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Adsorption Thermodynamics of Silica Gel−Water Systems†
... As mentioned by Tian et al. [5,6,[21][22][23][24][25][26], the correct determination of isosteric heat is fundamentally associated with defining the adsorbed phase. It was J. W. Gibbs who introduced this concept for heterogeneous systems in one of his first works in thermodynamics. ...
... It was J. W. Gibbs who introduced this concept for heterogeneous systems in one of his first works in thermodynamics. From the point of view of the definitions of Gibbs to describe the properties of a surface and the interface, the latter can be represented as a two-dimensional dividing surface without any volume [5,[21][22][23][24][25][26][27][28][29][30]; isosteric heat is often interpreted as the energy to transfer an adsorbate molecule from the bulk of the fluid phase to the adsorbed phase under some fixed thermodynamic conditions of the system such as temperature, total volume and amount of adsorbent [26][27][28][29][30][31]. Some authors have analyzed that the Gibbsian formalism predicts non-physical isosteric heat under maximum thermodynamic conditions of the adsorption isotherm. ...
... Some authors have analyzed that the Gibbsian formalism predicts non-physical isosteric heat under maximum thermodynamic conditions of the adsorption isotherm. However, unlike bulk systems, the properties of the adsorbed phase cannot be defined only with the excess surface area for each component [23][24][25][26]28]. Gibbs thermodynamics predict a non-physical isosteric heat when the adsorption isotherm exhibits a maximum [5,[28][29][30][31][32][33][34][35][36][37]. ...
This work presents the calorimetric study of five adsorbents with different chemical and textural characteristics: MOF-199, MCM-41, SBA-15, activated carbon prepared from corn cob (GACKP) and graphite. These solids were used to establish the differences between isosteric heats evaluated by three different methods: Clausius–Clapeyron (C-C), Chakraborty, Saha and Koyama (CSK) and Adsorption Calorimetry (A-Cal). The textural characterization results show solids that have values of specific surface area between 2271 m2·g−1 for the MOF-199 and 5.2 m2·g−1 for the graphite. According to the results obtained for the isosteric heats for each sample, the magnitude varies depending on the coverage of the adsorbate and the textural characteristics of each adsorbent. Solids with an organized structure have isosteric heat values that are coincident among the three methods. Meanwhile, heterogeneous solids such as activated carbon values evaluated by the CKS and C-C have a high dispersion method regarding the adsorption calorimetry method. The results obtained show that the adsorption calorimetry, being a direct experimental measurement method, presents less dispersed data. At low quantities, the isosteric heat of nitrogen adsorption decreased in the order MOF-199, GACKP, MCM-41, SBA-15 and Graphite. The order for the isosteric heats values was coherent with the surface characteristics of each of the solids, especially with the pore size distribution. Finally, throughout the coverage examined in this work, the isosteric heats for nitrogen adsorption determined by adsorption calorimetry (A-Cal) were larger than the evaluated by C-C and CSK indirect methods of vaporization. According to the results, it is shown that the adsorption calorimetry allows values of the isosteric heats of adsorption with an error of less than 2% to be established and also reveals the complex nature of the heterogeneity or homogeneity of the adsorbent.
... The experimental specific heat capacity and tap densities are shown in Fig. 2 and summarized in Table 1, showing a good agreement with the data available in the literature [44,[50][51][52][53], except for Empa RMF activated carbon that shows a higher specific heat capacity than typical commercial activated carbons. The specific heat capacity of water has been assumed to be = 1.271 − 5 ⋅ 2 − 8.170 − 3 ⋅ + 5.493 [54]. ...
... The reproducibility of the results could be significantly improved with an a posteriori equilibrium check and differences between duplicate measurements were ≤ 0.02 [g∕g]. Taking into account larger variations due to differences in measurement methodology in different laboratories and variation between sample batches, a good agreement was found with other data published in literature [6,50,[55][56][57]. The complete water adsorption isotherm data are made publicly available at [58]. ...
The deployment of adsorption cycles for heating and cooling purposes is often limited by poor efficiency and high reactor volumes, both determined by the adsorber material used. The appropriate pre-selection of the solid sorbent and the system design in the early stages of design can allow quick identification of the most promising solutions. In this work, a reliable and robust methodology for adsorber material screening and pre-selection is proposed and applied to a test set of state-of-the-art candidates. The improvement achieved in the adsorption equilibrium prediction with respect to the most frequently used model is above 60%. In addition, the adsorber material selection framework based on mixed-integer linear programming was applied to over 600 hypothetical cooling and mixed cooling/heating use cases. The analysis of exergy and volume performances allowed to emphasize differences of design strategies using different system objectives (i.e. minimizing the temperature of the heat sources and chosing compact materials). We provide the proof of feasibility of a harmonic pre-design of adsorbent materials and energy system and show that it can be used to narrow down the decision variables to the most promising options. This methodology can be considered as the foundation of more extended and automated design methods for real scenarios constrained by kinetics, material integration and costs.
... This behaviour is, in fact, typical for mesoporous materials and can be observed in other similar systems. Study of Chakraborty et al. (2009) shows calculations of isosteric heat on the example of silica gel (type RD) on the same magnitude as the samples used in this work starting as high as H • st = 3520 kJ kg −1 and equalizing roughly around H • st = 2670 kJ kg −1 . Similar values were also reported by Jänchen et al. (2004) around H • st ∼ 2500 kJ kg −1 . ...
... Another problem is connected with its low maximum uptake and wide pore size distribution causing a big part of its adsorption capacity to be over P∕P o > 0.5 , thus the resulting storage capacity is usually very low. However, thanks to the great commercial availability of these regular silica gel materials, the silica gel is still intensively studied in this context mostly as an easily comparable material or impregnated with inorganic salts (Li et al. 2010;Yu et al. 2013;Chakraborty et al. 2009). More favourable properties for direct use can be found in case of microporous silica gel. ...
Six samples from the TMPS family of mesoporous silica nano-materials from Taiyo Kagaku Co., Ltd. were studied for their potential as a medium for the adsorption thermal energy storage. Selected specimens are distinguished by their pore size from 1.9 to 4.1 nm and aluminium doping. As the adsorbate for the adsorption pair was selected water with the most advantageous properties of high latent heat and safe chemical properties. The tested materials doped with aluminium show high affinity towards the selected adsorbate and high uptakes. The theoretical storage energy density of the materials spans from 700 to 1700 kJ kg −1 based on the adsorption heat. The storage capacity depends mostly on the pore volume and partially on the pore size. The theoretical estimation shows the temperature gain of the adsorption potential as high as T = 23 • C for the material TMPS-1.5A with the smallest pore diameter and aluminium doping and as low as T = 6 • C for the TMPS-4R with the biggest pore diameter and without aluminium doping.
... This approximation makes no material difference to the arguments presented in this work, and in practice H W ∕ T is subsumed into the specific heat of the solid phase. Chakraborty et al. (2009) demonstrate how the sorption properties influence the apparent specific heat of silica gel (Type 125). When considering heat and mass transfer in stored food grains Thorpe (2022) noted that subsuming H W ∕ T into the specific heat of the solid phase is necessary when sorption data are incomplete, or internally inconsistent. ...
The thermal performance of ventilated beds of hygroscopic porous media depends strongly on the sorption properties of the solid phase. Furthermore, the published literature shows that the predicted performance of ventilated beds of hygroscopic porous media is extremely sensitive to the form and accuracy of the sorption isotherm. This is particularly apparent under idealized conditions when thermodynamic equilibrium is deemed to exist between the solid and fluid phases. When Tóth’s isotherm is invoked in an equilibrium model used to analyse the performance of a bed of initially warm and dry silica gel ventilated with cool, humid air, it is predicted that a shock wave develops downstream of air entering the bed. In contrast, it is shown that non-equilibrium solutions result in a transfer wave, the width of which decreases as the velocity of the interstitial air decreases. The Tóth isotherm gives rise to erroneous values of the integral heat of wetting of silica gel. Previously published studies of simultaneous heat and mass transfer in beds of hygroscopic materials refer to conceptual difficulties in interpreting the results, and some published mathematical analyses are somewhat terse. A secondary aim of this work is to assuage these difficulties by detailing the analyses in Supplementary Information.
... Ng et al. 30 confirmed that the SDWP for the adsorption systems could be optimized linearly with both evaporator and heat source temperatures. Chakraborty et al. 31 developed the surface thermodynamic properties of silica gel (SG) to optimize ACD systems' performance. Mitra et al. 32 presented a two-stage ACD system using SG as an adsorbent and air-cooled. ...
