履带车用锯齿型翅片传热器结构参数优选与性能研究

利用数值模拟的方法对履带车用锯齿型翅片散热器的翅片间距和翅片切口长度进行结构优选,引入了同功耗强化传热评价指标(performance evaluation criteria,PEC),对比了不同翅片间距和翅片切口长度的散热性能。研究结果表明:翅片间距和翅片切口长度分别为2mm和4mm时,翅片的综合性能最优。根据数值计算结果研制散热器样件,利用风洞试验台对翅片切口长度为4mm,翅片间距分别为1.5、2.0和2.5mm试验样件进行测试,试验结果与仿真结果较一致,误差在10%以内。通过试验数据拟合出适用于三种翅片间距锯齿形传热器在试验的雷诺数范围内的传热和阻力性能关联式,并分析了水侧流速对空气侧传热性能的影响。     

径向热管换热器壳程压降数值模拟及参数优化

通过对径向热管换热器壳程压力场的数值模拟,分析入口烟气速度对换热器压降的影响规律,并对换热器结构参数进行优化。结果表明:换热器迎风侧压力高于背风侧压力,沿烟气流动方向压力逐渐降低且呈线性分布;换热器压降随入口烟气速度的增加而增加,且其增加速率也相应增大。通过改变换热器结构参数,对换热器壳程压降进行分析研究,得到其结构优化参数:翅片高度小于26.5mm,翅片间距大于6.5mm,热管横向间距108～111mm,纵向间距120～125mm。     

CO_2微通道气冷器翅片结构对换热性能影响的模拟研究

本文选择适用于微通道换热器的CO_2换热关联式,创建CO_2微通道气冷器的二维模型。采用有限体积法将微通道分成多个微元段,利用Matlab结合Refprop软件计算每个微元段中的流动和换热。用实验结果验证了建立的仿真程序的合理性,模拟翅片结构对换热器性能的影响,依据信噪比的田口方法计算了翅片结构对换热器性能的贡献率,提出了适用于本模型的最佳翅片结构。得出:CO_2微通道换热量和压降随着空气侧的翅片间距和翅片高度的增大而减小,随着翅片宽度的增大而增大,翅片厚度的影响较小;翅片结构对微通道气冷器的性能影响的贡献率分别为:翅片高度42.45%,翅片间距25.73%,翅片宽度24.32%,翅片厚度为7.50%;最佳翅片结构为:翅片高度8 mm,翅片间距1.15mm,翅片宽度17.28 mm,翅片厚度0.08 mm。     

汽车水散热器设计软件开发

为了降低散热器的设计成本并提高计算精度,利用PowerBuilder开发了汽车水散热器设计软件,其计算功能包括校核计算、翅片间距优化计算、翅片高度优化计算、管长优化计算及管排数优化计算。对比分析试验表明:计算结果具有较高的精度。计算分析翅片间距、开窗角度、风速及冷却液中乙二醇百分比对散热器性能的影响。研究表明:减小翅片间距及增大风速可提高换热性能;减小开窗角度可降低风侧阻力;增大乙二醇百分比可降低冷却液出口温度。     

平直型散热器的正交设计和数值模拟

以芯片最高温度为试验指标,翅片高度、翅片厚度和翅片数目为影响因素,对平直型散热器进行正交设计和数值模拟,求出在影响因素的范围内平直型散热器的最佳结构参数。通过对正交试验结果的极差分析,找出散热器影响因素的主次顺序。并通过对优选出的散热器结构和原来的一款散热器进行流场和温度场的对比分析。     

基于ANSYS技术的CPU热管式散热器换热规律实验研究与数值模拟

CPU的工作温度是判断CPU性能的一项重要参数,为克服解析计算求取CPU温度精确值的困难,利用ANSYS有限元软件对热管式散热器与普通翅片散热器进行了热特性分析,模拟计算出稳态温度场分布,以及不同功率下CPU中心点的换热特性。研究结果表明,在稳定状态时,热管式散热器较普通翅片散热器具有极强的热传导性能;在CPU高功率工作时,普通翅片散热器CPU温度超过85℃无法满足换热要求,而热管式散热器CPU温度低于75℃,完全达到换热效果;模拟计算值与实验值最大相差4．1℃,应用数值模拟的方法研究CPU热管式散热器换热特性是可行。     

基于遗传算法的热管换热器优化设计

在对热管传热和热阻的关系进行分析的基础上,利用遗传算法进行优化得到了最合适的翅片间距和翅片高度.算例表明这种优化是准确有效的,达到了优化热管换热器性能的目的.     

