Experimental analysis of a novel cooling system driven by liquid refrigerant pump and vapor compressor

This study introduced a novel energy saving cooling system, i.e. a combined cycle coupled with a traditional vapor compression cycle with a pumped liquid two-phase cooling cycle. The system has two operation modes, i.e. the compression cycle mode driven by compressor and the pump cycle mode driven by refrigerant pump. A multi-purpose test bench was constructed to experimentally evaluate the performance of the integrated cycle system under various operation conditions. The effects of cycle working condition and the shift temperature between the two operation modes on the overall cycle performance were investigated in detail. It is found that the novel cycle system has a higher EER compared to the traditional compressor system when the ambient temperature is relatively low. The further experimental results and comparative annual energy saving analysis also indicated that the proper shift temperature is about −5 °C from the system EER and cooling capacity point of view.     

机械过冷CO_2跨临界制冷循环性能理论分析

采用蒸气压缩制冷循环(辅助循环)对CO_2跨临界制冷循环气体冷却器出口的CO_2流体进行冷却,可减小节流不可逆损失,提高循环性能。本文对机械过冷CO_2跨临界制冷循环进行热力学循环分析,结果表明:当在最优排气压力和最优过冷度两个参数条件下,循环存在最大COP。环境温度越高、蒸发温度越低,采用机械过冷方法使循环性能提升越显著,相对传统CO_2制冷循环,通过辅助循环可显著提高循环COP,降低CO_2排气压力和温度。相对CO_2压缩机,辅助循环压缩机的功耗较少。分析了辅助循环中采用11种不同制冷剂的性能,可得除R41外,其它10种工质对循环整体COP的提升程度差异不明显。综上所述,机械过冷CO_2跨临界制冷循环更适用于环境温度较高、蒸发温度较低的场合。     

Performance analysis of a combined vapor compression cycle and ejector cycle for refrigeration cogeneration

A hybrid vapor compression refrigeration (HVCR) system, which combines a vapor compression refrigeration (VCR) system and an ejector refrigeration (ER) system, was developed. The waste heat energy from the gas cooler in the VCR system is applied as driven source towards ER system.Thermodynamic investigations on the performance of the HVCR system, using CO₂ as a refrigerant, are performed with energetic and exergetic methods, and the comparative analyses with the VCR system are conducted. Comprehensive effects of key operating parameters on the system performance are also studied. The results indicate that for the same cooling capacity, the coefficient of performance (COP) of the HVCR system shows 25% higher COP and the total mechanical power consumption is reduced by 20% than that of conventional VCR system, respectively. The performance characteristics of the proposed cycle show its application potential in cooling and air-conditioning.     

An investigation of the performance of a scroll compressor under liquid refrigerant injection

In this study, fundamental and practical influence of liquid refrigerant injection on the performance of a refrigerant scroll compressor has been investigated experimentally and theoretically. In the theoretical analysis, a compression model of vapor/liquid mixture is developed by taking account of heat transfer from the cylinder wall to suction, compression and injection refrigerant. An experiment has been done under the condition of keeping the oil temperature constant in order to investigate the fundamental influence of the liquid refrigerant injection on the compressor performance, and the results were compared with the theoretical ones. It was found that the injection basically increases the compression power and decreases the compressor efficiency, though the situation depends on the condition of the heat transfer to the injection refrigerant. And furthermore, the performance of the liquid refrigerant injection compressor under practical operating condition without controlling the oil temperature has been investigated. Under this condition, the compressor showed recovery and slight improvement of performance due to the decrease of the oil and cylinder temperatures by the injection. In addition, influence of the refrigerant injection on the oil viscosity and refrigerant solubility in the oil, which relate mechanical loss and reliability of the compressor, have been discussed.     

Influence of liquid receiver on the performance of reversible heat pumps using refrigerant mixtures

A liquid receiver is normally included in reversible vapour compression heat pumps (RHPs) to temporarily store the excess refrigerant charge occurring due to change of operation mode. The presence of a liquid receiver influences the total amount of refrigerant charged into a system, and particularly when using refrigerant mixtures, could affect the system circulation composition. Using a computer simulation, this paper compares the performance of RHPs designed with and without a liquid receiver, when using R407C. It was shown that the presence of a receiver caused an increase in the positive shift in the circulating composition, resulting in improved capacity while reducing the system COP in both heating and cooling modes when compared to a system without a receiver.     

