SUMMARY

Falling-film evaporators have several advantages over flooded evaporators, including high heat transfer coefficients, low liquid inventory, and low pressure drop. Several possible configurations for falling-film evaporators, based primarily on films falling over horizontal or vertical round tubes, have been investigated. However, falling-films over rectangular horizontal tubes have received little attention. An investigation of falling-film evaporation of water at sub-atmospheric pressures over horizontal, rectangular tubes is proposed. The study will include an evaluation of flow distributor performance, visualization of the falling-films with quantification of key characteristics, determination of local and global evaporation heat transfer coefficients, and modeling of the heat transfer phenomena. First, experiments will be conducted to quantitatively compare the performance of eight flow distributors with water at atmospheric pressure. Then, high-speed video recordings of water falling as films during evaporation over rectangular horizontal tubes with a cross-section of 27.4 mm × 1.42 mm will be taken, and the results quantitatively analyzed. Finally, heat transfer coefficients will be measured over saturation temperatures ranging from 10 to 30°C, heat fluxes ranging from 10 to 20 kW m^-2, Reynolds numbers ranging from 50 to 450, and tube spacings ranging from 5 to 15 mm. This information will be used to model evaporation heat transfer in such flows, which can be applied to a wide variety of applications such as refrigeration, process heat exchange, and distillation.