Extended experimental investigation of a double-effect active solar still with a paraffin wax, in Owerri, Nigeria

In this work, an experiment-based study of a double-effect, single-slope active solar still (SSASS) is presented. The system comprises an upper and a lower basin incorporated with a paraffin wax acting as a phase change material (PCM). The use of phase change materials is very important due to their high storage density and the isothermal nature of the storage pro-cess. Paraffin wax was selected based on its attractive thermo-physical properties. The thermal behaviours of the system during the diurnal and nocturnal phases in both compartments were explored. Experimental results showed that the upper basin’s yield contributed more to the overall distillate production over a 24-hour cycle while that of the lower basin predominated the diurnal production. Though the PCM served as an energy source during the nocturnal phase, it did not translate to significant improvement in the yield of the lower basin. The heat retention ability of the lower glazing retarded the condensation of the humid air in the lower compartment during the off-sunshine period. Thus, the nocturnal yield of the system was largely driven by the improved temperature difference between the upper saline water and the upper glazing, as well as the stored thermal energy in the saline water mass before sunset. The system achieved a maximum yield of 2,450 ml/day and a yield rate of 232.5 ml/h. A maximum monthly average yield of 1,787 ml/day was realized in May and a minimum of 692 ml/day in July. Nocturnal distillate production accounted for an average of 55% of the total distillate recovered from the still daily. The system achieved an efficiency range of 12.20 - 32.21%. The cost of freshwater production from the system is estimated at 0.0508 $/L with a payback period of 267 days. Thus, this system is economically viable and suitable particularly, for low-income earners.