System performance of a combined heat and mass recovery adsorption cooling cycle: A parametric study

Based on the previous work of the authors [K.C. Leong, Y. Liu, Numerical study of a combined heat and mass recovery adsorption cooling cycle, Int. J. Heat Mass Transfer 47 (2004) 4761–4770], a numerical study of the effects of system design and operation parameters on the performance of a combined heat and mass recovery adsorption cycle is presented in this paper. The effects of bed dimensions, bed thermal conductivity, heat exchange fluid velocity, driven temperature and the degree of the heat recovery on the system performance are investigated. It is found that an increase in the driven temperature results in the increase of both the coefficient of performance (COP) and specific cooling power (SCP) of the adsorption cycle. On the other hand, the system performance can be severely deteriorated for velocities of the heat exchange fluid smaller than a critical value. An increase in the bed thickness will result in an increase in COP and a decrease in the SCP. The results of our simulations will provide useful guidelines for the design of this type of advanced adsorption cooling cycle.     

Performance study of a high efficient multifunction heat pipe type adsorption ice making system with novel mass and heat recovery processes

The purpose of this paper is to present the performance analysis of a multifunction heat pipe type adsorption ice maker with activated carbon–CaCl₂ as compound adsorbent and ammonia as refrigerant. For this test unit, the heating, cooling and heat recovery processes between two adsorbent beds are performed by multifunction heat pipes. A novel mass and heat recovery adsorption refrigeration cycle is developed. When mass recovery process is implemented before heat recovery process, the performance of the cycle with novel mass and heat recovery processes is much better than that for the cycle with the conventional mass and heat recovery processes. The experimental results show that the former cycle can increase the coefficient of performance (COP) and specific cooling power (SCP) by more than 17% compared with the latter cycle. In comparison with the basic adsorption cycle, the mass and heat recovery cycle can enlarge the cycled refrigerant mass and reduce the power consumption of boiler; the COP and SCP were improved by more than 11% when the mass recovery time was 20 s, while at the optimal mass recovery time of 40 s, the COP improvements for conventional and novel mass and heat recovery cycles are 43.8% and 68.7%, respectively. It was concluded that the novel mass and heat recovery processes are more beneficial to improve the performance of adsorption refrigeration system in comparison with the conventional mass and heat recovery processes.     

Numerical modeling of a zeolite/water adsorption cooling system with non-constant condensing pressure

A new transient two-dimensional model with non-constant condensing pressure for a zeolite/water adsorption cooling cycle is proposed in this paper. This numerical model focuses on the heat and mass transfer behaviors in the adsorber and is solved by the control volume method. Due to the heat transfer limitation in the condenser, the simulated pressure during the isobaric generation phase of the cycle is not constant and will decrease with time. Compared with the model for constant condensing pressure, the cycle duration and cycled adsorbate for the base case are increased. Furthermore, the effect of mass flow rate of condenser cooling water on system performance is also investigated. It is found that both COP and SCP increase with an increase in the mass flow rate of cooling water in the condenser.     

Numerical analysis of an advanced three-bed mass recovery adsorption refrigeration cycle

Numerical analysis of an adsorption cycle employing advanced three-bed mass recovery cycle with and without heat recovery is introduced in this paper. The cycle consists of three silica gel adsorbent beds with different heat utilization functions. The beds can be divided into two cycles with different desorption mechanisms. The working principle of the cycle is introduced, and performances of three-bed, single stage, and mass recovery adsorption cycles are compared in terms of coefficient of performance (COP) and specific cooling power (SCP). The paper also presents the effect of adsorber mass distribution and desorption time on performance. The results show that by applying heat recovery to the cycle, better COP values will be produced compared to that without heat recovery. The results also show that there is an optimum point of adsorber mass distribution and desorption time that produces optimum performance. Furthermore, the paper also compares the performances of the proposed cycle, a single-stage cycle, and a mass recovery cycle.     

A four-bed mass recovery adsorption refrigeration cycle driven by low temperature waste/renewable heat source

The study deals with an advanced four-bed mass recovery adsorption refrigeration cycle driven by low temperature heat source. The proposed cycle consists of two basic adsorption refrigeration cycle. The heat source rejected by one cycle is used to power the second cycle. Due to the cascading use of heat and cooling source, all major components of the system maintain different pressure levels. The proposed cycle utilize those pressure levels to enhance the refrigeration mass circulation that leads the system to perform better performances. The performance of the proposed cycle evaluated by the mathematical model at equilibrium condition and compared with the performance of the basic two-bed adsorption refrigeration cycle. It is seen that the cooling effect as well as COP of the proposed cycle is superior to those of the basic cycle. The performances of the cycle are also compared with those of the two-stage cycle. Results also show that though the cooling effect of the proposed cycle is lower than that of two-stage cycle for heat source temperature less than 70 °C, the COP of the cycle, however, is superior to that of two-stage cycle for heat source temperature greater than 60 °C.     

