Abstract
Experimental investigations of pool boiling heat transfer on microchannels of variable depth were conducted. The experiments were carried out for water and ethanol at atmospheric pressure. Microchannels of variable depth from 0.2 to 2.8 mm and width 0.5 mm were uniformly spaced on base surface with pitch of 1 mm. The comparison of heat transfer coefficients for surfaces with variable and constant depth of microchannels was made. At the low and medium heat fluxes structures with constant microchannel depth showed the best boiling heat transfer performance. EX-FH20 (Casio) camera was used to record the images of the entire surface of the specimen. The bubble growth mechanism on the enhanced surface was different from that of plain surface. Visualization investigations were aimed at identifying nucleation sites and determining the bubble growth cycle. Vapor bubbles generate in microchannel spaces, from where they move towards the fin tips, then grow and depart.
Highlights
The paper deals with experimental investigations of boiling heat transfer on a system of parallel horizontal channels
Boiling heat transfer enhancement for microchannels with variable depth (MCV) related to plain surface (α/α ps) is about 2 at heat fluxes 100 – 350 kW/m2
The performance of microchannels has proved especially good for the microchannels with constant depth (MC) surface (Fig. 7)
Summary
The paper deals with experimental investigations of boiling heat transfer on a system of parallel horizontal channels. This structures can be applied for cooling miniature integrated devices, such as microprocessors, by a direct or indirect method (as a thermosyphon or tube evaporator), substituting forced convection (traditional fan). Reference Cooke and Kandlikar [1] Cooke and Kandlikar [2] Jaikumar and Kandlikar [3]. Patil and Kandlikar [4]. Kalani and Kandlikar [5]. Jaikumar and Kandlikar [6] Kandlikar [7] [8] [9]. Configuration silicon micro-channels 40 – 200 μm wide and 180 – 275 μm deep, etched in silicon plates copper micro-channels 0.2 – 0.4 mm wide and 0.100 – 0.400 mm deep microchannels 300 m, 500 m and 762 m wide, three coating configurations: sintered-throughout, sintered-fin-tops, sintered-channels. microchannels (300—762 m wide, 200—400 m deep) with micro-porous coatings on the fin tops copper microchannels 245 – 470 m deep and 194 – 406 m wide copper 762 m wide and 400 m deep open microchannel; coating configurations as in [4] copper open microchannels with porous fin tops on (widths: 300—762 m, depths: 200—400 m) copper surface on 45o inclined microchannels (widths: 0.5—0.7 mm, depths: 0.5—1 mm) microchannels 0.2—0.4 mm deep, 0.3 mm wide copper microchannels 0.3 mm wide, 0.2—0.5 mm deep
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