Investigation of thermodynamic process in a humidifier of humidification-dehumidification system based on a computational fluid dynamics model

Humidification-dehumidification is well-suited for solar-powered operation. Packed bed humidifier is an essential system component for water evaporation. Computational fluid dynamics (CFD) simulation of the packed bed humidifier is a challenging multiscale task. The simultaneous capture of micro flow properties and macro transfer performance by existing CFD models is inadequate. This paper presents a novel CFD model for a structured packed bed humidifier. The Eulerian method is applied to the multiphase flow and several simplified models are proposed to evaluate the influence of the microstructure on the transfer properties. The model can predict the overall transfer performance and partially reflect the micro flow characteristics. It is found that the air temperature increases rapidly when the packing height is < 0.3 m, while the liquid temperature decreases rapidly when the height is > 1.65 m or <0.45 m. Under different conditions, the outlet relative humidity of the air is all between 95 % and 99 %. The maximum evaluation error of gained output ratio of the humidification-dehumidification system can reach 10 % under the saturated air assumption. With a maximum of 10.85 % and a minimum of 3.46 %, the proportion of sensible heat transfer in the total energy transfer decreases with the packing height.