Effects of Non-Darcian and Inlet Conditions on the Forced Convection Along a Vertical Plate With Film Evaporation

Abstract

The present study analyzes theoretically the non-Darcian effects and inlet conditions of forced convection flow with liquid film evaporation in a porous medium. The physical scheme includes a liquid–air streams combined system; the liquid film falls down along the plate and is exposed to a cocurrent forced moist air stream. The axial momentum, energy, and concentration equations for the air and water flows are developed based on the steady two-dimensional (2-D) laminar boundary layer model. The non-Darcian convective, boundary, and inertia effects are considered to describe the momentum characteristics of a porous medium. The paper clearly describes the temperature and mass concentration variations at the liquid–air interface and provides the heat and mass transfer distributions along the heated plate. Then, the paper further evaluates the non-Darcian effects and inlet conditions on the heat transfer and evaporating rate of liquid film evaporation. The numerical results show that latent heat transfer plays the dominant heat transfer role. Carrying out a parametric analysis indicates that higher air Reynolds number, higher wetted wall temperature, and lower moist air relative humidity will produce a better evaporating rate and heat transfer rate. In addition, a non-Darcy model should be adopted in the present study. The maximum error for predictions of heat and mass transfer performance will be 21% when the Darcy model is used.

Acknowledgments

Jin-Sheng Leu is an associate professor of aircraft engineering at Air Force Institute of Technology, Kaohsiung County, Taiwan. He received his Ph.D. in mechanical engineering from National Cheng-Kung University, Tainan, Taiwan, in 1994. His main research interests are heat transfer enhancement techniques (including active and passive techniques), liquid film evaporation application, and flow stability analysis.

Jiin-Yuh Jang is a distinguished university professor of mechanical engineering at National Cheng-Kung University, Tainan, Taiwan. He received his Ph.D. in mechanical engineering from the State University of New York at Buffalo, USA, in 1983. His research interests include heat exchanger CAD design, numerical and experimental studies of heat exchangers, energy conversion, and air conditioning fields. He is also an ASHRAE (American Society of Heating, Refrigeration and Air-conditioning Engineers) fellow.

Wen-Cheng Chou is a former M.S. graduate student (2009) in the Department of Mechanical Engineering, National Cheng-Kung University, Tainan, Taiwan. He received his B.S. degree from the Department of Mechanical Engineering, Chung Yuan Christian University, Chung Li, Taiwan, in 2007.