Numerical and experimental study on internally cooled liquid desiccant dehumidification concerning film shrinkage shape and vapor condensation

Falling film has been observed to shrink along its flow direction in a plate dehumidifier. The shrinkage of film reduces the absorption contact area and hence deteriorates the mass transfer performance. Another interesting phenomenon has also been observed, and the condensation of water vapor would occur on the non-wetted area in an internal cooling dehumidifier with a low cooling water temperature. Nevertheless, the film shrinkage and vapor condensation during the dehumidification process were seldom reported. This study developed a new model with the consideration of both the above two factors and phenomena. Besides, a new Sherwood number correlation was proposed based on the experimental data. The influences of different parameters on dehumidification performance were identified. The results indicated that the new model is able to predict the film shrinkage accurately with the average relative wetting ratio difference less than 4%, and the proposed Sherwood number correlation has high prediction accuracy with the mean absolute relative deviation of 7.1%. Then, the weather data of a typical summer day in Hong Kong was chosen to evaluate the influence of vapor condensation. It was found that compared with the situation without condensation, the relative increment of absolute moisture change ranges from 1.2% to 10.7% when concerning vapor condensation. The increment is closely related with the cooling water temperature and air humidity. In the typical summer day, the absolute moisture change has a relative 6.3% increment with the consideration of vapor condensation under certain operating conditions.