Adsorption Refrigeration Research Articles

Solar adsorption refrigeration system: Comparison between equilibrium, universal and transient model

Three models of different level of complexity are detailed in order to predict the cold production of a solar cooling device. The transient model consists on a heat and mass transfer model of the absorber, coupled with a solar collector model which conceives the ambient temperature as variable along the day and comprehends the evolution of the solar radiation throughout the day according the locations of the prototype to be analyzed in addition to the ideal models of the condenser and evaporator. The Equilibrium and Universal Model are both lumped models in which the spacial distributions of the variables and the heat and mass transfer resistance in the system are disregarded. The advantages and disadvantages of each model are discussed.The results of the models are compared with experimental data obtained from four methanol/activated-carbon adsorption refrigerator prototypes. The cold generated is underestimated 12%–20% by the transient model, while it is overestimated 22%–46% by the equilibrium model and 53%–66% by the universal model. Even when the transient model allows some improvements, is a useful tool to analyze the impact that different variables of a solar adsorption refrigeration system have in the generation of cold. The simpler models can be used for preliminary design and feasibility studies of solar adsorption refrigeration devices (SARS) whose results can be extrapolated on the premise of its overestimation of cold generation approximately given by this work.

Performance Assessment of Silica Gel-Water Solar Adsorption Refrigeration System in Egypt

Performance Assessment of Silica Gel-Water Solar Adsorption Refrigeration System in Egypt

Effect of refrigerant absorbent combinations in the corrosion resistance of copper as structural material in absorption refrigeration systems (ARS)

ABSTRACT The present research was focused on analyzing the corrosion resistance of copper in the presence of refrigerant-absorbent combinations such as lithium bromide (LiBr), lithium nitrate (LiNO3) and calcium chloride (CaCl2), used in Adsorption Refrigeration Systems (ARS). Electrochemical techniques such as open circuit potential, electrochemical impedance spectroscopy, electrochemical noise analyses and potentiodynamic polarisation curves were applied to study the test solution combination effect on the corrosion rate of copper as a structural material in ARS. OCP analyses reveal that the E corr shifted based on the temperature and test solution. Meanwhile, when the copper was immersed in LiBr/H2O + CaCl2 at 80°C, the corrosion current density (I corr) was lower (0.003 mA/cm2). Also, The R p estimated from EIS shows an increase at 80°C. Micrographs of the copper surface immersed in LiBr/H2O and LiBr + CaCl2 observed cracks and pits. But also, when the corrosion product layer was removed, a less heterogeneous surface was revealed.

Dynamic variation of bed parameters and time optimisation of solar adsorption refrigeration system based on CFD simulation

One major reason for the limited application of adsorption refrigeration systems is their lower refrigeration efficiency and performance compared to other alternatives. Additionally, there is limited research focused on optimizing the system performance over time. This paper presents a numerically validated thermodynamic model to analyse the effect of adsorption time on the performance efficiency enhancement of a solar adsorption refrigeration system. The adsorption rate model proposed by Sokoda and Suzuki has been used to evaluate the adsorption and desorption characteristics of water vapor on silica gel and the solar collector system has been fitted to a heat flow density equation based on measured concentrated solar heating. The water vapor adsorption capacity on silica gel as a function of temperature and pressure in the adsorption bed has been numerically evaluated during the four stages of the cooling cycle, namely adsorption, preheating, desorption, and cooling. The coefficient of performance and specific cooling power have been utilized as the major performance indicators, in the context of the influence of adsorption time on the refrigeration performance of the system. The simulation results revealed that, although increasing the adsorption time increased the system's cooling capacity, it also prolonged the cycle time and adversely affected the dynamics of preheating and desorption processes (due to increased solar input). As a result of the numerical simulation, an optimum value of adsorption time has been predicted to be 71 min corresponding to a coefficient of performance equal to 0.476 and a specific cooling power equal to 28.6 W/kg.

