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A survey of correlations for heat transfer and pressure drop for evaporation and condensation in plate heat exchangers
Abstract
Plate Heat Exchangers (PHEs) are used in a wide variety of applications including heating, ventilation, air-conditioning, and refrigeration. PHEs are characterized by compactness, flexible thermal sizing, close approach temperature, and enhanced heat transfer performance. Due to their desirable characteristics, they are increasingly utilized in two-phase flow applications. Detailed research on heat transfer and fluid flow characteristics in these types of exchangers is required to design and use plate heat exchangers in an optimal manner. This paper reviews the available literature on the correlations for heat transfer and pressure drop calculations for two-phase flow in PHEs as an initial process step in order to understand the current research status. Comparative evaluations for some of the existing correlations are presented in the light of their applicability to different refrigerants. Overall, there is a significant gap in the literature regarding two-phase heat transfer and fluid flow characteristics of these types of exchangers. © 2016 Elsevier Ltd and International Institute of Refrigeration. All rights reserved.
... Some studies addressed the application of plate heat exchangers for evaporation processes. Most of them dealt with refrigerants like R134a, R22, R290 R245fa or ammonia [22][23][24][25][26]. It has been found that the evaporation heat transfer coefficient (HTC) increases with increasing the refrigerant vapour quality and mass flux [22][23][24] as well as with increasing the heat flux and the refrigerant saturation temperature [24]. ...
... Most of them dealt with refrigerants like R134a, R22, R290 R245fa or ammonia [22][23][24][25][26]. It has been found that the evaporation heat transfer coefficient (HTC) increases with increasing the refrigerant vapour quality and mass flux [22][23][24] as well as with increasing the heat flux and the refrigerant saturation temperature [24]. Some studies dealt, however, with the evaporation of water as a refrigerant. ...
... To estimating the HTA, constant thermal transmittances for evaporation, condensation, a mixing of both and one phase heat exchange are assumed for both working fluids. Due to high deviations between different heat transfer correlations for pure refrigerants during condensation and evaporation of up to 300 % [24], a detailed calculation of the heat transfer is not undertaken, instead averaged and estimated values are used. ...
... One-phase liquid heat transfer coefficients are assumed as 5000 W m -2 K -1 [20] and for one-phase gas flows as 250 W m -2 K -1 . Averaged heat transfer coefficients for condensing, 1900 W m -2 K -1 , and evaporating, 2200 W m -2 K -1 , of pure working fluids were averaged from correlations for hydrofluorocarbon and hydrofluoroolefin presented by Shon et al. [25] and Eldeeb et al. [24]. No distinction is made if the working fluid is superheated or subcooled. ...
A computer‐aided process design methodology is used to determine the limits of NH3/H2O mixtures in different heat pump cycles from 20 °C to 150 °C. The evaluation is based on a defined parameter set consisting of the coefficient of performance, total heat transfer area and volumetric heat capacity. Simple cycles with two heat flows were chosen to meet good process integration capabilities. The results are shown in a sink outlet/temperature lift matrix considering current technical limits. R1366mzz(Z) in a standard compression cycle with internal heat exchanger serves as a benchmark. To provide temperatures up to 150 °C the lift of the heat pump has to increase to about 80 K of which only the wet compressions cycle with NH3/H2O is capable of. The working domains of NH3/H2O and R1366mzz(Z) are similar, when a two‐stage compression for NH3/H2O is applied. The working domain of different NH3/H2O heat pump cycles is investigated to provide temperatures up to 150 °C. An algorithm is developed, which maximizes coefficient of performance and volumetric heat capacity and minimizes compressor discharge temperature for given external temperatures and internal pressure limits.
... They offer numerous advantages, including compactness, flexible thermal sizing, enhanced heat transfer performance. These attributes make desorber particularly effective for high-temperature, high-pressure applications across a range of industries process heat recovery [1,4,5]. The ability to efficiently handle two-phase flows while minimizing volume requirements further underscores their utility in modern industrial systems. ...
A R T I C L E I N F O Keywords: Braze plate heat exchanger NH₃/H₂O mixture Heat transfer coefficient Experimental study: vapor absorption-compression heat pump A B S T R A C T The aim of this study is to experimentally evaluate of brazed plate heat exchangers used as desorbers in absorption-compression heat pump systems, with a particular emphasis on recovering industrial waste heat applications. To reduce installation cost two vertical desorbers operating in different modes were experimentally investigated the overall heat transfer coefficient, using an ammonia-water mixture as the working fluid. To optimize the heat exchanger efficiency of plate type heat exchangers, an efficient design of desorber is an important factor in improving the performance of the system. The studied desorber system consists of two plate heat exchangers that are connected in series. The thermal performance of these units was analyzed under a constant heat source having an inlet temperature of 70 • C and a mass flux of 115 kg/m²⋅s. Experimental results revealed that, by varying the strong solution mass flux from 5 to 36 kg/m²⋅s, the following performance changes were observed in Desorber 1: heat load increased from 5 to 20 kW, the overall heat transfer coefficient improved from 1.1 to 1.7 kW/m²⋅K, and thermal efficiency increased from 66 % to 86 %. For Desorber 2, the heat load decreased from 17 kW to 14 kW, the heat transfer coefficient varied from 1.1 to 1.5 kW/m²⋅K, and thermal efficiency increased from 66 % to 80 %. Additionally, the vapor mass fraction at the outlet of Desorber 2 ranged from 0.1 to 0.6 kg/kg. The highest-pressure drop was recorded in Desorber 1. These results offer important insights for enhancing the design and functionality of desorber units in high-temperature heat pump systems, contributing to the development of more efficient and cost-effective solutions for industrial waste heat recovery. Introduction Enhancing the design of brazed plate heat exchangers in vapor ab-sorption/compression heat pump (ACHP) systems is essential for reducing installation costs and improving overall efficiency. ACHP systems play a crucial role in recovery industrial waste heat by utilizing non-isothermal desorption and absorption processes, particularly when using zeotropic mixtures such as the NH₃/H₂O working fluid [1]. Unlike traditional isothermal evaporation and condensation, these processes enable better alignment with the heat source and sink temperature profiles of heat exchanger, thereby reducing entropy generation due to minimized temperature variances in heat exchangers. As a result, a better system performance prevails Additionally, the reduce saturation pressure of ammonia-water mixtures compared to pure ammonia facilitates higher outlet temperature of sink outlet and heat source for both heating and cooling at lower operating pressures, making them a superior choice for industrial heating and cooling applications. Plate heat exchangers have been designed in a variety of arrangements to meet the demanding requirements of enhanced heat transfer and lowering pressure drop performance across diverse industrial applications. Plate heat exchangers, in particular, consist of multiple corrugated plates stacked together, with their number and geometry adjustable to achieve specific thermal duty objectives. These exchangers demonstrate superior heat transfer efficiency, largely due to their ability to induce turbulent mixing even at low Reynolds numbers, making them highly effective in compact systems [2]. Moreover, plate heat ex-changers are increasingly favored over conventional shell-and-tube designs owing to their numerous advantages, including greater compactness, improved thermal performance, and the requirement for lighter structural supports [3]. The desorber plate braze plate exchanger plays a central role in industrial cooling processes, contributing significantly to energy conservation and thermal management. Desorber braze plate heat exchangers (DBPHEs) have gained prominence as efficient and compact alternatives to traditional shell-and-tube evaporator. They offer numerous
... utilized in floating LNG plants, offshore oil and gas treatment, and other fields. In recent years, these heat exchangers have also shown potential application in new-generation nuclear power, solar thermoelectric, hydrogen energy, and other fields [2,3]. Various factors such as offshore working space, pressure, manufacturing cost, and operational reliability limit the offshore heat exchangers for high-temperature reactors, supercritical carbon dioxide (S-CO 2 ), photothermal power generation, and hydrogen energy development. ...
The research reviews the study on the thermo‐mass transfer performance of heat exchangers under sloshing conditions in marine environments, aiming to promote the efficient utilization of new energy sources. It discusses the progress in the study of heat exchangers under different sloshing conditions, including theoretical models and comparisons of various swaying conditions, and comprehensively reviews the key factors influencing the enhancement or deterioration of heat transfer in heat exchangers. The research indicates that increasing the swing amplitude of spiral tube heat exchangers, reducing the swaying period, and other methods can enhance heat transfer; conversely, increasing the rolling amplitude of coil heat exchangers, extending the pitch period, and similar actions can weaken heat transfer. The mass flow rate of the working medium, steam quality, and the parameters of the sloshing motion affect the uniformity of medium distribution. When the sloshing factor is introduced, the correlation of heat transfer is highly related to the range of dimensionless numbers (such as Re and Pr) and the physical dimensions of the heat exchanger. Additionally, the article discusses techniques to mitigate the negative effects of swaying and improve heat transfer performance through improved distribution methods. Overall, the article provides significant insights into understanding the thermo‐mass transfer performance of heat exchangers in marine environments, offering valuable references for engineers and researchers in related fields.
... Studies on PHEs operating under two-phase heat transfer conditions have garnered increasing interest over the last few decades [58]. Although PHEs can function as either evaporators or condensers, research on heat transfer and pressure drop in evaporators has been more extensive than for condensers [59]. It is widely acknowledged that PHEs are susceptible to flow maldistribution issues when employed as direct expansion evaporators, primarily because of the unequal flow rates of liquid and vapor in each channel of a PHE [60,61]. ...
Plate heat exchangers are commonly used in various industrial applications, such as refrigeration, air conditioning, heat pumps, powerplants, and chemical industries. Plate heat exchangers are well known for their superior heat transfer performance, compactness, and low refrigerant charge. Despite offering several advantages, they suffer from flow maldistribution issues. The flow maldistribution can deteriorate both the heat transfer and pressure drop performance, ultimately resulting in a lower system efficiency where plate heat exchangers are deployed. The flow maldistribution issues become more pronounced when the heat exchanger size is relatively large and the number of plates is higher, limiting the deployment of plate heat exchangers in larger industrial systems. Consequently, analyzing and understanding the flow maldistribution behavior in plate heat exchangers and finding ways to mitigate flow maldistribution related issues become essential topics of interest. This review aims to address the effect of flow maldistribution on plate heat exchanger characteristics. First, the experimental and numerical works on flow maldistribution under single-phase and two-phase conditions are detailed. Subsequently, the end-channel and end-plate effects are discussed. Then, the methods to mitigate flow maldistribution in plate heat exchangers are outlined. Finally, based on a thorough literature survey and industrial requirements, future research directions are recommended.
