Characteristic analysis of heat and mass transfer process within structured packing humidifier

Humidifiers are the important devices for humidifying the air both in life and industrial production. This paper focuses on the heat and mass transfer processes inside the counter-flow packing humidifier at atmospheric pressure. Based on mass and energy balance, the mathematical model for the humidifier is established. The finite difference method is first adopted to calculate the specific scales of the packing and the relevant state distribution of the gas–liquid species at on-design conditions. Thus, the heat and mass transfer performance of the humidifier is also carried out at off-design conditions. The simulation results show that the required packing height at the design parameters is 3.38 × 10−1 m, while the supersaturation phenomenon begins at Z = 5.76 × 10−2 m, and the humidity ratio and supersaturated humidity ratio at humidifier outlet are 1.69 × 10−1 kg/kg and 1.64 × 10−3 kg/kg, respectively. In addition, for off-design analysis, as the liquid–gas ratio increases, the outlet water temperature and outlet air temperature increase by 14.3% and 7.47%, respectively, and the humid air reaches saturation earlier as the saturation point falls from 5.76 × 10−2 to 2.7 × 10−2 m. Within the range of the simulation conditions, the maximum account of droplets entrained in the humid air reaches 1.72 × 10−3 kg/kg, while the total packing pressure drop increases with the decrease in liquid–gas ratio. The effect of liquid–gas ratio and wet-bulb temperature of inlet air on the humidifier under design parameters can provide great reference significance for the design, optimization and regulation of humidifiers.