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.     

Experimental and Numerical Investigation of Enhancement of Heat and Mass Transfer in Adsorbent Beds

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沸石分子筛-水吸附工质对的吸附性能及导热性能

吸附工质对的吸附和传热性能是研究吸附式干燥、除湿及制冷的重要基础，由于吸附量与导热系数和吸附材料的性质、温度、压力等许多因素有关，需要通过实验来确定。该文通过对几种沸石分子筛的性能实验研究，测定了其最大吸附量、密度、吸附等压线及导热系数等一系列性能参数及其影响因素，并给出了实际循环过程中吸附床的温度、压力与吸附量之间的关系。研究表明沸石对水的吸附基本满足D—A方程，而沸石导热系数受温度以及吸附量的影响较大，随着温度及吸附量的增加而增加。     

Operational aspects of adsorption air‐conditioner used in diesel locomotive

A locomotive cabin adsorption air‐conditioner has been equipped in #DF4B‐2369 locomotive; and has been successfully run for 2 years. It is powered by waste heat from the exhaust of the diesel engine. The influence on heat transfer is described by the equivalent heat transfer coefficient or thermal resistance of components inside the adsorber. The variation of adsorption capacity is expressed by a non‐equilibrium adsorption function. The dynamic heat transfer process of adsorption air‐conditioning system is treated with the lumped parameter method. Some typical running experimental results are present. The diesel engine rotating speed and locomotive speed influenced on the refrigeration system are discussed. The maximum mean refrigeration power is regarded as an objective function. Based on experiments and theoretical analysis, the running characteristics of the air‐conditioning system are optimized. Some techniques of performance improvement are suggested as well. Copyright © 2006 John Wiley & Sons, Ltd.     

高温条件下接触热阻的数值模拟与试验研究

接触热阻是衡量接触界面间传热效率的重要指标之一。利用ANSYS有限元软件对高温条件下高温合金GH4169界面间的接触热阻进行了研究。通过光学显微镜获得高温合金表面的真实形貌,并在ANSYS有限元软件中重建其表面模型,基于结构力学理论对接触界面微观结构的弹塑性变形进行模拟,以及传热学分析获得接触界面间的接触热阻值。研究了界面温度与接触压力对接触热阻的影响,同时考虑了高温条件下接触界面间辐射换热的影响,最后利用试验测试装置进行验证。结果表明：理论模拟与试验测试的结果两者之间的最大误差为12.6%,高温合金界面间的接触热阻随着界面温度和接触压力的增加而减小;接触界面温差随着界面温度的增加出现先增大后减小的趋势。     

降低吸附式制冷系统驱动热源温度的研究进展

吸附式制冷是一种环境友好的制冷方式,可以利用低品位热能提供冷量,因此具有重要的节能意义。目前,吸附式制冷技术在太阳能热利用、工业余热利用等中低温余热领域已有应用,但对低于60℃热源的利用实例较少。降低吸附式制冷系统所需的驱动热源温度是扩大吸附式制冷系统使用范围的重要手段。吸附式制冷系统所需驱动热源温度与系统循环方式、吸附剂性能等因素密切相关。从二级/多级吸附式制冷循环、表面酸性强度与孔结构等影响吸附剂再生温度方面阐述了降低吸附式制冷系统驱动热源温度技术的国内外研究现状。分析结果显示,多级循环吸附式制冷系统可以降低装置的驱动热源温度,但装置结构较为复杂;低再生温度吸附剂能够拓宽吸附式制冷装置的驱动热源温度范围,吸附剂的脱附温度与表面极性、酸性、孔结构等参数有关,对吸附剂进行改性,吸附剂极性弱、酸性低的表面特性有利于降低脱附温度。另外,还介绍了数据中心余热驱动的吸附式制冷技术。开展降低吸附式制冷系统驱动热源温度的研究为低温余热高效利用提供了技术参考。     

太阳能固体吸附式制冰机热动力学性能分析模型及实验

分析了太阳能固体吸附式制冷装置中吸会床的传热传质计算过程，给出了求解模型的具体方法，运用数值传热学的方法，计算了在一定日照国徽能量条件下，系统装置的吸附床内的温度场分布，实验表明，所建立的模型能对太阳能固体吸附式制冷装置进行了性能动态模拟，为系统装置的优化设计提供了参考。     

固体吸附式制冷强化传热研究进展

吸附床的传热强化是影响固体吸附式制冷的主要因素。简述了吸附制冷的强化传热研究进展,介绍了几种常用的吸附床强化传热方法,提出了固体吸附式制冷强化传热的研究方向。     

Study of Thermal Conductivity and Geometry Wall Contact Resistance Effect of Granular Active Carbon for Refrigeration and Heat Pumping Systems

