亲水涂层对微通道换热器空气侧性能的影响

对微通道换热器进行了亲水表面处理,并对其性能进行了实验研究,分析了亲水处理对微通道换热器湿工况性能的影响。实验表明,亲水处理对换热器性能有利:与无涂层换热器相比,亲水处理换热器换热量最多增大7.0%,压降减小0.7%～18.9%。而随着翅片间距的减小和芯体厚度的增加,亲水处理带来的性能提升减弱。     

亲水涂层对翅片管式换热器空气侧性能的影响

为了分析亲水涂层对翅片管式换热器空气侧性能的影响,对干/湿工况下亲水涂层翅片和普通翅片管式换热器空气侧的压降和热阻进行对比试验。结果表明：相对于普通翅片管式换热器,在干工况下,亲水涂层翅片管式换热器空气侧压降略增大,空气侧热阻增大10%左右;在湿工况下,亲水涂层翅片管式换热器空气侧压降减小,空气侧热阻增大4%左右;亲水涂层翅片管式换热器空气侧热阻基本不受空气湿度的影响。     

冰箱微通道换热器积灰机理研究

冰箱微通道换热器表面灰尘沉积会导致空气侧压降增加,造成换热性能衰减。本文通过搭建微通道换热器积灰模拟实验台,研究了风速、灰尘种类、相对湿度、是否带电4个因素对微通道换热器积灰的影响。结果表明:低风速下,灰尘沉积在翅片迎风表面,较高风速时,积灰向翅片后缘扩展。粉末状灰尘几乎不能堆积,随着灰尘中纤维比例的增加,积灰速度也越来越快。当风速为1 m/s,风机固定功率下,100%颗粒、95%颗粒+5%纤维、92%颗粒+5%纤维+3%长纤维3种不同灰尘工况时,空气侧压降增长率分别为8.8%、451.4%、524.9%。95%颗粒+5%纤维和92%颗粒+5%纤维+3%长纤维不同灰尘工况下风量衰减率分别为31.6%和48.7%。当相对湿度为45%和65%时,空气侧压降增长率分别为451.4%和385.6%,风量衰减率分别为31.7%和26.4%。不带电和直流电5 V工况下的空气侧压降增加率分别为385.6%和278.3%,风量衰减率分别为26.4%和18.4%。     

冰箱微通道换热器积灰机理性研究

冰箱微通道换热器表面灰尘沉积会导致换热器压降增加，造成换热性能衰减。本文通过搭建换热器积灰模拟实验台，研究了风速、灰尘种类、湿度、是否带电等因素对换热器积灰的影响。结果表明：低速下，灰尘沉积在翅片迎风表面，在较高风速时，积灰向翅片后缘扩展。粉末状灰尘几乎不能堆积，随着灰尘中纤维所占比例的增加，积灰速度也越来越快。当风速为1 m/s，风机固定功率下，100%颗粒状灰尘、95%颗粒状灰尘+5%纤维、92%颗粒状灰尘+5%纤维+3%长纤维三种工况时，空气侧压降增长率分别为8.8%、451.4%、524.9%。95%颗粒状灰尘+5%纤维和92%颗粒状灰尘+5%纤维+3%长纤维工况下风量衰减率分别为31.6%和48.7%。当相对湿度为45%和65%工况时，空气侧压降增长率分别为451.4%和385.6%，风量下降率分别为31.7%和26.4%。不带电和交流电3 V工况下的空气侧压降增加率分别为385.6%和278.3%，风量下降率分别为26.4%和18.4%。     

翅片表面涂层对结化霜除灰特性影响的实验研究

为了解决空调换热器长时间运行后性能下降的问题,需要及时清除换热器翅片上沉积的粉尘。本文提出采用空调换热器自身的结化霜过程来实现除灰,并通过实验研究了不同翅片表面涂层对结化霜除灰效果的影响。为了对比不同翅片表面涂层的除灰效果,采用4种实验样件,包括空调换热器常用的无涂层铝片和无涂层铜片,以及通过微纳结构自组装方法制备的具有不同表面润湿性的带亲水涂层铜片和带疏水涂层铜片。通过搭建可视化实验台观测了不同样件表面的结化霜除灰过程,对比了不同样件的除灰速率与残留灰量。实验结霜工况为：样件表面温度-10 ℃,结霜时间1 h,环境温度27 ℃,相对湿度50%;化霜工况下样件表面温度为5 ℃。实验结果表明,带有疏水涂层的铜片在结化霜过程中的除灰效果最好,疏水样件上残留粉尘的质量仅是无涂层铝片上残留粉尘质量的1.9%,是无涂层铜片上残留粉尘质量的2.0%,是亲水铜片上残留粉尘质量的5.9%。     

