A model of combined boiling and evaporation of liquid films on horizontal tubes was developed. Specifically, this work was directed toward developing a heat transfer model applicable to the design of horizontal tube falling film evaportors for OTEC. The heat transfer process is modelled as combined boiling and evaporation of the liquid film. In modelling the behavior of single tubes special account is taken of heat transfer in the initial thermal developing region of the film. Predictions were found to agree favorably with the published experimental data for boiling and evaporation of thin water films on single horizontal tubes. The predicted upper and lower limits of heat transfer for ammonia on a vertical bank of plain horizontal tubes are 5.4 kW/m2-K and 3.1 kW/m2-K, respectively. The upper limit will be approached when the influence of between-tube evaporation and turbulence created by the liquid falling from one tube to the next are important. For an OTEC evaporator with plain tubes, the upper and lower limits of the overall U are 2.33 kW/m2-K and 1.82 kW/m2-K, respectively. With ammonia-side boiling enhancement, the overall U can be increased to about 3.8 kW/m2-K.

Heat and mass transfer is the core science for many industrial processes as well as technical and scientific devices. Automotive, aerospace, power generation (both by conventional and renewable energies), industrial equipment and rotating machinery, materials and chemical processing, and many other industries are requiring heat and mass transfer processes. Since the early studies in the seventeenth and eighteenth centuries, there has been tremendous technical progress and scientific advances in the knowledge of heat and mass transfer, where modeling and simulation developments are increasingly contributing to the current state of the art. Heat and Mass Transfer - Advances in Science and Technology Applications aims at providing researchers and practitioners with a valuable compendium of significant advances in the field.