Conjugate heat transfer in solar collector panels with internal longitudinal corrugated fins—Part I: Overall results

A computational study is conducted to examine the fully developed laminar flow and heat transfer characteristics in solar collector panels with internal, longitudinal, corrugated fins. The fins are integrally attached to the upper and lower panel walls. The objective of the study is to determine the effects of varying the fin pitch (or fin angle), the fin thickness, the ratio of the thermal conductivity of the panel walls and the fin to that of the fluid, and the thermal boundary condition on the panel heat transfer and pressure drop. The solutions of the momentum and energy equations are obtained by using a control-volume-based finite difference algorithm. The results of the study are also applicable to the design of internally-finned channels in compact heat exchangers. The overall panel heat transfer increases when the fin pitch (or the fin angle) is decreased, when the fin thickness is increased, and when the thermal conductivity ratio is increased. The streamwise pressure drop increases with decreasing fin pitch (or fin angle) and increasing fin thickness. For a fixed fin thickness, the selection of a small fin pitch (or fin angle) over the range studied results in a higher heat transfer enhancement per unit pumping power.     

Optimum configurations of vertical fins under condensation of saturated vapor

In the present study, an optimum fin shape envelope was determined via a theoretical procedure that minimized the fin volume subject to constrained heat transfer rate. A unified analysis is presented for both longitudinal and pin fins with vertical orientation of the fin surface. The analysis was carried out on the assumption of a power law fin temperature distribution. Under certain simplified conditions, this optimization model has been validated. Results obtained from the model are also compared with previously published results for the specific set of designed conditions. From optimization study, practical fin profiles are found under the condensation of quiescent vapor atmosphere.     

翅片结构对换热器结霜特性影响的实验研究

本文对空气源热泵的翅片管换热器表面霜层生长特性进行实验研究,通过红外热像仪对霜层表面温度进行测量,并用热电偶直接测量装置进行校核.分析了平片、波纹片、条缝片3种翅片类型及翅片节距对霜层厚度、结霜量、换热量的影响,并用霜层-湿空气界面条件等作为传热及传质驱动力分析了霜层生长规律.实验结果表明,波纹片及条缝片翅片换热器界面...     

Influence of developing flow on the heat transfer in laminar oscillating pipe flow

A theoretical analysis was performed to evaluate the influence of developing flow on the heat transfer associated with laminar oscillating pipe flow. Simplified analytical approaches are briefly discussed before an investigation based on the numerical solution of the conservation equations for mass, momentum and energy is presented, assuming constant wall temperature and an incompressible viscous fluid. Focusing on operating conditions as found in heat exchangers of regenerative thermal machines, like Stirling engines or Vuilleumier heat pumps, numerous calculations of the flow field and the heat transfer have been executed covering wide ranges of the characteristic dimensionless groups. The results are presented in tems of correlations of the mean Nusselt number averaged on the pipe length and a distribution function describing the local heat transfer. Furthermore, it is shown that the derived correlations are also applicable to compressible fluid flow, provided that the relative pressure amplitude is within the limits typical of regenerative thermal machines.     

风机盘管换热器遗传算法优化设计

本研究采用了基于遗传算法和耗散理论的传热优化方法,并进行了风机盘管换热器的优化设计。在对板翅管式结构的风机盘管换热器进行建模的基础上,针对两种不同的应用工况,即供冷用干式风机盘管换热器和供暖型风机盘管换热器,进行了结构优化设计和分析。优化目标选取了换热器的耗散热阻,而设计变量分别选取管间距、排间距、换热管外径、翅片间距和翅片数。为评价换热器的性能,还计算了换热器的换热量、空气侧和水侧阻力损失、总泵功和换热器效能。优化设计结果显示,在特定的设计参数和限制条件下,不仅换热器的耗散热阻值降低,其他方面性能也得到了明显提升。     

Second Law Analysis and Optimization of Elliptical Pin Fin Heat Sinks Using Firefly Algorithm

