R410A双级压缩热泵空调器的特性分析

针对空调器在夏季环境温度高,冬季环境温度低时制冷能力和制热能力不足的问题,提出采用双级压缩制冷循环的方案提高系统制冷量、制热量和制冷COP、制热COP。选择制冷剂R410A,双级循环为一级节流中间不完全冷却的方式进行比较和分析,计算得到单级和双级压缩制冷循环的性能参数变化特征;并说明了该循环最佳中间温度和单机两级压缩机配比的合理选择。     

应用于数据中心冷却的空气制冷循环系统性能分析

本文提出一种适用于数据中心冷却的空气制冷循环系统,采用数值模拟的方法研究了压比π、环境温度（室外环境温度Tk、室内制冷温度T0）、转动部件效率（压气机效率ηc、膨胀机效率ηt）对循环性能的影响规律及系统优化途径,并分析了由空气制冷与自然冷却组成的复合系统在典型气候区城市的适用性。结果表明：实际空气制冷循环存在最佳压比,其值介于1.5~2.0之间;循环单位制冷量、制冷性能系数COP随Tk的降低或T0的升高而增大;相比于压气机,膨胀机效率对系统性能的提升更为关键;在实际循环（ηc=ηt=0.8）的最佳压比工况下,增加回热可使制冷COP提升22%;复合系统在呼和浩特运行的AEER可达14.61,表明其在全年自然冷却时长较长的地区更具优势。     

水多级压缩式制冷循环理论研究

针对水作为制冷工质的特点，提出了以水三级压缩式制冷循环的系统流程，对循环性能系数COP、排气温度和输气容积比进行了分析和计算。分析表明，以水作为制冷工质，其循环的理论COP均高于R22、R134a。由于水压缩式制冷循环具有较高的排气温度，因而在中高温热泵领域，以水为工质是具有竞争力。     

CO2低温制冷循环热力学分析

通过对CO2单级压缩和双级压缩制冷循环的热力学分析得出,在一定的蒸发温度和冷凝温度下,CO2单级压缩制冷循环的COP比CO2双级压缩制冷循环的COP低、压差大、压比高.因此,CO2低温制冷循环系统应采用双级压缩制冷循环,为提高CO2双级压缩制冷循环的循环效率,应尽可能升高蒸发温度、降低冷凝温度,可以看出自然工质CO2双级压缩制冷循环有很好的发展前景.     

制冷工质引射式减压原理及其技术应用

分析常规蒸气压缩制冷系统存在的不足,介绍引射式减压原理,并将其技术应用于制冷(热泵)循环系统,提出新型压缩/喷射制冷循环系统。对改进后的新型制冷系统进行热力学分析,结合制冷工质R134a的制冷工况特性,得出改进后新型制冷系统的优越性能,即提高制冷系统的能量利用效率。对制冷和空调系统节能研究具有一定的指导意义。     

二甲醚作为中高温热泵工质的性能分析

对二甲醚（DME）作为中高温热泵工质的热工性能进行计算与分析,与传统热泵工质R22,R134a及自然工质R600a进行对比,并对变工况（冷凝温度75～95℃,固定循环温升45℃）进行理论计算。计算结果表明,DME制热性能参数与R134a接近,但COP值高于R134a,单位容积制热量在高温工况下具有更出色的性能。而且DME的GWP与ODP值均接近零,可作为绿色环保替代工质直接充注至R134a热泵系统,并可应用于中高温环境。     

R22替代工质回热循环的性能分析

R22的替代工质的制冷性能通常比R22差，采用回热循环是改善循环性能的一种方法，但是增加回热器会带来成本的增加，而且不同的制冷剂在回热循环中的COP及容积制冷量的变化也是不同的。针对上述问题，分析回热循环的特性和6种制冷剂（R290，R1270，R134a／R1270（0．45／0．55），R134a／R290（0．6／0．4），R407C和R410A）在回热循环中的容积制冷量和COP的变化特点。研究结果表明，R134a,／R1270，R290和R134a／R290系统使用回热器后，性能改善较大，R410A系统只有在高冷凝温度、高过热度时才有必要使用回热器，其余替代工质系统使用回热器，其系统性能改善不明显。     

R32和R22过热度对转子式压缩机制冷系统影响的对比

利用变频滚动转子式压缩机制冷循环实验台,研究了R32和R22制冷系统过热度对系统性能的影响。定量分析了R32制冷系统在过热状态下的一些规律,并且通过对比工况1#下R32和R22的系统参数,分析了R32优于R22的原因,研究了R32商用空调最佳过热度的调节范围。结果表明:R32制冷系统各项参数变化趋势与R22基本一致,R32制冷系统具有较好的制冷效果;在工况1#下,相比R22制冷系统,R32系统的制冷量提高约为42%,COP提高6.8%,系统压比增加7%左右,系统性能更稳定;在空调工况下,R32系统过热度控制在4℃以内,具有较好的节能效果。     

