Enhancement of Heat Transfer during Nitrogen Boiling on Capillary-Porous Coatings under Conditions of Intense Mass Forces at High-Speed Rotation of Cryostat

Abstract

This article presents the results of experimental studies of the efficiency of heat transfer under conditions of intense fields of mass forces on a flat rectangular (\(16 \times 24\) mm²) heat-transfer surface (HS) modified by additive manufacturing. A porous sinusoidal-form coating consisting of spherical bronze granules of average diameter of 35 \(\mu\)m was 3D printed on the brass base of the heat-transfer unit. The thickness of the coating was 150 \(\mu\)m in the deepenings and 300 \(\mu\)m on the ridges. Comparative experimental studies were carried out on an unmodified HS and modified HS in liquid nitrogen under conditions of centrifugal accelerations of up to 4090 g. The heat transfer was studied in the range of heat flux densities of \(4 \cdot 10^{4}{-}8.9\cdot 10^{5}\) W/m². It has been shown that in the range of heat flux densities of \(80,000<q< 320,000\) W/m², increase in the intensity of the mass force fields leads to growth in the heat transfer coefficient up to 4 times at transition from the developed boiling regime to the single-phase convection regime. In the region of developed boiling, for the heat flux density range corresponding to a given overload, the heat transfer coefficient normalized to the value of the heat transfer coefficient calculated as per the Borishansky relation for these conditions decreases with increasing centrifugal overload. The dependence of the relative heat transfer coefficient on the overload is close to the ratio \(\alpha_{\rm s}/\alpha_{\rm sB} \sim \eta^{-1/6}\).