... Plate heat exchangers (PHE) with corrugated channels were successfully employed for condensation and evaporation duties in refrigeration and air conditioning [18][19][20][21][22][23] and thermal desalination [24,25]. The corrugated PHE is efficient in two-phase applications due to its higher surface volume ratio and heat transfer coefficient than those of a shell-and-tube heat exchanger. ...
The prototype of a low-temperature thermal desalination system treating 2500 L day−1 of saline water was designed thermally and geometrically, to be integrated with a vacuum spray flash drum and spray nozzles, a plate heat exchanger-type condenser, and a thermosyphon solar water heater to produce potable water for a small community. The design bases were the feed flow rate, the feed temperature from 45 to 65 °C, the salinity of 0.035 kg kg−1, and the vacuum drum pressure from 2 to 6 kPa absolute. The estimated yield of potable water based on the simulated droplet dynamics was in the range of 68.91–75.80 %. The plate heat exchanger and the thermosyphon solar water heater were designed for effective condensation and passive heating, respectively.
... The heat transfer coefficients are calculated for both the single-phase water and the single-phase refrigerant using Equation (13). The Longo model [43], recommended by Aute et al. [44], is adopted for the condensation correlation of the refrigerant in the plate-type condenser, as detailed in Equation (22): ...
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This study develops a model for a chip-level two-phase cooling system in data centers and employs simulation to investigate its operational characteristics and performance. These findings offer valuable insights for practical implementation.
Abstract
As a powerful solution for heat dissipation in data centers, chip-level cooling continues to capture escalating attention in research and application domains. To accurately analyze system performance, identify potential avenues for system optimization, and inform future practical applications, we developed a steady-state, one-dimensional mathematical model for a novel pump-driven chip-level two-phase cooling system (PCTCS). This model was constructed based on our previous study and was confirmed against existing experimental data. Our simulations scrutinized PCTCS performance under default conditions and investigated the effects of key parameters, such as refrigerant type, condenser vertical positioning, and cooling water temperature. Results showed that the system could manage an 80 W power output from each CPU while maintaining CPU temperatures around 79 °C at a cooling water temperature of 45 °C. We discovered the choice of refrigerant had a significant impact on performance, with R32 outperforming R134a and R113. While the vertical position of the condenser influenced the PCTCS’s internal parameters, its overall impact on system performance was negligible. Moreover, provided the chip temperature remained within a safe range, our study found that increasing the cooling water temperature improved the energy efficiency ratio of the refrigerant pump and reduced the temperature difference between the chips and the cold source.
... The characteristics and properties of CF 3 I are provided in Table 2. Much research on various refrigerants in plate heat exchangers has been carried out over the years, which can be found reported by Amalfi et al. [21,22], Eldeeb et al. [23], and Tao and Ferreira [24]. However, CF 3 I is a working fluid whose heat transfer characteristics are still to be investigated. ...
Due to its low global warming potential (GWP) and good environmental properties, CF 3 I can be a suitable component t of refrigerant mixtures in the field of refrigeration and air conditioning. In this work, the local condensation heat transfer characteristics of CF 3 I were experimentally investigated in a plate heat exchanger (PHE). The condensation heat transfer experiments were carried out under conditions of vapor qualities from 1.0 to 0.0, at saturation temperatures of 25-30 • C, mass fluxes of 20-50 kg/m 2 s, and heat fluxes of 10.4-13.7 kW/m 2. Local heat transfer coefficients were found to vary in both the horizontal and vertical directions of the plate heat exchanger showing similar trends in all mass fluxes. In addition, the characteristics of local heat flux and wall temperature distribution as a function of distance from the inlet to the outlet of the refrigerant channel were explored in detail. The comparison of the experimental data of CF 3 I with that of R1234yf in the same test facility showed that the heat transfer coefficients of CF 3 I were comparable to R1234yf at a low vapor quality and a mass flux of 20 kg/m 2 s. However, R1234yf exhibited a transfer coefficient about 1.5 times higher at all vapor qualities and a mass flux of 50 kg/m 2 s. The newly developed correlation predicts well the experimentally obtained data for both CF 3 I and R1234yf within ±30%.
... Fig. 16 indicates that the heat transfer coefficients of ILs-based candidates are lower than that of H 2 O/ LiBr because of the unfavorable high viscosities and low thermal conductivities of ILs. For most working fluids, the heat transfer coefficients of the absorbers are lower compared to the generators because the heat transfer of boiling flow is stronger than that of condensation flow [79]. The heat transfer coefficient of the SHE is much lower than those of the absorber and generator because there are only single-phase flows in the SHE, while the absorber and generator are involved with two-phase flows. ...
... However, it considerably underestimates heat transfer intensity at increased velocities. A survey [36] presented different published empirical correlations for the calculation of heat transfer during condensation of refrigerants in PHE. The forms of correlations are different and depend on PHE tested and refrigerants investigated. ...
The process of steam condensation in the presence of non-condensing air inside channels of Plate Heat Exchanger (PHE) is investigated based on experimental data and the results of mathematical modelling. The model consists of a system of ordinary differential equations with nonlinear right parts, solved numerically on a computer. It describes the local process parameters distribution in channel. Each of the PHE tested samples consists of four corrugated plates with three channels between them for the flow of hot and cold streams. The experimental samples have different angles of corrugations to the longitudinal plate axis (60°, 45° and 30°). The applicability of heat-momentum and heat-mass transport analogies for such channels was confirmed, as also the preservation of the Equation for the correction on effect of transverse mass flux in criss-cross flow channels. The specific form of such Equation is proposed. It allows mathematical modelling of steam-air mixture condensation using single-phase correlations for PHE channels. The intensification of overall heat transfer compared to condensation in flat wall channels is observed. It enables the decrease of PHE heat transfer area from 2 up to 4 times compared to a flat wall channel for the same process conditions.
... Plate heat exchangers are widely used in industrial heat transfer applications as a type of highly efficient heat exchanger, especially in the case of phase change, such as condensers, evaporators and absorbers. Numerous research about heat transfer and pressure drop on condensation or evaporation in plate heat exchangers have been published [1][2], and the empirical correlations for two-phase heat transfer and pressure drop are diverse. However, the applicability of almost all of these correlations is limited; the deviation depends on the experimental background, working conditions and working fluids. ...
This paper experimentally investigates the condensation of R365mfc in a micro-structured corrugated gap with mixed 27°/63° chevron angle. The condensation mechanisms are analyzed by visualizing the flow patterns through a transparent polyurethane plate, and the measurements are carried out at saturation pressure 1.12 bar (pred = 0.034), mass flux between 6.14 and 44.56 kg/m²s and a mean vapor quality from 0.58 to 0.92. Six flow patterns are identified as the mass flux is decreasing: annular flow, wispy-annular flow, partial film flow, smooth liquid film flow, churn flow and slug flow. A flow pattern map is drawn as a function of mass flux and vapor quality, G ≈ 20 kg/m²s is considered as a transition, after which no partial film flow is observed. The combination of G ≈ 20 kg/m²s and x ≈ 0.83 is the transition of the condensation mechanism between gravity-controlled condensation and a combination of gravity-controlled and convection condensation. The frictional pressure drop increases with the increase of mass flux and vapor quality and is not influenced by flow patterns. The experimental heat transfer coefficients and frictional pressure drop are compared with the prediction results calculated by the correlations in the literature and a new heat transfer model is developed, which includes the individual heat transfer models of a gravity-controlled regime, a transition regime and a shear force-controlled regime as well as the transition criterion between these regimes. The new model predicts 97% of experimental data within ±30%, the root mean square error and the mean absolute error is 12.7% and 9% respectively.
... Für die Verdampfung des NH3/H2O-Gemischs mit hohem NH3-Massenanteil im Generator wird die Korrelation von [19] verwendet, um die Korrelation von [18] zu erweitern. Nach [20] kann die Korrelation von [19] für NH3-Massenfraktionen von 0,42 bis 0,62 verwendet werden. Die Korrelationen zur Berechnung der Wärmeübergangskoeffizienten von Wasser sind in TIL-Suite [10] implementiert und basieren auf den im VDI-Wärmeatlas [21] enthaltenen Formulierungen. ...
... Shell and tubes heat exchanger. Plate heat exchangers [190][191][192][193][194][195][196][197][198] are gas to gas and liquid to liquid heat exchangers. It consists of alternating plates in which hot and cold stream flow alternately through those plates. ...
Finding new sources of wasted heat is no longer the main challenge in heat recovery technology, it is summarized by proposing new ways for extracting the dissipated heat or by suggesting new hybrid systems that are composed of multi-recovery stages which maximize energy utilization and improve the system efficiency. Based on the aforementioned context, the purpose of the present PhD study is to suggest new hybrid heat recovery systems/concepts from exhaust gases and perform cases studies and parametric analyses to predict and optimize the thermal performance of the system.Two hybrid heat recovery systems are proposed in this PhD and studied analytically: Domestic Thermoelectric Cogeneration System (DTCS) and Domestic Thermoelectric Cogeneration Drying System (DTCDS). Optimization analyses are performed on a recently suggested heat recovery heat exchanger, named Multi-Tube Tank (MTT). New hybrid system is proposed that combines MTT with concentric tube heat exchanger to recover dissipated thermal energy from exhaust gases and cooling water respectively of a diesel electric generator.
... A detailed review of earlier research work and a discussion on the thermal-hydraulic performance of condensation in PHEs can be found in the book by Wang et al. [18]. A survey of correlations for heat transfer and pressure drop for condensation in PHEs is given by Eldeeb et al. [19]. Recently, Tao and Ferreira [20] assess eight heat transfer correlations and six frictional pressure drop correlations for condensation in PHEs with the database. ...
