有扰流片的矩形通道内空气流动和传热过程的数值模拟

以高温透叶片尾部区内部冷却为应用背景，对带顺排、错排扰流片肋的通道内空气流动和传热过程进行了数值模拟。计算结果表明，在相同雷诺数下，错排扰流片的阻力系数比针肋和顺排绕流片的阻力因子均增大约2%，而冷却能力分别增大约50%和9%。     

肋片振动对带肋矩形通道内流动和换热影响的数值研究

基于Fluent动网格及UDF编程技术对二维流场中振动带肋矩形直通道的流动与换热特性进行了数值模拟,分析了振幅和频率对其换热特性的影响。数值计算表明,相比于静止的带肋矩形直通道的换热,振动对其换热有一定的影响,并且随着振幅和频率的提高,振动强化换热效果越显著;振动同时也使通道内的流场结构发生了改变,振幅和频率的提高都能使通道内的静压迅速地增加,振动时静止通道内两肋片之间尺度大小不一的两个漩涡随着振幅、频率的提高,漩涡尺度相继变小,直至最后都被主流带走。     

矩形微通道内液体流动与传热的数值模拟研究

本文针对矩形微通道内单相流动和传热特性,利用CFD模拟分析软件对其进行三维数值模拟研究.微矩形通道宽为50μm,高为200μm,工质采用去离子水.模型以有限体积法离散,SIMPLEC方法求解速度、压力和温度耦舍方程组.讨论了流体热物性随温度变化和雷诺数对速度场和温度场的影响.并与理论预测值、参考文献值比较.分析结果显示,流体粘度随温度对触的影响和粘性耗散对热起始段的作用不能忽略.fRe数随Re数的增加而减小,Nu数不受Re数的变化影响.     

矩形微通道内流体流动特性的数值研究

对矩形微通道实体模型进行简化处理,并建立微通道内流体流动的数学模型.设定矩形微通道水力直径Dh=120～480 μm,入口雷诺数Re=ll.9～3 817.1,以20℃蒸馏水为流动工质,借助FLUENT分别对不同水力直径的三组矩形微通道内流体流动特性展开数值模拟研究,并将数值模拟结果与理论预测值及其他学者的研究结论进行对比.结果表明:随着微通道水力直径的减小,摩擦阻力系数、速度梯度和压强梯度都呈现增大趋势;在微尺度下,矩形微通道内临界Re提前,而且水力直径越小,临界Re值越小.     

叉排针肋楔型通道换热数值研究

应用湍流模型对涡轮叶片尾缘叉排针肋通道的换热与流动进行了三维数值模拟研究。为了研究冷却叶片尾缘处正压面与背压面之楔角对通道换热与流动的影响 ,在通道楔角θ为 0°～ 2 0°进行了数值模拟计算 ;为了研究 Reynolds数对通道换热与流动的影响 ,在 Re为 0 .5× 10 4～ 4 .0× 10 4进行了数值模拟计算。最后给出了一个最佳楔角     

交错内肋微通道的流动和传热特性研究

为了研究带有交错内肋微通道的流动和传热特性,采用数值模拟的方法分析了肋片的形状对微通道热力性能的影响,对比了矩形肋、菱形肋、三角形肋和圆形肋4种不同形状内肋结构的微通道和光滑矩形微通道的热力性能。结果表明：矩形肋、菱形肋、三角形肋和圆形肋微通道的努塞尔数Nu都大于光滑矩形微通道的努塞尔数Nu,最大值分别为光滑矩形微通道的2.59,2.71,2.90和2.48倍;肋片对微通道的传热特性具有显著的强化作用,这是由于流体在交错内肋的后方产生涡流,实现整个流场的全局强化传热,极大提升微通道传热特性;交错内肋的应用也增大了通道的摩擦系数,矩形肋、菱形肋、三角形肋和圆形肋微通道摩擦系数的最大值分别为光滑矩形微通道的8.66,7.96,17.50和5.96倍。     

柱肋对缩放层板冷却结构流动和传热的影响

柱肋作为一种冷却通道内的强化换热技术,对提高层板结构的冷却效率有着重要意义。为了研究柱肋对双层板结构冷却性能和流场的影响,数值模拟研究了柱肋高径比分别为1,0.6,0.2,吹风比分别为0.3,0.6,1.0,1.5的原模型和等比例放大5倍模型两种尺度层板冷却结构的冷却效率。结果表明：高径比的变化对原模型冷却效率的影响更加明显,对放大模型的冷却效率影响非常小;吹风比越大,高径比对冷却效率的影响越明显,吹风比从0.3增大到1.5,高径比为0.6的柱肋比高径比为1柱肋的综合冷却效率提高了2%～3%;高径比为0.6的柱肋具有最大的相对压力损失,高径比为0.2和1柱肋的相对应力损失比高径比为0.6时低0.01%～0.07%。     

