Comparative studies on performance of plain,perforated, threaded,and threaded–perforated pin fin: A numerical approach

A heat sink is a thermal management system for electrical and electronic appliances whose performance is a function of fin geometry, arrangement, and flow field. Earlier research addressed the enhancement in the heat dissipation capacity of the sink with a change in the geometry of the fin. However, the change should increase the heat transfer rate per unit weight and per unit volume. One such attempt is made in the present work, which deals with numerical forced convection heat transfer simulation over a pin fin with three different surface modifications, namely, threads, equilateral triangular perforation, and threads with perforations. A numerical investigation is performed for 0.5773–2.5574 mm pitch of threads, 3–4.8 mm size of perforation, and 2–8 m/s velocities of air. To describe the flow pattern around the fin and its variation with surface modification, streamline profiles are drawn which reveals that the fluid–solid interaction is improved either with threaded or perforated surface and is maximum for threaded–perforated fin. The enhanced convection rates bring down the local fin temperature and the maximum fin temperature, where the drop is more for the threaded surface than that of the perforated surface because of turbulence. A 10° drop in maximum fin temperature is achieved by replacing a plain pin fin with a threaded–perforated pin fin, and the drop is 8° with threads alone and 6° only with perforations. The increased fineness of threads and size of perforation further bring down the maximum fin temperature.     

Numerical investigation of fluid flow and heat transfer over louvered fins in compact heat exchanger

Numerical investigation of fluid flow and heat transfer characteristics over louvered fins and flat tube in compact heat exchangers is presented in this study. Three-dimensional simulations of single and double row tubes with louvered fins have been conducted. Simulations are performed for different geometries with varying louver pitch, louver angle, fin pitch and tube pitch and for different Reynolds number. Conjugate heat transfer and conduction through the fins are considered. The air-side performance of heat exchanger is evaluated by calculating Stanton number and friction factor. The results are compared with experiment and a good agreement is observed. The local Nusselt number variation along the top surface of the louver is calculated and effects of geometrical parameters on the average heat transfer coefficient is computed. Design curves are obtained which can used to predict the heat transfer and the pressure drop for a given louver geometry.     

Thermofluid characteristics of frosted finned-tube heat exchangers

The performance of frosted finned-tube heat exchangers of different fin types is investigated by experiments in this paper. The effects of the air flow rate, the air relative humidity, the refrigerant temperature, and the fin type on the thermofluid characteristics of the heat exchangers are discussed. The time variations of the heat transfer rate, the overall heat transfer coefficient, and the pressure drop of the heat exchangers are presented. The heat transfer rate, the overall heat transfer coefficient, and the pressure drop for heat exchangers with re-direction louver fins are higher than those with flat plate fins and one-sided louver fins are. The amount of frost formation is the highest for heat exchangers with re-direction louver fins.     

Optimum design of a longitudinal fin array with convection and radiation heat transfer using a genetic algorithm

In the present work, the optimization of a longitudinal fin array is investigated. Heat is transferred by conduction along the fins and dissipated from the fin surface via natural convection to the ambient and radiation to other fin surfaces and surrounding. The aim of the optimization is to find the optimum geometry and the number of fins in such a way that the rate of heat transfer from the array is maximized. A modified genetic algorithm is used to maximize the objective function which is defined as the net heat rate from the fin surface for a given length. The fin profile is represented by B-spline curves, where the shape of fin is determined by the positions of a set of control points. The effects of the base temperature, the fin length and the height of array on the optimum geometry and on the number of fins are investigated by comparing the results obtained for several test cases. In addition, the contributions of convective heat transfer and radiative heat transfer in net heat transfer are studied for these cases. The enhancement of heat transfer due to the optimum fin geometry is examined by comparing the results obtained for the optimum fin profile with those with conventional profiles.     

电机冷却用翅管换热器传热和阻力特性研究

研究了一种电机冷却用新型翅片开孔结构换热器的性能,对三种结构的翅片管换热器进行了换热和阻力性能测试,新型翅片换热器结构为翅片间距2.1 mm且翅片上具有开孔结构,对照组换热器分别为翅片间距2.1 mm无开孔换热器和翅片间距2.3 mm无开孔换热器。试验结果表明,相同Re数下,该种具有开孔结构换热器在所有换热器中换热性能最好,较2.1 mm无孔提升38%～39%,但同时压降损失也最大,较2.1 mm无孔提升41.9%～42.9%。采用j/f评价综合性能,结果显示,Re>6700时,新型翅片换热器性能优于同翅片间距无开孔换热器。文章还对这三种结构翅片管换热器进行了传热和阻力关联式拟合,可为相关理论研究和工程选用提供参考。     

