On the oscillatory nature of heat transfer in steady annular flow

Using a combination of high-speed infrared thermography and electrical-conductance sensors, we observe the surprisingly large effect of surface waves on the instantaneous heat transfer response at the heated wall in nominally-steady upward annular flow of steam-water mixtures. While the heat flux applied at the wall is constant, the passage of the waves causes significant periodic oscillations of the local heat transfer coefficient and wall superheat in the forced convective evaporation regime, with amplitudes and periods much higher than the fluctuations due to turbulent eddies. We discuss the physical mechanisms potentially responsible for the experimental observations.