In this paper, humidification process over a cross flow packed bed with an open air cycle is studied and a precision model is presented. Initial results show that air may become saturated with water vapor before leaving the packed bed. In this case excess water vapor condenses as mist in air stream that often is called supersaturated state. So the model was developed for both unsaturated and supersaturated states to predict accurately the outlet condition of the air and water streams. Then the model was validated by using experimental results obtained from an experimental facility. Comparison of the theoretical and experimental results confirms the ability of the supersaturated model at prediction of outlet condition of air and water streams. Effective parameters on development of supersaturated zone were studied. The proposed model can be used in designing HD desalination units and results better prediction of outlet condition of humidification process. (C) 2015 Elsevier B.V. All rights reserved.