双效复叠吸附式制冷循环的研究

为克服吸附式制冷能量利用效率不高的缺点,采用硅胶-水、分子筛-水分别作为两级循环的工作对以及两级循环中都用分子筛-水为工作对,构造了两种双效复叠式制冷循环.该循环可有效利用第二级循环的吸附热、析出蒸汽的显热,能有效提高热力完善度.建立了计算机模型,对系统和影响性能的一些参数进行了分析讨论.     

烧结型沸石分子筛(1 3X)-水有效导热系数之测定

研究了一种新型吸附式制冷单元管－烧结型13X沸石分子筛单元管的传热性能，指出：沸石层的传热性能是制约吸附式制冷（热）循环效率的主要因素。本文提出了一种测定含水沸石层工作过程有效导热系数的方法，并进行了实验测定。     

热阻、热漏和内不可逆性对两级吸收式制冷循环性能的影响

建立考虑工质与外部热源间的传热损失、内不可逆性损失及外部热源热漏损失的不可逆两级吸收式制冷循环模型,给出制冷系数和制冷率的一般关系。在6个换热器总热导率一定时,对循环性能进行优化,导出循环制冷率和制冷系数的基本优化关系,并得到制冷率和制冷系数的极值。通过数值算例,分析热阻、热漏和内不可逆性损失对循环性能的影响规律。     

低品位热驱动的混合工质喷射制冷循环研究

提出一种低品位热驱动的混合工质喷射制冷循环,将沸点相差较大的非共沸混合工质引入喷射制冷循环,采用两级分凝分离降低该新循环压比,实现在喷射制冷循环中获得较低的制冷温度和较高制冷效率。建立组成循环各部件热力学数学模型,在系统稳定运行的条件下,分析喷射器压比、冷凝温度和混合工质组分配比对新循环工作性能的影响。研究表明:采用混合工质R600/R290的喷射制冷循环可获得低于-20℃的制冷温度。     

一个带喷射器的两级吸收式制冷循环

提出一种带喷射器的两级吸收式制冷循环,部分低压发生器出口的制冷剂蒸气被高压发生器出口的制冷剂蒸气直接引射到冷凝压力。相比传统的两级吸收式制冷循环,由于部分制冷剂无需被高压溶液循环吸收和发生,因此新循环拥有更高的性能系数。以水-溴化锂作为工质的模拟结果显示,在部分工况下,新循环相对传统两级吸收式制冷循环的COP可提高20%以上。     

太阳能溴化锂吸收式制冷技术的研究进展

介绍了太阳能澳化锂吸收式制冷循环的工作原理和系统构成,具体阐述了该制冷循环的几种典型结构,包括单效、双效、两级以及三效涣化锂吸收式制冷循环,分析了各种制冷循环的优缺点以及目前研究进展;进一步讨论了太阳能澳化锂吸收式制冷机组的性能特点受冷媒水出口温度、冷却水进口温度、加热蒸汽温度、污垢系数及不凝性气体等诸多因素的影响;提出了太阳能溴化锂吸收式制冷技术现存问题,最后指出,随着科学技术的发展和绿色建筑的兴起,太阳能溴化锂吸收式制冷将会有非常大的发展前景。     

渔船发动机废热驱动的两级复叠吸收制冷循环性能分析

针对传统吸收式制冷无法达到较低温度以及自复叠吸收制冷在制得较低温度时系统性能系数过小的缺点,提出发动机废热驱动的两级复叠式吸收制冷循环用于捕获海产品的速冻保鲜。首先采用SRK方程获得了该循环高、低温级工质对R134a/DMF和R23/DMF的热力学性质参数,进而对循环进行了建模分析。通过直接搜索法得到了在不同工况下的最优高温级发生温度。发现在当吸收温度为30℃,冷凝温度为35℃,制冷温度在-40℃以上时,循环最佳蒸发冷凝温度和高、低温级发生温度分别为-3℃、106℃和140℃,此时循环COPint 可达到0.143。但该循环性能受吸收、冷凝温度影响较大,因此不太适合在海水温度过高的海域使用。     

内可逆四热源吸收式制冷循环的热经济性能优化

应用内可逆四热源吸收式制冷循环模型，分析吸收式制冷机受传热不可逆性影响时的热经济性能。在牛顿传热定律下，导出了循环的最佳热经济性目标和制冷系数的基本优化关系和最大热经济性目标及相应的制冷系数与比制冷率；通过数值算例，得出循环参数对循环的热经济性目标、制冷系数和比制冷率的影响关系。     

热漏对内可逆四热源制冷系统的影响

在恒温热源内可逆四热源吸收式制冷循环的基础上，建立不可逆吸收式制冷循环的模型，考虑环境热源到制冷空间的热漏以及工质与外部热源间的热阻损失，导出牛顿定律下循环的制冷率和制冷系数的基本优化关系、最大制冷系数及相应的制冷率和最大制冷率及相应的制冷系数；并通过数值计算分析了循环参数对循环的制冷率、制冷系数的影响。     