基于VB和MATLAB的同心圆热管传热分析与结构优化

建立同心圆热管结构参数计算模型,运用VB和MATLAB软件,并与自编程序相结合,分析同心圆热管传热特性。研究结果表明:单根热管外壁换热系数随着翅片间距的增大而增加,但翅片间距越大,其翅片传热面积越小,翅片间距须大于相邻两翅表面间流体的流动边界厚度之和。凝结换热系数随内管径的增大而减小。经计算,模拟同心圆热管的最佳充液率为43.2%。     

电子元件散热器翅片自然对流散热性能研究

针对室外电子设备在自然对流条件下的散热问题,设计开发了一种新型散热器翅片结构——翅片开孔式涡流发生器,易于加工且直接与翅片连接,不存在焊接的问题。利用数值模拟的方法探究了涡流发生器的布置方式与攻角对散热器散热的影响。结果表明:翅片开设三角孔,在翅片间空气流动过程中起到了明显的作用,有效降低了三角形涡流发生器造成的流动阻力,增加了空气的扰动;当涡流发生器间距为40 mm、攻角为15°时,散热器翅片高温热源区域的散热效果最好。     

1000MW直接空冷机组散热单元换热特性的数值模拟

以某1 000MW直接空冷机组为例,对机组散热器外部流场进行了数值模拟,分析了不同迎面风速、环境温度、翅片间距以及翅片厚度对散热器外部换热和流动特性的影响.结果表明:随着迎面风速的增大,散热器外部的传热系数和流动阻力均显著增大,环境温度对散热器外部换热和流动特性的影响并不明显,但对总散热量影响较大;较大的翅片间距能增大散热器外部的传热系数、减小流动阻力,但会使单位管长的换热面积减小,总散热量减小;对应于一定的迎面风速,存在较为合理的翅片间距和翅片厚度,迎面风速越大,合理的翅片间距越大,翅片厚度越小.     

翅片式热管散热器自然对流换热特性分析与多目标结构优化

采用数值计算方法对一种应用于半导体制冷片热端散热的翅片式热管散热器进行模拟,探究自然对流条件下不同翅片参数对散热器换热特性的影响。结合多目标遗传算法(NSGA-Ⅱ),以影响散热器散热的两个主要参数——翅片表面传热系数和肋面效率为优化目标,对散热器整体做出综合优化,并对优化结果进行K均值聚类分析,提出了翅片端优化原则。结果表明,肋面效率对散热器性能的影响有限,提高表面传热系数可显著降低散热器总热阻;与未优化方案相比,所选优化方案可使基板热端面温度下降3.5K,散热器热阻降低18.22%。     

Enhanced thermal performance analysis of buried heat transfer tubes thermal storage system filled with microcapsule particles

The heat transfer enhancement performance of a phase change buried tubes thermal storage system is influenced by major parameters such as arrangement of heat transfer tubes, fin structure and fin geometry size. We developed a three-dimensional numerical model with two different arrangements and five different enhanced heat transfer structures respectively. For the sake of analysis the effects of arrangement of heat transfer tubes, fin structure and fin geometry size. In addition, we applied the enthalpy-transforming model to obtain the liquid fraction and location of the solid-liquid interface at different time in the phase change process. The numerical results show that the melting time of the thermal storage system model with a triangle arrangement is about 6.1% longer than that of the model with a square arrangement. Besides, the melting time of the model with 55 mm tube pitch is about 16.7% shorter than that of tube pitch with 60 mm. Moreover, the buried tube thermal storage system models with circle fins have the shortest melting time, which is 18 seconds. Melting time of the model with circle fins is about 40% shorter than that of the model with smooth tube. In addition, the melting time of the model with 3 mm fin thickness is 10 seconds, which is the shortest. The model with thicker fins means the shorter time of melting process. Moreover, the melting time of the model with 10.5 mm fin spacing is about 23.5% shorter than that of the model with 12.5 mm fin spacing, which is 13 seconds. In conclusion, the main factor of the melting time is the heat transfer area. It provides a guidance for the design and reconstruction of the type of heat storage structure.     