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。     

地埋管换热器变热流工况下换热模型及其试验验证

在制冷空调产品及热泵热水机国家标准规定的名义工况下,比较CO2跨临界循环与R22,R410A和R404A单级蒸气压缩循环的理论循环效率。结果表明：在空调制冷名义工况下,R22理论循环效率最高,CO2的理论循环效率只有R22的50％～60％;在热泵热水机名义工况下,CO2的理论循环效率最高,可以达到R22的145％;CO2跨临界循环受冷却器压力及出口温度2个方面的影响,适当降低CO2冷却器出口温度可改善循环效率,应用CO2制冷剂需要通过改善循环和优化控制提高系统的能效。     

A combined-cycle refrigeration system using ejector-cooling cycle as the bottom cycle

A combined-cycle refrigeration system (CCRS) that comprises a conventional refrigeration and air-conditioning system using mechanical compressor (RAC/MC) and an ejector-cooling cycle (EJC) is proposed and studied. The EJC is driven by the waste heat from the RAC/MC and acts as the bottom cycle of the RAC/MC. A system analysis shows that the COP of a CCRS is significantly higher than a single-stage refrigeration system. Improvement in COP can be as high as 18.4% for evaporating temperature of the RAC/MC T_e at −5°C. A prototype of the CCRS was built and tested in the present study. Experimental results show that at T_e=−4.5°C, COP is improved by 14% for a CCRS. For T_e at 5°C, COP can be improved by 24% for a CCRS with higher condensing temperature of the RAC/MC. The present study shows that the CCRS using the ejector-cooling cycle as the bottom cycle of the RAC/MC is viable. Further improvement in COP is possible since the prototype is not designed and operated at an optimal condition.     

Hybrid vapor compression refrigeration system with an integrated ejector cooling cycle

A refrigeration system was developed which combines a basic vapor compression refrigeration cycle with an ejector cooling cycle. The ejector cooling cycle is driven by the waste heat from the condenser in the vapor compression refrigeration cycle. The additional cooling capacity from the ejector cycle is directly input into the evaporator of the vapor compression refrigeration cycle. The governing equations are derived based on energy and mass conservation in each component including the compressor, ejector, generator, booster and heat exchangers. The system performance is first analyzed for the on-design conditions. The results show that the COP is improved by 9.1% for R22 system. The system is then compared with a basic refrigeration system for variations of five important variables. The system analysis shows that this refrigeration system can effectively improve the COP by the ejector cycle with the refrigerant which has high compressor discharge temperature.     

Theoretical analysis and optimization of a hybrid CO2 transcritical mechanical compression – ejector cooling cycle

The paper provides the results of a design-theoretical study of a hybrid carbon dioxide (CO₂) transcritical mechanical compression – ejector cooling cycle. The hybrid cooling cycle is a combination of a CO₂ transcritical mechanical compression refrigeration machine (MCRM) powered by electricity, and an ejector cooling machine (ECM) driven by heat rejected from the CO₂ cooling cycle. Refrigerants R245ca, R601b (neopentane) and R717 (ammonia) are investigated as the working fluids of ECM in the present study. A method to determine the optimal design parameters and performance of the hybrid cooling cycle is presented. It is shown, that efficiency growth of the transcritical CO₂ cooling cycle due to ejector cooling cycle use is higher as evaporating temperatures are lower.     

Performance analysis of a combined system for cold and power

This paper presents a theoretical study of a combined thermal system, which combines the Rankine cycle and the ejector refrigeration cycle. This combined cycle produces power and refrigeration simultaneously. The thermal system could use low temperature heat sources. A simulation was carried out to evaluate the cycle performance using several working fluids as R123, R141b, R245fa, R601a and R600a. A one-dimensional mathematical model of the ejector was developed using the equations governing the flow and thermodynamics based on the constant area ejector flow model. The ejector is studied in optimal operating regime. The influence of thermodynamic parameters on system performance is studied. The results show that the condenser temperature, the evaporation temperature, the extraction ratio, the fluid nature and the generating temperature have significant effects on the system performances (the coefficient of performance of the combined cycle and the entrainment ratio of the ejector).     