双级溴化锂制冷循环的中间压力分析

通过中间压力双级溴锂制冷循环热系数影响的分析，提出最佳中间压力的计算方法，可简化和优化双级溴化锂制冷循环的热力计算，使其获得最高热力系数，并能对运行操作提供一个中压力的参考值。     

Analysis of a Finned Heat Exchanger Working in an Adsorption Refrigeration System Using Zeolite and Methanol

A new refrigeration system that uses a specially designed finned plate heat exchanger and works with zeolite and methanol is proposed. The integration of heat transfer and adsorption via a finned surface coated with zeolite CBV 901 and the use of a connected, twin active bed system to enable heat recuperation are novel features. The thermophysical properties of zeolite and methanol were first studied with the intention of designing a high performance heat exchanger (generator) for the adsorption refrigeration system. Here, the major problem is related to poor conductivity at the interface between the heat exchanger and the zeolite. The adsorbent must be heated (desorption phase) and then cooled (adsorption phase) back to ambient temperature in order to complete a thermodynamic cycle. To manufacture a sufficiently small system, there must be high rates of heat transfer in and out of the adsorbent. Therefore, the surface of the heat exchanger is finned in order to increase the heat transfer area (the fins are coated with 2 mm layer of specially prepared zeolite paste). The following characteristics were estimated from initial calculation: heating temperature, 120°C; outside tube temperature, 119.6°C; middle fin temperature, 117°C; and coated layer of zeolite paste temperature, 115.3°C. The mathematical code developed to calculate the effects of operating conditions and the Coefficient of Performance (COP) was presented at HPC 2001 in Paris. It is based on the Dubinin-Astakhov equation and thermodynamic analyses. The results obtained shows that 0.535 is the COP for a single bed and 0.925 for a double bed.     

Thermodynamic analysis of novel heat pump cycles for drying process with large temperature lift

Heat pump–assisted drying has been recognized a prospective technology to meet the requirement of energy saving. However, large temperature lift will be resulted by the single‐stage heat pump cycle during the high‐temperature drying, especially operating with low ambient temperature for open‐loop drying, which leads to insufficient heat output, high compression ratio, and low coefficient of performance (COP). Two heat pump cycles, namely, multitemperature cascade cycle and combined single‐stage cycle, are proposed to address the above problems in the drying process with large temperature lift in this paper. The effects of varying operation parameters on the heat pump cycles are analyzed to optimize the cycle performance. Afterwards, the above two cycles as well as a conventional cascade cycle, a two‐stage compression cycle, and a single‐stage compression cycle are compared with each other in terms of cycle performance and drying performance under specified drying conditions. It is indicated by the results that the COPs of the multitemperature cascade cycle and combined single‐stage cycle are about 95% and 88% higher than that of the single‐stage compression cycle, respectively. As for the two cascade cycles (ie, conventional cascade cycle and multitemperature cascade cycle), 49% more water evaporation with the same power input can be resulted by the added condenser and evaporator. Among the five analyzed cycles, the multitemperature cascade cycle is the most promising to be used in the retrofitting of the drying equipment with large temperature lift.     

Potential of a direct contact adsorption heat pump system for generating steam from waste water

An adsorption heat pump with a direct contact system for steam generation has been developed and the feasibility of the proposed system was confirmed both theoretically and experimentally. The basic cycle for the system has been proposed to use zeolite–water working pairs in the p‐T‐x equilibrium curve. To generate steam above 150°C from low‐energy level water at 80°C, a direct contact adsorption heat pump prototype was constructed. The experimental results show that steam could be generated by the direct contact system and the relationship between the amount of water adsorbed and the change in temperature with time is discussed. This study is expected to serve as a foundation for developing continuous adsorption heat pump systems for steam generation. Copyright © 2011 John Wiley & Sons, Ltd.     

Solar energy storage using chemical potential changes associated with drying of zeolites

Compact solar storage systems depend upon identification of systems which can store energy as chemical potential. Simple, noncorrosive, systems that operate at reasonably low temperatures are rare. The use of the heat of adsorption of moisture on zeolite molecular sieves is discussed here. The advantages of zeolites are high heats of adsorption (as much as 80 kJ mol⁻¹), large maximum adsorption capacity (0.2–0.3 kg H₂O/kg adsorbent) and easy control of the store following from control of heat output by regulations of flows of moist air. The disadvantages are the relatively high upper temperature required to utilize maximal storage capacities (up to 250°C) and cost. There is reason to project falling cost.

Zeolite storage is compared favourably with respect to capacity to water, stone, and heat of phase change systems. Compared to salt hydrates, acid solution, and salt solutions any capacity advantage is supplemented by low corrosion and opportunity for long term storage. Zeolites are compared favourably to alternative absorbent materials; alumina, charcoal, and silica gel.

The warm dry air output from a zeolite storage bed can be utilized not only in space heating but also in the drying of agricultural timber and fish products.     

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。     

Solar space heating and cooling with bi-heat source heat pump and hot water supply system

This paper describes a specific heat pump system that can solve the problem of low heating capacity at a low ambient temperature—one of the largest problems in the air-source heat pump system.

