Comparison of Fluid Flow and Thermal Characteristics of Plate-Fin and Pin-Fin Heat Sinks Subject to a Parallel Flow

In this study, we compare the thermal performances of the two types of heat sinks most commonly used in the electronic equipment cooling: plate-fin and pin-fin heat sinks. In order to obtain the fluid flow and thermal characteristics of heat sinks, an experimental investigation is conducted. Based on the experimental results of the present study and the available data from the existing literature, the correlations of the friction factor and the Nusselt number are suggested for each type of heat sink. Correlations for the pin-fin heat sinks are newly developed, while correlations for the plate-fin heat sinks are selected from previous models. By using the appropriate correlations, thermal resistances of the optimized plate-fin and pin-fin heat sinks are compared under fixed pumping power conditions. Finally, a contour map, which depicts the ratio of the thermal resistances of the optimized plate-fin and pin-fin heat sinks as a function of dimensionless pumping power and dimensionless length, is presented. The contour map indicates that optimized plate-fin heat sinks possess lower thermal resistances than optimized pin-fin heat sinks when dimensionless pumping power is small and the dimensionless length of heat sinks is large. On the contrary, the optimized pin-fin heat sinks have smaller thermal resistances when dimensionless pumping power is large and the dimensionless length of heat sinks is small.     

Comparison of thermal performances of plate-fin and pin-fin heat sinks subject to an impinging flow

In this paper, we compare thermal performances of two types of heat sinks commonly used in the electronic equipment industry: plate-fin and pin-fin heat sinks. In particular, heat sinks subject to an impinging flow are considered. For comparison of the heat sinks, experimental investigations are performed for various flow rates and channel widths. From experimental data, we suggest a model based on the volume averaging approach for predicting the pressure drop and the thermal resistance. By using the model, thermal resistances of the optimized plate-fin and pin-fin heat sinks are compared. Finally, a contour map, which depicts the ratio of the thermal resistances of the optimized plate-fin and pin-fin heat sinks as a function of dimensionless pumping power and dimensionless length, is presented. The contour map indicates that optimized pin-fin heat sinks possess lower thermal resistances than optimized plate-fin heat sinks when dimensionless pumping power is small and the dimensionless length of heat sinks is large. On the contrary, the optimized plate-fin heat sinks have smaller thermal resistances when dimensionless pumping power is large and the dimensionless length of heat sinks is small.     

Scroll heat sink: A novel heat sink with the moving fins inserted between the cooling fins

In this paper, a new type of a fan-integrated heat sink named a scroll heat sink is proposed and demonstrated. The most striking feature of the scroll heat sink is that heat dissipation and fluid pumping occurs simultaneously in the whole cooling space without requiring any additional space for a fan module. In the scroll heat sink, the moving fins, which rotate with two eccentric shafts, are inserted between the fixed (cooling) fins. By a relative motion between the moving fins and the cooling fins, a coolant is drawn into the space between them, takes heat away from the cooling fins, and the heated coolant is discharged out of the heat sink. In the present study, an experimental investigation is performed in order to demonstrate the concept of the scroll heat sink. Average coolant velocities and thermal resistances of the scroll heat sink are measured for various rotating speeds of the moving fins from 200 rpm to 500 rpm. Experimental results show that measured flow rates of the coolant are almost linearly proportional to the rotating speed of the moving fins. A theoretical model is also developed to estimate the required pumping power and the thermal resistance, and validated using experimental results. The theoretical model shows that optimized scroll heat sinks have lower thermal resistances than optimized plate-fin heat sinks under the fixed pumping power condition.     

3-Dimensional numerical optimization of silicon-based high performance parallel microchannel heat sink with liquid flow

A full 3-dimensional (3D) conjugate heat transfer model has been developed to simulate the heat transfer performance of silicon-based, parallel microchannel heat sinks. A semi-normalized 3-dimensional heat transfer model has been developed, validated and used to optimize the geometric structure of these types of microheat sinks. Under a constant pumping power of 0.05 W for a water-cooled microheat sink, the optimized geometric parameters of the structure as determined by the model were a pitch of 100 μm, a channel width of 60 μm and a channel depth of about 700 μm. The thermal resistance of this optimized microheat sink was calculated for different pumping powers based on the full 3D conjugate heat transfer model and compared with the initial experimental results obtained by Tuckerman and Pease in 1981. This comparison indicated that for a given pumping poser, the overall cooling capacity could be enhanced by more than 20% using the optimized spacing and channel dimensions. The overall thermal resistance was 0.068 °C/W for a pumping power of 2 W.     

