Evaluation of minimum desorption temperatures of thermal compressors in adsorption refrigeration cycles

The purpose of this paper is to identify the minimum desorption temperatures required to operate thermally driven adsorption beds of a solid sorption refrigeration system. The method is based on the evaluation of uptake efficiency of the adsorption bed and estimating there from conditions under which the compressor ceases to provide any throughput. The difference in the densities of the refrigerant between the inlet and outlet, the adsorption characteristics of the adsorbate–refrigerant pair and the void volume in the thermal compressor are the contributors to the manifestation of the desorption state. Among them, the void volume is a controllable parameter whose role is analogous to the clearance volume in a positive displacement compressor. The methodology has been tested out with three systems, namely, silica gel + water, activated carbon fiber + ethanol and activated carbon + HFC 134a systems. It is shown that waste heat at as low as 60 °C can operate these systems which make them good energy conservation devices through recovery of low grade process waste heat.     

Second-law-based thermodynamic analysis of two-stage and mechanical-subcooling refrigeration cycles

Thermodynamic analysis of HFC-134a vapor-compression refrigeration cycles is investigated by both the first and second laws of thermodynamics. Second-law analysis is carried out for both two-stage and mechanical-subcooling refrigeration cycles. The analysis is performed on each of the system components to determine their individual contribution to the overall system irreversible losses. It is found that most of the losses are due to a low compressor efficiency. Irreversibilities of expansion valves and condenser are also significant. In addition, it is shown that the optimum inter-stage pressure for two-stage and mechanical-subcooling refrigeration systems is very close to the saturation pressure corresponding to the arithmetic mean of the refrigerant condensation and evaporation temperatures. These results are compared with the existing practice in the industry. Furthermore, theoretical results of a two-stage refrigeration system performance are also compared with experimental values for a CFC-22 system.     

以R134a为制冷剂的喷射制冷理论分析及其CFD模拟

介绍以R134a为制冷剂的太阳能喷射制冷系统，并对系统核心部件喷射器进行CFD模拟，根据CFD模拟结果确定喷射器的最佳结构尺寸。在此基础上，对该系统进行理论分析。在发生温度90℃、蒸发温度0℃、冷凝温度34℃的条件下，系统COP可以达到0．182。     

改进的R23/R134a自复叠制冷系统试验台设计

为了研究R23/R134a混合工质自复叠制冷系统在变工况下的运行性能,更深入地了解系统各部件对自复叠循环的影响,设计一套试验装置。该装置对现有循环流程进行改进,增加了电磁阀、膨胀容器等部件。对该系统的运行工况、参数范围以及系统的各部件进行设计或选型,并介绍所搭建的试验台。     

Performance of ejector cooling systems using low ecological impact refrigerants

The theoretical behaviour of an ejector cooling system, using as working fluids propane, butane, isobutane, R152a and R134a, is obtained. The ejector works as a thermo-compressor that is simulated with a validated one-dimensional mathematical model, whose errors are lower than 6%. For a system unitary cooling capacity, a parametric study is carried out varying the generation, condensation and evaporation temperatures. From the obtained data, a complete analysis of the system performance can be achieved when the ejector and system operation parameters are considered. The best performance corresponds to the system using propane, because has the highest system coefficient of performance and its ejector has the maximum entrainment ratio value, the least area ratio value and the highest efficiency value. The considered generation temperature ranging from 70 °C to 95 °C is appropriate for low-grade energy sources assisting thermal cooling systems. After this system performance, come those in which R152a and R134a are employed, with isobutane and butane at the end. The obtained results represent potential design points of an efficient ejector cooling system operation, because to each combination of the above mentioned temperatures corresponds one and only one ejector geometry.     

二甲醚作为汽车空调制冷剂的性能研究

对二甲醚（DME）在用作汽车空调制冷剂与现有R134a汽车空调制冷剂在基础热力性质、汽车空调标准工况和变工况下制冷循环性能进行了对比分析，并作理论计算。分析表明：二甲醚的制冷性能与R134a基本相似，而性能系数COP却优于R134a。因此，更具环保优势的二甲醚是一种理想的潜在的汽车空调制冷剂。     

二甲醚作为汽车空调制冷剂的性能研究

本文对二甲醚（DME）用作汽车空调制冷剂的性能与现有汽车空调制冷剂R134a进行了对比。首先比较了二甲醚和R134a的基础热力性质，然后对二甲醚和R134a的汽车空调标准工况和变工况下制冷循环性能进行了详细的理论计算及分析。分析表明：二甲醚的制冷性能与R134a基本相似，而性能系数（COP）却优于R134a。因此，更具环保优势的二甲醚是一种理想的潜在的汽车空调制冷剂。     

改进的R23/R134a自复叠制冷系统实验研究

为了研究R23/R134a混合工质自复叠制冷系统在变工况下的运行性能,更深入地了解系统各部件对自复叠循环的影响,在已建成的自复叠循环系统实验台上进行实验研究.在冷凝温度较高的夏季,测试该自复叠实验装置所能达到的最低蒸发温度,并研究冷凝温度、工质充注质量分数及蒸发冷凝压力对该系统的影响.     

Performance degradation of a vapor compression refrigeration system under fouled conditions

Performance degradation due to fouling in a vapor compression cycle is investigated for various applications. Considering the first set of refrigerants i.e. R134a, R410A and R407C, from a first law standpoint, the COP indicates that R134a always performs better unless only the evaporator is being fouled. In contrast to this, from a second-law standpoint, the second-law efficiency indicates that R134a performs the best in all cases. Considering the second set of refrigerants i.e. R717, R404A and R290, from a first law standpoint, the COP indicates that R717 always performs better unless only the evaporator is being fouled. In contrast to this, from a second-law standpoint, the second-law efficiency indicates that R717 performs the best in all cases. Volumetric efficiency of R410A and R717 remained the highest under the respective conditions studied. Furthermore, performance degradation of the evaporator often has a larger effect on compressor power requirement while that of the condenser has an overall larger effect on the COP. A new performance degradation law is presented in light of the data generated, which can reduce the amount of experimentation and help predict relevant quantities of the refrigeration system.     

