Research PaperThe mass transfer coefficient assessment and productivity enhancement of a vertical tubular solar brackish water still

•A novel vertical tubular solar brackish water still is described.•Mass transfer coefficients are calculated from the experimental results.•The maximum discrepancy is relatively small compared with previous study.•The maximum yield can reach 653.89 g/h at operation pressure of 75 kPa.

This paper presents an experimental investigation of a single-effect vertical tubular solar brackish water desalination device, with an aim to determine the mass transfer coefficient and its enhancement. The device consists of two closely spaced concentric pipes. The outside of the inner pipe is covered with a wicking material and wetted with hot brackish water. The water vapor evaporated from the wicking material condenses on the inside of the outer pipe. The measured productivity and temperatures at various points are given for different wicking materials thickness, water flow rates and chamber pressure under the condition of given heating power. Mass transfer coefficients are calculated from the experimental results and then applied in the prediction of water productivity. The maximum discrepancy between the calculation yield and measurement yield is relatively small compared with previous study. In addition, it was found that the yield of the solar still is 23.9% higher when the chamber pressure is lower by 25 kPa due to the enhanced mass transfer. Similar, doubling the ambient air velocity can increase the water yield by about 17.0%.