Dynamic characteristics of a novel adsorption refrigerator with compound mass‐heat recovery

A three‐effect heat pipe (heat pipe heating, heat pipe cooling and heat pipe heat recovery) adsorption refrigeration system using compound adsorbent (calcium chloride and activated carbon) was designed. The dynamic characteristics of mass and heat pipe heat recovery were studied. The results show that mass recovery and heat pipe heat recovery can improve (specific cooling power) SCP and (coefficient of performance) COP greatly. The averaged SCP of the cycle with mass recovery and the cycle without mass recovery is 502.9 W/kg and 436.7 W/kg at about 30 °C of cooling water temperature and ?15 °C of evaporating temperature. The corresponding COP is 0.27 and 0.24 respectively. Copyright © 2011 John Wiley & Sons, Ltd.     

Study on heat and mass recovery in adsorption refrigeration cycles

An adsorption air conditioner has been developed and some operation results are summarized. Mass recovery process is proposed to improve the performance. Performance predictions are presented and show that mass recovery can play an important role to better the performance of adsorption refrigeration cycle. Coefficient of performance might be increased or decreased with mass recovery process due to different working conditions. Cooling capacity can be significantly increased with mass recovery process. The cycle with mass and heat recovery has a relatively higher improvement. It can also be seen that the cycle time will be much shorter and it will certainly enhance the cycle with higher cooling/heating power.     

Performance Comparison of Three-Bed Adsorption Cooling System With Optimal Cycle Time Setting

This article presents the optimal cycle time and performance of two different types of silica gel–water-based three-bed adsorption chillers employing mass recovery with heating/cooling scheme. A new simulation program has been developed to analyze the effect of cycle time precisely on the performance of the systems. The particle swarm optimization (PSO) method has been used to optimize the cycle time and then the optimum performances of two chillers are compared. Sensitive analysis of cycle time has been conducted using the contour plot of specific cooling power (SCP) with driving heat source temperature at 80°C. It is found that the center point of the contour indicates the maximum SCP value and optimal cycle time, which are comparable with the quantitative values obtained for the PSO method. Both three-bed mass recovery adsorption cycles can produce effective cooling at heat source temperature as low as 50°C along with a coolant at 30°C. The optimal SCP is similar for both cycles and is greater than that of the conventional two-bed adsorption system employing the same adsorbent–refrigerant pair. Consequently, the proposed comparison method is effective and useful to identify the best performance of adsorption cycles.     

Experimental performance of a silica gel–water adsorption chiller

A newly developed adsorption water chiller is described and tested. In this adsorption refrigeration cycle system, there is no refrigerant valve. Thus, the problem of mass transfer resistance occurring in the conventional systems when methanol or water is used as refrigerant and resulting in pressure drop during the flow of refrigerant inside the tubing is eliminated. To make the utilization of low heat source with temperature ranging from 70 to 95 °C possible, silica gel–water was selected as working pair. The experimental results proved that it is able to produce a cooling power of 6.3 kW with a COP of about 0.4. The test results demonstrate that, through the heat recovery, the COP can be increased by 34.4% while mass recovery has the effect of increasing the cooling power by 13.7% and the COP by 18.3%. The performances of the system were analyzed for varied condensation temperature and for varied evaporation temperature. Based on the first prototype, the second prototype is designed and manufactured to improve the performance. Primary test results demonstrate that the performance is highly improved. It has a COP of about 0.5 and cooling power 9 kW for 13 °C evaporation temperature.     

A small-scale silica gel-water adsorption system for domestic air conditioning and water heating by the recovery of solar energy

A small-scale silica gel-water adsorption system with modular adsorber, which utilizes solar energy to achieve the cogeneration of domestic air conditioning and water heating effect, is proposed and investigated in this paper. A heat recovery process between two adsorbers and a mass recovery process between two evaporators are adopted to improve the overall cooling and heating performance. First, the adsorption system is tested under different modes (different mass recovery, heat recovery, and cogeneration time) to determine the optimal operating conditions. Then, the cogeneration performance of domestic cooling and water heating effect is studied at different heat transfer fluid temperatures. The results show that the optimal time for cogeneration, mass recovery, and heat recovery are 600 s, 40 s, and 40 s, respectively. When the inlet temperature of hot water is around 85°C, the largest cooling power and heating power are 8.25 kW and 21.94 kW, respectively. Under the condition of cooling water temperature of 35°C, the obtained maximum COP_c, COP_h, and SCP of the system are 0.59, 1.39, and 184.5 W/kg, respectively.     

