Abstract
The paper presents experimental investigations into pool boiling heat transfer for open microchannel surfaces. Parallel microchannels fabricated by machining were about 0.3 mm wide, and 0.2 to 0.5 mm deep and spaced every 0.1 mm. The experiments were carried out for ethanol, and FC-72 at atmospheric pressure. The image acquisition speed was 493 fps (at resolution 400 × 300 pixels with Photonfocus PHOT MV-D1024-160-CL camera). Visualization investigations aimed to identify nucleation sites and flow patterns and to determine the bubble departure diameter and frequency at various superheats. The primary factor in the increase of heat transfer coefficient at increasing heat flux was a growing number of active pores and increased departure frequency. Heat transfer coefficients obtained in this study were noticeably higher than those from a smooth surface.
Highlights
Miniaturization and increasing power of electronic systems requires dissipation of a considerable amount of heat
The objectives of the present work are to determine the effect of microchannel width on the heat transfer coefficient (HTC) for ethanol and FC-72 and to identify diameters and frequency of departing bubbles
The heat transfer coefficient was independent of the microchannel depth
Summary
Miniaturization and increasing power of electronic systems requires dissipation of a considerable amount of heat. Modern technology miniaturizes devices and increases their demand for energy. Equipment that generates large heat fluxes is, for example, digital systems, nuclear reactors, internal combustion engines, gas turbines, etc. In the construction of heat exchangers, the aim is to reduce their volume and mass. Pool boiling is a passive cooling technique that allows dissipating large amounts of heat flux at low superheats. The boiling heat transfer coefficient (HTC) can be further increased by surface modification that involves changing roughness parameters, adding a porous layer, changing the structure of the surface by making small holes in it, and forming microfins or microchannels
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