【作者】 陈作义；

【导师】 张立志；

【作者基本信息】 华南理工大学 ， 化学工程， 2012， 博士

【摘要】 随着人们对室内舒适度要求越来越高，空调人均占有率大大增长,空调已经成为耗能大户。全热交换器由于能同时回收空气中显热和潜热，降低空调的能耗，因而具有广阔的发展前景。目前市场上流行的全热交换器以板翅式较多，除了膜材的选择异常关键外，翅片和流道结构对换热也有重大影响。交叉三角形波纹板换热器不仅结构简单，机械强度适中，而且通过流道的周期性扩张和收缩强化了内部流动，传热系数高，非常适合在空调的工况下使用。当前对此类结构的研究不多，且多以数值模拟为主。本文以实验为主、数值模拟与实验研究相结合来研究其传热和流动，从宏观和微观层面探讨了交叉三角形波纹板流道的传热机理和流动特性，并结合场协同理论，对研究结果进行分析，充分探讨影响流道的综合传热效果的各项因素，为工程设计提供理论支持。本课题的主要工作包括以下几个方面：(1)建立了交叉三角形波纹板流道的传热实验台。通过测试不同Re数、不同折叠角和不同热流边界条件下的流道各点的温度、压降和风速，计算得到流道平均摩擦系数、平均传热系数、平均努塞尔数、换热因子j、面积质量因子j/fD和传热强化综合性能指标PEC值等参数，并对上述参数的变化规律进行了整理归纳。同时也建立了交叉三角形波纹板流道的流动实验台。利用IFA300热线热膜风速仪测量了交叉三角形波纹板流道内的三维速度，对气流方向速度分量进行频谱分析，研究流道内部流动特性，并绘制出不同平面上的速度矢量场、湍流强度场和湍动能场。研究表明：交叉三角形波纹板流道很容易达到湍流；当Re=275时，流动趋于过渡流；当Re>1000，流动趋于湍流状态。(2)建立了交叉三角形波纹板流道的数学模型，用Fluent软件对不同条件下的交叉三角形波纹板流道进行了模拟，并将结果与实验结果进行了对比分析。研究表明：利用低Re数k ε湍流模型研究交叉三角形波纹板流道内的传热和流动最符合；非耦合壁面比实际耦合壁面的Nu数夸大35%；对不同壁面边界条件进行了模拟，给出了流道内部各截面的速度矢量场、温度场和湍动能场；并就数值模拟与实验数据的偏差进行了分析。(3)对比了交叉三角形波纹板流道与其他管式或板式流道的传热参数。与圆管、椭圆管、方管、三角形流道等管式流道作对比，交叉三角形波纹流道除摩擦系数较大外，其传热和阻力的综合性能均较优，主要是由于交叉三角形波纹流道的三角形交叉区域的顺时针的漩涡和复杂的二次流，强化了流动和传热。与平行平板流道、波纹板流道和人字形波纹流道相比，交叉三角形波纹流道摩擦系数适中，换热较为理想。综合考虑空调全热交换器应用的工况以及加工难度、加工成本、传热强化、阻力等各方面因素，交叉三角形波纹流道是一种较理想的选择。(4)通过实验和模拟，分别对折叠角(included angle)α为45°、60°、90°和120°的四种交叉三角形流道的实验和模拟数据进行处理，发现折叠角α对流动和传热有重大影响。除了对摩擦系数、努塞尔数、j因子、PEC值等宏观参数进行比较外外，文中还结合三维空间温度场的分布云图、速度场分布，从微观和宏观两个层面阐述折叠角的影响。结果表明，折叠角为90°的交叉三角形流道具有最优的传热性能，若以折叠角为90°的交叉三角形波纹流道的NuD、j、和PEC为基准，另外三种折叠角的NuD值约小30%~75%；j值分别约小14%~76%；PEC值分别约小24%~73%。(5)为探讨交叉三角形波纹流道内部流场的强化传热机理，从场协同理论的基本定义出发，研究了速度及速度梯度、温度梯度及压力梯度之间的场协同关系。通过编制自定义函数UDF，使用Fluent模拟计算获得不同折叠角时流场的β、θ和γ三种局部协同角的云图分布，从微观上验证折叠角的影响规律。同时也将不同壁面条件的局部协同角云图作了进一步分析对比。为了验证宏观传热参数fD、NuD、j、PEC等值的变化规律，也对局部协同角进行场均计算，获得体积平均协同角和积分中值平均协同角，所获得的场均协同角的变化规律能够解释宏观传热参数的变化规律。研究表明，Re取2000时，折叠角为90°交叉三角形波纹板流道的场均协同角值βVOL为74.1°，比其他折叠角的该值小1~2.3°；而同等Re数下的螺旋扁管、圆直管和平行平板流道的该值分别为77.2°、88.2°和88.6°，说明交叉三角形波纹板流道的场协同程度最优。更多还原

