Thermodynamic design procedure for solid adsorption solar refrigerator

The thermodynamic design procedure for solid adsorption solar refrigeration is presented and applied to systems using activated carbon/methanol, activated carbon/ammonia and zeolite/water adsorbent/adsorbate pairs. The results obtained showed that zeolite/water is the best pair for air conditioning application while activated carbon/ammonia is preferred for ice making, deep freezing and food preservation. In all cases, the system depends strongly on adsorption and condensation temperatures and weakly on the evaporator temperature. The maximum possible net solar COP was found to be 0.3, 0.19 and 0.16 for zeolite/water, activated carbon/ammonia and activated carbon/methanol, respectively, when a conventional flat plate solar collector is used.     

Experiments of a solar flat plate hybrid system with heating and cooling

Based upon the prior research of the solar hybrid water heater and refrigerator, a new flat plate solar hybrid system with heating and cooling was proposed and experimental prototype device was constructed. With this new hybrid system, the heat and mass transfer can be improved effectively both in desorption process and adsorption process. The conventional flat plate solar water heater collector absorber is immersed inside adsorbent bed in the new hybrid system. The experimental results show that not only the cooling effect can be obtained, but also both the sensible heat of the adsorbent bed and the adsorption heat can be recovered effectively to produce hot water for domestic use. The COP of this new flat plate hybrid system can reach 0.11 and the heat efficiency is about 0.45, this achievement has demonstrated an efficient way of the application of solar energy.     

Experimental study of a solidified activated carbon-methanol adsorption ice maker

In this paper, the experiments are performed on an adsorption ice maker driven by waste heat, which uses up to two beds. Each bed uses methanol as refrigerant and solidified activated carbon (120 kg adsorbent totally, 60 kg adsorbent per bed) as adsorbent. This system is designed to be driven by the waste heat of a 100 kW diesel engine. The experiments show that the cooling power could be enhanced by the mass recovery process up to 11%, and the heating power could be lowered by the heat recovery process up to 30%. The optimal cooling power of this prototype is about 2.0 kW and corresponds to a specific cooling power (SCP) is about 17 W/kg with both heat and mass recoveries between two beds. Considering the optimal adsorption time is much longer than optimal desorption time at the condition of ice making, the experiments are operated on a single bed (60 kg adsorbent per bed) and the adsorption time used in experiments is two times of desorption time, then the performance of a three-bed adsorption ice maker (120 kg adsorbent totally, 40 kg adsorbent per bed) is predicted by the results of experiments on this single bed. The results of prediction show that both COP and cooling power of three-bed operation could be enhanced greatly compared to the two-bed operation; optimal SCP and COP are respectively 22 W/kg and 0.239 when mass and heat recoveries proceed between three beds. Optimal ice productivity of this three-bed system is 21 kg/h when the water temperature is 25 °C and ice temperature is −7 °C.     

Study of a new solar adsorption refrigerator powered by a parabolic trough collector

This paper presents the study of solar adsorption cooling machine, where the reactor is heated by a parabolic trough collector (PTC) and is coupled with a heat pipe (HP). This reactor contains a porous medium constituted of activated carbon, reacting by adsorption with ammonia.We have developed a model, based on the equilibrium equations of the refrigerant, adsorption isotherms, heat and mass transfer within the adsorbent bed and energy balance in the hybrid system components. From real climatic data, the model computes the performances of the machine. In comparison with other systems powered by flat plate or evacuated tube collectors, the predicted results, have illustrated the ability of the proposed system to achieve a high performance due to high efficiency of PTC, and high flux density of heat pipe.     

吸附剂固化的发展与固化活性炭块的试验研究

吸附剂的固化成型被认为是增大吸附式制冷系统的制冷量一个可行的方法。本文一方面综述了吸附系统中吸附剂固化的发展现状，讨论各种固化技术和方法。另一方面总结了在我们实验室所涉及的活性炭固化研究工作，给出了以块状活性炭一甲醇为吸附工质对时比较合适的固化工艺参数。     

一种有潜力的吸附式制冷工作对——活性炭纤维—甲醇

吸附式制冷具有无ＣＦＣｓ问题、可利用低品位热能驱动、价格效用比高等一系列优点。由于一般吸附剂吸附／解吸时间长和单位质量制冷功率小使吸附式制冷的产品化受阻。活性炭纤维是一般吸附剂活性炭的较好替代物，其对甲醇的吸附容量为活性炭的２－３倍，而吸附／解吸时间仅为活性炭的１／１０左右。对紧凑式吸附式冰箱，活性炭纤维－甲醇是一种好的工作对。     

新型平板式太阳能冷热联供装置

在积累了太阳固体吸附式制冷循环研究的基础上，与现有的平板式太阳热水器制造技术紧密结合，提出了平板式太阳冷热联供循环方式，并在实验室内成功地制作了实物样机。该装置能有效地回收太阳固体吸附式制冷不中吸附床的显热及吸附热，且操作简便。实验结果有效地支持了所提出的设想，为太阳固体吸附式制冷的实用化应用打下了良好基础。     

Development of adsorption air-conditioning technology using modified activated carbon – A review

