymptotic fouling thermal resistance and threshold time on the Reynolds number, dimensionless concentration of fouling agent and dimensionless infused liquid viscosity that represents the different surface types in a unified manner. It is shown that the analytical model accurately predicts the fouling characteristics in up to about 97% of the data, based on which contour maps of optimum surface designs for minimizing fouling resistance are presented. The results provide information on designing surfaces for reduced fouling or for estimating the fouling characteristics for a given surface in applications.
This research explored the intricacies of water consumption and energy requirements within cooling systems designed for concentrated solar power plants. In the present work, an innovative hybrid cooling tower was presented and studied, aiming at reducing water consumption and preserving power generation efficiency. Experimental cooling towers were studied with four different cooling water qualities, elucidating that, compared to kaolinite, calcium carbonate has a substantial influence on fouling behavior as an additive to the cooling water. Through the establishment of correlations between water quality and critical fouling parameters such as fouling resistance Rf, deposition rates mf, and fouling thickness
f, the study provided valuable insights for predicting fouling behavior in similar operating conditions. Furthermore, the development and validation of a numerical code with both literature and experimental work was helpful in predicting the thermal performance of hybrid cooling along one-year operation. The assessment of three cleaning methods; water jet, air jet, and chemical cleaning, revealed distinct impacts on heat transfer and associated costs. Particularly noteworthy were the substantial improvements in heat transfer efficiency, especially with air jet cleaning, which enhanced heat transfer of the polymer bundles by 6.1% with no water consumption. These findings not only portend cost-effective maintenance practices but also endorse environmentally friendly approaches by significantly curtailing water usage, a pivotal progression in the sustainability of hybrids cooling systems.
A period of the fouling process in which there is no visible deposition and the fouling resistance is not yet positive is usually called the induction period. Depending on the heat transfer and operational conditions, the induction period may be occurred or not. Applying methods that lead to an increase in the induction period has recently been considered as modern fouling mitigation strategies. Contrary to the relatively large studies that have been conducted to identify and investigate the factors affecting the fouling growth period, operational parameters effect on induction period are not fully understood and quantified so far. If there is information about the cause of induction period and the factors affecting it, the induction period can be increased and fouling problems in heat exchangers can be greatly reduced or postponed. This study purpose is to investigate and summarize the operational parameters (e.g., fluid velocity, surface and bulk temperature, salt concentration and heat flux) affecting the induction period of calcium salts (e.g., CaSO4, CaCO3 and mixed of them) to identify the areas that have received less attention in the last 50 years.
In the present chapter, recent decade’s research on the crystallization fouling of calcium salts including calcium sulfate (CaSO4), calcium carbonate (CaCO3) and their combination were reviewed. The effects of the most important operational parameters affecting the formation of crystalline fouling such as flow velocity (u), fluid bulk temperature (Tb) and heat transfer surface temperature (Ts), salt concentration, applied heat flux (HF), and pH were categorized from various papers. The effects of these parameters were explained in the fouling growth period. Our goal is to create general ideas among crystallization fouling research and to identify the effects of various factors on this type of fouling. In addition, it is tried to show the strengths and weaknesses of the previous researches and the possibility of creating new research areas.
Introducing innovative and environmentally friendly fouling removal methods for water-filled pipelines is essential nowadays to increase pipelines' safety and productivity and eliminate the limitations of traditional descaling methods. In this paper, we investigate the capability of high-power ultrasonic waves and cavitation phenomenon as an influential online fouling removal tool to remove the build-up fouling with a thickness of 1 mm on the inner surface of 4-inch low-carbon stainless steel pipes filled with water. First, we developed a FEM simulation to investigate the effect of ultrasonic power on the acoustic pressure at different distances from the transducer attached point on the pipe using Comsol Multiphysics. After that, we conducted an experimental and statistical investigation to validate our result from FEM analysis using a transducer set and PZT-4 piezoelectric attached to the pipes' outer surface. The results showed that increasing the transducer's electrical power would raise the fluid's acoustic pressure. Furthermore, we indicate that increasing the electrical power to 400 W results in a higher fouling removal rate in the pipe.
Deposits of barium sulfate are a common issue in the oil and gas industry. The presence of these crystals impacts oil and gas production, causing technical problems such as inhibiting flow rate, increasing pressure in the pipe, and causing the pipe to break and be damaged. The results of this study show the formation of barium sulfate (BaSO4) crystals with the batch crystallizer method at 300 °C under the influence of the stirring rotation speed (0 rpm, 120 rpm, 240 rpm, 360 rpm, 480 rpm) and the additive concentration (0 ppm, 5 ppm, 10 ppm, 15 ppm, 2atm). In this study, the BaSO4 crystallization experiment was performed in a glass beaker using a magnetic stirrer with a stirring rotation speed to react BaCL2 and Na2SO4. The results demonstrated that adding zinc chloride (ZnCl2) and copper (ii) chloride (CuCl2) additives reduced the mass of crystals formed. The amount of barium sulfate scale that forms can be affected by the rotational speed of the stirrer. According to SEM analysis, the crystal morphology of BaSO4 was orthorhombic, indicating that this crystal shape was typical of barite crystals. While XRD analysis confirmed the formation of barium sulfate (barite) crystals, it also demonstrated that the crystals formed were solid barite crystals.
When industrial pipelines are used to transport production materials, the scale can easily form on the inner wall of a pipeline due to long-term contact with the liquid medium. Scaling in industrial pipelines is a common problem that poses a great threat to the production process and environmental protection. In this paper, the influence of temperature on the fouling removal process in pipes is studied. A finite element simulation model was established for guided wave propagation in pipes with different temperatures to obtain the acoustic pressure distribution along the pipes, showing that when the temperature increases, the acoustic pressure value on the solid–liquid surface of the pipes increases, and the cavitation threshold decreases. The experimental system for pipe descaling at different temperatures was established, when the temperature is from 20 to 60 °C, the descaling rate in the inner wall of the pipe far from the transducer is increased from 77.49 to 93.71%, the descaling rate in the inner wall of the pipe near the transducer is increased from 87.01 to 97.02%. The experimental results showed that the descaling performance is better when the pipeline temperature is higher.Compared with the traditional technology, the pipeline descaling technology based on ultrasonic guided waves is highly efficient, safe and eco-friendly, which can remove the fouling inside pipeline online without affecting the transportation. The above conclusions could provide a reference for further popularizing the application of the descaling technology based on ultrasonic guided wave.
Graphical abstract
LabVIEW program was written by computer to generate 10Vp-p sinusoidal continuous wave digital signal, and then the digital signal is converted into analog voltage signal by using a data acquisition card (DAQ), and then the analog voltage signal is amplified to 300Vp-p by input power amplifier. The amplified analog voltage signal is applied to the transducer, and the transducer converts the voltage signal into vibration signal to generate ultrasonic guided waves in the pipeline and remove dirt in the pipeline.