再循环重力供液制冷系统实验

对重力供液制冷系统形成再循环的条件和再循环时蒸发器的传热性能进行理论分析,建立相应的数学模型。将重力供液制冷系统与直接膨胀供液制冷系统进行比较,得到两种不同制冷系统工作特性上的差异。通过在焓差实验室中测定制冷系统在不同工况下的压力、风量、制冷量以及耗功等技术参数,得到重力供液制冷系统和直接膨胀供液制冷系统在室外干球温度一定的情况下传热系数、制冷量以及系统COP的变化规律。实验表明:再循环的形成可以增大制冷剂流速同时充分润湿传热表面,强化换热效果显著,在测试的工况下蒸发器的传热系数可增大近40%,COP最大提高7.6%,低温工况的增幅更大。     

A generalized analysis for cascading single fluid vapor compression refrigeration cycles using an entropy generation minimization method

This paper focuses on cascading an ideal vapor compression cycle and determining the optimal intermediate temperatures based on the entropy generation minimization method. Only superheating and throttle losses of the cycle are considered since they are inherent to the ideal vapor compression refrigeration cycle. The second law equations have been developed in terms of specific heats and temperature ratios with the intent of reducing involved property modeling. Also the entropy generation was expressed in terms of a single independent variable and minimized to develop an advanced rule for selecting optimum intermediate temperatures. Results for a cascade system operating between reduced temperatures of 0.684 and 0.981 with R-134a as the working fluid are presented. The approximate method presented here predicted the optimum intermediate reduced temperature for a two-stage system to be 0.88, a difference of 2% from the optimum. The method presented was a much better predictor of the optimum temperature than the geometric mean method which was 0.82, a difference of 5% from the optimum. The entropy generation distribution of the optimum solution was investigated. For a two-stage system, the lower stage and higher stage entropy generation was 44% and 56%, respectively. In comparison to the single stage, the two-stage reduced losses by 78%.     

蒸发冷却式热管与蒸气压缩复合数据中心空调系统性能实验研究

为解决传统数据中心空调系统能耗高和冷却效率低等问题,本文提出了带有蒸发式冷凝器的制冷剂泵驱动热管与蒸气压缩复合数据中心空调系统,实验分析了不同室外温度与冷凝器风速下系统的运行性能.结果表明:在热管模式下,当室外温度低于0℃时,降低冷凝器风速能够提升系统COP;当室外温度高于0℃时,增大室外机风速能够提高系统节能性.降低...     

R32经济器系统涡旋压缩机中间补气参数的分析与优化

为了优化带经济器的R32空气源热泵系统的制热性能,结合涡旋压缩机的结构以及实际运行特点,本文利用MATLAB建立了系统的数学模型,并通过实验数据验证了仿真结果,研究了在不同环境温度下系统的补气压力、准一级压缩内容积比对相对喷气量的影响.研究结果表明:经济器系统较普通热泵系统,更适宜在环境温度低于-10 ℃的工况下运行;...     

Cooling mechanism of a solar assisted air conditioner: An investigation based on pressure–enthalpy chart

This paper reports a theoretical study of a conventional vapor compression air conditioner combined with a solar energy source. This system comprises two parts: the cooling mechanism and the solar heat source to operate it. Only the cooling machine part will be considered here, in which the refrigerant temperature leaving the immersed coil inside the storage tank can be calculated directly from the pressure–enthalpy diagram of the operating refrigerant. The investigation has been made using a new low global warming potential refrigerant that belongs to HFO family as an alternative to two high global warming potential refrigerants that belong to HFC family. These are R-1234ze(E) as an alternative to R-134a and R-410A. Comparisons between the classical vapor compression air conditioner and the solar assisted air conditioner and also between the selected refrigerants are investigated. The effects of the refrigerant temperature leaving the storage tank on the main performance parameters such as the coefficient of performance, the gain based on compression work, and the required condenser surface area are discussed.     

