Numerical simulation of heat transfer and flow of cooling air in triangular wavy fin channels

Numerical computation models of air cooling heat transfer and flow behaviors in triangular wavy fin channels(TWFC) were established with structural parameters of fins considered.The air side properties of heat transfer coefficient and pressure drop are displayed with variable structural parameters of fins and inlet velocities of cooling air.Within the range of simulation,TWFC has the best comprehensive performance when inlet velocity vin=4-10 m/s.Compared with those of straight fins,the simulation results reveal that the triangular wavy fin channels are of higher heat transfer performances especially with the fin structural parameters of fin-height Fh=9.0 mm,fin-pitch Fp=2.5-3.0 mm,fin-wavelength λ=14.0-17.5 mm and fin-wave-amplitude A=1.0-1.2 mm.The correlations of both heat transfer factor and friction factor are presented,and the deviations from the experimental measurements are within 20%.

Efficiency of Photovoltaic Modules Using Different Cooling Methods: A Comparative Study

This paper presents an experimental investigation of the efficiency of a photovoltaic module using different cooling methods. The performance of the PV panels under different cooling techniques for the same operational conditions is explained. A special test rig was designed and installed in the Faculty of Engineering Technology, East Amman. All operating key variables such as solar radiation intensity, ambient and module temperatures using calibrated devices were measured and recorded as well as the electrical output. The present experiments results showed that the electrical efficiency of the tested PV panels is improved significantly when it was cooled. However, the best improvement obtained when a nanofluid (0.04% wt TiO2/water) is used as a cooling medium, while the PV panel cooled by using Aluminum rectangular fins showed the lowest efficiency improvement. Such results including the comparative analysis (under local operating conditions prevailing in Jordan) are in agreement with literature and could be useful for researchers and developers of solar power generation.

Experimental Study of Jet Nanofluids Impingement System for Cooling Computer Processing Unit

An experimental investigation of the jet nanofluids impingement heat transfer characteristics of mini-channel heat sink for cooling computer processing unit of personal computer is performed. The experiments are tested under the real personal computer operating conditions: no load and full load conditions. The experiments are performed for the following ranges of the parameters: coolant flow rate varies from 0.008 to 0.020 kg/s, the nozzle diameter is set to 1.00, 1.40, 1.80 mm, the distance nozzle-to-fins tip is 2.00 mm, the channel width of the mini-channel heat sink is 1.00 mm. The nanofluids with suspending of TiO2 particles in base fluid are used as a working fluids. It was observed that the average CPU temperatures obtained from the jet nanofluids impingement cooling system are 3.0%, 6.25% lower than those from the jet liquid impingement and from the conventional liquid cooling systems, respectively. However, this cooling system requires higher energy consumption.

Air Cooling of Mini-Channel Heat Sink in Electronic Devices

Heat transfer experiments were conducted to investigate the thermal performance of air cooling through mini-channel heat sink with various configurations. Two types of channels have been used, one has a rectangular cross section area of 5 × 18 mm2 and the other is triangular with dimension of 5 × 9 mm2. Four channels of each configuration have been etched on copper block of 40 mm width,30 mm height, and 200 mm length. The measurements were performed in steady state with air flow rates of 0.002 - 0.005 m3/s, heating powers of 80 - 200 W and channel base temperatures of 48°C, 51°C, 55°C and 60°C. The results showed that the heat transfer to air stream is increased with increasing both of air mass flow rate and channel base temperature. The rectangular channels have better thermal performance than trian- gular ones at the same conditions. Analytical fin approach of 1-D and 2-D model were used to predict the heat transfer rate and outlet air temperature from channels heat sink. Theoretical results have been compared with experimental data. The predicted values for outlet air temperatures using the two models agree well with a deviation less than ±10%. But for the heat transfer data, the deviation is about +30% to –60% for 1-D model, and –5% to –80% for 2-D model. The global Nusselt number of the present experimental data is empirically correlated as with accuracy of ±20% for and compared with other literature correlations.