Deposit formation in heat exchangers is an undesirable process in many industries. Severe fouling can potentially reduce the performance of heat exchangers compromising the efficiency of operating units. This research aimed to examine experimentally the effect of fluid bulk temperature (Tb) during deposition of CaCO3 solution under convective heat transfer and subcooled flow boiling conditions. To do so, several tests were performed at a constant concentration of CaCO3 solution (0.2 g/l) and Tb values of 55-75°C. Heat flux ranging from 13 to 83 kW/m² and fluid flow rates of 2 to 4 l /min) were also applied to investigate experimentally fouling resistance and heat transfer coefficient of CaCO3 solution. It was found that Tb would significantly affect the mechanism of deposit formation which has been less discussed in the past. Higher Tb changed the propensity of fouling resistance curve from linear to asymptotic, and the crystal type of deposit layer from aragonite to calcite. Results also showed that at low Tb (55°C), an increase in heat flux enhanced the fouling rate while at high Tb, an increase in heat flux reduced the fouling, due to increasing the evaporation rate of the solution. In addition, at low heat flux (13 kW/m²), an increase in the fluid flow rate led to higher fouling rate, whereas at high heat flux, increasing the fluid flow rate resulted in lower fouling rate.
Scale formation is a longstanding and unresolved problem in a number of fields, including power production, petroleum exploration, thermal desalination, and construction. Herein, a high‐temperature scale‐resistant slippery lubricant‐induced surface (HTS‐SLIPS) is developed by one‐step electrodeposition and lubricant infusion. The fractal cauliflower‐like morphology with lubricant oil is conducive to forming an ultralow contact angle hysteresis of ≈1°. The 10‐d real‐world boiling trial indicates that by replacing the uncoated surface with HTS‐SLIPS, the reduction in scale mass is greater than 200% because of the low surface free energy (4.3 mJ m⁻²) and outstanding smoothness (Ra = 41 ± 8 nm) of HTS‐SLIPS. Thanks to the scale retardation, the bubble departure frequency of HTS‐SLIPS is eightfold higher than that of uncoated surfaces, signifying superior heat transfer efficiency. In these demonstrations, HTS‐SLIPS coated spiral tube exhibits better flowability and lower pressure drop than the uncoated one. In addition, favorable compatibility between HTS‐SLIPS and mechanical vibration is experimentally verified to strengthen the descaling of SLIPS synergistically. It is anticipated that the simple and scalable coating fabrication approach will be applicable in numerous industrial high‐temperature processes where scale formation is encountered.
The electromagnetic frequency is one of the most important parameters in electromagnetic scale inhibition research, and most of the previous studies on the optimal frequency range used experimental analysis. In this paper, a computational model for the optimal frequency of CaCO3 scaling in copper pipes under the action of electromagnetic fields is introduced. By establishing the equivalent electric dipole pipeline physical propagation model of the two-layer medium of the pipe wall and the water body, the vector magnetic potential in the water body is deduced by the mirror method, and the electromagnetic field expression of the water body in the pipe is derived. According to the electromagnetic energy relationship, the optimal electromagnetic frequency range is calculated to be 70–75 kHz. Finally, experiments were performed to analyze the effect of electromagnetic fields in different frequency ranges on the scaling of CaCO3 in copper pipes, and the obtained results verified the accuracy of the optimal frequency calculation model for CaCO3 scaling in copper pipes under the action of electromagnetic fields.
Since the presence of suspended particles in any process stream as well as controlled experimental streams is undeniable, the need to investigate the effect of these particles on crystallization foulingis very important, a topic that has been overlooked in many previous studies. Effect of the simultaneous presence of particles besides the soluble salts on the crystallization fouling can make the analysis of fouling formation much more complicated. It was reported that depending on the type of particles, it can increase or decrease the crystallization fouling, and sometimes may be ineffective. In the present study, a critical review on the impact ofcrystalline (e.g., CaCO3 and CaSO4) and non-crystalline (e.g., Al2O3, SiO2) particles, as well as their combinationon the crystallization fouling are presented, and by collecting different results from effect of these particles, the need to consider these particles in future studies of crystallization fouling has been clearly over emphasized.
Accelerated fouling tests using water conditions more severe than actual project have been proven that it could not truthfully reflect the fouling development. To fill the research gaps of long-term fouling tests, three sets of continuous long-term fouling tests on eight enhanced tubes and one plain tube were performed over a duration of 86–143 days to explore the deposition behavior of the combined fouling. In this study, a decoupling method was presented to compare the heat transfer ability of different test tubes in different operation conditions. Detailed mechanisms of the effects of water velocity and tube geometries on the combined fouling process for enhanced tubes were revealed. Results showed that increased water velocity causes the introduction period of the fouling process to be reduced continuously. In addition, the asymptotic fouling resistance variation curve presented a downward parabola with increased water velocity. For one enhanced tube, the asymptotic fouling resistance decreased with the increase of water velocity from 0.9 m/s to 2.4 m/s. However, the plain tube presented asymptotic fouling resistance that first increased, and then, it decreased when the water velocity rose from 0.9 m/s to 2.4 m/s. In order to evaluate the performance of enhanced tubes when considering heat transfer, fouling, and pressure drop, a comprehensive performance evaluation criteria (CPEC) was proposed, and its calculation correlation was developed with an average error of 7.06%.
When industrial pipelines are used to transport production materials, the scale can easily form on the inner wall of a pipeline due to long-term contact with the liquid medium. Scaling in industrial pipelines is a common problem that poses a great threat to the production process and environmental protection. In this paper, the influence of temperature on the fouling removal process in pipes is studied. A finite element simulation model was established for guided wave propagation in pipes with different temperatures to obtain the acoustic pressure distribution along the pipes, showing that when the temperature increases, the acoustic pressure value on the solid-liquid surface of the pipes increases, and the cavitation threshold decreases. The experimental system for pipe descaling at different temperatures was established, when the temperature is from 20°C to 60°C, the descaling rate in the inner wall of the pipe far from the transducer is increased from 77.49–93.71%, the descaling rate in the inner wall of the pipe near the transducer is increased from 87.01–97.02%. The experimental results showed that the descaling performance is better when the pipeline temperature is higher.
A detailed experimental study is presented on fouling behavior of the anti-clogging perforated plate atomizer designed for high salinity applications, and compared with a conventional (plain-jet) airblast atomizer. Low-pressure regions around fast moving air in the outer layer of spray (as in conventional atomizers: plain-jet and prefilming) due to Venturi suction were identified as the root cause of atomizer clogging, as they facilitate salt accumulation on the atomizer surface from spray. Accordingly, severe atomizer fouling, and fluctuations in spray cone angle were observed in the conventional airblast atomizer over 2 hours at 100°C air and 50°C saline (44° to 76° at 35,000 ppm, and 44° to 91° at 100,000 ppm). In this regard, the perforated plate atomizer provides a novel liquid-film airblast atomization by maintaining a liquid-annulus film around the air outlet as the outer layer of spray. Doing so we achieved nearly complete suppression of fouling, and spray cone angle fluctuations (28° ± 1° at 35,000 ppm, and 30° ± 1° at 100,000 ppm). Later, novel liquid-film atomization was adopted in the conventional airblast atomizer. While, the conventional airblast atomization needed atomizer cleaning/maintenance after 35 minutes for 175°C air and 65°C saline at 100,000 ppm, the liquid-film atomization showed no sign of fouling over 14 hours. Hence, current work establishes a benchmark liquid-film airblast atomization mechanism in the anti-clogging perforated plate atomizer for complete suppression of fouling in airblast atomization. This extends the application of airblast atomizers from high evaporation jet engines to ZLD-HDH desalination systems, spraying, powder metallurgy, pharmaceuticals and hospitals, and spray drying and cooling.
