Effect of Decreasing Heat Transfer Surface Size on Boiling Heat Transfer

Abstract

Pool boiling heat transfer experiments were performed for small heat transfer surfaces at 0.101 MPa by using ethanol as test fluid. The test heat transfer surfaces were made of copper. The diameters of the heat transfer surfaces were 1.0, 2.0, 3.0, 5.0, 7.0 10.0 and 20.0 mm. When the heat flux was low, small isolated bubbles left from the heat transfer surface irrespective of size of the heat transfer surface. As the heat flux was increased, coalescent large bubbles were formed on the heat transfer surface in the case that the surface diameter was larger than 5.0 mm. Large bubbles left from place to place of the coalescent large bubbles on the heat transfer surface. In the case that the surface diameter was smaller than 3.0 mm, a single bubble stayed on the heat transfer surface and a single bubble periodically left form the bubble when the heat flux was increased to the middle and high heat flux region. As the diameter of the boiling surface became smaller, the boiling heat transfer was enhanced and the critical heat flux increased. The dependency of the critical heat flux on the heat transfer surface size was well correlated with the Ded and Lienhard relation developed for spheres.