Numerical analysis of the flow and heat transfer characteristics for forced convection-radiation in entrance region of an internally finned tubes

The flow and heat transfer characteristics of combined forced convection and radiation in the entrance region of internally finned tubes are investigated numerically in this paper. The uniform flow is considered for an inlet flow condition. A three dimensional parabolic problem is solved by a marching-type procedure envolving a series of two dimensional elliptic problems in the cross-stream plane. The SIMPLER-algorithm and Raithby's pressure-velocity coupling method are employed to analyze the flow and heat transfer characteristics. For the calculation of radiative heat transfer, the P₁-approximation and the weighted sum of gray gases method (WSGGM) are used. The effects of fin height, number of fins, optical thickness, reference temperature, and Planck number on the flow and heat transfer characteristics are examined. It was found that the effect of fin-height on the heat transfer characteristic is more dominant than that of number of fins. The present results show that the optimal non-dimensional fin height and number of fins are 0.4 and 16, respectively.     

大容量电力电子装置中板式水冷散热器的优化设计

为提高水冷散热器的散热能力、控制其温度均匀性,在散热器外形尺寸及流量一定的条件下,从理论上对层流范围内平板式水冷散热器的三个通道参数(通道数、散热片高度、散热片占空比)与散热器量纲一散热热阻的变化关系进行了推导。提出可根据这些变化关系来对任意尺寸平板式水冷散热器的各通道参数进行优化选择,在工程设计上具有很好的指导意义,仿真和试验结果证明了方法的有效性并表明:小通道尺寸的平板式水冷散热器对于解决大热流密度器件的散热更为有效,散热效率更高;在同样的参数情况下,流量增大则散热器效率降低,应综合考虑散热器流阻和流体平均温升的控制要求来选择流量。     

Geometry optimization of a cylindrical fin heat sink using mine blast algorithm

The heat sinks are utilized in electronic devices to eliminate heat from the chip and efficiently transmit it to the environment. Therefore, the optimal geometry sizes of fin heat sinks are the point of concern for manufacturers and designers. For this reason, the importance of optimization techniques particularly metaheuristics is understood. The design variables are width of heat sink, number of fins, fin height, and fin diameter. The various responses that have been considered are electromagnetic emitted radiations, thermal resistance, and mass of the heat sink investigated separately and simultaneously (multi-objective). Mine blast algorithm (MBA), as a recently developed optimizer, is inspired from explosion of mines. The optimum dimensions and values for each response have been obtained by the MBA and have been compared with other optimization methods in the literature. In terms of thermal resistance and mass responses, the MBA has offered better values, while for the emitted radiations, the obtained results obtained by Taguchi-based gray relational analysis (TGRA) was preferred. For manufacturing point of view, the MBA and TGRA both suggested better and efficient design. In addition, the value path analysis has been carried out to compare the trade-off among the considered responses. Finally, parametric sensitivity analyses have been implemented for design parameters, and discussions and comparisons have been carried out for the effects of each decision variable. By considering all responses, width of heat sink and fin height are considered as the most important and effective design parameters, respectively.     

高热流密度功率器件热设计及实验研究

雷达系统中的DAM模块发热量大,热流密度高,其散热性能直接影响功率器件运行的可靠性。对从功率器件到散热器之间的传热路径以及散热器风道侧参数进行优化设计,确定在热源上焊接铜板以降低热流密度、选择导热性能优异的界面接触材料、冷板局部焊接铜板以减小平面方向温度梯度、增加散热器翅片高度和加密散热器翅片排布等优化设计方法改进常规风冷散热方案,并对优化后的风冷散热方案进行实验研究,实验结果与仿真结果相吻合,验证了风冷散热优化方案的可行性。     

Comparison of performances of the various shapes of asymmetric fins

A comparison between the heat loss of the asymmetric triangular fin and the asymmetric trapezoidal fins which have various slopes of the fin’s upper lateral side is performed. The relation between the slope factor of the fin and the non-dimensional fin length for equal amount of heat loss is shown. Further, the relation between the Biot number and the non-dimensional fin length for equal amount of heat loss is given. For these analyses, a forced analytic method is used. In particular, the same equation is used for both the asymmetric triangular fin and the asymmetric trapezoidal fins just by adjusting the value of the slope factor. It is shown that this equation can also be applied to a rectangular fin with very good accuracy. The base temperature, thermal conductivity of fin’s material and the heat transfer coefficient are assumed constant.     

内翅式套管相变蓄热器蓄热特性的模拟研究

翅片的添加可以有效改善相变蓄热速率低的问题,研究翅片结构参数对蓄热器强化蓄热的影响具有重要意义.该文采用FLUENT软件对内翅式套管相变蓄热器蓄热特性进行模拟研究,考虑自然对流作用下,探讨了蓄热器内翅片个数,翅片高度,翅片厚度等因素对石蜡蓄热过程的影响.研究表明:自然对流在内翅式套管相变蓄热器蓄热过程中发挥重要作用;翅...     

