1.3. Different geometry
On the other aspect to reduce the initial cost a new geometry on the solar still were discussed by, R.Sathyamurthy et al [19]–[21] , Arunkumar et al [22], [23] and Ahsan et al [25]–[28].
1.3.1. Triangular pyramid
Ravishankar et al [19],investigated the various factors that affecting fresh water production in a triangular pyramid solar still. It has been reported that the depth of water and wind velocity over the solar still are the major parameter which will affect the fresh water production. Also it has the concluded that, at minimum depth of water the productivity is higher and with higher wind velocity improves the temperature difference. Ravishankar et al [20] investigated the performance of solar still at minimum water depth. It has been concluded that the accumulated yield of 4.2 kg/m2day was achieved for the experimental days. Ravishankar et al [21], experimentally investigated the effect of introducing phase change material on a triangular pyramid solar still for fresh water production for summer and winter condition. The effect of introducing PCM increased the efficiency by 35% than a conventional solar still. Also the fresh water production during summer and winter were found to be 4.5 and 3.4 kg/m2day respectively.
1.3.2. Pyramid type
Y. Taamneh and M. M. Taamneh [24], investigated the utilization of forced convection over the glass surface. The cooling of glass surface is done with a help of DC solar powered forced draught fan. The productivity of forced convection is increased by 10.81% than that of free convection. The accumulated yield of natural and forced convection pyramidal solar still is found to be 3.3 and 3.7 kg/m2day respectively.
1.3.3. Tubular
Ahsan et al [25]–[28], experimentally ...
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...en cover and ambient
The radiative heat transfer outside the solar still is a function of sky and glass temperature. The sky temperature is give as a function of ambient temperature, which is expressed as,
Radiative heat transfer rate is given by,
Substituting (20) in (19), which gives,
2.2. Energy balance
2.2.1. Energy balance of outlet water temperature
And the heat lost from the basin to the surroundings was neglected as it is assumed in section 2.
From the above equation,
And the average water temperature in the solar still can be expressed as,
2.2.2. Energy balance of glass surface
Heat energy absorbed by glass + Heat liberated by vapor inside the still = Heat lost due to convection and radiation by the outside glass surface
Fig.1 shows the schematic energy balance in the solar still. Table. 1 describes the physical properties used for mathematical modelling.