The Impact of Solar Radiation at Different Colombian Thermal Floors on an Adsorption Refrigeration Cycle

The process of energy transition in Colombia has sparked an exploration into appropriate geographical areas for the utilization of solar energy. The country’s rugged terrain and significant climate variability pose challenges for implementing standardized technologies uniformly across all regions. Consequently, this study aims to develop and apply a mathematical model to characterize the performance of a solar adsorption cooling system under the environmental conditions found in six distinct Colombian cities, taking into account different thermal profiles and extreme weather periods such as the El Niño and La Niña phenomena. The selected mathematical model was simulated in these cities, considering ambient temperature and solar radiation variables over a twelve-month period during these extreme weather phenomena and an additional twelve-month period representative of a typical year with minimal influence from these phenomena. The results indicated that despite a lower coefficient of performance (COP) compared to the other cities, Riohacha demonstrated a greater number of ice production days owing to its high levels of solar radiation.

Dynamic simulation and exergy-economic assessment of solar thermal refrigeration systems in different climates

In this paper, the performance of solar-thermal cooling systems for air conditioning application is investigated in different climates of Iran. Diverse climate types are considered which makes the results applicable to other countries. Available commercial refrigeration cycles that are capable of integration with solar-thermal collector systems including the closed liquid absorption cycle, closed solid adsorption cycle, and desiccant cycle are studied. First, a solar and climatic map is proposed and the representative cities have been selected for each climate. Then, the climate parameters related to each region are extracted to create an hourly database. Also, the cooling load of a reference building is modeled based on the climate database, each refrigeration cycle is simulated using thermodynamic equations, and the dynamic model is generalized daily for the hot season in each city. In the last step, each cooling system is examined using an exergy-economic analysis, and technical and economic indicators are compared. The results show that the most suitable solar-thermal refrigeration cycle that can be installed in the central plateau and semi-arid areas of Iran is the closed-cycle liquid absorption system. The annual average exergy-economic factor and the annual solar fraction in this cycle are 0.7578 and 0.57, respectively. In the southern coastal areas, due to the high humidity and air temperature in summer, the solid desiccant refrigeration system with an exergy-economic factor of 0.6978 and a solar fraction of 0.2416 is preferred. The suitable solar-thermal refrigeration cycle in the cold and mountainous regions of Iran is a solid adsorption system with a silica gel absorber. The annual solar fraction and average annual exergy-economic factor in this cycle are 0.5158 and 0.7394. Also, in northern moderate regions, the solid adsorption refrigeration system with an average annual exergy-economic factor of 0.409 and average exergy efficiency of 0.12 is comparatively beneficial.

Dynamic simulation and exergy analysis of adsorption chiller powered by low-grade waste heat from a fuel-cell system: Effect of multibed configuration and time constant

Energy usage for space cooling and air conditioning has been rapidly growing in recent years and is expected to increase further owing to global warming and climate change. Adsorption chillers can provide an eco-friendly solution to space cooling because they utilize low-grade thermal energy such as waste hot water produced by the primary power-generation unit. In this study, dynamic analysis of a fuel-cell-system-driven adsorption refrigeration system was performed to expedite the optimal multibed configuration and its operating conditions. The scope of the study was extended to investigate maximizing the waste heat utilization achieved via exergy analysis of multibed configurations. The adsorption-to-desorption time ratio was integrated into the physical configuration of the adsorption chiller, and a new variable was introduced as a “time constant” that controls the cycle time and, under ideal conditions, equates the heating requirements of different bed configurations. Dynamic simulations for different bed configurations were conducted to evaluate the performance, specific cooling capacity, and unutilized exergy in the outlet waste stream. Under the operating conditions of 25 °C and 80 °C cold water and hot water temperatures, respectively, the five-bed configuration with a time ratio of 0.25 proved to be optimal, resulting in increases of 45.8%, 10.2%, and 15.1% in the specific cooling capacity, performance, and exergy efficiency, respectively, compared with those of the conventional two-bed configuration. The four-bed configuration yields very similar results, but with a slightly lower specific cooling capacity.