Adsorption cooling and desalination (ACD) system presents a solution for water, energy, and environmental dilemma. This study expresses an enhancement of adsorption system performance in terms of cooling and desalination effects by improving an activated carbon Maxsorb III (Max) as an adsorbent. Max has been initially treated with HCl. Then, it has been activated by impregnating it in salt hydrates ((NH 4 ) 2 CO 3 ). Characterization methods, including XRD, N 2 and water adsorption isotherm, and water adsorption kinetics have been conducted for raw Max, treated Max, and activated Max with (NH 4 ) 2 CO 3 . The experimental values have been fitted with the Dubinin & Astakhov equilibrium model for isotherm and the model of linear driving force for kinetics. These fitted parameters have been utilized in a previously validated model to estimate adsorption cooling-desalination system performance with and without heat recovery. Max/(NH 4 ) 2 CO 3 achieves a water uptake of 0.53 kg H2O .kg ⁻¹ . Max/(NH 4 ) 2 CO 3 produces 13.2 m ³ .ton ⁻¹ of freshwater per day with a specific cooling power of 373 W.kg ⁻¹ and 0.63 COP. Also, the freshwater reaches 22.5 m ³ .ton ⁻¹ of Max/(NH 4 ) 2 CO 3 per day with condenser-evaporator heat recovery. These results indicate the potential of utilizing the Max material in dual cooling and desalination applications to achieve double what silica gel can offer.
... The magnitude of the enthalpy represents the energy (mainly thermal energy) required to desorb water vapor from the adsorbent, and the smaller the energy the more likely it is to occur. Chakraborty et al. (2009) obtained the enthalpy of adsorption of silica gel by To'th model as 2800 kJ/kg. Kim et al. (2016) used differential scanning calorimetry (DSC) and thermogravimetric analyzer (TGA) methods to obtain enthalpies of adsorption for MOF-801 and 13X molecular sieves of 3000 kJ/kg and 4000 kJ/kg, respectively. ...
... The basic behavior of silica gel for vapor absorption is physical adsorption, attributed to van der Waals forces and electrostatic forces between adsorbate molecules and surface atoms. The adsorbing mass is always in contact with the adsorbent and therefore follows the Henry or Dubin-Astokov isotherm [22,54]. As shown in Fig. 6, the adsorbent and the adsorbent mass reach the maximum absorption at equilibrium. ...
Adsorption desalination is an emerging desalination technology with low energy consumption, which is based on the principle of desalination by using the adsorption and desorption properties of solids with porous properties on water vapor. Compared with the traditional distillation and membrane methods, adsorption desalination can use renewable energy sources such as solar energy, geothermal energy, or industrial low-grade waste heat as the driving heat source, and thus has the excellent characteristics of being green and pollution-free. However, as a newly developed desalination technology, there is relatively little theoretical and experimental research on adsorption desalination, and it is still at the stage of small-scale experiments. This paper firstly introduces the adsorption theory and circulation process to clarify the key elements of this desalination method. Further, based on the available results, the related researches are analyzed and summarized according to the critical elements of the adsorption desalination system, i.e., preparation of adsorbents, optimization of system configuration, cyclic operating conditions, and combination systems. Finally, the future directions to be focused on for future research prediction are discussed, which will be useful for related studies in this field.
... The sensible heat contribution is obtained from the liquid water heat capacity C p;w and the difference between the desorption temperature T des and the initial desiccant temperature at ambient conditions T amb . The desiccant heat capacity, especially for porous materials, is significantly lower than the heat capacity of water and is, therefore, neglected (Chakraborty et al., 2009;Incropera et al., 2013). The parameters DH des and T des are ad(ab)sorbent-dependent properties (Kim et al., 2016;Fathieh et al., 2018). ...
Capturing water vapor from atmospheric air is a possible solution to local water scarcity, but it is very energy demanding. Energy consumption estimates of water-from-air technologies involving adsorption processes, thermo-responsive hydrophilicity switching polymers, air cooling processes, and reverse osmosis of deliquescent salt solutions reveal that these technologies are not competitive when compared to seawater desalination, and the use of fresh water and wastewater sources. They only become a viable option in the absence of local liquid water sources and when long-distance transport for socio-economic reasons is not an option. Interestingly, direct solar-driven technology for water-from-air production is an attractive means to disentangle the local water-energy nexus. It is expected that climate change will accelerate the introduction of water-from-air technologies in local water supply schemes. The optimal water-from-air technology depends on the climate, relative humidity, and temperature profiles. A world map is presented, indicating the optimal geographic location for each technology.
... Besides the issues related to the synthesis of MOFs, it is vital to analyze the adsorption thermodynamics of an adsorbentadsorbate system for determining the energetic performance of ACS as well as for system modeling. Chakraborty et al. [18] showed that isosteric heat of adsorption, specific heat capacity plays a vital role in calculating thermodynamic properties in adsorbed phase for water-silica gel system and help to improve system modeling. For CO 2 /activated carbon-based ACS, significant studies on adsorption thermodynamic were addressed to understand the efficiency of the systems [1,2,19]. ...
Utilization of water as a refrigerant in adsorption cooling systems is a challenging task due to the unavailability of suitable adsorbents. Recently, a new class of porous material, metal-organic frameworks (MOFs), is heightening interest as the potential adsorbent for water adsorption due to its crucial S-shaped adsorption isotherm characteristics. Additionally, the high surface area, large pore volume, and higher affinity towards water vapor outshined MOFs over other porous materials to be used as adsorbent in water-based adsorption cooling system (ACS). However, their industrial production could be obstructed due to economic and ecological limitations. Therefore, in this study, an energy-efficient, environment friendly, rapid and ultrasonication assisted room temperature green synthesis procedure for MOF-801 is reported with additional finding of optimum synthesis condition. Several characterization techniques are employed to ensure the structural stability of the synthesized MOFs and their applicability in ACS. The reaction time of the green synthesized MOF-801 was reduced by eight times than the conventional one while ensuring excellent system performance, which makes this process promising for industrial production.
... The spherical particles of amorphous material are 2-20 nm in size, which form the silica by sticking with each other [55]. Silica gel is a preferred adsorbent due to its ability to take up a reasonable amount of water (up to 40% by mass) [56] without considerable change in volume or structure and capacity to release water when mildly heated [57]. Systems with two or more beds are used in the literature [58] regarding the improvement in energy efficiency, and several studies have also reviewed AD systems. ...
Adsorption-based desalination (AD) is an emerging concept to co-generate distilled fresh water and cooling applications. The present study is aimed to provide a comprehensive review of the adsorption desalination systems and subsequent hybridization with known conventional cycles such as the multiple-effect AD (MED), solar regenerable, integrated evaporator-condenser cascaded, and ejector integrated systems. The systems are investigated for energy consumption, productivity enhancement, and performance parameters, including production cost, daily water production, and performance coefficient. Comprehensive economic aspects, future challenges, and future progress of the technologies are discussed accordingly to pave researchers' paths for technological innovation. Traditional AD systems can produce specific daily water production of 25 kg per kg of adsorbent. The solar adsorption desalination-cooling (ADC) showed a promising specific cooling power of 112 W/kg along with a COP of 0.45. Furthermore, for a hybrid MEDAD cycle, the gain output ratio (GOR) and performance ratio (PR) is found to be 40%, along with an augmented water production rate from 60% to two folds. The AD technology could manage the high salinity feed water with the production of low salinity water with a reasonable cost of US$0.2/m 3 .
... Numerous studies related to entropy generation on adsorption cooling cycles are based on the Second law of Thermodynamics. For example, Chakraborty et al. [20,21] developed the thermodynamic property surfaces to understand the enthalpy and entropy of adsorption for a single component adsorbent + adsorbate systems, from which one can calculate the energetic performances of A-HT system. In another study, Meunier et al. [22] showed that even under ideal transfer and isotherm heat reservoirs conditions, the COP of adsorption chiller still could not reach the ideal Carnot limit, which is mainly related to the system irreversibility caused by the temperature gap between the heat reservoirs and the adsorption beds. ...
This article presents the entropy flow and generation of an adsorption assisted heat transformation (A-HT) system. Hence the Gibbs analogy and the thermodynamic property fields of adsorbents + water systems are employed to formulate the entropy balance of adsorption beds. Later, the experimentally confirmed isotherms, kinetics and bed heat exchanger data are applied for computing the energetic performances of adsorption system in terms of entropy flow and generation, from which one can calculate (i) the system-performances with respect to heating and cooling capacities, specific water production and the overall efficiency and (ii) dissipations from each component of A-HT systems. The temperature entropy-flow (T-Sf) maps show close loops for the evaporator, the condenser and the beds indicating the stored energy under batch operating conditions of A-HT cycle. It is observed that the entropy generation (Sg) are mainly contributed by various processes such as mass and heat transfer, de-superheating and flushing of heat transfer fluids. The highest entropy generation occurs in the adsorption bed during desorption period, and the least Si is found in the evaporator. The proposed temperature-entropy maps can be applied to design each component of bed heat exchanger with minimum entropy generation. It is found that the entropy flow and generation depend on the periods of batch operation, the heating source temperature, and the quality of porous adsorbents.
... However, it has some issues like large volume of adsorption bed and low specific cooling power (SCP) due to poor thermal conductivity, small adsorption capacity of solid adsorbents and low heat and mass transfer efficiency, which hinder the industrialization and commercial application of adsorption cooling technology. Compared to chlorofluorocarbons and alcohols, the refrigerant water has advantages of high latent heat of vaporization (~ 2400 kJ/kg), environmental protection and safety, etc. Water can be used to form working pairs with various kinds of porous materials like silica gel [5][6][7][8][9], zeolite [10][11][12][13][14] and metal-organic frameworks [15][16][17][18][19][20][21] (MOFs), etc. Among them, as a new kind of porous crystals, MIL-101 (Cr) [19] is considered as one of the most promising MOFs materials in the field of adsorption cooling due to its high BET specific surface area (3000-4000 m 2 /g), large adsorption capacity (1.50 g/g ads ) for water, low desorption temperature (70-90 °C) and excellent adsorption/desorption stability. ...
