The evaporation of a saturated porous layer inside an inclined airflow channel Yin Chou, Ruey-Jen Yang * Department of Engineering Science, National Cheng Kung University, 1 University Road, Tainan 70101, Taiwan Received 24 November 2005; received in revised form 3 March 2006; accepted 21 April 2006 Available online 24 July 2006 Abstract This study investigates the enhancement in the heat and mass transfer of liquid film evaporation obtained by introducing a liquid- saturated porous layer within an inclined flow channel. The liquid and air streams are modeled as two coupled laminar boundary layers incorporating non-Darcian models of the inertia and boundary effects and the numerical solution is obtained by means of a fully implicit finite difference method. The effects of the porosity (e), porous layer thickness (d), inclined angle (u), ambient relative humidity (/) and Lewis number (Le) on the average heat and mass transfer performance are thoroughly examined. It is found that the porous layer enhances the heat and mass transfer performance. Specifically, the numerical results indicate that the average Nusselt number (Nu) and the Sherwood number (Sh) both increase with increasing u, with decreasing e and d .The increase in / results in the decreasing in Nu and increasing in Sh. Additionally, the influence of the porosity (e) on the heat and mass transfer performance becomes more sig- nificant as the thickness of the inclined angle (u) decreases. Ó 2006 Elsevier Inc. All rights reserved. Keywords: Liquid film evaporation; Porous medium; Heat and mass transfer 1. Introduction Liquid film evaporation is an effective latent heat trans- fer mechanism widely utilized in the field of energy for many different applications, including chemical distillation, air conditioning, cooling towers, drying, desalination, and so forth. The physical scheme for liquid film evaporation consists of a thin liquid film flowing down a heated plate, with the liquid film exposed to a forced air stream. Since part of the liquid evaporates into the air stream, liquid film evaporation has a high heat transfer coefficient, low feed rates and another specific advantage of liquid film evapora- tion. However, conducting a theoretical analysis of the liquid film evaporation problem is complicated because the transport phenomena involve coupled heat and mass transfer at the liquid film-air interface. Previous studies generally examined the liquid film evap- oration problem using simplified 1-D or 2-D mathematical models. For example, a 1-D model was used to develop the governing equations for mass, mass species, momentum and energy conservation by applying the conservation laws to control volumes of the liquid film and the moist air (Maclaine-Cross and Banks, 1972, 1981; Wassel and Mills, 1987; Peres-Blanco and Bird, 1984). Maclaine-Cross and Banks (1972, 1981) analyzed the heat and mass transfer characteristics in a wet surface heat exchanger. Their theo- retical results were found to be 20% higher than the corre- sponding experimental data. Wassel and Mills (1987) presented a 1-D design methodology for a counter-current falling film evaporative cooler. Their results indicated that narrow flow passages were more effective than conven- tional designs in improving the thermal performance of the evaporative condenser. A 1-D model of heat and mass transfer in a vertical single-tube exchanger was formulated by Peres-Blanco and Bird (1984). Early studies using 2-D models to investigate heat and mass transfer in an air 0142-727X/$ - see front matter Ó 2006 Elsevier Inc. All rights reserved. doi:10.1016/j.ijheatfluidflow.2006.04.007 * Corresponding author. Tel.: +886 6 200 2724. E-mail address: rjyang@mail.ncku.edu.tw (R.-J. Yang). www.elsevier.com/locate/ijhff International Journal of Heat and Fluid Flow 28 (2007) 407–417