开缝翅片管换热器表面积尘与压降特性的实验研究

翅片管换热器表面沉积的粉尘会导致换热器压降增加。本文搭建了换热器积灰可视化实验台,选取开缝翅片管换热器为测试样件,在风速范围为1.0~2.3 m/s,喷粉浓度范围为2.1~10.8 g/m~3的条件下进行实验,研究了换热器表面的粉尘沉积特性及空气侧压降变化。结果表明:粉尘主要沉积在翅片迎风面的前缘开缝处以及换热管的迎风面上;高风速有利于粉尘沉积并增大积灰前后压降增幅,在风速变化范围内,粉尘沉积量最多增加98.4%,积灰前后压降增幅最多增加93.8%;提高喷粉浓度有利于粉尘沉积并增大积灰前后的压降增幅;在喷粉浓度变化范围内,粉尘沉积量最多增加22.8%,积灰前后压降增幅最多增加28.6%;在积灰过程中,空气侧压降比粉尘沉积量更快达到稳定状态。     

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。     

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。     

低气压下翅片管换热器空气侧传质特性实验研究

本文实验研究了两个具有不同翅片间距的平翅片管式换热器在低环境气压以及析湿工况下空气侧的传质特性,在环境气压为40～100 kPa,换热器入口空气风速为0.5～4 m/s,入口空气相对湿度为50％～90％,入口空气干球温度为27℃,水流速为1.65 m/s的实验工况下,分析了环境气压、换热器迎面风速、翅片间距及入口空气相...     

防腐方式对翅片管式换热器管外性能的影响

对比3种防腐类型翅片管式换热器和普通翅片管式换热器在风洞测试的试验数据,探讨防腐方式对管外换热特性及压降的影响。当迎面风速在1~4 m/s范围内时,预喷涂型翅片管式换热器的空气侧热阻比普通翅片管式换热器增加不超过15%,空气侧压降差异可忽略;因为铜翅片具有良好的导热性,铜翅片管式换热器的空气侧热阻比普通翅片管式换热器约低4%,空气侧压降差异较小;整体电泳型翅片管式换热器的空气侧热阻比普通翅片管式换热器小,且二者热阻差值随风速增大而减小,压降则反之。结合盐雾试验和实际工程应用中得到的经验,认为整体电泳型翅片管式换热器是这几种防腐方式中的最佳方案。     

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。     

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%。     

空调器用换热器的换热量衰减率测试方法

为了快速评估空调器用换热器长期运行后的换热量衰减情况,本文提出一套通过测试换热器加速积尘前后的换热量来预测其换热量衰减率的测试方法。该测试方法中,采用负反馈模式精确调节换热器迎风面的粉尘浓度,能够在加速积尘时间内维持换热器迎风面粉尘浓度的稳定性;通过对加速积尘循环空间与换热量测试风道进行一体化设计,能够在不需要移机时实现加速积尘与换热量测试之间的切换。在入口空气温度为45℃、流速为1. 5 m/s,入口水温为21℃、流速为0. 5 m/s的工况下对该测试方法的可靠性和一致性进行了验证,结果表明:换热器迎风面粉尘浓度能够稳定维持在目标浓度120 mg/m3,波动范围在±20%内;对4种具有不同结构的换热器样件进行了多次换热量衰减率测试,其换热量衰减率相对偏差均在±10%之内,表明该测试方法具有较好的一致性。     

凹印机换热器结构性能的优化

目的大幅度优化凹印机的工作性能,为干燥箱提供持续稳定的热源。方法依据流体力学与传热学理论对换热器进行仿真分析,研究翅片管换热器的换热效率与翅片高度、翅片间距、换热管排列方式的映射关系。结果换热器的换热效率随翅片间距的增加而减少,选择3 mm间距时效果较优,较低的翅片高度使换热器结构更加紧凑;在正三角形、转角正三角形、正方形、转角正方形排列方式中,正三角形排列方式出口温度均匀且换热效率最高。结论选取凹印机换热器的结构时尽量选择翅片间距小、翅片高度低、正三角形排列的换热器,为企业选用最优性能的换热器提供理论依据。     

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%。     

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...     

Numerical model of particle deposition on fin surface of heat exchanger

Dust particle deposition on fin surface has a significant influence on the performance of fin-and-tube heat exchangers, and the purpose of this study is to develop a numerical model for predicting the particle deposition rate on fin surface. In the model, the particle trajectories were calculated by the particle motion equation; the particle deposition on the fin surface was described based on the critical impact angle and the critical sticking velocity of incident particles; the particle deposition on the formed fouling layer was described based on the critical impact angle, the critical sticking velocity and the critical removal velocity of incident particles. The particle distributions on fin surface predicted by the model agree well with the images captured in the visualization experiment. The predicted particle deposition weight per unit area can describe 88% of the experimental data within a deviation of ±20% and the mean deviation is 12.8%.     

