Experimental study of pool-boiling CHF on small plate : effects of surface inclination angle and size

Abstract

Considerable experiments and analytical works have been devoted to investigate pool-boiling CHF in various conditions. In addition, several mechanistic models have been suggested for the prediction of the CHF at infinite horizontal upward facing plate: these models have been continuously modified as progress has been made in understanding the physical mechanisms leading to CHF. Recently, pool boiling CHF conditions at inclined heated surface and curved surface have appeared and been highlighted with respect to practical applications. Although a few experimental studies have been conducted as a result of requests from the industry, the understanding has lagged behind concerning CHF behavior with inclination angle, the effect of size on CHF and phenomenological information related to bubble behavior at inclined plates. In the present study, to identify CHF behavior for different inclination angles as well as the effect of size on CHF, pool-boiling experiments were conducted with small flat plates submerged in a pool of saturation water. The experiments were performed at 7 different inclination angles (0˚; horizontal downward facing plate, 30˚,60˚,90˚,120˚,150˚&180˚; horizontal upward facing plate) using 6 different test sections (width: 3 cm & 4 cm, length: 10cm, 15 cm & 20 cm). The CHF generally increased with increases in inclination angle and a transition angle, at which CHF increase rate with inclination angle suddenly changed, was identified between 0˚$ and 30˚: CHF sharply increased up to the transition angle and increased gradually beyond that angle. Considering present experimental results and previous studies, the transition angle must be affected by, and increased with the increase in the characteristic length (diameter in disc test section and width in plate test section). In addition, CHF values of the 30˚ inclined plates were higher than those of the 60˚ inclined plate. The effects of width and length were noticeable in the W4 series (W4L10, W4L15 &...