Plate heat exchangers are widely used for two-phase heat transfer in the industrial applications, and recently more attention has been paid to the plate heat exchangers with enhanced surface due to their better heat transfer performance. In this paper, the local condensation heat transfer coefficients are studied using R134a in a micro-structured plate heat exchanger. In order to obtain a more accurate prediction model, a series of measurements are conducted under various operating conditions. The mass flux of R134a varied from 47 kg/m ² s to 77 kg/m ² s, the saturation pressure in the condenser ranged from 6.32 bar to 8.95 bar, and the value of the heat flux was between 13 kW/m ² and 22 kW/m ² . The local two-phase Nusselt number increases with the increase of the mass flux. As the saturation pressure increases, the local two-phase Nusselt number increase at the beginning of the condensation and decrease at the end of the condensation. However, the effect of heat flux on local heat transfer is irregular, due to the interaction of these parameters in the experiment. Comparing with the unstructured plate heat exchanger, R134a condenses faster at the beginning of the process in the micro-sturctured plate heat exchanger, and the local heat transfer performs better when the vapor quality is lower. Combing with the phenomenon that the overall heat flux in micro-structured plate is larger under the same working conditions, it shows that the overall heat transfer of the micro-structured plate is improved, but the local heat transfer uprades only at lower vapor qualities. A new correlation is developed, it predicts all the experimental data within the root mean square error 10%, and a new correlation for the waterside is suggested as well.
... This is because the heat transfer coefficients in heat exchangers are the functions of temperature, pressure, thermophysical properties, geometric constraints, and flow characteristics [32][33][34]. For instance, many studies reported the plate chevron angle (ß) as the most important geometric parameter governing the thermodynamic performance of PHXs [35][36][37][38][39]. Similarly, flow rate, fluid properties, and heat duty also have a remarkable effect on thermohydraulic performance [40][41][42]. The optimization studies have also reported multiple geometric and process parameters that control the PHX performance [43][44][45][46]. ...
Integration of energy recovery section with thermal desalination systems improves their performance from thermodynamics, economics, and environmental viewpoints. This is because it significantly reduces input energy, heat transfer area, and capital cost requirements. Above all, the system outlet streams can achieve thermal equilibrium with the environment by supplying heat for useful preheating purposes thus reducing the environmental impacts. The plate heat exchangers are generally employed for this purpose as preheaters. The current paper presents a comprehensive investigation and optimization of these heat exchangers for thermal desalination systems applications. An experimentally validated numerical model employing Normalized Sensitivity Analysis and Genetic Algorithm based cost optimization is developed to investigate their performance at assorted operating conditions. The analysis showed that the heat transfer coefficient, pressure drop, and outlet water cost were improved by an increase in feed flow rate. However, with an increased flow rate, the comprehensive output parameter (h/ΔP) decreased due to the high degree increase in pressure drop. Moreover, an increase in the chevron angle reduced the heat transfer coefficient, pressure drop, and water cost. Finally, the optimization lowered the heat transfer area by ~79.5%, capital investment by ~62%, and the outlet cost of the cold stream by ~15.7%. The operational cost is increased due to the increased pressure drop but the overall impact is beneficial as Ctotal of equipment is reduced by ~52.7%.
Heat exchangers are indispensable components of industrial processes, significantly impacting the environment by reducing pollution and conserving energy. The rising adoption of plate heat exchangers (PHEs) in industries is fueled by their compact design, and ability to operate effectively in minimal temperature differentials, emphasizing the need for energy efficient PHE. This paper extensively reviews diverse aspects of studies on PHEs, covering critical parameters like novel profile designs, innovations, biomimicry, end plate effects, structural analysis, design, multi-objective optimization, and a comparison of cross flow and counter flow arrangements. It includes in depth examinations of different passive techniques like surface roughness impact, embossment types, and the role of fins in enhancing heat transfer. Capsule type embossing outperforms corrugated PHEs having high Nusselt number (Nu) and low friction factor (f). Research findings also show that wire inserts can lead to a pressure drop increase of up to 72%, while wavy chevron designs can reduce pressure drop by approximately 30%. Additionally, novel gasket modifications have been reported to enhance heat transfer by 75%, while biomimetic lung-pattern approaches have demonstrated a 68% reduction in friction factor. The review explores profile based studies and showcases recent innovations in technology, materials, and design approaches for PHEs. This paper also summarizes the multi-objective optimization strategies and real world case studies that illustrate diverse applications and also suggests the scope and recommendations for future work. This comprehensive review is a valuable resource for researchers, engineers, and practitioners, enhancing understanding of factors driving innovation in PHEs.
Plate Heat Exchangers (PHEs) are becoming more significant day by day in many heat transfer applications. They usually consist of thin, rectangular, pressed stainless steel plates that are stacked together such that hot and cold fluid streams alternately pass through the inter-plate passages. The plates have corrugated patterns that not only increase the effective surface area for heat transfer but also modify the flow field to provide enhanced thermalhydraulic performance. The plate surface corrugations readily promote enhanced heat transfer through several mechanisms, including swirl or vortex flows, boundary layer disruption and reattachment, small hydraulic diameter passageways, and increased effective heat transfer area The purpose of the present study is to investigate the boiling and condensation heat transfer of low GWP refrigerants such as CF3I and mixture refrigerant R454B inside a plate heat exchanger. The refrigerant flow channel is formed by two plates with chevron-shaped grooves in the test section, which has eight plates in total. On other plates, channels for cooling or heating water are formed and the local temperature distribution is measured. According to the evaporation or condensation process, the refrigerant in this experiment flows in the middle of three vertical flow channels in the test section, moving either upward or downward. When evaporation is taking place, heat source water is moving downward in the outer two channels while refrigerant is moving upward in the middle channel. In the test section, there are 160 measurement points in total with 4 sets of 8 symmetrical points in the horizontal direction and 5 symmetrical points in the vertical direction. A total of 20 thermocouples were installed in the test section for the measurement of the wall temperature of the refrigerant and heat source water side in order to measure the local heat transfer characteristics of the CF3I and the mixture refrigerant R454B. Local heat transfer coefficient was obtained under the experimental conditions of the masse flux of 20 kg/m2s and 50 kg/m2s for CF3I and 10 kg/m2s and 50 kg/m2s for R545B. The local heat transfer coefficient of the refrigerant CF3I and the mixture refrigerant R454B are found to vary horizontally and vertically. The result shows that the local heat transfer increases with increasing mass flux and vapor quality. The experimentally obtained data of CF3I and R454B were compared with that of R1234yf and R454C, respectively and correlations with available literature. A prediction method for heat transfer coefficient is developed to predict the condensation heat transfer coefficient of pure working fluids.
The model of a single flow channel of a plate heat exchanger (PHE) has been established, and the condensation characteristics of vapor with different saturation temperatures and vapor superheating levels have been investigated. The results show that with a higher vapor saturation temperature, the average surface heat transfer coefficient (HTC) increases. The HTC of saturated steam at a saturation temperature of 348.15 K is about 104.1% higher than that at a saturation temperature of 323.15 K. The influence of vapor superheating is weaker compared to that of the saturation temperature. With the increase of vapor superheat, the surface average HTC first increased and then decreased. The HTC of superheated vapor with a vapor superheating of 10 °C is about 0.72% higher than that of saturated vapor. In industrial applications, it is appropriate to control the vapor inlet superheating to be between 5-10°C.
This paper presents an experimental investigation on local heat transfer characteristics of single-phase flow in a plate heat exchanger (PHE). The local heat transfer coefficient is evaluated using a test section with PHE geometry for measuring wall temperature distribution. The test section of 1.5 mm thickness is employed to consider the heat conduction effect of the heat transfer plate. The results indicated that the local heat transfer coefficient is influenced by the development of the thermal boundary layer along the flow direction and the maldistribution of water flows along both the direction perpendicular to the flow and the stacking direction. The harmonic mean heat transfer coefficient calculated by the measured local heat transfer coefficient agrees with the average heat transfer coefficient evaluated by the modified Wilson plot method within ±25 % and within ±16 % for the hot side and the cold side, respectively.
Increasing energy usage efficiency requires enhanced heat energy recuperation between process streams in the industry and civic sector with waste heat utilization. The condensation of different vapours is the process encountered in many industrial applications. Increasing the heat recuperation in this process is possible with efficient heat transfer equipment, among which a Plate Heat Exchanger (PHE) is at the leading position. A number of research works have been conducted in recent years concerning construction development and heat transfer enhancement in conditions of limited pressure drop to increase PHE performance in condensation processes. The results of studies on heat transfer and pressure drop in the two-phase condensing flow inside channels of PHE with different geometries of corrugations are discussed. In many implementations, the total pressure drop allowable for gaseous streams in heat exchangers is relatively small. The structure of two-phase flow in PHE channels of complex geometry is very different than in tubes and flat wall channels. The relative differences in approaches to enhance PHE performance in condensation processes based on its modelling, optimisation and design are analyzed. The directions and prospects for future developments are formulated, and potential savings for the economy and the environmental footprint is presented.
Process models using simplified heat exchanger (HE) models are often analyzed using methods based on derivatives or optimization procedures, where even small numerical errors can cause algorithms to fail. This article explores the use of numerical approximations for calculating pinch temperature and UA-value, including novel high-order polynomial methods using equidistant and Chebyshev grids. The results show that the mainstream methods, where LMTD and pinch temperature are calculated from grid values, are 2–5 times slower than the high-order methods if requiring accuracy better than 1%. If a 0.01% accuracy is needed high-order methods are often 10–20 times faster. Numerical errors in high-order schemes with pure fluids converge quickly to zero when increasing the grid size, and schemes with more than 30 grid points generate errors less than 1E-4%. High-order methods were less successful for fluid mixtures, where a novel hybrid high and low-order pinch temperature scheme is recommended.
The results of mathematical modelling and experimental study of plate heat exchangers (PHEs) in steam-air mixture condensation are presented. The mathematical model is validated by test data for PHE in the industry and for five experimental samples with corrugation angles, 30°, 45°, and 60° and corrugation heights 5, 7.5 and 10 mm. With no limited pressure drop in PHE, its heat transfer area can be decreased up to 4 times with the plate's corrugations angle of 60°. When pressure drop on the side of condensing stream is limited, at a small mass fraction of air, PHE with corrugated plates' heat transfer area can be smaller than in PHE assembled from flat plates about 1.5 times ± 11% at channels of different corrugations geometries. For commercially produced plate-and-frame PHE, the pressure losses at channel entrance and distribution zones should be accounted. For plates with a corrugations angle of 60°, their share in total pressure drop can be from 7% up to 39.3%, while at a corrugations angle of 30°, up to 59%. The final choice of corrugation angle and height for plates designed for specific duty can be made by solving a future optimisation problem with a developed mathematical model.
