Computational Design and Optimisation of Pin Fin Heat Sinks with Rectangular Perforations

The benefits of using pin heat sinks (PHSs) with single, rectangular slotted or notched pin perforations, are explored computationally, using a conjugate heat transfer model. Results show that the heat transfer increases monotonically while the pressure drop decreases monotonically as the size of the rectangular perforation increases. Performance comparisons with PHSs with multiple circular perforations show favourable heat transfer and pressure drop characteristics. However, the reduced manufacturing complexity of rectangular notched pins in particular provide strong motivation for their use in practical applications. Detailed parameterisation and optimisation studies into the benefits of single rectangular notch perforations demonstrate the scope for improving heat transfer and reducing mechanical fan power consumption yet further by careful design of pin density and pin perforations in PHSs

A Numerical Investigation of the Thermal-Hydraulic Characteristics of Perforated Plate Fin Heat Sinks

The benefits of using notch, slot and multiple circular perforations in plate fin heat sinks (PFHSs), are investigated numerically, using a conjugate heat transfer model. Comparisons show that each type of perforation can provide significantly reduced pressure drops over PFHSs but that fins with slot perforations provide the most effective design in terms of heat transfer and pressure drop. The practical benefits of each type of perforated fin for micro-electronics cooling is also explored and their capabilities of achieving low processor temperatures for reduced mechanical power consumption are quantified

Experimental investigation and numerical simulation of inline strip fins heat sinks

Orientador: Carlos Alberto Carrasco AltemaniDissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia MecânicaResumo: Uma investigação experimental e simulações numéricas foram efetuadas no presente trabalho para obter as características do escoamento e da transferência convectiva de calor de dois dissipadores térmicos análogos. Um deles continha aletas retas contínuas e o outro, aletas retas em tiras alinhadas, ambos resfriados por um escoamento forçado de ar paralelo à sua base. Os resultados experimentais foram obtidos em regime permanente, com os dois dissipadores montados em um duto retangular sem regiões de folga. A velocidade média do escoamento de ar nos canais entre as aletas dos dissipadores foi variada de 4 a 20 m/s, correspondendo a uma faixa do número de Reynolds do escoamento nesses canais entre 810 e 3.800. A resistência térmica dos dissipadores foi baseada no coeficiente convectivo médio nos seus canais, utilizando como referência a temperatura de entrada de ar nos dissipadores. Os dissipadores térmicos também foram analisados como trocadores de calor com a razão das capacidades térmicas igual a zero. Os resultados experimentais incluíram a queda de pressão do escoamento de ar nos dissipadores, o número de Nusselt médio nos canais formados entre as aletas, a resistência térmica convectiva e a efetividade dos dois dissipadores térmicos investigados. Eles indicaram que a queda de pressão do escoamento e o coeficiente convectivo são maiores no dissipador com tiras alinhadas. Apesar da menor área de troca de calor do dissipador com tiras alinhadas, o seu coeficiente convectivo médio foi maior o suficiente para que a sua resistência térmica fosse menor do que a do dissipador de aletas contínuas. Além disso, quando os dois dissipadores foram tratados como trocadores de calor, considerando a mesma faixa de vazão de ar, a efetividade do dissipador com aletas em tiras foi nitidamente maior. As simulações numéricas foram efetuadas adotando dois tratamentos distintos: um considerava aletas de espessura desprezível na mesma temperatura da base. O outro considerava a sua espessura finita em contato térmico perfeito com a base. Os resultados das simulações, comparados com os resultados experimentais, indicaram uma boa concordância para o dissipador de aletas contínuas. Para o dissipador com aletas em tiras alinhadas, as simulações efetuadas com os dois tratamentos numéricos não apresentaram uma concordância tão boa com os resultados de laboratório. Esta dificuldade sugere que a complexidade do escoamento nos canais com aletas em tiras não pode ser captada de forma precisa pelos tratamentos numéricos utilizados neste trabalhoAbstract: An experimental investigation and numerical simulations were performed in the present work to obtain the flow and convective heat transfer characteristics of two analogous heat sinks. One of them had continuous straight fins and the other, inline strip fins, both cooled by forced airflow parallel to their base. The experimental results were obtained under steady state conditions, with the two heat sinks mounted in a rectangular duct without any by-pass. The average airflow velocity in the channels between the fins was varied from 4 to 20 m/s, corresponding to a range of the Reynolds number of the flow in these channels from 810 to 3,800. The heat sinks thermal resistance was based on the average convective coefficient in their channels, using as reference the heat sink inlet air temperature. They were also treated as heat exchangers with a heat capacity ratio equal to zero. The experimental results included the airflow pressure drop in the heat sinks, the average Nusselt number in the interfin channels, the convective thermal resistance and the effectiveness of both heat sinks. They indicated that the flow pressure drop and the average convective coefficient are larger for the strip fins heat sink. In spite of the strip fins heat sink smaller heat exchange area, its larger average convective coefficient was enough to make its thermal resistance smaller than that of the continuous fins heat sink. When the two heat sinks were considered as heat exchangers, considering the same range of airflow rate, the strip fins heat sink effectiveness was pronouncedly larger. The numerical simulations were performed using two distinct treatments: one considered the fins with no thickness, isothermal with the fins base temperature. The other considered the fins thickness, in perfect thermal contact with the fins base. The simulation results, compared to the experimental results, indicated a good agreement for the continuous fins heat sink. For the inline strip fins heat sink, the simulations performed with both numerical treatments did not present the same good agreement with the laboratory results. This difficulty suggests that the complexity of the flow in the channels of the strip fins heat sink cannot be captured in precise form by the adopted numerical treatments used in this workMestradoTermica e FluidosMestre em Engenharia Mecânic