Decoupled thermal–hydraulic analysis of an air-cooled separated heat pipe for spent fuel pools under natural convection

An investigation of the decoupled thermal–hydraulic analysis of a separated heat pipe spent fuel pool passive cooling system(SFS)is essential for practical engineering applications.Based on the principles of thermal and mass balance,this study decoupled the heat transfer processes in the SFS.In accordance with the decoupling conditions,we modeled the spent fuel pool of the CAP1400 pressurized water reactor in Weihai and used computational fluid dynamics to explore the heat dissipation capacity of the SFS under different air temperatures and wind speeds.The results show that the air-cooled separated heat pipe radiator achieved optimal performance at an air temperature of 10℃ or wind speed of 8 m/s.Fitted equations for the equivalent thermal conductivity of the separated heat pipes with the wind speed and air temperature we obtained according to the thermal resistance network model.This study is instructive for the actual operation of an SFS.

Heat Transfer Characteristics of Square Micro Pin Fins under Natural Convection

In order to comply with the recent demand for downsizing of the electric equipment, the minia- turization and the improvement in heat transfer performance of a heat sink under natural air-cooling are increasingly required. This paper describes the experimental and numerical investigations of heat sinks with miniature/micro pins and the effect of the pin size, pin height and the number of pins on heat transfer characteristics of heat sinks. Five types of basic heat sink models are investigated in this study. The whole heat transfer area of heat sinks having the different pin size, pin height and the number of pins respectively is kept constant. From a series of experiments and numerical analyses, it has been clarified that the heat sink temperature rises with increase in the number of pins. That is, the heat sink with miniaturized fine pins showed almost no effect on the heat transfer enhancement. This is because of the choking phenomenon occurred in the air space among the pin fins. Reflecting these results, it is confirmed that the heat transfer coefficient reduces with miniaturization of pins. Concerning the effects of the heat transfer area on the heat sink performance, almost the same tendency has been observed in other three series of large surface area, that is, higher pin height. Furthermore as a result of studying non-dimensional convection heat transfer performance, it was found that the relation between the Nusselt number (Nu) and the Rayleight number (Ra) is given by Nu = 0.16 Ra0.52.

660MW锅炉水冷壁管道泄漏分析

火电厂锅炉材料失效泄漏是机组非计划停运的主要原因之一,导致因材料失效而泄漏的原因错综复杂,但鳍片焊接引起的失效泄漏相对较少。以某电厂660MW机组锅炉侧墙垂直水冷壁泄漏为基础,通过金属材料宏观分析、力学分析、金相检测等方法对失效管道进行试验,并结合现场实际情况分析泄漏原因。试验结果表明:本次管道泄漏为管道鳍片拉裂,裂纹扩展至水冷壁管道,导致管道在高温、高压下爆管泄漏。

间接空冷翅片管束临界防冻特性及防冻裕量研究

间接空冷翅片管束目前缺乏全面的冬季防冻运行参数。为此,首先凝练了管束防冻模型,包括热平衡方程、水侧和空气侧输运准则方程、防冻约束条件;其次依托典型顺逆流式空冷翅片管束,分析了2类管束临界防冻特性和防冻裕量;最后探究了中间型、左侧型、侧面型进水方式管束的临界值特点。结果表明:环境温度和入口水温降低、风速增加,管束防冻流量增加,且入口水温越低,风速影响更突出;逆流式管束防冻性能劣于顺流式管束,随风速增加或入口水温降低,二者差异扩大;入口水温抬升对防冻裕量影响分为3个梯次,为显著增加区间(0℃, 10℃]、变化缓慢区间(10℃, 20℃]、基本不变区间(20℃, 40℃],不可一直增加入口水温来防冻;中间型管束防冻性能优于左侧型和侧面型,空冷燃煤火电或核电机组应优先选用。研究结果可为我国空冷机组冬季防冻运行提供指导。

空冷器翅片结构对冷却性能的影响研究

空冷器作为热交换设备的重要组成部分,在工业和机械系统中发挥着关键作用。旨在深入探讨空冷器翅片结构对冷却性能的影响,进而为空冷器翅片结构设计提供一定的参考。介绍了空冷器翅片的基本原理及其在空冷器中的作用,在此基础上,进一步探讨了空冷器的冷却性能评估指标,并进一步分析了空冷器翅片结构对冷却性能的影响,进而为空冷器翅片结构的优化设计提供一定的参考。

Correlations Based on CFD and Their Applications in Optimization for Staggered and Parallel Plate Fin Heatsinks

Both parallel and staggered plate fin arrays have shown promise for use inhigh performance heatsinks regard of its individual manufacturing costs. The geometrical andoperational parameters are very important to their cooling performance as heatsinks in practicalapplications. Fluent 5.0 commercial CFD (computational fluid dynamic) code is used to simulate theflow and heat transfer of those heatsinks of different realistic parameters. Based on thosesimulations, two correlations, concerning Nusselt number and friction factor as the functions ofgeometrical and operational parameters, FB (fin-base area ratio), PR' (ratio of spanwise pitch tolengthwise pitch) and Re, were developed. From the both, the performance comparisons for optimizinggeometrical and operational parameters of a fixed dimension heatsink are shown at constant pumpingpower and constant thermal resistance. Several optimized parameters were obtained can out performthe staggered ones.