Aiming at the poor heat conduction performance of porous MIL-101 applied in adsorption cooling process, few layer graphene (FLG) was selected as a promising thermal conductive additive to enhance thermal conductivity of MIL-101. The factors which influencing thermal conductivity of MIL-101/FLG composites were investigated. Thermal conductive mechanism of FLG for MIL-101 was discussed. Adsorption/desorption characteristics of water on the MIL-101/FLG composites were determined. Results show a two-dimensional structure of FLG with no defects and high degree of order is beneficial to the improvement of thermal conductivity for MIL-101/FLG composites. At 30 °C and bulk density of 0.55 g/cm3, thermal conductivity of MIL-101/20%FLG and MIL-101/25%FLG composite is 6.5 and 11.3 times higher than that of MIL-101. Thermal conductivity of MIL-101/FLG composites is related to the alignment direction of FLG and test direction of heat flow, and the interfacial thermal resistance between MIL-101 and FLG. Adding FLG in the MIL-101/FLG composites does not affect adsorption/desorption mechanism of water on the MIL-101. The addition of FLG can strengthen mass transfer and thermal diffusion process on the surface of MIL-101. Adsorption rate constant of water on the MIL-101/25%FLG composite is 2.05 times higher than that of MIL-101. The desorption temperatures and desorption activation energies of water on MIL-101/20%FLG and MIL-101/25%FLG composites are lower than those of MIL-101. It can provide basic research for the development of new adsorption water chiller working pair (MIL-101/FLG–water) with high efficiency.
... Secondly, for a retrofit application of an existing MED-AD configuration, the temperature difference (ΔT) can now be increased from a conventional ΔT of 3-3.5 K to about 6 to 7 K, and consequently doubling the water production rates from the MED. Detailed research on the AD cycles have been studied and made available by many researchers [24][25][26][27][28] where their experiment and simulation results highlighted that the portable water production and PR of the desalination could be increase up to 2-3 times by the hybrid concept [20,23]. ...
The hybridization of desalination processes is one of the most promising technologies to overcome the current limitations of desalination technologies while maximizing the advantages of individual processes in practice. Multi-effect distillation (MED) and adsorption desalination (AD) hybrid desalination process has been investigated in this study to maximize the utilization of energy input in desalination. Two different thermal desalination technologies have been integrated, and the synergetic impact of utilizing energy enhanced the performance of the hybrid system. The synergetic thermodynamic model has been developed in this study and the experimental results from the pilot unit, with a nominal production capacity of 10 m³/day, installed at KAUST, KSA have been affirmed the proposed model. Both the water production and the universal performance ratio (UPR) have been improved 2–5 times in different quality of the heat source (40–60 °C) to the MED. Moreover, the MED-AD hybrid process is enabled to scavenge the energy from the ambient temperature below 30 °C for the desalination. The utilized energy of both thermal and flash evaporation in all operation conditions, and individual effects has been inventoried to analyze the thermodynamic synergy of the hybridization. In the sole MED operations, the energy input in the first effect is carried over to the following effects, and part of it is used for thermal evaporation. However, due to the AD driven flash evaporation, the energy used in evaporation of the following effect is shown greater than the previous effect. The developed synergetic model of MED-AD hybrid system and its experiment with 4-effects MED pilot have demonstrated the potential of the hybrid system and its application to the industrial processes.
... The sensible heat term of the right hand-side is related to cooling water and hot water during the adsorption and desorption phases, respectively. Also, Q st represents isosteric heat of adsorption which is determined by (Chakraborty et al., 2009), ...
Due to the drawbacks of conventional methods of desalination, the adsorption desalination system has been introduced as a replacement with several advantages such as capability of using low-grade waste heat, low cost, and production of cooling as its second output. The aim of the paper is to provide a conceptual theoretical framework based on new advanced adsorption desalination and cooling system configured of double-cycle multi-bed dual-evaporator with internal heat recovery. As an innovative approach, the cycles are coupled through integrated equipment, working as a condenser for one of the cycles and a high-pressure evaporator for the other one. System performance is investigated in terms of specific daily water production (SDWP), low and high-pressure cooling capacities (SCPLP and SCPHP), and overall conversion ratio (OCR). It is shown that not only SDWP of the proposed configuration increases by 20 percent in comparison to the single-cycle multi-bed dual evaporator system, but also it is capable of producing considerable amounts of two grades of cooling water. The proposed configuration with 9.6 m3 of SDWP along with 24 and 25 Rton/ton of high and low-grade cooling capacities could be a suitable alternative to conventional configurations of adsorption desalination. Furthermore, a full sensitivity analysis is carried out by manipulating several system parameters, and the system performance is evaluated.
... Therefore, AHP contributes to the conservation of electrical energy and environmental protection of using low-grade industrial waste heat or solar heat and refrigerant having zero ODP and zero GWP. Notable researchers extensively studied several adsorbent/refrigerant pairs for application to AHP systems, for instances; silica gel-water [5,6,[8][9][10][11][12][13][14]; ...
Adsorption cooling systems powered by low-grade thermal or renewable energy are considered as a potential alternative to the vapor compression systems. To improve the performance and compactness of the system, this study focuses on the synthesis and characterization of activated carbon (AC) composite employing graphene nanoplatelets (GNPs) namely H-grade and C-grade, and polyvinyl alcohol. The influence of GNPs on the porous properties, thermal conductivity, and ethanol adsorption characteristics of composites have been experimentally investigated. Porous properties results show that the studied composites possess high surface area and pore volume with microporous nature. The C-grade contained composite shows the higher porous properties compared to H-grade, however, thermal conductivity for the later one is the highest. The highest thermal conductivity is found to be 1.55 W m −1 K −1 for H-grade (40 wt%) contained composite which is 23.5 times higher than that of powder AC. Ethanol adsorption characteristics on studied composites are conducted gravimetrically at adsorption temperatures 30-70 °C. Experimental data are also fitted with Tóth and Dubinin-Astakhov (D-A) isotherm models within ± 5% RMSD and found 23% improvement of effective volumetric uptake for H25 (20 wt %) composite compared to parent AC. The instantaneous ethanol adsorption uptake onto composites has also been presented for adsorption temperature 30 °C and evaporator pressure at 1.8 kPa.
... This can be explained by the decrease of the isosteric heat of adsorption with the increase of the membrane surface coverage preferentially by the water molecules, since the main materials of the membrane (silica and alumina) are hydrophilic. This effect of the degree of surface coverage on the isosteric heat of adsorption was observed experimentally for silica-alumina materials [43], and for silica gel [44]. Fig. 11 shows the graphical representation of the pre-exponential factor and permeation activation energy as a function of the feed molar fraction. ...
A commercial silica water selective membrane was evaluated experimentally. Additionally, its potential application in the synthesis of 1,1-Diethoxybutane was studied from the process intensification point of view. The membrane performance was evaluated experimentally, at different compositions and temperatures, by measuring the flux and permeate composition of binary and ternary mixtures. The effect of composition and temperature on the species permeances was also studied. For ethanol and butyraldehyde the permeances depend only on the temperature, following an Arrhenius equation; while for the water, its permeance depends on both temperature and composition, following a modified Arrhenius equation. Altogether, the permeation data obtained in the present work combined with reaction and adsorption data from previous works allowed a comparison, by simulation, between the PermSMBR and simulated moving bed reactor (SMBR) for the synthesis of 1,1-Diethoxybutane. Results showed that the PermSMBR, operating at 50 °C, presents an improvement of about 7% in both productivity (34.3 ) and desorbent consumption (1.73 LEth/kgDEB).
... To perform the experiment a pair of adsorbent and refrigerant is selected which is also very important to design thermal compression refrigeration/heat pump system. Extensive studies have been conducted to investigate the performance of adsorption cooling/heat pump systems considering various adsorbent/refrigerant pairs such as silica gel/water [7,8], zeolite/water [9], activated carbon/CO 2 [10], activated carbon/methanol [11] and activated carbon/ethanol [12,13] among other working pairs. Hornbostel et al. [5] studied the characteristics of carbon sorbent for CO 2 capture using a temperature programmed TGA. ...
The objective of this study is to evaluate adsorption kinetics of ethanol onto different surface treated functional activated carbons with controlled oxygen content experimentally at different temperature ranges using a thermo gravimetric analyzer (TGA) unit which has an accuracy of 0.1×10-6 g for the vapor uptake, and the results are logged continuously. The surface diffusion time constant and overall mass transfer coefficient are also estimated from the experimentally measured data. These data are useful for the design of adsorption cooling, refrigeration and heat pump systems and are unavailable in the literature.
