新能源车用CO2空调系统泄漏特性仿真研究

CO₂作为一种安全、高效且环境友好的自然工质,是未来汽车空调制冷剂替代方案的重要选择。考虑到CO₂系统制冷剂泄漏导致乘员舱气体体积分数超标的舒适及安全问题,本文使用三维仿真软件STAR-CCM+搭建乘员舱CO₂制冷剂泄漏仿真模型,仿真分析两种不同泄漏速率和泄漏圆孔孔径下乘员舱乘客面部测点CO₂体积分数的动态变化情况。在50 g/s的高CO₂泄漏速率下,面部CO₂体积分数在泄漏完成时能够达到9%以上,需要切换送风模式提供新风来降低乘员舱内CO₂体积分数;在0.1 g/s的低CO₂泄漏速率下,泄漏完成时面部CO₂体积分数不超过3%,处于呼吸安全区范围。     

电动汽车热管理技术研究进展全文替换

电动汽车热管理技术是驾乘安全与舒适的重要保证,是电动汽车发展的核心关键技术之一。本文从电动汽车热管理需求、发展历程以及关键零部件技术发展几个方面,梳理总结了电动汽车热管理技术的研究现状与发展趋势,并进一步从环保制冷剂替代,智能化控制与乘员舱舒适性提升方面对电动汽车热管理未来技术发展进行了阐述与展望,以期为业内同行提供参考。     

可燃制冷剂R32室内空调器泄漏扩散特性的实验研究

制冷剂R32具有良好的环保特性和热工性能,但其可燃性限制了它的应用推广,因此需要对R32的安全性进行分析。实验研究了分体壁挂式空调用制冷剂R32在空调运行时,蒸发器不同泄漏位置和不同泄漏速度对室内R32浓度分布的影响,得出R32在空调运行时的泄漏扩散特性。研究表明:可燃性制冷剂R32在室内机蒸发器处发生泄漏时,泄漏过程可分为快速泄漏阶段和低速泄漏阶段;蒸发器出口泄漏比蒸发器入口泄漏危险性高;仅在蒸发器出口大流量泄漏时,室内机附近区域R32浓度最大值为16.79%,超过可燃下限(14.4%)16.6%。可燃浓度持续了22 s,存在着火的可能性,但概率较低;排风作用对各测点的浓度衰减影响强烈,可有效降低室内R32的浓度。     

R32制冷剂泄漏位置对浓度分布与室内安全性的实验研究

本文通过实验研究的方法,对比分析了R32制冷剂在泄漏量为3.6 kg,不同泄漏位置时,R32气体在室内不同平面的浓度扩散规律,并通过典型平面首次达到可燃下限（LFL）的时间和可燃风险时间来分析室内的安全性影响。结果表明：随着泄漏位置高度的增加,制冷剂浓度扩散速率在沿高度方向上逐渐趋于一致,浓度上升速率和浓度下降速率分别保持在约0.5%/min和0.06%/min。当制冷剂气体从房间上部水平方向泄漏改变为垂直向下泄漏时,泄漏口附近平面处最大浓度及浓度扩散速率均减小约50%,可燃危险时间减少了约78%;房间下部的的可燃危险时间随泄漏位置高度的升高而逐渐增大。当泄漏位置位于房间上部和顶部时,房间底部区域最先达到LFL值,其余位置处泄漏口附近平面处最先达到LFL值。     

R134a汽车空调及整车降温性能仿真优化分析

本文通过KULI仿真软件搭建整车降温模型,计算并分析了中间换热器(又称同轴管,IHX)、后出风吹面装置以及乘员舱衣帽架对乘员舱降温性能的影响,对比了其单一装置及其组合方案对整车降温性能的影响。分析结果显示当取消单一功能配置时,衣帽架对乘员舱降温性能影响较大,平均温度升高2.2~2.4℃;后吹面装置次之,平均温度升高0.6~0.8℃;同轴管的影响最小,平均温度升高0.2~0.4℃。而且衣帽架单一装置对乘员舱降温性能的影响大于同轴管和后出风吹面装置组合对乘员舱降温的影响。通过仿真计算为整车及后续车辆开发提供了一定的理论依据及优化方案。     

电动汽车热泵空调系统室外换热器结霜特性实验研究

针对电动汽车热泵空调系统在冬季运行时室外换热器易结霜而影响系统制热性能的问题,本文设计搭建实验系统并进行研究,分析了多流程微通道换热器的结霜特性。实验结果表明:室外换热器表面霜层生长和表面温度下降两个因素之间为联动关系,各流道霜层分布呈不均匀状态,换热器内两相制冷剂密度不同且受重力影响,导致产生气液相分离和在流道内分布不均的状况。另外,室外换热器表面霜覆盖率的增长会导致室外换热器制冷剂侧的温度、压缩机吸排气压力、制热量等降低,引起导致压缩机单位功耗增加,以环境温度为0℃的数据为例,当霜覆盖率达77. 4%时,吸气压力、排气压力和制热量的降幅分别为33. 4%、12. 1%和25. 8%,单位功耗增幅为32. 0%,导致系统运行的稳定性降低,使制热量无法满足乘员舱制热需求。     

