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ISSN Online: 2377-424X

ISBN Print: 978-1-56700-421-2

International Heat Transfer Conference 15
August, 10-15, 2014, Kyoto, Japan

Effect of Heat Transfer Surface Structure on Boiling Heat Transfer and Flow Characteristics in a Horizontal Narrow Channel

Get access (open in a dialog) DOI: 10.1615/IHTC15.fbl.009840
pages 2723-2734

Sinopsis

Higher performance cooling device is required for temperature control of electronic devices and equipments. A two-phase flow loop type thermal control system has attracted attention. Requirements on the heat transfer performance in the cold plate are reduction of temperature difference in heat transfer by boiling heat transfer enhancement, increase in critical heat flux, and improvement in responsibility when an electronic device starts operation. One important aspect of boiling heat transfer enhancement is to increase the number of active nucleation sites for a given wall superheat or heat flux, and another is departure frequency of vapor bubbles from the heating surface. Porous structure on heat transfer surface is considered to be effective, and reported that such structure improved boiling heat transfer coefficient. Asano, et al.[2011, Proc. of 23rd IIR Int. Congress of Refrigeration, paper No. 644] applied thermal spray copper coating on copper heating surface in a horizontal narrow channel, and boiling experiments were carried out for forced convective heat transfer using HCFC-123 as the refrigerant. In their report, boiling heat transfer could be quite enhanced in nucleate boiling. However, deterioration in heat transfer coefficient was observed under the condition of high heat flux and high quality. Since the deteriorated heat transfer coefficient was still higher than that for the smooth surface, they concluded that the deterioration was caused by a boiling mode transition from nucleate boiling to forced convective evaporation. The main purpose of this study is to clarify the boiling flow structure for the heating surface with a thermal spray coating. A test channel with the width of 20 mm, the length of 300 mm, and the height of 4 mm was placed horizontally. The bottom surface with the length of 100 mm in the center of the channel was replaced by a copper block for the heat transfer surface. Thermal spray coating was manufactured on the heating surface. The heat transfer performance was measured in saturated flow boiling experiments of FC72. Liquid holdup was measured by a capacitance method simultaneously. The relationship between heat transfer and liquid hold-up characteristics is examined for varied heat flux and vapor quality, and these results are compared with those for adiabatic flows. Moreover, these resuts are also compared with those for a smooth surface to consider the effect of boiing heat transfer enhancement on the liquid hold-up characteristics.