... Accordingly, research and development on the utilization of natural and/or alternative refrigerants in heat pump systems has been intensified. Studies showed that adsorption heat pump system can utilize natural or alternative refrigerants and it can be driven by waste heat or solar heat of temperature below 100°C [2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Among all natural refrigerants, carbon dioxide (CO 2 ) offers a number of advantages including excellent thermo-physical properties, high volumetric capacity. ...
Adsorption of carbon dioxide onto highly porous activated carbon based consolidated composite adsorbent has been experimentally investigated. Experiments have been conducted at temperatures of 30, 50, 70 ºC and pressures up to 7 MPa using magnetic suspension adsorption measurement unit. The innovative adsorption isotherms data have been correlated using three isotherm models namely, Langmuir, Tóth, and modified Dubinin-Astakhov (D-A). The studied models successfully fitted with the experimental data and Tóth isotherm model shows a better fitting. Results showed that the volumetric adsorption capacity of CO2 onto the studied consolidated composite is higher than that of CO2 onto parent activated carbon powder (Maxsorb III). The isosteric heat of adsorption of the studied pairs has been calculated from isotherm data. The performance of ideal adsorption cooling cycle, employing consolidated composite adsorbent/CO2 pair, has also been simulated at three different evaporator temperatures, namely 5, 10 and 15 ºC along with a coolant temperature of 25 ºC and heat source temperatures ranging from 45 to 90 ºC. The estimated thermodynamic parameters and isotherm data are important for further development of CO2 based adsorption cooling systems.
... where S s is assumed to be indifferent to P and ϕ. Chakraborty et al. [30] derived the entropy change as ...
This paper introduces a novel time-scheduling scheme for adsorption desalination (AD). Mathematically, a critical bed pressure of the Toth isotherm is defined as the pressure above which the uptake ratio scarcely changes. Heat balance equations of sorption beds for precooling, adsorption, preheating, and desorption are unified into a single equation. This general governing equation is used to model AD systems, which consists of an arbitrary number of bed pairs with specifically preset initial thermal phases. A theoretical minimum of switching interval is derived as a function of thermal properties of reaction beds and heat exchangers. In the new time scheduling scheme, no bed pairs are in an identical process schedule, because each bed has its initial time lag (ITL) when the operation starts. We found that specific AD performances vary noticeably depending on the ITL values, the num- ber of beds, and more importantly, the number of beds in a time-lag group. There must be an optimal ITL for given operational parameters, which can distinctly increase the water production rate without using extra heat sources. This can dynamically optimize the relative performance of desalination rates and cooling capacities of AD processes.
... Two approaches have been used to improve the performance of AHP systems: chemical engineering-based and material-based approaches. For the latter approach, various adsorbenteadsorbate pairs, such as silica gelewater [3,4], zeoliteewater [5], activated carbon (AC)eCO 2 [6], ACewater [7], ACemethanol [8,9], and ACeethanol [1,9] pairs, have been considered because adsorptive and thermal characteristics depend not only on individual properties of the adsorbent and adsorbate, but also on their combination. Demir et al. [10] discussed problems and solutions associated with AHP systems. ...
To develop high-performance activated carbons (ACs) for adsorption heat pumps (AHPs), it is important to characterize the adsorption behaviors of the refrigerant molecules in the pores of ACs. Not only pore structures, such as pore size and shape, but also surface functionalities strongly influences the adsorption behaviors, especially for polar molecules, such as water and ethanol, which are typical refrigerants for AHP. In this study, we examined the influence of surface functional groups on the adsorption behaviors of ethanol molecules in carbon micropores using model ACs with different amounts of oxygen-containing surface functional groups but comparable porosities. For the AC with an increased amount of surface functional groups, ethanol adsorption/desorption isotherms showed significant decreases in the adsorption amounts and shortened adsorption equilibrium times compared to those with less surface functional groups throughout the entire relative pressure region. This suggests diffusional hindrance of ethanol molecules in micropores with abundant surface functional groups. To verify our hypothesis, we examined the influence of surface functional groups on the adsorption behavior of ethanol molecules using a solid-state NMR technique. The NMR results revealed that the hydroxyl group of ethanol molecules strongly interacts with the surface functional groups, giving rise to an oriented adsorption of ethanol molecules in the micropores with oxygen-containing surface functional groups. Furthermore, electrochemical analyses confirmed that diffusion resistance of electrolyte ions in the micropores increases after the introduction of oxygen-containing surface functional groups, which supports our hypothesis.
... To perform the experiment a pair of adsorbent and refrigerant is selected which is also very important to design thermal compression refrigeration/heat pump system. Extensive studies have been conducted to investigate the performance of adsorption cooling/heat pump systems considering various adsorbent/refrigerant pairs such as silica gel/water [7,8], zeolite/water [9], activated carbon/CO 2 [10], activated carbon/methanol [11] and activated carbon/ethanol [12,13] among other working pairs. Hornbostel et al. [5] studied the characteristics of carbon sorbent for CO 2 capture using a temperature programmed TGA. ...
... After six months from the beginning of measurements they obtained a net COP of 0.13. Silica gel-water as an adsorbent/adsorbate pair had been used in several studies [22][23][24]. For example, Wang et al. [23] developed a novel silica gel-water adsorber. ...
The current work demonstrates a developed model of a solar adsorption refrigeration system with specific requirements and specifications. The recent scheme can be employed as a refrigerator and cooler unit suitable for remote areas. The unit runs through a parabolic trough solar collector (PTC) and uses olive waste as adsorbent with methanol as adsorbate. Cooling production, COP (coefficient of performance, and COPa (cycle gross coefficient of performance) were used to assess the system performance. The system’s design optimum parameters in this study were arrived to through statistical and experimental methods. The lowest temperature attained in the refrigerated space was 4 °C and the equivalent ambient temperature was 27 °C. The temperature started to decrease steadily at 20:30 – when the actual cooling started – until it reached 4 °C at 01:30 in the next day when it rose again. The highest COPa obtained was 0.75.
One of the essential factors for water adsorption on silica gels is the concentration of silanol groups on the silica surface. However, no systematic investigation on the adsorption of sour gas components, methane (CH4), carbon dioxide (CO2), and hydrogen sulfide (H2S) on silica gels with different textural properties and surface silanol concentrations, has been conducted. Three silica gels of 22, 30, and 60 Å pore sizes, with silanol concentrations of αtotal = 2.516, 2.340, and 2.152 OH nm-2, respectively, were studied in this work. The adsorption data for CH4, CO2, H2S, and H2O at T = 0, 25, and 50 °C on the 22 and 30 Å pore size silica gels were presented, and a comparison of the data for the 60 Å pore size silica gel on the same adsorbates was conducted. All three silica gels showed an adsorption affinity in the order of H2O > H2S > CO2 > CH4. The isosteric heats of adsorption of H2O and H2S had a greater dependence on the silanol concentration than CO2 and CH4. At p < 10 bar, there was no difference in the adsorption per m2 of CH4 between the silica gels (n ads = 1.7 mmol m-2, for all silicas at p = 10 bar), while higher pressures resulted in greater adsorption capacity in the larger pore volume silica gels (at p = 20 bar: n ads = 3.0, 3.3, and 3.4 mmol m-2 for the 22, 30, and 60 Å pore size silicas, respectively). H2S adsorption at low pressures (p < 4 bar) was larger on the samples with larger silanol concentrations (at p = 3 bar: n ads = 6.1, 4.7, and 4.5 mmol m-2 for the 22, 30, and 60 Å pore size silicas, respectively), but above p = 4 bar, the 60 Å pore size silica had a greater adsorption capacity than the 30 Å pore size (at p = 5 bar: n ads = 8.0, 6.0, and 6.2 mmol m-2 for the 22, 30, and 60 Å pore size silicas, respectively).
The CO2 sorption behavior of commercially available zeolites such as 3A, 4A, 5A, and 13X is considered at low temperatures for CO2 removal from ambient air or direct air capture (DAC). Low silica zeolites are typically not effective CO2 sorbents in the presence of water, as they preferentially competitively adsorb water from humid gas streams, resulting in high sorbent regeneration costs. We hypothesize that low silica zeolites may function as efficient physisorbents for DAC if deployed at cold temperatures where the absolute humidity of air is low. Two modes of deployment of low silica zeolites for DAC at cold temperatures are explored here. Based on the CO2 isotherms of the zeolites at -20 °C with different H2O surface loadings, zeolite 5A was selected for evaluation in a competitive H2O and CO2 coadsorption process as the first mode of deployment. Despite the low absolute humidity at -20 °C compared to that at 25 °C, H2O adsorption and accumulation result in a 39% decrease in the CO2 adsorption capacity of 5A, rendering the process energetically expensive. In the second mode of deployment, focusing on estimates of the thermal energy requirements, zeolite 13X with silica gel as a desiccant in a two-stage, two-bed process is found to provide a potentially energetically feasible process (4359 MJ/tCO2) for cold-temperature DAC. Cyclic adsorption and desorption cycles swinging between -20 and 200 °C with 0.04% and 99.9% CO2, respectively, are conducted to experimentally support the thermal energy calculations using a temperature swing adsorption (TSA) process. Water production using available cooling energy from cold ambient air offers the potential to reduce the cost of DAC, as do additional process design modes such as vacuum swing adsorption and advanced heat management systems.
