整体翅片式微通道换热器的数值模拟

采用CFD数值模拟的方法,对整体翅片式微通道换热器空气侧的流动与传热特性进行研究,用场协同的原理分析翅片参数(长度、高度、间距)对换热器性能的影响,并与传统微通道换热器空气侧性能进行对比。结果表明:在考查的翅片尺寸范围内,随着翅片长度的缩短、高度的增加、间距的减小,温度场和速度场的协同性随之改善,有利于换热效果的提高;与传统的微通道换热器相比,整体翅片式微通道换热器空气侧换热性能变差,但是阻力大大降低,总体性能有所改善。     

星型翅片管换热器结霜过程的数值模拟

采用数值模拟的方法对星型翅片管换热器的结霜过程进行了研究。得到了霜层厚度和霜层密度等物性参数的变化规律,分析了其空气侧结霜过程中的传热传质特性,研究了翅片高度和翅片个数两个参数对结霜过程的影响。结果表明,结霜现象会造成换热器换热性能的恶化,并且翅片个数越多、翅片高度越小,传热恶化更严重。     

微通道换热器两相流分布研究现状与展望

两相流进入微通道换热器容易出现分布不均匀的现象,显著降低微通道换热器的性能.本文对微通道换热器两相流分布的研究动态进行了归纳与分析,主要介绍了微通道换热器中两相流分布特性的影响因素、提升微通道换热器中两相流分布均匀性的技术方案、微通道换热器两相流分布特性的仿真研究及相分离技术在微通道换热器中的应用;论述了两相流在微通道...     

微通道换热器结霜特性及换热性能实验研究

结霜是制约微通道换热器在制冷及空调系统应用的主要因素之一。针对微通道换热器结霜问题,本文基于相变驱动力分析了结霜机理,观察了不同环境因素下冷表面霜层生长形貌,并实验研究了湿空气温度、含湿量、气流速度及冷却液温度对微通道换热器结霜特性及换热性能的影响。结果表明:湿空气含湿量及气流速度是影响微通道换热器结霜的主要因素,结霜时间为15 min,含湿量为5.75 g/(kg干空气)工况下,换热器表面结霜量比含湿量为3.58 g/(kg干空气)时提高了63.87%;气流速度为2.5 m/s工况下,换热器表面结霜量比气流速度为1 m/s时增加了55.4%。随着结霜时间的增长,湿空气温度、冷却液温度越低,含湿量、气流速度越大,换热量下降趋势越明显。     

换热器结霜和化霜研究进展

分别从换热器结霜化霜现象的影响、改善结霜的措施以及除霜控制三个方面,论述了近年来国内外对于换热器结霜化霜问题的研究,并分析了微通道换热器在结霜化霜问题上遇到的问题,提出相应的研究方向。     

关于延缓空气源热泵换热器结霜的研究现状与展望

在分析结霜机理的基础上,从室外环境参数、蒸发器结构、翅片结构和表面特性、外加驱动力四个方面介绍了空气源热泵换热器延缓结霜的国内外研究现状,并提出了目前仍然存在的问题和解决这些问题的研究方向。     

三排变片距翅片盘管换热器结霜特性实验研究

为改善空气源热泵室外翅片盘管换热器在低环境温度下沿空气流动方向结霜不均匀、首排结霜量较大进而导致热泵除霜间隔较短、制热能力下降等问题,对不同翅片片距组合的变片距翅片盘管换热器在低环温工况下运行及结霜的情况进行实验研究。结果表明：变片距翅片盘管换热器在低环温条件下可有效延长迎风面管排发生结霜堵塞的时间、对于结霜生长速度和结霜质量也有抑制作用。变片距翅片盘管换热器在结霜中后期阶段换热功率更高,在合理的翅片间距组合下,变片距翅片盘管换热器可以在不损失过多换热功率的情况下延长换热器迎风面管排结霜堵塞的时间,如样品4的平均换热功率比样品1低6.02%,而除霜间隔延长了37 min。     

结霜工况下不同结构微通道蒸发器换热性能实验研究

针对微通道蒸发器结霜问题,设计了具有相同换热面积的单层和双层微通道蒸发器。基于制冷剂分布平定参数(RDP)分析了不同结构微通道蒸发器制冷剂分布对结霜的影响,并对比分析了单、双层微通道蒸发器在结霜工况下的换热性能。研究表明:单层蒸发器RDP高于双层蒸发器,结霜30min时,双层蒸发器结霜量高于单层蒸发器1.1倍,随着结霜时间的增长,蒸发器制冷剂压损逐渐降低,空气侧阻力逐渐升高。单层蒸发器和双层蒸发器的换热量分别减少56.4%、72%,制冷剂压损分别下降26.5%、53.05%,空气阻力分别增大30.08%、51.55%,结霜对双层蒸发器出风温度均匀性影响更大。单层结构的微通道蒸发器比双层结构更适用于结霜工况。     