The commercial success of sorption refrigeration and heat pump systems depends on a good heat and mass transfer in the adsorbent bed, which allows higher coefficients of performance and greater specific heating or cooling power that reduce capital costs. In this study the thermal conductivity and thermal contact resistance of vibrated and compressed granular active carbon and binary mixtures of active carbon are investigated using two types of conductivity measurements: a steady-state measurement between flat plates and a transient hot tube measurement. With these results is possible to draw conclusions on how the wall geometry, particle size distribution, and bulk density affect the overall thermal performance. Results show that using binary mixtures of grains and powder gives results superior to those of either grains or powder alone. The conductivity of the binary mixtures increases roughly linearly with bulk density and the 2/3 grain mixture achieves the highest densities. The method used to achieve compaction (vibration or compression) did not seem to affect the result. Thermal contact resistances reduce with increasing density but do vary with the mixture ratio, also appearing to be best with a 2/3 grain–1/3 powder mixture.     

Heat and mass transfer during adsorption of ammonia in a cylindrical adsorbent bed: thermal performance study of a combined parabolic solar collector, water heat pipe and adsorber generator assembly

In this paper we present the study of adsorption refrigerator which use an activated carbon-pair ammonia. The ability of activated carbons to adsorb large mass of ammonia makes them ideal for use in adsorption refrigeration and pump systems. These systems have not reasonable efficiency. In order to make these systems economically viable, their size must be reduced. This implies a need for a rapid heating and cooling the adsorbent/refrigerant pair. However, the main problems to be overcome is related to the poor heat transfer in the adsorbent bed. So, it is necessary to study and understand the heat and mass transfer within the bed and to improve it. A detailed model of heat and mass transfer into the generator has been developed. For a given heat flux, temperature and adsorbed mass have been computed in every point at each step time along the adsorbed bed (generator). Experimental installation simulating an adsorption machine working within a temperature ranging from 20 to 250 °C and pressure ranging from 0 to 2.5 × 10⁶ Pa, allows for identification of the generator's equivalent thermal conductivity and internal heat transfer coefficient. These two parameters are then used to simulate thermal performance of a design whose features include the insertion of stainless steel water heat pipe (HP's) condensers into the generator. The HP's evaporator heat input is of solar origin using a compound parabolic collector (CPC). Nominal Solar coefficient of performance, COPs =14.37% obtained through both Adimensional Exergy Loss (AEL), and COP study, shows the competitiveness of the proposed design.     

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 BaCl₂–MnCl₂–NH₃, 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 CaCl₂–NH₃, 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.     

太阳能冷管的研究及其进展

太阳能冷管以沸石分子筛—水为工质对，在一根玻璃管内完成吸附式制冷循环，一根冷管即为一个制冷单元，成功地解决了太阳能吸附式制冷技术难以转化为成果的问题。本文综述了作者近几年来对太阳能冷管首创性提出，以及其结构性能的研制和改进情况。采用真空集热方式和选择性涂层加强冷管对太阳能的吸收，采用整体固化复合吸附剂提高吸附床的吸附和脱附性能。本文还介绍了已制作的三代太阳能冷管型制冷系统的试验样机，在单一提供制冷的基础上，提出了既可以制冷又可以供热水的多功能太阳能冷管。目前，实验结果表明，最新的多功能太阳能冷管COP可达0．268，太阳能制冷与供热的总效率可达87．7％。     

Performance of a dual-purpose solar continuous adsorption system

A conceptual design and performance of a dual-purpose solar continuous adsorption system for domestic refrigeration and water heating is described. Malaysian activated carbon and methanol are used as the adsorbent–adsorbate pair. The heat rejected by the adsorber beds and condensers during the cooling process of the refrigeration part is recovered and used to heat water for the purpose of domestic consumption. In a continuous 24-h cycle, 16.9 MJ/day of heat can be recovered for heating of water in the storage tanks. In the single-purpose intermittent solar adsorption system, this heat is wasted. The total energy input to the dual-purpose system during a 24-h operation is 61.2 MJ/day and the total energy output is 50 MJ/day. The latter is made up of 44.7 MJ/day for water heating and 5.3 MJ/day for ice making. The amount of ice that can be produced is 12 kg/day. Using typical value for the efficiency of evacuated tube collector of water heating system of 65%, the following coefficient of performances (COP's) are obtained: 44% for adsorption refrigeration cycle, 73% for dual-purpose solar water heater, 9.1% for dual-purpose solar adsorption refrigeration and 82.1% for dual-purpose of both solar water heater and refrigerator.     