肋角度对矩形通道壁面换热影响的研究

采用非结构化网格和realizab lek-ε紊流模型,求解三维N-S方程,对带肋和气膜孔矩形通道在入口雷诺数9×104,气膜孔总出流比0.22时进行了换热特性的数值模拟。分析了肋角度对各个壁面换热特性的影响规律。结果表明,带肋和气膜孔的通道流场非常复杂,扰流肋的存在使各壁面的换热都得到了增强,但增强幅度的差别较大。     

组合肋通道流动与传热特性的数值分析

本文采用数值模拟的方法研究了一种新型组合肋通道的流动与传热特性,主要对比了不同肋型通道的传热性能和阻力性能,考察了雷诺数、肋间距和肋高对通道壁面特征数的影响规律.结果 表明与矩形肋、半圆肋通道相比,组合肋通道的综合传热性能最好,且阻力损失小.     

带扰流片的矩形通道的实验研究

以高温透平叶片冷却为应用背景，对带有顺排、错排扰流片的矩形通道进行了实验研究。实验结果表明：在相同的雷诺数下，错排扰流片比顺排扰流片具有更好的强化换热效果，即便保持相同的流动阻力，错排扰流片的冷却效果仍强于顺排扰流片。     

Parametric study of unsteady flow and heat transfer in a pin-fin heat exchanger

A numerical study has been carried out to analyze the unsteady three-dimensional flow and heat transfer in a parallel-plate channel heat exchanger with in-line arrays of periodically mounted rectangular cylinders (pins) at various Reynolds number and geometrical configurations. The three-dimensional unsteady Navier-Stokes and energy equations are solved using higher order temporal and spatial discretizations. The simulations have been carried out for a range of Reynolds number based on cylinder width (180-600) and a Prandtl number of 6.99 (corresponding to water). Conjugate heat transfer calculations have been employed to account for the conduction in the solid cylinder and convection in the fluid. The thermal performance factor (TPF) increases significantly when the flow becomes unsteady. The choice of aspect ratio of the cylinders is judged by their relative increase in friction factor and heat transfer at transitional Reynolds number. The TPF is found to increase with the increase in pitch of the cylinders. The increase in channel height enhances the TPF though the heat transfer decreases at higher channel height.     

Numerical study of turbulent flow and heat transfer from an array of thick plates

Convective heat transfer in turbulent flow from an array of blunt plates is numerically studied. The flow is assumed to be steady, two dimensional, incompressible and turbulent. A modified two equation k–ε model with the preferential dissipation modification is incorporated to determine accurately turbulent flow field, as well as the recirculation pattern along the entrance region of the plates. To predict the local variations of turbulence quantities in the k equation, a three-layer, near wall turbulence model was examined based on the wall function. The governing equations are solved using finite volume technique based on the bounded skew hybrid difference scheme BSHD, and the PISO algorithm to iterate for pressure corrections. The solutions were obtained using a two-pass procedure, devised to allow for the correct use of the wall functions. Computations for Re_D were obtained in the range 2.5·10⁴ to 10⁶; Prandtl numbers of 1, 2, 5, and 10 and blockage ratios of 5 % through 30 %. Results of friction coefficient, and Nusselt number distribution for the combined entry length problem are presented for different flow conditions and plates thickness. These findings are in accord with previously published experimental and theoretical results of a single plate.     

Numerical simulation of roughness effects on flow and heat transfer in microchannels at slip flow regime

A numerical simulation for studying fluid flow and heat transfer characteristics in microchannels at slip flow regime with consideration of slip and temperature jump is studied. The wall roughness is simulated in two cases with periodically distributed triangular microelements and random shaped micro peaks distributed on the wall surfaces. Various Knudsen numbers have used to investigate the effects of rarefaction. The numerical results have also checked with available theoretical and experimental relations and good agreements has achieved. It has been found that rarefaction has more significant effect on flow field in microchannels with higher relative roughness. The negative influence of roughness on fluid flow and heat transfer found to be the friction factor increment and Nusselt number reduction. In addition high influence of roughness distribution and shape has been shown by a comparison of Poiseuille and Nusselt numbers for tow different cases.     