One of the most significant considerations in the design of a heat sink is thermal management due to increasing thermal flux and miniature in size. These heat sinks utilize plate or pin fins depending upon the required heat dissipation rate. They are designed to optimize overall performance. Elliptical pin fin heat sinks enhance heat transfer rates and reduce the pumping power. In this study, the Firefly Algorithm is implemented to optimize heat sinks with elliptical pin-fins. The pin-fins are arranged in an inline fashion. The natureinspired metaheuristic algorithm performs powerfully and efficiently in solving numerical global optimization problems. Based on mass, energy, and entropy balance, three models are developed for thermal resistance, hydraulic resistance, and entropy generation rate in the heat sink. The major axis is used as the characteristic length, and the maximum velocity is used as the reference velocity. The entropy generation rate comprises the combined effect of thermal resistance and pressure drop. The total EGR is minimized by utilizing the firefly algorithm. The optimization model utilizes analytical/empirical correlations for the heat transfer coefficients and friction factors. It is shown that both thermal resistance and pressure drop can be simultaneously optimized using this algorithm. It is demonstrated that the performance of FFA is much better than PPA.     

Optimization of liquid cooling fins in microelectronic packaging

The present study investigates the heat transfer from a fin of the combination of cone and frustum of a cone immersed in boiling FC-72. The temperature distribution within the fin is determined with the help of a three-dimensional finite element computation technique using linear axisymmetric elements. From the temperature distribution, the fin base temperature gradients at various base temperature excesses are obtained. The numerical results are found to be in good agreement with published experimental data. Parametric studies have been carried out using this numerical method. An artificial neural network is used to consolidate additional data from the parametric studies. The genetic algorithm is then applied to the case of a fixed volume fin, in order to determine the dimensions which optimize the heat transfer per unit volume. It is observed that the heat transfer per unit volume decreases with fins of increasing volumes. Conclusively, the technique used in the analysis is able to provide a fast and accurate guideline to select and design the cooling for microelectronic systems.     

Thermal analysis of a constructal T-shaped porous fin with radiation effects

This paper presents an analytical technique based on the decomposition method to determine the temperature distribution and thermal performance parameters of a constructal T-shape porous fin. The effect of radiation on natural convective heat transfer is considered in the analysis. The governing energy equations of the stem and flange part of this T-shaped porous fin for the aforementioned conditions are highly nonlinear. The adopted decomposition solution gives an explicit expression of temperature distribution in the fin as a function of a coordinate expressed by infinite power series from which fin performance parameters and heat transfer rates can easily be calculated without the need of linearization. The effects of different geometric and thermophysical parameters on the dimensionless temperature distribution and fin performances are studied. Finally, the increase in heat transfer is noticed by selecting porous medium condition in the fin.     

Limits of one-dimensional solutions for orthotropic annular fins under dehumidifying operating conditions

Thermal performance characteristics of orthotropic material annular fins subjected to dehumidifying operating conditions are studied using two-dimensional finite element method. The method accounts for non-linear temperature–humidity ratio psychrometric relationship under both partially and fully wet operating conditions. Limits of one-dimensional solutions for orthotropic material fins subject to dehumidifying conditions are investigated in somewhat more detail by introducing dimensionless parameters. The dry fin parameter that fully governs fin efficiency under a set of operating conditions is also defined. The optimum fin dimensions are also estimated for a set of operating conditions and fixed fin volume.     

大型速冻设备蒸发器高效传热技术的试验研究

不同结构型式蒸发器的传热系数不同,选择7种不同结构的蒸发器模型,分析比较翅片形状、管径大小以及管子排列方式对蒸发器传热系数的影响,得出在不结霜工况下,传热系数最高的蒸发器结构是连续整体带波纹翅片叉排变节距结构的结论。对这种结构的蒸发器进行试验测试,得到与理论计算相符的传热系数值。     

Optimum plate-fin heat sinks by using a multi-objective evolutionary algorithm

This article demonstrates the practical applications of a multi-objective evolutionary algorithm (MOEA) namely population-based incremental learning (PBIL) for an automated shape optimization of plate-fin heat sinks. The computational procedure of multi-objective PBIL is detailed. The design problem is posed to find heat sink shapes which minimize the junction temperature and fan pumping power while meeting predefined constraints. Three sets of shape design variables used in this study are defined as: vertical straight fins with fin height variation, oblique straight fins with steady fin heights, and oblique straight fins with fin height variation. The optimum results obtained from using the various sets of design variables are illustrated and compared. It can be said that, with this sophisticated design system, efficient and effective design of plate-fin heat sinks is achievable and the best design variables set is the oblique straight fins with fin height variation.     