Performance analysis of adsorption refrigeration using a composite adsorbent with improved heat and mass transfer

Adsorption refrigeration is a typical environmental protection and energy-saving waste heat utilization refrigeration technology. However, improving the heat and mass transfer performance of adsorption beds is crucial to the wide-spread applications of adsorption refrigeration systems. In this paper, three types of composite adsorbents are proposed: adsorbents with improved heat transfer, improved mass transfer, and simultaneously improved heat and mass transfer. Both characteristics of adsorption and heat transfer are tested and compared. Based on the experimental results, the use of these three types of composite adsorbents in the adsorption refrigeration system is further examined. The results indicate that the silica gel (SG)/MIL-100/CF (SGMC) composite outputs the highest cooling capacity and exhibits a coefficient of performance (COP) comparable to that of a composite adsorbent with improved mass transfer. The cooling capacity and COP of the proposed SGMC system compared with those of the traditional SG–water system increase by 22% and 12.8%, respectively, and the refrigeration cycle time is shortened by 16.7%. Based on the optimal SGMC system, the impact of operation parameters is further investigated, and optimum parameters are selected to enhance the overall system performance.

Performance of Solar Adsorption Cooling System Using Methanol and Activated Carbon as a Working Pair

The need for renewable energy sources is higher than ever due to rising global warming, climate change, and ozone depletion. For refrigeration and air conditioning applications, adsorption refrigeration systems are viable alternatives cooling techniques. This study is a topic and part of the M.Sc. thesis. A field solar-powered ice maker unit was created, studied, tested, and evaluated on the 13th and 30th of May, 2022. Activated carbon and methanol pair was used to set up a refrigeration system in Baghdad (Al Dora). Experimental tests were carried out outdoors to determine the coefficient of performance COP and specific cooling power SCP of the system. The results showed that the lowest temperature obtained at the evaporative surface was (4 oC) and (3 oC) for the 13th and 30th of May, respectively, at the opening time of the valve between the evaporator and the generator at 9 pm. In addition, the amounts of methanol condensate were (0.340 kg) and (0.344 kg) for the 13th and 30th of May, respectively, while the maximum cycle coefficient of performance (COP) and specific cooling power SCP are about 0.57 and 0.14 kW/kga.c , respectively

Study of Dynamic Sorption in Adsorption Refrigeration Cycle

This paper shows the characteristics of temperature and adsorbed (water vapor) mass rate distribution in the adsorber unit which is the key part to any adsorption refrigeration system. The temperature profiles of adsorption/desorption phases (Dynamic Sorption) are measured experimentally under the operating conditions of 90oC hot water temperature, 30oC cooling water temperature, 35oC adsorption temperature and cycle time of 40 min. Based on the temperature profiles, The mass transfer equations for the annulus adsorbent bed are solved to obtain the distribution of adsorption velocity and adsorbate concentration using non-equilibriummodel. The relation between the adsorption velocity with time is investigated during the process of adsorption. The practical cycles of adsorption and desorption were stated dependent on the variables obtained from the experiment and equations calculations.The results show that the adsorption velocity is diminished after a period of 20 min. The maximum value of the adsorbed water vapor concentration on silica gel is 0.12 kg water/kg adsorbent (adsorption phase) and the minimum value of the water content into silica gel is 0.04 kg water/kg adsorbent (desorption phase) producing a dynamic sorption of kg water/kg adsorbent.

