In order to comply with the recent demand for downsizing of the electric
equipment, the minia- turization and the improvement in heat transfer
performance of a heat sink under natural air-cooling are increasingly required.
This paper describes the experimental and numerical investigations of heat
sinks with miniature/micro pins and the effect of the pin size, pin height and
the number of pins on heat transfer characteristics of heat sinks. Five types
of basic heat sink models are investigated in this study. The whole heat
transfer area of heat sinks having the different pin size, pin height and the
number of pins respectively is kept constant. From a series of experiments and numerical
analyses, it has been clarified that the heat sink temperature rises with
increase in the number of pins. That is, the heat sink with miniaturized fine
pins showed almost no effect on the heat transfer enhancement. This is because
of the choking phenomenon occurred in the air space among the pin fins.
Reflecting these results, it is confirmed that the heat transfer coefficient
reduces with miniaturization of pins. Concerning the effects of the heat
transfer area on the heat sink performance, almost the same tendency has been
observed in other three series of large surface area, that is, higher pin
height. Furthermore as a result of studying non-dimensional convection heat
transfer performance, it was found that the relation between the Nusselt number
(Nu) and the Rayleight number (Ra) is given by Nu = 0.16 Ra0.52.
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