Design Optimisation and Analysis of Heat Sinks for Electronic Cooling

Since industrial devices create power dissipation in the form of heat created as a by-product, which can have a negative effect on their performance, certain temperature limit constraints are required for almost all these applications to work within suitable conditions. That is, these engineering devices might fail in some way if these limitations are surpassed by overheating. In all the related industries, inexorable increases in power densities are driving innovation in heat exchange techniques. Furthermore, electronic devices are becoming smaller at the same time as their thermal power generation increases. Thus, heat sinks can be applied for cooling critical components in many important applications ranging from aero-engines and nuclear reactors to computers, data centre server racks and other microelectronic devices. The most common cooling technique for heat dissipation for thermal control of electronics is air cooling. Reduced cost, simplicity of design, the easy availability of air, and increased reliability are the main benefits of this cooling method. Heat sinks with a fan/blower are commonly used for air-cooled devices as a forced convection heat transfer. An amount of heat is dissipated from the heat source to environmental air utilising a heat sink as a heat exchanger, which is a vital practice employed in air-cooling systems. This transfer mechanism is easy, simple and leads to reduced cost and increased reliability, and pinned heat sinks are more beneficial than plate fin heat sinks. The main interest of this study is to investigate the benefits of using perforated, slotted, and notched pinned heat sinks with different configurations to reduce CPU temperature and fan power consumption to overcome the pressure drop and maximise a heat transfer rate through the heat sink. An experimental heat sink with multiple perforations is designed and fabricated, and parameter studies of the effect of this perforated pin fin design on heat transfer and pressure drops across the heat sinks are undertaken, to compare it to solid pinned heat sinks without perforations. Experimental data is found to agree well with predictions from a CFD model for the conjugate heat transfer and turbulent airflow model into the cooling air stream. The validated CFD model is used to carry out a parametric study of the influence of the number and positioning of circular perforations, and slotted/notched pinned heat sinks. Then, the multi-objective optimum pinned heat sink designs are tested to obtain CPU temperature and fan power consumption as lowest as possible through the heat sink. In addition, the limitations in application of pinned heat sinks based on the pin density and applied heat flux are reported for active air-cooling electronic systems. An overview of the findings indicates that the CPU temperature, the fan power consumption, and the heat transfer rate in terms of Nusselt number are enhanced with the number of pin perforations and slotted/notched pinned heat sinks, while the locations of the pin perforations are much less influential. These benefits arise due to not only the increased surface area but also to the heat transfer enhancement near the perforations through the formation of localised air jets. Finally, the perforated heat sinks will be lighter in weight compared with solid pinned heat sinks