Phenomenological modeling of quenching during falling liquid film cooling of high-temperature wall

Abstract

The wetting velocity that is the propagation velocity of a liquid film falling along a high temperature wall is of considerable importance in a variety of technical applications such as emergency core cooling in nuclear power plant, heat exchangers, and metallurgical processes. To predict the wetting velocity, the quenching model that consists of the heat transfer coefficient (HTC) distribution and the quenching temperature is needed. Since direct measurements of these quantities were technically difficult, most of the existing quenching models were developed so as to match the calculated wetting velocity with the experimental data. It was therefore unknown if the existing models can be applied to the conditions under which their predictive performance was not tested. In this work, to develop a new quenching model that is applicable in wide range of experimental conditions, transient of the wall temperature profile during quenching was measured using a high-speed infrared camera. A silicon wafer that was transparent against infrared rays was utilized as the wall. In addition, a normal high-speed camera was used to understand the hydrodynamic phenomena encountered during quenching. As a result, it was found that nucleate boiling in the liquid film was the main heat transfer mechanism near the wetting front and the width of the area where significant heat transfer occurred was in the same order of magnitude as the size of nucleation bubbles. Based on these findings, a phenomenological quenching model was developed. It was shown that the present model predicts the wetting velocity more accurately than the existing ones not only for the present data but also for those accumulated in different conditions. It was hence considered that the present model well describes the thermal-hydraulic phenomena encountered near the wetting front during quenching.