Unexpected heat transfer oscillations in steady annular flow detected by synchronized infrared and liquid film sensor measurements

Abstract

Simultaneous measurement of liquid film characteristics and heat transfer in annular two-phase flow is a major experimental challenge. In this study, we implement an innovative integrated infrared (IR) heater and liquid film electrical-conductance sensor in combination with high-speed IR thermography, which results in an accurate, synchronized and co-located measurement of liquid film characteristics and local heat transfer at the heated surface in diabatic annular two-phase flow. The measurements reveal that disturbance waves have a significant effect on the instantaneous heat transfer response in nominally-steady vertically upward annular flow of steam-water mixtures. Although the heat flux applied at the wall is constant in time, the passage of the waves causes significant periodic oscillations of the local heat transfer coefficient and wall superheat in the forced convective evaporation regime, which are reported in this study.