适用于制冷系统泄漏探测的制冷剂质量计算模型

本文提出一种适用于制冷系统泄漏探测的制冷剂质量计算模型。通过该模型可以实时计算出制冷系统内部各部件内的制冷剂质量,并实现对制冷系统的泄漏探测。在制冷剂质量计算模型中,开发了基于温度信号进行相区划分的换热器分区制冷剂质量计算模型,提出了基于理论和显式表达式的压缩机及连接管路的制冷剂质量计算模型。验证结果表明,该模型对制冷剂质量的最大计算误差为3. 18%。     

汽车空调制冷剂泄漏预防控制技术研究

汽车空调在使用过程中,其制冷系统中的制冷剂会发生泄漏,从而引发一系列故障,同时泄漏的制冷剂也对空气环境造成影响。本文从汽车空调目前现有的制冷剂泄漏预防控制技术进行了研究分析,并提出了新的预防控制策略方案。     

制冷剂冷却电池的纯电动汽车热管理系统夏季工况模拟

以纯电动汽车整车热管理系统为研究对象,本文提出纯电动汽车整车热管理方案,研究在夏季工况下的整车热管理性能。电池与乘客舱采用制冷剂并联冷却,利用热管的高导热系数来传递热量,电机采用液冷,并在新欧洲驾驶循环工况下用系统模拟的方法进行测试。结果表明:经过64 s,乘客舱温度从35℃降至24℃,随后乘客舱始终围绕设定温度24℃上下波动;电池温度经过68 s从35℃降至25℃,然后在整车控制策略下,使其维持稳定温度;电机温度在市内循环缓慢增长,在郊区循环急速增长,但维持在80℃以内。     

电动汽车空调与电池热管理系统设计与匹配

本文对电动汽车空调系统和电池热管理系统的基本功能进行了构想,在此基础上设计了系统的原理图并对系统的基本功能进行了分析。此外,文中对系统关键零部件的性能参数给出了选型方法,最后对整车环模试验数据和多工况下路试试验数据进行分析。结果表明,本文所设计匹配的电动车空调及电池热管理系统能满足乘员舱的制冷及采暖需求,同时也能为电池组提供较适宜工作温度环境。     

Diesel combustion of oil and refrigerant mixture during pump-down of air conditioners

Compressor-destruction accidents during the pump-down operation of air conditioners were experimentally investigated. Assuming air penetration into refrigerant tubes, the gaseous mixture of the air, refrigerant, and lubricating oil for a compressor was compressed by the compressor with different refrigerant concentrations, and the diesel combustion of the mixture was examined. The compressor was simulated by a small-scale engine. R1234yf, R32, R410A, R134a, R22, and R125 were tested as refrigerants. The mixture burned via adiabatic compression when the refrigerant concentration was low, which means that accidents during the pump-down were caused by the diesel combustion of the mixture. The refrigerant burned and caused intense pressure increase. The mixture without the oil did not burn under any refrigerant concentration, which suggests that oil is necessary for the combustion. These phenomena were observed in the results for R1234yf, R32, R410A, R134a, and R22. Thus, combustion was observed under certain conditions even for refrigerants categorized as non-flammable.     

R1234yf热泵技术综述与潜力分析

为了满足逐步严苛的环保法规要求,R1234yf成为车用热泵制冷剂R134a的热门替代制冷剂之一。本文对R1234yf热泵技术的研究进行了综述与分析,其GWP<1,各方面性质均符合车用热泵系统的工作需求。在传热效果上,R1234yf的沸腾传热性能略优于R134a,且冷凝过程压降比R134a低5%~10%,优于R134a系统。在诸多R1234yf和R134a系统的仿真和实验研究中,R1234yf热泵性能略低于R134a,但可以通过优化零部件、强化补气、改善工况等方式使其与R134a十分接近甚至超越。R1234yf低压饱和压力比R134a高约15%,可以适配更高的压缩机转速,低温下制热性能比R134a更好,且较低的压缩机排气温度使系统工作更为稳定,强化补气的效果也优于R134a。因此,R1234yf在车用热泵中具有较好的工作性能和发展前景,可以作为R134a的替代制冷剂。     

新一代制冷剂HFO-1234yf的热物性模型

基于Peng-Robinson通用状态方程,采用基团贡献原理以及多项式拟合方法,建立了符合精度要求的新型LGWP制冷剂HFO-1234yf的热物性模型,并对模型进行了验证,利用数学软件对模型进行编程求解,得到了较为全面的HFO-1234yf制冷剂的热物性数据。将HFO-1234yf制冷剂与R134a及R417A制冷剂的热物性能进行了对比,结果显示HFO-1234yf的饱和蒸汽压力与定压比热容和R134a的表现相似,二者的饱和蒸气压均低于R417A,HFO-1234yf制冷剂与R134a和R417A相比,其饱和状态焓值较低,这将导致HFO-1234y系统运行时的性能系数不高。该模型能为HFO-1234yf制冷剂在汽车空调以及固定式空调制冷设备上的应用提供理论依据。     

