Analysis of the performance of the evaporator of automotive air conditioning system

The purpose of this research was to establish a theoretical model for the evaporator of automotive air conditioning system and conducting simulations to evaluate the effect of operation parameters, environmental conditions, and design parameters on the performance of evaporator. An automotive air conditioning system primarily consists of four components: the compressor, the condenser, the refrigerant controller, and the evaporator. The refrigerant flow in the evaporator can be divided into two regions: the evaporating region and the superheat region. The refrigerant in the first region is a two-phase flow, while the refrigerant in the latter region is in the state of superheated vapor. The air flowing through the interior of the evaporator can also be divided into two zones: the unsaturated zone and the saturated zone. Water vapor is condensed in the saturated zone while in the unsaturated zone, no water condenses. Because the refrigerant flow and the airflow are perpendicular to each other, the distribution of refrigerant in the evaporating region and the superheat region does not coincide with the distribution of air in the unsaturated zone and the saturated zone. This study examines the effects of different design parameters, environmental conditions and operating parameters on the cooling capacity and superheat of an air conditioning system. Design parameters include the length of the refrigerant channel, the length of the air channel, and the thickness of the fins. Environmental conditions include the air inlet temperature and absolute humidity. Operation conditions include the refrigerant inlet enthalpy, inlet air flow rate, and refrigerant mass flow rate. Results of simulation demonstrated that fins with 50 micron meters width has the greatest cooling capacity for identical outer dimensions; thicker or thinner fins only decreased cooling capacity. Under different outer dimensions, longer refrigerant tubes and air channels created a greater cooling capacity. However, the increase in cooling capacity becomes less and less if the refrigerant flow was fixed because the heat transfer capability of the gaseous refrigerant was limited. In this study, an increase of 19% in cooling capacity can be reached as the length of refrigerant channels was increased, and the increased length of the air channels can promote the cooling capacity by 22%. Besides, it was found in this study that a decrease in the refrigerant inlet enthalpy, the inlet air flow rate, the air inlet temperature, and the inlet absolute humidity, or an increase in the refrigerant mass flow rate, would extend the superheat region and decrease the refrigerant’s superheat. It was also found that the cooling capacity of air conditioners is extremely sensitive to changes in the refrigerant mass flow rate and the inlet enthalpy, and variations more than 50% were found in the operating ranges examined in this study. However, changes in the inlet temperature, absolute humidity, and inlet air flow rate only resulted in variations between 10% and 20% in the examined ranges of conditions. Finally, a correlation among these variables and the simulated cooling capacity was obtained in this study, enabling the relevant researchers to evaluate automotive air conditioning performance under different environmental conditions and operation parameters more easily.     

冷凝对隧道通风热压的影响分析

为研究空气水分冷凝现象对隧道通风热压的影响,采用现场实测的某地下通风隧道空气参数以及文献中某隧道自然通风的测试数据,对选用的有限差分法隧道通风传热传质过程及热压计算数学模型进行了验证;并采用数值模拟方法研究分析了不同隧道入口空气温度、相对湿度及通风速度条件下,隧道内空气冷凝现象、沿程空气温度以及热压的变化规律。研究结果表明:冷凝会增大空气与壁面的传热量,使隧道内的空气降温速度减慢,导致通风热压变小,并且该影响会随入口空气温度与相对湿度的升高而增强,随风速提高而减弱;当未发生冷凝时,隧道沿程空气温度分布及热压几乎不受空气湿度的影响。以一个全纵向通风的地下隧道为例,在4~8月,隧道会出现较大范围的冷凝现象,考虑冷凝计算所得热压比不考虑冷凝时低30%,对应的自然风风速平均偏差为0.5 m·s^-1;在其余月份,不考虑空气冷凝计算所得通风热压与考虑冷凝时相同。因此计算湿热季节通风热压或对应的自然风风速时,应考虑冷凝的影响;其余季节可按不考虑冷凝的方法简化计算隧道热压。     

Experimental study on performance characteristics of cold storage heat exchanger for ISG vehicle