风冷螺杆热泵机组制冷剂替换试验研究

对R22、R407c、R134a三种制冷剂的基本物性及热力性能进行了分析比较，并在风冷螺杆热泵机组基础上进行了替换试验研究。结果表明：R407c为最佳替换R22的制冷剂；R134a替换后能效比较高，但制冷（热）量衰减过多，同时R134a的运行压力过低不太适合热泵工况。     

板式蒸发器换热性能的数值模拟Ⅰ:数学模型

采用分布参数法对波纹型多通道单流程板式蒸发器建立数学模型,通过计算局部蒸发换热系数和摩擦压降可以简化板式蒸发器内复杂三维流动的换热关系.总结了文献已有的各种换热和压降关联式,并添加到模型控制方程组中.基于此模型,可对目前应用较广的R134a和R410A制冷荆的板式蒸发器在小换热温差下的换热性能进行研究.     

板式蒸发器换热性能的数值模拟Ⅱ:结果及分析

在已建立的数学模型的基础上,对板式蒸发器换热能力进行了数值模拟.针对应用较广的R134a和R410A制冷剂来比较和分析板式蒸发器在小的温差下的换热性能.在三种不同的计算工况下简要分析了各种热力参数的变化对蒸发器整体换热性能的影响.不同的制冷剂,其换热系数和压降差别较大,相同工况下采用R410A替代R22,板式蒸发器的换热性能可提高8.5%～10.0%,且压降可大幅降低.     

R134a/R600a混合制冷剂应用于大型空气源热泵的性能研究

R134a作为当前主要的R22替代制冷剂,在应用于空气源冷水(热泵)机组,尤其是在热泵运行时会出现能效降低、容易结霜等问题。本研究尝试在R134a的大型螺杆式空气源热泵机组中混合少量R600a来改善机组性能。通过对混合制冷剂物性计算、理论循环性能计算和机组试验,表明添加R600a后的混合制冷剂能显著改善热泵机组的运行性能,并有效提高机组运行可靠性。同时,虽然R600a具有可燃性,但是对于运行时置于室外,介质为水且添加比例不高的空气源热泵机组,这是一个简单、安全、可行的改进方案。     

R134a和R22在水源热泵应用中的性能研究和比较

用R134a和R22作为制冷剂在相同的水源热泵系统里进行实验,对比研究了各自的性能及其冷凝出水范围。实验结果表明:在相同的蒸发进水温度和冷凝出水温度下R22有着较高的制热量,高约30%,但是R134a的COP相对较高,高约5%;特别是在高温时R134a的压比以及功耗都在正常的工作范围内。     

R11与R134a离心式制冷机组性能比较

从环保、节能、热力性能及装置等方面对化工企业使用的R11与R134a大型离心制冷机组进行比较,并对R134a离心机组在使用过程中的常见问题提出改进建议。     

R134a单元式风冷冷风机组冷凝器设计

单元式风冷冷风空调机组普遍采用波纹翅片管冷凝器。对冷凝器进行设计的关键是确定制冷工质在铜管内的冷凝换热系数及空气在翅片侧的表面换热系数，同时也需要考虑空气流过冷凝器的压降，以便选择风机。采用数学模型及换热关联式计算相关参数，在此基础上对R134a单元式风冷冷风空调机组的冷凝器进行设计。     

R134a在水平强化管外凝结换热的实验研究

对氟利昂R134a在水平单管外的凝结换热性能进行了试验研究,试验管为光管和三根强化管,采用热阻分离法得到蒸气侧凝结换热系数。试验结果表明:光管管外Nusselt理论值与实验数据偏差小于10%。强化管No.1-3的传热性能均好于光管,当Re=40000时,No.1-4管的总传热系数分别为:5295,5818,5904,1502W/m2.K。在相同热流密度条件下,No.1-3管的管外换热系数分别是光管的7.0-8.8倍,9.0-10.8倍,9.9-12.0倍。管外强化后,管内外的换热系数已比较接近。     

R134a单元式风冷冷风空调机蒸发器设计

以理论模型为基础，对R134a单元式风冷冷风机组翅片管式蒸发器进行设计。应用管内流动沸腾换热模型仿真分析R134a的质量流量对沸腾换热的影响，利用外掠翅片管束换热关联式计算管外翅片侧表面换热系数，进而得出翅片管蒸发器总传热系数，利用计算结果进行设计。     

R134a螺杆制冷压缩机的泄漏特性研究

螺杆制冷压缩机已广泛用于工业制冷和中央空调装置中,在商用制冷与空调领域也有着良好的应用前景。本利用一套螺杆压缩机设计计算软件,对Ｒ１３４ａ螺杆制冷压缩机的泄漏特性进行了研究。首先根据螺杆压缩机的结构特点,定义了五种泄漏通道,并针对这些通道的特点,建立了相应的数学模型。然后针对不同转速和运行工况,计算了制冷剂通过这些通道的泄漏及其对压缩机效率的影响。借助分析有关计算结果,得出了一些可用于指导实际机器设计的结论。     

回热循环在R134a汽车空调系统中的应用

本文通过试验方法对回热循环在R134a汽车空调系统中的应用进行了试验研究。试验结果表明具有回热器的空调系统其COP和制冷量都能得到一定程度的提高,同时指出,低压侧压降是设计回热器时的一个关键参数,应注意减少低压侧压力损失。