Performance comparison of natural refrigerants based cascade systems for ultra-low-temperature applications

Theoretical analyses and optimisation are carried out with ethane, ethylene and nitrous oxide as the low-temperature (LT) fluids in a cascade system for ultra-low-temperature refrigeration applications to examine the effects of design and operating parameters. Finally, performance improvement has been investigated employing an internal heat exchanger. Optimal intermediate temperature (IT) correlations have been developed. Ethane is superior in terms of coefficient of performance (COP), whereas nitrous oxide is superior in terms of volumetric cooling capacity as an LT fluid. With increase in compressor efficiency, COP increases; however, with little influence on the optimum IT. Using an internal heat exchanger in the LT circuit, the cooling COP can be increased for ethane and ethylene; however, there is marginal decrease in COP for N ₂O. Ammonia is not suitable as a HT fluid for some operating conditions where the optimum IT is lower than the normal boiling point and propylene may be a suitable substitute with a penalty on COP.     

Models of thermodynamic and transport properties of POE VG68 and R410A/POE VG68 mixture

The thermodynamic properties of a refrigerant-oil mixture are the foundation to predict the performance of air-conditioning and refrigeration systems and to evaluate the influence of oil on heat transfer and pressure drop. Models of the thermodynamic and transport properties of POE VG68 and R410A/POE VG68 mixture were provided based on the analysis of state-of-the-art correlations. New models were developed by modifying the coefficients in existing correlations with multiple regression method according to experimental data. The maximum deviation of the predicted values of these models to the experimental data is within 5%. These models can be used for R410A/POE VG68 to obtain accurate and reliable thermodynamic and transport parameters to evaluate the influence of POE VG68 on the performance of an R410A air-conditioning and refrigeration system. __________ Translated from Journal of Shanghai Jiaotong University, 2007, 41(3): 404–410 [译自: 上海交通大学学报]     

Comparison of low temperature mixed refrigerant cycles for separation systems

Numerous mixed refrigerant cycles (MRCs) were developed in the past several decades in different applications. In this paper, two sets of low temperature MRCs are developed and simulated for a typical olefin plant utilizing a mixture of methane, ethane, propane and nitrogen as cycle working fluid to replace the pure ethylene refrigeration cycle that is used in conjunction with propylene refrigeration cycle in conventional plants. The key parameters of the cycles including mixture compositions and operating pressure levels are optimized to meet the objective of minimum shaftwork in compressor. The results show that different cycle configuration has different optimal mixture composition and low and high operating pressures. The results of exergy analysis reveal that the main location of the exergy loss in the cycles is the heat exchanger system. Also, the Carnot factor versus heat flow diagram is provided to identify the distribution of inefficiencies in the heat exchangers for each cycle. The simulation results show that MRCs can improve the thermodynamic performance of refrigeration system using the optimal working fluid mixture composition, optimal high and low operating pressures and optimal arrangement of the cycle components. Copyright © 2008 John Wiley & Sons, Ltd.     

基于高温工质R245fa的太阳能平板集热器集热过程动态模拟

提出了一种以R245fa为循环工质的气液分离双级太阳能集热系统.对第一级集热系统的集热过程进行了动态数值模拟.结果表明,系统的集热过程受太阳辐射强度的影响最大,受系统肩动温度的影响较小.当系统从环境温度启动达到工质蒸发状态时.减少循环工质的质量或增大集热面积均能有效地减少系统的运行时间,而增大系统集热面积是较佳方案.     

Performance of heat pumps charged with R170/R290 mixture

In this study, thermodynamic performance of R170/R290 mixture is measured on a heat pump bench tester in an attempt to substitute R22. The bench tester is equipped with a commercial hermetic rotary compressor providing a nominal capacity of 3.5 kW. All tests are conducted under the summer cooling and winter heating conditions of 7/45 °C and −7/41 °C in the evaporator and condenser, respectively. During the tests, the composition in R170/R290 mixture is varied from 0% to 10% with an interval of 2%. Test results show that the coefficient of performance (COP) and capacity of R290 are up to 15.4% higher and 7.5% lower, respectively than those of R22 for two conditions. For R170/R290 mixture, the COP decreases and the capacity increases with an increase in the composition of R170. The mixture of R170/R290 mixture at 4%/96% composition shows the similar capacity and COP as those of R22. For the mixture, the compressor discharge temperature is 17–28 °C lower than that of R22. For R170/R290 mixture, there is no problem with mineral oil since the mixture is composed of hydrocarbons. The amount of charge is reduced up to 58% as compared to R22. Overall, R170/R290 mixture is a good long term ‘drop-in’ candidate from the view point of energy efficiency and greenhouse warming to replace R22 in residential air-conditioners and heat pumps.     