Adsorption air-conditioning technology has attracted much attention recently due to its environmental friendly property. Some successes have been reported in the literature on the adsorption technology for air-conditioning applications. This paper presents an overview of the researches which had been carried out on adsorption refrigeration system with the commonly used adsorbent and adsorbate working pairs, solar adsorption refrigeration and adsorption technologies in automobile. Activated carbon has been widely used as the adsorbent in adsorption refrigeration system. However, one of the bottlenecks which prevent the improvement of the adsorption refrigeration technology using activated carbon is the use of the readily available commercial activated carbon without prior treatment, which has resulted in relatively lower performance as compared to the conventional absorption and vapour compression technologies. Various modification methods on activated carbon are thus discussed in this paper for future development and improvement of adsorption air-conditioning system.     

Simulation of hydrogen storage tank packed with metal-organic framework

Hydrogen adsorption in high surface metal-organic framework (MOF) has generated significant interest over the past decade. We studied hydrogen storage processes of MOF-5 hydrogen storage systems with adsorbents of both the MOF-5 powder (0.13 g/cm³) and its compacted tablet (0.30 g/cm³). The charge–discharge cycles of the two MOF-5 adsorbents were simulated and compared with activated carbon. The physical model is based on mass, momentum and energy conservation equations of the adsorbent-adsorbate system composed of gaseous and adsorbed hydrogen, adsorbent bed and tank wall. The adsorption process was modeled using a modified Dubinin–Astakov (D–A) adsorption isotherm and its associated variational heat of adsorption. The model was implemented by means of finite element analysis software Comsol Multiphysics™, and the system simulation platform Matlab/Simulink™. The thermal average temperature from Comsol simulation is used to fill the gap between the system model and the multi-dimensional models. The heat and mass transfer feature of the model was validated by the experiments of activated carbon, the simulated pressure and temperatures are in good agreement with the experimental results. The model was further validated by the metal-organic framework of Cu-BTC and is being extended its application to MOF-5 in this study. The maximum pressure in the powder MOF-5 tank is much higher than that in the activated carbon tank due to the lower adsorbent density of MOF-5 and resulting lower hydrogen adsorption. The maximum pressure in the compacted MOF-5 tank is a little bit lower than that in the activated carbon tank due to the higher adsorbent density and resulting higher hydrogen adsorption. The temperature swings during the charge–discharge cycle of both MOF-5 tanks are higher than that of the activated carbon tank. These are caused mainly by pressure work in the powder MOF-5 tank and by adsorption heat in the compacted MOF-5 tank. For both MOF-5 hydrogen storage systems, the lumped parameter models implemented by Simulink agree well with experimental pressures and with pressures and thermal average temperatures from Comsol simulation.     

A new zero energy cool chamber with a solar-driven adsorption refrigerator

A new zero energy cool chamber (ZECC) consisting of two cooling systems, a solar-driven adsorption refrigerator and an evaporative cooling system, was developed and then evaluated as low-cost and eco-friendly cooling storage for storing fruit with moderate respiration rates. The solar-driven adsorption refrigerator, consisting of a solar collector containing activated carbon as an adsorbent, a condenser and an evaporator, cools water based by evaporating methanol and adsorbing it on activated carbon, and then makes ice. The methanol adsorbed on the activated carbon is desorbed by applying solar heat. The ice is then used to cool the storage space, which can be done for a long time without the need for electricity. The evaporative cooling system also cools the storage space by evaporating water from the wet walls containing wet filler. The combined use of two cooling systems reduced the average inside temperature of the new ZECC to 12.07 °C compared with an average outside temperature of 31.5 °C and extended the shelf life of tomatoes from 7 to 23 days. These results suggest that the new ZECC proposed here is low-cost and energy-saving and is useful for storing fruit and vegetables in areas where electricity is unavailable.     

基于平行流铝扁管吸附床传热性能的模拟研究

吸附床是吸附式制冷系统的关键部件。吸附床的换热能力对吸附式制冷系统的各项性能有显著影响。文章针对应用于吸附床的传统换热器和扁管换热器的不足之处,设计出一种新型平行流铝扁管吸附床,并建立了该吸附床的二维传热模型,以温度随时间的变化情况为分析指标,分析翅片的间距、高度、厚度,以及吸附剂体积分数等因素对吸附床传热性能的影响,从而优化调整吸附床的结构,提高其换热性能。分析结果表明:当翅片高度约为70 mm时,吸附床的换热能力达到峰值;当翅片厚度大于1.5 mm时,翅片厚度的增加对吸附床传热性能的影响比较微弱;当吸附剂体积分数由0.25逐渐增大至0.45时,吸附剂的等效传热系数约增加了50%。     

A new type adsorber for adsorption ice maker on fishing boats

A new type of adsorber for an adsorption ice maker on fishing boats, which uses a compound adsorbent (activated carbon and CaCl₂) and ammonia working pair, is designed. This type of heat pipe adsorber solves the problem of incompatibility between ammonia, copper, seawater and steel. The heating/cooling power for the adsorption/desorption process of the adsorbent, which is required to be transferred by one heat pipe in the adsorber, is computed by the test results of the adsorbent, and the heat transfer performance of one heat pipe in the adsorber is simulated according to the theory of the two phase closed thermosyphon. The heat transfer performance of the heat pipe can meet the heat demands for adsorption/desorption of the adsorbent when the evaporating temperature is −15 °C and the cycle time is 10 min. A test unit is set up to test the heating/cooling performance of the heat pipe type adsorber, and the experimental results are coincident with the simulation. The performance of a two bed adsorption ice maker with heat pipe adsorbers is predicted, and the cooling power is about 17.1–17.8 kW at the evaporating temperature of −15 °C and cycle time of 10 min with mass recovery between two 29 kg compound adsorbent beds.     

