Spiral multiple-effect diffusion solar still coupled with vacuum-tube collector and heat pipe

A novel solar still with spiral-shape multiple-effect diffusion unit is developed in the present study. The test results of a 14-effect unit coupled with vacuum-tube solar collector (absorber area 1.08 m2) show that the highest daily pure water production is 40.6 kg d− 1. The measured highest productivity based on the area of glass cover, solar absorber, and evaporating surface is 34.7, 40.6, and 7.96 kg m− 2 d− 1, respectively, which are much higher than the published results. The measured solar distillation efficiency is 2.0-3.5. The performance enhancement results mainly from the lateral diffusion process in the spiraled still cell. The vapor flow generated by heat input can flow freely and laterally through the spiral channel down to the end when solar heat input is high. Besides, the larger evaporating and condensing area at the outer cell may increase heat and mass transfer at the outer cell.