Thermal performance of plate-fin heat sinks under confined impinging jet conditions

This paper utilizes the infrared thermography technique to investigate the thermal performance of plate-fin heat sinks under confined impinging jet conditions. The parameters in this study include the Reynolds number (Re), the impingement distance (Y/D), the width (W/L) and the height (H/L) of the fins, which cover the range Re = 5000–25,000, Y/D = 4–28, W/L = 0.08125–0.15625 and H/L = 0.375–0.625. The influences of these parameters on the thermal performance of the plate-fin heat sinks are discussed. The experimental results show that the thermal resistance of the heat sink apparently decreases as the Reynolds number increases; however, the decreasing rate of the thermal resistance declines with the increase of the Reynolds number. An appropriate impingement distance can decrease the thermal resistance effectively, and the optimal impingement distance is increased as the Reynolds number increases. Moreover, the influence of the impingement distance on the thermal resistance at high Reynolds numbers becomes less conspicuous because the magnitude of the thermal resistance decreases with the Reynolds number. An increase of the fin width reduces the thermal resistance initially. Nevertheless, the thermal resistance rises sharply when the fin width is larger than a certain value. Increasing the fin height can increase the heat transfer area which lowers the thermal resistance. Moreover, the influence of the fin height on the thermal resistance seems less obvious than that of the fin width. To sum up all experimental results, Reynolds number Re = 20,000, impingement distant Y/D = 16, fin width W/L = 0.1375, and fin height H/L = 0.625 are the suggested parameters in this study.     

A porous model for the square pin-fin heat sink situated in a rectangular channel with laminar side-bypass flow

This work illustrates the compact heat sink simulations in forced convection flow with side-bypass effect. Conventionally, the numerical study of the fluid flow and heat transfer in finned heat sinks employs the detailed model that spends a lot of computational time. Therefore, some investigators begin to numerically study such problem by using the compact model (i.e. the porous approach) since the regularly arranged fin array can be set as a porous medium. The computations of the porous approach model will be faster than those of the detailed mode due to the assumption of the volume-averaging technique. This work uses the Brinkman–Forchheimer model for fluid flow and two-equation model for heat transfer. A configuration of in-line square pin-fin heat sink situated in a rectangular channel with fixed height (H = 23.7 mm), various width and two equal-spacing bypass passages beside the heat sink is successfully studied. The pin-fin arrays with various porosities (ε = 0.358–0.750) and numbers of pin-fins (n = 25–81), confined within a square spreader whose side length (L) is 67 mm, are employed. The numerical results suggest that, within the range of present studied parameters (0.358 ? ε ? 0.750, 25 ? n ? 81 and 1 ? W/L ? 5), the pin-fin heat sink with ε = 0.750 and n = 25 is the optimal cooling configuration based on the maximum ratio of Nusselt number to dimensionless pumping power (Nu/(ΔP × Re³)). Besides, based on medium Nu/(ΔP × Re³) value and suitable channel size, W/L = 2–3 is suggested as the better size ratio of channel to heat sink.     

Orientation effect on heat transfer of a shrouded LED backlight panel with a plate-fin array

This study reports thermal performance of a shrouded 348 mm × 558 mm aluminum plate-fin heat sink subject to various input powers and orientations. Effects of clearance (C) and the orientation on the heat transfer of the heat sink were investigated. Results show that the clearance effect is detectable only in a “window region” between 5 mm and 10 mm where an appreciable rise of heat transfer coefficient is encountered. As the tilted angle (θ) of the LED panel is increased, the heat transfer coefficient is reduced and the clearance effect on heat transfer becomes more pronounced. The heat transfer coefficients are similar between two cases in which the tilted angles of the LED panel are supplementary irrespective of clearance and input power. Except the cases of a horizontal heat sink, heat transfer coefficient of the shrouded heat sink having a fin array facing downward is usually slightly higher than that having supplementary tilted angle.     

