Experimental Study of Wavy Fin Aluminum Plate Fin Heat Exchanger

An experimental study of the air-side thermal hydraulic performance of the aluminum wavy fin in heat exchanger was performed. A series of tests were conducted for 16 wavy fin samples with different geometry parameters. The experimental correlation equations of the wavy fin about the heat transfer and pressure drop are set up using the multiple regression method. The parametric study on the performance of the wavy fins is carried out using the Taguchi method. The study results show that the ratio of the wavy fin amplitude and wavy length is the most important factor that affects the overall thermal hydraulic performance.     

矩形肋片热沉(火积)耗散率最小与最大热阻最小构形优化的比较研究

针对矩形肋片热沉, 分别以最大热阻最小化和基于(火积)耗散定义的当量热阻最小化为优化目标, 采用二维传热模型并结合有限元数值仿真对其进行构形优化, 比较了两种目标下的热沉最优构形, 并分析了全局参数(综合了对流换热系数、肋片占据的总面积及其热导率的函数)和材料占比对两种目标(最大热阻、当量热阻)及其对应最优构形的影响. 结果表明: 热沉外形固定时, 两种目标下均不存在最优的肋片厚度; 热沉外形自由变化时, 两种目标下的最优构形存在一定的差异. 此外, 全局参数对两种目标下的最优构形均没有影响, 而材料占比对两种目标下的最优构形均有较大影响. 提高全局参数和材料占比均可以减小最大热阻最小值和当量热阻最小值, 但对两种目标的减小程度不同. 总体上, 调节热沉结构参数使当量热阻最小, 可以同时获得很好的局部极限性能; 而调节热沉结构参数使最大热阻最小, 获得的整体平均散热性能却较差. 因此, 对本文热沉模型进行优化时, 以当量热阻最小化为优化目标更合理.     

Experimental Investigation of the Effect of Flow Arrangements on the Performance of a Micro-Channel Heat Sink

Abstract

An experimental study is carried out to investigate the effect of entrance and exit conditions that prevail due to different flow arrangements on the thermal performance of a copper micro-channel heat sink. Three flow arrangements—U-type, S-type, and P-type—were considered for the analysis with a test piece having inlet and outlet plenum dimensions of 10 mm × 30 mm × 2.5 mm with an array of parallel micro-channels having an individual width of 330 μm and a uniform channel depth of 2.5 mm. Performance evaluations for different flow conditions at inlet and outlet plenums were made by maintaining constant heat supply at 125 W, 225 W, and 375 W with varying Reynolds number ranging from 224 to 1,121. Nusselt number and pressure drop were computed by measuring temperature difference and pressure drop across the inlet and outlet plenum for various test combinations. Maximum heat transfer was observed for the U-type flow arrangement, followed by the P-type and S-type; maximum pressure drop was noted for the S-type flow arrangement, followed by the U-type and P-type arrangements for a constant Reynolds number. A detailed analysis of the experimental results indicate that from a pressure drop point of view, the P-type flow arrangement is preferred, whereas from the heat transfer point of view, the U-type is found to be a better option.     

Experimental Investigation on Pressure Drop and Heat Transfer Characteristics of Copper Metal Foam Heat Sink

Abstract

The effect of the cooling performance of a copper metal foam heat sink under buoyancy-induced convection is investigated in this work. Experiments are conducted on copper metal foam of 61.3% porosity with 20 pores per inch. The pressure drop experiment is carried out to find the permeability and foam coefficient of the porous media. It is found that the property of porous media changes by changing the angle of inclination of the porous media from a horizontal to a vertical position while keeping the orientation and porosity the same. The Hazen-Dupuit Darcy model is used to curve-fit the longitudinal global pressure drop versus the average fluid speed data from an isothermal steady-flow experiment across the test section of the porous medium. The study concludes that the permeability and foam coefficient for copper foam is found to be 1.11 × 10^?7 m² and 79.9 m^?1, respectively. The heat transfer study shows that the thermal performance of copper metal foam is 35–40% higher than the conventional aluminum metal heat sink under an actual conventional mode.     

