Thermal performance of plate-fin vapor chamber heat sinks

Since vapor chambers exhibit excellent thermal performance, they are suited to use as bases of heat sinks. This work experimentally studies the thermal performance of plate-fin vapor chamber heat sinks using infrared thermography. The effects of the width, height and number of fins and of the Reynolds number on the thermal performance are considered. Experimental data are compared with corresponding data for conventional aluminum heat sinks. The results show that generated heat is transferred more uniformly to the base plate by a vapor chamber heat sink than by a similar aluminum heat sink. Therefore, the maximum temperature is effectively reduced. The overall thermal resistance of the vapor chamber heat sink declines as the Reynolds number increases, but the strength of the effect falls. The effect of the fin dimensions on the thermal performance is stronger at a lower Reynolds number. At a low Reynolds number, a suitable number of fins must be chosen to ensure favorable thermal performance of the vapor chamber heat sink. However, at a high Reynolds number, the thermal performance improves as the fin number increases.     

Partially heated heat sinks in a zero-bypass

The need to improve the thermal performance of heat sinks remains a design priority for thermal engineers. Most of the considerations so far have involved various shapes and sizes of the fin designs. This numerical study evaluates the influence of the heating position on the thermal performance of a plate-fin heat sink in a zero-bypass characterized by the thermal resistance data obtained from experiments. For the heating positions evaluated, the central heating position offers the least thermal resistance. In practice, many cooling systems, like in electronic components, involve heat sinks with partially heated sections; therefore, evaluating the best position to place the heat sinks could be a fairly cheap way of enhancing the thermal performance.     

Thermal performance measurement of heat sinks with confined impinging jet by infrared thermography

In this paper, the thermal performance of heat sinks with confined impingement cooling is measured by infrared thermography. The effects of the impinging Reynolds number, the width and the height of the fins, the distance between the nozzle and the tip of the fins, and the type of the heat sinks on the thermal resistance are investigated. The results show that increasing the Reynolds number of the impinging jet reduces the thermal resistance of the heat sinks consistently. However, the reduction of the thermal resistance decreases gradually with the increase of the Reynolds number. The thermal resistance can be decreased by increasing the fin width combined with an appropriate Reynolds number. Increasing the fin height to enlarge the area of heat transfer also decreases the thermal resistance, but the effects are less conspicuous than those on altering the fin width. An appropriate impinging distance with minimum thermal resistance can be found at a specific Reynolds number, and the optimal impinging distance increases as the Reynolds number increases. Generally speaking, the thermal performance of the pin–fin heat sinks is superior to that of the plate–fin heat sinks because the pin–fin heat sinks consist of smaller volumes but greater exposure surfaces.     

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.     

Experimental study of impingement cooling by heat sinks with thin longitudinal fins for LSI packages

This paper reports on the impingement cooling characteristics of a heat sink with thin longitudinal fins of 0.2 mm thickness, which are spaced with a fin-pitch in the range 0.5 mm to 2.0 mm. The air cooling of the heat sink comes from a slot-shaped orifice positioned above the heat-sink center. The breadth of the gap between the fin tops and the inlet orifice is in the range 0 mm to 10 mm. The thermal resistance of the thin longitudinal fins used is about 50% to 57% that of the thick longitudinal fins now in commercial use. The cooling performance of the thin-plate fins is almost the same as that of optimally arranged pin-fins with the same total surface area. A maximum value of six times the heat transfer rate of a single flat plate having the same base area was observed for the thin-plate fins. A comparison of cooling performance between impingement and channel flow systems was conducted. The performance of impingement cooling systems is almost unaffected by the breadth of the gap between the fin tops and the inlet orifice (or, for channel cooling, the upper wall). On the other hand, the performance of channel-cooling systems decreases significantly as the gap widens. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 25(7): 449–459, 1996     

Effects of outlet port positions on the jet impingement heat transfer characteristics in the mini-fin heat sink

Effects of outlet port positions on the jet liquid impingement heat transfer characteristics in the mini-rectangular fin heat sink are numerically investigated. The three-dimensional governing equations for fluid flow and heat transfer characteristics are solved using finite volume scheme. The standard k-ε turbulent model is employed to solve the model for describing the heat transfer behaviors. The predicted results obtained from the model are verified by the measured data. The predicted results are reasonable agreement with the measured data. The outlet port positions have significant effect on the uniformities in velocity and temperature. Based on the results from this study, it is expected to lead to guidelines that will allow the design of the cooling system to ensure the electronic devices at the safe operating temperature.     