This study aims at inhibiting the formation of calcium carbonate in heat exchangers by using guided ultrasonic waves associated with the heterodyne effect of multiple frequencies. To provide a proof of concept, an experimental approach on a plate and joint heat exchanger was considered and complemented by a modeling approach. This study explains how to identify areas susceptible to calcium carbonate deposition. The scaled surface is analyzed using a 3 D digital microscope, the preferential deposition areas are identified and the fraction of the surface occupied by calcium carbonate is determined. In addition, modeling was performed to detect areas sensitive to temperature and fluid flow. The modeling was validated using experimental data from a scaled plate analyzed with a 3 D microscope. As a predictive tool, this model could be particularly useful in identifying effective strategies to mitigate or even eliminate fouling.
In this study, the pressure-drop (flow resistance) and nanoparticle deposition characteristics of multiple twisted tapes (MTTs) with partitions were experimentally investigated in turbulent duct flows using air as working fluid. Penetration tests for nano-sized particles and pressure drop measurements were performed in the empty duct and ducts fitted with twisted tapes (TTs), and zones under the same pumping power condition. A co-swirling arrangement was used for MTT inserts. Different nanoparticle diameters (5–100 nm), Reynold numbers (4000–11000), TT twist ratios (3 and 7), number of tapes (1, 2, and 4), and partition schemes were considered in the present investigation. It was found that the penetration efficiency of nanoparticles generally increased with the diameter of nanoparticles and Reynold number. The nanoparticle deposition velocity was always higher in ducts fitted with MTTs than in ducts equipped with a single twisted tape (STT). The results also showed that the ratios of nanoparticle deposition velocities for TT-equipped ducts to the empty duct ranged from 1.8 to 13.7, while the corresponding ratios of friction factor varied from 1.4 to 3.2. Beside, TTs with a smaller twist ratio offered higher particle deposition velocities and flow resistances than TTs with a larger twist ratio. Furthermore, empirical correlations for friction factor, nanoparticle penetration efficiency, and deposition velocity were proposed, respectively. The fouling resistance caused by accumulation of deposited particles was analyzed and the results showed that the maximum resistance decreased with the increasing Reynolds number, but was comparable for particle size between 50 nm and 100 nm.
A polymer flood pilot has been ongoing in the Schrader Bluff viscous oil reservoir at Milne Point on the Alaska North Slope. The results from the pilot are encouraging. However, a major concern of the operator is the influence of polymer on the production system after breakthrough, especially the fouling in heat exchangers. This work applies a multiexperimental approach to study the severity of polymer-induced fouling in both dynamic and static states of produced fluids to determine safe operating conditions. Dynamic scale loop (DSL) tests were conducted to study fouling due to polymer at different skin temperatures (165–350°F) in a dynamic state of fluid flow where the fluids’ flow mimics the residence time of fluids in the heat exchanger of the field pilot. Static deposit tests were also conducted at similar skin temperatures of 165–250°F using a novel experimental apparatus designed and built in-house. It was found that at higher skin temperatures of 250–350°F, tube blocking was observed in the DSL tests, whereas the tests at 165–200°F did not show any tube blocking, even in a more extended test period. The deposit test showed that the deposit rate generally increases with skin temperature, and the presence of polymer aggravates the fouling. The copper tube performs best when the skin temperatures are 165–200°F, while the stainless steel tube performs best at a skin temperature of 250°F. These experiments also manifested the influence of the cloudpoint of the solution as the deposit rate increased significantly when the skin temperature was higher than the solution cloudpoint. The study provides a source of practical guidance to the field operations.
Heat exchangers in service experience accumulation of undesired materials (fouling), which diminishes heat exchanging performance with the increase in pressure drop and pumping power. The overall design of heat exchanger may significantly be influenced by fouling because fouling causes huge economic loss due to its impact on initial cost of heat exchanging operation, operating cost, maintenance cost, mitigation measures, and performance. To control fouling, researchers have made great efforts to study the fouling phenomena, its development, interface effects, and mitigation approaches. The ions of dissolved salts diffuse through the boundary layer and gradually accumulate on the heated surfaces.
Researchers have embarked into mitigation approaches to save money and protect the environment, although the deposition phenomenon is still under investigation. Fouling on heat exchanger surfaces could be mitigated by alteration of heat exchanging surfaces, modifying heat exchanger operating parameters, adding chemical additives, and addition of particles such as metals, nonmetals and their composites, natural fibers. Conventional chemical additives currently in use create environmental hazards, considering that the researchers have tried to explore green additives such as carboxymethylcellulose (CMC), cationic inulins (CATINs), polyallylamine (PALAM), gelatin, and bio-based functionalized nanomaterials. That are more benign to the environment and pose no threat to health.
The addition of particulate matter, such as pellets of lead, has created erosion and environmental hazards, which finally prompted the use of biodegradable natural fibers to modify the onset of deposition by boundary layer scavenging and to interact with the turbulent eddies to reduce the rate of mass transfer of the foulant to the heated surfaces. Particle size and flexibility have a positive influence on fouling mitigation where nanoparticles and smaller natural fibers are more effective. However, efforts are given to develop chemicals exceptionally benign to the environment. The present chapter focuses on fouling phenomena, fouling interfaces, fouling models, environment of fouling, consideration of heat exchanger fouling in design, and mitigation of fouling.
Due to the complexity of scaling mechanism, conclusions obtained from different experiments could be controversial. To reveal the scaling mechanism at the molecular level, this work studies the effect of temperature, ion concentration, and substrate material on CaCO3 scaling via molecular simulation. Molecular dynamics (MD) calculations show that CaCO3 tends to form above a specific critical temperature in different systems. Affected by the interaction of scaling ions and clusters, the scaling ability of Fe(1 1 1) first increases and then decreases with increasing concentration. Moreover, the results of MD and density functional theory (DFT) show that the scaling capacity of Fe(1 1 1), Ni(1 1 1), and Cu(1 1 1) decreases successively. This work would throw light on studying scaling mechanism in complex environment.