Thermal Analysis of Melting Occurring Inside a Finned Rectangular Enclosure Equipped with Discrete Pulsed Protruding Heat Sources

This paper numerically investigates the effect of the location of a horizontal fin on the melting of a phase change material(PCM)inside a rectangular enclosure heated by multiple discrete pulsed protruding heat sources.The fin and the phase change material filling the enclosure store the thermal energy extracted from the heat sources,in sensible and latent forms.The heat sources are assumed to simulate electronic components undergoing a superheating technical issue.By extracting heat from the electronics,the PCM plays the role of a heat sink.To analyze the thermal behavior and predict the cooling performance of the proposed cooling system,we derive a nonlinear mathematical model based on mass,momentum and energy conservation laws.Several numerical investigations are conducted to quantify the influence of the fin position on the thermal behavior and the cooling performance of the heat sink.Predictions include the transient maximum temperature occurring inside the heat sources and the liquid volume.A comparison between our numerical results and experimental data selected from the literature shows a good agreement.The main conclusion is that the presence of the fin leads to a slight increase in the melting time.

某微通道液冷板的性能分析与优化

针对电子设备工作时局部温度过高问题,提出了翅柱与流道相结合的结构设计。分别将平行四边形翅柱、沙漏型翅柱、双层平行四边形翅柱内置于流道中,保证相同的流道截面积、冷却液进口流量与温度,借助仿真软件ICEPAK分别对这三种液冷板的散热性能进行仿真分析,并利用试验来加以验证仿真结果的可靠性。结果表明:三种优化后的冷板散热性能都优于常规通道冷板。其中,平行四边形翅柱冷板散热性能最差;双层平行四边形翅柱冷板散热性能最好,但流阻较大;沙漏型翅柱冷板散热性能适中,流阻明显小于前两者。

水平柱群通道全氟己酮过冷沸腾传热特性研究

为提升散热量不断增加的电力电子器件冷却系统的高效换热能力,提出采用全氟己酮为工质的水平双直角五边形肋柱通道流动沸腾换热系统对其进行冷却。通过实验的方法制作了入口当量直径为3.81 mm的五边形柱群通道结构,对通道内流动沸腾的平均及沿程换热特性展开了研究,实验工况如下:壁面热流密度为50~400 kW·m^(-2),入口流速为0.1~0.9 m·s^(-1),入口过冷度为15~35℃。结果表明:当热流密度低于100 kW·m-2时,单相对流占主导,增加流速与过冷度能够明显促进壁温降低;当热流密度高于200 kW·m^(-2)时,沸腾吸热占主导,增加流速与过冷度时壁温的降低幅度不明显;在热流密度为400 kW·m^(-2)、过冷度为15℃的工况下,柱群通道的平均传热系数最高;通道沿流向的局部传热系数总体呈现上升趋势,随着热流密度的增大、流速与过冷度的降低,通道出口传热系数相比进口的增长更加显著,此时通道内流体沿流向的沸腾剧烈程度发展速度更快、通道出口的沸腾程度更剧烈。该研究可为水平柱群通道内流动沸腾传热的最佳工况设计提供理论基础。

一种新型叉排直肋表面的流阻及换热性能研究

本文研究了新型变截面叉排直肋结构的流阻与换热性能。采用数值模拟技术研究了变截面及另外两组对比组,并建立了雷诺数与努塞尔数、进出口压差、传热因子j和摩擦因子f之间的关系图。最终从数值模拟的结果可以计算出,在雷诺数为600时,变截面肋片的传热因子j比普通叉排直肋高约23.5%,比翼型叉排直肋也高出约14.4%;同时普通叉排直肋的摩擦因子f比变截面叉排直肋高约197.7%,翼型叉排直肋也比变截面叉排直肋高约31.2%。相对于普通叉排直肋肋片,翼型叉排直肋和变截面叉排直肋能在有效提高散热效率的情况下,大幅减小压降,并且变截面叉排直肋的换热性能比翼型叉排直肋更好,压降也更低。在航空飞机等需要高换热性能和低压降时,可以优先使用变截面叉排直肋。

