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The heat transfer characteristics of steam condensation flow in a vacuum horizontal long tube were studied experimentally when the saturation temperature varies from 50 to 70°C,mass flow rate is no more than 11 kg/(m 2 •s) and temperature differences between steam and cooling water are 3, 5 and7°C respectively. The results of experiments indicate that the steam temperature decreasesand the condensation temperature difference decreases first and then increases along the flow direction. The effects of mass flow rate and total temperature difference on temperature distribution are also discussed in the paper. The condensation heat transfer coefficient increases first and then decreases along the flow direction. The heat transfer coefficient increases with mass flow rate in most cases, but may decrease in the first section at high mass flow rate. The heat transfer coefficient also increases with saturation temperature and decreases with condensation temperature difference. The heat transfer rate decreases along the flow direction and increases with mass flow rate.

A B S T R A C TThe horizontal-tube falling film evaporation is a widely adopted technique in multiple-effect distillation desalination plant. It has a high heat transfer coefficient under quite small temperature difference. In this paper, an experimental equipment for horizontal-tube falling film evaporation was set up. Experiments were carried out to show how the heat transfer coefficient is affected by different parameters including heat flux, circumference direction of tubes, spray density, evaporation temperature, and experimental fluid. Results indicate that the heat transfer coefficient decreases after a little increase with growth of spray density. The heat transfer coefficient decreases along the tube circumference, but at the bottom of the tube, it shows increasing trend. In addition, a simple comparison between seawater and fresh water in heat transfer coefficient is also provided.