Numerical investigation on supersaturation phenomenon of humid air in the humidification process

Abstract

In order to improve the safety and stability of pneumatic equipment, in this paper, the supersaturation phenomenon of humid air and its formation, evolution mechanism during the humidification process, are revealed and evaluated in detail with the defined evaluation criterion. In term of the finite difference method, the integrated mathematical models for humidification process are established, considering the unsaturated, saturated and supersaturated state of humid air. The influence laws of the specified critical parameters on the supersaturation characteristics of humid air are obtained at off-design conditions. The simulation results first reveal that the effects of specific surface area of porous media on the supersaturation phenomenon is affinitive with the liquid-gas ratio. It is found that a lower value both of inlet water temperature and inlet relative humidity will slightly weaken the entrainment ratio, while the inlet air temperature has a significant reaction to it, with a minimum value of 1.5 × 10−3 kgkg−1 at the conditions of Twi = 70°C, φi = 0.5 and Tai = 30°C. It is also obtained that raising the inlet wet-bulb temperature is effective to reduce the entrainment ratio. Furthermore, in the process of the development of supersaturation phenomenon, the entrainment ratio increases rapidly at the humid air outlet for all the cases, which are of great value for humidity control in aerodynamic systems.