Abstract
The paper presents investigations into pool boiling heat transfer for open microchannel surfaces. The experiments were carried out with saturated FC-72 at atmospheric pressure. Parallel microchannels fabricated by machining were about 0.2 to 0.4 mm wide and 0.2 to 0.5 mm deep. Analyzed surfaces with microchannels allowed to obtain heat transfer coefficients within the range of 6.1 – 9.8 kW/m2K, which in relation to the flat surface gives a 3 – 5 - fold increase in HTC. One of the reasons for the increase in the heat transfer coefficient when increasing the heat flux was the growing number of active nucleation sites at the bottom of microchannels and its side surfaces.
Highlights
The use of a refrigerant phase change on a properly designed enhanced surface gives the possibility of obtaining significant values of heat transfer coefficients
The results showed that in comparison to the smooth surface, pool boiling heat transfer was significantly enhanced by the micro-pin-fin surfaces and the maximum superheat was considerably decreased
The investigated surfaces with open microchannels provided higher heat transfer coefficients compared to smooth surfaces
Summary
The use of a refrigerant phase change on a properly designed enhanced surface gives the possibility of obtaining significant values of heat transfer coefficients. The percentage increases observed in CHF for the samples with nanowires were 38.37%, 40.16%, 48.48% and 45.57% whereas the percentage increase in the heat transfer coefficient were 86.36%, 95.45%, 184.1% and 131.82% respectively as compared to the bare copper surface. Whereas in the publication [3] boiling curves for FC-72, depending on pressure (100 - 300 kPa) and subcooling (0 - 72 K) were obtained using a silicon heater coated with microporous layers. In the paper [4] experiments were carried out on these surfaces at atmospheric pressure, using FC-72 as the working fluid. The results showed that in comparison to the smooth surface, pool boiling heat transfer was significantly enhanced by the micro-pin-fin surfaces and the maximum superheat was considerably decreased
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