This is the 9th Heat Powered Cycles Conference. The first edition of the conference was held at Nottingham in 1997. This time the event was co-organized by the University of the Basque Country, (Bilbao, Spain), The University of Applied Sciences, Vorarlberg, (Austria), and GamaTech Thermal Solutions, (Brazil). The conference took place at the University of the Basque Country and hosted by the Department of Energy Engineering at the University of the Basque Country by Prof. Jesús María Blanco Ilzarbe. In addition to formal presentations of technical papers, including invited Keynote papers, the event includes poster sessions and two Special Sessions, being one related to Intelligent Thermal Energy Systems and The Energy in the Post-Covid Scenario, along with a full social program. The conference is concerned with scientific and technological innovations relating to the efficient and economic use of heat, derived from all its sources, for the production of cooling, heating, and mechanical power either independently or co-generatively.
Subject areas of particular interest include; hybrid cycles, ORCs, Stirling cycle machines,
thermo-acoustic engines and coolers, sorption cycle refrigerators and heat pumps, jet-pump (ejector) machines, temperature amplifiers (heat transformers), chemical heat pumps, new working fluids, mass and heat transfer phenomena, desalination of brackish water and seawater, compact heat exchanger research (including foams and other micro-channel research), thermo-economics, process optimisation and modelling, process, and cycle thermodynamics.
This is the 9th Heat Powered Cycles Conference. The first edition of the conference was held at Nottingham in 1997. This time the event was co-organized by the University of the Basque Country, (Bilbao, Spain), The University of Applied Sciences, Vorarlberg, (Austria), and GamaTech Thermal Solutions, (Brazil). The conference took place at the University of the Basque Country and hosted by the Department of Energy Engineering at the University of the Basque Country by Prof. Jesús María Blanco Ilzarbe. In addition to formal presentations of technical papers, including invited Keynote papers, the event includes poster sessions and two Special Sessions, being one related to Intelligent Thermal Energy Systems and The Energy in the Post-Covid Scenario, along with a full social program. The conference is concerned with scientific and technological innovations relating to the efficient and economic use of heat, derived from all its sources, for the production of cooling, heating, and mechanical power either independently or co-generatively.
Thermodynamic properties of various sorbents, namely carbon-based sorbents, silica gel and metal-organic frameworks (MOFs) were assessed and compared based on their adsorption isotherms at 25, 30 and 35 °C. The isotherms were measured in a custom-made and calibrated environmental chamber using a gravimetric method. Gibbs free energy demonstrated the spontaneity of the adsorption process and the hygroscopicity variation of the sorbents depending on their surface chemistry. The carbon-based sorbent, nanoporous sponges (NPS), and one of the MOFs, Cr-MIL-101, had lower sorbent-adsorbate interactions and thus had integral enthalpies converging rapidly to the heat of vaporization of pure water. As such, these samples would release less heat during an adsorption step with partial filling of the sorbent. Integral entropy showed that, for most of the environmental conditions, adsorbed water molecules had an entropy equivalent to pure water for most of the sorbent materials, except for the silica gel due to its higher energy sites and higher water-sorbent interactions. NPS and Cr-MIL-101 were shown to be entropically advantageous for the recovery/removal of water. Enthalpy and entropy can provide favorable conditions to perform adsorption-desorption cycles in a practical water capture system.
A silica gel-based system that demonstrates cost-effectiveness, stability and easy maintenance, is proposed, and the corresponding simulations are performed in this study. With the system, depressurization and CHF enhancement can be simultaneously realized. Several parameters such as the particle size, initial steam partial pressure and containment free volume on the steam removal efficiency are considered to assess the overall applicability of the system to nuclear power plants. The adsorption process becomes saturated in relatively short periods, and peak pressures by ejected high-temperature steam can be mitigated thereby. Besides, the silica gel-based system will show great functionality, especially for the small-sized reactors.
The goal of this study was to determine the physicochemical properties of a variety of geologic materials using inverse gas chromatography (IGC) by varying probe gas selection, temperature, carrier gas flow rate, and humidity. This is accomplished by measuring the level of interaction between the materials of interest and known probe gases. Identifying a material's physicochemical characteristics can help provide a better understanding of the transport of gaseous compounds in different geologic materials or between different geological layers under various conditions. Our research focused on measuring the enthalpy (heat) of adsorption, Henry's constant, and diffusion coefficients of a suite of geologic materials, including two soil types (sandy clay-loam and loam), quartz sand, salt, and bentonite clay, with various particle sizes. The reproducibility of IGC measurements for geologic materials, which are inherently heterogeneous, was also assessed in comparison to the reproducibility for more homogeneous synthetic materials. This involved determining the variability of physicochemical measurements obtained from different IGC approaches, instruments, and researchers. For the investigated IGC-determined parameters, the need for standardization became apparent, including the need for application-relevant reference materials. The inherent physical and chemical heterogeneities of soil and many geologic materials can make the prediction of sorption properties difficult. Characterizing the properties of individual organic and inorganic components can help elucidate the primary factors influencing sorption interactions in more complex mixtures. This research examined the capabilities and potential challenges of characterizing the gas sorption properties of geologic materials using IGC.
The previously published studies based on the performance prediction of solar-powered adsorption chillers generally incorporate fixed heat/mass recovery (HR/MR) cycle times which remain unchanged during the entire course of operation of the adsorption chiller. In reality, the dynamics of the HR/MR processes are continuously subject to change due to temporal variations in the solar radiation intensity, and thus fixed HR/MR cycle times might not prove to be compatible with the actual dynamics of a transient solar-powered chiller operation. The current study proposes a numerical scheme for performance modeling of a commercial-scale adsorption chiller with adaptive HR/MR cycle times following the adsorption/desorption (ads/des) cycle. A novel model of the MR cycle has been proposed which, according to the best knowledge of the authors, cannot be find anywhere in the previously published literature. The ads/des→HR→MR→des/ads half cycle has been predicted to yield an almost 52% higher cycle-averaged value of coefficient of performance (COP), an almost 16% higher value of specific cooling power (SCP), and a roughly 146% higher value of solarCOP (COPsc) than the ads/des→MR→HR→des/ads half cycle over the entire course of operation of the adsorption chiller till sunset.
Adsorption carbon capture technology has been considered as one of the most promising technologies to control the CO2 level in the atmosphere. From the view of thermodynamics, the adsorbed-bulk gas phase equilibrium system should be well developed for accurately elaborating the mechanism of CO2 adsorption. Since thermodynamic properties of the adsorbed CO2 plays a significant role in the cyclic analysis of carbon capture technology, in this work, the Gibbs’ thermodynamic graphical method was extended to the expression of thermodynamic properties of the adsorbed CO2 as a specific case study. The 3-dimensional (3D) thermodynamic surface was established to determine the thermodynamic properties of the adsorbed CO2 in the thermodynamic equilibrium state. The temperature and pressure were treated as the individual variables to calculate the thermodynamic properties of the adsorbed CO2, including the adsorption capacity, chemical potential, entropy, and internal energy. Finally, the internal energy-adsorption capacity-entropy 3D thermodynamic surface of the adsorbed CO2 was obtained by the Gibbs’ thermodynamic graphical method. The thermodynamic surface established in this work will contribute and/or accelerate the research of the actual adsorption thermodynamic cycle and new findings are encouraged to be updated to our database to enhance the development on thermodynamic characteristics of the adsorption technology.
The knowledge of the isosteric heats (Qsto) is essential to design porous adsorbents for calculating the performances of adsorption-assisted cooling, separation and gas storage systems. This paper presents a thermodynamic framework to calculate the interaction potentials and isosteric heats for water adsorption on SiO2 structures. Here both Lennard Jones (LJ) and electrostatic potentials are considered. It is found that (i) Qsto varies from 1.37 eV (∼131 kJ/mol) to 0.54 eV (∼52 kJ/mol) for the adsorption of one water molecule on various pore sizes of SiO2 structure, and (ii) Qsto depends on the pore size (H). Qsto is found to be very high in the super-micro-pore regions. The density functional theory (DFT) is applied to calculate Qsto for the adsorption of water on silica. Here water-water interactions are not considered. Later Qsto for five types of silica gels are obtained from experimentally-measured isotherms data at low pressures (up to 0.15 kPa) and wide range of temperatures. The simulation result agrees well with the experimental data.
Metal-organic frameworks (MOFs) have recently attracted enormous interest over the past few years in energy storage and gas separation, yet there have been few reports for adsorption cooling applications. Adsorption cooling technology is an established alternative to mechanical vapor compression refrigeration systems and is an excellent alternative in industrial environments where waste heat is available. We explored the use of MOFs that have very high mass loading and relatively low heats of adsorption, with certain combinations of refrigerants to demonstrate a new type of highly efficient adsorption chiller. Computational fluid dynamics combined with a system level lumped-parameter model have been used to project size and performance for chillers with a cooling capacity ranging from a few kW to several thousand kW. These systems rely on stacked micro/mini-scale architectures to enhance heat and mass transfer. Recent computational studies of an adsorption chiller based on MOFs suggests that a thermally-driven coefficient of performance greater than one may be possible, which would represent a fundamental breakthrough in performance of adsorption chiller technology. Presented herein are computational and experimental results for hydrophyilic and fluorophilic MOFs.
