Experimental Investigation of Flat-Plate Oscillating Heat Pipe for Thermal Spreading Applications

Abstract

The thermal performance of a flat-plate oscillating heat pipe (FP-OHP) operating as a heat spreader – a non-traditional heating/cooling configuration for any FP-OHP - was experimentally investigated. The copper FP-OHP had overall dimensions of 101.6 x 101.6 x 3.18 mm 3 , possessed two layers of 1.02 x 1.02 mm² microchannels and was filled with acetone to a filling ratio of approximately 80%. One side of the FP-OHP was centrally heated with a 9 cm² square heat source and the other side was firmly attached to the base of a copper pin fin heat sink which was uniformly cooled with cross-flowing air at speeds of either: 1 m/s, 2 m/s, and 3 m/s within a wind tunnel. The maximum surface temperature of the FP-OHP – as well as that of an identically-sized piece of copper (with same heat sink attached) – was measured for various heat fluxes and air speeds. Relative to pure copper, the FP-OHP was capable of providing for a 10-15 % reduction in total thermal resistance, depending on air speed and heat input. At the maximum heat input of 230 W, the maximum FP-OHP surface temperature did not exceed 100 oC at an air speed of 3 m/s. Since the maximum surface temperature oscillated with time for all air speeds investigated, this indicates the successful operation of the FP-OHP within the thermal spreading configuration. However, a critical heat input, which varied with air speed, is required to initiate the FP-OHP for the accompanying thermal enhancement. Although the FP-OHP can help to enhance heat transfer, the improvement was not significant indicating that the heating mode directly affects the heat transfer performance of a FP-OHP heat spreader.