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.     

Modelling and performance study of a continuous adsorption refrigeration system driven by parabolic trough solar collector

This article suggests a numerical study of a continuous adsorption refrigeration system consisting of two adsorbent beds and powered by parabolic trough solar collector (PTC). Activated carbon as adsorbent and ammonia as refrigerant are selected. A predictive model accounting for heat balance in the solar collector components and instantaneous heat and mass transfer in adsorbent bed is presented. The validity of the theoretical model has been tested by comparison with experimental data of the temperature evolution within the adsorber during isosteric heating phase. A good agreement is obtained. The system performance is assessed in terms of specific cooling power (SCP), refrigeration cycle COP (COP_cycle) and solar coefficient of performance (COP_s), which were evaluated by a cycle simulation computer program. The temperature, pressure and adsorbed mass profiles in the two adsorbers have been shown. The influences of some important operating and design parameters on the system performance have been analyzed.The study has put in evidence the ability of such a system to achieve a promising performance and to overcome the intermittence of the adsorption refrigeration systems driven by solar energy. Under the climatic conditions of daily solar radiation being about 14 MJ per 0.8 m² (17.5 MJ/m²) and operating conditions of evaporating temperature, T_ev = 0 °C, condensing temperature, T_con = 30 °C and heat source temperature of 100 °C, the results indicate that the system could achieve a SCP of the order of 104 W/kg, a refrigeration cycle COP of 0.43, and it could produce a daily useful cooling of 2515 kJ per 0.8 m² of collector area, while its gross solar COP could reach 0.18.     

Study of the effect of finned tube adsorber on the performance of solar driven adsorption cooling machine using activated carbon–ammonia pair

Solar refrigeration represents an important application of solar energy due to the excellent matching between the high sunshine and the refrigeration needs. Solar adsorption refrigeration devices are among the significant techniques used to meet the needs for cooling requirements. Several solar refrigeration systems have been proposed and are under development such as sorption systems including liquid/vapor, solid/vapor absorption, adsorption, vapor compression and others. The purpose of this paper is to identify the influence of a cylindrical adsorber on the performances of a solar adsorption refrigerating machine. The adsorber heated by solar energy contains an activated carbon–ammonia pair; it is composed by many cylindrical tubes welded using external fins. A model based on the conservation equations of energy and mass in the adsorber has been developed and well described. Using real solar irradiance data as well as many initial conditions, the model computes for each point and in the considered time interval during the day, the temperature, the adsorbed mass, the pressure inside the adsorber and the solar performance coefficient (COP). The results show that the optimal diameter of the adsorber with fins is greater than the one without fins. Moreover the mass cycled in the case of an adsorber equipped with external fins is more significant than the one without fins, and the maximal temperature reached in the adsorber with fins attains 97 °C while in the adsorber without fins reaches 77 °C. Thus, the performances of the solar adsorption refrigerating machine with an adsorber equipped with fins are higher than the machine without fins.     

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.     

Research and development of consolidated adsorbent for adsorption systems

Adsorption heat pump and refrigeration systems are noiseless, non-corrosive and environment friendly. For these reasons the research activities in this sector are still increasing to solve the crucial points that make these systems not yet ready to compete with the well-known vapor compression system. There is an increasing interest in the development and use of adsorption chillers due to their various economic and impressive environmental benefits, enabling solar energy or waste heat to be used for applications such as district networks and cogeneration plants. In order to increase the cooling power, much effort has been devoted to enhance materials heat transfer properties. Consolidated adsorbent could be the solution. This paper provides a literature review on current progress of consolidated adsorbent for adsorption systems. A number of consolidated technologies of adsorbent are discussed. The related work at our laboratory is also discussed.     

A review on adsorption refrigeration technology and adsorption deterioration in physical adsorption systems

As one kind of environmentally friendly refrigeration, the adsorption refrigeration has attracted many attentions in resent decades. This paper introduces the researches of adsorption refrigeration systems with the commonly used working pairs, advanced adsorption cycles, heat and mass transfer enhancement and attempts of adsorption refrigeration applications. Poor heat and mass transfer problem is a bottleneck to prevent the improvements of the adsorption refrigeration technique. Two ways to enhance the heat and mass transfer are discussed in this paper. The adsorption deterioration of adsorbent, another obstacle to physical adsorption refrigeration applications, is also pointed out. And the possible reasons and the possible methods are analyzed.