Impact of the surface enhancement on the heat transfer in a minichannel

Abstract

This paper presents results concerning flow boiling heat transfer in three parallel vertically oriented and asymmetrically heated rectangular minichannels. Each minichannel was 1.7 mm deep, 16 mm wide and 180 mm long. The heated element for Fluorinert FC-72 flowing in the minichannels was a thin alloy foil. Infrared thermography was used to determine changes in the temperature on the outer smooth side of the foil. Two-phase flow patterns were observed through a glass pane. The heated surfaces in contact with the fluid in the minichannels differed in roughness. In one minichannel the heated surface was smooth. In the other two, the heated surface was enhanced. Two types of surface enhancement were analyzed: a surface with unevenly distributed minicavities and a surface coated with metallic powder applied by soldering. This paper analyzes the effects of the microstructured heated surface on the heat transfer coefficient. The results are presented as relationships between the heat transfer coefficient and the distance along the minichannel length and as boiling curves. The experimental data obtained for the two types of enhanced heated surfaces was compared with the results recorded for the smooth heated surface. The highest local values of the heat transfer coefficient were reported for the enhanced foil with minicavities.