Investigation of Temperature Field of Falling Film Based on Planar Laser-Induced Fluorescence

Falling film is widely applied in the industry due to its efficient heat and mass transfer. The temperature field distribution is essential for the research of heat transfer characteristics and mechanisms. However, few studies have been conducted on the temperature field measurement of the falling film in the pipe. In this paper, the reasons for the distortion of fluorescence intensity in the flow and radial directions are investigated for falling water film. A fluorescence intensity-temperature calibration curve is fitted with Gaussian compensation and exponential attenuation compensation for global temperature visualization. The falling water film thermal characteristics are analyzed qualitatively, demonstrating that the relationship between interface temperature and film thickness is not exactly inverse but rather shifts in phase. Moreover, combining the temperature distribution with the liquid film flow topology, two potential hydrodynamic behaviors are interpreted. In the combination between the disturbance wave and base film, the high-temperature liquid flows rapidly from the base film to the colder wave peak. Whereas in partially isolated waves, the internal flow circulation in the wave front drives the homogeneous mixing of local temperature.