环保用板翅式换热器的数值模拟与试验研究

选取矩形截面平直翅片板翅式换热器的矩形单通道运用fluent软件进行数值模拟。首先对不同波高和波距的三组九种几何尺寸的翅片在同一工况下进行数值模拟,选出每组中传热和阻力综合性能最优者。然后对选出的三种翅片在不同工况下进行数值模拟,最终选出一种传热和阻力综合性能最优的。并对实物换热器进行试验研究,同时将试验结果和数值模拟结果进行对比分析,验证了数值模拟的正确性。     

A numerical study of flow behavior in the shell and helical finned-tube heat exchanger

Extended surfaces mostly aim to improve the heat transfer upon increasing the area of heat transfer. In this paper, the influence of using fins on flow behaviors and the heat transfer of the shell and tube heat exchanger has been investigated. In this regard, the present results are verified with available experimental data in the literature for a helical tube without fins. The effects of fin density (fin per inch), its height, and material have been studied on the heat transfer rate. In addition, the effects of radial pitch and the number of coil loops are studied. The results indicate that implementing extended surfaces significantly increases the heat transfer rate. The increase of fin density from 8 to 12 and the height from 11.5 to 13.5 mm enhances heat transfer up to 48% and 43% depending on Dean number, respectively. The rise of coil pitch augments the overall heat transfer, and it is more efficient at lower Dean numbers. The predicted results also show that the fin material does not have any significant effect on heat transfer.     

Experimental study of the effects of structured surface geometry on water spray cooling performance in non-boiling regime

Experiments were conducted to study the effects of enhanced surfaces on heat transfer performance during water spray cooling in non-boiling regime. The surface enhancement is straight fin. The structures were machined on the top surface of heated copper blocks with a cross-sectional area of 10 mm×10 mm. The spray was performed using Unijet full cone nozzles with a volumetric flux of 0.044–0.053 m³/(m²·s) and a nozzle height of 17 mm. It is found that the heat transfer is obviously enhanced for straight fin surfaces relative to the flat surface. However, the increment decreases as the fin height increases. For flat surface and enhanced surfaces with a fin height of 0.1 mm and 0.2 mm, as the coolant flux increases, the heat flux increases as well. However, for finned surface with a height of 0.4 mm, the heat flux is not sensitive to the coolant volumetric flux. Changed film thickness and the form of water/surface interaction due to an enhanced surface structure (different fin height) are the main reasons for changing of the local heat transfer coefficient.     

Numerical study of the fin efficiency and a modified fin efficiency formula for flat tube bank fin heat exchanger

In this paper, a three-dimensional numerical heat transfer analysis has been performed in order to obtain the temperature distribution and the fin efficiency using the experimentally determined local heat transfer coefficients from the naphthalene sublimation technique and heat and mass transfer analogy. The influences of the fin material, fin thickness, and transversal tube pitch on the fin efficiency are studied for flat tube bank fin heat exchangers. The fin efficiency, obtained by a numerical method using the averaged heat transfer coefficient, is compared with that using the local heat transfer coefficient. The reliability of the generally used formula for fin efficiency is tested also, and then a modified fin efficiency formula with a new equivalent fin height is provided. The results show that the difference between the fin efficiency obtained by the numerical method using the local heat transfer coefficient and the fin efficiency using the averaged heat transfer coefficient is small, but the fin efficiency obtained by the generally used formula is lower than that obtained by the numerical method using the local heat transfer coefficient; the fin efficiency obtained by the modified formula matches very well with the fin efficiency obtained by the numerical method using the local heat transfer coefficient. The modified formula for the fin efficiency calculation is more reliable, and it can be applied directly to the design of a flat tube bank fin heat exchanger and also will be useful in engineering applications.     