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.     

Multi-parameters optimization for microchannel heat sink using inverse problem method

This work describes an inverse problem method to optimize the geometric design for microchannel heat sinks using a novel multi-parameter optimization approach, which integrates the simplified conjugate-gradient scheme and a fully developing three-dimensional heat transfer and flow model. Overall thermal resistance is the objective function to be minimized with number of channels, N, channel aspect ratio, α, and the ratio of channel width to pitch, β, as search variables. With a constant bottom area (10 mm × 10 mm), constant heat flux applied to the heat sink bottom surface (100 W cm^?2), and constant pumping power (0.05 W), the optimal design values are N = 71, α = 8.24, and β = 0.6, with a minimum overall thermal resistance of 0.144 K W^?1. Increasing pumping power reduces overall thermal resistance of the optimal design; however, the design’s effectiveness declines significantly under high pumping power. The N and α values in the optimal design increase and β decreases as pumping power increases.     

Multi-objective thermal design optimization and comparative analysis of electronics cooling technologies

A multi-objective thermal design optimization and comparative study of electronics cooling technologies is presented. The cooling technologies considered are: continuous parallel micro-channel heat sinks, in-line and staggered circular pin-fin heat sinks, offset strip fin heat sinks, and single and multiple submerged impinging jet(s). Using water and HFE-7000 as coolants, Matlab’s multi-objective genetic algorithm functions were utilized to determine the optimal thermal design of each technology based on the total thermal resistance and pumping power consumption under constant pressure drop and heat source base area of 100 mm². Plots of the Pareto front indicate a trade-off between the total thermal resistance and pumping power consumption. In general, the offset strip fin heat sink outperforms the other cooling technologies.     

Experimental investigations on phase change material based finned heat sinks for electronic equipment cooling

This paper reports the results of an experimental investigation of the performance of finned heat sinks filled with phase change materials for thermal management of portable electronic devices. The phase change material (PCM) used in this study is n-eicosane and is placed inside a heat sink made of aluminium. Aluminium acts as thermal conductivity enhancer (TCE), as the thermal conductivity of the PCM is very low. The heat sink acts as an energy storage and a heat-spreading module. Studies are conducted for heat sinks on which a uniform heat load is applied for the unfinned and finned cases. The test section considered in all cases in the present work is a 80 × 62 mm² base with TCE height of 25 mm. A 60 × 42 mm² plate heater with 2 mm thickness is used to mimic the heat generation in electronic chips. Heat sinks with pin fin and plate fin geometries having the same volume fraction of the TCE are used. The effect of different types of fins for different power level (ranging from 2 to 7 W) in enhancing the operating time for different set point temperatures and on the duration of latent heating phase were explored in this study. The results indicate that the operational performance of portable electronic device can be significantly improved by the use of fins in heat sinks filled with PCM.     

Experimental investigations on thermal performance enhancement and effect of orientation on porous matrix filled PCM based heat sink

Thermal performance in terms of enhancement ratios and the effect of orientation of a copper porous matrix filled phase change material (PCM) based heat sink are experimentally studied in this paper. N-eicosane is used as the phase change material. A copper open cell metal foam, press fitted into an aluminium casing is the thermal conductivity enhancer. In PCM based heat sinks, low thermal conductivity associated with PCMs makes the use of enhancement techniques inevitable for better thermal performance. A plate heater with an overall dimension of 60 × 42 mm² with 2 mm thickness is used to mimic the heat generation in electronic chips. The effect of orientation of the heat sink on thermal performance is studied by developing a tracking system, capable of placing the heat sink at any specified orientation.     

