带扰流圆柱肋楔形通道的流动与换热数值研究

建立了带扰流圆柱肋楔形通道内的换热与压力损失数值计算模型,采用ANSYS-CFX商用软件数值研究了楔形通道内叉排和顺排柱肋的换热与压损特性,分析了流动与结构参数的影响规律。结果表明:随雷诺数的增大,柱肋表面、柱肋排以及通道底面的平均努赛尔数呈增大趋势;随着x/D的增大,柱肋表面和柱肋排的平均努赛尔数有所降低;随着楔形通道收缩角的增大,柱肋表面和通道底面的平均努赛尔数略有增强;相同条件下的叉排柱肋换热效果要好于顺排柱肋换热效果。范宁摩擦系数随雷诺数增加而略有增大,随x/D增大有较大的降低,随着收缩角的增大而增大。在计算参数内,叉排柱肋且x/D为1.5时的热力性能系数最高。     

不同组合方式下新型凹凸壳换热板通道的换热性能研究

应用数值模拟方法对新型凹凸壳换热板通道的流动换热特性进行了研究,凹凸壳在流动方向上取顺排和叉排两种组合方式。结果表明:无论是叉排还是顺排,每个凹凸壳内都产生3个纵向涡,位于壳底部的纵向涡扰动程度最小,换热强化主要作用于凹凸壳部位;叉排时x方向相邻两壳之间也形成两个纵向涡,纵向涡大大强化了壳壁面的换热,叉排时虽然产生较多的纵向涡,但通道的流动阻力较大,使得流体的整体扰动程度不大,换热系数较顺排时提高不明显;Re=4930时,与叉排组合的凹凸壳通道相比,顺排组合的j因子增加了5.63℅,f因子减小了39.1℅,凹凸壳顺排组合时的j、f因子比酒窝板增加8.44℅和7.9℅。     

管内插入网状肋强化换热的数值研究

采用三维数值模拟方法研究了网状肋用于圆形通道的流动换热特征,分析了雷诺数Re、肋的形状、肋的网格间距、肋的直径以及流体与固体的导热系数比kf/ks对通道平均阻力系数和换热性能的影响,并引入换热性能评价指标PEC对2种网状肋进行了比较.结果表明:管内插入网状肋对流动阻力系数和换热性能有很大影响;方形肋的换热效果比圆形肋好,但其阻力较大;随着Re的减小,2种肋的降温效果均增强;肋的网格间距越小,则换热效果越好但阻力越大;随着肋直径的增大和流体与固体导热系数比kf/ks的减小,换热效果增强.     

热渗耦合下的地埋管换热器管群排列方法研究

为了确定地源热泵工程中地埋管换热器管群的最优排列方法和管间距,建立了热渗耦合下的地埋管换热器管群三维传热模型。利用Fluent软件通过数值方法模拟了不同排列方法、不同管间距下的换热器出水口温度,着重研究了存在地下水渗流时管群排列方法对换热能力的影响,并且提出了管群单位面积换热量这一评价指标。研究结果表明,叉排管群的换热能力要高于顺排管群,地下水的渗流作用使之更加明显。无论是叉排还是顺排,管群的换热能力都和地下水渗流方向密切相关。     

涡轮叶片尾缘典型结构的流动与换热特性研究

针对涡轮叶片尾缘"冲击+扰流柱"复合典型冷却结构,通过分析内部流场和换热特性,揭示"冲击+扰流柱"冷却结构中流动发展的过程以及冲击对压力分布和流场分布的影响,揭示涡轮叶片尾缘区内射流冲击扰流柱排通道内换热机理,详细分析了冲击下各个表面的换热情况。结果表明,压比的增大能够有效改善冷却通道端壁的换热性能,但同时增大了压力损失;在两种冲击距离下,n=3d换热效果优于n=6d,但是n=6d的下游换热覆盖效果优于n=3d。顺排时,冲击孔的平均换热系数大约是扰流柱的1.5倍;叉排时,冲击孔的平均换热系数大约是扰流柱的3倍,而其它部位的平均换热系数受排列方式的影响很小。因此,"冲击+扰流柱"冷却结构的匹配,对于优化涡轮叶片尾缘区域的换热及其重要。     

不同排列方式下三角翼波纹翅片管换热器的换热性能比较

应用三维数值模拟的方法对加装三角翼涡发生器的波纹翅片管换热器的流动换热特性进行了研究.3排换热圆管按顺排和叉排2种方式排列.结果表明:三角翼产生的纵向涡包括1个主涡和1个角涡.顺排布置时,纵向涡不但改善了尾迹区的换热,同时还大大强化了三角翼下游管排壁面的换热;叉排布置时,纵向涡在遇到后一个波谷时很快被抑制,换热的强化主要作用于尾迹区.ReD=3000时,与无三角翼的波纹翅片相比,三角翼波纹翅片的j、f,因子在顺排和叉排布置中分别增加了15.4%、10.5%和13.1%、7.0%.在不同排列方式下,三角翼产生的纵向涡均提高了波纹翅片管换热器的换热性能.     

