新型组合翅片换热器数值研究

通过对传统多排管翅式换热器的研究分析,提出第1排为平片且后部为开缝翅片的新型组合翅片换热器,并对传统和新型组合翅片2种形式换热器内的空气流动和换热进行数值分析。结果表明,新型组合翅片换热器的综合换热性能比传统翅片的提升5％～8％。     

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。     

采用窗片的5 mm管换热器在湿工况下换热性能的实验研究

在湿工况下,对11个采用百叶窗翅片的5 mm管换热器进行了实验研究,并分析了翅片间距、进口空气相对湿度等因素对空气侧换热性能的影响。研究结果表明:换热量随翅片间距的增加而减小,且比7 mm管或更大管径换热器更明显;换热量受进口空气相对湿度的影响小;在翅片底部出现水桥,而在7 mm管或者更大管径换热器中不曾出现。根据实验数据开发了预测5 mm翅片管换热器换热性能的j因子关联式,误差在士20%以内。     

空气换热器用翅片管簇的展望及换热性能的比较研究

一、翅片类型及展望翅片式空气换热器的翅片形式大体可分为:1.绕片式:园管绕园翅片,和椭园管绕椭园翅片。2.串片式:园管串园翅片,园管串矩形翅片,园管串大形板片式翅片,椭园管串矩形翅片,和椭园管串椭园翅片等。     

扁管和百叶窗式微通道换热器空气侧阻力的实验研究

在迎面风速1~4m/s、雷诺数100~500,迎风面尺寸600mm×550mm以及环境温度20℃工况条件下,测试了微通道换热器空气侧阻力,对比分析了测试结果与不同关联式计算结果,表明现有不同关联式间预测结果相差较大,其中Davenport的关联式与实验值较为接近,但实验值也仅有其预测值的55%~66%。实验也表明微通道换热器空气阻力与换热量和迎风面积相同的平翅片圆管换热器空气阻力相当,认为独特的扁管结构和较小的换热器厚度是其减小空气阻力的有效手段。     

板翅式换热器板翅结构强度影响因素分析

为了提高不锈钢板翅式换热器的承压能力,利用有限元软件ANSYS,对不锈钢锯齿型板翅结构进行强度分析,讨论了翅距、翅厚、节距、翅高、翅片形成半径及压差等对翅片强度及安全性能的影响.计算结果表明,由于焊缝和锯齿型翅片几何结构的综合影响,焊缝和两排翅片连接处成为受力薄弱环节.翅距、翅厚、压差是影响翅片强度的重要因素,翅距减小,翅厚增大,翅片内外通道压差减小时,翅片的承压能力越强安全性能越好;翅高、翅片节距、翅片加工尺寸对翅片的安全性能影响较小.     

空调换热器长期运行性能衰减的加速实验研究

为研究长期积尘对空调室外机性能衰减的影响,本文采用对空调室外换热器进行加速测试方法,在高粉尘浓度环境下短时间积尘模拟实际空调在低粉尘浓度下长期运行时的积尘效果,从而加快换热器的积尘进程以达到加速测试的目的。基于上述方法搭建了换热器加速测试实验台,对具有不同翅片结构与管排数的3种换热器样件进行2～10 h的加速积尘测试,预测其在室外运行1～5年后的性能衰减效果。测试结果表明:空调换热器使用5年后,1排管波纹翅片换热器、2排管波纹翅片换热器和2排管平直翅片换热器的压降增幅分别为21.8%、29.5%和25.0%,换热量衰减率分别为11.2%、19.3%和18.0%。     

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。     

杭氧换热设备公司“大型空分设备高效换热器翅片研制与示范”项目通过验收

<正>2017年2月18日《杭氧报》报道,日前,杭氧换热设备有限公司与浙江大学联合开发的"大型空分设备高效换热器翅片研制与示范"项目,通过了杭州市科学技术委员会的验收。该项目针对目前空分设备用管翅式换热器的使用场合,对管子形状和排列方式、翅片形式和间距、流体方式布置等进行优化设计,确定合理的技术方案。通过对翅片结构流场数值模拟和试验研究,提出最优翅片参数,为不同应     

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.     