Modeling and energy simulation of the variable refrigerant flow air conditioning system with water-cooled condenser under cooling conditions

As a new system, variable refrigerant flow system with water-cooled condenser (water-cooled VRF) can offer several interesting characteristics for potential users. However, at present, its dynamic simulation simultaneously in association with building and other equipments is not yet included in the energy simulation programs. Based on the EnergyPlus's codes, and using manufacturer's performance parameters and data, the special simulation module for water-cooled VRF is developed and embedded in the software of EnergyPlus. After modeling and testing the new module, on the basis of a typical office building in Shanghai with water-cooled VRF system, the monthly and seasonal cooling energy consumption and the breakdown of the total power consumption are analyzed. The simulation results show that, during the whole cooling period, the fan-coil plus fresh air (FPFA) system consumes about 20% more power than the water-cooled VRF system does. The power comparison between the water-cooled VRF system and the air-cooled VRF system is performed too. All of these can provide designers some ideas to analyze the energy features of this new system and then to determine a better scheme of the air conditioning system.     

汽车空调PSX-A制冷系统

汽车空调,由于车速的变化,车室内冷量会随车速变动而波动,尤其是高速或怠速时,能否稳定室内的温度是世界各国极为关注的课题。为此,本文提出一种汽车空调制冷系统,即 PSX—A制冷系统。该系统能解决上述难题,其在各种车速改变的情况下,能自动保持车室内冷量的恒定,达到车室恒温。PSX—A制冷系统,比美 CCOT [Cycling Clutch OrifriceTube]。M—5斜板式压缩机能量控制,VIR部件[Valves—In—Receives]等系统适应范围更广,系统筒单,性能优越,成本低,维修调试方便,是行之有效的系统。     

Helmholtz-Type Equations of State for Hydrocarbon Refrigerant Mixtures of Propane/n-Butane, Propane/Isobutane, n-Butane/Isobutane, and Propane/n-Butane/Isobutane

Highly accurate thermodynamic property models for binary and ternary hydrocarbon mixtures containing propane, n-butane, and isobutane have been developed. In the present model, reliable equations of state explicit in Helmholtz free energy for these three hydrocarbons that have already been developed by the present authors have been adapted. The excess term used to represent the contribution of mixing was optimized for each binary mixture by using the available experimental thermodynamic property data including PTx, isochoric heat capacity, and saturation properties (bubble-point pressures, mole fractions in the vapor phase, and saturated vapor- and liquid-densities) as input data. A generalized correction for the three binary mixtures, besides the ideal mixing, consists of only four terms in its functional form, the structure of which was determined by simultaneous optimization to the input data for the three binary mixtures by employing a stepwise regression analysis. The bank of terms, that is a matrix of candidate terms applied for the regression, was carefully prepared through detailed observation of the nonideal mixing representation of the experimental data of the three binary mixtures. No additional adjustable parameters were used in the present model for the ternary propane/n-butane/isobutane mixture. Based on comparisons with the available experimental data and values from the developed equations of state, the present models for the three binary and the ternary hydrocarbon mixtures accurately represent most of the reliable experimental data. In addition, the graphical tests of the derived thermodynamic properties show that the models, including that for the ternary mixture, provide a physically sound representation of all the thermodynamic properties over the entire fluid phase.     

制冷系统热力学参数查询系统的设计及实现

应用Visual Basic和MATLAB进行软件开发。软件设计遵循了模块化的原理,结构清晰,易于测试和调试。软件的主要功能是对制冷剂热力学参数进行查询,本软件将对制冷装置设计计算问题起到简化作用。     

分户热计量室温平衡温度的计算方法及验证

目的利用房间热平衡法和冷却函数法来解决室内平衡温度计算,即户间传热的.方法使用房间热平衡法和冷却函数法计算室内平衡温度,并用冷却函数法模拟室温规律.结果热平衡法和冷却函数法的计算结果具有一直性,通过实际算例计算了不供暖房间的室内平衡温度与利用冷却函数法模拟的室温规律结果相吻合得很好.结论两种计算方法都可以计算室内平衡温度,由于房间热平衡法是静态的方法,易于运用,便于掌握,因此可优选它作为计算室内平衡温度的方法.