Optimal design of geometric parameters of double-layered microchannel heat sinks

This work uses an optimization procedure consisting of a simplified conjugate-gradient method and a three-dimensional fluid flow and heat transfer model to investigate the optimal geometric parameters of a double-layered microchannel heat sink (DL-MCHS). The overall thermal resistance R_T is the objective function to be minimized, and the number of channels N, channel width ratio β, lower channel aspect ratio α_l, and upper channel aspect ratio α_u are the search variables. For a given bottom area (10 × 10 mm) and heat flux (100 W/cm²), the optimal (minimum) thermal resistance of the double-layered microchannel heat sink is about R_T = 0.12 °C/m²W. The corresponding optimal geometric parameters are N = 73, β = 0.50, α_l = 3.52, and, α_u = 7.21 under a total pumping power of 0.1 W. These parameters reduce the overall thermal resistance by 52.8% compared to that yielded by an initial guess (N = 112, β = 0.37, α_l = 10.32, and α_u = 10.93). Furthermore, the optimal thermal resistance decreases rapidly with the pumping power and then tends to approach an constant value. As the pumping power increases, the optimal values of N, α_l, and α_u increase, whereas the optimal β value decreases. However, increasing the pumping power further is not always cost-effective for practical heat sink designs.     

Experimental and numerical investigation of low melting point metal based PCM heat sink with internal fins

In this paper, low melting point metal (LMPM), eutectic alloy Bi_31.6In_48.8Sn_19.6 (E-BiInSn), was adopted as phase change material for potential thermal management applications. First, E-BiInSn was prepared and its main thermophysical properties were characterized. Then, transient thermal performances of E-BiInSn based heat sinks with internal crossed fins were tested, in comparison with that of organic PCM (octadecanol) which has close melting point. Three types of heat sink structures which have different number of internal fins were studied. Three heating conditions were applied, namely 80 W (2.2 W/cm²), 200 W (5.6 W/cm²) and 320 W (8.9 W/cm²). For all of the cases, E-BiInSn exhibited much superior thermal performance than that of octadecanol. Furthermore, cyclic test of the E-BiInSn heat sink was carried out, which showed good repeatability and stability, and without supercooling. Finally, a simplified 3D conjugate numerical model was developed to simulate the melting process of LMPM heat sink, which showed good agreement with the experimental results. This simplified model would be much useful in practical thermal design and optimization of LMPM heat sink, for that it would significantly save the computational time consumption.     

Effects of inlet geometry on heat transfer and fluid flow of tangential micro-heat sink

The paper presents the geometric optimization of the micro-heat sink with straight circular microchannels with inner diameter of D_i = 900 μm. The inlet cross-section has a rectangular shape and positioned tangentially to the tube axis with the four different geometries. The fluid flow regime is laminar and water with variable fluid properties is used as a working fluid. The heat flux spread through the bottom sink surface is q = 100 W/cm². Thermal and hydrodynamic performances of the heat sink are compared with results obtained for conventional channel configuration with lateral inlet/outlet cross-section. Besides, the results are compared with the tangential micro-heat sink with D_i = 300 μm. For all the cases, the thermal and hydrodynamic results are compared on a fixed pumping power basis.     

Investigation of a multiple piezoelectric–magnetic fan system embedded in a heat sink

Previous studies have investigated the thermal performance of embedding a single piezoelectric fan in a heat sink. Based on this work, a multiple piezoelectric–magnetic fan system (“MPMF”) has been successfully developed that exhibits lower fan power consumption, optimum fan pitch and an optimum fan gap between the fan tips and the heat sink. In this study, the cooling performance and heat convection improvement for the MPMF system embedded in a heat sink are evaluated at different fan tip locations. The results indicate that the fan tip location of the MPMF system at x/S_l = 0.5 and y/S_h = 0 is an optimum configuration, improving the thermal resistance by 53.2% over natural convection condition for the fan input power of 0.1 W. The MPMF system breaks the thermal boundary layer and causes fluctuations inside the fins of the heat sink to enhance the overall heat transfer coefficient. Moreover, the relationship between the convection improvement and the Reynolds number for the MPMF system has been investigated and transformed into a correlation line for nine different fan tip locations to provide a means of predicting the cooling performance for the MPMF system embedded in a heat sink.     

