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 an
integrated microchannel and micro pin fins for different solid volumes so that the peak temperature in
the 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.