水平管外二氧化碳膜状凝结传热分析

综述了水平低翅片管外凝结传热的基本模型,阐述了二氧化碳制冷剂的物性特点,讨论了表面张力与凝液滞留角及二氧化碳管外凝结换热系数的关系,分析了翅片密度、环形翅片管尺寸对翅片效率、滞留角、凝结换热系数以及传热增强比的影响,优化了外翅片管的齿高与齿距,并求得相应的强化传热增强比.结果表明,对于根径为20mm的低翅片管,最佳翅片密度为每米435个翅片,最佳齿高为5.1mm,最佳齿距2.3mm.     

基于热阻网络模型的硅基微槽热沉多目标优化设计

微槽热沉具有传热效率高、可靠性强的优点,可用于对微尺度高热流密度电子元件进行冷却。为满足其性能需求和控制成本,在对微槽热沉进行设计时需要对其传热能力和流动阻力同时进行优化。传统研究采用的热阻网络模型较为简单,不能很好地反映热阻和流动阻力对微槽道截面形状拓扑变化的响应,且其优化对象通常为既定截面的形状尺寸。为此提出一种基于离散化方法的单层硅基微槽热沉热阻网络模型,将热沉鳍片细分为厚度较小的微元,根据微元热阻对微元宽度的响应及微元热阻对整体热阻的贡献来描述微槽道的整体热阻。以微泵输出功率为优化边界条件,压降和热阻为优化目标,通过SQP（sequential quadratic programming,序列二次规划）方法对层流状态下四边形等截面硅基微槽热沉进行尺寸优化,利用CFD（computational fluid dynamics,计算流体动力学）对优化结果进行模拟和验证。结果表明,当鳍片高度较低时,鳍片截面形状为矩形,随着鳍高增加,截面形状有向三角形发展的趋势。在设计区间内,微槽道截面为梯形、鳍片截面为三角形时传热效率与压降相对占优。用边界点法和理想点法优化模型求得微槽道高度、鳍底宽、槽底宽、槽顶宽的优化结果分别为500,50,64.5,114.5 μm和500,50,50,100 μm。该方法能根据设计需求调整评价函数,同时计算结果具有重要工程意义,为微槽热沉设计人员提供参考。     

Thermal performance and optimization of hyperbolic annular fins under dehumidifying operating conditions – analytical and numerical solutions

The thermal performance of hyperbolic profile annular fins subjected to dehumidifying operating conditions is studied. An analytical solution for completely wet fin is derived using an approximate linear temperature–humidity relationship. A numerical solution using actual psychrometric relationship for completely and partially wet operating conditions is then obtained to account for the actual temperature–humidity ratio psychrometric relationship under both partially and fully wet operating conditions. An excellent agreement is observed between analytical and numerical solutions for completely wet fin. The fin optimization is presented based on the analytical solution of completely wet fin. Finally, a finite element formulation is used for studying the two-dimensional effects of orthotropic thermal conductivity on the thermal performance of fin under partially and fully wet operating conditions.     

A study on airside performance of geometry combination fins using large scale model

This study investigated the pressure drop and heat transfer characteristics of heat exchanger according to the arrangement of fins as well as fin configuration by the similitude experiments with the finned-tube geometry scaled as large as four times. Colburn j factor, Fanning friction factor, f, and goodness factors are compared to each other to estimate performance of each case for four different kinds of fins, which are louver, double side slit, single side slit and plain fin. Results show that heat transfer would be altered by fin arrangement and that friction loss is more affected by fin configurations than by the fin arrangements. In particular, heat transfer depends more on the shape of front row than that of rear row. The heat transfer rate of combined fin arrangement increases a lot more under the same pressure drop than that of conventional fin arrangement. This indicates that the heat exchanger of higher efficiency would be designed by the proper combination of fins of different shapes.     