机车空气滤清系统CFD数值模拟分析

对机车空气滤清系统进行空气动力学特性数值模拟,研究分析机车空气滤清系统的流动阻力损失和空气滤清系统中间腔体内横置式滤清器流动均匀性,并进一步研究不同进气量下,空气滤清系统中间风道的阻力特性.滤清器采用多孔介质模型,横置式滤清器分为上下两排,采用顺排和叉排(上4下5和上5下4)的不同排列方式.研究结果表明:叉排的排列方式...     

旋转对非圆形扰流柱排换热影响的数值模拟

对有非圆形叉排扰流柱排的旋转矩形通道的换热旋转效应进行了数值模拟。扰流柱排的几何参数为/=4,/=1.33,/=2.7。来流雷诺数=20000下,旋转数o=0～0.3时对三种不同形状(方形、钻石形和液滴形)的扰流柱旋转矩形通道的换热研究。结果表明:迎风面与背风面的平均数都随着o的增加而增大;钻石形扰流柱排通道的换热最强,其次为方形、液滴形;此外,研究发现随着旋转的增强,矩形通道端壁各段的换热变化呈现出不同的规律,进口区端壁的换热会增强,而扰流柱排区以及尾缘区的换热则先减后增。     

带交错叉排肋的矩形通道流场和壁面换热特性的数值模拟

为了获得高的换热系数和流动损失小的涡轮叶片内冷通道,提出了在上下壁面交错叉排布置肋的通道结构,利用数值计算的方法研究了通道各个壁面的换热特性、流动特性和流体的温度分布规律。入口雷诺数变化范围为30000~120000。采用结构化网格进行网格划分,利用realizablek-ε湍流模型和增强壁面函数封闭方程。计算结果表明,所提出的通道结构不仅在带肋的上下壁面具有较高的换热系数,大约为2.2~2.4,光滑的左右壁面的换热也增强了1.4~1.6倍,通道内的温度分布呈现出同心圆的分布,在靠近壁面的位置,二次流动较强。     

燃气轮机通道宽高比对换热特性的影响

采用结构化六面体网格和κ-ε湍流模型,求解三维N-S方程,对直冷却通道内置不同宽高比的W型扰流肋片在入口雷诺数为20 000时的空气流动与换热特性进行数值模拟。分析了不同肋片通道的宽高比对肋间壁面的换热效果和流动损失的影响,并对通道的宽高比进行全局寻优。结果表明,肋片通道的宽高比是影响带肋片直冷却通道的整体换热效果和综合冷却效率的主要因素,并存在一一对应的关系,整体换热效果最好时所对应的肋片宽高比为5,考虑热量损失的情况下换热效果最好时所对应的肋片宽高比为0. 48。     

Heat transfer from multiple row arrays of low aspect ratio pin fins

Pin fin arrays are used in many applications to enhance heat transfer. In modern gas turbines, for example, airfoils are designed with sophisticated internal and external cooling techniques. One method for cooling is routing air from the compressor through intricate cooling channels embedded in turbine airfoils. Heat transfer from the blade to the coolant air can be increased by installing arrays of cylindrical pedestals often referred to as pin fins. Pin fin arrays increase heat transfer by increasing the flow turbulence and surface area of the airfoil exposed to the coolant.For the current study, experiments were conducted to determine the effects of pin spacing on heat transfer and pressure loss through pin fin arrays for a range of Reynolds numbers between 5000 and 30,000. Results showed that spanwise pin spacing had a larger effect than streamwise spacing on array pressure loss while streamwise spacing had a larger effect than spanwise spacing on array heat transfer.     

Optimization of short micro pin fins in minichannels

Finned minichannels are modeled in order to optimize microstructure geometry and maximize heat transfer dissipation through convection from a heated surface. Six pin fin shapes – circle, square, triangle, ellipse, diamond and hexagon – are used in a staggered array and attached to the bottom heated surface of a rectangular minichannel and analyzed. Also, using square pin fins, different channel clearance over fins are investigated to optimize the fin height of the fins with respect to that of the channel. Fin width and spacing are investigated using a ratio of fin width area to the channel width. Fin material is then varied to investigate the heat dissipation effects. Triangular fins with larger fin height, smaller fin width, and spacing double the fin width maximizes the number of fins in each row and yields better performance. Correlations describing the Nusselt number and the Darcy friction factor are obtained and compared to previous ones from recent studies. These correlations only apply to short fins in the laminar regime. Completely understanding the effects of micro pin fins in a minichannel is essential to maximizing the performance in small scale cooling apparatuses to keep up with future electronic advancements.     

A comparative study of the airside performance of heat sinks having pin fin configurations

This study performs an experimental study of pin fin heat sinks having circular, elliptic, and square cross-section. A total of twelve pin fin heat sinks with inline and staggered arrangements were made and tested. The effect of fin density on the heat transfer performance is examined. For an inline arrangement, the circular pin fin shows an appreciable influence of fin density whereas no effect of fin density is seen for square fin geometry. This is associated with the unique deflection flow pattern accompanied with the inline circular fin configuration. For the staggered arrangement, the heat transfer coefficient increases with the rise of fin density for all the three configurations. The elliptic pin fin shows the lowest pressure drops. For the same surface area at a fixed pumping power, the elliptic pin fin possesses the smallest thermal resistance for the staggered arrangement.     