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

Using CFD software FLUENT, we investigated the effect of the angle of inclination of a plate heat shield on the thermal and hydraulic performance of a plate-fin heat sink. The variation of this angle causes a substantial and complicated variation of the flow field in space both upstream and downstream near such a heat sink. This distinctive behavior modifies the pressure drop between the inlet and outlet of the investigated duct, but that variation influences only slightly the flow field in the space from fin to fin, and thus the thermal resistance of the heat sink. This trend is further smoothed with increasing Reynolds number and height of the heat sink. As a compromise between the demands of small thermal resistance and a small pressure drop, the angle of inclination of a plate heat shield must be chosen carefully.     

Thermal analysis of a metal foam subject to jet impingement

The present study conducted a thermal analysis on a FeCrAlY foam subjected to jet impingement cooling in a horizontal channel. The temperature distribution of the metal foam is captured with infrared thermography imaging camera for different jet velocities (219.5 ≤ Pe ≤ 548.9). Two dimensional numerical studies have been conducted to obtain the temperature contour of the metal foam and compared to the thermographic images. The thermographic images show inconsistencies in temperature variation across the metal foam due to the porosity within the metal foam. The temperature contours of the metal foam obtained numerically are found to be similar to the thermographic images. The top portion of the metal foam directly impinged by the jet of low velocities shows lowest temperature, but the heat near the heated surface is transferred majorly through conduction.     

Study of impingement cooling of heat sinks for LSI packages with longitudinal fins

This paper describes an experimental and a semi-empirical study on the impingement cooling characteristics of heat sinks with longitudinal fins of a type suitable for LSI packages. The experiments were performed with a variety of different fins. To enhance impingement cooling, one long rectangular inlet orifice (slit) over the center of the heat sink was found to offer the best structure. The optimum orifice width is about 1/6 of the base width of the heat sink. The thermal resistance at a fixed volumetric flow rate and orifice width varies little with size of the gap between the fin tops and inlet orifice, but gaps near 2 mm slightly lower the resistance. Correlations are proposed between the thermal resistance of the heat sink and the geometry of the longitudinal fins. The accuracy of the predicted thermal resistances was found to be within ±25% of the experimental data. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 25(8): 537–553, 1996     

Prediction algorithm of thermal resistance for impingement cooling of heat sinks for LSI packages with pin-fin arrays

This paper is a semi-empirical report on an algorithm for the prediction of thermal resistance for impingement cooling of pin-fin heat sinks for LSI packages when the inlet orifice is relatively large and is located over the center of the sink. We present a physical model suitable for these types of heat sinks, based on flow visualization results. The model divides the flow region into five parts: I) the top surfaces of the fins where they are directly under the inlet orifice, II) the portions of the vertical surfaces of the pin-fin cylinders, where those surfaces are directly below the inlet port, III) the surface of the base to which the fins are attached, excluding the areas occupied by the feet of the fins themselves, IV) the portions of the vertical surfaces of the fin-cylinders excluding those portions of the surfaces that are directly below the inlet port (complementary to region II), V) the portions of the top surfaces of the pins, excluding those portions directly below the inlet port (complementary to region I). We predicted thermal resistance values for heat sinks with pin-fin arrays, for a variety of orifice diameters, gaps, pin-fin diameters, and heights, and number of fins. These values agreed with experimental data within ±30%. © 1997 Scripta Technica, Inc. Heat Trans Jpn Res, 25(7): 434–448, 1996     

