Abstract
Complex experimental investigations were conducted in the area of pool boiling heat transfer on extended surfaces with internal tunnels limited by perforated foil. The experiments were carried out for water and R-123 at atmospheric pressure. The tunnel surfaces were fabricated from 0.05 – 0.1 mm thick perforated copper foil (pore diameters: 0.3, 0.4, 0.5 mm) sintered with mini-fins formed by 5 and 10 mm high rectangular fins and horizontal inter-fin surface. The effect of the main fin height, pore diameters and tunnel pitch on nucleate pool boiling was examined. Substantial enhancement of heat transfer coefficient was observed for the investigated surfaces. The highest increase in the heat transfer coefficient was obtained for the 10 mm high fins – about 50kW/m 2 K for water and 15 kW/m 2 K for R-123. The investigated surfaces showed boiling heat transfer coefficients similar to those of existing tunnel-pore structures.
Highlights
The trend toward miniaturization of mechanical and electronic equipment components is the driving force behind ever better cooling technologies designed to prevent exceeding maximum allowable operating temperatures
There are a variety of passive and active methods of boiling heat transfer enhancement – this paper focuses on the system of subsurface mini-tunnels restrained by a porous structure in a form of perforated foil
Wider pitch reduces the number of tunnels but the walls separating the tunnels are thicker, which results in lower temperature drop along the main fins height and higher superheat at the fin tips, the bubbles departure site
Summary
The trend toward miniaturization of mechanical and electronic equipment components is the driving force behind ever better cooling technologies designed to prevent exceeding maximum allowable operating temperatures. Nakayama et al [2] used tunnels of rectangular cross-sections with triangular pores They found that the surface pores of about 0.1 mm in size (equivalent to inscribed circle diameter) gave the best heat transfer enhancement for the boiling of water, R-11 and liquid nitrogen. The best results were obtained for fins of 1.5 mm pitch, 0.7 – 1.0 mm height and foil holes diameters of. The reverse was true for R-123: the best surfaces were those with perforated foil and hole diameters of 0.4 and 0.5 mm
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