新型压缩／喷射冰箱混合制冷循环理论及实验研究

针对双门冰箱冷冻室及冷藏室温差较大的特点,提出了一种新型压缩/喷射混合制冷循环,并加工制造了新循环冰箱,降低了冷藏室与蒸发器之间由于温差过大造成的有效能损失。以R12以及它的可能替代物R152a、R134a、R22/R152a等作为制冷剂的模拟计算结果表明:新循环性能系数COP及容积制冷量较原蒸汽压缩循环有明显提高。实验结果表明:新循环冰箱,具有明显的节能效果。     

环丙烷热力性能的理论分析与实验研究

通过对RC270、R600a及R134a三种制冷剂热力性能的理论研究,对比分析表明RC270的单位容积制冷量比R600a大144.5%,比R134a大33.8%,其性能系数COP比R600a高出5.9%,比R134a高出9.7%;同时,针对家用冷藏冷冻箱BCD-228,根据国家标准的相关要求,对家用冷藏冷冻箱分别使用RC270、R134a两种制冷剂的制冷循环性能进行了实验研究,实验结果表明,RC270比R134a节能4.7%,能效指数降低2.9%,研究结果对RC270新型制冷剂推广应用具有一定的参考价值。     

独立式过冷循环对改善单级蒸气压缩制冷系统性能分析

过冷循环是改善单级蒸气压缩制冷系统性能的有效途径。本文以基加利修正案后可选替代制冷剂为分析对象,对带独立式过冷循环的单级蒸气压缩制冷循环的压缩机单位容积制冷量、压力比、排气温度、压缩机功耗、系统性能系数、损失和效率随蒸发温度的变化规律进行分析。结果表明:在固定蒸发温度和固定冷凝温度时,存在最佳过冷度Tsopt使系统COP最大。在最佳过冷度下,独立过冷循环使得系统的性能系数COP明显增大,采用独立过冷循环使R744提高性能效果最明显,R717增大幅度最小。13种不同的工质中,R600a、R152a、R161、R134a、R1234ze系统性能系数COP高于R22。独立过冷循环使系统压缩机总输入功W和损减少, 效率η_χ明显增大。文章揭示了不同工质在引入独立过冷循环的单级蒸气压缩式制冷循环的变化规律,为单级蒸气压缩式制冷循环性能改进提供参考。     

梯级吸排气循环理论及应用

为了提升蒸气压缩式制冷/热泵装置的能效,提出了一种新循环——梯级吸排气循环.通过设置数个具有一定梯度的吸排气压力,实现制冷剂对换热流体温度的梯形逼近,有效减小蒸发器与冷凝器的传热不可逆损失,同时降低循环压比.梯级吸排气循环的实际节能效果受多种因素影响,研究表明:换热流体温度变化幅度以及蒸发器与冷凝器传热能力强弱对其节能...     

回热器对制冷循环性能影响的研究

分析了回热器对理论制冷循环性能的影响,考虑了制冷剂质量流量变化和压力损失时的影响,推导出了回热器对制冷循环性能影响的理论计算方法.并计算出了R22、R134a等常用制冷剂及替代制冷剂在标准工况下回热器对理论制冷循环性能的影响,对工程实践有一定的指导意义.     

一种喷射器膨胀直接供液制冷循环及性能分析

很多环保制冷剂如(R1234ze(E))具有蒸发压力低的特点,影响了其制冷性能。提出了将两相喷射器作为膨胀部件,将汽液分离后的纯液体供给蒸发器的直接供液式喷射器膨胀制冷循环(EERC)。以汽车空调系统为例,研究了循环COP与单位容积制冷量,结果表明采用R1234ze(E)的EERC循环相对于采用R134a的传统循环(TRC)COP提升在22%以上,并且容积制冷量也得到大幅提升,与采用R134a的容积制冷量的差距从33%左右减小到了6%—12%;在高冷凝温度和低蒸发温度工况下,性能改善更加明显。直接供液式EERC无论是直接用来替代现有制冷循环,还是用在环保制冷剂特别是低压环保制冷剂替代传统制冷剂的场合都是一个很好的选择。     

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。     

碳氢化合物在冷冻箱系统中的试验研究

通过对同一台冷冻箱的不同制冷剂循环系统的反复测试,从制冷循环的多个参量分析中给出了替代制冷剂R600a/R290的实际循环效果,非共沸混合制冷剂作为中小型制冷装置中的直接替代物,能够满足原系统的温度、压力要求,其充注量仅为R12的35%～40%.     