In order to decrease the collector area required, the heat pump system is operated by the air-source during the daytime, but at night or at a very low ambient temperature it can be operated with hot water which has been produced by the collector in the daytime. The effect of the solar energy on the air-source heat pump system has many advantages in the moderate winter climate of Japan. The hot water supply system includes an auxiliary electric heater.

The experiment has been carried out with a prefabricated test house, which has been constructed in Nara with double glazed windows and high thermal insulation. The results of this experiment are that solar energy enhances the total electric energy savings, increases the heating capacity at low ambient temperature, and eliminates the need for reverse cycle defrosting operation, etc.     

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。     

Exergetic analysis of a double stage LiBr–H2O thermal compressor cooled by air/water and driven by low grade heat

In the present paper, an exergetic analysis of a double stage thermal compressor using the lithium bromide–water solution is performed. The double stage system considered allows obtaining evaporation temperatures equal to 5 °C using solar heat coming from flat plate collectors and other low grade thermal sources. In this study, ambient air and water are alternatively used as cooling fluids without crystallization problems up to condensation–absorption temperatures equal to 50 °C. The results obtained give the entropy generated, the exergy destroyed and the exergetic efficiency of the double stage thermal compressor as a function of the absorption temperature. The conclusions obtained show that the irreversibilities generated by the double stage thermal compressor will tend to increase with the absorption temperature up to 45 °C. The maximum value corresponds to 1.35 kJ kg⁻¹ K⁻¹. The entropy generated and the exergy destroyed by the air cooled system are higher than those by the water cooled one. The difference between the values increases when the absorption temperature increases. For an absorption temperature equal to 50 °C, the air cooled mode generates 14% more entropy and destroys 14% more exergy than the water cooled one. Also, the results are compared with those of previous studies for single and double effect air cooled and water cooled thermal compressors. The conclusions show that the double stage system has about 22% less exergetic efficiency than the single effect one and 32% less exergetic efficiency than the double effect one.     

Comparative study on adsorbent characteristics for adsorption thermal energy storage system

The adsorption performance of the thermal energy storage (TES) system changes depending on the material properties of the adsorbent itself, but the change of the hardware structure can also substantially change the adsorption characteristics. In this study, a laboratory‐scale adsorption‐based TES system was constructed, and the adsorption performance of three adsorbents was evaluated in the same system to compare the adsorption performance between adsorbents. The adsorption characteristics of silica gel, zeolite 13X, and 4A, which are the most preferred adsorbents in the physical adsorption‐based TES system, were selected for evaluation. Experiments with each adsorbent were performed, including heat recovery to evaluate the heat transfer effect and the amount of heat recoverable in the actual TES system. Experimental results have identified several key characteristics of the adsorption and performance of each adsorbent in the TES system, as well as operating parameters that determine the influence of adsorption performance on the TES system. The actual energy storage density of the adsorbent is affected not only by the enthalpy of adsorption of the material itself but also by other factors. These factors include the difference in thermal conductivity that causes a difference in temperature distribution and the magnitude of mass transfer resistance due to the shape of the adsorbent particle and the actual TES system reactor structure. If the reaction heat generated during the adsorption reaction cannot be effectively released, the adsorption performance is significantly lowered due to the increased temperature of the reactor inside. This phenomenon was commonly observed in adsorbents examined in the present study. The uptake amount, X [g/g], was increased by allowing the inside of the reactor to be maintained at a lower temperature through heat recovery. In case of silica gel, the temperature rise during adsorption reaction is not high due to the difference of isotherm characteristics compared with zeolites, but it is possible to absorb more amount of adsorbate and to recover heat for a longer time. The energy storage density is affected by the temperature increase effect and the uptake amount of adsorbate during the adsorption reaction. The experimental results show that the energy storage density of zeolite 13X is 15% and 28.7% higher than that of silica gel and 4A, respectively, and the temperature rise due to heat generation during adsorption reaction is also high, which is advantageous in adsorption TES system performance.     

Adsorption properties of a natural zeolite–water pair for use in adsorption cooling cycles

The equilibrium adsorption capacity of water on a natural zeolite has been experimentally determined at different zeolite temperatures and water vapor pressures for use in an adsorption cooling system. The Dubinin–Astakhov adsorption equilibrium model is fitted to experimental data with an acceptable error limit. Separate correlations are obtained for adsorption and desorption processes as well as a single correlation to model both processes. The isosteric heat of adsorption of water on zeolite has been calculated using the Clausius–Clapeyron equation as a function of adsorption capacity. The cyclic adsorption capacity swing for different condenser, evaporator and adsorbent temperatures is compared with that for the following adsorbent–refrigerant pairs: activated carbon–methanol; silica gel–water; and, zeolite 13X–water. Experimental results show that the maximum adsorption capacity of natural zeolite is nearly 0.12 kg_w/kg_ad for zeolite temperatures and water vapor pressures in the range 40–150 °C and 0.87–7.38 kPa.