A three-dimensional non-equilibrium model for an intermittent adsorption cooling system

Intermittent adsorption cycles, driven by low temperature heat, like solar heat, instead of electricity or natural gas, can achieve substantial fossil energy savings. In this paper, the mathematical model for the coupled heat and mass transfer in the adsorber of an intermittent adsorption cooling system is set up. The model includes four submodels: heat transfer in heating/cooling fluids, heat transfer in the metal tube, heat transfer in the fins, and heat and mass transfer in the adsorbent. The model for the heat and mass transfer in the adsorbent is a three-dimensional non-equilibrium model which takes into account both the internal and the external mass transfer resistance in the adsorbent. An experiment has been done to validate the model. With some modifications, the model can be used in system optimization and design of adsorption cycles driven by solar energy or waste heat.     

固体吸附式冷管循环工作过程的动态模拟与分析

针对余热驱动吸附式冷管单元(直径16mm,总长1020mm)制冷循环过程的变压吸/脱附特性,采用线性驱动力(LDF)模型,建立了动态的传热传质数学模型。对吸附式冷管的主要部件——吸附器和冷凝/蒸发器在加热解吸和冷却吸附不同阶段的工作过程,分别建立了耦合的动态方程。对所提出的模型进行分析和合理简化后,利用数值方法对模型进行了求解,获得了冷管单元吸附器、冷凝/蒸发器的循环工作参数的动态变化规律,计算结果与实验结果较好地吻合。为吸附式冷管单元及其组合式制冷系统进一步的优化设计和实用化的改进研究提供了重要参考。     

Analysis of the performance of a multi-bed adsorption heat pump using a solid-side resistance model

An analysis of the coefficient of performance and specific cooling power for a four-bed adsorption heat pump, using a solid-side resistance model, is presented. Methanol and an activated carbon are the adsorption pair. An Arrhenius form of solid-side mass diffusivity was adopted. A plate-fin type insert was considered as the heating/cooling element in adsorbers. The result shows that, for large grain-size activated carbon, the intra-particle mass diffusion resistance significantly affects the adsorption and regeneration rates. Both the coefficient of performance and the specific cooling power increase with the overall heat transfer coefficient, regeneration and evaporation temperatures, but decrease with an increase of the condensing temperature and time constant of the insert. The coefficient of performance considerably increases with a decrease of the insert heat capacitance. An optimum cycle time, corresponding to a maximum specific cooling power, was found. To achieve a high specific cooling power for short cycle time operations, small grain-size activated carbon should be selected as the adsorbent. In addition, a small time constant of the insert and a large overall heat transfer coefficient are also highly recommended.     

Design and performance prediction of a novel double heat pipes type adsorption chiller for fishing boats

A novel double heat pipe type adsorber, which uses compound adsorbent of CaCl₂ and expanded graphite to improve the adsorption performance, is designed. The double heat pipes are integrated into the adsorbers in order to solve the problem of the corrosion between seawater and the steel adsorber in ammonia system and improve the heat transfer performance of the adsorber. There are two kinds of heat pipes integrated with the adsorber. One is the split type heat pipe for heating the adsorber in desorption phase, the other one is the two-phase closed thermosyphon heat pipe for cooling the adsorber in adsorption phase. The performance of two-adsorber adsorption chiller integrated with double heat pipes is predicted. The heat transfer performance of the heat pipes can meet the heat demands for adsorption/desorption of the adsorbent when the heating/cooling time is 720 s and mass recovery time is 60 s. When the exhaust gas temperature is 550 °C, the cooling water temperature is 25 °C, the inlet and outlet chilled water is −10 and −15.6 °C, respectively; the simulation results show that the cooling power and COP of this adsorption system are 5.1 kW and 0.38, respectively.     

