Critical Heat Flux on a Horizontal Plate in Saturated Pool Boiling at High Pressure

Abstract

Observation of boiling behavior and measurement of critical heat flux (CHF) were carried out for saturated water boiling on a horizontal, upward-facing plate at pressures from atmospheric to 7 MPa. The heating surface was made of nichrom with 20μm in thickness, 4 mm in width, and 27.5 mm in length. The primary bubbles diminish in size approximately with the inverse of the pressure and commence to coalesce in the very low heat flux region to form coalesced bubbles. The detached coalesced bubbles continuously increase in size with increases in the heat flux and grow to about 10 mm in equivalent diameter even at high pressure of 5 MPa. Detachment frequency of the coalesced bubbles was insensitive to the heat flux and pressure. The CHF was predicted based on the macrolayer dryout model where an empirical correlation of detachment frequency derived in the present paper and a correlation of macrolayer thickness previously proposed by the author and a coworker were used. The predicted CHF agrees fairly well with the measured values.