Thermal Analysis for Heat Transfer Enhancement in Perforated Pin Fins of Various Shapes with Staggered Arrays

The present work investigates the enhancement of heat transfer rate through staggered pin fins of different shapes with different perforation geometries, namely circular, diamond shaped and elliptical type. Three dimensional computational fluid dynamics simulation has been carried out to analyze the effects of fin geometry and dimension of perforation as well as the shape of fin to enhance heat transfer rate against pressure loss. Results show that the heat transfer rates of perforated fins up to certain perforation number and size are always greater than the solid ones and with the change of fin shape and perforation geometry heat transfer rate also improves significantly. On the other hand pressure drop through heat sink decreases not only with increasing perforation number but also with the size of perforation. Moreover, variation of pressure drop of perforated fins is influenced with fin geometry.     

Orthotropic thermal conductivity effect on cylindrical pin fin heat transfer

Analytical equations for temperature distribution and heat transfer rate from a cylindrical pin fin with orthotropic thermal conductivity, encountered in the use of thermally enhanced polymer composites, are derived and validated using detailed finite-element results. The thermal performance of such fins was found to depart from the classical fin solution with increasing radial conductivity-based Biot number. The in depth analysis of developed orthotropic axi-symmetric pin fin temperature and heat transfer rate equation is carried out to better understand the heat flow rate in such fins.     

Numerical estimation of pressure drop and heat transfer characteristics in annular‐finned channel heat exchangers with different channel configurations

In this numerical investigation, three‐dimensional analysis has been used to study the effect of finned channels configuration of (circular, square, and triangular shape) and fin spacing with four rows in staggered arrangements. The finite volume method with k‐ ω turbulent model is applied to estimate the heat transfer and flow characteristics. The results illustrate that the development of the boundary layer between the fins surfaces is credited to the finned channels configuration, fin spacing, and Reynolds number. Moreover, the results of pressure drop and heat transfer with various channel configuration and different fin spacings (1.6, 2, and 4 mm) are presented and validated with the available correlations. The triangular‐finned channel with 1.6 mm fin spacing offered higher heat transfer enhancement followed by square‐ and circular‐finned channels. A considerable agreement was observed when the current findings and the existing correlations were compared, with a maximum deviation of 15% for all the cases.     

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.     

Conjugate heat transfer in channels with heat-conducting inclined fins

Conjugate heat transfer in a finned channel with equally spaced fins placed transversely to the flow direction following in-line and staggered arrangements is evaluated. The fins and channel walls are heat-conducting and are fully coupled to a turbulent fluid flow problem. The hydrodynamic and thermal effects of the fin blockage ratio, fin angle, and flow velocity were investigated. The simulations show that the fin arrangement is of paramount importance on the performance of the heat exchanger: the staggered fin configuration provided lower pressure drop and higher heat transfer rate than the in-line fin arrangement for different flow conditions.     

Single-Phase Cryogenic Flow and Heat Transfer Through Microscale Pin Fin Heat Sinks

Single-phase heat transfer and pressure drop of liquid nitrogen in microscale heat sinks are studied experimentally in this paper. Effects of geometrical variations are characterized on the thermofluidic performance of staggered microscale pin fin heat sinks. Pitch-to-diameter ratio and aspect ratio of the micro pin fins are varied. The pin fins have square shape with 200 or 400 μm width and are oriented at 45 degrees to the flow direction. Thermal performance of the heat sinks is evaluated for Reynolds numbers (based on pin fin hydraulic diameter) from 108 to 570. Results are presented in a nondimensional form in terms of friction factor, Nusselt number, and Reynolds number and are compared with the predictions of existing correlations in the literature for micro pin fin heat sinks. Comparison of flow and heat transfer performance of the micro pin fin heat sinks reveals that at a particular critical Reynolds number of ～250, pin fin heat sinks with the same aspect ratio but larger pitch ratio show a transition in both friction factor and Nusselt number. In order to better characterize this transition, visualization experiments were performed with the Fluorinert PF5060 using an infrared camera. At the critical Reynolds number, for the larger pitch ratio pin fin heat sink, surface thermal intensity profiles suggest periodic flapping of the flow behind the pin fins at a Strouhal number of 0.227.     

翅柱复合型冷却器表面传热性能的数值研究

提出一种用于油液冷却的新型翅柱复合型冷却器,并应用SIMPLE算法对于其二维简化模型在不同工况下的表面传热及流动阻力进行数值模拟。将模拟结果与试验和经验关联式相比较,吻合情况良好,表明此算法和所简化的模型是合理的。根据数值模拟结果研究这种传热表面的传热机理,分析翅柱位置及几何参数对流动与传热的影响,对该新型翅片的推广及优化设计有较大帮助。