Energy and exergy analyses of a hybrid adsorption refrigeration system for simultaneous production of cold water and dry air

Current adsorption refrigeration systems are limited by dehumidification methods and produce either cold water or cold dry air. The single cooling product greatly hinders their application into situations where multiple cooling outputs are needed. In order to address this issue, this paper introduces a hybrid adsorption refrigeration system using efficient desiccant coated heat exchangers to provide both cold water and dry air via the deep utilization of input heat sources. In this study, the performance of the hybrid system is experimentally investigated from a combined perspective of energy and exergy. Results show that the hybrid system can simultaneously output cold water and dry air with a heat source of 50–80 °C. A low-temperature cooling water is beneficial to system performance, while an optimum input hot water temperature exists. At a coolant-side temperature of 25 °C, the COP reaches its maximum of 0.238 under a heat source temperature of 60 °C, and the highest exergetic efficiency is quantified as 13.9% when powered by 50 °C hot water. Increasing inlet air temperature or relative humidity facilitates the COP improvement but has a negligible effect on the exergetic efficiency. In comparison with a traditional adsorption air conditioning system, the hybrid system has a wider range of input hot water temperatures and is more advantageous in terms of cooling exergy and exergetic efficiency. This hybrid system firstly enables adsorption refrigeration to export dual cooling products of cold water and dry air, which is expected to extend adsorption refrigeration into fully automatic industrial fields.

On the best coefficient of performance and specific heating or cooling power combination for adsorption refrigerators and heat pumps

The performance parameters of adsorption refrigerators or heat pumps are the coefficient of performance (COP) and the specific cooling power (SCP) or specific heating power (SHP), respectively. Higher COPs are associated with the longer cycle times required for more complete desorption and adsorption processes, resulting in a lower number of cycles per unit time and consequently in lower SCP or SHP, unless large masses of adsorbent material are used. The inverse situation occurs for shorter cycle times, associated with smaller COPs and higher SCP or SHP. This behavior leads to a relevant question: what is the combination of COP and SCP or SHP corresponding to the optimal performance of adsorption refrigerators or heat pumps? Although this question is recurrent in literature, its objective answer is still lacking. This work proposes an objective criterion to answer this question, setting the best balance between the COP and the SCP or SHP of adsorption refrigerators or heat pumps, as corresponding to the minimum unit cost of the obtained useful effect. The proposed criterion allows obtaining the cycle time that corresponds to the searched optimal performance. The dependence of the COP and the SCP or SHP on the cycle time can be obtained from numerical simulations for an adsorption system. Once these dependencies are known, it can be identified the cycle time leading to the minimum unit cost of the obtained useful effect, which corresponds the best balance between the COP and the SCP or SHP.

Investigation of stepwise porosity and perforated fins in finned tube adsorption bed for adsorption refrigeration

Adsorption refrigeration is a green refrigeration technology. The characteristics of its key component, the adsorption bed, directly affect the operational performance of the entire system. In this study, two novel types of structures, stepwise porosity and perforated fins, were applied to three types of conventional finned tube adsorption beds to improve heat and mass transfer. Using the finite element analysis method, the impacts of porosities and perforations were systematically evaluated to clarify the application range and development potential of this new technology. The results indicate that the overall performance of the system using a finned tube adsorption bed with an annular outer fin is better than that of a plate outer fin and annular inner fin. Stepwise porosity can help maintain the system coefficient of performance (COP) and reduce the degradation of the specific cooling power (SCP) when the finned tube adsorption bed is designed with a long fin or large fin spacing. The perforated fin structure improved the refrigeration performance of the finned tube adsorption bed. Stepwise perforation affects the values of the COP to some extent, but the variations in the value of the SCP are minor. Stepwise perforation combined with stepwise porosity might be a potential structure for further improving heat and mass transfer in the adsorption bed.

Simulation of the performance of continuous solar-powered adsorption refrigeration system for optimal use in Zaria, Nigeria

Cooling without electricity is the reason for solar adorption refrigeration systems. The epileptic power supply, especially in developing countries, makes solar refrigeration a very attractive option. This is coupled with the abundance of solar energy, making it a favourable alternative power source amongst other power mixes. This article introduces a solar adsorption refrigerator that continually generates cooling using solar energy as a standalone. Thus, this study aims to simulate and analyse the feasibility of refrigeration from a system that uses a blend of zeolite-based adsorbents and water (H2O) as adsorbate pairs via four solar concentrating collectors, two for adsorption and two for desorption using TRNSYS 16.0 simulation software. Unlike the conventional refrigeration system, the compressor was replaced with a solar concentrating collector while other components, such as the condenser, evaporator, and throttling valves, remained. The findings demonstrate that the technology delivered continuous cooling, and due to the comparatively intense beam radiation during the middle of the day, the cooling rate increased.