车辆散热器耦合传热模拟研究

通过合理简化,建立了百叶窗翅片散热器的耦合传热模型,利用大型CFD软件FLUENT对具有不同结构参数的百叶窗散热器的流体流动和传热性能进行研究。将数值模拟结果与文献试验关联式计算结果进行对比,验证了数值模拟方法的正确性。分析了百叶窗翅片主要结构参数（百叶窗间距、百叶窗倾角、翅片间距、翅片宽度等）对传热因子j和摩擦因子f...     

Effects of fin pitch and tube diameter on the air-side performance of tube bank fin heat exchanger with the fins punched plane and curved rectangular vortex generators

Tube bank fin heat exchangers with vortex generators are widely used in the field of industrial applications. The effects of the fin pitch and the tube diameter on the air-side performance of the tube bank fin heat exchanger with plane rectangular vortex generators (PRVG) and curved rectangular vortex generators (CRVG) are experimentally studied in this paper. Performance comparison is carried out between the fins with PRVG and CRVG. The experimental results show that both PRVG and CRVG can effectively enhance heat transfer performance compared with the plain fin. Both the fin pitch and the tube diameter have obvious effect on f compared with the effect on Nu, especially for the fin with PRVG. The characteristics of Nu, f, and Nu/f^1/3 are different for the fins with PRVG and CRVG. The fin with CRVG has a better heat transfer performance than the fin with PRVG for all the cases studied in this paper.     

Heat Transfer and Fluid Flow Characteristics of Microchannel with Oval-Shaped Micro Pin Fins

A novel microchannel heat sink with oval-shaped micro pin fins (MOPF) is proposed and the characteristics of fluid flow and heat transfer are studied numerically for Reynolds number (Re) ranging from 157 to 668. In order to study the influence of geometry on flow and heat transfer characteristics, three non-dimensional variables are defined, such as the fin axial length ratio (α), width ratio (β), and height ratio (γ). The thermal enhancement factor (η) is adopted as an evaluation criterion to evaluate the best comprehensive thermal-hydraulic performance of MOPF. Results indicate that the oval-shaped pin fins in the microchannel can effectively prevent the rise of heat surface temperature along the flow direction, which improves the temperature distribution uniformity. In addition, results show that for the studied Reynolds number range and microchannel geometries in this paper, the thermal enhancement factor η increases firstly and then decreases with the increase of α and β. In addition, except for Re = 157, η decreases first and then increases with the increase of the fin height ratio γ. The thermal enhancement factor for MOPF with α = 4, β = 0.3, and γ = 0.5 achieves 1.56 at Re = 668. The results can provide a theoretical basis for the design of a microchannel heat exchanger.     

Experimental and numerical investigation of heat transfer in a miniature heat sink utilizing silica nanofluid

In this paper, heat transfer characteristics of a miniature heat sink cooled by SiO₂–water nanofluids were investigated both experimentally and numerically. The heat sink was fabricated from aluminum and insulated by plexiglass cover plates. The heat sink consisted of an array of 4 mm diameter circular channels with a length of 40 mm. Tests were performed while inserting a 180 W/cm² heat flux to the bottom of heat sink and Reynolds numbers ranged from 400 to 2000. The three-dimensional heat transfer characteristics of the heat sink were analyzed numerically by solving conjugate heat transfer problem of thermally and hydrodynamically developing fluid flow. Experimental results showed that dispersing SiO₂ nanoparticles in water significantly increased the overall heat transfer coefficient while thermal resistance of heat sink was decreased up to 10%. Numerical results revealed that channel diameter, as well as heat sink height and number of channels in a heat sink have significant effects on the maximum temperature of heat sink. Finally, an artificial neural network (ANN) was used to simulate the heat sink performance based on these parameters. It was found that the results of ANN are in excellent agreement with the mathematical simulation and cover a wider range for evaluation of heat sink performance.     

