汽车空调平行流式冷凝器优化换热的研究

建立平行流式冷凝器翅片的数学模型,应用Fluent软件对影响风冷式冷凝器传热的风速、翅片高度、翅片间距、翅片厚度、翅片接触面宽度等因素进行模拟计算研究,得出反映影响平行流式冷凝器传热的流场特性和传热特性的数据.该研究对设计平行流式冷凝器和优化平行流式冷凝器的换热起到一定参考作用.     

车用百叶窗翅片管式换热器对空气侧强化传热作用的研究进展

百叶窗翅片管式换热器是车用换热器主要选型之一,其结构对空气侧强化传热作用有着极其重要的影响。本文总结了近几年来国内外在百叶窗翅片管式换热器的结构参数对空气侧强化传热影响方面的研究,包括翅片间距、管排数、翅片高度、百叶窗开窗角度、翅片厚度及翅片形状对空气侧换热系数、压降的影响。最后,在百叶窗结构的基础上,提出了在翅片上打孔形成百叶型多孔翅片来进一步强化空气侧换热的建议。     

多元平行流冷凝器的数值模拟研究

采用能量平衡的方法对多元平行流冷凝器建立计算模型,对管内制冷剂和管外空气侧的流动和换热进行了数值分析,模拟结果与实验结果吻合良好进行了比较。研究表明:由于多元平行流冷凝器的变流程结构及制冷剂的相态变化,制冷剂侧传热系数、压降,制冷剂压力和温度及干度沿管长出现多次突变。     

散热器空气侧百叶窗翅片结构参数优化

对散热器空气侧的百叶窗翅片建立三维流固耦合的模型,运用Laminar方法进行数值模拟,结果表明传热与压降特性与实验关联式吻合较好,模型得以验证;为进一步阐明汽车内散热器空气侧的强化传热翅片的性能,分别考察了不同的翅片高度、窗翅高度、翅片厚度和翅片节距等结构参数对传热系数和压降的影响,得到了一组综合性能较好的百叶窗翅片结构参数。     

收腰型铝散热器的空气侧优化

为寻找一种与收腰管匹配效果更好的散热翅片结构,先应用正交试验与模拟仿真对收腰管百叶窗散热器翅片的4个主要结构参数,即翅片间距F_p、百叶窗间距L_p、百叶窗宽度L_w和百叶窗角度L_a进行优化,得到各结构参数对散热器传热性能和压降性能的影响规律,即百叶窗角度L_a影响最大,翅片间距L_p影响最小。随后,在此基础上提出了散热翅片的优化方案。最后,利用风洞试验对优化前后的散热器性能进行了比较。结果显示,优化后的百叶窗翅片结构可以明显提高散热器空气侧的传热,同时降低了风阻。     

微型多元平行流冷凝器的流程布置和风速优化

阐述了多元平行流冷凝器的结构组成,对单双层冷凝器热力性能试验进行了分析,最终得到流程布置不同以及风速不同情况下的微型冷凝器压降、质量等曲线,进而达到了寻找流程布置以及空气风速对冷凝器的影响规律的目的,并得到了冷凝器的最优流程布置和最优风速方案。     

正弦波纹翅片管换热器传热和阻力特性的试验研究

对不同翅片间距、不同管排数的9个正弦波纹翅片管换热器元件进行了试验研究,给出了工业常用雷诺数范围内各元件翅片侧空气的换热和阻力性能关联式。文中还给出了包括翅片间距及管排数影响的通用关联式,为设计和选用正弦波纹大套片换热器提供了依据。     

多元平行流冷凝器流程布置的模拟研究与分析

根据多元平行流冷凝器的特点,采用分布参数法对其建立了稳态数学模型.对不同流程数的多元平行流冷凝器的传热和流动性能进行了模拟计算和分析比较,发现了增加流程数对换热量和制冷剂侧压降影响的规律;得出了为保证冷凝器合适的压降,不宜使整体流程数过多的结论.同时,对多元平行流冷凝器的多种各流程扁管排数分配方式进行了模拟比较.结果表明:各种各流程扁管排数分配方式对冷凝器的换热量影响相对较小,主要影响制冷剂侧压降的变化;两相段应该作为冷凝器芯体的主体部分,以保证整个冷凝器有较高的换热性能;由于过冷段扁管排数对制冷剂侧压降影响较大,不宜过少.     