Because of the electric field method has the characteristics of energy saving, environmental protection and high efficiency, it is the focus of research in this field at present. In this study, a molecular dynamics method was used to simulate the effect of an electric field on the interaction of Ca2+ and CO32− in calcium carbonate solution with the surface of calcite crystals (1, -1, 0), and through experiments, the performance of an electric field with an intensity of 1000–1400 V/m (step 100 V/m) to inhibit calcium carbonate deposition on the heat transfer surface was studied. The simulation results showed that the binding energy of Ca2+ and CO32− to the surface of calcite crystals (1, -1, 0) decreased after the application of an electric field. By analysing the diffusion coefficient and radial distribution function of Ca2+ and CO32−, the electric field was shown to effectively prevents the diffusion and combination of to the calcite (1, -1, 0) crystal plane, which can effectively prevent the growth of calcium carbonate on the heat transfer surface. The experimental results showed that the fouling resistance is significantly reduced after electric field treatment. The results of scanning electron microscopy (SEM) and macroscopic analysis of fouling on heat transfer surface also show that electric field can effectively inhibit fouling. When the electric field intensity is 1300 V/m, it has the best anti-scaling effect. Therefore, the calculation results are basically consistent with the simulation conclusions.
Calcium sulphate is one of the major fouling that lead to serious operating problems in industries. The mitigation of calcium sulphate scaling by physical water treatment (PWT) in an operating heat exchanger using zinc and tourmaline as catalytic materials is presented in this paper. The PWT is defined as a non-chemical effective fouling retardation method which exhibits promising protection to protect the environment and maintain a green environment. Catalytic materials such as (zinc and tourmaline) are capable of tackling fouling problems. Experiments were conducted in this study to verify and evaluate the performance of the PWT method. Artificially hardened water at 300 mg L−1 was used as the cooling water for deposit analysis. The velocity of the cooling water (i.e. hard water) was varied from 0.3 to 0.8 m s−1 and the bulk temperature of the solution was maintained at 45°C. The experimental running time was set at 10 h each step. The artificially hardened water concentration was monitored under various velocities. Complex metric titration was implemented to measure the concentration of calcium sulphate every 2 h for cases with and without PWT-treated cooling water flow. The results showed that the reduction in calcium sulphate formation for case with PWT higher compared to those without PWT. However, it was observed that the performance of the PWT decreases gradually overtime, which needs to be addressed in future work.
Laboratory corrosion immersion tests were carried out to investigate the effectiveness of a physical water treatment (PWT) using zinc and ceramic tourmaline-based catalytic materials for the control of carbon steel corrosion in acidic still water (i.e., pH 4.5–5). The tests were carried out at different water temperatures over 168 h. Our results showed a maximum of 22 % reduction in the corrosion rate using PWT in comparison with the control case. Furthermore, the corrosion products depicted more agglomerated particles after the PWT treatment. In both cases, differences were observed in the crystal structures, showing in general lower corrosion activity when PWT was used. The present results could find potential applications in water distribution systems and where metallic materials are exposed to stagnant acidic water.
Turbulent friction and heat transfer behaviors of dispersed fluids (i.e., uttrafine metallic oxide particles suspended in water) in a circular pipe were investigated experimentally. Viscosity measurements were also conducted using a Brookfield rotating viscometer. Two different metallic oxide particles, γ-alumina (Al2O3) and titanium dioxide (TiO2), with mean diameters of 13 and 27 nm, respectively, were used as suspended particles. The Reynolds and Prandtl numbers varied in the ranges l0-I0 and 6.5-12.3, respectively. The viscosities of the dispersed fluids with γ-Al2O3 and TiO2 particles at a 10% volume concentration were approximately 200 and 3 times greater than that of water, respectively. These viscosity results were significantly larger than the predictions from the classical theory of suspension rheology. Darcy friction factors for the dispersed fluids of the volume concentration ranging from 1% to 3% coincided well with Kays' correlation for turbulent flow of a single-phase fluid. The Nusselt number of the dispersed fluids for fully developed turbulent flow increased with increasing volume concentration as well as the Reynolds number. However, it was found that the convective heat transfer coefficient of the dispersed fluid at a volume concentration of 3% was 12% smaller than that of pure water when compared under the condition of constant average velocity. Therefore, better selection of particles having higher thermal conductivity and larger size is recommended in order to utilize dispersed fluids as a working medium to enhance heat transfer performance. A new correlation for the turbulent connective heat transfer for dilute dispersed fluids with submicron metallic oxide particles is given by the following equation: Nu = 0.021 RePr.
Scaling often leads to a series of technical and economical problems in industrial plants and equipments by blocking water flow in pipes or limiting heat transfer in heat exchangers. While most contemporary studies are focusing on crystallization at heat-exchanger surfaces and scaling on nanofilters in desalination plants, very little work has been done investigating scale formation on pipe and vessel walls. A comprehensive investigation of the effects of various process parameters in controlling the formation of calcium sulfate scale in pipes was undertaken. Supersaturation ratio, run time, and operational hydrodynamics were altered systematically to determine their influence on the scale growth rate. The results confirmed that the deposition of gypsum on pipe walls was significantly affected by these process parameters.
The accumulation of unwanted crystalline deposits (fouling) reduces the efficiency of heat exchanger considerably. In order to mitigate fouling, many measures have been taken including the use of low-energy surface and antifoulant. In this investigation, the CaCO3 fouling experiments in both cooling water and pool-boiling systems were performed, the induction period as well as the removal of fouling was studied, and the fouling morphology was also investigated by scanning electron microscopy and atomic force microscopy (AFM). Compared with the copper surface, the self-assembled monolayers low-energy surface can prolong the induction period of fouling in the cooling water system. The induction period increases with decreasing initial surface temperature and fluid velocity. When the heat flux is fixed in different experiments, an increase in the fluid velocity will result in a decrease in the initial surface temperature. Under this condition, owing to the interactional effects between surface temperature and fluid velocity, the induction period increases with increasing fluid velocity. The removal experiments were carried out both in the induction period and in the post-induction period. The results show that only in the induction period can the fouling resistance be reduced owing to the weaker adhesion strength of fouling. In the presence of antifoulant polyacrylic acid (PAA), the crystal forms are changed and the fractal dimensions of CaCO3 morphologies increase for both the cooling water and the pool-boiling systems. AFM images show that the steps are bunched for CaCO3 formed in the pool-boiling system, and in the presence of PAA, the step spacing is widened compared to the case in the absence of PAA.
Calcium carbonate scale deposition from its sludge on aluminium metal surface was studied and compared with copper. Ethylenediamminetetraacetic acid (EDTA) was used as a scale inhibitor and the experiments were carried out at 60 and 100 °C. The samples were characterised by XRD, FTIR and SEM techniques. The study revealed that the deposition of scale on the substrate is not only influenced by the chelating agent and temperature but also depends on the type of metal. This phenomenon of metal-induced polymorphic stabilisation and morphological changes has so far been not reported and the possible mechanism is discussed.