The effect of microwave regenerated adsorbent bed on the performance of an adsorption heat pump

The heat transfer problem of an adsorption heat pump during the regeneration of adsorbent bed was investigated numerically. A numerical analysis of the heat and mass transfer in an adsorbent bed during an adsorption heat pump cycle, achieved with both conventional and microwave heating, was successfully simulated. The influence of the microwave heating on the performance criteria of an adsorption heat pump was investigated. The distributions of temperature, pressure and adsorbate concentration of adsorbent bed through the radius of the bed were analyzed. The Clausius–Clapeyron diagram was constructed for both cases. The period of the cycle was improved by about 20% with the microwave regeneration, since the period of the isobaric desorption process for a microwave heated cycle was enhanced by 51% relative to the period of the isobaric desorption process for a conventional heated cycle. The COP for the microwave heated cycle was improved by 61% according to the conventional heated cycle.     

Simulation of an intermittent adsorptive solar cooling system

An analytical model of the adsorption solar cooling cycle is presented. This model accounts for heat and mass transfers in a porous bed in a two-dimensional transient process. After an experimental validation based on a solar icemaker using the activated carbon---methanol pair, a parametric study is presented. The influence of the choice of the activated carbon and condensing temperature is studied.     

Design and Investigation of Heat Transfer in a New Adsorbent Bed With CPC for Solar Adsorption Refrigeration Systems

This article presents the design and the heat transfer study in a novel adsorbent bed with compound parabolic concentrator (CPC) for solar adsorption chillers. The objectives of the study were to investigate the heat transfer in the adsorbent bed experimentally, and to verify the fins layout through finite-element analysis (FEA) simulation. CPCs with different concentration ratios were experimentally tested and an appropriate design of CPC was selected for a prototype. The prototype was designed with the objective of improving the heat and mass transfer ability of the adsorbent bed. Fins were placed in the transverse direction under the receiver area of each CPC. Spaces were provided from three sides of the adsorbent for easy movement of the refrigerant. FEA software was used to study the effect of the fins layout and fins pitch. The experimental results showed that the heat was efficiently transferring up to the end and extended parts of the bed. Simulation results indicated that the present strategy of placing the fins in a transverse direction gives uniform heat distribution compared to a fins layout with fins placed in a longitudinal direction. The proposed design scheme will be helpful to improve the system performance by increasing the heat and mass transfer ability of an adsorbent bed.     

Transient analysis and performance prediction of a solid adsorption solar refrigerator

The transient analysis and performance prediction of a solid adsorption solar refrigerator, using activated carbon/methanol adsorbent/adsorbate pair are presented. The mathematical model is based on the thermodynamics of the adsorption process, heat transfer in the collector plate/tube arrangement, and heat and mass transfers within the adsorbent/adsorbate pair. Its numerical model developed from finite element transformation of the resulting equations computes the collector plate and tube temperatures to within 5 °C. The condensate yield and coefficient of performance, COP, were predicted to within 5% and 9%, respectively. The resulting evaporator water temperature was also predicted to within 5 °C. Thus the model is considered a useful design tool for the refrigerator to avoid costly experimentation.     

Thermal effect of the adsorption heat on an adsorbed natural gas storage and transportation systems

This paper experimentally studies the thermal effect that results from the adsorption heat on both the charge and discharge performance of adsorbed natural gas (ANG) storage and transportation systems. Two storage tanks built with temperature systems and security control were used during the adsorption and desorption process. Temperature, flow rate and discharge amount were recorded experimentally at 2, 3 and 4 MPa adsorption pressures, using different activated carbon (AC) as an adsorbent bed. Results show that the central region of the adsorbent bed suffers from the severest temperature fluctuation of the charge and discharge process. It was observed that the best discharged amount was 4 MPa using, G1220 Extra AC as an absorbent bed. Conclusions detected that it is possible mitigate the temperature fluctuations with improved AC properties and the amount of NG desorbed is linearly proportional to the respective tank’s hydraulic volumes.     

Zeolite-active carbon compound adsorbent and its use in adsorption solar cooling tube

The “zeolite-water” pair adsorption process has been extensively studied for its application in cooling system. This paper presents a compound zeolite-active carbon adsorbent (CZACA) which enhances the heat transfer in the adsorbent bed by absorbing solar energy directly and decreases the desorption cycle time in a solar cooling system. Experimental study of a special solar cooling tube using this adsorbent is discussed. The effects of some operating parameters on the system performance are also evaluated.