平行流冷凝器百叶窗翅片结构优化

建立平行流冷凝器百叶窗翅片的三维流动和换热模型,并对不同迎面风速下百叶窗翅片的流动和换热性能进行数值模拟,计算结果与试验结果具有较好的一致性,验证计算模型和方法的正确性。在此基础上,建立8种结构形式的百叶窗翅片模型,并对其空气侧的换热和流动过程进行仿真,分析结构形式和排列方式对百叶窗翅片换热量和空气阻力的影响,结果表明:增加开窗区域数能够有效提高翅片的换热性能,增加百叶窗的转向区数目能够有效降低进出口的压降。     

微通道换热器翅片结构优化

采用STAR-CCM+软件中的共轭传热模型对微通道换热器空气侧的流动及换热进行仿真,并利用试验结果对仿真结果进行验证,表明仿真模型的准确性可以满足工程设计要求.改变翅片开窗角度和开窗数进行仿真,结果表明,翅片开窗角度为45°且开窗数为14个时,微通道换热器空气侧换热量最大,压降相对较小.     

家用空调器中平行流冷凝器翅片参数对空气侧传热流动性能的影响

为了推广平行流冷凝器在家用空调器中的应用,根据经验传热及压降关联式,采用数值模拟的方法,研究家用空调器中平行流冷凝器翅片参数对其空气侧传热流动性能的影响规律.结果表明:适当减小平行流冷凝器的翅片高度和翅片间距,可提高其换热系数、增加压降,保证其换热性能变化较小.     

基于蒙特卡罗法的平行流冷凝器的翅片参数优化

运用蒙特卡洛法,在家用空调运行工况下,对平行流冷凝器空气侧的传热和流动性能进行了优化计算,分析了翅片的各种几何参数组合对换热系数和压力损失的影响.得出了影响换热系数的主要因素是翅片高度和百叶窗长度,同时增大两者既可以快速增大换热系数又可以降低压力损失;影响压力损失的主要因素是翅片宽度,因为翅片宽度的微减能带来压力损失的大大将低,但换热系数不受翅片宽度的影响;并同时得出影响换热系数和压力损失的次要影响因素是翅片间距和百叶窗角度.翅片间距减少、百叶窗角度增大均会引起换热系数与压力损失的增大.用这种优化方法得出的结论进行翅片参数组合的平行流冷凝器,可以在满足压力损失需要的情况下大大提高其换热性能.     

电冰箱用微通道冷凝器制冷剂侧传热与压降特性试验研究

建立电冰箱换热器试验台,对具有百叶窗翅片的微通道冷凝器制冷剂侧的传热和压降进行测试。结果表明:随着制冷剂质量流速的增加,冷凝器换热量、换热系数及制冷剂流动压降均增大,在冷凝压力为1.46MPa,制冷剂质量流速从90 kg/(m~2·s)增加到150 kg/(m~2·s)时,换热量、换热系数和压降分别增加63%,116%和166%;随着冷凝压力的升高,换热量增大,换热系数减小,在制冷剂质量流速为150 kg/(m~2·s)时,冷凝压力为1.46 MPa与冷凝压力为1.16 MPa相比,换热量增加12%,换热系数降低39%。     

组合管径圆弧翅片换热性能的数值模拟

针对空调器室内机换热器空气侧的流动和换热问题,利用FLUENT软件,本文研究了开缝圆弧翅片以及组合管径开缝圆弧翅片对换热器的换热量和空气侧压降的影响,并与原开缝三折翅片换热器进行比较。结果表明,开缝圆弧翅片换热器的换热量大于原开缝三折翅片换热器,而空气侧压降略有增大。随着小管径数量增大,开缝圆弧翅片换热器的换热量逐渐减小,但压降也逐渐减小。相比于开缝三折翅片换热器,当开缝圆弧翅片换热器为10根小管时,其压降增大5%左右,但换热量却有2%左右的提高,且铜管材料节省了14.5%,有很好的应用前景。     

多元平行流冷凝器传热流动性能研究

平行流冷凝器空气侧采用间断型扩展表面的波纹型百叶窗翅片,制冷剂侧采用小水力直径的非圆截面微通道多孔铝制扁管,选用适合于该微尺度强化换热结构的传热和压降关联式,对某规格的平行流冷凝器建立数学模型并在一定工况下进行数值模拟.结果分析表明,制冷剂在非圆截面微通道内的冷凝过程中,表面张力对表面传热系数的强化效果明显;通过改变流程数和各流程管数来改变冷凝过程中的流通截面而达到调整流速的作用,从而可以保持较高的冷凝换热系数和较低的流动压降,与常规换热器相比具有显著的优越性.     

微通道冷凝器空气侧性能的实验研究

对13个微通道冷凝器空气侧性能进行实验研究,分析空气侧换热系数和压降与迎面空气流速、翅片片距、百叶窗翅片开窗数、扁管宽度及扁管高度之间的关系,并将实验值与3个不同的百叶窗翅片换热及压降关联式的预测值进行比较。结果表明：翅片片距和扁管宽度对空气侧性能影响较大,3个关联式中Kim—Bullard关联式预测偏差相对最小,换热系数的预测偏差在0～-30％以内,摩擦系数的偏差在±20％偏差范围内。最后基于已有实验数据,对KimBullard关联式进行重新拟合。     

翅片管式冷凝器性能分析及多目标优化

针对翅片管式冷凝器构建稳态分布参数模型,利用试验数据验证模型,换热量误差在±3%以内。利用该模型对不同结构参数下的冷凝器性能进行仿真,分析管径、翅片间距、管间距等对管翅式冷凝器性能以及成本的影响。利用多目标遗传算法(MOGA)优化结构参数,其中综合性能优化的方案中换热量增加0.08%,成本降低0.43%,制冷剂侧压降降低3.71%,空气侧压降降低13.66%。     

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。     

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。     

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.     