Oil/water (O/W) emulsion is daily produced and difficult to be treated effectively. Ceramic membrane ultrafiltration is one of reliable processes for the treatment of O/W emulsion, yet still hindered by membrane fouling. In this study, two types of Fe2O3 dynamic membranes (i.e., pre-coated dynamic membrane and self-forming dynamic membrane) were prepared to mitigate the fouling of support ceramic membrane in O/W emulsion treatment. Pre-coated dynamic membrane (DM) significantly reduced the fouling of ceramic membrane (i.e., 10% increase of flux recovery rate), while self-forming dynamic membrane aggravated ceramic membrane fouling (i.e., 8.6% decrease of flux recovery rate) after four filtration cycles. A possible fouling mechanism was proposed to explain this phenomenon, which was then confirmed by optical images of fouled membranes and the analysis of COD rejection. In addition, the cleaning efficiency of composite membranes (i.e., Fe2O3 dynamic membrane and support ceramic membrane) was enhanced by substitution of alkalescent water backwash for deionized water backwash. The possible reason for this enhancement was also explained. Our result suggests that pre-coated Fe2O3 dynamic membrane with alkalescent water backwash can be a promising technology to reduce the fouling of ceramic membrane and enhance membrane cleaning efficiency in the treatment of oily wastewater.
CaCO3 scale deposition from its sludge was studied on copper substrate. Ethylenediamminetetraacetic acid was used as chelating agent and tested for its influence on the deposition. The experiments were carried out at 60 and 100 °C and the effect of direct heating and indirect heating was studied. The samples were characterized by XRD, FTIR and SEM techniques. The data revealed that the complex forming nature of EDTA, the shape of the crystallite and area of contact are the key factors for the deposition of CaCO3 on metal surface.
Fouling can be defined as adherent deposits of unwanted compounds that are formed by the precipitation of soluble salts from water and crystal growth on the surfaces of processing equipment. The deposition layer becomes an insulating layer that deteriorates the heat transfer efficiency and shortens the service life. The development of functionalized nanomaterial leads to multi-functionality, such as the ability to adsorb scaling cations with high thermal conductivity, which is very important for heat transfer applications to manage the fouling problems. The purpose of this study was to evaluate the mitigation of calcium carbonate scaling by applying EDTA-treated MWCNT-based water nanofluids on heat exchanger surfaces. A set of fouling experiments was conducted by using additive EDTA-treated MWCNT-based water nanofluids (benign to the environment) to verify the additives’ retardation of the fouling rate of deposition. Fouling solution for deposit analysis was prepared by using 300 mg/L of artificially-hardened calcium carbonate solution. Also the assessment of the deposition of calcium carbonate on the heat exchanger surface with respect to the inhibition of crystal growth was conducted by Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectrometry (EDS). The results showed that the formation of calcium carbonate crystals can be retarded significantly by adding MWCNT-EDTA additives to the solution.
A novel ultrasonic assisted direct contact membrane distillation hybrid process was designed and the effect of ultrasonic irradiation on humic acid (HA) fouling mitigation during membrane distillation process was investigated. Although permeate flux declines were negligible (less than 5%) for the ranges of HA concentration studied, ultrasonic irradiation could enhance the permeate flux more than 30% without destroying HA rejection. The higher the concentration factor was, the larger the ultrasonic enhancement of permeate flux could be obtained. Severe permeate flux decline can be found when CaCl2 was added into the HA solution. The presence of Ca2+ would aggravate HA organic fouling phenomenon and resulted in a thick and dense HA fouling layer on membrane surface. The HA fouling increased heat transfer resistance and reduced the pores available for vapor transfer, both the permeate flux and thermal efficiency of the PTFE membrane declined. Under ultrasonic irradiation, ultrasonic wave refreshed the liquid-membrane interface continuously and alleviated the deposition of HA aggregates. Therefore, although there were still some HA fouling scattered on membrane surface, most of the membrane pores could be kept open and clean, the relative permeate flux can maintain above 94% and was hardly affected by concentration factor increasing.
The condition of supersaturation or supercooling is not a sufficient cause for a system to begin to crystallize. Before crystals can develop, there must exist in the solution a number of minute solid bodies, embryos, nuclei, or seeds that act as centers of crystallization. Nucleation may occur spontaneously or it may be induced artificially. It is not always possible, however, to decide whether a system has nucleated of its own accord or whether it has done so under the influence of some external stimulus. Nucleation can often be induced by agitation, mechanical shock, friction, and extreme pressures within solutions and melts, as shown by the early experiments of Young and Berkeley. The erratic effects of external influences such as electric and magnetic fields, spark discharges, ultraviolet light, X-rays, sonic, and ultrasonic irradiation have also been studied over many years, but so far, none of these methods has found any significant application in large-scale crystallization practice.
Publisher Summary
As soon as stable nuclei—that is, particles larger than the critical size—have been formed in a supersaturated or supercooled system, they begin to grow into crystals of visible size. Surface-energy theories are based on the postulation that the shape a growing crystal assumes is that which has a minimum surface energy. Diffusion theories presume that matter is deposited continuously on a crystal face at a rate proportional to the difference in concentration between the point of deposition and the bulk of the solution. The mathematical analysis of the operation is similar to that used for other diffusion and mass-transfer processes. The suggestion by Volmer that crystal growth is a discontinuation process, taking place by adsorption, layer by layer on the crystal surface, led to the adsorption-layer theories, several notable modifications of which have been proposed in recent years.
Fluidized particles in liquid–solid fluidized bed exchangers are able to remove deposits from walls and thus are able to prevent fouling or scaling. Particle distribution is an important parameter for the performance of fouling prevention. In this paper, the Eulerian multiphase fluid model was adopted to simulate the particle distribution in the fluidized bed heat exchanger incorporating tube bundle arranged in parallel. The porous media model was applied in the zone of the tube bundle to analyze the pressure loss through the vertical tube. Factors influencing the particle distribution including the velocity, volume fraction of the solid phase and the property of the particle were discussed respectively. Particle distribution became more uniform in the high velocity due to the full fluidization of particle in each tube. With the increase in density or diameter of particle, particle maldistribution took place because the sedimentation velocity of these particles was so great that particles could not run into the tubes on both sides. With the increasing of volume fraction of solid phase, particle distribution became slightly more uniform. However increment of particle would bring about greater flow resistance and reduce the usage life of particle and devices. Therefore amount of injected particle should be adjusted according to parameters such as effect of fouling prevention, pressure drop etc. A comparison of the simulation results with the experimental measurements was carried out, showing good agreement.
Fouling mitigation research has been extended to investigate the effects of fibre concentration, fibre length, and fibre flexibility, on heat transfer fouling with supersaturated calcium sulphate solutions. Two long-fibre softwood pulp fibres (pine and spruce) of similar mean length but different fibre flexibility were used as well as a short-fibre, hardwood eucalypt pulp. Fouling was prevented altogether with a 0.25% suspension concentration of long-fibre pine fibres for more than 46 days, and for 38 days with a 0.1% suspension of short-fibre. At 0.05%, concentration, the onset of fouling was delayed for 14.5 days with the short-fibre hardwood pulp. The final asymptotic level of fouling was about 30% of the fibre-free fouling solution. The shorter-fibre hardwood pulp fibres are more effective than either of the long-fibre softwood pulps at the same concentration of 0.05% (higher population). Fouling started at about 1.8 days for both long fibre pulps at 0.05% concentration, and heat transfer augmentation was still achieved in the induction period. Stiffer pine fibres were more effective at fouling mitigation than the more flexible spruce fibres. An equal percentage mixture of hardwood and pine pulp at 0.05% concentration also showed that the shorter hardwood fibres are more effective in mitigating fouling.