The effect of serrated fins on the flow around a circular cylinder

An experimental study is performed to investigate the characteristics of near wake flow behind a circular cylinder with serrated fins using a constant temperature anemometer and flow visualization. Various vortex shedding modes are observed. Fin height and pitch are closely related to the vortex shedding frequency after a certain transient Reynolds number. The through-velocity across the fins decreases with increasing fin height and decreasing fin pitch. Vortex shedding is affected strongly by the velocity distribution just on top of the finned tube. The weaker gradient of velocity distribution is shown as increasing the freestream velocity and the fin height, while decreasing the fin pitch. The weaker velocity gradient delays the entrainment flow and weakens its strength. As a result of this phenomenon, vortex shedding is decreased. The effective diameter is defined as a virtual circular cylinder diameter taking into account the volume of fins, while the hydraulic diameter is proposed to cover the effect of friction by the fin surfaces. The Strouhal number based upon the effective diameters seems to correlate well with that of a circular cylinder without fins. After a certain transient Reynolds number, the trend of the Strouhal number can be estimated by checking the ratio of effective diameter to inner diameter. The normalized velocity and turbulent intensity distributions with the hydraulic diameter exhibit the best correlation with the circular cylinder’s data.     

锯齿形翅片散热器风冷性能试验研究

文中从试验的角度研究了锯齿形翅片散热器的风冷性能。锯齿形翅片散热器具有结构复杂、不易仿真实施的特点。文中系统介绍了锯齿形风冷散热器的典型结构形式以及风冷性能测试系统原理、性能和测试分析结果,从试验实测的角度研究了锯齿形翅片散热器的应用选型及其与散热量、风量、风压等的关系,分析了翅片参数(翅高、翅宽、翅片节距)对散热性能的影响,对电子产品散热的风冷设计具有较高的参考价值。     

平直翅片热管散热器的正交数值模拟优化

文中以平直翅片热管散热器为研究对象,研究了翅片厚度、翅片间距、翅片高度、翅片宽度和热管直径 5 个结构参数对翅片换热性能和阻力特性的影响,采用正交实验设计的方法设计了上述结构参数的 15 个组合方案,利用 CFD 数值模拟的方法对每个组合方案下翅片的流动换热性能进行了模拟。以努塞尔数 Nu 、阻力系数f、传热性能综合评价指标(Performance Evaluation Criteria, PEC)作为评价指标,在每个评价指标下利用极差分析挑选出性能最优的组合方案。 该方法能快速获得散热器结构的优化方案,并分析出主要影响因素,对工程应用有一定的指导意义。 结果表明:影响 Nu 和 f 的最主要因素是热管直径,影响 PEC 的最主要因素是翅片厚度。 对于本文研究的散热器,其最优参数组合方案为:翅片厚度为 0. 6 mm,翅片间距为 2. 2 mm,热管直径为 6 mm,翅片高度为 65 mm,翅片宽度为 28 mm。     

一种新型换热器用于小型分体空调的试验与分析

用一种带有百叶窗翅片微型通道扁平管道的平行流动平行翅片的新型换热器PF2替代标准带有平板翅片圆管换热器RTPF作为室外换热器,并在一家用空调装置中进行了试验研究.试验装置采用了大金提供的型号为RXR28EV1B9、以R410A为制冷剂的家用小型分体式热泵空调器.在此装置上对PF2换热器及原装置上RTPF换热器在空调工况下进行了试验性研究,比较分析了两换热器在同一系统上的性能,并给出了试验结果.     

Numerical simulation of natural convection in annuli with internal fins

The solution for the natural convection in internally finned horizontal annuli is obtained by using a numerical simulation of time-dependent and two-dimensional governing equations. The fins existing in annuli influence the flow pattern, temperature distribution and heat transfer rate. The variations of the fin configuration suppress or accelerate the free convective effects compared to those of the smooth tubes. The effects of fin configuration, number of fins and ratio of annulus gap width to the inner cylinder radius on the fluid flow and heat transfer in annuli are demonstrated by the distribution of the velocity vector, isotherms and streamlines. The governing equations are solved efficiently by using a parallel implementation. The technique is adopted for reduction of the computation cost. The parallelization is performed with the domain decomposition technique and message passing between sub-domains on the basis of the MPI library. The results from parallel computation reveal in consistency with those of the sequential program. Moreover, the speed-up ratio shows linearity with the number of processor.     

基于COMSOL Multiphysics的三角形肋片传热数值模拟

以三角形肋片为研究对象,采用COMSOL Multiphysics软件得到三角形肋片的温度场分布,并分析肋片长度和高度比对肋片传热性能的影响.结果表明：肋片温度从根部到顶部依次降低.最大无量纲温度最小值下的肋片形状受参数影响较为明显,试验所得结果为肋片的优化设计提供了重要指导.     

微型汽车散热器百叶窗翅片高度的优化设计

为了得到更合理的微型汽车散热器的百叶窗翅片结构,采用Fluent软件,对散热器翅片进行了数值分析.通过修改其关键尺寸(翅片高度),得到了不同高度下散热器翅片的阻力因子f和散热因子j,并引入无量纲参数j/f1/3来评价其综合性能.优化结果是当翅片高度为8.94mm时,综合性能最佳.     

