Experimental study on the effect of flow velocity on supersaturation and the visualization of mist generation of humid air fanned into the cooled chamber

Abstract

Mist and fog can form abruptly and locally in enclosed environments such as mountain roads, railway stations, and air-conditioned indoor arenas. This often leads to traffic delays and accidents due to reduced visibility. This study aims to predict the occurrence of mist formation due to heterogeneous spatial condensation based on ambient conditions such as temperature, relative humidity, and flow velocity. This study attempts to elucidate the influence of the flow velocity of humid air on mist formation through changes in light transmittance of the light-emitting diode (LED), temperature, relative humidity, and water vapor content. The experimental setup included two acrylic containers, each measuring 500 mm on a side, connected by a duct that could be opened. During the experiment, mist was generated and observed using a digital camera and LED light when humid air, heated to approximately 30 °C in one container, was fanned into another container cooled to 5-20 °C at a flow velocity of 0.5-1.8 m/s. The results led to the classification of mist generation into three states: thick, faint, and invisible. The transmittance of LED light and the water vapor content were found to be influenced by both the temperature and flow velocity in the cooled container. In particular, when the temperature difference between the heated and cooled containers was large, the flow velocity significantly affected the saturated vapor pressure in the cooled container, leading to supersaturation and prominent mist formation.