Adsorption Working Pairs Research Articles

Investigating maximum temperature lift potential of the adsorption heat transformer cycle using IUPAC classified isotherms

Adsorption heat transformer (AHT) cycle is capable of upgrading the low-grade waste heat to a higher temperature. The maximum temperature lift of the AHT cycle can represent its theoretical performance limit. However, such a metric is currently absent from the literature due to the scarcity of fundamental studies on the heat upgrading sorption cycles. Therefore, in the present study, three models are proposed to derive the ‘maximum temperature lift’ of a typical AHT cycle: (i) heat engine heat pump representation, (ii) the 2nd law of thermodynamic formulation, and (iii) complete preheating. The first two models are developed based on the reversible cycle approach, whereas the 3rd model incorporates adsorbed phase properties. Thus, the first two models might be considered as the formulations for the thermodynamic temperature limit (lift) of an AHT cycle while the 3rd model is specific to the nature of a particular adsorbent + adsorbate pair which might be close to practical applications. The reversible models predict a maximum temperature lift of 22∘C to 58∘C for heat source temperatures between 50∘C to 80∘C. The 3rd model exhibits lower values of maximum temperature lift compared to the reversible models, owing to the inclusion of material properties in its formulation. The performance of the models is demonstrated by determining the maximum temperature lift of four water-based adsorption working pairs, each featuring distinct IUPAC (International Union of Pure and Applied Chemistry) isotherm types. This study will help propel the working pair selection and the thermodynamic modeling of sorption cycles to achieve its near maximum capability.

Emerging sorption pairs for heat pump applications: an overview

The research efforts to find an alternative system for the cooling/heating application have been intensified worldwide since the imposition of international restrictions on production and use of refrigerants accountable for ODP and GWP. Nowadays, the demand for the cooling/heating system is increased also due to safeguarding the adverse environmental effect which results in additional consumption of electrical energy and ecological problem. The use of adsorption system is considering as a promising alternative for the last few decades. The low heat and mass transfer coefficient of the adsorbent material is the main bottleneck of the adsorption cooling/heating system and resulting in large size and low performance. To make the system commercially competitive with the conventional system, high-performance refrigerant/adsorbent pairs are required. In this review, the favorable achievement in adsorbent development in terms of porous properties and their interaction with natural refrigerants is focused. Current application of different working pairs and their future prospect with special reference to their utilization are studied. Future research direction of adsorption working pairs is also analyzed.

Water loading lift and heat storage density prediction of adsorption heat storage systems using Dubinin-Polanyi theory—Comparison with experimental results

Simulating adsorption-based heat storage devices requires knowledge of both the adsorption equilibria and the adsorption enthalpies of the adsorbent materials involved. The Dubinin-Polanyi theory of micropore filling can be used as a tool to reduce the experimental work for the thermodynamical characterization of various adsorption working pairs. In particular it can be used for the deduction of adsorption enthalpies from adsorption equilibrium data. In this work we assess if this theory can be employed to predict the outcome of experiments performed on a lab-scale heat storage device. For that purpose, we present a numerical model of the sorption chamber, which describes the sorption behavior by means of the Dubinin-Polanyi theory. The simulated heat storage densities and water loading lifts are compared to experimentally determined data of two granulated zeolite samples, namely a zeolite Na-X and a zeolite Ca-X, under various humidity conditions.

A Comparison of Heat Storage Densities of Zeolite Granulates Predicted by the Dubinin-polanyi Theory to Experimental Measurements

Thermochemical heat storage devices based on water adsorption on microporous materials are a viable option for heat storage applications. The Dubinin-Polanyi theory of micropore filling has been widely applied for the thermodynamical characterization of various adsorption working pairs. It has been used for the deduction of adsorption enthalpies from adsorption equilibrium data. How well the theory predicts the dependence of storage densities on the storage cycle characteristics remains to be clarified as it is vital for technology assessment and design. This study compares the heat storage densities predicted by the Dubinin-Polanyi theory to experimentally determined data of two granulated zeolite samples, namely a Na-X and a Ca-X, under various humidity conditions.

