The present paper deals with horizontal-base pin fin heat sinks in free convection. The sinks have the same base dimensions and variable fin pitch. They are made of aluminum, and there is no contact resistance between the base and the fins. The fins have a constant square cross-section. The effect of fin pitch on the performance of the sink is studied experimentally and numerically. In the experiments, the heat sinks are heated using foil electrical heaters. The heat input is set, and temperatures of the base and fins are measured. In the corresponding numerical study, the sinks are modeled using the Fluent 6 software. The results show that heat transfer enhancement due to the fins is not monotonic. The differences between sparsely and densely populated sinks are analyzed. Also analyzed are the effects of the sink edges on the total heat transfer. A relative contribution of outer and inner fin rows in the sink is assessed, together with the effect of fin location in the array on the heat transfer rate from an individual fin. Dimensional analysis of the results is attempted, and a correlation presenting the Nusselt number vs. the Rayleigh number is suggested, where the inter-fin spacing serves as the characteristic length.

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