Performance Assessment of an Ice-Production Hybrid Solar CPV/T System Combining Both Adsorption and Vapor-Compression Refrigeration Systems

The technology of a hybrid solar concentration photovoltaic/thermal (CPV/T) system is an efficient way of converting solar energy to heat and electrical power, in which overall energy-extraction efficiency is at its highest. In this study, numerical dynamic simulation models were developed for a hybrid solar CPV/T system and an adsorption refrigeration system (ARS). Under the climatic conditions of Riyadh all year round, the electrical and thermal powers generated by the CPV/T system were used to estimate the ice production of both the vapor compression refrigeration system (VCS) and the ARS. The CPV/T system can provide a thermal energy of 37.6 kWh and electrical energy of 24.7 kWh a day on average over the year using a 12.5 m2 facing area of Fresnel lenses. The ARS employed an advanced approach which used Maxsorb III adsorbent packed in two aluminum foam beds. An optimum cycle time of the ARS was adapted for each month to match the variation in the thermal energy, while a variable-speed compressor was chosen for the VCS. Due to its higher coefficient of performance (COP), the proposed solar hybrid system can produce 494.4 kg of ice per day while sharing 84.5% of the VCS. The average solar COP over the year of the hybrid system can attain 0.875, which represents a promising value for a solar ice-production system.

Adsorption Refrigeration Optimization via Response Surface Methodology Using Waste Heat in a Ship

Adsorption Refrigeration Optimization via Response Surface Methodology Using Waste Heat in a Ship

Design and experimental study on a small-scale silica gel/water adsorption chiller with heat and mass recovery scheme for solar energy use

Silica gel/water adsorption refrigeration is regarded as a suitable solution for scalable solar cooling application in current stage but it needs necessary improvements in system design and performance. In this paper, authors present detailed thermal design of a small-scale silica gel-water adsorption chiller with heat and mass recovery scheme. Besides, the adsorption system is built for performance test under typical medium solar hot water temperature (70 °C). The results show the adsorption chiller can be stably and reliably operated while cooling power ranges from 2.2 to 3.6 kW. COP and SCP can reach 0.485 and 140.3 W·kg−1, respectively, at 70/30/25 °C hot/cooling/chilled water inlet temperatures. The increase of cooling water inlet temperature from 26 °C to 32 °C causes 11.2 % and 28.9 % declines of COP and SCP, respectively. However, the increase of chilled water inlet temperature from 12 °C to 25 °C contributes to 61.1 % and 114.1 % increments of COP and SCP, respectively. In addition, inlet temperatures of both cooling and chilled water have greater influence on SCP than COP. Through this study, better understanding of adsorption chiller thermal design and its performance under medium solar hot water temperature is obtained.

Modeling and optimizing a two-bed adsorption cooling system with a modified mass recovery process

A two-bed adsorption refrigeration cycle (ARC) with a new proposed modified mass recovery process is investigated (modeled, optimized and compared with ARC cycle with conventional mass recovery process) here. This proposed modified mass recovery process increases the system cooling capacity and cycle exergy efficiency. These achievements reached by opening the connecting valve between two beds during mass recovery process as usual, but continuing cooling of adsorption bed by water even during mass recovery process. Thus, the refrigerant vapor moved from desorber to adsorber bed in this situation by two effects, the higher pressure of refrigerant vapor in desorber bed and also due to higher effect of adsorption process for cooling of this bed by water. Furthermore, at the end of the proposed modified mass recovery process, the equilibrium pressure of beds was closer to the evaporator pressure than that for ARC with conventional mass recovery process. Thus, the new switched adsorption bed could connect to evaporator even during pre-cooling process. This makes connecting time period of evaporator and adsorber longer than that for ARC with the conventional mass recovery process. The above effects increased the amount of refrigerant vapor adsorbed in the adsorption bed which increased ARC cooling capacity as well. Finally to study the effects of various design variables, a two bed ARC with the proposed modified mass recovery cycle is modeled and optimized for a specific cooling capacity by considering coefficient of performance and exergy destruction as two objective functions. Results for a system with 14 kW (4 refrigeration tons) cooling capacity showed 0.555, 0.284 and 1719.6 kJ for optimum values of coefficient of performance (COP, with 0.9% increase), exergy efficiency (14% increase) and total exergy destruction (16.2% decrease), respectively in comparison with those for ARC with the conventional mass recovery process.