Experimental studies on equilibrium adsorption isosteres and determination of the thermodynamic quantities of polar media on alumina Al2O3

Abstract The present work is a revieif of theoretical and experimental study on the adsorption performance of the adsorbent Alumina (Al2O3) used in the adsorption system. An experimental investigation on the equilibrium adsorption isosteres at low pressure (< 1 atm) of working pairs Al2O3/H2O and Al2O3/C2H6O2 is carried out. The isovolume measurement method is adopted in the test setup to directly measure the saturated vapor pressures of working pairs at vapor-liquid equilibrium (dG=0 and dμi=0). Quantity adsorbed is determined from pressure, volume and temperature using gas law. The isosteric heat of adsorption is calculated from the slope of the plot of lnP versus 1/T different amounts of adsorbate onto adsorbent as follows: 0,01 vol% Al2O3/H2O; 0,03 vol% Al2O3/H2O; 0,1 vol% Al2O3/H2O; 0,01 vol% Al2O3/C2H6O2; 0,03 vol% Al2O3/C2H6O2; 0,1 vol% Al2O3/C2H6O2. This study shows that adsorption working pair Al2O3 C2H6O2 has better adsorption performances than those of the A2O3/H2O. Surface acidity! is a most important property! far both adsorption and catalysis and therefore is examined structure of active sites of alumina surface. Thermodynamic parameters such as isosteric heat of adsorption, isosteric enthalpy and entropy of adsorption are critical design variables in estimating the performance and predicting the mechanism of an adsorption process and are also one of the basic requirements for the characterization and optimization of an adsorption process

Integrated adsorption-ORC system: Comparative study of four scenarios to generate cooling and power simultaneously

Adsorption cooling and Organic Rankine Cycle (ORC) systems are promising technologies that can be used to exploit the abundant amount of low grade heat sources such as solar energy, geothermal energy and waste heat from industrial processes. In this study, a two bed adsorption cooling cycle has been integrated with an ORC to simultaneously generate cooling and power utilising AQSOA-ZO2 (SAPO-34)/water and silica-gel/water as adsorption working pairs and R245fa, R365mfc and R141b as ORC working fluids. Four different scenarios of integrated adsorption-ORC system have been investigated, where in the first three scenarios, adsorption system is set up as a topping system, while ORC is set up as a bottoming system. The first one utilized the waste heat of adsorption to power the ORC system with no additional heat and named as Adsorption Heat Recovery Scenario (AHRS). In the second scenario the adsorption return heating fluid is used to power the ORC system (Return Adsorption Heating Fluid Scenario RAHFS). In the third scenario (Heat Exchanger Scenario HES), the cooling and heating sources leaving the adsorption system enter a heat exchanger, where additional heat can be added to the cooling fluid in order to power the ORC system. In the fourth scenario (Return ORC Heating Fluid Scenario RORCHFS), the ORC is considered to be as a topping system, while the adsorption system considered as bottoming system and the return ORC heating fluid can be used to power the adsorption cycle. Results show that when using AHRS, the integrated adsorption-ORC system can achieved system efficiency of 70% using silica-gel/water and R141b and 60% using SAPO-34/water and R141b. In addition, the maximum Specific Power (SP) and Specific Cooling Power (SCP) can be achieved utilising SAPO-34 and R141b with values of 208W/kgads and 616W/kgads respectively. This work highlights the potential of using integrated adsorption cooling system and ORC to generate cooling and power simultaneously.

Adsorbent working pairs for solar thermal energy storage in buildings

In this study, the thermodynamic analysis of several adsorption working pairs for adsorption heat storage applications at domestic level is presented. The selected working pairs employ different working fluids (i.e. water, ethanol, ammonia, methanol) and different adsorbent materials such as classical zeolites, silica gels, alumino-phosphates, composite sorbents and activated carbons. The simulations have been performed taking into account desorption temperatures in the range between 80 °C and 120 °C, compatible with non-concentrating solar thermal collectors, under seasonal heat storage working conditions. The composite sorbent MWCNT-LiCl with both water and methanol as working fluid showed the highest heat storage density under practical working boundary conditions. Among the standard adsorbents, the zeotype AQSOA Z02 showed promising achievable heat storage densities. Classical working pairs, such as zeolite 13X/water, commonly employed for heat storage applications, are not suitable for this working range. Finally, also the influence of the metal to sorbent mass ratio, due to the heat exchanger, was investigated, demonstrating that it can reduce the achievable amount of heat released to the user up to 30%.