Investigation of Ti6Al4V and AA7075 alloy embedded nanofluid flow over longitudinal porous fin in the presence of internal heat generation and convective condition

The thermal attributes of porous fin due to radiation and natural convection have been carried out in the presence of nanofluid flow. The geometry of the fin taken for the analysis is rectangular profiled longitudinal fin. The temperature-dependent internal heat generation condition is also considered along with Darcy's model. The two types of nanofluid containing titanium alloy(Ti6Al4V) and aluminium alloy(AA7075) immersed in water is considered for the investigation.The modelled nonlinear ordinary differential equation is numerically solved by the Runge–Kutta–Fehlberg technique. The impact of geometric parameter on the heat transfer analysis of the fin due to the flow of both nanofluids is plotted and consequences are physically interpreted. It is observed that the presence of the water-based titanium alloy better enhances the fin heat transfer rate.     

垂直均匀射流下CPU散热器换热性能的数值分析

对垂直射流下CPU散热器的流场及温度场进行了数值模拟,得到了CPU散热器流场及温度场的分布规律,指出近底面肋片间存在回流区,明显影响传热。分析了CPU散热器在射流时不同情况下的散热性能,计算所得数据有助于CPU散热器的设计与改进。     

冷藏柜风冷冷凝器流动传热的影响因素分析

建立了数学模型,通过计算对影响食堂冷藏柜风冷冷凝器流动传热的主要因素进行了研究,分析认为:设计该类冷凝器要综合考虑各因素选取合理的翅片间距、风速、污垢热阻,严格控制冷凝器加工工艺和采取必要的维护,是保障冷藏柜高效运行的有力措施。     

微方肋冷却系统的换热特性

采用去离子水为冷却介质,对自行设计的不同结构微方肋散热器内的换热特性进行实验研究,结果表明:在进口温度为20 ℃、进口流量为57.225 L/h、底面平均温度为73.4 ℃时,散热器散热量可达2.83106 W/cm2,可以满足当前高热流密度散热需求;当散热面温度一定时,散热量随着散热器进口流量的增加而增加,但增速随散热器底面温度的增加变缓;努谢尔特数随雷诺数的增加而成幂次方增加,常规针肋结构和微针肋结构换热关系式不满足微方肋散热器特性。为了更好地表达微方肋散热器内的换热特性,拟合了微方肋散热器内对流换热关系式。     

基于热阻网络的大功率LED热管散热研究

LED结温高一直是大功率LED发展的技术瓶颈,随着单位热流密度的不断攀升,在自然冷却条件下,单纯的直肋热沉散热方式已不能满足散热要求。应用热管技术设计了热管散热系统,对该系统的传热机理和传热路线进行分析,建立该系统对应的热网络模型,对各部分热阻进行分析与计算,求得总的理论总热阻,计算得出理论结温;同时应用有限元方法对该系统进行仿真分析,对LED模块（0.025 m0.025 m0.005 m）输入30 W 电功率,得出其仿真结温稳定在58.19℃,满足结温小于65℃的要求,说明应用热管的散热系统满足设计要求。由热阻网络模型计算得出的理论结温为57.43℃,与仿真结果相差0.76℃,其误差仅为1.31％,验证了理论分析计算的正确性,对实际工程中热设计具有指导意义。     

Heat transfer and Marangoni flow in a circular heat pipe using self-rewetting fluids

In this study, Marangoni flow and heat transfer enhancement in a heat pipe have been investigated. The experiments were carried out at different heat inputs. A constant temperature water bath was used at the condenser section at three temperature levels. Heat transfer coefficients and thermal resistances of the heat pipe were measured for pure water and water/butanol solutions. The experimental results confirmed that the heat pipe filled with butanol solutions showed better thermal performance than the water-filled heat pipe. At maximum heat flux, 25% heat transfer improvement was obtained when 7 wt% butanol solution was used instead of pure water.     

管肋式辐射器排热特性的数值分析与优化设计

为得到按单面辐射方式布置的管肋式空间辐射器的排热特性，建立了相应的数学模型．采用数值模拟方法分析了管内流体温度、肋片几何尺寸和等效热沉温度对辐射器排热特性的影响，得到了不同参数值下辐射器单位面积排热量以及特定参数范围内的辐射器肋片最佳宽度和肋片效率．数值模拟结果对辐射器的工程结构设计以及空间站热管理方案的优化分析具有一定的参考价值．     

Experimental study of heat transfer characteristics in oscillating fluid flow in tube

In the present work, an experimental investigation of heat transfer enhancement parameters of the oscillating flow heat exchanger under different frequencies, tidal displacement, and heat fluxes is carried out. The effect of different parameters on experimental effective thermal conductivity and convective heat transfer coefficient in cooling region is studied using correlations given by different researchers. A correlation for experimental effective thermal conductivity in terms of S²√ω is derived based on experimental data. This correlation is useful for predicting the optimum value of S²√ω before onset of turbulence.     

