Effect of condensing cover material on yield of an active solar still: an experimental validation

An attempt has been made to evaluate inner and outer glass temperature and its effects on yield. Numerical computations have been performed for a typical day in the month of December, 2005, for the climatic condition of New Delhi (latitude: 28E35N N; longitude: 77E12N E and an altitude of 216 m above mean sea level). Higher yield was observed for an active solar distillation system as compared to the passive mode due to higher operating temperature differences between water and inner glass cover. The parametric study has also been performed to find out the effects of various parameters, namely thickness of condensing cover, collector absorbing surface, wind velocity and water depth of the still. It is observed that there is significant effect on daily yield due to change in the values of collector absorbing surface, wind velocity and water depth. For all the cases, the correlation of coefficients (r) between predicted and experimental values have been verified and they showed fair agreement with 0.90 < r < 0.99 and root mean square percent deviation 3.22% < e < 22.64%. Effect of condensing cover materials, namely copper and polyvinyl chloride (PVC), on daily yield have also been investigated and compared.

The present study indicates the importance of the active distillation at lower water depth. Inner glass temperature plays a key role to determine the yield. The daily yield is more for active distillation as compared to passive mode using inner glass temperature. Yield is also directly related to thermal conductivity of condensing cover materials; copper gives a greater yield compared to glass and plastic due to higher thermal conductivity.