Thermal analysis of CPU with CCC and copper base plate heat sinks using CFD

This paper describes experimental and theoretical investigations of heat sinks with different base plate material mounted on CPUs. The thermal model of the computer system with heat sinks which is created using Gambit (for preprocessing) and the simulation is carried out using Fluent (for solver execution and post processing). The following parameters are considered: fin thickness, fin height, and number of fins. Primarily in this paper different base plate thickness and base plate materials are optimized for maintaining the cost and thermal performance of a heat sink. In this research work, the thermal model of the computer system with a slot parallel plate fin heat sink design has been selected, and the fluid flow and thermal flow characteristics of heat sinks are studied. The slot parallel plate fin heat sinks have been used with copper base plates and carbon carbon composite (CCC) base plates to enhance the heat dissipation. The results and conclusion obtained in this present work are found to be in good agreement with numerical results. A complete computer chassis with slot parallel plate heat sinks is investigated varying the thickness of base plate, and the performances of the heat sinks are compared. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20342     

Optimum thermal design of microchannel heat sinks by the simulated annealing method

By adopting the simulated annealing method, a three-dimensional numerical simulation is executed to minimize the thermal resistance of the microchannel heat sink corresponding to the optimum specification under the fixed flow power. The depths of the microchannel heat sink in this study are fixed at either 1 cm or 2 cm. Based on the theory of the fully developed flow, the pressure drop between the inlet and exit in each single channel can be analytically derived if the flow power and the associated specification of the microchannel heat sink are fixed in advance. Then, this pressure drop will be used as the input condition to calculate the temperature distribution of the microchannel heat sink. For the first part of the optimum analysis, the fin width, and channel width are chosen as the design variables to find their optimum sizes. As to the second part of the present analysis, three design variables including channel height, fin width and channel width are individually prescribed as a suitable range to search for their optimum geometric configuration when the other specifications of the microchannel heat sink are fixed as 24 different cases.     

Heat transfer and pressure loss characteristics of very compact heat sinks with plate fins cooled by jets

High-performance and very compact heat sinks have been developed for effective cooling of VLSIs with high heat-generation densities. Their heat transfer and pressure loss characteristics in air-jet cooling have been experimentally studied. The highly compact heat sinks were plate-fin arrays with a very small fin pitch of 0.4–2.0 mm. The rectangular jet nozzle width that gave the highest cooling performance was 30 to 40% of the streamwise length of the heat sinks. The influence of fin height on heat transfer became weak when the ratio of the height to the thickness of the fin exceeded approximately 35. When the air flow rate was constant, the thermal conductance increased as the fin pitch decreased. For a constant fin pitch, heat sinks with smaller fin thickness showed larger thermal conductance at a given blower power consumption. In our experimental range, the heat dissipation rate per unit heat sink volume increased as the base plate area of the heat sink became small. © 1998 Scripta Technica, Heat Trans Jpn Res, 27(6): 399–414, 1998     

A review of heat and fluid flow characteristics in microchannel heat sinks

Heat transfer and flow characteristic in microchannel heat sinks (MCHS) are extensively studied in the literature due to high heat transfer rate capability by increased heat transfer surface area relative to the macroscale heat sinks. However, heat transfer and fluid flow characteristics in MCHS differ from conventional ones because of the scaling effects. This review summarizes the studies that are mainly based on heat transfer and fluid flow characteristic in MCHS. There is no consistency among the published results; however, everyone agrees on that there is no new physical phenomenon in microscale that does not exist at macroscale. Only difference between them is that the effect of some physical phenomena such as viscous dissipation, axial heat conduction, entrance effect, rarefaction, and so forth, is negligibly small at macroscale, whereas it is not at microscale. The effect of these physical phenomena on the heat transfer and flow characteristics becomes significant with respect to specified conditions such as Reynolds number, Peclet number, hydraulic diameter, and heat transfer boundary conditions. Here, the literature was reviewed to document when these physical phenomena become significant and insignificant.     