Based on the known scientific literature, there are no correlations in the scientific literature to predict the two-phase heat transfer coefficients of Hydrofluoroethers pure fluids and zeotropic mixtures used in plate heat exchangers. This work has allowed the development of evaporation and condensation correlations for such fluids. Correlations based on dimensionless numbers and working fluids critical properties gave promising results, with a prediction of the two-phase heat transfer coefficient around 15% for heat source and 50% for cooling source which led respectively to a prediction of 4% and 6% for the global thermal power exchanged. The behavior of the organic Rankine cycle heat sources and the working fluids used within was also been studied. For this purpose, the influence of the heat sources flow rates variation on the performance of the hot and cold exchangers was analyzed. Results obtained showed a similar behavior and performance variation of the heat exchangers both when using pure fluids and zeotropic mixtures. Zeotropic mixtures working fluids in ORC system are often supposed in the literature to significantly increase the performance of this thermodynamic cycle due to better heat transfer at the hot source. Nevertheless, the great majority of these studies are numerical and do not take into account the interactions and system effects existing within the thermodynamic cycle when using a mixture instead of a pure fluid. This work has allowed to highlight this complexity and to provide a better understanding of the use of zeotropic mixtures.
Heat exchanger plays a crucial role in the functioning of chemical industries, diary and food processing industries, and thermal plants. The enhancements in heat exchangers are mainly aimed at minimizing the energy consumption. An efficient heat exchanger is one that provides high heat transfer rate with minimum pumping power at low cost for energy saving. PHEs are used in various engineering fields due to their simplicity, flexibility, and maintainability related to others. In this paper, passive surface enhancement methods for single-phase and two-phase flow and application of nanofluids in different types of PHE are reviewed. The effect of geometrical parameters on hydraulic-thermal performance and occurrence of fouling deposits in PHE are also discussed. The chevron angle is found to be the most dominating geometrical parameter to change the flow properties. HTC, Nu, and ΔP increased with the increase in β, γ, and ϕ. For the two-phase flow, ΔP increased with the rise in vapor quality, mass flow rate and reduced with increase in saturation pressure. The optimum geometrical parameters for maximum heat transfer are β: 30°-60°, γ: 0.075–0.6, and φ: 1.18–1.3. The use of nanofluids in laminar flow condition is suggested by most of the literature.
Fouling of heat exchanger surfaces is a major concern in the industry, resulting in performance losses through a decrease in the overall heat exchange coefficient. Control methods exist but are costly and have a strong environmental impact. Thus, the use of physical treatments is very promising, because the action is done on the clogged surface, in the bulk or in the solution. The present study shows the influence of ultrasonic guide waves on the crystallization of calcium carbonate inside a plate heat exchanger from scaled water. An experimental pilot was set up to study the scaling phenomenon. Several operating parameters such as flow rate, duration, and temperature were experimentally varied in order to identify their influence on the scale deposition in the heat exchanger. Subsequently, a thermodynamic prediction was performed by geochemical modeling using the Phreeqc software in order to get an idea of the nature of the deposit formed after the heating of scaled water. The main objective of this work was the determination of the impact of ultrasonic treatment on the mineral deposit, qualitatively and quantitatively. Therefore, four types of experiments lasting three days are presented in this paper to experimentally show the influence of ultrasound generated by a 35-50 kHz transducer on scale formation. The amount of solid deposited in grams/per day/area, the polymorphism of the formed crystals, and the number, size and size distribution of the particles were analyzed. Disassembly of the exchanger allowed access to the distribution of scale on the plates, and thus justified the choice of location for the 35-50 kHz transducer. It was also possible to estimate the thickness of the scale experimentally by 3D digital microscopy and to ensure the absence of microcrystals in the pores of the plate by analyzing the surface roughness. The results obtained were compared to the experimental measurements with and without the presence of the 35-50 kHz transducer. This allowed the evaluation of the effect of guided ultrasonic waves for the prevention of scale deposits. The presence of a single medium power transducer reduced mineral scale deposition in a plate and gasket heat exchanger by 76%.
Numerical analysis of the thermal and flow behavior of CuO-water nanofluid under turbulent regions in a shell and tube heat exchanger was conducted using ANSYS Fluent. Twenty-nine (29) nm diameter CuO nanoparticles, and water as base fluid were used in the study. The nanofluid was simulated at different particle loading (0.1 to 1%vol), and under three sets of Reynolds number (ranging from 17,000 to 71,000), to study the effects on heat transfer coefficient, pressure drop, and nanofluid thermal and hydrodynamic behavior. Increasing the particle loading and Reynolds number was found to enhance both the heat transfer rate and pressure drop. A maximum of 48% enhancement in the heat transfer was observed at the highest particle loading, but with the consequence of doubled pressure drop. Performance indices greater than 1 were attained for particle loading below 0.25%vol, regardless of the Reynolds number. The conditions that produced the highest index were at the lowest particle loading and lowest Reynolds number. No significant difference in the flow behavior between water and CuO-water nanofluid was observed. However, the thermal profiles for 0.1%vol CuO-water nanofluid highlighted the enhancements in heat transfer along the shell and tube heat exchanger.
This investigation aims to compare the experimental and theoretical ammonia boiling heat transfer coefficient in a plate heat exchanger (PHE). Measured data were gathered during functioning of a single stage vapor mechanical compression refrigeration system placed in the Thermal Systems Research Center of the Technical University of Civil Buildings Bucharest (TUCEB). Experimental values fall within the range of 1377–3050 W/m²K. Theoretical values were obtained from 12 correlations confirmed by the literature to date, developed for similar working conditions. The experimental values are close to the theoretical ones for Shah and Jokar correlations applied for a vapor quality of 0.5. The theoretical values are in the range of 1440–2076 W/m²K and 1558–2318 W/m²K, respectively. Shah correlation predicted 82.35% of all data within the ±30% error band at an MAE value of 14.23%, and Jokar et al. predicted 76.47% of all data within the ±30% error band with an MAE value of 17.7%.
Theoretical research of the constructal optimization of marine steam power plants is introduced in this study from two aspects: ship steam power plants and ocean thermal energy conversion plants. First, reviews are conducted on the main heat exchange component models of ship steam power plants, including the evaporator, superheater, economizer, whole boiler and condenser, main heat exchange, and energy conversion components, and system models of ocean thermal energy conversion plants, including the evaporator, condenser, dual-pressure turbine, and whole system. Then, constructal optimization of the main components of the two power plants and constructal thermodynamic optimization of the ocean thermal energy conversion plant based on modern thermal theories such as entropy generation minimization theory, finite time thermodynamics theory, entransy theory, and constructal theory are introduced. The similarities and differences in the results obtained before and after optimization, as well as the different optimization objectives and system structures, are extensively compared. Finally, the application prospects of constructal thermodynamic optimization to the optimal designs of energy transfer and conversion processes are made considering theoretical research on reduced energy consumption of power plants.
Plate frame heat exchangers are common in liquid-coupled vapor compression systems due to their compactness and ease of maintenance. In some of these systems, the refrigerant within the evaporator can enter the heat exchanger as a subcooled liquid. As a result, the refrigerant passes through three different phases: single-phase liquid, two-phase fluid, and a superheated vapor. Unfortunately, there have been limited prior studies that have identified the best method to predict performance under these circumstances. Furthermore, previous investigations have not evaluated refrigerant evaporation in large industrial sized plate frame heat exchangers under conditions experienced in the present study experimental test facility, especially at mass fluxes below 7 kg m⁻² s⁻¹. In the present investigation, a model was developed to predict the performance of plate and frame heat exchangers when the fluid enters as a subcooled liquid and exits as a superheated vapor. The model used full-sized plate heat exchanger geometry that was discretized into 20 sections to accurately capture local heat transfer and pressure drop effects. The model was validated using an R134a counter flow heat exchanger used in a turbo-compression cooling system test facility that had subcooled liquid entering the evaporator at low mass fluxes. A variety of empirical correlations were evaluated to determine what combination yielded the best predictive capability over the following range of conditions: 5.8 < G < 6.8 kg m⁻² s⁻¹, 2 < q’’ < 2.8 kW m⁻², and 10°C < Tsat < 15°C. When the correlations used a fixed control volume length in the heat flux calculation, the most accurate combination resulted in a mean absolute error of 5.5%. Future studies can use the approach described here to optimize heat exchanger size and performance.
The vapour condensation is typical for processes of waste heat recovery from exhaust gases. It complicates the selection of condensers and requires reliable correlations for estimation of heat transfer coefficients and pressure drop in the unit. In the presented paper, a novel model was elaborated to be applied for commercially produced plate heat exchangers (PHEs) assembled from plates with different geometries of corrugations, which accounts the change of process parameters at the main corrugated field, in PHE collectors and channels distribution zones. The process of waste heat recovery from exhaust gases after tobacco drying is discussed in the case study. The pilot unit assembled with PHE of TS-6MFG type manufactured by Alfa Laval was installed at a tobacco factory. The examined condensing media was an incoming air-steam mixture with 10 % of air content and temperature equal to 140 °C. The comparison of modelling results and data of industrial operation has shown good accuracy of prediction. It allowed recommending obtained correlations and developed a mathematical model for the design of plate heat exchangers in applications with heat utilisation from exhaust gases after drying processes in the industry, with a considerable saving of heat energy. In the considered example, it is up to 640 kW or 2,090 kJ/kg of exhaust gases.