基于CFX对管式换热器在烟气余热回收中的改进

通过对换热器结构特点的分析,提出在换热管外壁添加圆形翅片以此来提高管式空气换热器的余热回收。利用CFX软件模拟分析新型换热器的传热特性,通过分析翅片厚度、翅片间距、翅片高度得出,翅片厚度为0.8mm、翅片间距为3mm、翅片高度为12.5mm,换热器的换热性能最佳。     

高温CO_2冷风机的数值计算

用分布参数法建立数学模型,对CO2冷风机在高温工况下进行仿真模拟计算。分析计算了管内制冷剂侧的传热特性,以及管间距与翅片间距对换热系数和压降的影响。结果表明,由于随着干度的增加,管内CO2流型不断发生变化,管内侧换热系数和压降也随之变化。在设计冷风机时,应综合考虑翅片间距与管间距对冷风机总换热系数及空气侧压降的影响。     

Impacts of fouling and cleaning on the performance of plate fin and spine fin heat exchangers

An experimental study was conducted to investigate the effects of air-side fouling and cleaning on the performances of various condenser coils used in unitary air-conditioning systems. A total of six condenser coils with different fin geometry and row number were tested. Performance tests were performed at three different conditions: clean-as-received, after fouling, and after cleaning. In all cases, it was observed that the fouling was mostly confined to the frontal face of the heat exchanger as reported in the previous investigations. The amount of deposited dust was more dependent on fin geometry for the single-row heat exchangers than for the double-row heat exchangers. The predominant effect of fouling was to cause a more significant increase in air-side pressure drop than a degradation in heat transfer performance. For the single-row heat exchangers, the pressure drop increased by 28 to 31%, while the heat transfer performance decreased by 7 to 12% at the standard air face velocity of 1.53 m/s depending on fin shape. For the double-row heat exchangers, the pressure drop increased by 22 to 37%, and heat transfer performance decreased by only 4-5% at the same air face velocity. Once the contaminated coils were cleaned according to the given cleaning procedure the original performance of the heat exchangers could almost be recovered completely. The pressure drop could be restored within 1 to 7% and the heat transfer performance could be recovered to within 1 to 5% of the originally clean heat exchangers. Therefore, it is concluded that a periodic application of the specified cleaning technique will be effective in maintaining the thermal performance of the condenser coils.     

管带式冷凝器空气侧性能研究

管带式五孔口琴管是用于汽车空调上的一种新型冷凝器。本文研究了其空气侧性能，并通过模拟计算对波纹百叶翅片提出了Colbum j因子和摩擦系数，因子的计算关联式。实验数据与计算结果的比较表明，当迎面风速在3．0～5．5m／s时，j因子和f因子的计算误差分别在1％和10％以内。     

Characteristic analysis of condensate carry-over according to the surface tensions in the wet and the dry conditions on the fin surfaces of heat exchangers

Typically, condensate forms as droplets on the fin surfaces and may bridge the space between the fin surfaces. This is due to the dry characteristics inherent to the fin surface. The droplets increase the air-side pressure drop. In the case of high air velocities, these droplets may be blown off the fins and entrained in the air stream. To minimize the formation of condensate droplet, the wet ability of the fins must be improved. The carry-over velocity is affected by fin surface characteristics. To avoid carry-over in the air conditioner having the highest air velocity of 1.5 m/sec, the dynamic contact angle (DCA) should be at least lowly under 60°.     

