Experimental investigations of solar desalination unit based on humidification and dehumidification processes are presented in this work. The test rig is designed, constructed, and tested. The experiments were tested at Baghdad University, college of engineering, Mechanical engineering department (33.3° latitude north, 44.36° Longitude East). The effects of Linear Fresnel Lenses have been studied in this work. Different cases are investigated such that: they were placed on the 3rd and 4th absorbers of the PTC, they were placed on the humidifier chamber and they were placed on the 2nd and 3rd absorbers of the PTC. when lenses were placed on the humidifier to concentrate solar energy on the transparent glass cover the absorber surface temperature was increased by 8.2 % at 14:00 pm, the inlet temperature of the oil was increased by 7.1 % while the outlet oil temperature was increased by 14 % and water production is increased as (31.2 %) at 14:00 pm is higher than that when these lenses were placed on absorbers