Thermal-fluid characteristics of plate-fin heat sinks cooled by impingement jet

This work experimentally and numerically studies the thermal-fluid characteristics of plate-fin heat sinks under impingement cooling by adjusting the impinging Reynolds number, the impingement distance, and the fin dimensions. The parameters and the ranges under consideration are the impinging Reynolds number (Re = 5000–25,000), the impingement distance (Y/D = 4–28), the fin width (W/L = 0.08125–0.15625) and the fin height (H/L = 0.375–0.625). The results show that the heat transferred by the heat sink increases with the impinging Reynolds number. The thermal performance can be improved significantly even at low impinging Reynolds number. However, the improvement becomes indistinct as the impinging Reynolds number increases. The thermal resistance declines as the impingement distance increases, and is minimal at Y/D = 20 for various impinging Reynolds numbers. Additionally, the thermal resistance increases as the impingement distance increases further. Increasing the fin width can effectively reduce the thermal resistance. However, as the fin width increases beyond a particular value, the thermal resistance increases dramatically. Reducing the thermal resistance by increasing the fin height depends on a suitable impinging Reynolds number and fin width. Therefore, the effect of the fin height is weaker than that of the impinging Reynolds number or the fin width.     

Thermal performance of flat vapor chamber heat spreader

Experiments were performed to examine the spreading thermal resistance of centrally positioned heat sources and the thermal performance of a water charged, gravity assisted flat vapor chamber to be used for electronic cooling. Parametric studies including different heat fluxes and operating temperatures were conducted, and the effect of the relevant parameters on the cooling performance in terms of the spreading resistance was presented and discussed. The present vapor chamber heat spreader showed a heat removal capacity of 220 W/cm² with a thermal spreading resistance of 0.2 °C/W.     

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.     

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.     

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.     

Effect of orientation for phase change material (PCM)-based heat sinks for transient thermal management of electric components

Phase change material (PCM)-based heat sink, consisting of a conventional, extruded aluminum sink embedded with appropriate PCMs, can potentially be used for cooling of mobile electronic devices such as personal digital assistants (PDAs) and notebooks which are operated intermittently. During the use of such mobile devices, the orientation changes from time to time. A numerical investigation was carried out to study the effect of orientation of heat sink on the thermal performance of the combined cooling system to determine if it affects the thermal performance of a PCM-based cooling system significantly.     

Thermal investigations on LED vapor chamber-based plates

This study utilizes a thermal-performance experiment with the illumination-analysis method to discuss the thermal performance of three kinds of LED based plates comparing the experiments, theories, and simulation thermal resistances. The results show that the thermal performance of the LED vapor chamber-based plate is better than that of the LED copper-based plate with an input power above 5 W. And the experimental thermal resistance values of LED copper- and vapor chamber-based plate are 0.41 °C/W and 0.38 °C/W at 6 W respectively. And the illumination of 6 Watt LED vapor chamber-based plate is 5% larger than the 6 Watt LED aluminum-based plate. Thus, the LED vapor chamber-based plate has the best thermal performance above 5 W.     

On the thermal cooling of central processing unit of the PCs with vapor chamber

An experimental investigation on the thermal cooling of vapor chamber for cooling computer processing unit of the personal computer is performed. Two different configurations of the vapor chambers with de-ionized water as working fluid are tested under the real operating conditions of PCs. Parametric studies including different aspect ratios, fill ratios, and operating conditions of PC on the CPU temperature are considered. It was found that the vapor chamber cooling technique has significant effect on the thermal cooling of CPU. Average CPU temperatures obtained from the vapor chamber cooling system are 4.1%, 6.89% lower than those from the conventional cooling system for no load and 90% operating loads, respectively. In additional, this cooling system requires 6.89%, 10.53% lower energy consumption for no load and 90% operating loads, respectively. The results of this study are of technological importance for the efficient design of cooling systems of the personal computers or electronic devices to enhance cooling performance.     

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.     

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.     