Effect of desorption parameters on performance of solar water-bath solid adsorption ice-making system

A novel solar water-bath solid adsorption ice-making system with activated carbon-methanol as adsorption working pairs was designed and constructed. The experimental results demonstrated that the desorption temperature and the desorption time had important influences on performance of the ice-making system. The daily ice-making capacity of 5.1 kg and refrigeration cycle coefficient of performance (COP) of 0.0322 could be obtained when the desorption temperature was maintained at 94 °C. However, there were no ice-making phenomenon when the desorption temperature was respectively maintained at 85 °C and 75 °C. With the increasing of desorption time from 7 h to 12 h when the desorption temperature was maintained at 94 °C, the COP of the system dropped gradually from 0.0507 to 0.0370, and the heat utilization efficiency decreased from 0.5969 to 0.4608 due to the gradual increase of energy imported into the system. The daily ice-making capacity increased rapidly from 5.5 kg to 7.6 kg when the desorption time increased from 7 h to 10 h, however, the daily ice-making capacity increased slightly from 7.6 kg to 7.7 kg when the desorption time was increased from 10 h to 12 h. There was an optimal desorption time of 10 h for the system.

Effective thermal conductivity and permeability of compact compound ammoniated salts in the adsorption/desorption process

For halide salt-ammonia working pairs, thermal conductivity and permeability always change with the adsorption/desorption concentration because of swelling and agglomeration phenomena during the processes of complexation and decomposition. Correspondingly, heat and mass transfer performance, which both affect the adsorption refrigeration performance, will be influenced. To provide an overview of the process mentioned above, solidified composite adsorbents that utilize expanded natural graphite (ENG) as the matrix were developed for eight different salts. Thermal conductivity and permeability were investigated for three different ratios between ENG and salt in the ammoniating process. The resulting data were compared with the data for the adsorbents that did not adsorb ammonia. The results indicate that the thermal conductivity and permeability of ammoniated salts have a strong dependence on the salt ratio and the consolidated density of the compound adsorbent. In regard to the adsorbent that was not adsorbed, the optimal thermal conductivity was 1.73 W/(m K) for the adsorbent of CaCl2-ENG with a density of 550 kg/m3 when the salt ratio was 75%. The optimal permeability was 9.02 × 10−11 m2 for the adsorbent of BaCl2-ENG with a density of 450 kg/m3 when the salt ratio was 83% in converging mode. Furthermore, the thermal conductivity and permeability of the compact compound ammoniated salts varied significantly with different concentrations of ammonia. The largest increase in thermal conductivity was as high as 1.25 W/(m K)during the adsorption process, whereas the largest decrease in permeability was as high as 5.08 × 10−11 m2 for different adsorption states. For the different adsorption working pairs, the thermal conductivity and permeability ranged from 0.62 to 2.98 W/(m K) and 1.47 × 10−14–8.13 × 10−11 m2, respectively.

A Novel Exhaust-Driven Adsorption Icemaker on a Fishing Boat

Adsorption refrigeration is an effective way to use low-grade energy sources such as industrial waste heat without damaging the environment. A novel exhaust-driven adsorption icemaker on a fishing boat is introduced in this paper. Based on the previous study, combining with the single adsorption cooling tube technique, this paper presents an adsorption cooling unit with unique structure driven by exhaust waste heat (hereinafter referred to as "waste heat cooling tube" WHCT). Different with the previous tubular structured adsorption bed, WHCT is made of seamless stainless steel pipe, the adsorbent bed, evaporator / condenser are all placed in one tube. Adsorption working pair of calcium chloride-ammonia has been proposed and developed for adsorption cooling. The working principle and structure are introduced in this paper.