锯齿与打孔翅片表面性能数值模拟

以两种翅片表面(锯齿翅片、打孔翅片)为研究对象,采用 FLUENT 软件模拟和分析不同结构参数和数对翅片表面传热与流动阻力的影响,得出不同结构参数和操作参数下两种翅片的表面性能曲线;分别分析了锯齿翅片的翅片高度、翅片间距、翅片厚度和切开长度以及打孔翅片开孔率对翅片表面流动与传热性能影响;分析比较了两种翅片的性能.     

Heat transfer analysis of fin-and-tube heat exchangers with flat and louvered fin geometries

This paper analyzes the fluid flow and heat exchange on the air side of a multi-row fin-and-tube heat exchanger. A comparison is given between fin-and-tube heat exchanger characteristics with flat and louvered fins in a wider range of operating conditions defined by Reynolds number (based on fin spacing and air frontal velocities). The detailed representation of calculated data for the louvered heat exchanger shows significantly better heat transfer characteristics and a slightly higher pressure drop. The CFD procedure was validated by comparing the numerical simulation results with the experimental results showing the minimal average Nusselt number deviation and an almost perfectly corresponding pressure drop.     

Heat transfer from a cylindrical,heavily finned surface

The transfer of heat from a strongly heated, heavily finned surface is examined. The material of the surface and of the fins has high thermal conductivity (copper), while the heat transfer fluid has comparatively low thermal conductivity (oil). Under these conditions, increase in the number of fins and reduction of the distance between them makes possible a high value of the coefficient of heat transfer from the heated surface to the fluid.Notation R₂ and r₁ radii of cylindrical surface at tip and base of fins, respectively - r, z coordinate axes - angle between planes of adjacent slots - x slot width - b anda coordinates of tip and base of fin - thermal conductivity of fin material - t fin temperature - u mean fluid temperature over slot width - coefficient of heat transfer from fin surface to fluid - c specific heat of fluid - v fluid velocity (since the viscosity is considered constant over the flow, v is also constant) - q density of heat flux through base of fin - specific weight of fluid - ¯t, ¯u Laplace transforms - p Laplace transform parameter, s-auxiliary quantity determined from equation (13) - I, K, J, Y Bessel functions - u⁰ mean fluid temperature over height of slot     

Analytical and numerical modeling of steady periodic heat transfer in extended surfaces

This paper deals with the analytical and numerical approaches that have been used to study periodic or oscillatory heat transfer processes occurring in extended surfaces. The details pertain to harmonic oscillations but many of the methods can be applied to more general periodic functions. For linear problems, the techniques include complex combination, Laplace transforms, finite differences, and boundary elements. For the nonlinear situations, approaches such as finite differences, finite elments, and different combinations of complex temperature, perturbation, series expansions, straightline, and finite differences have proved effective. Following a brief introduction, the applications of each approach are discussed in detail. Both straight and annular fin configurations are covered and the profile shapes include rectangular, trapezoidal, triangular, and convex parabolic. The periodic conditions involve oscillating base temperature, oscillating base heat flux, oscillating environment temperature, convection at the fin's base through a fluid with oscillating temperature, and some combinations of these conditions. The nonlinear problems discussed cover radiating and convecting-radiating fins, fins with variable thermal conductivity and coordinate dependent heat transfer coefficients, and systems with fin-to-fin, fin-to-base, and fin-to-environment radiative interactionsThis article is dedicated to the memory of first author's younger brother, Mohammed Iqbal, Civil Services of Pakistan, who became an innocent victim of human savagery in 1971 in what was then East Pakistan     

套片式翅片管机械胀接接触热阻分析与模拟优化

本文采用有限元模拟方法,得到了套片式翅片管换热器机械胀接的翅片与基管间的胀后节点接触应力分布。提出模拟的总体接触应力并不是节点接触应力算术平均的观点和总体接触应力的计算式。通过对套片式换热器试件进行传热性能实验,获取了翅片与基管之间的接触热阻数值,由模拟计算的总体接触应力与实验接触热阻数值,计算两者的关联式。采用有限元模拟方法预测各种胀接量下的总体接触应力及最优的胀接尺寸,利用弹塑性理论计算对比模拟计算进行验证。结果发现,材料弹塑性理论计算结果与模拟计算结果的相对偏差为7. 3%,偏差较小,证明两者均具有效性。