Environment-friendly adsorption (AD) cycles have gained much attention in cooling industry and its applicability has been extended to desalination recently. AD cycles are operational by low-temperature heat sources such as exhaust gas from processes or renewable energy with temperatures ranging from 55 °C to 85 °C. The cycle is capable of producing two useful effects, namely cooling power and high-grade potable water, simultaneously. This article discusses a low temperature, waste heat-powered adsorption (AD) cycle that produces cooling power at two temperature-levels for both dehumidification and sensible cooling while providing high-grade potable water. The cycle exploits faster kinetics for desorption process with one adsorber bed under regeneration mode while full utilization of the uptake capacity by adsorbent material is achieved employing two-stage adsorption via low-pressure and high-pressure evaporators. Type A++ silica gel with surface area of 863.6 m2/g and pore volume of 0.446 cm3/g is employed as adsorbent material. A comprehensive numerical model for such AD cycle is developed and the performance results are presented using assorted hot water and cooling water inlet temperatures for various cycle time arrangements. The cycle is analyzed in terms of key performance indicators i.e., the specific cooling power (SCP), the coefficient of performance (COP) for both evaporators and the overall system, the specific daily water production (SDWP) and the performance ratio (PR). Further insights into the cycle performance are scrutinized using a Dühring diagram to depict the thermodynamic states of the processes as well as the vapor uptake behavior of adsorbent. In the proposed cycle, the adsorbent materials undergo near saturation conditions due to the pressurization effect from the high pressure evaporator while faster kinetics for desorption process is exploited, subsequently providing higher system COP, notably up to 0.82 at longer cycle time while the COPs for low-pressure and high-pressure evaporators are recorded to be 0.33 and 0.51, respectively.
Packed beds are the simplest fluid–solid contact systems for water vapour adsorption from humid air. They usually are free from mechanical problems due to their non-moving parts and provide a high volume of adsorbents for fluid–solid interaction. However, issues relating to heat effects, pressure drop and the residence time of the fluid in the bed present significant challenges to the efficient adsorption of water vapour within them. These issues related to the packing structure coupled with the difficulties involved in visualising fluid flow within non-transparent beds further creates barriers in understanding fluid behaviour in the bed.
In this paper, a critical review of water vapour adsorption in solid desiccant packed beds has been carried out to provide insights into packed bed adsorption process and its associated thermal effects. Crucial to this, is the insight provided into the packing structure and its influence on the adsorption process, the transport phenomenon in the bed, the heat of adsorption generating the thermal effects and thermal enhancement strategies for packed beds. Various approaches and models for analysing the adsorption process mainly involving flow and pressure drop, heat and mass transfer within packed beds have been reviewed. The potential for the thermal enhancement strategies employed in various studies to achieve isothermal adsorption process in packed beds have also been reviewed.
An analytical investigation on the performance of adsorption–compression hybrid refrigeration systems with two different cycle configurations, cascade type and subcool type has been performed. In the former type, a cascade condenser is used which works as a condenser for mechanical compression cycle and evaporator for adsorption cycle. In the latter type, an evaporative subcooler is used which subcool the fluid of mechanical compression cycle. The refrigerants examined for the mechanical compression cycle are R134a, R152a, R1234yf and R1234ze whereas ethanol is the refrigerant for the adsorption cycle. The main feature of the proposed system is the capability to significantly reduce work input for the mechanical compressor which results up to 30% energy saving potential depending on the selection of refrigerant and system configuration. Based on the thermodynamic properties and laws the study analyzed the effect of the major design parameters such as evaporation temperature, compressor discharge pressure and desorption temperature on the system performances.
An analytical investigation on the performance of adsorption–compression hybrid refrigeration systems with two different cycle configurations, cascade type and subcool type has been performed. In the former type, a cascade condenser is used which works as a condenser for mechanical compression cycle and evaporator for adsorption cycle. In the latter type, an evaporative subcooler is used which subcool the fluid of mechanical compression cycle. The refrigerants examined for the mechanical compression cycle are R134a, R152a, R1234yf and R1234ze whereas ethanol is the refrigerant for the adsorption cycle. The main feature of the proposed system is the capability to significantly reduce work input for the mechanical compressor which results up to 30% energy saving potential depending on the selection of refrigerant and system configuration. Based on the thermodynamic properties and laws the study analyzed the effect of the major design parameters such as evaporation temperature, compressor discharge pressure and desorption temperature on the system performances.
We have developed a thermodynamic framework to calculate adsorption cooling cum desalination cycle performances as a function of pore widths and pore volumes of highly porous adsorbents, which are formulated from the rigor of thermodynamic property surfaces of adsorbent-adsorbate system and the adsorption interaction potential between them. Employing the proposed formulations, the coefficient of performance (COP) and overall performance ratio (OPR) of adsorption cycle are computed for various pore widths of solid adsorbents. These results are compared with experimental data for verifying the proposed thermodynamic formulations. It is found from the present analysis that the COP and OPR of adsorption cooling cum desalination cycle is influenced by (i) the physical characteristics of adsorbents, (ii) characteristics energy and (iii) the surface-structural heterogeneity factor of adsorbent-water system. The present study confirms that there exists a special type of adsorbents having optimal physical characteristics that allows us to obtain the best performance.
This study focuses on the water quality assessment (feed, product and brine) of the pilot adsorption desalination (AD) plant. Seawater from the Red Sea is used as feed to the AD plant. Water quality tests are evaluated by complying the Environmental Protection Agency (EPA) standards with major primary and secondary inorganic drinking water pollutants and other commonly tested water quality parameters. Chemical testing of desalinated water at the post desalination stage confirms the high quality of produced fresh water. Test results have shown that the adsorption desalination process is very effective in eliminating all forms of salts, as evidenced by the significant reduction of the TDS levels from approximately 40,000 ppm in feed seawater to less than 10 ppm. Test results exhibit extremely low levels of parameters which are generally abundant in feed seawater. The compositions of seawater and process related parameters such as chloride, sodium, bromide, sulfate, calcium, magnesium, and silicate in desalinated water exhibit values of less than 0.1 ppm. Reported conductivity measurements of desalinated water are comparable to distilled water conductivity levels and ranged between 2 and 6 μS/cm while TOC and TIC levels are also extremely low and its value is less than 0.5 ppm.
The pervaporation performance of a commercial silica membrane (Pervatech BV) was evaluated for dehydration of aqueous n-butanol solutions. The influence of the operation parameters, such as feed composition, temperature and permeate pressure was experimentally investigated in terms of permeation flux, separation factor, permeance and membrane selectivity. The membrane exhibited high flux, 3.53 kg/ m(2) h, combined with a separation factor equal to 150, at 70 degrees C and for 10 wt.% water in feed. The mole fraction of water in the permeate ranged from 98.7% to 99.2% at 70 degrees C. The information collected is of most importance to design and optimize a pervaporation process for the dehydration of n-butanol, which can be integrated with an intensified technology, the simulated moving bed reactor, used in the synthesis of the green fuel, 1,1-dibutoxyethane.
This paper presents a theoretical framework for the understanding of pressurized adsorption systems using the statistical rate methodology. Utilizing results from the statistical rate theory, basic thermodynamic variables including enthalpy (ha), entropy (sa) and the specific heat capacity (cpa) of the adsorbed phase are derived using the thermodynamic requirements of chemical equilibrium, Gibbs law, as well as Maxwell relations. A built-in constant (K) describes the adsorbed molecular partition function (q^s) and it captures the heterogeneous properties of the adsorbent + adsorbate pair at equilibrium states. Improved adsorbed-phase volume considerations were incorporated in the formulations of these variables where they could be utilized with relative ease for analyzing the energetic performances of any practical adsorption system. In this paper, we have demonstrated how derived thermodynamic quantities can bridge the information gap with respect to the states of adsorbed-phase, as well as resolving some theoretical inconsistencies that were found in previously derived quantities. Experimentally, the adsorption isotherms of Propane (refrigerant) on Activated Carbon Powder (Maxsorb III) for temperatures from 5°C to 75°C and pressures up to 8 bars are presented and they are used to illustrate the behaviors of the adsorbed-phase during uptakes, temperatures and pressure excursions or changes.
The transient heat and mass transfer in a desiccant packed bed containing varying particle diameter distribution along the axial direction has been investigated using the pseudo gas controlled approach that considers the heat conduction in the bed. The numerical results of the present model and the experimental data from literature show good agreement with a maximum root of mean square of errors of 3% and 2% for exit air temperature and humidity ratio, respectively. The improvement in the total mass adsorbed and/or reduction in pressure drop has been investigated for various cases of packed bed namely, uniform particle diameter, linear, parabolic and cubic ascending and descending distributions. It has been found that there is a 25.7% reduction in pressure drop with negligible reduction in the total mass adsorbed for a desiccant bed with cubic type particle size distribution when compared to the bed with uniform particle diameter of 1.0 mm. A threshold flow velocity exists below which the total mass adsorbed is independent of particle diameter distribution type.