Study on the adsorption isosteres of the composite adsorbent CaCl 2 and expanded graphite

A test setup was built to study the adsorption performance of the composite adsorbent used in the adsorption system. The isovolume measurement method is adopted in the test setup to measure the adsorption isosteres of the composite adsorbent and ammonia working pair. The adsorption isosteres are the curves of the adsorption pressures variation with adsorption temperatures at constant adsorption quantity, which are convenient for the calculation of the adsorption heat and selection of the adsorption working pairs. The adsorption heats were calculated according to the adsorption isosteres, three clear crest values indicate that there were three types of reaction during the reaction processes of ammoniate calcium chloride and ammonia. The kinetic model of adsorption isosteres is obtained by the Temkin model, it is useful to estimate the adsorption performance of the working pairs and useful to guide the design of adsorption system.

A comparison of the performances of adsorption and resorption refrigeration systems powered by the low grade heat

In order to study the refrigeration performances of the resorption refrigeration technology, the resorption working pair of BaCl 2–MnCl 2–NH 3, which has the similar working requirements for the heat source and cooling source, and also could satisfy the similar refrigeration requirements with the adsorption working pair of CaCl 2–NH 3, is studied by simulation and experiments. In the simulation the mass transfer resistance is not considered for the systems, and the refrigeration performances related with heat transfer performances are studied, results show that the resorption refrigeration system has a higher refrigeration power and COP (coefficient of the refrigeration performance) because the refrigeration effect is generated by the reaction heat compared to the latent heat of evaporation. After the simulation the experimental test unit is constructed, and the experimental data are analyzed. Results show that the resorption rate is influenced by the critical mass transfer performance very much, and the refrigeration performance is lower than that of adsorption system. The resorption system also has the problem of the larger refrigeration power loss for the reason of the sensible heat requirement of low temperature adsorber. How to improve the mass transfer performance of resorption system and decrease the influence on the refrigeration power by the sensible heat requirement of low temperature adsorber will be the key research directions for the application of resorption refrigeration systems.

Study on the adsorption performance of composite adsorbent of CaCl 2 and expanded graphite with ammonia as adsorbate

A novel constant volume test unit was built to study the adsorption performance of a new type composite adsorbent. This test unit can measure the adsorption isosteres of the working pairs. The adsorption isosteres are the curves of the adsorption pressure variation with the adsorption temperatures at constant adsorption quantities. Compared to the former test results of isothermals and isobars, the isosteres are better for the calculation of the adsorption heat, desorption heat and the selection the adsorption working pairs. Three experimental results were obtained: the first result was that the expanded graphite powders were superior to the expandable graphite powders to facilitate the transportation of working fluid in the composite adsorbent. The second one was that the composite adsorbent treated by solution is more homogeneous than the simple mixed composite adsorbent and the treated composite adsorbent has a better mass transfer performance. The last one was that the adsorption isosteres was the same one not only in the heating process but also in the cooling process and this performance was not relevant to the homogeneity of the composite adsorbent.

Mathematical simulation and experimental study of a modified zeolite 13X–water adsorption refrigeration module

In order to investigate the performance of the adsorption cooling module (16 mm in diameter and 1020 mm in length) with zeolite 13X and water as the adsorption working pair, a dynamic heat and mass transfer model was established based on the linear driving force (LDF) model. For the working process of the main parts of the module, including adsorber and condenser/evaporator, the coupled dynamic equations were set up for each stage of heating/desorbing and cooling/adsorbing, respectively. The model was then solved using the finite difference method, and the performance of the adsorber and condenser/evaporator of the module were analyzed. The calculated results were validated with experimental data and good agreement was observed. By means of the model, simulation and optimization of the adsorption cooling module can be further studied.

The performance of two adsorption ice making test units using activated carbon and a carbon composite as adsorbents

The available adsorption working pairs applied to adsorption refrigeration system, which utilize activated carbon as adsorbent, are mainly activated carbon–methanol, activated carbon–ammonia, and composite adsorbent–ammonia. The adsorption properties and refrigeration application of these three types of adsorption working pairs are investigated. For the physical adsorbents, consolidated activated carbon showed best heat transfer performance, and activated carbon–methanol showed the best adsorption property because of the large refrigerant amount that can be adsorbed. For the composite adsorbents, the consolidated composite adsorbent with mass ratio of 4:1 between CaCl 2 and activated carbon, showed the highest cooling density when compared to the granular composite adsorbent and to the merely chemical adsorbent. The physical adsorption icemaker that employs consolidated activated carbon–methanol as working pair had the optimum coefficient of refrigeration performance (COP), volume cooling power density (SCP v ) and specific cooling power per kilogram adsorbent (SCP) of 0.125, 9.25 kW/m 3 and 32.6 W/kg, respectively. The composite adsorption system that employs the consolidated composite adsorbent had a maximum COP, SCP v and SCP of 0.35, 52.68 kW/m 3 and 493.2 W/kg, respectively, for ice making mode. These results are improved by 1.8, 4.7 and 14 times, respectively, when compared to the results of the physical adsorption icemaker.