新型降温系统不同参数对数据机房降温效果的影响研究

针对一种以液氮为换热介质,以翅片管换热器为换热设备的新型降温系统,通过CFD模拟了系统运行参数与换热器结构参数对机房降温效果的影响。结果表明:液氮的入口流量在40~58 L/h范围内变化时对室内温度影响较小;换热器的翅片间距由7 mm增大到12 mm时,室内温度与机柜内部温度分别升高了8.0、2.2℃;而翅片直径由46 mm增大到58 mm时,室内温度及机柜内部温度均呈现先降低后升高再降低的趋势。

基于液冷的锂离子电池液冷板设计及优化

新能源汽车的快速发展对电池热管理技术提出了更加严格的要求。液体冷却方式可以有效将电池运行温度控制在一个适宜的范围,使电池获得高效的充放电能力。在常规的大平板液体通道中,对流换热能力会随着液体边界层的发展而逐步恶化,导致电池散热能力下降。因此,基于常规流道设计出内部带有鳍式结构的液体通道,此种鳍式结构会将液体边界层进行重新初始化,提高换热效率。通过与常规流道结构分析对比,发现带有鳍式结构的异向流动的双通道具有更强的散热能力。然后针对冷却液流速、液体通道的宽度以及鳍式结构的深度这3个因素进行分析,结果发现:增大冷却液流速、液体通道的宽度以及鳍式结构的深度可以提升电池散热效果,但会存在极值,需要通过合理调节以上3个参数,才能得到最佳的散热效果。

扁平空冷翅片管内换热与流动特性数值研究

扁平翅片管结构复杂,换热方式耦合多样,以往研究难以用常规实验与关联式方法,完整复现并分析管内热流特性。基于分布参数热力学理论,提出耦合换热模型描述翅片管两相流与空气间的换热,并将模型应用于1m长度工程管,通过数值求解,得到管内温度、热流密度、换热系数、液膜厚度、剪切力、压力降沿两相流和冷却空气流向全域内的变化规律:随着冷却空气横向流动,扁平管凝结性能急剧降低,热流密度从空气入口处20000W/m^(2)降至出口处5000W/m^(2);翅片管钎焊层热流密度高达14000W/m^(2),因此应注重提升钎焊层对翅片管换热的增强效用。管内两相流定性为环状流,随着两相流动,倾斜管能有效地将平板液膜汇聚到下半圆,平板液膜厚度沿管深增长缓慢,全管段液膜增长范围为16~25μm;平板热流密度和凝结空冷翅片管空气侧对流换热系数管深无下降趋势,这与工程管对应管段的实验结果相符。

工程机械车辆发动机冷却系统仿真与优化

文章分析工程机械车辆发动机冷却系统基本原理及主要部件性能,采用AMESim仿真软件搭建冷却系统的仿真模型,基于风洞实验验证模型的准确性;研究环境温度、水泵传动比以及散热器翅片波距对冷却系统的影响,并探讨冷却系统性能的优化路径。结果表明,环境温度过高会使冷却系统性能显著下降,适当提高水泵传动比和降低散热器翅片波距可以提高冷却系统的冷却性能。该文设计的2款散热器通过优化散热器翅片波距提高了冷却系统性能。

Sandwich Structure Design of a Cooling Fin for Battery Modules Against Impact Loads

Lithium-ion batteries(LIBs)are widely employed in electric vehicles owing to their high power density,long cycle life,and environmental friendliness.However,LIBs are hazardous in the event of a crash,leading to thermal runaway.In this study,the basic structure of a battery module is analyzed to improve the crashworthiness of LIBs.A simplified finite element model of the battery module structure,which is a battery unit composed of two pouch cells and a cooling fin,is set up and verified by conducting module-level simulations.The simulation results reveal that the cooling fin in the battery module has the potential to absorb energy.Six sandwich configurations are introduced to modify the cooling fin.With a unidirection-ally stiffened double hull USDH structure serving as an example,a parametric analysis is conducted,demonstrating that the sandwich height does not influence the areal density;a small height of 3 mm can make the material work sufficiently while avoiding early buckling of the structure.Further,the crashworthiness of different sandwich configurations with the same areal density and height is compared,leading to three deformation modes.USDH and circular core structures are found to be able to effectively reduce the peak force and improve the energy absorption ability.