The Effect of Coalescent Vapor Bubbles Formed on a Honeycomb Porous Plate on the CHF in a Saturated Pool Boiling

Abstract

The critical heat flux (the CHF) in a saturated pool boiling of water was investigated experimentally under the attachment of a honeycomb porous plate on the heated surface. In the previous study, the CHF was shown experimentally to be enhanced to more than double that of a plain surface. According to the proposed capillary limit model, the CHF can be increased by decreasing the thickness of the honeycomb porous plate. However, the CHF could not be greatly enhanced under the condition that the thickness of the honeycomb porous plate was comparable to the thickness of the macrolayer formed beneath vapor masses. As a result, it was found that honeycomb porous plates should be composed by the superposition of two kinds of porous materials and each of the honeycomb porous plates must fulfill the following conditions for CHF enhancement in a saturated pool boiling. First, a honeycomb porous plate, installed just on the heated surface, has very fine pores to supply water to the heated surface by strong capillary action, and the thickness of it should be as thin as possible to decrease the pressure drop caused by water flow inside the honeycomb porous plate. Second, the other honeycomb porous plate , placed just on the honeycomb porous plate stated above , is structured to hold a sufficient amount of water in order to prevent the inside of the honeycomb porous plate from drying out during a coalescent vapor bubble staying on a honeycomb porous plate .