Distribution characteristics of falling film thickness on horizontal tube evaporators

The aim of this study is to examine experimentally the thickness variations of a falling film on plain and hydrophilic horizontal tube evaporator surfaces in order to enhance the performance of the horizontal tube evaporators. The hydrophilic surfaces are acquired by exposing them to plasma irradiation for a 120 s time period. A test loop has been installed, and by using electrical film thickness measuring devices, the distributions of the formed liquid thickness layer around the hot plain and hydrophilic surfaces are determined at different operating conditions. By analyzing the experimental data, the present results show that the film thickness around the hydrophilic tube changes with the same pattern around the plain tube. The film distribution along the peripheral angle is non-symmetrical, minimum film thickness values are more likely to appear at a different angular position of 90 degrees-120 degrees under various conditions. The film thickness is significantly decreased for hydrophilic surfaces. The film thickness mainly increases as the flow rate increases, while it decreases as the tube diameter increases, the evaporation pressure increases, the inlet water subcooling increases, and tube surface temperature increases. The feeder height has a minor influence on the film thickness. Comparison between the current results and results acquired by another researcher is in good agreement between 2.0% and 18%.