Fouling formation on heat exchanger surfaces due to crystallization of inverse solubility salts is one of the fundamental problems in process industries. Despite numerous studies carried out in recent years, comprehensive understanding of crystallization fouling mechanism remains a challenge to chemical engineers. In this review, we first focus on the basic crystallography during deposition of calcium salts, paying attention to crystal structures and crystal forms, as well as nucleation and the subsequent crystal growth process. We then endeavor to relate a number of factors to fouling rate, which may be classified into three categories: solution composition, operating parameters, and heat exchanger surface characteristics. Each aspect is discussed from the crystallization viewpoint (science) and in terms of possible industrial applications (practice). Combining the basic knowledge of crystallography with the information from experimental investigations, several fouling mitigation methods have also been described that may reduce fouling. It is hoped that some of the ideas discussed here will provide possible economic and environmental benefits. Finally, we also try to throw some light on the future direction for research.
The microstructure features of particulate fouling on convective heating surfaces play a dominant role on the deposition process in coal-fired utility boilers. Starting with the analysis of the main fouling mechanism, a particulate collision deposition numerical model based on the discrete element method is proposed in this paper. Applying the present method, the numerical simulation of the process of particulate deposition on a tube and a rectangular plate was carried out. The results show that simulated deposition can exactly reflect the microstructure characteristics of real fouling on boilers' heating surfaces, such as porous structure and porosity. The fractal features of the inner porous microstructure and surface morphology of the simulated deposition was further studied in this study. The investigation results indicate that the characteristics of the particle–pore interface and the surface topography, which are heterogeneous and anisotropy, can be quantitatively characterized by the fractural dimensions (FD) of pore contour and surface profile, respectively. The results of FD estimation using a box-counting method show that with decreasing porosity, the FD of pore contour increases and the FD of surface profile decreases. Additionally, particulate diameter plays a role on the fractal features of particulate deposition.
Crystallization fouling occurs when dissolved salts precipitate from an aqueous solution. In the case of inversely soluble salts, like calcium carbonate (CaCO3), this may lead to crystal growth on heated walls. Crystallization may also take place in the bulk solution either via homogeneous nucleation or heterogeneous nucleation on suspended material.In this paper, surface crystallization of CaCO3 and crystallization in the bulk fluid and its effect on the fouling rate on a heated wall are studied. The fouling experiments are done in a laboratory scale set-up of a flat plate heat exchanger. Accuracy of the results is analyzed by uncertainty analysis. SEM and XRD are used to determine the morphology and the composition of the deposited material.The uncertainty analysis shows that the bias and precision uncertainties in the measured wall temperature are the largest source of uncertainty in the experiments. The total uncertainty in the fouling resistance in the studied case was found to be ±13.5% at the 95% confidence level, which is considered to be acceptable.Surface crystallization rate is found to be controlled by the wall temperature indicating that the surface integration dominates the fouling process. The flow velocity affects the fouling rate especially at high wall temperature by decreasing the fouling rate with increasing flow velocity. Crystallization to the bulk fluid is found to enhance significantly the fouling rate on the surface when compared to a case in which fouling is due to crystal growth on the surface.
Desalination capacity has rapidly increased in the last decade because of the increase in water demand and a significant reduction in desalination cost as a result of significant technological advances, especially in the reverse osmosis process. The cost of desalinated seawater has fallen below US$0.50/m3 for a large scale seawater reverse osmosis plant at a specific location and conditions while in other locations the cost is 50% higher (US$1.00/m3) for a similar facility. In addition to capital and operating costs, other parameters such as local incentives or subsidies may also contribute to the large difference in desalted water cost between regions and facilities. Plant suppliers and consultants have their own cost calculation methodologies, but they are confidential and provide water costs with different accuracies. The few existing costing methodologies and software packages such as WTCost© and DEEP provide an estimated cost with different accuracies and their applications are limited to specific conditions. Most of the available cost estimation tools are of the black box type, which provide few details concerning the parameters and methodologies applied for local conditions. Many desalination plants built recently have greater desalinated water delivery costs caused by special circumstances, such as plant remediation or upgrades, local variation in energy costs, and site-specific issues in raw materials costs (e.g., tariffs and transportation). Therefore, the availability of a more transparent and unique methodology for estimating the cost will help in selecting an appropriate desalination technology suitable for specific locations with consideration of all the parameters influencing the cost. A techno-economic evaluation and review of the costing aspects and the main parameters influencing the total water cost produced by different desalination technologies are herein presented in detail. Some recent developments, such as the increase of unit capacity, improvements in process design and materials, and the use of hybrid systems have contributed to cost reduction as well as reduction in energy consumption. The development of new and emerging low-energy desalination technologies, such as adsorption desalination, will have an impact on cost variation estimation in the future.
An apparatus was built to study heat transfer fouling on different heat exchanger pipe surfaces by visually observing the progressive fouling deposition under the same solution conditions. Test pipes were centrally located in a cylindrical tank with a concentric vertical agitator to give constant and uniform flow conditions near the pipe surface. Pipes with either smooth or roughened surfaces provided quantitative data on the progressive build-up and the composition of the deposits. The calcium sulphate deposition on four different metal surfaces (copper, aluminium, brass, and stainless steel) was investigated. The results show that fouling increases with time but at a decreasing rate over set intervals. The deposition also increases with the increasing thermal conductivity of the metal, or the total surface energy. Chemical reaction fouling along with particulate and crystallisation fouling occurred on reactive surfaces when corrosive chemicals were used, and this was compared with crystallisation-only fouling on non-reactive surfaces. Bleached Kraft softwood pulp fibres at various concentrations were added to the fouling solution to study their affects on fouling on the hydraulically smooth pipes. Fouling was retarded with only a low fibre concentration and reduced further as fibre concentration was increased.
Crystallization behavior and polymorphism of CaCO3 were studied at different temperatures (from 60 to 240 °C) under the influence of ethylenediaminetetraacetic acid (EDTA). The samples were characterized using powder X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), Scanning electron microscope (SEM) and field emission scanning electron microscopy (FESEM). In the absence of EDTA, a calcite–aragonite binary mixture was resulted between 60 and 170 °C above which calcite alone was formed. The presence of EDTA significantly influenced the crystallization behavior and composition of different polymorphs of CaCO3 varied with temperature. Formation of a binary calcite–aragonite mixture at 60 °C, ternary calcite–vaterite–aragonite mixture at 100 °C, a binary aragonite–vaterite mixture at 130 °C, a binary calcite–aragonite mixture at 170 °C, purely aragonite at 200 °C and vaterite with very little aragonite at 230 °C confirmed that temperature affects the crystallization process in the presence of EDTA. Rhomboidal calcite, needle/rod like aragonite and flower like vaterite were obtained under different conditions. At 230 °C, a unique flower like morphology was observed for vaterite. The efficacy of EDTA on CaCO3 scale inhibition between 60 and 230 °C is discussed.