The ISG (Idle Stop and Go) system isvery useful in the automobile industry because it increases fuel consumption and reduces green house gas emissions. However, when the engine is on standby, the air-conditioning system does not work due to compressor inactivity, causing thermal discomfort to passengers. This study examines the thermal storage system, which is a cold storage heat exchanger integrated with a current evaporator. The experiments were conducted for an optimum cold storage heat exchanger design with various fin heights and densities, a number of stacking evaporator plates, refrigerant flow circuits inside the evaporator, and PCMs (Phase Change Materials) in the heat exchanger. The effects of coldness-release performance were examined with various ambient temperatures and air flow volume rates to the cold storage heat exchanger. The visualization of PCM’s freezing and melting was conducted with the cold storage heat exchanger. From the results, we found that the air discharge temperature of the air-conditioning system that was applied to the optimum cold storage heat exchanger was delayed around 540 seconds compared to the current air-conditioning system to reach 24 °C. Thus we can say that the cold storage heat exchanger integrated with an evaporator is an effective solution for ISG vehicles in maintaining thermal comfort in vehicle cabins during short engine stops.     

基于模糊理论的沥青路面热风加热多参数优化

为了优化就地热再生热风加热参数，提高热风加热沥青路面的加热效果，基于有限元方法，建立了热风加热装置加热沥青路面的模型，模拟计算了热风加热沥青路面的过程，通过试验验证了仿真模型及参数设置的正确性。采用正交试验设计方法研究了热风温度、热风速度、出风孔离地高度对加热效果的影响。提出了基于模糊理论的热风加热效果评价方法，引入综合模糊评价指标代替沥青路面温度场、对流换热系数和加热过程中的能量利用率等单一评价指标对沥青路面加热效果进行评价，采用独立性权系数法确定了各指标的权重系数，仿真分析验证了综合模糊指标评价方法的有效性。结果表明：在加热装置的设计参数范围内，热风温度对沥青路面表面温度及分布均匀性影响最大，热风速度对换热系数影响最大，出风孔离地高度对能量利用率影响最大。以沥青路面温度场、对流换热系数和能量利用率等单一指标为优化目标获得的最佳加热参数组合，仅能保证各自指标最优，但其他指标较差；以综合模糊评价指标E_CFI为优化目标得到的最佳热风加热参数组合，可以同时获得较好的沥青路面温度场、对流换热系数和能量利用率。研究方法和结论为沥青路面热风加热参数的选择和加热效果的评价提供了一种有效可行的途径。     

汽车前风窗玻璃除霜除雾数值模拟分析和研究

利用CFD方法对汽车内部流场进行了模拟,定量分析了车内气流的速度、温度、湿度、以及车窗玻璃的温度和空气的传热量等参数,进而对汽车前风窗玻璃除霜除雾进行数值模拟,对其除霜除雾效率和效果进行分析,为汽车除霜除雾工程应用提供参考.     

基于平行流蒸发器结霜问题的试验研究及解决方案

平行流蒸发器具有紧凑、高效的特点,在汽车空调中使用得越来越多。但其存在冷凝水排放不畅、制冷剂在扁管内分配不均等问题,在高湿情况下易发生结霜现象。本文针对某平行流蒸发器,在不改动空调系统其它部件的前提下,通过调整蒸发器本身结构、温度传感器位置及温度区间,实现了无结霜、出风温度均匀,空调系统性能得以提高。     

汽油机活塞内冷油腔振荡冷却特性的仿真研究

为研究汽油机活塞内冷油腔在高转速下的振荡冷却效果,搭建了计算流体力学仿真模型,模拟研究了额定转速下内冷油腔的机油瞬态分布、壁面换热系数和换热速率,分析了机油喷射速度、喷孔直径、机油温度等喷射参数的影响,并采用Box-Behnken组合设计,以换热速率最大化为目标优化了喷射参数。结果表明,换热速率除了受喷射速度和机油温度的交互作用影响外,还与腔内充油率决定的机油振荡状况有关,并可与喷孔直径拟合成抛物线关系。     

Numerical analysis and experimental study on the performance optimization of cold storage heat exchanger integrated with evaporator

The ISG (Idle Stop and Go) systems are commonly used in modern automobiles because they are economical and environmental friendly technology. However, when a vehicle stops, the air-conditioning system stops, resulting in thermal discomfort to passengers in the cabin. This paper examines a cold storage heat-exchanger (CSH) integrated with an evaporator. The position of the cold storage parts inside a heat exchanger was analyzed through numerical simulations using FLUENT to create an adequate design for a CSH. The CSH performance was then examined with various airflow volumes and optimized experimentally in terms of the refrigerant flow circuit and fin density in the heat exchanger. Next, an experiment on the coldness release performance of the CSH was conducted in the air-conditioning system. The cold storage system with optimized CSH experiment resulted in lower air discharge temperatures (3.5 °C ~ 4.9 °C) than current air-conditioning systems, and delayed the warm-up by approximately 155 seconds to reach 18 °C temperature of air discharge. For this study, the CSH is an effective solution for the ISG-applied vehicles with less investment by transforming current air-conditioners’ structures more effectively.     