Two-phase closed thermosyphon vapor-chamber system for electronic cooling

This article experimentally investigates a two-phase closed thermosyphon vapor-chamber system for electronic cooling. A thermal resistance net work is developed in order to study the effects of heating power, fill ratio of working fluid, and evaporator surface structure on the thermal performance of the system. The results indicate that either a growing heating power or a decreasing fill ratio decreases the total thermal resistance, and the surface structure also influences the evaporator function prominently. A reasonable agreement with Rohesnow's empirical correlation is found for the evaporator. An optimum overall performance exists at 140 W heating power and 20% fill ratio with sintered surface, and the corresponding total thermal resistance is 0.495 °C W⁻¹.     

Cooling performance of a microchannel heat sink with nanofluids

In this paper, the cooling performance of a microchannel heat sink with nanoparticle–fluid suspensions (“nanofluids”) is numerically investigated. By using a theoretical model of thermal conductivity of nanofluids that accounts for the fundamental role of Brownian motion, we investigate the temperature contours and thermal resistance of a microchannel heat sink with nanofluids such as 6 nm copper-in-water and 2 nm diamond-in-water. The results show that the cooling performance of a microchannel heat sink with water-based nanofluids containing diamond (1 vol.%, 2 nm) at the fixed pumping power of 2.25 W is enhanced by about 10% compared with that of a microchannel heat sink with water. Nanofluids reduce both the thermal resistance and the temperature difference between the heated microchannel wall and the coolant. Finally, the potential of deploying a combined microchannel heat sink with nanofluids as the next generation cooling devices for removing ultra-high heat flux is shown.     

Study on the vapor chamber with refrigerant R-141b as working fluid for HDD cooling

The heat within the operating drive is mainly generated by the SPM, VCM, magnetic read/write head sensor, and windage loss. Temperature is often quoted as the most important environmental factor affecting disk drive reliability. The results of the investigation on the thermal cooling of vapor chamber with refrigerant R-141b as working fluid for cooling hard disk drive are presented. It was found that the vapor chamber cooling technique has a significant effect on the thermal cooling of hard disk drive. At the optimum condition (20% fill ratio of working fluid) that results in minimum HDD temperature, average HDD temperatures of VC with refrigerant R-141b as working fluid are 10.73% and 23.37% lower than those with water as working fluid and those without VC, respectively. The results of this study are of technological importance for the efficient design of cooling systems of the personal computers or electronic devices to enhance cooling performance.     

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 of aluminium‐foam CPU heat exchangers

This study investigates the performance of existing central processing unit (CPU) heat exchangers and compares it with aluminium‐foam heat exchangers in natural convection using an industrial set‐up. Kapton flexible heaters are used to replicate the heat produced by a computer's CPU. A number of thermocouples are connected between the heater and the heat sink being used to measure the component's temperature. The thermocouples are also connected to a data‐acquisition card to collect the data using LabVIEW program. The values obtained for traditional heat exchangers are compared to published data to validate experiments and set‐up. The validated set‐up was then utilized to test the aluminium‐foam heat exchangers and compare its performance to that of common heat sinks. It is found that thermal resistance is reduced more than 70% by employing aluminium‐foam CPU heat exchangers. The results demonstrate that this material provides an advantage on thermal dissipation under natural convection over most available technologies, as it considerably increases the surface‐area‐to‐volume ratio. Furthermore, the aluminium‐foam heat exchangers reduce the overall weight. Copyright © 2005 John wiley & Sons, Ltd.     

Optimum thermal performance of microchannel heat sink by adjusting channel width and height

A three-dimensional numerical model of the microchannel heat sink is presented to study the effects of heat transfer characteristics due to various channel heights and widths. Based on the theory of a fully developed flow, the pressure drop in the microchannel is derived under the requirement of the flow power for a single channel. The effects of two design variables representing the channel width and height on the thermal resistance are investigated. In addition, the constraint of the same flow cross section is carried out to find the optimum dimension. Finally, the minimum thermal resistance and optimal channel width with various flow powers and channel heights are obtained by using the simulated annealing method.     

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.     

Three-dimensional numerical simulation of heat and fluid flow in noncircular microchannel heat sinks

A three-dimensional model of heat transfer and fluid flow in noncircular microchannel heat sinks is developed and analyzed numerically. It is found that Nusselt number has a much higher value at the inlet region, but quickly approaches the constant fully developed value. The temperature in both solid and fluid increases along the flow direction. In addition, the comparison of thermal efficiencies is conducted among triangular, rectangular and trapezoidal microchannels. The result indicates that the triangular microchannel has the highest thermal efficiency.     

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.