Three dimensional numerical analyses and optimization of offset strip-fin microchannel heat sinks

This paper presents a numerical study on laminar forced convection of water in offset strip-fin microchannels network heat sinks for microelectronic cooling. A 3-dimensional mathematical model, consisting of N–S equations and energy conservation equation, with the conjugate heat transfer between the heat sink base and liquid coolant taken into consideration is solved numerically. The heat transfer and fluid flow characteristics in offset strip-fin microchannels heat sinks are analyzed and the heat transfer enhancement mechanism is discussed. Effects of geometric size of strip-fin on the heat sink performance are investigated. It is found that there is an optimal strip-fin size to minimize the pressure drop or pumping power on the constraint condition of maximum wall temperature, and this optimal size depends on the input heat flux and the maximum wall temperature. The results of this paper are helpful to the design and optimization of offset strip-fin microchannel heat sinks for microelectronic cooling.     

Experimental investigation of header configuration on two-phase flow distribution in plate-fin heat exchanger

The two-phase flow distribution in a plate-fin heat exchanger has been experimentally studied under different operation conditions. The results indicate that two-phase flow distribution is more complex and nonuniform than that of single-phase flow. The distribution uniformity of liquid-phase deteriorates with the decrease of Re_gas and Re_liq. The distribution uniformity of gas-phase deteriorates with Re_liq, but improves with Re_gas. The improved header with perforated baffle can effectively improve the uniformity of two-phase flow distribution and dryness distribution. The values of S_liq, S_gas and S_dry decrease by 5.4–44.0%, 4.7–35.0% and 11.7–30.0%, respectively. The conclusion is of great significance in the optimum design of plate-fin heat exchanger.     

受限空气射流冲击矩形柱鳍热沉换热实验研究

采用实验方法研究了受限空气冲击射流与矩形柱鳍热沉相结合的散热方式应用于芯片冷却的换热规律,采用最小二乘法对实验数据进行了拟合,并最终获得平均努塞尔数关于雷诺数、喷口高度-孔径比及普朗特数的实验准则方程。在此基础上将这种散热方式与其他空冷方式进行了换热能力的比较,结果表明此种散热方式的换热能力大大超过其他空冷方式。最后,对实验系统误差进行了分析,根据误差传递理论求得的平均努塞尔数的实验相对误差不超过6%。     

Method to improve geometry for heat transfer enhancement in PCM composite heat sinks

Use of composite heat sinks (CHS), constructed using a vertical array of ‘fins’ (or elemental composite heat sink, ECHS), made of large latent heat capacity phase change materials (PCM) and highly conductive base material (BM) is a much sought cooling method for portable electronic devices, which are to be kept below a set point temperature (SPT). This paper presents a thermal design procedure for proper sizing of such CHS, for maximizing the energy storage and the time of operation until all of the latent heat storage is exhausted.For a given range of heat flux, q″, and height, A, of the CHS, using a scaling analysis of the governing two dimensional unsteady energy equations, a relation between the critical dimension for the ECHS and the amount of PCM used (?) is determined. For a ?, when the dimensions of the ECHS are less than this critical dimension, all of the PCM completely melts when the CHS reaches the SPT. The results are further validated using appropriate numerical method solutions. A proposed correlation for chosen material properties yields predictions of the critical dimensions within 10% average deviation. However, the thermal design procedure detailed in this paper is valid, in general, for similar finned-CHS configurations, composed of any high latent heat storage PCM and high conductive BM combination.     

Heat transfer and pressure loss characteristics of very compact heat sinks

High-performance compact heat sinks have been developed for the effective cooling of high-density LSI packaging. Heat transfer and pressure loss characteristics of the heat sinks in both air-cross-flow and air-jet cooling have been experimentally studied. The present heat sinks were of plate-fin and pin-fin arrays with a fin pitch of 0.7 mm. The plate-fin heat sinks had higher cooling performance than the pin-fin heat sinks in the range of large airflow rates both in air-cross-flow and air-jet cooling. The thermal conductance in cross-flow cooling was 20 or 40% larger than that in jet cooling. The correlation of Colburn j-factor/Fanning friction factor versus the Reynolds number for the present heat sinks was found to be very close to that of a conventional large-size heat exchanger. © Scripta Technica, Heat Trans Asian Res, 28(8): 687-705, 1999