新型同轴套管式换热器强化传热研究

同轴套管式地热能开采技术是用于中深层地热能开采的有效方式。为了增强同轴套管式换热器的换热效率,提出了一种带螺旋翅片的新型同轴套管式换热器。基于有限体积法,对比分析新型与普通型同轴套管式换热器的换热性能,得到螺旋翅片结构对换热性能的影响,揭示其强化传热机理。结果表明：通过增加螺旋翅片的翅高或减小螺旋翅片的螺距,可有效增强同轴套管式换热器内流体流动的湍流动能,达到提高换热性能的目的;与普通光滑管换热器相比,翅高为19 mm,螺距为300 mm的新型换热器在雷诺数为27000时,努赛尔数提高了35.5%,摩擦系数提高了91%,热性能系数达到最高1.093;增加翅片和减小螺距都可以增加采出温度和采热功率,翅高为19 mm,螺距为300 mm换热器较光滑管换热器采热温度提高了5.4 K,采热功率提高了32.4%。为高效同轴套管式换热器设计提供了理论依据。     

Thermal characteristics of louvered fins with a low-reynolds number flow

A heat recovery system is crucial for the effective use of energy where heat rejection from production processes is unavoidable and must be reused. The response of the louvered fins to the low-Reynolds number hot gas is yet to be reported in the literature for the application of a heat exchanger on low-speed hot plume arising from heat sources in production processes. This study focuses on the effects of the louvered fin heat exchanger’s design parameters, which include the louver pitch and louver angle, on the convective heat transfer, which defines the thermal interaction between the hot, buoyant, naturally-induced air and the louvered fins. The resulting Colburn factors (j) are compared with those derived under forced convection with a similar range of low Reynolds number (233 to 1024). All experiments are done on a 15:1 scaled-up model. The fin aspect ratios between the fin spacing and louver pitch are set at 0.75, 1, and 1.5, while the louver angles are set at 18°, 23°, 30°, 35°, and 40°. The Colburn factor strongly depends on the louver angle, especially at the lower range of the Reynolds number. The decreasing aspect ratio induces more hot buoyant air into the louver-formed channels, increasing the heat transfer rate. When the fin angle increases towards 30°, a larger Colburn factor is produced. However, the heat transfer characteristic drops as the angle goes beyond 30°. The highest j for the low speed flow is attained when the louver angle is 30° and the fin aspect ratio is 1.     

某机载毫米波雷达天线仿真热设计

针对某型机载毫米波雷达天线热设计难题,提出了热管结合强迫风冷的新型冷却方式,设计了专用风道。应用数值模拟方法首先对T/R组件进行了热仿真计算,其次对天线背部风机抽风、吹风进行了仿真比较,再对散热翅片和风量分配进行了仿真优化,最后对3 km高空状态进行了仿真计算。计算结果表明,天线背部风机吹风明显好于抽风;翅片厚度0.8 mm,翅片数134,占空比23.8%的翅片结构散热较好;限流板阻力系数为5时风量分配较均匀;高空环境下满足天线工作要求。该方式合理可行,满足系统热设计要求,为同类产品的热设计提供了重要参考。     

矩形肋片散热器几何参数对散热的影响分析

为考察矩形肋片散热器几何参数对散热效果的影响规律,文中应用热仿真分析软件Flotherm对矩形肋片散热器在不同结构参数下的模型进行了自然对流散热计算,通过对比分析不同模型的温度和热阻计算结果,探讨了散热器基板参数和肋片参数对其散热性能的影响。分析表明,改变散热器肋片的高度、长度和间距可有效降低散热器的热阻。这些几何参数可以作为散热器热设计变量,以进一步对散热器进行优化设计。     

Optimization of a reversed trapezoidal fin using a 2-D analytic method

A reversed trapezoidal fin with variable fin base thickness is optimized based on the fixed fin volume by using a two-dimensional analytic method. The variation of temperature along the normalized Y position at the fin tip is presented. For fixed fin volumes, the maximum heat loss, the corresponding optimum fin effectiveness, fin base height and fin tip length as a function of the fin base thickness, fin shape factor and the fin volume are presented. One of the results shows that both the optimum heat loss and the optimum fin length increase with the increase of the value of fin shape factor.     

板翅式换热器翅片对传热和阻力性能影响的研究

随着科技的日益进步,换热器正朝着紧凑化、轻重量、小型化的方向发展。板翅式换热器作为紧凑式换热器之一,能很好地满足这一特性。本文立足于一台翅片材料为铝的板翅式换热器算例,通过理论分析和实际计算,研究了板翅式换热器的翅片厚度、板间距以及翅片节距的变化对换热器传热性能和阻力性能的影响,旨在为板翅式换热器的优化设计提供更加详实的理论依据。     

双面犁法加工整体翅片管的成形数学模型

建立了双面犁法加工整体翅片管的成形数学模型 ,推导了翅片结构参数与加工用量及刀具几何参数之间的关系 ,为优选翅片结构参数以达到最佳传热效果提供了理论依据。理论分析和试验结果均表明 ,对于某一刀具 ,翅片高度和平均翅厚均随挤压深度和进给量的增加而增大