The pressure drop in the two-phase condensing flow of air-steam mixture inside channels of plate heat exchanger (PHE) with different geometries of corrugations is studied based on experiments and one-dimensional mathematical modelling. The experiments were made with five samples of the PHE channel. In three of them plates with corrugations inclination angles 30, 45 and 60 degrees at the same height of corrugations 5 mm. The other two plates corrugations height was 7.5 and 10 mm at the same pitch to height ratio and inclination angle of 60 degrees. The correlation of pressure drop data for all experimental samples by average process parameters is not able to give acceptable accuracy. The correlation for local pressure gradients in two-phase condensing flow is identified using a developed one-dimensional mathematical model. The model of separated flows of phases is employed for channel zones close to air-steam mixture entrance. Further on channel length with an increase of liquid phase quantities, its combination with the dispersed annular flow structure model is used. The proposed equations can be included in the mathematical model when designing PHE and optimising the geometrical form of corrugations on its plates for steam condensation processes from an air-steam mixture.
div class="section abstract"> This paper investigates the pressure drop with and without condensation inside a charge air cooler. The background to this investigation is the fact that the stored condensate in charge air coolers can be torn into the combustion chamber during different driving states. This may result in misfiring or in the worst-case lead to an engine failure. In order to prevent or reduce the accumulated condensate inside charge air coolers, a better understanding of the detailed physics of this process is required. To this end, one single channel of the charge air side is investigated in detail by using an experimental setup that was built to reproduce the operating conditions leading to condensation. First, measurements of the pressure drop without condensation are conducted and a good agreement with experimental data of a comparable heat exchanger reported in Kays and London [ 1 ] is shown. In case of condensation it is observed that the accumulated condensate leads to an increase in pressure drop. An equilibrium state is established between the condensate formed and the one discharged from the charge air cooler, which leads to pressure fluctuations. Furthermore, the amount of the accumulated condensate in the charge air cooler is considered when determining the Fanning friction factor. It is shown that with this consideration the two-phase pressure drop can be described by the single-phase Blasius approach in the investigated operating range of the charge air cooler. The mean deviation of the measured data from the correlation amounts to about 3.8%.
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There are two basic modes of condensation, namely, film condensation and dropwise condensation. Heat transfer coefficients during dropwise condensation are much higher than those during film condensation. This chapter is concerned with film condensation and discusses dropwise condensation. All material is applicable only to non‐metallic fluids unless otherwise noted. The chapter deals with condensation of mixtures and provides information on single component vapors. It is devoted to liquid metals. It is unlikely that the mechanism of heat transfer of liquid metals be quite different from that of non‐metallic fluids. Most probably, the apparent discrepancy is because the resistance of metallic condensate is very small compared with that of non‐condensables, which prevents accurate measurement of heat transfer coefficient.
This chapter is about boiling of saturated liquids prior to critical heat flux. It considers a variety of heat exchangers. This includes circular and non‐circular channels, tube bundles, coils, etc. Further, heat transfer of liquid metals is very different from that of non‐metallic fluids. Therefore, these topics also addressed. The chapter deals with various problems such as effect of gravity. It deals with single‐component pure non‐metallic fluids unless otherwise noted. There are many types of plate heat exchangers. The most widely used type are those with herringbone or chevron plates. Other types include plain plate, serrated fin, and plate fin types. These are discussed in this chapter. In the refrigeration industry, falling film evaporators are increasingly replacing the flooded evaporators that have upwards crossflow, described in this chapter. The advantages offered by falling film evaporators include higher heat transfer coefficients and lower charge of refrigerant.
Plate heat exchangers are used regularly in the heating, ventilating, air conditioning, and refrigeration industry. There is an urgent need for detailed and systematic research regarding heat transfer and the fluid flow characteristics of these types of exchangers. As an initiative in this respect, a literature search is presented on plate heat exchangers. New correlations for evaporation heat transfer coefficient and friction factor are introduced, which are applicable to various system pressure conditions and plate chevron angles. The correlations are based on actual field data collected during several years of installation and operation of chillers, and they are intended to serve as design tools and perhaps as a starting point for future research.
This article presents a study on heat transfer in condensation of pure and mixtures of hydrocarbons in a compact welded plate heat exchanger. Three pure fluids (pentane, butane, and propane) and two mixtures (butane + propane) have been used. The operating pressure ranges from 1.5 to 18 bar. For pure fluids, two heat transfer mechanisms have been identified. For low Reynolds numbers, the condensation occurs almost filmwise and the heat transfer coefficient decreases with increasing Reynolds number. For higher values of the Reynolds number, the heat transfer coefficient increases gently. The transition between the two regimes is between Re = 100 and 1,000 and depends on the operating conditions. For mixtures, the behavior is different. For low Reynolds numbers, mass transfer affects heat transfer and reduces the heat transfer coefficient by a factor of up to 4. Correlations for filmwise and in-tube condensation do not predict the results accurately, and a specific correlation is proposed for pure fluid condensation. For mixtures, the condensation curve method does not allow mass transfer effects to be taken into account, and more work is required to establish an accurate predictive model.
Experimental heat transfer coefficients are reported for HFC-134a and CFC-12 during in-tube single-phase flow, evaporation and condensation. These heat transfer coefficients were measured in a horizontal, smooth tube with an inner diameter of 8.0 mm and a length of 3.67 m. The refrigerant in the test-tube was heated or cooled by using water flowing through an annulus surrounding the tube. Evaporation tests were performed for a refrigerant temperature range of 5–15°C with inlet and exit qualities of 10 and 90%, respectively. For condensation tests, the refrigerant temperature ranged from 30 to 50°C, with et and exit qualities of 90 and 10%, respectively. The mass flux was varied from 125 to 400 kg m−2 s−1 for all tests. For similar mass fluxes, the evaporation and condensation heat transfer coefficients for HFC-134a were significantly higher than those of CFC-12. Specifically, HFC-134a showed a 35–45% increase over CFC-12 for evaporation and a 25–35% increase over CFC-12 for condensation.
Plate heat exchangers are used regularly in the heating, ventilating,
air conditioning, and refrigeration industry. There is an urgent
need for detailed and systematic research regarding heat transfer
and the fluid flow characteristics of these types of exchangers.
As an initiative in this respect, a literature search is presented
on plate heat exchangers. New correlations for evaporation heat transfer
coefficient and friction factor are introduced, which are applicable
to various system pressure conditions and plate chevron angles. The
correlations are based on actual field data collected during several
years of installation and operation of chillers, and they are intended
to serve as design tools and perhaps as a starting point for future
research.
This paper deals with the design of plate heat exchangers for processes in single-phase, evaporation and condensation. Some results are given for the thermal and hydraulic performance of corrugated channels in single phase flow. The flow pattern is analysed to give some local information on the heat transfer and the velocity field. In two phase flows, the heat transfer coefficient and the pressure drop are correlated with models originally developed for smooth tubes. Some recommendations are proposed for future research.
Abstract This paper presents a new model for refrigerant boiling inside Brazed Plate Heat Exchangers (BPHEs) based on a set of 251 experimental data previously obtained by the authors which includes data points relative to HFC refrigerants (HFC236a, HFC134a, HFC410A), HC refrigerants (HC600a-Isobutane, HC290-Propane, HC1270-Propylene), and also a new low Global Warming Potential (GWP) HFO refrigerant (HFO1234yf). The new model includes specific equations for nucleate and convective boiling. The new model was compared against a set of 505 experimental data obtained by different laboratories, which includes HFC134a, HFC410A, HFC507A and HCFC22 data points with different plate geometries. The mean absolute percentage deviation between experimental and calculated data is around 20%.
This paper presents a new computational procedure for refrigerant condensation inside herringbone-type Brazed Plate Heat Exchanger (BPHE). A transition point between gravity controlled and forced convection condensation was found for an equivalent Reynolds number around 1600. At low equivalent Reynolds number (<1600) the heat transfer coefficients are not dependent on mass flux and are well predicted by a simple model based on the Nusselt (1916) equation for vertical surface. For higher equivalent Reynolds number (>1600) the heat transfer coefficients depend on mass flux and condensate drainage is controlled by the combined actions of gravity and vapour shear. A new model was developed for predicting the heat transfer coefficients in the forced convection condensation region. This new model was also applied to super-heated vapour condensation by using the equation of Webb (1998) to account for super-heating effects. The new computational procedure was compared against data from the literature: the mean absolute percentage deviation between experimental and calculated heat transfer coefficients was lower than 16%.
The chapter presents the experimental data with no particular theory, to search for significant effects of physical parameters. The present method gains power, scope, and speed by avoiding redundancies among the fluid properties, which otherwise lead to intolerable and unhelpful complexity of analysis and to a confusing multiplicity of correlations that look different but are often numerically rather similar. The chapter examines existing correlations, finding a reason for the fact that they are often numerically similar, despite using very different properties that leads to the improved method of analysis. It has always required a major effort of data reduction to compare experimental data with correlations that involve many properties. Comparisons between competing claims of different correlations are confused by uncertainties and indeed errors in tabulated property values, especially for uncommon fluids or old tabulations. These problems are greatly reduced by using a simpler correlation for example, in terms of reduced pressure, where the only tabulated property required for each fluid is critical pressure. The chapter concludes that taking advantage of that simplicity, correlations of a more subtle type can be considered without undue labor in data reduction.
The boundary-layer equations of momentum and energy are written in a modified integral form and solved for the case of laminar film condensation along a vertical flat plate. The analysis differs from previous works by employing the more realistic boundary condition of stationary vapor at large distances instead of zero velocity gradient at the interface. Solutions for both the liquid film and vapor boundary layer are given for the case μv ρv ≪ μρ. Velocity and temperature profiles are obtained using perturbation method and the modified integral boundary-layer equations. The results show a significant negative velocity gradient at the interface as a result of vapor drag except for small values of kΔt/μλ. Theoretical heat-transfer coefficients are computed and found to be lower than previous theories, especially for low Prandtl numbers. Comparison with experimental heat-transfer data is given. The heat-transfer results are also presented in the form of an approximate formula for ease of application.
The plate heat exchanger (PHX) has been widely used as a heat exchanger in fresh water generators (FWGs) at low mass flux conditions. In this study, the flow boiling heat transfer and pressure drop characteristics of water in a PHX for the FWG were measured by varying mass flux from 14.5 to 33.6 kg m−2 s−1, heat flux from 15.0 to 30.0 kW m−2, and mean vapor quality from 0.09 to 0.6 in the pressure range of 112–121 kPa. The flow boiling heat transfer of water in the PHX was in the convective boiling region. The flow boiling heat transfer coefficient decreased with increasing mean vapor quality and decreasing mass flux. However, the effect of the heat flux on the flow boiling heat transfer coefficient was almost negligible. In addition, the two-phase frictional pressure drop increased with increasing mean vapor quality and mass flux, but it remained nearly constant according to the heat flux. Two-phase heat transfer and pressure drop correlations for water in PHXs were developed based on the measured data. The proposed heat transfer and pressure drop correlations showed mean absolute deviations of 4.4% and 10.4%, respectively, compared with the measured data.