跨临界CO2两相流引射制冷系统性能实验研究

对跨临界CO2两相流引射制冷系统性能进行了实验,分析了工况及引射器几何参数对系统性能的影响,结果表明:在实验工况范围内,跨临界CO2两相流引射制冷系统制冷量和COP随气体冷却器压力的升高而升高,随气体冷却器出口温度的升高而降低。对于使用不同喉部直径喷嘴的系统,在相同工况下,引射器喷嘴喉部直径较大的系统的性能较好。对于使用不同直径混合室的系统,随着气体冷却器压力的升高,使用小直径混合室的系统COP变化较大;当气体冷却器压力较低时,使用大直径混合室的系统COP较高,而当气体冷却器压力较高时,使用小混合室直径的系统性能较好。在相同工况下,与传统跨临界CO2循环进行比较,两相流引射制冷循环系统COP最大可提高14%。     

Design-theoretical study of cascade CO2 sub-critical mechanical compression/butane ejector cooling cycle

In this paper an innovative micro-trigeneration system composed of a cogeneration system and a cascade refrigeration cycle is proposed. The cogeneration system is a combined heat and power system for electricity generation and heat production. The cascade refrigeration cycle is the combination of a CO₂ mechanical compression refrigerating machine (MCRM), powered by generated electricity, and an ejector cooling machine (ECM), driven by waste heat and using refrigerant R600. Effect of the cycle operating conditions on ejector and ejector cycle performances is studied. Optimal geometry of the ejector and performance characteristics of ECM are determined at wide range of the operating conditions. The paper also describes a theoretical analysis of the CO₂ sub-critical cycle and shows the effect of the MCRM evaporating temperature on the cascade system performance. The obtained data provide necessary information to design a small-scale cascade system with cooling capacity of 10 kW for application in micro-trigeneration systems.     

Use of ejectors in a multi-evaporator refrigeration system for performance enhancement

In this study, an improved cooling cycle for a conventional multi-evaporators simple compression system utilizing ejector for vapour precompression is analyzed. The ejector-enhanced refrigeration cycle consists of multi-evaporators that operate at different pressure and temperature levels. A one-dimensional mathematical model of the ejector was developed using the equations governing the flow and thermodynamics based on the constant-area ejector flow model. The model includes effects of friction at the constant-area mixing chamber. The energy efficiency and the performance characteristics of the novel cycle are theoretically investigated. The comparison between the novel and conventional system was made under the same operating conditions. Also, a comparison of the system performances with environment friendly refrigerants (R290, R600a, R717, R134a, R152a, and R141b) is made. The theoretical results show that the COP of the novel cycle is better than the conventional system.     

双分层水箱太阳能喷射制冷循环特性

本文提出一种采用双分层水箱的太阳能喷射制冷循环,分层水箱热分层显著,颇具可用能储存优势,结合大小水箱各自的优势弥补因太阳日辐射量波动而导致太阳能利用率不高、太阳能驱动的喷射制冷效率较低等问题。采用逐时冷负荷分析法分析了双分层水箱太阳能喷射制冷系统特性,结果表明:该制冷循环高品位能耗约为普通机械压缩制冷循环的1/5,较传统水箱太阳能喷射制冷循环全天工作时间约多4 h,日产冷量提高36.8%,且分层水箱喷射制冷系统的逐时制冷量与办公室逐时冷负荷更吻合。     

Performance analysis of a two-stage mechanical compression–ejector cooling cycle intended for micro-trigeneration system

This paper provides the results of a performance analysis of a two-stage mechanical compression–ejector cooling cycle. In the proposed cooling system the compression process is realized in two stages: by a mechanical compressor as the first stage and by an ejector as the second stage. Ammonia (R717) is investigated as the working fluid for the cooling system in the present study. The influence of the middle pressure, and evaporating and condensing temperatures on the characteristics of the cooling system is analyzed. Based on the obtained results a pilot small-scale two-stage refrigeration unit with cooling capacity of 10 kW intended for application in micro-trigeneration systems is designed.     

Development and performance analysis of a multi-temperature combined compression/ejection refrigeration cycle using environment friendly refrigerants

A combined compression/ejection refrigeration cycle intended for the simultaneous production of cold for refrigeration and freezing, and operating based on environment friendly refrigerants is proposed and analyzed in this study. This makes it possible to valorize the low-temperature heat sources in the ejector cycle, thereby reducing the share of mechanical energy otherwise required to operate the conventional two-stage vapor compression system.A selection of eight candidates' fluids was performed. The developed simulation model helped to establish the strong dependence between system performances and the ratio of the cooling capacities of refrigeration and freezing. In addition to the effect of the temperature level of cold production, the influence of the ambient temperature on system performance was also analyzed when using refrigerants R290, R152a and R134a.