While significant progress has been made in the mitigation of heat exchanger fouling, the challenge to reduce its impact on heat exchanger performance is still enormous. Many mitigation and cleaning techniques that have found their way into regular plant operation have been developed by an empirical trial-anderror approach. These antifouling strategies have few or even no links to academic research findings, since industry and academic research institutions have traditionally approached the problem of fouling from different aspects. To optimize the effectiveness of mitigation methods, which highly depends on the dominant fouling mechanisms and influential operating conditions, and to develop new approaches for fouling mitigation, closer collaboration between the two communities is essential. For the past 15 years, conferences on heat exchanger fouling have been held at bi-yearly intervals to facilitate innovative thinking and to explore new theoretical and practical approaches. These conferences have successfully provided a forum for experts from industry, academia, and government research centers from around theworld to present their latest research and technological developments in the areas of fouling mitigation and cleaning technologies. The meetings in San Luis Obispo (1995), Lucca (1997), Banff (1999), Davos (2001), Santa Fe (2003), Kloster Irsee (2005), Portugal and Tomar (2007) were organized by Engineering Conferences International. The 8th conference in this series was organized by the present authors under the auspices of EUROTHERM in Schladming, Austria, in June 2009. In total, 100 participants attended this meeting, presenting 81 papers/posters, which were the highest numbers in any meeting of this series to date. The following papers in this special issue of Heat Transfer Engineering have been selected from the contributions to the 2009 Fouling Conference in Schladming after a careful refereeing and revision process. The full e-proceedings of the 2009 conference as well as those from the previous conferences from 2003 until 2007 can be obtained free of charge from http://heatexchanger-fouling.com. They cover various aspects of heat exchanger fouling, along with updated state-of-the-art fouling mitigation and cleaning strategies. Their content is of significant value for researchers, plant operators, equipment manufacturers, chemical suppliers, and heat exchanger cleaning companies. This website also contains the actual information about the next conference in this series (Heat Exchanger Fouling and Cleaning IX), which is scheduled for June 5-10, 2011 on the beautiful island of Crete, Greece.
Purpose
To study the hydrodynamic and thermal behaviors of a turbulent flow of nanofluids, which are composed of saturated water and Al 2 O 3 nanoparticles at various concentrations, flowing inside a tube submitted to a uniform wall heat flux boundary condition.
Design/methodology/approach
A numerical method based on the “control‐volume” approach was used to solve the system of non‐linear and coupled governing equations. The classical κ ‐ ε model was employed in order to model the turbulence, together with staggered non‐uniform grid system. The computer model, satisfactorily validated, was used to perform an extended parametric study covering wide ranges of the governing parameters. Information regarding the hydrodynamic and thermal behaviors of nanofluid flow are presented.
Findings
Numerical results show that the inclusion of nanoparticles into the base fluid has produced an augmentation of the heat transfer coefficient, which has been found to increase appreciably with an increase of particles volume concentration. Such beneficial effect appears to be more pronounced for flows with moderate to high Reynolds number. In reverse, the presence of nanoparticles has induced a rather drastic effect on the wall shear stress that has also been found to increase with the particle loading. A new correlation, Nu fd =0.085 Re 0.71 Pr 0.35 , is proposed to calculate the fully‐developed heat transfer coefficient for the nanofluid considered.
Practical implications
This study has provided an interesting insight into the nanofluid thermal behaviors in the context of a confined tube flow. The results found can be easily exploited for various practical heat transfer and thermal applications.
Originality/value
The present study is believed to be an interesting and original contribution to the knowledge of the nanofluid thermal behaviors.
An experimental set-up was built to study heat transfer fouling of different pipe materials used in heat exchangers. Fouling mitigation investigations using wood pulp fibres in suspension in the fouling liquid were also performed. The new set-up allows progressive visual observation of fouling with time together with a recorded history under the same solution conditions. On completion, the tube under investigation could be removed to obtain quantitative data on the progressive build up of the deposit as well as the composition of the deposit.The experimental technique involved a pipe test specimen being centrally located in a cylindrical tank concentric with a vertical agitator to give constant and uniform flow conditions near the tube surface. The investigation of calcium sulphate deposition on four different metal surfaces (copper, aluminium, brass and stainless steel SS 316 respectively) and a polycarbonate surface reveals that the fouling increases with time but at a decreasing rate. The deposition on a metal surface can be seen to increase with increasing thermal conductivity and decreasing total surface energy over the range of experiments. Low surface energy material such as polycarbonate causes less attraction to the floating crystals and receives less deposition in comparison to the SS surface.Bleached Kraft softwood fibres at various concentrations were added to the solution to examine their effects on fouling. The results indicate that fouling is reduced as fibre concentration increases. It was also found that the fouling on stainless steel, brass and copper surfaces were all retarded in presence of fibre in the solution.
This is a remarkable new reference and text that will cover the analysis and design of heat exchangers, detailing major new research and practical advances in the field. Topics considered include heat exchangers, planning, appropriate technology, design, engineering, and research programs.
An equation was derived for the calculation of heat and mass transfer
coefficients in the case of pipe and channel flow, taking into account
the experimental data for high Reynolds and Prandtl numbers. The
equation is valid for the transition region and for the range of fully
developed turbulent flows. It is pointed out that it is not possible to
obtain a generally valid heat transfer equation in the form proposed by
Nusselt (1909). An equation of general validity can, however, be derived
by making use of the fundamental form developed by Prandtl (1944) on the
basis of momentum theory.
Sea water is a complex aqueous environment with a large tendency for scale formation, which is usually ascribed to scaling from dissolved salts and suspended particles. Scale formation is causing many problems in thermal processes such as desalination and steam generation plants. In a typical desalination plant, ca. 40 % of the heat transfer area is provided to allow for scale formation problems, which is equivalent to a ca. 10 % increase of the whole capital cost of the plant. The main constituents forming scale in sea water environments, i.e., calcium carbonate, calcium sulfate and magnesium hydroxide, are extensively investigated in the present work. In order to obtain a better understanding of the scaling tendency of the seawater environment, an experimental unit was precisely designed and coupled with a data acquisition system for continuous monitoring of the investigated parameters. Significant factors affecting scale formation such as concentration of salts, flow velocity, water temperature and pH of the environments were studied at length using mild steel and stainless steel (smooth and rough). Hydrodynamic parameters such as Reynolds number and shear stress were used in the analysis of the collected data and revealed the role of shear stress in the effective removal of scale. The Kern-Seaton scale model was used to calculate the fouling resistance in each case and the values obtained were compared with the experimental results. A modification of this model was also undertaken to provide better agreement with experimental findings.