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.     

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.     

Evaluation of microchannel condenser characteristics by numerical simulation

This paper presents the development of a finite-volume-based numerical condenser model that considers important factors such as non-uniform air temperature and velocity at the front, fin conduction, refrigerant-side maldistribution caused by pressure balance between tubes, and air-side distribution for multislabs. Air-side and refrigerant-side microscale heat transfer and pressure drop correlations are carefully compared. The model results match well with lab test results for one-slab and two-slab microchannel heat exchangers on heat transfer and pressure drop. Several simulations are conducted to determine the impact of return air temperature, tube wall temperature, and non-uniform refrigerant flow rate. In addition, optimization results are analyzed by changing the number of flat tubes in each pass for both types of heat exchangers.     

空调用翅片管式换热器腐蚀及防护研究进展

空调用翅片管式换热器长期使用会受到一定程度的腐蚀,影响换热器的换热性能,导致整个空调系统的能效降低.本文介绍了翅片管式换热器3种主要的腐蚀机理:蚁巢腐蚀、点蚀和间隙腐蚀,从形貌、压降及传热特性3个方面分析了腐蚀对翅片管式换热器性能的影响,结果表明:翅片管式换热器腐蚀后,传热系数和换热量均减小,空气侧压降受影响较小,在5...     

小管径椭圆管开缝翅片换热器的数值模拟

对小管径椭圆管开缝翅片换热器空气侧的流动与传热特性进行数值模拟,对影响其换热性能的2个主要参数椭圆管偏心率和开缝翅片开缝错列高度分布进行优化,与传统管翅式换热器换热性能进行比较。模拟结果表明:当椭圆管两轴之比Rx:Ry=2:3(偏心率),开缝高度分布为0.8 mm,0.6 mm和0.4 mm时,换热效果最好。与传统管翅式换热器相比,小管径椭圆管开缝翅片换热器换热系数提高10%~20%,而压降几乎相等,总体换热性能提高。     

Heat transfer characteristics of flat plate finned-tube heat exchangers with large fin pitch

The objective of this study is to provide experimental data that can be used in the optimal design of flat plate finned-tube heat exchangers with large fin pitch. In this study, 22 heat exchangers were tested with a variation of fin pitch, number of tube row, and tube alignment. The air-side heat transfer coefficient decreased with a reduction of the fin pitch and an increase of the number of tube row. The reduction in the heat transfer coefficient of the four-row heat exchanger coil was approximately 10% as the fin pitch decreased from 15.0 to 7.5 mm over the Reynolds number range of 500–900 that was calculated based on the tube diameter. For all fin pitches, the heat transfer coefficient decreased as the number of tube row increased from 1 to 4. The staggered tube alignment improved heat transfer performance more than 10% compared to the inline tube alignment. A heat transfer correlation was developed from the measured data for flat plate finned-tubes with large fin pitch. The correlation yielded good predictions of the measured data with mean deviations of 3.8 and 6.2% for the inline and staggered tube alignment, respectively.     

Numerical analysis of evaporation performance in a finned-tube heat exchanger

This study discusses the effects of the heat exchanger type, refrigerant, inner tube configuration, and fin geometry on evaporator performance by adopting updated correlations of EVSIM, a numerical analysis model based on the tube-by-tube method developed by Domanski. The heat exchanger types considered are the cross-counter flow type and cross-parallel flow type. The refrigerants considered for the numerical test as a working fluid are R-134a, R-410A and R-22. For inner tube configuration, enhanced tube and smooth tube cases are considered. For the air side evaporation performance, heat exchangers using plate fins, wavy fins and slit fins are analyzed. Results show that the heat transfer rate of the cross-counter flow type heat exchanger is 3% higher than that of the cross-parallel flow type with R-22. The total heat transfer rate of the evaporator using R-410A is higher than those using R-22 and R-134a, while the total pressure drop of R-410A is lower than those of R-22 and R-134a. The heat transfer rate of the evaporator using enhanced tubes is two times higher than that using smooth tubes, but the pressure drop of the enhanced tube is 45–50% higher than that of the smooth tubes. The evaporation performance of slit fins is superior to that of plate fins by 54%.