Research on the chemical adsorption precursor state of CaCl2-NH3 for adsorption refrigeration

As a type of chemical adsorption working pair, the physical adsorption occurs first for CaCl 2 -NH 3 because the effective reaction distance for van der Waals force is longer than that for chemical reaction force, and this physical adsorption state is named the precursor state of chemical adsorption. In order to get the different precursor states of CaCl 2 -NH 3 , the different distances between NH 3 gas and Ca 2+ are realized by the control of different phenomena of swelling and agglomeration in the process of adsorption. When the serious swelling exists while the agglomeration does not exist in the process of adsorption, experimental results show that the activated energy consumed by adsorption reaction increases for the reason of longer distance between Ca 2+ and NH 3 , and at the same time the performance attenuation occurs in the repeated adsorption cycles. When the agglomeration occurs in the process of adsorption, the activated energy for the transition from precursor state to chemical adsorption decreases because the distance between NH 3 gas and Ca 2+ is shortened by the limited expansion space of adsorbent, and at the same time the performance attenuation does not occur. The adsorption refrigeration isobars are researched by the precursor state of chemical adsorption; results also show that the precursor state is a key factor for isobaric adsorption performance while the distribution of Ca 2+ does not influence the permeation of NH 3 gas in adsorbent.

Environmentally benign working pairs for adsorption refrigeration

This paper begins from adsorption working pairs: water and ethanol were selected as refrigerants; 13x molecular sieve, silica gel, activated carbon, adsorbent NA and NB, proposed by authors, were selected as adsorbents, and the performance of adsorption working pairs in adsorption refrigeration cycle was studied. The adsorption isotherms of adsorbents (NA and NB) were obtained by high-vacuum gravimetric method. Desorption properties of adsorbents were analyzed and compared by thermal analysis method. The performance of adsorption refrigeration was studied on simulation device of adsorption refrigeration cycle. After presentation of adsorption isotherms, the thermodynamic performance for their use in adsorption refrigeration system was calculated. The results show: (1) the maximum adsorption capacity of water on adsorbent NA reaches 0.7 kg/kg, and the maximum adsorption capacity of ethanol on adsorbent NB is 0.68 kg/kg, which is three times that of ethanol on activated carbon, (2) the refrigeration capacity of NA–water working pair is 922 kJ/kg, the refrigeration capacity of NB–ethanol is 2.4 times that of activated carbon–methanol, (3) as environmental friendly and no public hazard adsorption working pair, NA–H 2O and NB–ethanol can substitute activated carbon–methanol in adsorption refrigeration system using low-grade heat source.

Adsorption performances and refrigeration application of adsorption working pair of CaCl2-NH3

The adsorption performance of CaCl2−NH3 is studied under the condition of different expansion spaces for adsorbent, and the relationships between adsorption performance of CaCl2−NH3 and the phenomena of swelling and agglomeration during adsorption are researched. It is found that the performance stability is related to the ratio of expansion space to the volume of adsorbent r as, and the performance attenuation is serious in the case of large r as. Severe adsorption hysteresis exists in the process of adsorption and desorption at the same evaporating and condensing temperatures, which is related to the stability constant of chemical reaction. This phenomenon cannot be explained by the theory of physical adsorption. Moderate agglomeration will be beneficial to the formation of ammoniate complex; the magnitude of expansion space will affect adsorption performance. Analysis shows that the activated energy needed in the process of adsorption for the sample with r as. of 2∶1 is less than that for the sample with r as of 3∶1. The refrigeration performance of CaCl2−NH3 is predicted from experiments. The cooling capacity of one adsorption cycle is about 945.4 kJ/kg for the adsorbent with an r as of 2∶1 at the evaporating temperature of 0°C.