A steady and quasi-steady state analysis on the CO2 hybrid ground-coupled heat pumping system

This article contains the steady and quasi-steady state analysis on a CO₂ hybrid ground-coupled heat pumping system for warm climates. The hybrid system uses a combination of ambient air and ground boreholes as a heat sink for the cooling mode, while only the ground boreholes are used as a heat source in the heating mode. The steady state analysis suggests that the optimal control strategy of gas cooler pressure for a CO₂ hybrid transcritical cycle is based on the optimal cooling COP value and the ratio of heat rejected to ambient air. This optimal control strategy is important for decreasing the annual ground thermal imbalance performance of ground boreholes. In addition, the quasi-steady state model of a CO₂ hybrid ground-coupled heat pumping system is constructed for the hourly simulation with different boundary conditions. Simulation results show the details of the system operating characteristics both for heating and cooling modes and the COP values with different operating and design conditions are presented.     

A strategy to optimize the charge amount of the mixed refrigerant for the Joule–Thomson cooler

The performance of the mixed refrigerant (MR) Joule–Thomson cooler is mainly dependent on the MR circulation composition for a given hardware. However, it is difficult to charge the MR to the desired circulation composition, due to the composition shift. In the present study, a novel strategy was proposed to solve this problem. In this strategy, the MR Joule–Thomson cooler is first charged with the initial charge amount, which is obtained by estimating the MR inventory in the cooler using the homogeneous model. Afterwards, the cooler is started and the MR circulation composition is adjusted to the corresponding optimal composition by adding the MR charge amount stepwise. Additionally, this strategy was verified by an experiment with a ternary mixture of methane, ethane and i-butane. The experimental results indicated that the MR circulation composition was able to be adjusted to the corresponding optimal circulation composition approximately within the relative deviation of ±5%.     

Theoretical study and design of a low-grade heat-driven pilot ejector refrigeration machine operating with butane and isobutane and intended for cooling of gas transported in a gas-main pipeline

This paper describes the construction and performance of a novel combined system intended for natural gas transportation and power production, and for cooling of gas transported in a gas-main pipeline. The proposed system includes a gas turbine compressor, a combined electrogenerating plant and an ejector refrigeration unit operating with a hydrocarbon refrigerant. The combined electrogenerating plant consists of a high-temperature steam–power cycle and a low-temperature hydrocarbon vapor power cycle, which together comprise a binary vapor system. The combined system is designed for the highest possible effectiveness of power generation and could find wide application in gas-transmission systems of gas-main pipelines. Application of the proposed system would enable year-round power generation and provide cooling of natural gas during periods of high ambient temperature operation. This paper presents the main results of a theoretical study and design performance specifications of a low-grade heat-driven pilot ejector refrigeration machine operating with butane and isobutane.     

Performance of vapor compression systems with compressor oil flooding and regeneration

Vapor compression refrigeration technology has seen great improvement over the last several decades in terms of cycle efficiency through a concerted effort of manufacturers, regulators, and research engineers. As the standard vapor compression systems approach practical limits, cycle modifications should be investigated to increase system efficiency and capacity. One possible means of increasing cycle efficiency is to flood the compressor with a large quantity of oil to achieve a quasi-isothermal compression process, in addition to using a regenerator to increase refrigerant subcooling.In theory, compressor flooding and regeneration can provide a significant increase in system efficiency over the standard vapor compression system. The effectiveness of compressor flooding and regeneration increases as the temperature lift of the system increases. Therefore, this technology is particularly well suited towards lower evaporating temperatures and high ambient temperatures as seen in supermarket refrigeration applications. While predicted increases in cycle efficiency are over 40% for supermarket refrigeration applications, this technology is still very beneficial for typical air-conditioning applications, for which improvements in cycle efficiency greater than 5% are predicted. It has to be noted though that the beneficial effects of compressor flooding can only be realized if a regenerator is used to exchange heat between the refrigerant vapor exiting the evaporator and the liquid exiting the condenser.     