热泵车外换热器制冷剂侧结构分析

针对电动车热泵空调系统车外换热器不能使用传统平行流换热器的问题,采用分布参数法建立了稳态数学模型,利用该模型研究了在结霜工况下制冷剂侧结构,包括流程数、各流程扁管布置方式、扁管宽度和微通道孔高对换热及压降的影响,仿真结果表明在保证换热器出口达到过热的情况下,应当尽可能的减小流程数以降低制冷剂侧压降,同时在空气侧压降的限制下,可以适当的增加扁管宽度来减小制冷剂侧压降,孔高的增加会使得换热量和制冷剂侧压降同时减小,但是换热量衰减很小,所以适当增加孔高也是一个减小制冷剂侧压降的方法。     

不同工况下超疏水表面的凝露特性研究

超疏水表面能减少液滴的附着，减少液滴存在带来的热阻增加，提高空调、发电和海水淡化的效率。本文实验研究了不同冷表面温度(2～8℃)、空气湿度(40%～80%)、倾斜角度(0°～90°)下，超疏水表面冷凝液滴的生长特性，分析不同工况对超疏水表面凝露的影响。结果表明：随着冷表面温度的降低，液滴平均半径和表面液滴覆盖率逐渐增大，冷表面温度越低，液滴生长速率越快；在不同湿度工况下，高湿度下超疏水表面液滴生长较快，但随着时间增加，低湿度下液滴生长半径将超过中高湿度，且低中湿度工况下冷表面液滴覆盖率远小于高湿度；随着倾斜角度增大，液滴临界扫掠半径逐渐减小，垂直表面相比水平表面液滴覆盖率减少42%。     

两种换热器在车用四通阀热泵系统中的对比研究

PTC加热效率较低对电动汽车行驶里程影响较大,因此开发效率更高的热泵系统十分必要。实验搭建了四通阀热泵系统,并将两种不同流程排布的小管径换热器与微通道换热器分别被用于室外侧,在制冷、制热模式下进行了实验对比,由实验结果可知,在制热模式低风速下,小管径换热器相比微通道换热器,能力可以高出10.5%,而COP与微通道换热器相近;在制冷模式低风速下,小管径换热器样件能力可高出3.8%,COP可高出22.8%。但随风速的提高,小管径换热器能力和COP提升并不明显,而微通道换热器随风速提升幅度较大,由上可知,在风速较低的怠速和城市工况中,使用小管径换热器作为车用热泵的外侧换热器使用拥有一定的优势。     

微通道换热器用于重力热管系统的试验研究

针对重力热管内压降影响换热器换热性能的问题,设计2款微通道换热器,每个风冷式热管系统的蒸发器和冷凝器使用同种类型微通道换热器.在机房干球/湿球温度为35℃/24℃,室外环境温度5℃,10℃和15℃下进行换热性能测试.结果 表明:在相同试验工况下,微通道换热器的水力直径越大,其换热能力越大;蒸发器进口的制冷剂为过冷态,制...     

换热器壳程结构的实验研究及节能分析

为对管壳式换热器不同壳程结构进行实验研究,设计建造了普通单弓形折流板圆管换热器和无折流板的椭圆扭曲管换热器实验台。通过测试换热器管壳两侧的传热系数、压降和换热量等参数,对比分析了两种不同壳程结构的换热器在相同尺寸下、相同工况的传热性能。实验结果表明椭圆扭曲管管侧的表面传热系数比普通圆管和折流板换热器均有大幅度提高,随雷诺数的增大,管内表面传热系数约为普通圆管的1.27～1.43倍,管外壳程表面传热系数约为普通圆管的1.36～1.76倍,能够有效提高换热效率。另外与传统的单弓形折流板换热器相比,壳程压降显著减小,约为折流板换热器的30～35%。椭圆扭曲管换热器既强化了管内传热,又减小了壳程压降,是一种非常有效的提高换热效率的手段。综合比较管壳侧的传热效率,发现在低雷诺数工况椭圆扭曲管换热器的节能效果更好。     

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。     

Air-side performance evaluation of three types of heat exchangers in dry,wet and periodic frosting conditions

The performances of three types of heat exchangers that use the louver fin geometry: (1) parallel flow parallel fin with extruded flat tubes heat exchanger (PF²), (2) parallel flow serpentine fin with extruded flat tubes heat exchanger (PFSF) and (3) round tube wave plate fin heat exchanger (RTPF) have been experimentally studied under dry, wet and frost conditions and results are presented. The parameters quantified include air-side pressure drop, water retention on the surface of the heat exchanger, capacity and overall heat transfer coefficient for air face velocity 0.9, 2 and 3 m/s, air humidity 70% and 80% and different orientations. The performances of three types of heat exchanger are compared and the results obtained are presented. The condensate drainage behavior of the air-side surface of these three heat exchanger types was studied using both the dip testing method and wind tunnel experiment.     

