Evaluation of Modification Priestley - Taylor and Penman Models Radiation Component to Estimate Evaporation from Solar Stills

The more accurate estimate of evaporation in Solar Stills is considered as an important step in the planning and design of condensation irrigation system in hot and dry region. Since received radiation to evaporation surface is different inside and outside the Still، to initial estimate of evaporation in Stills، can not apply the commonly techniques used in open surface water. The main purpose of this study is modification of Penman model (as a compound and base model to estimate evaporation from open surface) radiation component and Priestley – Taylor model (as a recommended radiation model for estimating evaporation from closed environments such as greenhouses) to estimate the evaporation rate from the Solar Stills. Comparison of measured and estimated values over the one-year period of the study showed that modification the radiation component have a positive effect in more accurate estimate of evaporation from Solar Stills. The results showed that the modified Penman model is capable of estimate evaporation from Still with R2 0. 950، MBE= 1. 116 (mm/day) and RMSE=1. 258 (mm/day).