Effect of recooling cycle on performance of hydrogen fueled scramjet

Hydrogen fueled scramjet is a candidate for use as the engine of the aerospace plane. Many methods to increase the fuel heat sink (cooling capacity) are widely carried out to meet the cooling requirement of scramjet engine. Especially, recooling cycle (RCC) has been newly proposed for actively cooled scramjet to increase fuel heat sink for cooling. With the working process of fuel cooled scramjet defined as a recuperated cycle, the difference between regenerative cooling (RC) and RCC in the characteristics of heat recovery, heat extraction and heat reinjection are compared first, and the scramjet performance of under RC and RCC mode is compared through off-design comparison analysis at different Mach numbers and equivalence ratios to evaluate the effect of recooling cycle on the performance of scramjet using a coupled heat transfer and flow model. It can be seen through analysis and comparison that recooling cycle can save the fuel mass flow rate for cooling, and make maximum use of the recovered heat. And the specific impulse of a scramjet can be greatly promoted as well.     

利用热管强化吸附床内的传热传质

为了强化吸附式制冷吸附床内的传热传质，设计了利用高效传热元件热管作为内翅片的吸附床。在能量守恒关系和吸附平衡方程的基础上建立了吸附床的数学模型，并对此模型用数值方法进行了求解。求解结果表明利用热管元件可以显著的改善吸附床内的传热传质过程，缩短了吸附式制冷的循环时间，提高了系统的效率，该数学模型为吸附床的设计参数的选择和优化等提供了依据。     

An adsorption air conditioning system to integrate with the recent development of emission control for heavy-duty vehicles

The recent development to control the emissions of large diesel engines has provided opportunities for heat-driven cooling methods in vehicles. An adsorption air conditioning system is therefore proposed in this work for heavy-duty truck application. This system is powered by engine waste heat when the engine of a truck is running. When the engine is off, it can be operated by fuel fired heaters, a newly implemented technology to reduce truck idling. Hence, this system can not only reduce engine emissions but also improve the overall energy efficiency. A lumped parameter model of the system using zeolite-water as its working pair is developed, and the adsorption capacity of zeolite is simulated with the linear driving force model. The dynamic performance of the system and a parametric study on adsorbent mass transfer, operating temperatures and cycle operating periods are presented. Alternative working pairs and the potential to commercialize the system are also discussed. This system may be designed to satisfy the cooling requirement for idle reduction of long-haul trucks.     

Heat and Mass Transfer in Adsorption-chemical Cooling with Phase Transitions in a Sorbent

The complex model of heat and mass transfer during adsorption and chemical heat conversion is presented. It includes combined effect of physical and chemical adsorption and accompanying ammonia condensation/evaporation directly inside the sorber taking into account the conjugate heat transfer between the sorbent and the heat-transfer fluid. It was found that the specific cooling power and average cooling temperature are one-valued function of a ratio of the sorber length to the mass flow of heat-transfer fluid. The use of condensation/evaporation in a sorbent can increase the temperature effect more than twice.     

Autonomous Adsorption Cooling—Driven by Heat Storage Collected from Solar Heat

This study investigates the performance of an adsorption chiller driven by thermal heat collected from solar collectors’ panels with heat storage. The heat is reserved in a storage tank and the reserved heat is used to drive the adsorption chiller. The investigation was carried on the climatic conditions of Dhaka, Bangladesh. Heat transfer fluid goes from the collectors to the adsorption cooling unit, then from the adsorption cooling unit to the storage tank. It is seen that heat storage is more effective than direct solar coupling; however, it requires more collectors, depending on the size of the storage tank. The analysis shows that cycle time is one of the most influential parameters for the solar-driven adsorption cooling system. It is seen that the size of the collector can be reduced if the proper cycle time is adjusted. The analysis also revealed that the system with 22 collectors (each of 2.415 m²) along with 1000 s cycle time provides better performance for the base run conditions. It is also seen that the solar-driven adsorption chiller with heat storage works well beyond the sunset time.     

The effects of operation parameter on the performance of a solar-powered adsorption chiller

A solar-powered adsorption chiller with heat and mass recovery cycle was designed and constructed. It consists of a solar water heating unit, a silica gel-water adsorption chiller, a cooling tower and a fan coil unit. The adsorption chiller includes two identical adsorption units and a second stage evaporator with methanol working fluid. The effects of operation parameter on system performance were tested successfully. Test results indicated that the COP (coefficient of performance) and cooling power of the solar-powered adsorption chiller could be improved greatly by optimizing the key operation parameters, such as solar hot water temperature, heating/cooling time, mass recovery time, and chilled water temperature. Under the climatic conditions of daily solar radiation being about 16–21 MJ/m², this solar-powered adsorption chiller can produce a cooling capacity about 66–90 W per m² collector area, its daily solar cooling COP is about 0.1–0.13.