Parametric and design optimization investigation of a wavy fin and tube air heat exchanger using the T-G technique

The focus of this paper is to optimize the air-side performance of a wavy fin and tube heat exchanger at different design parameters on an individual target response using the Taguchi method. However, a statistical concept, gray relational analysis, is also studied for combined optimization, considering all target responses at a time. Based on the heat exchanger requirement, parametric study for the air-side is regarded as a more significant heat transfer and lower frictional factor. Experimental correlations were available and used for the 27 orthogonal runs. Investigation revealed the highest 47.06% fin pitch, 37.24% fin pitch, 25.46% air velocity, and 23.9% fin thickness contribution ratio for the target response of friction factor (TPF), heat transfer coefficient, and Colburn factor, respectively, with the application of the Taguchi method in a heat exchanger. GRG gives an optimum set of design parameters, A3B3C2D1E3F2G1, for wavy fin and tube of fin pitch of 6 mm, tube row number of 6, waffle height 1.8 mm, fin thickness 0.12 mm, and air velocity 5 m/s. Also, longitudinal tube pitch is 27.5 mm, and transverse tube pitch of 24.8 mm, at which TPF is maximum while the friction factor is minimal. The Colburn factor is the most significant, minor friction factor, and the heat transfer coefficient and TPF are the most considerable in GRG. Hence, an improved heat transfer performance design of a wavy fin and tube heat exchanger is achieved using the above techniques.     

Transversal tube pitch effects on local heat transfer characteristics of the flat tube bank fin mounted vortex generators and their sensitivity to nonuniform temperature of the fin

The tube bank fin is commonly used to increase the area of the heat transfer surface with a small heat transfer coefficient of a heat exchanger. If vortex generators (VGs) are punched on the fin surface, the heat transfer performance of the fin can be improved. This paper focused on the effect of transversal tube pitch on the local heat transfer performance of the three-row flat tube bank fin mounted with VGs. On the fin surface, constructing the flow channel but without mounted VGs, the transversal tube pitch was greater, and the span averaged Nusselt number downstream was larger because fewer interactions of vortices would be generated from different VGs located upstream. When the area goodness factor was used as the criteria on the condition of one tube unit of heat exchanger for commonly used fin materials and fin thickness, the transversal tube pitch has considerable effect on the heat transfer enhancement of VGs. Large transversal tube pitch is more sensitive to fin material than to fin thickness.     

Effect of fin pitches on the optimum heat transfer performance of crimped spiral fin-and-tube heat exchangers

This study conducted experiments on the optimized fin pitch for crimped spiral fin-and-tube heat exchangers. The experiments covered a size range of 2.4–6.5 mm, which is the manufacturing limitation for this kind of fin. The water-flow arrangement used in this experiment combined the parallel cross-flow and the counter cross-flow in a two-row configuration. Ambient air was used as the working fluid on the air-side, and hot water was used on the tube-side. The effects of fin pitches on the heat transfer coefficient and pressure drop characteristics were studied. The results clearly showed that the convective heat transfer coefficient (h_o) for a fin pitch of 2.4 mm is relatively low compared with that of other fin pitches with the same air frontal velocity. Using larger fin pitches (i.e., 4.2, 6.2, and 6.5 mm) resulted in negligible differences in the pressure drop. Moreover, this work introduces the parameter of three performances indexes, which can be expressed as the ratio of the desired output to the required input, for optimization purposes. Due to the difference in optimum fin pitch obtained by these performance indexes, an intersection analysis was conducted. The results indicated that the optimum fin pitch is 4.2 mm for this work, which could be valuable for the effective design for industrial thermal-system applications.