Ammonia is a naturally occurring environment friendly refrigerant with attractive thermo-physical properties. Experimental investigation of heat transfer and pressure drop during steady state evaporation of ammonia in a commercial plate heat exchanger has been carried out for an un-symmetric 30°/60° chevron plate configuration. Experiments were conducted for saturation temperatures ranging from -25°C to -2°C. The heat flux was varied between 21 kW m-2 and 44 kW m-2. Experimental results show significant effect of saturation temperature, heat flux and exit vapor quality on heat transfer coefficient and pressure drop. Current mixed plate configuration data are compared with previous studies on the same heat exchanger with symmetric plate configurations. This comparison highlighted importance of optimization in selection of the heat exchangers. Correlations for two phase Nusselt number and friction factor for each chevron plate configuration considered are developed. A Nusselt number correlation generalized for a range of chevron angles is also proposed.
Experiments to measure the condensation heat transfer coe�cient and the pressure drop in brazed
plate heat exchangers (BPHEs) were performed with the refrigerants R410A and R22. Brazed
plate heat exchangers with di�erent chevron angles of 45�, 35�, and 20� were used. Varying the
mass
ux, the condensation temperature, and the vapor quality of the refrigerant, we measured the
condensation heat transfer coe�cients and the pressure drops. Both the heat transfer coe�cient and
the pressure drop increased proportionally with the mass
ux and the vapor quality and inversely
with the condensation temperature and the chevron angle. Correlations of the Nusselt number and
the friction factor with the geometric parameters are suggested for the tested BPHEs.
An algorithm for the steady-state simulation of a plate heat exchanger is presented, which takes into account a general unit with n flow channels, in which the hot and cold streams may flow co- or countercurrently, according to any of the possible flow patterns: series or parallel flow, with either single or multipass arrangements. The temperature profiles are calculated using the numerical method originally proposed by T. Zaleski, K. Klepacka [J. Mass Heat Transfer 35 (5) (1992) 1125], which approximates the solution for each channel by a linear combination of exponential functions. In order to validate the developed algorithm, simulation results were compared with exact analytical solutions available for simple cases and experimental data. Once validated, the algorithm was successfully utilised to simulate the steady-state operation of an industrial plate heat exchanger used for pasteurising milk.
This paper presents the heat transfer coefficients and the pressure drop measured during condensation of the new low Global Warming Potential (GWP) refrigerant HFO1234yf inside a brazed plate heat exchanger: the effects of saturation temperature, refrigerant mass flux and vapour super-heating are investigated. The heat transfer coefficients show weak sensitivity to saturation temperature and great sensitivity to refrigerant mass flux. At low refrigerant mass flux (<20 kg m−2 s−1) the heat transfer coefficients are not dependent on mass flux and condensation is controlled by gravity. For higher refrigerant mass flux (>20 kg m−2 s−1) the heat transfer coefficients depend on mass flux and forced convection condensation occurs. The condensation heat transfer coefficients of super-heated vapour are from 8 to 11% higher than those of saturated vapour. HFO1234yf exhibits heat transfer coefficients lower (10–12%) and frictional pressure drop lower (10–20%) than those of HFC134a under the same operating conditions.
A new model has been developed for the analysis of plate heat exchangers with multi-fluid, multi-stream and multi-pass configurations. The model divides the entire heat exchanger into multiple slices in the direction of fluid flow. For the channels in each slice, the wall temperatures are assumed to be constant such that each channel can be solved without the need of knowing the fluid condition in the adjacent channels. In the top level, all the slices are iterated using a successive substitution approach. The model is capable of handling both single-phase and two-phase flow. In general, plate heat exchangers are used with two to three fluids, but the model is capable of handling more than three fluids wherein each fluid can undergo phase change. The model was verified against the P-NTU closed form expressions for single-phase flow in plate heat exchangers with various flow configurations. The model was validated against in-house experimental data for single-phase water, two-phase ammonia and R22 boiling. The effect of discretization and the speed up on multiple cores was investigated.
This paper presents the experimental heat transfer coefficients and pressure drop measured during vaporisation of the new low Global Warming Potential (GWP) refrigerant HFO1234yf inside a Brazed Plate Heat Exchanger (BPHE): the effects of heat flux, mass flux, saturation temperature (pressure) and outlet conditions are investigated. The heat transfer coefficients show great sensitivity to heat flux and outlet conditions and weak sensitivity to saturation temperature (pressure). The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow and therefore a quadratic dependence on refrigerant mass flux. The saturated boiling experimental heat transfer coefficients are reproduced by two well-known equations for nucleate boiling, Cooper (1984) and Gorenflo (1993), with reasonable agreement. The heat transfer and pressure drop measurements are complemented with IR thermography analysis in order to quantify the portion of the heat transfer surface affected by vapour super-heating.
Plate heat exchangers (PHE’s) are being used to an increasing extent as refrigerant evaporators but published information on their performance in this mode is rather limited. In this paper, two-phase heat transfer and pressure drop characteristics are presented for PHE’s when used as refrigerant liquid over-feed evaporators. Laboratory experiments were carried out with three industrial PHE’s having different chevron angle combinations, using refrigerant R134a and R507A. Measurements were made over ranges of mass flux, heat flux and corresponding outlet vapour qualities, and the effects of these parameters on the thermal and hydraulic performance of the evaporators were evaluated. Additional field test data of thermal performance were collected from ammonia and R12 water chillers, operating as thermosiphon evaporators. Based on all these data, empirical correlations are proposed for predicting the refrigerant boiling heat transfer coefficient and two-phase frictional pressure drop in PHE’s.
Plate heat exchangers are gaining acceptance in absorption refrigeration systems due to their high transfer rates, compactness, and low refrigerant charge. Nevertheless, boiling heat transfer and pressure drop studies with mixtures in plate heat exchangers (PHEs) are scarce.In this study, the experimental data of Táboas et al. (2010) on flow boiling of ammonia/water in a plate heat exchanger are compared with the predicted values using the correlations available in the open literature for the boiling heat transfer coefficient and pressure drop. In addition, this study proposes a new correlation based on a separate model by which to obtain the boiling coefficient. The new correlation uses a transition criterion, divided into an apparent nucleate boiling region where pure convective boiling cannot appear, and a region with competition between convective and apparent nucleate boiling. The correlation proposed can predict 98% of data from Táboas et al. (2010) within 20% error.
Experiments are carried out here to measure the evaporation heat transfer coefficient hr and associated frictional pressure drop ΔPf in a vertical plate heat exchanger for refrigerant R-410A. The heat exchanger consists of two vertical counterflow channels which are formed by three plates whose surface corrugations have a sine shape and a chevron angle of 60 deg. Upflow boiling of refrigerant R-410A receives heat from the hot downflow of water. In the experiments, the mean vapor quality in the refrigerant channel is varied from 0.10 to 0.80, the mass flux from 50 to 100 kg/m2s, and the imposed heat flux from 10 to 20 kW/m2 for the mass system pressure fixed at 1.08 and 1.25 MPa. The measured data indicate that both hr and ΔPr increase with the refrigerant mass flux except at low vapor quality. In addition, raising the imposed heat flux is found to significantly improve hr for the entire range of the mean vapor quality. However, the corresponding friction factor fsp is insensitive to the imposed heat flux and refrigerant pressure. Based on the present data, empirical correlations are provided for hr and fsp, for R-410A in the plate heat exchanger.
The evaporation heat transfer coefficient and pressure drop for refrigerant R-134a flowing in a plate heat exchanger were investigated experimentally in this study. Two vertical counterflow channels were formed in the exchanger by three plates of commercial geometry with a corrugated sine shape of a chevron angle of 60 deg. Upflow boiling of refrigerant R-134a in one channel receives heat from the hot down flow of water in the other channel. The effects of the mean vapor quality mass flux, heat flux, and pressure of R-134a on the el,evaporation heat transfer and pressure drop were explored. The quality change of R-134a between the inlet and outlet of the refrigerant channel ranges from 0.09 to 0.18. Even at a very low Reynolds number, the present flow visualization of evaporation in a plate heat exchanger with the transparent outer plate showed that the flow in the plate heat exchanger remains turbulent It is found that the evaporation heat transfer coefficient of R-134a in the plates is much higher than that in circular pipes and shows a very different variation with the vapor quality from that bl circular pipes, particularly in the convective evaporation dominated regime at high vapor quality. Relatively intense evaporation on the corrugated surface was seen from the flow visualization. Moreover, the present data showed that both the evaporation hear transfer coefficient and pressure drop increase with the vapor quality. At a higher mass flux the pressure drop is higher for the entire range of the vapor quality but the evaporation heat transfer is clearly better only at the high quality. Raising the imposed wall heat flux was found to slightly improve the heat transfer, while at a higher refrigerant pressure, both the heat transfer and pressure drop are slightly lower. Based an the present data, empirical correlations for the evaporation heat transfer coefficient and friction factor were proposed.
Experiments on the evaporative heat transfer and pressure drop in the brazed plate heat exchangers were performed with refrigerants R410A and R22. The plate heat exchangers with different 45°, 35°, and 20° chevron angles are used. Varying the mass flux of refrigerant (13–34 kg/m2s), the evaporating temperature (5, 10 and 15 °C), the vapor quality (0.9–0.15) and heat flux (2.5, 5.5 and 8.5 kW/m2), the evaporation heat transfer coefficients and pressure drops were measured. The heat transfer coefficient increases with increasing vapor quality and decreasing evaporating temperature at a given mass flux in all plate heat exchangers. The pressure drop increases with increasing mass flux and quality and with decreasing evaporating temperature and chevron angle. It is found that the heat transfer coefficients of R410A are larger than those of R22 and the pressure drops of R410A are less than those of R22. The empirical correlations of Nusselt number and friction factor are suggested for the tested PHEs. The deviations between correlations and experimental data are within ±25% for Nusselt number and ±15% for friction factor.