Numerical investigation for improved heat transfer characteristics in micro‐fin tubes

Generally, internal micro‐fin tubes are used for increasing the life and performance of electronic devices. The micro‐fins enhance the heat transfer rate by increasing the surface area with an increase of the pressure drop. In this study, heat transfer and pressure drop are analyzed by varying Reynolds number with the increase in the number of fins in tubes. Heat transfer and pressure drop, together with turbulence kinetic energy of micro‐fin tubes (helical and straight) and a smooth tube, have been evaluated for different Reynolds numbers (60 000, 40 000, 20 000, and 2000) at a constant temperature of 350 K, which clearly establishes laminar to turbulent flow. It is observed that the helical micro‐fin tube has a better result compared with the straight micro‐fin tube and smooth tube at Reynolds numbers 60 000, 40 000, and 20 000 at velocity 2, 1, and 0.5 m/s, respectively. This study is an attempt to establish a comparison of different micro‐fin geometries with varying Reynolds numbers, concluding that a high Reynolds number is suitable for the same.     

Thermal-hydraulic performance of novel louvered fin using flat tube cross-flow heat exchanger

Experimental studies were conducted to investigate the air-side heat transfer and pressure drop characteristics of a novel louvered fins and flat tube heat exchangers. A series of tests were conducted for 9 heat exchangers with different fin space and fin length, at a constant tube-side water flow rate of 2.8 m³/h. The air side thermal performance data were analyzed using the effectiveness-NTU method. Results were presented as plot of Colburn j factor and friction factor f against the Reynolds number in the range of 500–6500. The characteristics of the heat transfer and pressure drop of different fin space and fin length were analyzed and compared. In addition, the curves of the heat transfer coefficients vs. pumping power per unit heat transfer area were plotted. Finally, the area optimization factor was used to evaluate the thermal hydraulic performance of the louvered fins with differential geometries. The results showed that the j and f factors increase with the decrease of the fin space and fin length, and the fin space has more obvious effect on the thermal hydraulic characteristics of the novel louvered fins.     

Effects of Different Fin Spacings on the Nusselt Number and Reynolds Number in Perforated Finned Heat Exchangers

In this study, the effect of holes placed on perforated finned heat exchangers on convective heat transfer was experimentally investigated. Six-millimeter-diameter holes were opened on each circular fin on a heating tube in order to increase convective heat transfer. These holes were placed on the circular fins in such a way as to follow each other at the same chosen angle. The holes created turbulence in a region near the heating tube surface on the bottom of the fin. Experiments were then performed to analyze the effect of this turbulence on heat transfer and pressure drop. These experiments were carried out at five different fin spacings at the angular locations of 30° and 60° in order to determine the optimum fin spacing. Moreover, further experiments were carried out for counterflow and parallel-flow arrangements to determine the effects of the flow directions of the heating fluid and heated fluid. Results show an increase in Nusselt number with increasing modified Reynolds number. In addition, when different fin spacing to heating tube external diameter ratios were examined, at a ratio of 0.414 and angular locations of 30° and 60°, 11% and 8.6% increase in heat transfer were obtained, respectively, for parallel-flow arrangement compared to counterflow. For parallel flow, pressure drop values were 3.5% and 3.8% lower at 30° and 60°, respectively.     

Optimization of peripheral finned-tube evaporators using entropy generation minimization

The peripheral finned-tube (PFT) is a new geometry for enhanced air-side heat transfer under moisture condensate blockage (evaporators). It consists of individual hexagonal (peripheral) fin arrangements with radial fins whose bases are attached to the tubes and tips are interconnected with the peripheral fins. In this paper, experimentally validated semi-empirical models for the air-side heat transfer and pressure drop are combined with the entropy generation minimization theory to determine the optimal characteristics of PFT heat exchangers. The analysis is based on three independent parameters, i.e., porosity, equivalent particle diameter and particle-based Reynolds number. The total heat transfer rate is a fixed constraint. The optimal heat exchanger configurations, i.e., those in which the entropy generation number reaches a minimum, are calculated for constant heat flux and constant tube wall temperature boundary conditions. Performance evaluation criteria of fixed geometry, fixed face area and variable geometry were implemented. In all cases, it was possible to determine a combination of independent parameters that provided a minimum entropy generation rate.     

