A Comparison of Four Solution Methods for the Analysis of a Trapezoidal Fin

A comparison is made of the temperature profile and the heat loss from a trapezoidal fin using four methods. These four methods are the one- and two-dimensional analytical, the two-dimensional finite difference and a two-dimensional modified finite difference method. The two-dimensional analytical method was arbitrarily chosen as the reference. The non-dimensional fin length is restricted to be less than 2 to prevent errors which might occur due to large values of Δx in the finite difference methods. The values of the Biot number range from 0.01 to 1.0 while the thermal conductivity of the fin and fin’s convection coefficients are assumed constant. The results show that (1) in the view of the heat loss from the trapezoidal fin, all four methods can be used to obtain the solutions within 3% with each other for the given range of Biot number and the non-dimensional fin length, (2) for the non-dimensional temperature, the one-dimensional analytical method does not produce good results as compared to the other three methods when the Biot number is 1.0, and (3) by using a two-dimensional modified finite difference method instead of the two-dimensional finite difference method, the relative difference in the heat loss as compared to a two-dimensional analytical method is reduced considerably.     

Optimization of a 3-D thermally asymmetric rectangular fin

The non-dimensional fin length for optimum heat loss from a thermally asymmetric rectangular fin is represented as a function of the ratio of the bottom surface Biot number to the top surface Biot number, fin tip surface Biot number and the non-dimensional fin width. Optimum heat loss is taken as 98% of the maximum heat loss. For this analysis, three dimensional separation of variables method is used. Also, the relation between the ratio of the bottom surface Biot number to the top surface Biot number and the ratio of the right surface Biot number to the left surface Biot number is presented.     

Optimization of geometrically asymmetric straight trapezoidal fins

Journal of Mechanical Science and Technology - Geometrically asymmetric trapezoidal fins with variable slope of fin’s top surface are optimized for fixed fin volumes. Convection from the...     

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.     

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.     

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.     

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.     

Approximate method of determining the optimum cross section of microhannel heat sink

Microchannels are at the forefront of today’s cooling technologies. They are widely being considered for cooling of electronic devices and in micro heat exchanger systems due to their ease of manufacture. One issue which arises in the use of microchannels is related to the small length scale of the channel or channel cross-section. In this work, the maximum heat transfer and the optimum geometry for a given pressure loss have been calculated for forced convective heat transfer in microchannels of various cross-section having finite volume for laminar flow conditions. Solutions are presented for 10 different channel cross sections: parallel plate channel, circular duct, rectangular channel, elliptical duct, polygonal duct, equilateral triangular duct, isosceles triangular duct, right triangular duct, rhombic duct and trapezoidal duct. The model is only a function of the Prandtl number and the geometrical parameters of the cross-section, i.e., area and perimeter. This solution is performed with two exact and approximate methods. Finally, in addition to comparison and discussion of these two methods, validation of the relationship is provided using results from the open literature.     

水冷盘式制动器散热结构优化

为提高水冷盘式制动器散热性能,基于强化对流传热原理,通过添加扰流柱对制动器散热结构进行优化,设计了4种扰流柱散热结构,运用CFD方法模拟制动盘流固耦合传热过程,采用Fluent软件进行热流固耦合仿真计算,获得制动盘温度特性和换热特性以及流动阻力特性,并使用综合性能评价因子对不同扰流柱散热结构进行评价。结果表明:通过在安装盘水槽内添加扰流柱可以有效地提高水冷盘式制动器的散热效果;在相同的工作条件下,正三角形扰流柱散热结构的盘面温度最低,平均努塞尔数与流动阻力最高,其综合散热性能较圆形、椭圆形以及水滴形扰流柱散热结构分别提高了3.4%,2.4%和4.4%,较无扰流柱散热结构提高了6.7%,正三角形扰流柱散热结构具有更好的综合散热性能。研究结果为水冷盘式制动器散热结构的优化设计提供了参考。     

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.     