换热器表面结霜的特性与翅片效率公式的分析

分析换热器表面的结霜特性。及其对换热器性能的影响。从理论上分析几种结霜下的换热器翅片效率公式。并对各公式的结果进行比较。提出了一种更为合理的翅片效率公式形式。     

微通道换热器两相分配特性对空调系统性能的影响

微通道换热器作为新一代换热器逐渐被使用在家电领域,其结霜、除尘、排水、分液等都是目前亟待解决的问题。通过R22家用空调系统的标准性能实验台,对三种流程数不同的微通道换热器用作冷凝器和蒸发器时,温度分布均匀性和其对系统性能的影响进行实验,研究发现,微通道换热器在用作冷凝器和蒸发器时,温度分布不均对系统性能的影响分别达到7.3%和3.5%,并且流程数对于温度分布均匀性的影响在作为冷凝器和蒸发器时是不同的。     

Experimental investigation of the surface temperature and water retention effects on the frosting performance of a compact microchannel heat exchanger for heat pump systems

Frost formation on a louvered fin microchannel heat exchanger was experimentally investigated in this paper with the aim of determining the dominant factors affecting the time of frosting and frost growth rate. A novel methodology was developed to measure frost thickness and frost weight at intervals during the frosting period. Frost mass and thickness growth rates, corresponding coil heat transfer, capacity degradations and air pressure drop are measured and discussed. The experimental data showed that at a given air dry bulb temperature, the fin surface temperature and air humidity are the primary parameters that influence the frost growth rates. Water retention and air velocity had a secondary impact on the frosting performance. From digital images of the frost growth it was observed that frost does not nucleate from the water droplets retained in between fins but it developed from the leading edges of the fins.     

翅片结构对换热器结霜特性影响的实验研究

本文对空气源热泵的翅片管换热器表面霜层生长特性进行实验研究,通过红外热像仪对霜层表面温度进行测量,并用热电偶直接测量装置进行校核.分析了平片、波纹片、条缝片3种翅片类型及翅片节距对霜层厚度、结霜量、换热量的影响,并用霜层-湿空气界面条件等作为传热及传质驱动力分析了霜层生长规律.实验结果表明,波纹片及条缝片翅片换热器界面...     

Effect of louver angle on performance of heat exchanger with serpentine fins and flat tubes in frosting: Importance of experiments in periodic frosting

This paper presents the air-side pressure drop and overall heat transfer coefficient characteristics for serpentine-louvered-fin, microchannel heat exchanger in periodic frosting. It focuses on quantification of the effects of louver angle on heat transfer and pressure drop and on defrost and refrost times. Nine heat exchangers differing in louver angle and fin pitch (i.e. louver angle 15° to 39° and fin pitch 12 to 18 fpi) are studied. The face velocity was 3.5 m s⁻¹ and inlet air relative humidity of 70% and 80%.The major finding of this paper is seen in the proof that it is necessary to perform experiments in several consecutive cycles to be able to understand the situation in operation of the heat exchangers and that geometry that is the best in first frosting test does not stay the best in real operation where multiple consecutive frosting occurs.     

Experimental investigation of adverse effect of frost formation on microchannel evaporators,part 1: Effect of fin geometry and environmental effects

This study experimentally investigated the frost growth on louvered folded fins in microchannel heat exchangers when used in outdoor air-source heat pump systems. The effects of surface temperature, fin geometries, and air environmental conditions were studied. The overall aim was to isolate and quantify the effect of geometry from surface temperature effects. Experimental data of frost weight, local frost thickness, air pressure drop across the coils, time of frost–defrost cycles and heat transfer rates were recorded. Data showed that the frosting time and the frost growth rates depended mainly on the local fin surface temperature. Lower fin density was beneficial because it delayed the blockage of the air flow. The fin length and fin depth had minor effects on frosting performance. The air humidity had a fairly significant effect on rate of frost formation while air velocity seemed to have a small effect on the frost growth rate.     

An experimental study on frosting of laminar air flow on a cold surface with local cooling

This paper presents the heat and mass transfer characteristics of the humid airflow in frosting conditions. A flat plate of aluminum with cooling modules at the central region was used for the simulation of flat surface part of the fin of the heat exchanger. The local surface temperature of the plate and the local thickness and total mass of the frost on the plate were measured to analyze the heat and mass transfer characteristics. In order to analyze the frosting characteristics, an analysis algorithm was developed, which can provide the local air temperature, the frost surface temperature, the sensible and the latent heat flux distributions at the test plate. Also, by integrating the local heat flux distribution, the average heat flux characteristics were analyzed. The present experiment and analysis found that the characteristic of the upstream airflow was very different from that of the downstream airflow.