A study on heat transfer enhancement using straight and twisted internal fin inserts

The present study investigated the effect of internal aluminum fins with a star-shape cross-section on the heat transfer enhancement and pressure drop in a counterflow heat exchanger. A concentric-tube heat exchanger was used with water as the working fluid. The heat transfer rate increased by 12–51% over a plain tube value, depending on internal fin configurations used. However, the pressure drop also increased substantially by 286–399%. The results showed that a straight-fin configuration is the best to produce a heat transfer increase in a counterflow heat exchanger. Twisted fin configurations did not further increase the heat transfer rate.     

球突翅片的传热流动特性及等效热阻数值分析

为了提高翅片管换热器的传热系数和减小压降,提出了一种球突型翅片,通过数值模拟研究其传热与流动性能,同时应用(火积)耗散理论对其传热的不可逆性进行分析。计算结果表明:与平片相比,其传热能提高26.21%～39.53%,而阻力系数仅提高16.62%～27.04%,同时综合性能增加16.54%～32.56%;这说明该翅片具有高传热系数低压降的特点,是一种性能优良的翅片。通过(火积)耗散分析可以看出:球突翅片的等效热阻减小,其传热的不可逆性减弱。     

Convective heat transfer and pressure drop of annular tubes with three different internal longitudinal fins

Pressure drop and heat transfer characteristics of air in three annular tubes with different internal longitudinal fins were investigated experimentally at uniform wall heat flux. The tested tubes have a double‐pipe structure with the inner blocked tube as an insertion. Three different kinds of fins, plain rectangle fin, plain rectangle fin with periodical ridges and wave‐like fin, were located peripherally in the annulus. The friction factor and Nusselt number can be corrected by a power‐law correction in the Reynolds number range tested. It was found that the tube with periodical ridges on the plain fin or with wave‐like fin could augment heat transfer; however, the pressure drop was increased simultaneously. In order to evaluate the comprehensive heat transfer characteristics of the tested tubes, two criteria for evaluating the comprehensive thermal performance of tested tubes were adopted. They are: 1) evaluating the comprehensive heat transfer performance under three conditions: identical mass flow, identical pumping power, and identical pressure drop; 2) the second law of thermodynamics, i.e., the entropy generation. According to the two different evaluating methods, it was found that the tube with wave‐like fins provided the most excellent comprehensive heat transfer performance among the three tubes, especially when it was used under higher Reynolds number conditions. © 2007 Wiley Periodicals, Inc. Heat Trans Asian Res, 37(1): 29–40, 2008; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/htj.20186     

Forced convection heat transfer and pressure drop for a horizontal cylinder with vertically attached imperforate and perforated circular fins

In this study, the effect of holes placed on perforated finned heat exchangers on convective heat transfer experimentally investigated. Six millimeter-diameter holes were opened on each circular fin on a heating tube in order to increase convective heat transfer. These holes were placed on the circular fins in such a way as to follow each other at the same chosen angle. The holes created turbulence in a region near the heating tube surface on the bottom of the fin. Some experiments were then performed to analyze the effect of this turbulence on heat transfer and pressure drop. These experiments were carried out at six different angular locations in order to determine the best angular location. In addition, a perforated finned heater was compared with an imperforate finned heater to observe the differences. In the cases of the Re above the critical value, Nusselt numbers for the perforated finned positions are 12% higher than the Nusselt numbers for the imperforate state. Moreover, a correlation has been obtained between the Re and Nu in the Re number above the critical value and the Re below the critical value. Meanwhile, correlations regarding pressure drops in the flow areas have been obtained.     

Constructal entransy dissipation rate minimization of a disc

Disc cooling problem is optimized by taking entransy dissipation rate minimization as optimization objective. The non-dimensional mean temperature difference of the disc cooling model with radial high conducting fins inserted is deduced. The effects of the fin geometry, the fin aspect ratio, the ratio between the high conductivity and low conductivity, the relative amount of high conductivity material and the number of high conducting fins on the entransy dissipation rate of disc cooling are analyzed. The optimization results show that the high conducting fin should be extended to the centre of circle as the heat transfer effect of the high conducting fins is improved, and there exists an optimal fin aspect ratio corresponding to minimum entransy dissipation rate for different high conducting effects of the fin, and the number of high conducting fins has a slight effect on the entransy dissipation rate. Comparison with those for maximum temperature difference minimization shows that the constructs based on entransy dissipation rate minimization are different from those based on maximum temperature difference minimization, but the optimal constructal shape changing potentials of the number of fins and the relative amount of high conductivity material are similar.     