This paper presents experimental results on evaporation heat transfer for flow boiling of ammonia and of R134a in a chevron-pattern corrugated plate heat exchanger (PHE). The measurements enable the evaluation of a quasi-local heat transfer coefficient along the plate, which in turn allows discussing the two-phase distribution and the heat transfer mechanism during evaporation in a plate channel. The saturation temperature varied between 268KTNH3s283K(3.55barpRs5.73bar) for ammonia and 265KTR134as283K(2.157barpRs4.14bar) for R134a. The heat transfer coefficient is discussed in relation to the vapor quality, mass flux, heat flux and the type of refrigerant. The secondary fluid is a water/ethylene glycol mixture flowing in counter flow or parallel flow arrangement within the PHE. It is shown that the parallel flow case yields better overall performance than the counterflow case, and that plates with low chevron angle corrugations increase the evaporation heat transfer. Comparison with the limited data available from the literature shows good agreement. The Danilova equation and the Steiner boiling correlation are adapted to PHEs and show the need for further theoretical development.
A simple dimensionless correlation for predicting heat-transfer coefficients during film condensation inside pipes is presented. It has been verified by comparison with a wide variety of experimental data. These include fluids water, R-11, R-12, R-22, R-113, methanol, ethanol, benzene, toluene, and trichloroethylene condensing in horizontal, vertical, and inclined pipes of diameters ranging from 7 to 40mm. One data set for condensation inside an annulus has also been analyzed. The range of parameters covered includes reduced pressures from 0.002 to 0.44, saturation temperatures from 21 to 310°C, vapor velocities from 3 to 300m/s, vapor qualities from 0 to 100%, mass flux 39000-758 000kg/m2 h, heat flux from 158 to 1 893000W/m2, all liquid Reynolds numbers from 100 to 63 000, and liquid Prandtl numbers from 1 to 13. The mean deviation for the 474 data points analyzed was found to be 15.4%.
This paper presents the experimental tests on HFC-134a condensation inside a small brazed plate heat exchanger: the effects of refrigerant mass flux, saturation temperature and vapour super-heating are investigated.A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 20kg/m2s. For refrigerant mass flux lower than 20kg/m2s, the saturated vapour heat transfer coefficients are not dependent on mass flux and are well predicted by the Nusselt [Nusselt, W., 1916. Die oberflachenkondensation des wasserdampfes. Z. Ver. Dt. Ing. 60, 541–546, 569–575] analysis for vertical surface. For refrigerant mass flux higher than 20kg/m2s, the saturated vapour heat transfer coefficients depend on mass flux and are well predicted by the Akers et al. [Akers, W.W., Deans, H.A., Crosser, O.K., 1959. Condensing heat transfer within horizontal tubes. Chem. Eng. Prog. Symp. Ser. 55, 171–176] equation. In the forced convection condensation region, the heat transfer coefficients show a 30% increase for a doubling of the refrigerant mass flux. The condensation heat transfer coefficients of super-heated vapour are 8–10% higher than those of saturated vapour and are well predicted by the Webb [Webb, R.L., 1998. Convective condensation of superheated vapour. ASME J. Heat Transfer 120, 418–421] model. The heat transfer coefficients show weak sensitivity to saturation temperature. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow and therefore a quadratic dependence on the refrigerant mass flux.
The objective of this work is to contribute to the development of plate heat exchangers as desorbers for ammonia/water absorption refrigeration machines driven by waste heat or solar energy. In this study, saturated flow boiling heat transfer and the associated frictional pressure drop of ammonia/water mixture flowing in a vertical plate heat exchanger is experimentally investigated.Experimental data is presented to show the effects of heat flux between 20 and 50 kW m−2, mass flux between 70 and 140 kg m−2 s−1, mean vapour quality from 0.0 to 0.22 and pressure between 7 and 15 bar, for ammonia concentration between 0.42 and 0.62. The results show that for the selected operating conditions, the boiling heat transfer coefficient is highly dependent on the mass flux, whereas the influence of heat flux and pressure are negligible mainly at higher vapour qualities. The pressure drop increases with increasing mass flux and quality. However, the pressure drop is independent of the imposed heat flux.
Measurements on a semi-welded plate heat exchanger (PHE) and on various versions of the nickel-brazed PHE were performed in a large experimental refrigeration rig. Experiments were carried out with the refrigerant ammonia, which was completely evaporated in vertical upward flow in PHEs connected in a U-type manner. A multiple linear regression analysis produced three Nusselt number correlations for the different PHEs that can predict the measured Nusselt number decently. The values for the C-coefficient (in the correlation of the two-phase multiplier) for the higher Reynolds number are somewhat higher than those reported in other investigations. An inlet flow distributor in the semi-welded heat exchanger made it possible to achieve a higher performance at low ΔTout. The nickel-brazed heat exchanger with an integrated inlet flow distributor was found to have a better performance compared to a nickel-brazed heat exchanger without the flow distributor.
Plate heat exchangers were first developed about 100 years ago but have won increasing interest during the last two decades, primarily due to the development of methods of manufacturing brazed plate heat exchangers. This type of heat exchanger offers very good heat transfer performance in single-phase flow as well as in evaporation and condensation. Part of the reason is the small hydraulic diameters, typically being less than 5 mm. Other advantages of plate heat exchangers are the extremely compact design and the efficient use of the construction material. In spite of their long use, the calculation methods for predicting heat transfer and pressure drop are not widely known. It is the purpose of this article to present such calculation methods for single-phase flow and for flow boiling and to discuss some of the specifics of this type of heat exchangers.
This paper presents the heat transfer coefficients and the pressure drop measured during HFC-410A condensation inside a commercial brazed plate heat exchanger: the effects of saturation temperature, refrigerant mass flux and vapour super-heating are investigated. The heat transfer coefficients show weak sensitivity to saturation temperature and great sensitivity to refrigerant mass flux and vapour super-heating. At low refrigerant mass flux (20 kg/m²s) the saturated vapour condensation heat transfer coefficients depend on mass flux and are well predicted by Akers et al. [W.W. Akers, H.A. Deans, O.K. Crosser, Condensing heat transfer within horizontal tubes, Chem. Eng. Prog. Symp. Series 55 (1959) 171-176] equation: forced convection condensation occurs. In the forced convection condensation region the heat transfer coefficients show a 30% increase for a doubling of the refrigerant mass flux. The condensation heat transfer coefficients of super-heated vapour are 8-10% higher than those of saturated vapour and are well predicted by Webb [R.L. Webb, Convective condensation of superheated vapor, ASME J. Heat Transfer 120 (1998) 418-421] model. A simple linear equation based on the kinetic energy per unit volume of the refrigerant flow is proposed for the computation of the frictional pressure drop. (author)
Approximate solutions of heat transfer in plate heat exchangers are obtained using exponential approximations for the temperature in each stream. Numerical results obtained by the method presented have been compared with the exact analytical solutions. About 300 cases have been analysed.RésuméDes solutions approchées de transfert thermique dans les échangeurs à plaques sont obtenues en utilisant des approximations exponentielles pour les températures dans chaque écoulement. Des résultats numériques obtenus par la méthode présentée ont été comparés avec les solutions analytiques exactes. Environ 300 cas ont été analysés.ZusammenfassungMit Hilfe eines exponentiellen Näherungsverfahrens für die Temperaturberechnung in beiden Massenströmen eines Plattenwärmeaustauschers konnte eine Näherungslösung für den Wärmeaustausch gefunden werden. Die mit diesem Verfahren numerisch berechneten Ergebnisse werden mit exakten analytischen Lösungen verglichen. Ungefähr 300 verschiedene Fälle werden dabei analysiert.РефератC иcпoльзoвAниeм экcпoнeнциAльныч пpиближeний для тeмпepAтyp в пoтoкe пoлyчeны пpиближeнныe peшeния зAдAч тeплoпepeнocA в плAcтинчAтыч тeплooбмeнникAч. Пpoвeдeнo cpAвнeниe чиcлeнныч peзyльтAтoв c тoчными AнAлитичecкими peшeниями. ПpoAнAлизиpoвAнo oкoлo 300 cлyчAeв.
This paper presents recent measurements of heat transfer coefficient obtained during condensation of R32 inside a commercial brazed plate heat exchanger (BPHE). The experimental data show the effect of refrigerant mass velocity, vapor quality, temperature difference (saturation-to-wall) and inlet vapor superheating. In particular, the specific mass velocity is varied between 15 and 40 kg m−2 s−1 and the outlet vapor quality between 0.0 and 0.65, while inlet vapor superheating goes from 5 to 25 K. The saturation temperature is kept constant at around 36.5 °C, which can be considered a usual temperature level for water cooled heat pump applications. The present authors provide a numerical procedure to calculate the condensation heat transfer in the BPHE, accounting also for the superheating effect. This model is assessed by comparisons with the experimental measurements relative to R32, R410A, and R744.
This paper presents experimental results on partial condensation of 15 K superheated vapours of R407C and R410A inside two Brazed Plate Heat Exchanger (BPHE) prototypes with different geometrical characteristics, plate designs and aspect ratios. The condensation heat transfer coefficients have been measured at constant inlet saturation temperature of 41.8 °C and 36.5 °C for R407C and R410A, respectively. The refrigerant mass velocity has been varied from 15 to 40 kg m−2 s−1 whereas the outlet vapour quality between 0.01 and 0.58. The experimental results have also been compared with those previously measured by Mancin et al. (2011) during condensation of R407C and R410A inside a BPHE prototype with different plate dimensions and two refrigerant channels. Furthermore, the condensation heat transfer coefficients have been used to validate a new model recently proposed by Mancin et al. (2011), which can be used to simulate the condensation process through the BPHE.
The evaporation heat transfer experiments were conducted with an oblong shell and plate heat exchanger without oil in the refrigerant loop using R-410A, a mixture of 50 wt% R-32 and 50 wt% R-125 that exhibits azeotropic behavior. An experimental refrigerant loop has been established to measure the evaporation heat transfer coefficient h r of R-410A in a vertical oblong shell and plate heat exchanger. Four vertical counter-flow channels were formed in the oblong shell and plate heat exchanger by four plates having a corrugated trapezoid shape of a 45° chevron angle. The upflow of the boiling R-410A in one channel receives heat from the hot downflow of water in the other channel. The effects of the refrigerant mass flux, average heat flux, refrigerant saturation temperature, and vapor quality of R-410A on the measured data were explored in detail. The results indicate that a rise in the refrigerant mass flux causes an increase in the h r . Raising the imposed wall heat flux was found to slightly improve h r . Finally, at a higher refrigerant saturation temperature, the h r is found to be lower. Based on the present data, an empirical correlation of the evaporation heat transfer coefficient was proposed.