圆翅片叉排热管散热器流动和传热特性数值分析

文中针对三维坐标系下,圆翅片叉排热管散热器的流动和传热特性进行数值模拟研究。分析了三个主要影响因素:翅片间距、翅片厚度和排间距对平均换热系数、流动摩擦系数和热阻的影响。翅片间距分别为6mm、7mm和8mm,翅片厚度分别为0.8mm、1mm和1.2mm,排间距分别为21.7mm、23mm和24.3mm。模拟结果表明:随着迎面风速增加,摩擦系数减小,传热热阻减小;随着翅片厚度的增加,摩擦系数减小、换热能力增强,热阻在大Re时增大明显。随着翅片间距的增大,摩擦系数增大,换热能力提高,热阻增大;随着排间距的增大,摩擦系数在正三角形管排布时的值上下变动,且只有排间距显著增大时,换热能力和热阻才会增大。     

车用散热器百叶窗翅片结构仿真优化

随着现代发动机技术的进步,发动机功率和性能的提升,也对发动机散热器提出了更高的要求。在兼备良好的散热性能和稳定性的同时,更要求散热器结构紧凑,以实现轻型化。通过对车用发动机管带式散热器的局部翅片和整体散热器进行三维建模,分析百叶窗翅片角度、翅片波距、翅片波高对空气侧压降影响,并对影响散热器散热性能主要因素进行分析。然后采用了多孔介质代替翅片的方法,模拟整体散热器的散热性能,并对比实验结果验证仿真模型准确性。最后拟合仿真数据的总传热系数和空气侧压降系数,建立粒子群算法优化数学模型。在不改变散热器外形尺寸和空气侧压降符合设计标准的情况下,优化散热器的翅片结构。翅片结构优化后,空气侧压降基本不变,散热量提升了11.6%。     

基于梯度翅片换热器的热电发电系统性能研究

本文建立了热电发电系统(TEG)多物理场数值模型,并充分考虑换热器流体影响,综合研究了具有不同热侧换热器翅片结构的TEG系统性能。在雷诺数为1000~10000范围内,分析了流体沿程温度分布特征、泵功及热电发电模块的能量转换特性.所研究的三种翅片结构包括:全流道等高度直翅片(Fin-1)、下游强化梯度翅片(Fin-2)以及上游强化梯度翅片(Fin-3).研究表明,通道长高比及热电材料覆盖率一定,热电发电功率及转换效率随流量呈二次曲线变化关系,存在最匹配流量使得系统发电性能最佳。等高度直翅片对流量的变化敏感,随流量增大,则压损增大,导致系统净输出功率及发电效率无收益.而梯度翅片可以在更大范围内产生正收益;下游强化梯度翅片具有最佳的流体沿程温度均匀性,但沿程局部热阻却最大.综合考虑沿程局部热阻分布及泵功消耗,上游强化梯度翅片TEG系统净转换效率最高,因此局部热阻分布及泵功综合因素应为TEG内的换热器合理设计的关键。     

Heat Transfer and Hydrodynamic Performance Analysis of a Miniature Tangential Heat Sink Using Al2O3–H2O and TiO2–H2O Nanofluids

In this article, thermal and hydrodynamic performances of a miniature tangential heat sink are investigated experimentally by using Al₂O₃–H₂O and TiO₂–H₂O nanofluids. The effects of flow rate and volume concentration on the thermal performance have been investigated for the Reynolds number range of 210 to 1,100. Experimental results show that the average convective heat transfer coefficient increases 14 and 11% and the bottom temperature of the heat sink decreases 2.2°C and 1.6°C by using Al₂O₃–H₂O and TiO₂–H₂O nanofluid instead of pure distilled water, respectively.