Investigation on wave morphology and temperature distribution of falling liquid film in a vertical tube

Abstract

The waves of the falling liquid film have a strong interaction with its temperature, and the flow and heat transfer mechanisms contained therein are of great significance for optimizing industrial equipment and improving energy efficiency. In this paper, the thickness and temperature field of the liquid film in a vertical tube were measured simultaneously based on planar laser-induced fluorescence (PLIF). The wave morphology, as well as the temperature distribution within the liquid film, was analyzed by high-speed imaging visualization and the film temperature extraction method, respectively. With the increase of the Reynolds number, an evolution of the wave morphology from ripples to high-frequency disturbance waves and finally to solitary waves was observed. The method of Dynamic Mode Decomposition (DMD) was developed to reconstruct the flow field and calculate the characteristic frequencies in the flow, from which the wave features under different wave morphologies were revealed. It was found that the temperature variation of the liquid film at the gas-liquid interface was accelerated by the waves from the results of the temperature distribution of the liquid film. Besides, the low-temperature micro clusters observed in the solitary waves can be considered as one mechanism of the enhancement of heat transfer in the liquid film.