Desalination, other than the natural water cycle, is hailed as the panacea to alleviate the problems of fresh water shortage in many water stressed countries. However, the main drawback of conventional desalination methods is that they are energy intensive. In many instances, they consumed electricity, chemicals for pre- and post-treatment of water. For each kWh of energy consumed, there is an unavoidable emission of Carbon Dioxide (CO2) at the power stations as well as the discharge of chemically-laden brine into the environment. Thus, there is a motivation to find new direction or methods of desalination that consumed less chemicals, thermal energy and electricity.This paper describes an emerging and yet low cost method of desalination that employs only low-temperature waste heat, which is available in abundance from either the renewable energy sources or exhaust of industrial processes. With only one heat input, the Adsorption Desalination (AD) cycle produces two useful effects, i.e., high grade potable water and cooling. In this article, a brief literature review, the theoretical framework for adsorption thermodynamics, a lumped-parameter model and the experimental tests for a wide range of operational conditions on the basic and the hybrid AD cycles are discussed. Predictions from the model are validated with measured performances from two pilot plants, i.e., a basic AD and the advanced AD cycles. The energetic efficiency of AD cycles has been compared against the conventional desalination methods. Owing to the unique features of AD cycle, i.e., the simultaneous production of dual useful effects, it is proposed that the life cycle cost (LCC) of AD is evaluated against the LCC of combined machines that are needed to deliver the same quantities of useful effects using a unified unit of $/MWh. In closing, an ideal desalination system with zero emission of CO2 is presented where geo-thermal heat is employed for powering a temperature-cascaded cogeneration plant.
This paper presents the thermo-economic analysis of the adsorption desalination (AD) cycle that is driven by low-temperature waste heat from exhaust of industrial processes or renewable sources. The AD cycle uses an adsorbent such as the silica gel to desalt the sea or brackish water. Based on an experimental prototype AD plant, the life-cycle cost analysis of AD plants of assorted water production capacities has been simulated and these predictions are translated into unit cost of water production. Our results show that the specific energy consumption of the AD cycle is 1.38 kWh/m which is the lowest ever reported. For a plant capacity of 1000 m/d, the AD cycle offers a unit cost of $0.457/m as compared to more than $0.9 for the average RO plants. Besides being cost-effective, the AD cycle is also environment-friendly as it emits less CO2 emission per m generated, typically 85% less, by comparison to an RO process.
The Polanyi potential ΔF = -RTln(p/ps) was demonstrated to adequately describe the sorption equilibrium between water vapor and a CaCl2-in-silica gel composite sorbent. Approximation formulas for calculating the dependence of the value of adsorption of water on ΔF and the dependence of heat of sorption on the adsorption value were derived. A comparison of experimental and theoretical data for a temperature-independent curve and sorption isobars was performed.
A theoretical framework for the estimation of the isosteric heat of adsorption between an adsorbate (vapor) and an adsorbent (solid) is proposed based on the thermodynamic requirements of chemical equilibrium, Maxwell relations, and the entropy of the adsorbed phase. The derived equation for the isosteric heat of adsorption is verified against three sets of judiciously selected adsorbent + adsorbate data that are found in the literature and the predictions are found to agree within the experimental uncertainties of the reported data.
This article presents the dynamic modelling of a single effect two-bed adsorption chiller utilizing the composite adsorbent “CaCl2 confined to KSK silica gel” as adsorbent and water as adsorbate, which is based on the experimentally confirmed adsorption isotherms and kinetics data. Compared with the experimental data of conventional adsorption chiller based on RD silica gel + water pair, we found that the new working pair provides better cooling capacity and performances. From numerical simulation, it is also found that the cooling capacity can be increased up to 20% of the parent silica gel + water adsorption chiller and the coefficient of performance (COP) can be improved up to 25% at optimum conditions. We also demonstrate here that the best peak chilled water temperature suppression, and the maximum cooling capacity can be achieved by the optimum analysis for both cycles.
The heats of sorption of water vapor on the calcium chloride (or lithium bromide)-porous matrix (KSK and KSM silica gels and MSM-41 sorbent) composite sorbents and on pure silica gels were measured by calorimetry. It was shown that samples based on KSK mesoporous silica gel can feature (a) adsorption on the surface of silica gel (pure or modified with salt ions) with a heat effect of Q = 76-84 kJ/mol (at sorption values w < 1.0 wt %), (b) formation of lower crystal hydrates of the salt with Q = 66-72 kJ/mol (at 1 wt % < w < 9-14 wt %), and (c) vapor absorption with Q = 50-54 kJ/mol by a salt solution in pores (at w > 9-14 wt %). Sorption mechanisms (a) and (c) were also observed for samples based on KSM microporous silica gel and MSM-41. The possibility of the formation of solid salt hydrates in micropores was discussed. It was revealed that the heats of sorption measured in the regions of formation of hydrates and solutions are close to those obtained earlier by the sorption method. It was shown that the introduction of a hygroscopic salt into silica gel pores substantially increases the sorption capacity of the composite system compared to the initial host matrix.
This article presents theoretical modelling of a novel electro-adsorption chiller (EAC) amalgamating two individually low coefficient-of-performance (COP) cycles into a combined cycle, which has the potential to increase the COP by several fold. Modelling demonstrates a multi-disciplinary engineering-science application of the physical properties of thermo-electrics, adsorption isotherms and kinetics to the simulated behaviour of engineering components of an EAC, such as thermal mass capacities, valve characteristics and internal heat and mass transfer resistances. Predictions of EAC performance are validated with results from an experimental prototype to instill greater confidence in the future miniaturization of EACs.
A general thermodynamic treatment of adsorption equilibrium is proposed which follows the lines of the thermodynamics of solutions in that the properties of a real system are compared with those of an ideal reference system. For adsorption, two possible reference systems are the ideal localized monolayer and the ideal non-localized monolayer. These are examined and their range of usefulness is discussed generally ; their application to experimental data is considered in the following paper of this series. A short discussion is also given of the relation between the present method and the Polanyi potential theory.
The paper describes the successful amalgamation of the thermoelectric and the adsorpion cycles into a combined electro-adsorption chiller (EAC). The symbiotic union produces an efficiency or COP (coefficient of performance) more than threefold when compared with their individual cycles. The experiments conducted on the bench-scale prototype show that it can meet high cooling loads, typically 120 W with an evaporator foot print of 25 cm2, that is 5 W/cm2 at the heated surface temperature of 22° C, which is well below that of the room temperature. The COPs of the EAC chiller vary from 0.7 to 0.8, which is comparable to the theoretical maximum of about 1.1 at the same operating conditions. With a copper-foam cladded evaporator, the high cooling rates have been achieved with a low temperature difference. In addition to meeting high cooling rates, the EAC is unique as (i) it has almost no moving parts and hence has silent operation, (ii) it is environmentally friendly as it uses a nonharmful adsorbent (silica gel), and (iii) water is used as the refrigerant.
The search for fresh or potable water remains a pressing concern throughout many regions of the world. Although most of the Earth's surface is covered by oceans, the effort to provide for the world's inhabitants with fresh or potable water seems to be insurmountable; at least one billion people do not have access to clean and fresh water. The World Health Organization (WHO) reported that about 41% of the Earth's population lives in water-stressed areas, and the number of people in the water scarce regions may climb to 3.5 billion by the year 2025. Thus, innovative and cost-effective desalination technologies for producing fresh water are needed to provide practical solutions.
This paper is a generalization of Part V of this series. We show here that the usual solution thermodynamics can be recast into an equivalent but alternative form which is more natural and useful in adsorption work. Relations between the two systems of thermodynamics are pointed out. The extension to the case of sorption from a mixture of gases is included.
The thermodynamics of an adsorbate on an inert adsorbent is discussed in some detail. Heats of adsorption are given particular attention in an attempt to clarify and extend the available methods in this field. It is found that the true equilibrium ΔH=TΔS of adsorption for adsorbate molecules is given by (∂ lnp/∂T)[open phi]=−ΔH/RT2,where [open phi] is the two-dimensional spreading pressure.
The relation of the work of Rowley and Innes to the present paper is considered.
A prototype adsorption desalination facility is experimentally studied, and the performance tests are conducted with and without the heat and mass recovery procedures. The experiments show that practical and yet effective methods could yield a significant boost to the specific daily water production and performance ratio of the desalination plant by 15.7% and 42.5%, respectively.
The effects of the two critical assumptions, an ideal bulk gas phase and a negligible adsorbed phase molar volume, on the calculated isosteric heats of adsorption were studied. The isosteric heats of adsorption of ethane, propane, and butane on heterogenous activated carbon were calculated in three different ways: 1) using the classic Clausius-Clapeyron equation; assuming ideal gas for the bulk gas phase, while taking into account the adsorbed phase volume; and 3) relaxing both assumptions by nonlocal density functional theory (NDFT), and describing the bulk gas by the Carnahan-Starling equation of state plus a mean-field attraction (CSPMA).