扁管空冷器翅片结构优化研究

基于带翅片的扁管空冷器的传热过程,对带翅片的扁管建立模型,并利用该模型在不同的翅片长度及不同风速下进行数值模拟,分析了翅片长度的选择与迎面风速的关系。分析结果表明,当翅片长度增加到一定值后,通过增加翅片长度的手段来强化换热性能收效很小;在低迎面风速下,翅片长度不要过长;在高迎面风速下,仍存在较大的传热温差,空气出口温度的增加只能通过增加翅片长度来完成。     

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。     

Optimization of a rectangular profile annular fin based on fixed fin height

The optimum performance and fin length of a rectangular profile annular fin are presented using a variations separation method. For fixed fin height, the optimum fin length and efficiency are arbitrarily defined as those for which the heat loss is in the range between 90% and 99% of the maximum heat loss. The maximum heat loss, the maximum effectiveness, the minimum fin resistance, the optimum fin length and the optimum efficiency are presented as a function of the inside fluid convection characteristic number, fin base thickness, fin height and ambient convection characteristic number. One of the results shows that the optimum fin length decreases almost linearly with the increase of the fin base thickness.     

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.     

A rectangular fin optimization including comparison between 1-D and 2-D analyses

Both 1-D and 2-D analytic methods are used for a rectangular fin optimization. Optimum heat loss is taken as 98% of the maximum heat loss. Temperature profile using 2-D analytic method and relative error of temperature along the fin length between 1-D and 2-D analytic methods are presented. Increasing rate of the optimum heat loss with the variation of Biot number and decreasing rate of that with the variation of the fin base length are listed. Optimum fin tip length using 2-D analytic method and relative error of that between 1-D and 2-D analytic methods are presented as a function of Biot numbers ratio.     

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。     

铜翅片管热水器的特性研究

以铜翅片管换热器为研究对象,通过合理的简化模型,以相邻2片换热片(取半片)及其之间的烟气通道作为计算区域,利用流体力学软件CFX对烟气通道的流动状况和换热情况进行了数值模拟。研究了管径、翅片厚度和翅片间距对排烟温度的影响,结果表明随着管径和翅片间距的增大排烟温度升高,随着翅片厚度增大排烟温度降低,排烟温度的升高或降低将影响排烟损失的大小,从而影响热效率。该数值模拟结果对改进翅片结构以提高热效率有一定指导意义。     

Analytical integration of the equation of gradually varied flow for triangular channels

The solution of the gradually-varied-flow equation allows the tracing of the flow depth along a channel length. No closed-form solution is available in the technical literature for this differential equation for triangular channels based on Manning’s formula. In current research, by applying Manning’s formula, an analytical solution to compute the length of the gradually-varied-flow profile for triangular channels is derived. Moreover, the dimensionless profiles for subcritical and supercritical flow in both a mild slope and a steep slope triangular channel are presented. Finally, using the proposed solution, the computation steps of the discharge for a given triangular channel are presented. The direct solution presented in this study can be used for triangular irrigation ditches and triangular channels.     

Optimum design of vaporizer fin with Liquefied Natural Gas by numerical analysis

Generally, the temperature drop under 0°C on vaporizer surface creates frozen dews. This problem seems to increase as the time progress and humidity rises. In addition, the frozen dews create frost deposition. Consequently, heat transfer on vaporizer decreases because frost deposition causes adiabatic condition. Therefore, it is very important to solve this problem. This paper aims to study of the optimum design of used vaporizer at local LNG station. In this paper, experimental results were compared with numerical results. Geometries of numerical and experimental vaporizers were identical. Studied parameters of vaporizer are angle between two fins (Φ) and fin thickness (TH_F). Numerical analysis results were presented through the correlations between the ice layer thickness (TH_ICE) on the vaporizer surface to the temperature distribution of inside vaporizer (T_IN), fin thickness (TH_F), and angle between two fins (Φ). Numerical result shows good agreement with experimental outcome. Finally, the correlations for optimum design of vaporizer are proposed on this paper.