An experimental investigation of forced convective cooling performance of a microchannel heat sink with Al2O3/water nanofluid

Experiments were conducted to investigate forced convective cooling performance of a copper microchannel heat sink with Al₂O₃/water nanofluid as the coolant. The microchannel heat sink fabricated consists of 25 parallel rectangular microchannels of length 50 mm with a cross-sectional area of 283 μm in width by 800 μm in height for each microchannel. Hydraulic and thermal performances of the nanofluid-cooled microchannel heat sink have been assessed from the results obtained for the friction factor, the pumping power, the averaged heat transfer coefficient, the thermal resistance, and the maximum wall temperature, with the Reynolds number ranging from 226 to 1676. Results show that the nanofluid-cooled heat sink outperforms the water-cooled one, having significantly higher average heat transfer coefficient and thereby markedly lower thermal resistance and wall temperature at high pumping power, in particular. Despite the marked increase in dynamic viscosity due to dispersing the alumina nanoparticles in water, the friction factor for the nanofluid-cooled heat sink was found slightly increased only.     

Experimental analysis of flow and heat transfer in a miniature porous heat sink for high heat flux application

A novel miniature porous heat sink system was presented for dissipating high heat fluxes of electronic device, and its operational principle and characteristics were analyzed. The flow and heat transfer of miniature porous heat sink was experimentally investigated at high heat fluxes. It was observed that the heat load of up to 280 W (heat flux of 140 W/cm²) was removed by the heat sink with the coolant pressure drop of about 34 kPa across the heat sink system and the heater junction temperature of 62.9 °C at the coolant flow rate of 6.2 cm³/s. Nu number of heat sink increased with the increase of Re number, and maximum value of 323 for Nu was achieved at highest Re of 518. The overall heat transfer coefficient of heat sink increased with the increase of coolant flow rate and heat load, and the maximal heat transfer coefficient was 36.8 kW(m² °C)^?1 in the experiment. The minimum value of 0.16 °C/W for the whole thermal resistance of heat sink was achieved at flow rate of 6.2 cm³/s, and increasing coolant flow rate and heat fluxes could lead to the decrease in thermal resistance. The micro heat sink has good performance for electronics cooling at high heat fluxes, and it can improve the reliability and lifetime of electronic device.     

Numerical study of confined slot jet impinging on porous metallic foam heat sink

This study numerically investigates the impinging cooling of porous metallic foam heat sink. The analyzed parameters ranges comprise ε = 0.93/10 PPI Aluminum foam, L/W = 20, Pr = 0.7, H/W = 2–8, and Re = 100–40,000. The simulation results exhibit that when the Re is low (such as Re = 100), the Nu_max occurs at the stagnation point (i.e. X = 0). However, when the Reynolds number increases, the Nu_max would move downwards, i.e. the narrowest part between the recirculation zone and the heating surface. Besides, the extent to which the inlet thermal boundary condition influences the prediction accuracy of the Nusselt number increases with a decreasing H/W and forced convective effect. The application ranges of H/W and Re that the effect of the inlet thermal boundary condition can be neglected are proposed. Lastly, comparing our results with those in other studies reveals that the heat transfer performance of the Aluminum foam heat sink is 2–3 times as large as that without it. The thermal resistance is also 30% less than that of the plate fin heat sink for the same volumetric flow rate and the 5.3 mm jet nozzle width. Therefore, the porous Aluminum foam heat sink enhances the heat transfer performance of impinging cooling.     

The application of the CFD and Kriging method to an optimization of heat sink

The shape optimization of the plate-fin type heat sink with an air deflector is numerically performed to minimize the pressure loss subjected to the desired maximum temperature and geometrical constraints. A function evaluation using the FVM, in general, is required much computational costs in fluid/thermal systems. Thus, global approximate optimization techniques have been introduced into the optimization of fluid/thermal systems. In this study, the Kriging method, which is one of the metamodels, associated with the computational fluid dynamics (CFD) is used to obtain the optimal solutions. The Kriging method can dramatically reduce a computational cost by 1/6 times compared to that of the SQP method so that its efficiency can be validated. The results also show that when the temperature rise is less than 40 K, the optimal design variables are B₁ = 2.44 mm, B₂ = 2.09 mm, and t = 7.58 mm.