Thermodynamic study of integrated proton exchange membrane fuel cell with vapour adsorption refrigeration system

With the rising usage of fossil fuels, there is an urgent need to develop new technologies specifically based on renewable energy sources to power the vehicles running on fuel. A fuel cell is an electrochemical cell that is used to convert the chemical energy of a fuel directly to electric power. Fuels cells possess advantages such as smaller size, high efficiency, silent operation, etc. However, there can be significant variations in the size and power output of the fuel cells depending upon the application. The focus of this paper is to estimate the performance of an integrated system comprising of Polymer Exchange Membrane Fuel cell (PEMFC) and vapour adsorption refrigeration system to produce electric output and cooling effect simultaneously. The adsorption system in this study is based on activated carbon and methanol combination. The effect of operating parameters such as the operating temperature, current density and evaporator temperature on the energy and exergy efficiency of the system is presented. The study shows a remarkable improvement in the performance of the integrated system compared to PEMFC alone. The results show that the system energy and exergy efficiency decrease as the current density value increases. Maximum system energy and exergy efficiency of 63.01% and 29.88% are achieved. In addition, a maximum energy efficiency of 65.39% was reported at an evaporator temperature of 5 °C and a current density of 0.8 A/cm2.

Experimental analysis of condensation-pump dilution refrigerators

<sec>Subkelvin refrigeration is necessary for many frontier research fields such as condensed-matter physics, astronomical observation, and quantum computing. Dilution refrigeration utilizes the entropy increase of <sup>3</sup>He atoms when they flow from the concentrated phase to dilute phase to provide cooling, and has the advantages of continuous operation, large cooling power and no electromagnetic interference. It is the most widely used method among subkelvin refrigeration at present. For research scenarios requiring small cooling powers, the condensation-pump dilution refrigerator utilizes a condensation pump to achieve cold cycle of <sup>3</sup>He, with no need of complex ambient pump systems or gas circuits, and has become a new research topic because of its compact structure, convenient operation and low cost.</sec><sec>A condensation-pump dilution refrigerator is built and investigated in this work. The refrigerator consists of a mixing chamber, a continuous tube-in-tube heat exchanger, a still, and a condensation pump, and it is precooled by a GM-type pulse tube cryocooler below 4 K and an adsorption refrigerator below 400 mK. The <sup>3</sup>He evaporates from the still, condenses in the condensation pump and provides cooling in the mixing chamber after being precooled in the heat exchanger.</sec><sec>By means of the multi-temperature measuring system, the cold cycle of the dilution refrigerator can be summarized as three stages: precooling by the adsorption refrigerator, cycle start-up, and continuous dilution cooling. The operating characteristics of the system are analyzed. The experiments showed that the lowest no-load temperature reached 108 mK when the condenser temperature was 378 mK. Meanwhile, the temperature oscillation appeared, and the possible reasons are analyzed. In the future, the system performance will be improved by 1) adjusting the spiral mode and position of the continuous tube-in-tube heat exchanger and 2) increasing the heat transfer area between the cold plate and the fluid in the mixing chamber to reduce the fluid-solid temperature difference.</sec><sec>The refrigerator introduced in this work can easily expand many existing cryogenic platforms working at higher temperatures, and effectively support developments of high-end equipment.</sec>