Effect of a shield on the hydraulic and thermal performance of a plate-fin heat sink

The hydraulic and thermal performance of a plate-fin heat sink undergoing cross flow forced convection with the introduction of a shield was investigated. With a CFD numerical method, the influence of fin width, fin height, number of fins and Reynolds number were assessed without and with a shield. A shield that tends to decrease the bypass flow effect has a great influence on the variation of the thermal fluid field and the performance of the heat sink. The results of attaching a shield show that more coolant fluid is forced to flow into the fin-to-fin channel to enhance the heat transfer, increasing the pressure drop; this trend is significant at low Reynolds numbers. The decrease of thermal resistance due to the shield diminishes with increasing fin height, but increasing the width of the fins has a more radical effect. For a shield at a particular Reynolds number, the fin geometry should be selected carefully to fit the demands of enhanced effectiveness of heat transfer and decreased power consumption.     

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.     

Measurement of performance of plate-fin heat sinks with cross flow cooling

This work assesses the performance of plate-fin heat sinks in a cross flow. The effects of the Reynolds number of the cooling air, the fin height and the fin width on the thermal resistance and the pressure drop of heat sinks are considered. Experimental results indicate that increasing the Reynolds number can reduce the thermal resistance of the heat sink. However, the reduction of the thermal resistance tends to become smaller as the Reynolds number increases. Additionally, enhancement of heat transfer by the heat sink is limited when the Reynolds number reaches a particular value. Therefore, a preferred Reynolds number can be chosen to reduce the pumping power. For a given fin width, the thermal performance of the heat sink with the highest fins exceeds that of the others, because the former has the largest heat transfer area. For a given fin height, the optimal fin width in terms of thermal performance increases with Reynolds number. As the fins become wider, the flow passages in the heat sink become constricted. As the fins become narrower, the heat transfer area of the heat sink declines. Both conditions reduce the heat transfer of the heat sink. Furthermore, different fin widths are required at different Reynolds numbers to minimize the thermal resistance.     

Flow and heat transfer in compact offset strip fin surfaces

Experimental studies of air-side heat transfer and pressure drop characteristics of offset strip fins and flat tube heat exchangers were performed. A series of tests were conducted for 9 heat exchangers with different fin space, fin height, fin strip length and flow length, at a constant tube-side water flow rate of 2.5 m³/h. The characteristics of the heat transfer and pressure drop of different fin space, fin height and fin length were analyzed and compared. The curves of the heat transfer coefficients vs. the pumping power per unit frontal area were then plotted. Moreover, the enhanced heat transfer mechanism of offset strip fins was analyzed using field synergy theory. The results showed that fin length and flow length have more obviously effect on the thermal hydraulic characteristics of offset strip fins. __________ Translated from Journal of Shanghai Jiaotong University, 2007, 41(3): 366–369, 375 [译自: 上海交通大学学报]     

Thermal Enhancement from Pin Fins by Using Elliptical Perforations with Different Inclination Angles

Many of the proposed methods introduce the perforated fin with the straight direction to improve the thermal performance of the heat sink. The innovative form of the perforated fin (with inclination angles) was considered. Present rectangular pin fins consist of elliptical perforations with two models and two cases. The signum function is used for modeling the opposite and the mutable approach of the heat transfer area. To find the general solution, the degenerate hypergeometric equation was used as a new derivative method and then solved by Kummer's series. Two validation methods (previous work and Ansys 16.0‐Steady State Thermal) are considered. The strong agreement of the validation results (0.31% to 0.52%) lends to the reliability of the presented model. It was found that use of the perforated fin leads to decreased thermal resistance and improvement in the thermal performance of the pin fin by enhancing the heat transfer and increasing Nusselt number. Also, the increase of the inclination angle, size, and number of perforations can be used to optimize the present model by maximizing the heat transfer area and minimizing both the weight and length of the pin fins.     

The heat transfer characteristics of liquid cooling heat sink with micro pin fins

This paper numerically and experimentally investigated the liquid cooling efficiency of heat sinks containing micro pin fins. Aluminum prototypes of heat sink with micro pin fin were fabricated to explore the flow and thermal performance. The main geometry parameters included the diameter of micro pin fin and porosity of fin array. The effects of the geometrical parameters and pressure drop on the heat transfer performance of the heat sink were studied. In the experiments, the heat flux from base of heat sink was set as 300 kW/m². The pressure drop between the inlet and the outlet of heat sink was set < 3000 Pa. Numerical simulations with similar flow and thermal conditions were conducted to estimate the flow patterns, the effective thermal resistance. It was found that the effective thermal resistance would reach an optimum value for various pressure drops. It was also noted that the effective thermal resistance was not sensitive to porosity for sparsely packed pin fins.