Quick and empirical correlations for refrigerant pressure drop in mobile air conditioning system evaporators

In heat exchanger design and simulation, a precise refrigerant pressure drop prediction is difficult because of limited correlation's accuracy. In the present paper, several quick and accurate empirical correlations for refrigerant pressure drop of the typical evaporators (laminated plate evaporator and minichannel parallel flow (MCPF) evaporator) used in mobile air conditioning (MAC) system were proposed. A factor which was related with the refrigerant mass flow rate, thermodynamic properties and refrigerant status was introduced. The types of evaporator and refrigerant were considered in the correlations which were available under typical MAC evaporator application conditions. The analysis results showed the refrigerant pressure drops were implied in a linear relationship with the proposed factor. The predicted data agreed with the experimental data very well. For laminated palate evaporators, the average deviations were 1.8% and 0.7% for R134a and R1234yf, respectively. For MCPF evaporator, the average deviations were 4.5% and 0.6% for R134a and R1234yf, respectively.     

Measurement of vapor viscosity of R1234yf and its binary mixtures with R32, R125

The vapor viscosities of the new refrigerant R1234yf and its binary mixtures, R32+R1234yf, R125+R1234yf, were measured at atmospheric pressure with a falling-ball-type viscometer. The combined expanded uncertainty of the measurement apparatus was less than 1.5%. The binary mixtures consisted of 20.0, 30.0, 40.0, and 50.0 wt% R32 for R32+R1234yf and of 20.0, 35.0, 50.0, and 70.0 wt% R125 for R125+R1234yf. The viscosities of R1234yf were correlated with the Chapman–Enskog gas kinetic theory and those of binary mixtures were correlated with the Wilke mixture rule. The average absolute deviation (AAD) is 0.189% for R32+R1234yf and 1.169% for R125+R1234yf. The deviations of experimental viscosities of the binary mixtures from data calculated using RefProp v9.1 were also obtained. The AAD is 0.555% for R32+R1234yf and 1.479% for R125+R1234yf.     

Condensation heat transfer coefficients of R1234yf on plain, low fin, and Turbo-C tubes

In this study, external condensation heat transfer coefficients (HTCs) of HFC134a and R1234yf are measured on a plain, low fin, and Turbo-C tubes at the saturated vapor temperature of 39 °C with the wall subcooling of 3-8 °C. R1234yf is a new alternative refrigerant of low greenhouse warming potential for replacing HFC134a, one of the greenhouse gases in Kyoto protocol, used extensively in automobile air conditioners and other refrigeration systems. Test results show that the condensation HTCs of R1234yf are very similar to those of HFC134a for all three surfaces tested. For the development of heat transfer correlations, thorough property measurements are needed for R1234yf in the near future.     

欧盟汽车空调指令对汽车企业的影响分析

欧盟汽车空调指令2006/40/EC要求汽车空调制冷剂GWP值≤150,目前,广泛使用的R134a制冷剂的GWP值为1300,因此,R134a逐渐会被禁用,新型制冷剂HFO-1234yf逐步被推广,取代R134a.重点研究了两种制冷剂的性能差异,替代趋势,及空调指令在欧盟的执行情况,以及国内自主汽车企业的应对措施.     

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.     

Drop-in replacement in a R134 ejector refrigeration cycle by HFO refrigerants

The present work reports a numerical analysis of a single-phase supersonic ejector working with R134a as well as hydrofluoroolefin (HFO) refrigerants R1234yf and R1234ze(E). Comparisons were made regarding the ejector performances under varying operating conditions and refrigerant mixture proportions. The calculations have been then extended to an existing ejector heat driven refrigeration cycle (EHDRC). R1234yf appears to be a good candidate for drop-in replacement of R134a in a real EHDRC, while using R1234ze(E) would induce some modifications due to its thermodynamic properties. Maintaining the same pressure ratio for the ejector would lead on one hand to better entrainment ratio using R1234ze(E) and on the other hand to reduced coefficient of performance (COP) and cooling power by 4.2% and 26.6% in average, respectively. Using R1234yf under the same conditions induces a decrease of 5.2% for the entrainment ratio, 9.6% for the COP and 19.8% for the cooling power in average.     

R32和R32/R1234yf混合工质黏度实验测量及模型

本文针对含HFOs类混合制冷剂黏度开展实验和模型研究。采用振动弦法黏度计对R32纯质和R32/R1234yf混合制冷剂黏度进行了实验测量,测量的温度范围分别为263~350 K、263~360 K,压力最高均为30 MPa,实验系统黏度测量的不确定度为2%。本文共获得了177组实验数据,利用得到的实验数据,基于硬球模型分别拟合了R32纯质和R32/R1234yf混合制冷剂黏度方程。R32纯质黏度实验数据与方程的平均绝对偏差为0.28%,最大绝对偏差为0.92%;R32/R1234yf混合工质黏度实验数据与方程的平均绝对偏差为0.69%,最大绝对偏差为2.09%。由此可见,实验数据和黏度模型吻合较好,为R32和R32/R1234yf混合制冷剂的应用研究提供了重要参考依据。