不同环境参数对SK型翅片管式换热器结霜换热性能的影响

以SK型翅片管式换热器为研究对象,在循环式风洞中对其结霜工况下的性能进行试验研究,研究了入口空气流速和相对湿度等环境参数对SK型翅片管式换热器性能的影响。研究结果表明：结霜工况下,翅片表面未覆盖满霜层时,在雷诺数Re=3602～5509,进口相对湿度？=60%～80%范围内,空气侧对流换热系数随迎面风速的增大而增大,随相对湿度的增加而增加;换热器表面阻力降随着流速的增加而增大,随着相对湿度的增大而增大。实验结果表明,空气相对湿度对SK型翅片管式换热器性能的影响远大于空气流速的影响。     

Effects of biofouling on air-side heat transfer and pressure drop for finned tube heat exchangers

Experimental investigations on the effects of biofouling on air-side heat transfer and pressure drop for three biofouled finned tube heat exchangers and one clean finned tube heat exchanger were performed. Artificial accelerated method of microorganism growth on the fin surface was used for simulating the biofouled finned tube heat exchangers. Experimental results indicate that the effects of biofouling on the air-side heat transfer coefficient decreases 7.2% at 2.0 m/s when the biofouled area ratio is 10%, while it decreases 15.9% at 2.0 m/s when the biofouled area ratio is 60%, and biofouling causes a 21.8% ～ 41.3% increase in pressure drop when the air velocity is between 0.5 and 2.0 m/s. The increase of inlet air velocity is helpful to improve the long-term performance of finned tube heat exchanger. Biofouling makes the hydrophilic coating failure, and the condensation water easily converges on the fin surface where biofouling grows.     

除湿换热器串联换热器强化除湿降温性能实验研究

除湿换热器可以同时处理显热与潜热负荷,但由于吸附热的影响,存在热湿负荷处理不同步及显热负荷处理能力不足的问题。本文提出了在除湿换热器后面串联一个显热换热器对空气进行二次处理,搭建了实验台对除湿换热器串联换热器情况下除湿降温过程的动态性能进行测试,并且在实验中分析了水温、进风温度、湿度、速度等主要参数对除湿量、降温量、制冷功率、COP的影响。结果表明:增加显热换热器可以大幅度增加处理空气的平均降温温差,在除湿初期阶段效果尤为明显,同时系统的制冷量也明显提高。此外,分析各参数对实验结果的影响可知,冷水温度与热水温度升高都可以有效提高系统制冷量与COP,空气的温湿度升高会提升系统性能,空气流速变慢对系统平均除湿量与有效除湿时间有明显的提升。     

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.     

不同空气侧风速下微通道蒸发器换热特性实验研究

搭建微通道蒸发器性能实验台,采用控制变量法研究不同空气侧风速下微通道蒸发器表面温度分布、制冷剂进出口压力的变化规律,计算换热量和换热系数,从而分析空气侧风速对微通道蒸发器的流量分配特性和换热效果的影响。结果表明,随着风速增大,微通道蒸发器制冷剂流量分配不均匀性增大,进出口压力波动振幅和周期增加,压降增大,风速2 m/s时微通道蒸发器换热效果最佳。     

采用表面喷锌及喷硅扁管的微通道换热器长效特性研究

腐蚀特性是全铝微通道换热器的主要特征之一。对两种不同表面处理方式的挤压扁管：表面喷锌挤压扁管和表面喷硅挤压扁管的长效特性进行了对比研究。对采用这两种不同表面处理方式的挤压扁管的微通道换热器样件,分别进行了7天和14天的盐雾腐蚀实验(SWAAT),对比腐蚀前后两个换热器样品的换热量、空气侧压降和总热阻变化情况。结果表明,采用表面喷硅扁管的微通道换热器的长效特性优于采用表面喷锌扁管。     

Performance evaluation of a CO2 heat pump system for fuel cell vehicles considering the heat exchanger arrangements

A novel CO₂ heat pump system was provided for use in fuel cell vehicles, when considering the heat exchanger arrangements. This cycle which had an inverter-controlled, electricity-driven compressor was applied to the automotive heat pump system for both cooling and heating. The cooling and heating loops consisted of a semi-hermetic compressor, supercritical pressure microchannel heat exchangers (a gas cooler and a cabin heater), a microchannel evaporator, an internal heat exchanger, an expansion valve and an accumulator. The performance characteristics of the CO₂ heat pump system for fuel cell vehicles were analyzed by experiments. Results for steady and transient state performance were provided for various operating conditions. Furthermore, experiments to examine the arrangements of a radiator and an outdoor heat exchanger were carried out by changing their positions for both cooling and heating conditions. The arrangements of the radiator and the outdoor heat exchanger were tested to quantify cooling/heating effectiveness and mutual interference. The improvement of heating capacity and coefficient of performance (COP) of the CO₂ heat pump system was up to 54% and 22%, respectively, when using preheated air through the radiator instead of cold ambient air. However, the cooling capacity quite decreased by 40–60% and the COP fairly decreased by 43–65%, for the new radiator-front arrangement.