Department of Mechanical Engineering

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Browsing Department of Mechanical Engineering by Subject "Bejan number"

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  • Item
    Open Access
    Constructal design of combined microchannel and micro pin fins for electronic cooling
    (International Journal of Heat and Mass Transfer, 2013-07-10) Adewumi, O.O; Bello-Ochende, T.; Meyer, J.P
    This paper presents a three-dimensional numerical study of steady, laminar, incompressible flow and forced convection heat transfer through a microchannel heat sink with micro pin fin inserts for both fixed and variable axial lengths. The objective of the study was to optimise the geometric configuration of anintegrated microchannel and micro pin fins for different solid volumes so that the peak temperature inthe configuration was minimised. The effect of the micro pin fins on the optimised microchannel was also investigated. The geometric optimisation of the integrated microchannel and micro pin fin was carried out using a computational fluid dynamics (CFD) code with a goal-driven optimisation tool subject to global constraints. The optimisation procedure was carried out in two steps. Firstly, the microchannel configuration was optimised without the micro pin fins inserted and the results were compared with similar work found in the open literature. This optimisation was carried out for both fixed and relaxed lengths. Thereafter, the integrated design of the microchannel and micro pin fins was optimised. The effect of the Bejan number on the solid volume fraction, channel aspect ratio and hydraulic diameter, pin fin aspect ratio, minimised peak temperature and maximised thermal conductance were reported. Results showed that as the Bejan number increased, the minimised peak temperature decreased. Also, the maximum thermal conductance increased with the optimised microchannel structure with three to six rows of micro pin fin inserts. Diminishing return set in when the number of rows of micro pin fin inserts was greater than three for the fixed length but for the relaxed length, as the number of rows increased, the results improved but when it exceeded six diminishing returns set in for a fixed solid volume of 0.9 mm3. For each Bejan number used in this study, there was an optimum channel hydraulic diameter and aspect ratio, solid volume fraction and pin fin aspect ratio that satisfied the global objective.
  • Item
    Open Access
    Constructal heat transfer and fluid flow enhancement optimisation for cylindrical micro-cooling channels with variable cross-section
    (Wiley, 2021) Olakoyejo, O.T.; Adelaja, A.O.; Adewumi, O.O.; Oluwo, A.A.; Bello, S.K.; Adio, S.A.
    This study applies constructal theory to conduct a numerical optimization of three‐dimensional cylindrical microcooling channels with the solid structure subjected to internal heat generation. The cylindrical channels are designed as variable cross‐section configurations that experience conjugate heat transfer and fluid flow, where water is used as the coolant. The research aims to optimize the channel configurations subject to a fixed global solid material volume constraint. The key objectives are to minimize the global thermal resistance and friction factor. The coolant is pushed through the channels by pressure drop represented as Bejan number. The main design parameters are the inlet and outlet diameters at a given porosity. The channel configuration and the structure elemental volume are permitted to change to find the best design parameters that minimized thermal resistance and friction factor, so that the cooling effect is enhanced. An ANSYS FLUENT code is used to obtain the best optimal parameter of the configuration that enhances thermal performance. The influence of Bejan number on optimized inlet and outlet diameters led to minimization of thermal resistance and friction factor and maximization of Nusselt number. The results show distinctive optimal inlet and outlet diameters that enhance the overall performance of the system in the range of 1.018 × 10−2 ≤ (din /L) opt ≤ 1.5381 × 10−2 and 1.0838 × 10−2 ≤ (dout /L)opt ≤ 1.6134 × 10−2, respectively.