Conjugate heat transfer in solar collector panels with internal longitudinal corrugated fins—Part I: Overall results

A computational study is conducted to examine the fully developed laminar flow and heat transfer characteristics in solar collector panels with internal, longitudinal, corrugated fins. The fins are integrally attached to the upper and lower panel walls. The objective of the study is to determine the effects of varying the fin pitch (or fin angle), the fin thickness, the ratio of the thermal conductivity of the panel walls and the fin to that of the fluid, and the thermal boundary condition on the panel heat transfer and pressure drop. The solutions of the momentum and energy equations are obtained by using a control-volume-based finite difference algorithm. The results of the study are also applicable to the design of internally-finned channels in compact heat exchangers. The overall panel heat transfer increases when the fin pitch (or the fin angle) is decreased, when the fin thickness is increased, and when the thermal conductivity ratio is increased. The streamwise pressure drop increases with decreasing fin pitch (or fin angle) and increasing fin thickness. For a fixed fin thickness, the selection of a small fin pitch (or fin angle) over the range studied results in a higher heat transfer enhancement per unit pumping power.     

Numerical Study of Air Compressibility During Horizontal Pneumatic Transport

Using numerical simulations, the effect of the compressibility of air on the flow pattern of particles and pressure drop in the presence of particles during horizontal pneumatic transport operating under negative pressure was examined. The length and inside diameter of the pipeline were 30 m and 40 mm, respectively, and the chosen particles (4 mm in diameter) had densities of ρ_p = 1000 and 2000 kg/m³. The mean air velocities at pipe the inlet were U_inlet = 19, 22, and 28 m/s, and the range of the mass flow rate ratios of particle to air, μ, was varied up to 2.0. For a given inlet air velocity, the difference in the flow pattern between compressible and incompressible flow calculation is generally small. For ρ_p = 1000 kg/m³ particles the additional pressure drop in compressible flow increases when μ is above 0.5 and U_inlet is 28 m/s, μ is above 1.3 and U_inlet is 22 m/s, and μ is above 1.5 and U_inlet is 19 m/s. In these cases, the particle flow pattern is homogeneous. For ρ_p = 2000 kg/m³ particles, the pressure drop increases only when μ is above 1.5 and U_inlet is 28 m/s. The difference is not noticeable when the particle flow pattern is heterogeneous. Also, the difference in the additional pressure drop is much larger during homogeneous flow than heterogeneous flow.     

汽车空调暖风机热交换器的优化设计

提高汽车空调性能的主要方式是提高热交换器的换热效率. 由于汽车内部空间的限制,不能单纯依靠增加热交换器体积的方法来提高热效率,因此对热交换器结构优化设计将具有现实意义. 利用Flnent求解和正交设计的方法对汽车暖风机热交换器进行优化设计. Fluent软件可以模拟热交换器的流动和传热过程,正交设计的方法可以建立回归方程,因此可以得到出口温度的数学模型,该模型定量地描述了翅片间距、翅片高度及水管间距对换热效率的影响,优化汽车暖风热交换器的结构,最后通过试验证明了优化设计结果的准确性.优化热交换器的结构参数：翅片间距为1.1 mm,翅片高度为6.9 mm,管距为5.2 mm.根据Fluent模拟仿真得到出口温度的回归方程：Y=307.308+2.333X₁ +0.677X₂+0,561X₃-2.501X₁²,影响出口温度的因素依次为翅片间距、翅片高度和水管间距.Fluent模拟仿真和正交试验设计相结合的方法有助于产品结构分析和优化设计.     

风机盘管换热器遗传算法优化设计

本研究采用了基于遗传算法和耗散理论的传热优化方法,并进行了风机盘管换热器的优化设计。在对板翅管式结构的风机盘管换热器进行建模的基础上,针对两种不同的应用工况,即供冷用干式风机盘管换热器和供暖型风机盘管换热器,进行了结构优化设计和分析。优化目标选取了换热器的耗散热阻,而设计变量分别选取管间距、排间距、换热管外径、翅片间距和翅片数。为评价换热器的性能,还计算了换热器的换热量、空气侧和水侧阻力损失、总泵功和换热器效能。优化设计结果显示,在特定的设计参数和限制条件下,不仅换热器的耗散热阻值降低,其他方面性能也得到了明显提升。     

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.