R290/R134a用于家用空调器的性能匹配分析

对具有低可燃性的R290/R134a空调器样机与原R290空调器进行性能对比试验,并改变制冷剂充注量、毛细管长度、电子膨胀阀步数、换热器管径等对系统进行优化设计,使系统达到最佳匹配效果。试验结果表明：优化后的R290/R134a空调器样机的制冷能力最高达2 786 W,能效比为3.41,符合国家标准GB12021.3—2010的2级能效的要求。     

Performance study on air-cooled household refrigerator with cold storage phase change materials

The air-cooled frost-free refrigerator has become the main power consumer among household appliances. This study presents a new air-cooled household refrigerator that uses PCM in the fresh food and freezing chambers. Operational characteristics and performance test results are provided in the conditions of off-peak refrigeration with PCM and conventional refrigeration with/without PCM. Results show that refrigeration off-peak modes resulted in the peak temperature difference between M-packs and maximum temperature increase of M-packs in the freezing chamber. The energy consumption of the refrigerator is relatively increased. The energy consumption of the refrigerator prototype with PCM under the original control mode is reduced by 18.6% and the compressor ON-time ratio is reduced by 13.6% compared with the refrigerator prototype without PCM. Frost-free refrigerator with PCM under original control type exhibits advantages in terms of energy consumption and food quality.     

Performance optimization of a Lorenz-Meutzner cycle charged with hydrocarbon mixtures for a domestic refrigerator-freezer

A Lorenz-Meutzner cycle (called the “LM cycle”) for a domestic refrigerator-freezer (RF) has energy saving potential because of lower entropy generation in the fresh food compartment (R)-evaporator and lower compression ratio due to higher mean evaporating temperature, compared to a conventional cycle using pure refrigerant. In this study, a thermodynamic analysis for the optimum compositions of hydrocarbon (HC) mixtures and cycle specifications was performed. In addition, the effects of the refrigerant charge, capillary tube, compressor capacity, and mixture composition on the performance of the LM cycle using R-290/R-600 were investigated experimentally. Based on the experimental data, the energy consumption of the optimized LM cycle using R-290/R-600 (40:60%) was 11.2% lower than that of a bypass two-circuit cycle using R-600a in the same RF platform.     

Investigation on gradient thermal cycle for power and refrigeration cogeneration

In order to improve energy utilization efficiency of low grade heat, a novel gradient thermal cycle for power and refrigeration cogeneration is proposed. The cycle is cascaded with two stages based on different thermal driven temperature. The first stage is pumpless Organic Rankine Cycle (PRC) while the second stage is two-stage sorption refrigerator. R245fa is selected as the working fluid of PRC, whereas CaCl₂-BaCl₂-NH₃ working pair is chosen for two-stage sorption refrigerator. Different heat source temperatures from 80°C to 95°C are adopted for analysis and comparison. Results indicate that the highest average power output and cooling effect are able to reach 204 W and 0.91 kW under the condition of 95°C heat source temperature and 10°C refrigeration temperature. For different heat source temperatures, total energy and exergy efficiency of the gradient thermal cycle for power and refrigeration cogeneration range from 9.49% to 9.9% and 10.9% to 11.8%, respectively. For gradient thermal cycle exergy efficiency of heat utilization ranges from 24% to 18.8% which is 126.5% and 70.9% higher than the PRC and two-stage sorption refrigerator, respectively, when the heat source temperature is 80°C.     

Experimental study of R1234yf as a drop-in replacement for R134a in a domestic refrigerator

This paper presents an experimental study for three identical domestic refrigerators using R1234yf as a drop-in replacement for R134a. An alternative methodology was proposed to estimate the optimal mass charge for R1234yf; with the use of such methodology, new evidences were sought on the thermal behavior of the refrigerator compartments as well as at the heat exchangers. Additionally, energy performance for both refrigerants was measured, and, finally, a TEWI analysis was conducted. For the type of refrigerator evaluated, results showed that R1234yf presented an average (for the 3 refrigerators) of 0.4 °C for the fresh food compartment, and 1.2 °C for the freezer, among different charges with respect to R134a. The optimal charge for R1234yf was 92.2 g, which is about 7.8% lower than the one for R134a, which represents a small increase of 4% in energy consumption in comparison to R134a. Finally, the TEWI analysis for the R1234yf was 1.07% higher than the R134a.     