TBM施工引水隧洞降温技术研究

TBM施工时,岩温和机械发热所产生的大量热量会导致隧洞内的温度环境恶化,TBM掘进面附近的温度控制是影响连续长距离掘进的重要因素之一。为制定合理的TBM施工段降温措施,采用传热学理论,对采用压入式独头通风的TBM施工隧洞内的温度分布规律进行研究,并以引汉济渭岭北段TBM 5#斜井工区为例进行验证。通过引入空调工程中焓值的概念,确定TBM隧洞人工降温的冷负荷,对常见的降温措施进行对比讨论,进而确定TBM施工隧洞的降温措施。研究表明： 隧洞内的空气温度与隧洞壁温、通风风温、通风风量、盾构的发热功率、隧洞周长、通风长度、风管侧壁传热系数和隧洞侧壁的换热系数等参数有关;对于TBM掘进面附近高温、高湿的环境,只能采取人工制冷降温措施进行降温     

Experimental study on performance of automotive air conditioning system using R-152a refrigerant

Recently, as climate changes have manifested worldwide, every country is making efforts to prevent ozone depletion and global warming. In the automotive industry, R-134a refrigerant is widely used in air conditioning systems because it has zero ozone depletion potential (ODP). Unfortunately, its global warming potential (GWP) is high. Therefore, alternative refrigerants are needed as a replacement for R-134a. R-152a is considered to be one of the better alternative refrigerants due to zero ODP and low GWP. In this paper, the performance of an automotive air conditioning system using R-134a and one using R-152a are compared experimentally at the bench level. The experimental apparatus simulated a real automotive air conditioning system consisting of a cabin and engine room structure. The cooling capacity, condensing capacity, coefficient of performance (COP) and power consumption characteristics of the automotive air conditioning system are evaluated by changing the air velocity entering the condenser and the compressor rotation speed with the optimized refrigerant charge amount. Also, the performance of the R-152a system was investigated by changing the thermostatic expansion valve which is set of values. The results of this study show that the R-152a system is slightly better than the R-134a system, not only under driving conditions but also under idling condition. R-152a refrigerant thus shows promise as an alternative refrigerant to replace the current standard, R-134a, in automotive air conditioning systems.     

质子交换膜燃料电池低电密运行参数的优选分析

通过对质子交换膜燃料电池低电密运行的正交试验研究,分析了过量空气系数、冷却水入口温度、阴极入口处的相对湿度以及阴极入口压力这4个运行参数对质子交换膜燃料电池性能的影响。     

一种整车环境散热器性能检测方法及模型

汽车散热器是汽车冷却系统的重要组成部分,使其内部的冷却液和通过其表面的空气进行热交换来降低冷却液温度,防止发动机过热而损坏,文章主要在整车环境条件下研究散热器在不同转速和不同迎面风速时的散热能力大小,并构建冷却液流量、散热器表面风速场及散热器散热系数的整车散热器散热模型。     

高黎贡山隧道施工热环境通风降温计算方法应用研究

为解决高地温隧道施工热环境难题、掌握隧道中的热源和冷源的能量平衡控制方法，以传热学原理为基础，通过能量守能定律，推导得出无高温水出露和有高温水出露2种工况下的新风量计算公式。以大瑞铁路高黎贡山隧道为例进行研究，得到以下结论： 1）推导得出的理论公式具有一定的可靠性，计算误差可控制在6%左右； 2）增大通风量可使洞内相对湿度大幅度降低，通风降湿效果明显； 3）低温、低湿新鲜风可以有效改善隧道内环境质量，但存在局限性，应因地制宜地选取热环境控制方法。     

平行流冷凝器在大型货车空调中的应用

空调系统是现代货车的重要组成部分,空调系统性能的优劣关系到驾驶安全。平行流冷凝器作为新一代高效冷凝器,具有体积小、结构紧凑、换热效率高等诸多优点,可提高货车空调性能。本文就平行流冷凝器在大型货车上的应用进行了分析,总结出：在货车上应用平行流冷凝器不仅投资可减少,还可以降低油耗和变暖总当量（TEWI）,节能和环保效果较好...     