We have developed the complete thermodynamic property fields for a single-component adsorbent + adsorbate system. These equations enable us to compute the actual specific heat capacity, the partial enthalpy, and the entropy, which are essential for the analyses of single-component adsorption processes. Conventionally, the specific heat capacity of the adsorbate is assumed to correspond to its liquid phase specific heat capacity and more recently to that of its gas phase. We have shown that the actual specific heat capacity of the adsorbate could differ significantly from what has been conventionally assumed. A simple but improved expression for the adsorbate specific heat capacity is also proposed.
We consider the thermodynamics of adsorption of gases in porous solids from both the perspective of absolute properties which appear naturally in theoretical studies and that of excess properties which are measured in experiments. Our thermodynamic description starts by treating the gas (or gas mixture) plus porous solid system as a mixture to which we can apply solution thermodynamics. We show that equations for the absolute thermodynamic properties for adsorption in rigid porous materials do not require an explicit reference to the pressure of the fluid confined in the porous material. We discuss how to relate absolute properties to excess properties by using an estimate of the helium void volume. We illustrate the thermodynamic formalism with calculations for a simple thermodynamic model in which the Langmuir equation is used to describe the absolute adsorption isotherm and the ideal gas equation of state is used for the bulk properties. The simplified model explains the apparently anomalous behavior of the thermodynamic functions for adsorption at high pressure up to 1000 bar.
The adsorption characteristics of pure water vapor onto two different types of silica gel at temperatures from (298 to 338) K and at different equilibrium pressures between (500 and 7000) Pa were experimentally studied by a volumetric technique. The thermophysical properties such as the skeletal density, Brunauer−Emmett−Teller surface area, pore size, pore volume, and total porosity of silica gel were determined. The Tóth isotherm model is found to fit all of the experimental data within the experimental errors. The experimental isotherms and the computed enthalpies of adsorption are compared with those of various researchers and found to be consistent with a chiller manufacturer's data.
A systematic study of the thermal conductivity of beds of moist silica gel is presented. The influence of porosity, water content, total gas pressure and temperature is determined through measurements under transient conditions with the transient hot-strip (THS) method and under static conditions in a bench-scale reactor. The predictions of the effective thermal conductivity of the beds from four different simple models (Russell, geometric mean value, unit-cell model and stochastic model) agree reasonably well with the experimental results. The unit-cell model is extended in order to account for the water sorbed in the micropores and describes satisfactorily the dependency of the effective thermal conductivity on the water content.
Analytical expressions are developed, based on a lattice statistics model incorporating the Bragg-Williams approximation and a random heterogeneous surface described by a uniform distribution of energies, for predicting the single-component isosteric heat of adsorption and differential adsorbed phase heat capacity as a function of temperature, surface coverage, lateral interactions, and adsorbent heterogeneity. A parametric study demonstrates that these four factors all affect the isosteric heat of adsorption but with different magnitudes at different conditions. The temperature dependence of the isosteric heat of adsorption is always related to, and accompanied by, the adsorbent surface heterogeneity. The differential adsorbed phase heat capacity has a very weak temperature dependence and is not directly affected by lateral interactions. The molar adsorbed phase heat capacity is in most cases higher than the gas phase heat capacity. The deviation between the molar adsorbed and gas phase heat capacities depend mostly on surface coverage and surface heterogeneity and weakly on the lateral interactions and temperature. The derived expressions are used also to predict the isosteric heat of adsorption and adsorbed phase heat capacity from regressed parameters obtained from experimental adsorption isotherm data in the literature. Comparisons show that the molar adsorbed phase heat capacity can sometimes exceed it by 20% or more, depending on the regressed value of the heterogeneity parameter. These results have significant implications for adsorption-process modeling.
Thermodynamic equations are developed for adsorption of multicomponent gas mixtures in microporous adsorbents based on the principles of solution thermodynamics. The conventional spreading pressure and surface area variables, which describe 2-D films, must be abandoned for adsorption in micropores, in which spreading pressure cannot be measured experimentally or calculated from intermolecular forces. Adsorption is divided into two steps: (1) isothermal compression of the gas, (2) isothermal immersion of clean adsorbent in the compressed gas. Thermodynamic functions (Gibbs free energy, enthalpy, and entropy) from solution thermodynamics provide a complete thermodynamic description of the system. Applications are described for characterization of adsorbents, gas storage at high pressure, mixture adsorption, enthalpy balances, molecular simulation, adsorption calorimetry, and shape selectivity in catalysis.
This letter presents a thermodynamic formulation to calculate the minimum driving heat source temperature of an advanced solid sorption cooling device, and it is validated with experimental data. This formalism has been developed from the rigor of the Boltzmann distribution function and the condensation approximation of adsorptive molecules. An interesting and useful finding has been established from this formalism that it is possible to construct a solid sorption refrigeration device that operates in a cycle transferring heat from a low temperature source to a heat sink with a driving heat source at a temperature close to but above ambient.
A thermodynamic framework for calculating the specific heat capacity (C<sub>p</sub>) of a single component adsorbent + adsorbate system has been derived and developed using the classical thermodynamics, and these are essential for the design of adsorption processes. The derived formulation of the C<sub>p</sub> is compared with the experimentally measured C<sub>p</sub> of adsorbent + adsorbate systems. The purpose of this letter is to fill up the information gap with respect to the state of adsorbed phase to dispel the confusion as to what is the actual state of the adsorbed phase.
A novel silica gel–water adsorption chiller is designed and its performance is predicted in this work. This adsorption chiller includes three vacuum chambers: two adsorption/desorption (or evaporation/condensation) vacuum chambers and one heat pipe working vacuum chamber as the evaporator. One adsorber, one condenser and one evaporator are housed in the same chamber to constitute an adsorption/desorption unit. The evaporators of two adsorption/desorption units are combined together by a heat-pipe heat exchanger to make continuous refrigerating capacity. In this chiller, a vacuum valve is installed between the two adsorption/desorption vacuum chambers to increase its performance especially when the chiller is driven by a low temperature heat source. The operating reliability of the chiller rises greatly because of using fewer valves. Furthermore, the performance of the chiller is predicted. The simulated results show that the refrigerating capacity is more than 10 kW under a typical working condition with hot water temperature of 85 °C, the cooling water temperature of 31 °C and the chilled water inlet temperature of 15 °C. The COP exceeds 0.5 even under a heat source temperature of 65 °C.
Reference Fluid Thermodynamic and Transport Properties, NIST Standard Reference Database, Physical and Chemical Properties Division Version 7. Received for review
- M L Huber
Huber, M. L. Reference Fluid Thermodynamic and Transport Properties, NIST Standard Reference Database, Physical and Chemical Properties Division, 2002; Vol. 23, Version 7. Received for review June 25, 2008. Accepted October 18, 2008. JE800458K 452 Journal of Chemical & Engineering Data, Vol. 54, No. 2, 2009
A New Generation Cooling Device Employing CaCl 2 -in-silica gel-Water System Thermal Conductivity of a Microporous Particulate Medium: Moist Silica gel
- B B Saha
- A Chakraborty
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- Y I Aristov
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- B Carlsson
(21) Saha, B. B.; Chakraborty, A.; Koyama, S.; Aristov, Y. I. A New Generation Cooling Device Employing CaCl 2 -in-silica gel-Water System. Int. J. Heat Mass Transfer 2008, doi:10.1016/j.ijheat-masstransfer.2008.06.018. (22) Bjurströ, H.; Karawacki, E.; Carlsson, B. Thermal Conductivity of a Microporous Particulate Medium: Moist Silica gel. Int. J. Heat Mass Tran. 1984, 27, 2025–2036.
Silica gel and bonded phases
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Scott, R. P. W. Silica gel and bonded phases;
Measurement of Thermophysical Properties of Aqueous LiBr-solutions At High Ttemperature and Concentrations
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- I Greiter
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Feuerecker, G.; Scharfe, J.; Greiter, I.; Frank, C.; Alefed, G. Measurement of Thermophysical Properties of Aqueous LiBr-solutions At High
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Reference Fluid Thermodynamic and Transport Properties, NIST Standard Reference Database, Physical and Chemical Properties Division
- E W Lemmon
- M O Mclinden
- M L Huber
Lemmon, E. W.; Mclinden, M. O.; Huber, M. L. Reference Fluid
Thermodynamic and Transport Properties, NIST Standard Reference
Database, Physical and Chemical Properties Division, 2002; Vol. 23,
Version 7.
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A New Generation Cooling Device Employing CaCl 2 -in-silica gel-Water System
- B B Saha
- A Chakraborty
- S Koyama
- Y I Aristov
Saha, B. B.; Chakraborty, A.; Koyama, S.; Aristov, Y. I. A New
Generation Cooling Device Employing CaCl 2 -in-silica gel-Water
System. Int. J. Heat Mass Transfer 2008, doi:10.1016/j.ijheatmasstransfer.2008.06.018.
- E W Lemmon
- M O Mclinden
- M L Huber
Lemmon, E. W.; Mclinden, M. O.; Huber, M. L. Reference Fluid
Thermodynamic and Transport Properties, NIST Standard Reference
Database, Physical and Chemical Properties Division, 2002; Vol. 23,
Version 7.