This paper focuses on the design and modeling of the humidification dehumidification desalination (HDH) process. The process is only found on experimental or very small pilot scale. Literature studies are rather limited and it includes a number of experimental investigations, performance evaluation, and measurements of the heat and mass transfer coefficients. This study includes useful and new data on the evaluation of the heat transfer coefficient of the humid air stream in the condenser unit. The analysis develops a correlation for the heat transfer coefficient for the humid air stream as a function of the Reynolds and Prandtl numbers. Also, detailed evaluation of the system performance is presented as a function of the system temperatures and the inlet relative humidity of the air stream. Results are presented for variations in the humidifier height, heat transfer area of the condenser, flow rate of cooling water, performance ratio (defined as kg of product water per 1 kg of heating steam), and flow rates of the air and water streams. Results show the need for further system optimization through experimental measurements and mathematical modeling to determine the design and operating conditions that provides the lowest unit product cost. (c) 2008 Elsevier B.V. All rights reserved.