Performance of an auto refrigerant cascade refrigerator operating in liquid refrigerant supply (LRS) mode with different cascade heat exchangers

Auto refrigerant cascade (ARC) refrigerators operating with zeotropic mixtures provide refrigeration at temperatures less than 173 K (?100 °C) using a single compressor. Different authors have suggested different cascade heat exchangers for ARC refrigerators. There is no study in literature that suggests at what temperature ranges one, two or three cascade heat exchangers are necessary. In this paper the performance of an ARC refrigerator operating in the liquid refrigerant supply mode and operating with optimized hydrocarbon mixtures and different cascade heat exchangers is studied. The optimum number of cascade heat exchangers (stages) to be used for different operating temperatures is suggested.     

N_2O跨临界双级压缩带膨胀机制冷循环

将天然工质N_2O用于跨临界循环,建立了相应的理论模型,比较了CO_2和N_2O用于跨临界两级压缩膨胀制冷循环的性能.结果表明:N_2O用于跨临界两级蒸气压缩膨胀制冷循环中的综合性能要优于CO_2.在所选定的工况范围内,N_2O系统的C_(cop)值(性能系数)比CO_2最多提高9.6%,当气冷器出口温度越低、蒸发温度越高时,N_2O系统的C_(cop)值增加越明显;N_2O系统的最优高压压力远低于CO_2,在气体冷却器出口温度为40 ℃时,最优高压侧排气压力最多降低了16.2%;N_2O系统在排气温度、单位质量制冷量方面也较CO_2具有优势.最后提出通过降低气体冷却器出口温度来提高跨临界带膨胀机制冷循环性能和降低最优高压侧排气压力的观点.     

Experimental study on the performance of a vapor injection high temperature heat pump

In this study, a vapor injection technique was applied in a high temperature heat pump (HTHP) for providing hot water at temperatures up to 88 °C. A prototype HTHP system with economizer vapor injection was developed and its performance was experimentally investigated under various operating conditions. Results showed that the vapor injection pressure had a large effect on heating capacity and on refrigerant temperature at the inlet of the electronic expansion valve (EEV). As the injection pressure increased from 0.82 to 0.98 MPa, the vapor injection flow ratio increased from 7.3% to 22.61% and the heating capacity increased by 7%. The system COP did not show significant change although the COP trend showed an optimal value for the injection pressure. The refrigerant temperature at the EEV inlet showed a subcooling of more than 16 °C under all studied conditions, which improved the EEV operating reliability.     

Determination of optimum refrigerant charge for domestic refrigerator unitsDétermination de la charge optimale en frigorigène des réfrigérateurs ménagers

A method is given of assessing the optimum refrigerant (R12) charge for domestic refrigerators employing a capillary tube expansion device. This amound of refrigerant was found to depend mostly on the volumes of the evaporator and condenser in broad accordance with an earlier theoretical analysis which, however, tended to overestimate the optimum quantity. Experimental measurements were made with different charges and it was concluded that ambient air temperature was not a significant factor. The coefficient of performance was shown to be more sensitive to overfilling than underfilling.     

Determination of optimum refrigerant charge for domestic refrigerator units

A method is given of assessing the optimum refrigerant (R12) charge for domestic refrigerators employing a capillary tube expansion device. This amound of refrigerant was found to depend mostly on the volumes of the evaporator and condenser in broad accordance with an earlier theoretical analysis which, however, tended to overestimate the optimum quantity. Experimental measurements were made with different charges and it was concluded that ambient air temperature was not a significant factor. The coefficient of performance was shown to be more sensitive to overfilling than underfilling.     

制冷剂充注量对冷柜系统影响的实验研究

对BD/C-183A、BD/C-165两种型号的冷柜进行了充注量的实验研究，总结了不同充注量和不同环境温度对冷柜冷冻速度，吸气温度和压缩机机壳温度的影响规律，理论上进行了合理的解释，同时提出了合理的风机布置方案，对于了解冷柜在偏离设计工况条件下运行时的性能，解决在恶劣环境下压缩机温度过高问题，有一定的指导意义。最后，简述了毛细管长度和充注量的匹配关系。