考虑通风与围岩条件的寒区隧道温度场模型及作用规律研究

为了解决寒区隧道温度场的预测问题,为寒区隧道抗冻设防提供指导,结合传热学、流体力学的基本方法,根据能量守恒原理,推导寒区隧道风流温度场的传热模型,并在此基础上,借助有限差分方法,探讨通风和围岩条件对寒区隧道温度场分布的作用规律。研究结果表明: 1)入口风温越低,风流速度越大以及断面越大,相同位置处洞内温度越低,这是由于进入洞内的冷空气更多,入口风温每降低5 ℃,同位置洞内风流温度平均降低3. 8 ℃; 2)风流温度决定了离壁面一定范围的围岩温度大小,风流温度越低,冻结深度与受到影响的围岩范围更大; 3)初始岩温越大,围岩温度分布曲线越陡峭,围岩导热系数则相反,且初始岩温每增加 5 ℃,冻结深度减少0. 24 m,受影响的围岩径向深度减少0. 32 m。     

并联结构换热器模块中冷却空气流量的分配

为提高车辆换热器模块的匹配设计能力,针对冷却风在并联结构换热器模块中的流量分配进行数值模拟和试验研究。在计算中把复杂的翅片结构简化为多孔介质模型,并采用RNGk-ε湍流模型进行模拟。通过换热器模块的风洞试验对数值计算结果进行验证。结果表明由于各换热器的阻力特性不同,流量的分配与设计时的理想状态存在较大的差异,阻力小的换热器中风速高,相对流量变大。     

Experimental studies on the heating performance of the PTC heater and heat pump combined system in fuel cells and electric vehicles

In this study, a combined system consisting of a heat pump and a PTC heater was developed as a heating unit in electric vehicles. The system consists of a compressor, a condenser, an evaporator, an expansion device and a PTC heater. Experiments were conducted to examine the steady-state performance and dynamic characteristics of this system. The compressor speed, outdoor air inlet temperature, and indoor air inlet temperature were varied, and the performance of the system was experimentally investigated. The heating capacity, compressor power consumption and COP were obtained. Warm-up experiments were performed to investigate the dynamic characteristics of the system with a heat load of 1.5 kW in the indoor chamber. For the heat pump system, the PTC heater and the combined system, the heating performance and efficiency were investigated to determine an optimal control method. The results of this study agree well with the experimental results available in literature. This study provides experimental data of good quality for heating system design and the development of electric vehicles.     

转速对甲醇HCCI燃烧特性的影响试验研究

在一台双缸4冲程柴油机上实现了甲醇均质压燃的试验,分析了发动机转速对甲醇均质压燃燃烧特性的影响。试验结果表明：过量空气系数和进气温度一定的情况下,随着发动机转速在一定范围内的升高,缸内压力、压力升高率和放热率均有所升高,且存在一个最佳的转速,使得压力、压力升高率和放热率处在较好的水平。     

多年冻土路基对流换热试验方法

对流换热是多年冻土地区路基对外热交换的重要形式。利用自行开发的热风环境试验机,考虑不同路面材料类型、风速变化、温度梯度3个因素,对影响冻土路基温度场的对流换热状况进行室内模拟试验研究。研究表明：风速、温度梯度、路面材料类型3个因素对于对流换热系数有着交互影响,随着风速与温度梯度的增加,对流换热系数呈上升趋势。沥青路面材料的对流换热系数较水泥路面材料稍大。研究中给出了不同状况下对流换热系数的回归公式,并分别给出青藏高原地区沥青混凝土路面及水泥混凝土路面对流换热系数的推荐值。     

二甲醚用作汽车空调制冷剂的实验研究

根据二甲醚的热物理性质对二甲醚的制冷循环性能进行了分析,并在R134 a汽车空调系统上对二甲醚的制冷性能进行了测试。结果表明:由于二甲醚的气相和液相黏度都比较小,使用二甲醚作为制冷剂可以减小系统的阻力,有利于系统制冷性能的提高。二甲醚可以直接灌注式替代R134 a,但会造成蒸发器出口过热度降低,需对膨胀阀弹簧预紧力进行调整,才能充分发挥二甲醚的制冷性能。