Ocean thermal energy conversion systems are expected to be the next-generation energy production systems. In these systems, a plate heat exchanger is used for improving the power generation efficiency, and ammonia or an ammonia/water mixture is used as a working fluid.In this study, boiling heat transfer coefficients of pure ammonia are measured on a vertical flat PHE (a plate heat exchanger), for elucidating and characterizing the behavior of ammonia on a compact plate evaporator, a type of PHEThe measurement results show that local boiling heat transfer coefficients increase with increasing vapor quality. Further, the effects of saturation pressure, mass flow rate, and average heat flux on the boiling heat transfer coefficient are elucidated. An empirical correlation for the local boiling heat transfer coefficient is derived using the Lockhart-Martinelli parameter. Further, a visualization experiment of boiling phenomena of ammonia is performed to elucidate the relation between boiling behavior and heat transfer.
This paper presents the heat transfer coefficients and the pressure drop measured during HFC refrigerants 236fa, 134a and 410A saturated vapour condensation inside a brazed plate heat exchanger: the effects of saturation temperature (pressure), refrigerant mass flux and fluid properties are investigated. The heat transfer coefficients show weak sensitivity to saturation temperature (pressure) and great sensitivity to refrigerant mass flux and fluid properties. A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 20 kg/m2s that corresponds to an equivalent Reynolds number around 1600–1700. At low refrigerant mass flux (Gr < 20 kg/m2s) the heat transfer coefficients are not dependent on mass flux and are well predicted by the Nusselt [20] analysis for vertical surface: the condensation process is gravity controlled. For higher refrigerant mass flux (Gr > 20 kg/m2s) the heat transfer coefficients depend on mass flux and are well predicted by Akers et al. [21] equation: forced convection condensation occurs. In the forced convection condensation region the heat transfer coefficients show a 25–30% increase for a doubling of the refrigerant mass flux.The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow and therefore a quadratic dependence on mass flux.HFC-410A shows heat transfer coefficients similar to HFC-134a and 10% higher than HFC-236fa together with frictional pressure drops 40-50% lower than HFC-134a and 50–60% lower than HFC-236fa.
The paper presents an approximate prediction of heat transfer during steam condensation inside a tube on the basis of the analogy between hydraulic resistance and heat transfer in accordance with Reynolds' theory. It describes experimental results obtained by the authors during the condensation of steam inside tubes with diameter of 18 mm and lengths up to 12 m at pressures up to 90 bar. Theoretical and experimental results agree satisfactorily. It also describes original experimental results on tube hydraulic resistance during condensation of steam therein. Finally, it describes experimental results on the conditions of heat transfer during condensatory flow of steam inside tube bundle.
This paper presents the heat transfer coefficients and pressure drop measured during HC-600a, HC-290 and HC-1270 saturated vapour condensation inside a brazed plate heat exchanger: the effects of refrigerant mass flux, saturation temperature (pressure) and fluid properties are investigated.The heat transfer coefficients show weak sensitivity to saturation temperature (pressure) and great sensitivity to refrigerant mass flux and fluid properties. A transition point between gravity controlled and forced convection condensation has been found for a refrigerant mass flux around 15–18 kg m−2 s−1. In the forced convection condensation region the heat transfer coefficients show a 35–40% enhancement for a 60% increase of the refrigerant mass flux. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow.HC-1270 shows heat transfer coefficients 5% higher than HC-600a and 10–15% higher than HC-290, together with frictional pressure drop 20–25% lower than HC-290 and 50–66% lower than HC-600a.
Heat transfer and associated frictional pressure drop in the condensing flow of the ozone friendly refrigerant R-410A in a vertical plate heat exchanger (PHE) are investigated experimentally in the present study. In the experiment two vertical counter flow channels are formed in the exchanger by three plates of commercial geometry with a corrugated sinusoidal shape of a chevron angle of 60°. Downflow of the condensing refrigerant R-410A in one channel releases heat to the upflow of cold water in the other channel. The effects of the refrigerant mass flux, imposed heat flux, system pressure (saturated temperature) and mean vapor quality of R-410A on the measured data are explored in detail. The results indicate that the R-410A condensation heat transfer coefficient and associated frictional pressure drop in the PHE increase almost linearly with the mean vapor quality, but the system pressure only exhibits rather slight effects. Furthermore, increases in the refrigerant mass flux and imposed heat flux result in better condensation heat transfer accompanying with a larger frictional pressure drop. Besides, the imposed heat flux exhibits stronger effects on the heat transfer coefficient and pressure drop than the refrigerant mass flux especially at low refrigerant vapor quality. The friction factor is found to be strongly influenced by the refrigerant mass flux and vapor quality, but is almost independent of the imposed heat flux and saturated pressure. Finally, an empirical correlation for the R-410A condensation heat transfer coefficient in the PHE is proposed. In addition, results for the friction factor are correlated against the Boiling number and equivalent Reynolds number of the two-phase condensing flow.
The characteristics of evaporation heat transfer and pressure drop for refrigerant R134a flowing in a plate heat exchanger were investigated experimentally in this study. Two vertical counter flow channels were formed in the exchanger by three plates of commercialized geometry with a corrugated sine shape of a chevron angle of 60°. Upflow boiling of refrigerant R134a in one channel receives heat from the hot downflow of water in the other channel. The effects of the heat flux, mass flux, quality and pressure of R134a on the evaporation heat transfer and pressure drop were explored. The preliminary measured data for the water to water single phase convection showed that the heat transfer coefficient in the plate heat exchanger is about 9 times of that in a circular pipe at the same Reynolds number. Even at a very low Reynolds number, the present flow visualization in a plate heat exchanger with the transparent outer plate showed that the flow in the plate heat exchanger remains turbulent. Data for the pressure drop were also examined in detail. It is found that the evaporation heat transfer coefficient of R134a in the plates is quite different from that in circular pipe, particularly in the convective evaporation dominated regime at high vapor quality. Relatively intense boiling on the corrugated surface was seen from the flow visualization.
More specifically, the present data showed that both the evaporation heat transfer coefficient and pressure drop increase with the vapor quality. At a higher mass flux the pressure drop is higher for the entire range of the vapor quality but the heat transfer is only better at high quality. Raising the imposed wall heat flux was found to slightly improve the heat transfer. While at a higher system pressure the heat transfer and pressure drop are both slightly lower.
Subcooled flow boiling heat transfer characteristics of refrigerant R-134a in a vertical plate heat exchanger (PHE) are investigated experimentally in this study. Besides, the associated bubble characteristics are also inspected by visualizing the boiling flow in the vertical PHE. In the experiment two vertical counterflow channels are formed in the exchanger by three plates of commercial geometry with a corrugated sinusoidal shape of a chevron angle of 60°. Upflow boiling of subcooled refrigerant R-134a in one channel receives heat from the downflow of hot water in the other channel. The effects of the boiling heat flux, refrigerant mass flux, system pressure and inlet subcooling of R-134a on the subcooled boiling heat transfer are explored in detail. The results are presented in terms of the boiling curves and heat transfer coefficients. The measured data showed that the slopes of the boiling curves change significantly during the onset of nucleate boiling (ONB) especially at low mass flux and high saturation temperature. Besides, the boiling hysteresis is significant at a low refrigerant mass flux. The subcooled boiling heat transfer coefficient is affected noticeably by the mass flux of the refrigerant. However, increases in the inlet subcooling and saturation temperature only show slight improvement on the boiling heat transfer coefficient.
Saturated flow boiling heat transfer and the associated frictional pressure drop of the ozone friendly refrigerant R-410A (a mixture of 50 wt% R-32 and 50 wt% R-125) flowing in a vertical plate heat exchanger (PHE) are investigated experimentally in the study. In the experiment two vertical counter flow channels are formed in the exchanger by three plates of commercial geometry with a corrugated sinusoidal shape of a chevron angle of 60°. Upflow boiling of saturated refrigerant R-410A in one channel receives heat from the downflow of hot water in the other channel. The experimental parameters in this study include the refrigerant R-410A mass flux ranging from 50 to 125 kg/m2 s and imposed heat flux from 5 to 35 kW/m2 for the system pressure fixed at 1.08, 1.25 and 1.44 MPa, which respectively correspond to the saturated temperatures of 10, 15 and 20 °C. The measured data showed that both the boiling heat transfer coefficient and frictional pressure drop increase almost linearly with the imposed heat flux. Furthermore, the refrigerant mass flux exhibits significant effect on the saturated flow boiling heat transfer coefficient only at higher imposed heat flux. For a rise of the refrigerant pressure from 1.08 to 1.44 MPa, the frictional pressure drops are found to be lower to a noticeable degree. However, the refrigerant pressure has very slight influences on the saturated flow boiling heat transfer coefficient. Finally, empirical correlations are proposed to correlate the present data for the saturated boiling heat transfer coefficients and friction factor in terms of the Boiling number and equivalent Reynolds number.
This paper presents the experimental heat transfer coefficients and pressure drop measured during HFC refrigerant 134a, 410A and 236fa vaporisation inside a small brazed plate heat exchanger: the effects of heat flux, refrigerant mass flux, saturation temperature, outlet conditions and fluid properties are investigated. The experimental results are reported in terms of refrigerant side heat transfer coefficients and frictional pressure drop. The heat transfer coefficients show great sensitivity to heat flux and outlet conditions and weak sensitivity to saturation temperature. The frictional pressure drop shows a linear dependence on the kinetic energy per unit volume of the refrigerant flow. HFC-410A shows heat transfer coefficients 40–50% higher than HFC-134a and 50–60% higher than HFC-236fa and frictional pressure drops 40–50% lower than HFC-134a and 50–60% lower than HFC-236fa. The experimental heat transfer coefficients are compared with two well-known equations for nucleate boiling [M.G. Cooper, Heat flows rates in saturated pool boiling – a wide ranging examination using reduced properties, Advanced Heat Transfer, Academic Press, Orlando, Florida, 1984, pp. 157–239; D. Gorenflo, Pool boiling, in: E.U. Schlünder (Ed.), VDI Heat Atlas, Dusseldorf, Germany, 1993, Ha1-25] and a correlation for frictional pressure drop is proposed.