R410a和R22平行流冷凝器变工况特性的比较

对比研究了分别采用R22及其替代工质R410a的平行流冷凝器在室外变工况下性能的同异。通过建立平行流冷凝器的稳态分布参数模型,仿真研究了不同冷凝温度下R410a和R22的变工况特性,并引入质能比的概念对这两种工质的单位换热量所需制冷剂质量的多少进行了比较。仿真结果是R410a和R22的换热量、制冷剂侧压降和制冷剂质量随工况和冷凝温度的改变具有的相似的变化趋势,且R410a具有较高的换热量和较低的压降;两者的质能比随进风温度和进风量的升高均呈基本一致的向上抛物线的变化趋势,且R410的质能比低于R22。可以得出R410a与R22具有相似的变工况特性,适合替代R22应用于采用平行流冷凝器的汽车空调。并且R410a在传热、流动性能和降低制冷剂充注量方面均优于R22。     

汽车空调平行流式冷凝器空气侧性能研究

建立了平行流冷凝器的数学模型,根据所建模型得到的计算结果和试验结果对比,其误差范围在5%内.并针对迎面风速对冷凝器性能影响进行了分析,为平行流式冷凝器性能优化设计提供了重要的参考.     

影响风冷式热泵蒸发器结霜性能因素的研究

研究了在热泵工况下变化参数对风冷热泵蒸发器霜形成率的影响，获得了入口空气相对湿度、温度、流速以及翅片间距等参数对蒸发器结霜量和空气侧压降的变化规律。计算结果和实验测试的结果吻合较好，研究结论对翅片管式蒸发器设计具有重要意义。     

Heat transfer and pressure drop amidst frost layer presence for the full geometry of fin-tube heat exchanger

The present study numerically solves the flow and thermal fields in the full geometry of heat exchanger modeling with frost layer presence on the heat exchanger surface. The effects of air inlet velocity, air inlet temperature, frost layer thickness, fin pitch, fin thickness, and heat exchanger shape on the thermo-hydraulic performance of a fin-tube heat exchanger are investigated. Heat transfer rate rises with increasing air inlet velocity and temperature, and decreasing frost layer thickness and fin pitch. Pressure drop rises with increasing air inlet velocity and frost layer thickness, and decreasing fin pitch. The effect of fin thickness on heat transfer and pressure drop is negligible. Based on the present results, we derived the correlations, which express pressure drop and temperature difference between air inlet and outlet as a function of air inlet velocity and temperature, as well as frost layer thickness.     

空调性能试验装置用热管空气热回收器的数值模拟

采用CFD方法对热管空气热回收器进行了数值模拟研究,分析了其冷凝段和蒸发段空气侧的温度场和速度场。模拟了不同管排组合方式、不同室内外温差及不同风量对热管空气热回收器换热性能的影响。结果表明,1对1管排组合的总换热量最大,2对2管排组合其次,4对4管排组合最小;并发现模拟结果与试验结果误差在5%以内,验证了所建模型的合理性。模拟结果为实际工程应用提供数据支持。     

A non-intrusive method for evaluation ammonia mass flow rate in the condenser for diffusion-absorption refrigerators

Studies of diffusion-absorption (DAR) refrigerators have intensified, as well as the market's interest in increasing energy efficiency through cogeneration systems. Several studies have been published with the objective of improving the coefficient of performance, through the most different procedures. This article evaluates a non-intrusive method for the calculation of the ammonia mass flow rate at the inlet of the expansion device. The required parameters are geometric data and condenser temperature. The air-side convection heat transfer coefficient was calculated considering six empirical correlations. Then, throughout an energy balance in the condenser, the mass flow rate was computed. Four correlations predicted similar heat transfer coefficient. Thus, it is possible to estimate the ammonia mass flow using only the geometric data and the condenser temperatures. The strategy adopted to achieve this goal it was to use only the geometric data and the temperatures of the condenser and to calculate the energy balance in the superheated and saturation phases, since the absence of the subcooling in the condenser is a characteristic of the DAR cycle.