Study on heat and mass transfer distance of water-film evaporation in limited space using dual-wavelength digital holographic interference

Abstract

To study the heat and mass transfer between evaporating water film and air in limited space, the temperature and humidity distributions of air near the flowing water film were measured using dual-wavelength digital holographic interference (DHI). The holograms were recorded by CMOS with two different wavelengths of 532 nm and 671 nm. We derived the relationships between the phase changes reconstructed from the holograms and the air temperature and humidity changes based on the Edlen formulas. A water film evaporation (WFE) model was built to generate steady water film and demonstrate the heat and mass transfer in air countercurrent to the water film, which flows down on the copper plate. The model has two symmetrical tunnels isolated by a copper plate in the middle, allowing to compare the cases of heat and mass transfer with and without evaporation. The measurement precision is checked by comparing the reconstructed results with the sensor measured values and by calculations of heat balance and dimensionless Nusselt and Sherwood numbers. Based on the measurement results, the concept of feature transfer distance (FTD), is proposed, which characterizes the intensity of heat and mass transfer. By analyzing FTD, the main influencing factors of heat and mass transfer were obtained.