【Abstract】 Due to the increased requirements in people’s indoor comfort, air conditioning systemshave been widely used. Energy consumption for air conditionings is very large. The total heatexchanger, which can effectively recovery sensible and latent heat from ventilation air, hasattracted much attention. Up until now, plate fin total heat exchanger is the most popular onein the market. Besides membrane materials, the structures have significant impacts on thefluid flow and heat transfer for the plate fin heat exchanger.Cross corrugated triangular duct heat exchanger is better because of its high strength.Further, the flow is enchanted by the periodic expansion and contraction in the flowingchannels, which gives rise to heat transfer coefficients. Therefore the cross corrugatedtriangular duct heat exchanger is quite applicable to air conditioning systemss. Althoughthere are many reports on cross corrugated triangular ducts, they are mostly only focused onnumerical simulation. This paper addresses this problem, by the combination of experimentaland numerical studies. In addition, field synergy theory is employed to analyze the numericalresults. These works would provide a theoretical basis for engineering design. The mainworks are summarized as following:(1) A test rig for heat transfer in cross corrugated triangular ducts is set up. The frictionfactor and heat transfer coefficient are tested under different Reynolds numbers, includedvarious angles and various heat flux boundary conditions. The variations of these parametersare analyzed.Further, a test rig for fluid flow in the cross corrugated triangular ducts is set up. Tostudy the flow characteristics inside the channels, three velocity components are measuredusing IFA300high speed hot wire anemometer. Spectrum analysis is carried out for velocitycomponents. The velocity vectors fields in the different plane are plotted by the Tecplotsoftware. The turbulence intensity contours and the turbulence kinetic energy contours arealso plotted. The results show that the flow in the cross corrugated triangular ducts becomesturbulent easily. When Re is275, the flow has become transitional. When Re is above1000,the flow has become turbulent.(2) A mathematical model for cross corrugated triangular ducts is developed and solvedby Fluent software. The established model is validated by the experimental data. It has beenfound that the results obtained by the low Reynold number k ε turbulence model fit theexperimental results best. Compared to the conjugated wall surface, the Nusselt numbersobtained for an ideal wall surface increase35%. The velocity vectors, the temperature contours and the turbulence kinetic energy contours inside channels are given. Further, thedeviations between the simulated and the experimental data are analyzed.(3) Comparisons between the heat transfer parameters in the cross corrugated triangularducts and those in other shapes tubed or parallel plate channels are made. Compared to roundtubes, elliptical tubes, square tubes and triangular tube ducts, the friction factor in thecross corrugated triangular ducts is relatively larger. However, the integrated performances ofheat transfer and resistance are better. It is because that fluid flow is enhanced by theclockwise vortexes and the complex secondary flows appearing in triangular cross regions.Compared to parallel plate channels, corrugated plate channels, herringbone corrugatedchannels, the friction factor for the cross corrugated triangular ducts is moderate but the heattransfer is relatively higher. Considering application prospect, processing cost, heat transferenhancement and resistance for total heat exchanger, the cross corrugated triangular duct is anideal choice.(4) For included angles (α)45°,60°,90°and120°, the experimental and numerical datain the cross corrugated triangular ducts are investigated. It is found that the fluid flow andheat transfer are seriously influenced by the included angles. Besides the analyses of themacroscopic parameters such as friction factor, Nusselt number, j factor and PEC values,macro level parameters are also disclosed with temperature and velocity contours. It is foundthat the cross corrugated triangular duct with90°included angle has the best heat transferperformance. For included angles45°,60°and120°, the average Nusselt number (NuD), jfactor and PEC value decrease30%~75%,14%~76%and24%~73%, respectively.(5) To disclose the heat transfer enhancement mechanism in the cross corrugatedtriangular duct, the field synergies between velocity gradient, temperature gradient andpressure gradient are investigated. Effects of the included angles on the fluid flow and heattransfer are discussed by analyzing the contours ofβ、θandγlocal synergy angles withdifferent included angles. Further, the contours of the local synergy angles under differentwall conditions are analyzed and compared. To validate the performances of the macroscopicheat transfer parameters such as fD、NuD、j and PEC, the volume average synergy angles andthe integral mean synergy angles are calculated and analyzed. The results are used to disclosethe variations of the macroscopic heat transfer parameters. It can be found that when Re is2000, the field averaged synergy angle (βVOL) for cross corrugated triangular duct with90°included angle is74.1°, which is1~2.3°less than that for other included angles. The value is14.1°less than that for a straight tube and14.5°less than that for a parallel flat plates duct.更多还原