脉冲管制冷机蓄冷器中交变流动过程理论分析

建立了交变流动蓄冷器热力学模型,分析了蓄冷器中气体微团的热力学变化过程,经计算得出了一周期内总热量和压力波与质量流之间相位的关系,对蓄冷器在制冷系统中的作用提出了新的认识,并通过对脉冲管蓄冷器中交变流动热力学特性的分析,对比一典型的双向进气型脉冲管制冷机的实验测量结果,分析了双向进气环流产生的直流分量对蓄冷器的影响,对脉冲管双向进气产生的直流分量对脉冲管制冷性能的影响提出了新的解释。     

Testing of propane/isobutane mixture in domestic refrigeratorsEtude sur un mélange propane/isobutane dans les réfrigérateurs domestiques

The performance of a propane/isobutane (R290/R600a) mixture was examined for domestic refrigerators. A thermodynamic cycle analysis indicated that the propane/isobutane mixture in the composition range of 0.2 to 0.6 mass fraction of propane yields an increase in the coefficient of performance (COP) of up to 2.3% as compared to CFC12. For the actual tests, two commercial refrigerators of 299 and 465 l were used. For both units, all refrigeration components remained the same throughout the tests, except that the length of the capillary tube and amount of charge were changed for the mixture. Each refrigerator was fully instrumented with more than 20 thermocouples, two pressure transducers, and a digital watt/watt-h meter. For each unit, both ‘energy consumption test’ and ‘no load pull-down test’ were conducted under the same condition. The experimental results obtained with the same compressor indicated that the propane/isobutane mixture at 0.6 mass fraction of propane has a 3–4% higher energy efficiency and a somewhat faster cooling rate than CFC12. The mixture showed a shorter compressor on-time and lower compressor dome temperatures than CFC12. In conclusion, the proposed hydrocarbon mixture seems to be an appropriate long term candidate to replace CFC12/HFC134a from the viewpoint of energy conservation requiring minimal changes in the existing refrigerators.     

Thermal performance analysis for hot-wall condenser and evaporator configurations in refrigeration appliances: Analyse des performances thermiques pour des configurations de condenseurs et d'évaporateurs sous paroi chaude, pour des applications frigorifiques

A sensitivity study is presented about the investigation of the influence exerted by the design parameters on the thermal performance of those refrigeration appliances employing hot-wall condenser and evaporator configurations, compared to the usual refrigerators, in which external heat exchangers are used.The heat transfer rates inside the wall of the hot-wall refrigerator were evaluated by means of a parametric finite element model; in particular, a chest freezer for domestic applications was considered. A thermodynamic approach was employed to assess the relative heat transfer merits of the apparatus (in respect of a usual refrigerator) from the point of view both of the thermodynamic performance and of capacity. The sensitivity analysis of the design parameters affecting the performance was developed (for fixed working temperatures) with reference to the thickness of the metallic plates, the thickness of the insulating foam, the evaporator and condenser tube diameters and pitches, and the thermal contact resistance between the tubes and the plates.The results show the great importance of the 2-D heat conduction in the metallic plates (`fin efficiency effect'), evidencing how the plate thickness and the thermal contact resistance between the refrigerator plates and the tube serpentines affects the global effectiveness of the system.Some practical suggestions are drawn in conclusion on the criteria which should be adopted in the thermal design of a hot-wall refrigerator.     

Start-up and shut-down operation in a reciprocating compressor refrigeration system with capillary tubes

Refrigerant migration during start-up and shut-down cycles can affect energy losses. Two reciprocating compressor refrigeration systems were studied: (1) a conventional cycle with refrigerant migration through the capillary tube after compressor shut-down and (2) a system in which a magnetic cut-off valve was closed on compressor shut-down. It was found that by preventing the refrigerant from migrating during shut-down, energy losses during start-up could be reduced, resulting in a 4% decrease in motor power input at this time. A computer program has been developed to calculate energy losses due to refrigerant migration.     

可逆脉管制冷循环与斯特林制冷循环的比较

建立了可逆脉管制冷机的等温－绝热模型，着重考虑脉管中过程对制冷机性能的影响，并与斯特林制冷机等温模型的计算机结果进行比较。结果表明，在理想工况下，可逆脉管制冷机的效率约为斯特林制冷机的８５％，制冷量约为７２％。可逆脉管制冷机配气活塞的最佳运动相位与斯特林制冷机基本相同。     

振荡管结构对气波制冷机制冷性能影响的研究

振荡管是入射气体与管内循环气进行能量交换的场所，是气波制冷机的一个重要组成部分。其结构形式的不同对管内流动产生很大的影响，进而影响气波制冷机的制冷性能。在分析了各种结构振荡管对气波制冷机性能的影响的基础上，着重分析了双开口振荡管的结构及制冷原理、管内的流动并通过实验研究了其对气波制冷机性能的影响。结果表明，采用双开口振荡管不仅能消除反射激波提高制冷效率，而且大大地优化了整机的结构，使体积仅为原来的十分之一左右。