This paper presents a study on the mitigation of calcium carbonate scaling in a double-pipe heat exchanger by physical water treatment (PWT) using zinc and tourmaline as catalytic materials. Artificially-hardened water at 300 mgL−1 was utilized as the fluid medium to form fouling deposits. The cooling water (i.e., hard water) velocity was varied from 0.3 to 0.8 ms−1. The inlet temperatures were maintained at 86 ± 1° C and 22 ± 1° C for hot- and cold-water sides, respectively. The results show that in PWT-treatment case, the fouling resistances are 13–50% lower than those in no-treatment case. The SEM image of the deposit shows a blunt shape crystal structure in case of PWT-treatment, while a pointed crystal structure in case of no-treatment. The calcium content of deposits formed in the cases of PWT-treatment is lower by 17–22% than those of the no-treatment, which corresponds to a thinner fouling in case of PWT-treatment.Highlights► Physical water treatment (PWT) is a non-chemical method for scaling mitigation. ► We present the use of catalytic materials as PWT to mitigate scaling in heat exchangers. ► PWT using tourmaline and zinc decreased the fouling resistance by 13–50%. ► There was lower calcium content for deposits after PWT-treatment. ► PWT-treatment case showed thinner fouling deposits when checked visually.
The effect of flow hydrodynamics on kinetics of precipitation of sparingly soluble salts that cause fouling of process equipment has not been addressed previously. Precipitation of sparingly salts from solutions is usually considered to be due to crystallization on the surface. Precipitation in the bulk or in the boundary layer and its subsequent deposition has been traditionally neglected and to our knowledge, no previous research work has focused on this important area. Computational fluid dynamics was used as a tool to examine the effect of flow on and the location within the flow domain where calcium sulphate precipitation occurs. Initially, isothermal conditions were used to isolate the effect of flow; non-isothermal conditions were examined for turbulent flows usually encountered in heat exchange systems. Precipitation kinetics was modelled using a simple second-order reaction usually used in fouling of calcium sulphate. In laminar flow, the characteristics of the velocity distribution led to the emergence of radial concentration gradients and as a result a radial diffusive flux was induced. Similar behaviour was evident under turbulent conditions but not to the same extent. In turbulent flow, particles were mainly produced in the viscous sub-layer rather than in the turbulent bulk. The reduced velocity within the laminar flow or turbulent viscous sub-layer increased the residence time within these regions, enabling precipitation to take place and more particles to form. The generated particles could deposit by particulate fouling in addition to the fact that consumption of ionic species by precipitation in the boundary layer would induce ionic concentration gradient resulting in diffusion of ions to the walls and further crystallization fouling on the walls. Deposit layer formed by crystallization on the surface has a different structure than that formed by particulate fouling. The effect of velocity and residence time on fouling, its mechanisms, and deposit structure should not be overlooked.
Mineral scale deposits such as calcium carbonate and phosphate, calcium oxalate, barium and strontium sulfate, magnesium silicate and others and colloidal inorganic species such as silica present important challenges for process water applications. When silica is left uncontrolled it forms hard and tenacious deposits that are difficult and hazardous to remove. Conventional phosphonate mineral scale inhibitors do not inhibit silica formation and deposition. Chemical cleaning is not free from hazards and requires operational shut-downs. Another challenge is corrosion of critical metal surfaces of industrial equipment. Last but not least, biofouling due to the development of microorganisms. This paper is focused on the presentation of the general scope of these problems and their solutions. More specifically, it concentrates on (a) inhibition of colloidal silica formation, (b) colloidal silica dissolution, and (c) metallic corrosion, in water applications by use of designed chemical approaches. The additives used for silica inhibition were polyaminoamide dendrimers, polyethyloxazoline and polyethyleneimine polymers. For silica dissolution the dissolvers tested were carboxymethyl inulin (CMI), Genesol 40 (a proprietary blend of additives), polyacrylic acid. In principle, silica inhibition is a function of time and inhibitor dosage. Silica dissolution is dependent in a rather unpredictable fashion on the structure of the dissolver, time and dosage. Mild steel corrosion inhibition has been achieved by synergistic use of zinc ions and polyphosphonate anions that create protective films.
A wide variety of industrial processes involve the transfer of heat energy between fluids in process equipment. As a result of this energy exchange unwanted deposits accumulate on the process surfaces causing a resistance to energy transfer. These deposits reduce the heat recovery and can restrict fluid flow in the exchanger by narrowing the flow area. Prevention and control of fouling is costly and time consuming. In many situations, fouling can be reduced but not necessarily eliminated. Fouling is a major unresolved problem in heat transfer.In general, the heat exchangers evaluated in this study were exposed to untreated lake water for typical conditions. After the prescribed time period the exchangers were taken off line and evaluated. Conclusions and observations regarding fouling of brazed heat exchangers, exposed to once-through lake water, are presented here. Transient observations and photographs of the exchanger surfaces are given. Results are presented that compare these heat exchangers to test plates, also exposed to lake water. The progressive change of surface appearance with increasing immersion times is presented.
Convective heat transfer coefficient is strongly influenced by the mechanism of flow during forced convection. In this paper, the effect of pipe roughness on friction factor and convective heat transfer in fully developed turbulent flow are briefly discussed. A correlation for the friction factor applicable in the region of transition to the fully developed turbulent flow regime is proposed. Using this relationship, some new approximation formulae are proposed to predict the convective heat transfer coefficients in the pipes with a relative roughness of ε/D⩽0.05. The effectiveness parameter for the heat transfer is investigated as a function of the pipe roughness, Reynolds number and Prandtl number. The effect of fouling is also briefly discussed. The predictions of the proposed correlations are compared with the experimental data and with some other previous correlations given in the literature.
In ‘classical’ modelling approach for crystallisation fouling the deposition rate is taken as a function of concentration driving force multiplied by an Arrhenius type temperature dependent function. Although nucleation sites are known to have a significant impact on crystallisation; this effect is not considered in the ‘classical’ modelling. This particular approach to define the deposition rate is elaborated and discussed in the current study. The effect of nucleation sites on calcium sulphate crystallisation fouling has been investigated in a plate heat exchanger where the quantity of the nucleation sites is affected by the presence of crystalline particles in process solution and an increase in the amount of deposits forming on heat transfer surfaces.
Successful elimination of cooling tower treatment chemicals was demonstrated. Three towers functioned for long periods of time with ozone as the only treatment for the water. The water in the systems was reused as much as 30 times (cycles of concentration) without deleterious effects to the heat exchangers. Actual system blow-down was eliminated and the only makeup water added was that required to replace the evaporation and mist entrainment losses. Minimum water savings alone are approximately 75.1 1/kg/year. Cost estimates indicate that a savings of 55 percent was obtained on the systems using ozone. A major problem experienced in the use of ozone for cooling tower applications was the difficulty of accurate concentration measurements. The ability to control the operational characteristics relies on easily and accurately determined concentration levels. Present methods of detection are subject to inaccuracies because of interfering materials and the rapid destruction of the ozone.
An overview is given of the thermodynamics and kinetics of CaCO3 formation and dissolution and how surface and nanoparticulate chemistry are important in understanding reactivity. Topics covered are major marine carbonate materials, carbonate mineral precipitation and dissolution kinetics relevant to seawater, oceanic sources of marine carbonates, dissolution of CaCO3 and response of carbonate-rich sediments to the acidification of the ocean due to rising atmospheric pCO2.
- J W Mullin
J.W. Mullin, Crystallisation, fourth ed. Butterworth-Heineman, London,UK, 2001.
- J W Mullin
Mullin, J.W., Crystallisation. 4th ed. 2001, London,UK: Butterworth-Heineman.