翅片管换热器在析湿工况下的积灰特性及对空气侧压降的影响

空调器室内机多数采用翅片管换热器,会因制冷运行过程中表面析湿而粘附灰尘,导致空气流动阻力增大。本文选用空调器中常用的平直翅片、波纹翅片和开窗翅片作为测试样件,翅片间距范围为1.5～2.2 mm,研究了翅片管换热器在析湿工况下的积灰特性及积灰对空气侧压降的影响。结果表明:翅片表面的析湿量决定积灰程度,析湿液滴分布越密集、液桥数量越多,翅片迎风面的堵塞程度越严重且空气侧压降越大。在相同析湿工况下,具有复杂结构的开窗翅片和小翅片间距更容易积灰并增大空气侧压降,因此降低翅片结构复杂程度并适当增大翅片间距有利于空调器的防尘。在积灰过程中,随着换热器表面粉尘沉积量增加,空气侧压降先增大后保持稳定。     

翅片结构对翅片管换热器积灰与压降影响的实验研究

积灰对具有不同翅片结构的翅片管换热器均会造成长效性能的衰减。本文搭建了换热器积灰可视化实验台,研究了翅片结构对积灰量及积灰后空气侧压降的影响。测试样件的翅片类型包括平直翅片、波纹翅片和开窗翅片;翅片间距范围为1.3~1.8 mm。实验结果表明:开窗翅片管换热器表面最容易沉积粉尘并增大积灰后压降,与平直翅片相比,波纹翅片和开窗翅片表面粉尘沉积量分别提高了25.6%和52.8%、积灰后压降增量分别提高了44.4%和165.6%;对于开窗翅片,小翅片间距有利于积灰并增大积灰后压降,与翅片间距1.8 mm的样件相比,翅片间距1.5 mm和1.3 mm的样件表面粉尘沉积量分别提高了26.2%和43.2%、积灰后压降增量分别提高了24.1%和49.4%;在积灰过程中,随着粉尘沉积量的增加,翅片管换热器空气侧压降先增大后保持稳定。     

Air-side thermal hydraulic performance of multi-louvered fin aluminum heat exchangers

An experimental study on the air-side heat transfer and pressure drop characteristics for multi-louvered fin and flat tube heat exchangers has been performed. For 45 heat exchangers with different louver angles (15–29°), fin pitches (1.0, 1.2, 1.4 mm) and flow depths (16, 20, 24 mm), a series of tests were conducted for the air-side Reynolds numbers of 100–600, at a constant tube-side water flow rate of 0.32 m³/h. The inlet temperatures of the air and water for heat exchangers were 21 and 45°C, respectively. The air-side thermal performance data were analyzed using effectiveness-NTU method for cross-flow heat exchanger with both fluid unmixed conditions. The heat transfer coefficient and pressure drop data for heat exchangers with different geometrical configurations were reported in terms of Colburn j-factor and Fanning friction factor f, as functions of Reynolds number based on louver pitch. The general correlations for j and f factors are developed and compared to other correlations. The f correlation indicates that the flow depth is one of the important parameters for the pressure drop.     

Effect of inlet humidity condition on the air-side performance of an inclined brazed aluminum evaporator

The effect of air inlet humidity condition on the air-side heat transfer and pressure drop characteristics for an inclined brazed aluminum heat exchanger has been investigated experimentally. For a heat exchanger with a louver angle of 27°, fin pitch of 2.1 mm and flow depth of 27.9 mm, a series of tests are conducted for the air-side Reynolds numbers of 80–400, with variation of inlet humidity condition. The heat transfer data are obtained for wet condition only and the pressure drop data are measured for both dry and wet conditions. The inlet air temperature and relative humidity range are 12 °C and 60–90%, respectively. The inclination angles (θ) from the vertical position are 0, 14, 45, and 67° clockwise (leeward direction). The inclination angles affect moderately the sensible heat transfer coefficient for wet condition, and the pressure drops for both dry and wet conditions increase systematically with the inclination angle. The heat transfer and pressure drop characteristics under wet condition are not influenced substantially by the air inlet humidity for θ 45°. The effect of the louver directions at the inlet and outlet of the inclined heat exchanger on the performance is also addressed.     

空冷凝汽器蛇形翅片扁平管空气侧流动与换热特性研究

针对应用于电站直接空冷凝汽器的蛇形翅片扁平单排管,对其空气侧的流动及换热特性进行了数值模拟。给出了该管件基本结构的雷诺数和欧拉数随迎面风速的变化关联式;结果显示,同一迎面风速下,随着翅片间距、高度的增大,换热变差,流动变好。但当间距增加到一定程度时,风速与间距对换热流动性能的影响都变得很小。风速越大,换热性能对翅片间距、高度越敏感,而流动则相反,需根据实际工况来选择合适的翅片间距及高度。     

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.