平行流热管管内流动与传热的数值模拟研究

为研究平行流热管的工作机理,本文基于Fluent软件中的VOF模型编写了蒸发冷凝相变的UDF程序,对不同功率下平行流热管管内两相流动和传热过程进行了数值模拟研究。模拟结果显示了初始阶段平行流热管管内的气液分布,启动阶段管内包括泡状流、弹状流、环状流等复杂流型的转变过程,稳定工作阶段工质在各并联管路中互激振荡流动。在高加热功率下,管内工质的互激振荡流动更为剧烈,热量输送距离更远。研究结果为平行流热管换热器的优化设计提供了参考依据。     

受限空气射流冲击矩形柱鳍热沉换热实验研究

采用实验方法研究了受限空气冲击射流与矩形柱鳍热沉相结合的散热方式应用于芯片冷却的换热规律,采用最小二乘法对实验数据进行了拟合,并最终获得平均努塞尔数关于雷诺数、喷口高度-孔径比及普朗特数的实验准则方程。在此基础上将这种散热方式与其他空冷方式进行了换热能力的比较,结果表明此种散热方式的换热能力大大超过其他空冷方式。最后,对实验系统误差进行了分析,根据误差传递理论求得的平均努塞尔数的实验相对误差不超过6%。     

滑移区气体-颗粒流动与传热特性研究

针对气体-颗粒微尺度流动与传热过程开展数值模拟研究,所构建模型中气体处理为可压缩、变物性流体,并在颗粒表面采用速度滑移和温度跳跃边界条件以考虑气体稀薄效应。在数值模拟基础上,研究分析稀薄效应对颗粒与其周围气体流动与换热的影响程度,并进一步提出新的阻力系数与传热努谢尔特数关联式。研究结果表明,气体稀薄效应将减小颗粒阻力系数,同时抑制颗粒与其周围气体的传热过程。     

Numerical study of pin-fin heat sink with un-uniform fin height design

This study presents the numerical simulation of the heat sink with an un-uniform fin height with a confined impingement cooling. The governing equations are discretized by using a control-volume-based finite-difference method with a power-law scheme on an orthogonal non-uniform staggered grid. The coupling of the velocity and the pressure terms of momentum equations are solved by the SIMPLEC algorithm. The well-known k–ε two-equations turbulence model is employed to describe the turbulent structure and behavior. The parameters include the Reynolds number (Re = 15,000 and Re = 25,000) and 12 un-uniform fin height designs (Type-b to Type-m). The objective of this study is to examine the effects of the fin shape of the heat sink on the thermal performance. It is found that the junction temperature can be reduced by increasing the fin height near the center of the heat sink. The results also show that there is a potential for optimizing the un-uniform fin height design.     

Numerical study on heat transfer of turbulent channel flow over periodic grooves

A numerical investigation of turbulent forced convection in a two-dimensional channel with periodic transverse grooves on the lower channel wall is conducted. The lower wall is subjected to a uniform heat flux condition while the upper wall is insulated. To investigate turbulence model effects, computations based on a finite volume method, are carried out by utilizing four turbulence models: the standard k − ε, the Renormalized Group (RNG) k − ε, the standard k − ω, and the shear stress transport (SST) k − ω turbulence models. Parametric runs are made for Reynolds numbers ranging from 6000 to 18,000 with the groove-width to channel-height ratio (B/H) of 0.5 to 1.75 while the groove pitch ratio of 2 and the depth ratio of 0.5 are fixed throughout. The predicted results from using several turbulence models reveal that the RNG and the k − ε turbulence models generally provide better agreement with available measurements than others. Therefore, the k − ε model is selected to use in prediction of this complex flow. In addition, the results of the heat transfer coefficient, friction factor, skin friction coefficient and thermal enhancement factor are also examined. It is found that the grooved channel provides a considerable increase in heat transfer at about 158% over the smooth channel and a maximum gain of 1.33 on thermal performance factor is obtained for the case of B/H = 0.75. This indicates that the reverse/re-circulation flow in a channel with transverse grooves can improve the heat transfer rate.     

Numerical analysis of heat flow in contact heat transfer

A finite difference analysis of heat conduction problem in a cylinder terminating in a frustum of a cone is presented. The constriction can be either in vacuum or in a gaseous environment. A fine mesh of 2500 × 800 was used for the construction of the grid such that very small constrictions could be analysed sufficiently accurately. Small constrictions i.e., small contact areas separated by large voids filled with a gas are typical of most practical applications involving contact heat transfer. The result of the finite difference analysis shows that gap conductance is predominant for all the gases considered. Gap-to-solid conductance ratio increases as the cone angle decreases due to the decrease of gap thickness. It also indicates that increase of conductance ratio is less significant at higher constriction angles. Finally, predicted conductance parameters are compared with the experimental results for different interfacial gases and a very good agreement is obtained.