Effect of Cell Size of a Honeycomb Porous Plate Attached to a Heated Surface on CHF in Saturated Pool Boiling

Abstract

The critical heat flux (CHF) in a saturated pool boiling of water was investigated experimentally under the condition in which a honeycomb porous plate is attached to the heated surface. In a previous study, the CHF was shown experimentally to be approximately 2.5 times (approximately 2.51 MW/m2) compared to that of a plain surface for the case of a honeycomb porous plate with a vapor escape channel width of 1.4 mm and a channel height (plate thickness) of 1.0 mm (Mori and Okuyama (2009)). The enhancement is considered to result from the capillary supply of liquid onto the heated surface and the release of generated vapor through the channels. In the present paper, the vapor escape channel width was varied in the range of 1.4 mm to 7.9 mm, which was smaller than the Taylor instability wavelength (approximately 15.6 mm), and the effect of the channel width on the saturated pool boiling CHF of water has been investigated. The CHF values predicted by capillary limit models were compared with measured values. As a result, the main mechanisms for CHF enhancement using a honeycomb porous plate were shown to be due to liquid supply to the heated surface as a result of not only capillary suction but also the inflow of liquid through vapor escape channels from the top surface due to gravity. The ratio of the contribution in the mechanisms of the CHF enhancement was found to depend on the vapor escape channel widths. In particular, in the case of a larger cell width, the CHF was enhanced primarily due to the inflow of liquid through vapor escape channels from the top surface.