A Small Scale Thermosyphon Heat Exchanger.

A small circular heat transfer cell was used to study the cooling of a disc heat source by a thin evaporating liquid film. This small scale thermosyphon is a thermal spreader and a passive heat sink in that the interfacially induced liquid flow rates are controlled by the heat input. To determine the pressure gradient, the evaporating liquid film profile is viewed interferometrically through the objective of a microscope which is equipped with a scanning microphotometer to measure its thickness profile. Experimental data for the operation of the cooling device with pure fluids n-alkanes, Freon 113 are presented. The combined use of an evaporating thin circular film in the shape of an extended meniscus and condensation within a small volume gives an effective heat spreader for the cooling of small electronic heat sources. The surface heat flux and heat transfer coefficient can be enhanced by increasing the interline-lengtharea ratio.