Energy, exergy and economic analysis of a novel immersion tapered solar still for combination with solar concentrator

The methods of strengthening moisture condensation rate of solar still will make its structure complicated. Here, a novel immersion tapered solar desalination device composed of a solar concentrator and a tapered solar still in this paper, which can easily achieve condensation enhancement by water cooling. The heat and mass transfer characteristics of the tapered solar still is assessed experimentally and theoretically, and the mathematical models of energy transfer and exergy destruction in the still are established to analyze various aspects of its performance including yield, energy, exergy and economics. The results show that the calculated values of the mathematical model are in good agreement with the experimental results, and the variation trend is consistent. When the heating power is 170 W, the steady-state evaporation temperature of the single-effect still is 74.1 degrees C, and the deviation from the theoretical calculation result is 1.2 %. The steady-state freshwater yield rate is 37.63 g/15 min, and the deviation from the theoretical calculation result is 19.6 %. The double-effect still can effectively recycle the heat loss, and its freshwater yield rate and gain output ratio (GOR) can reach 64.88 g/15 min and 0.99 in steady state operation. Immersion water cooling of the still can significantly improve its heat and mass transfer characteristics and freshwater yield rate, and the higher the operating temperature, the greater the performance improvement of the still by immersion water cooling. When the heating temperature is 75 degrees C, the temperature difference between evaporation surface and condensation surface of the 1st effect and 2nd effect of the still with immersion water cooling are 4.9 degrees C and 19.3 degrees C, respectively, which are 2.7 degrees C and 12.0 degrees C higher than those under natural air cooling conditions. At this time, the freshwater yield rate of the still under immersion water cooling conditions reached 0.732 kg/h, which is 0.446 kg/h higher than that under natural air cooling conditions. What's more, the cost per liter of freshwater production (CPL) and payback period for the double-effect immersion tapered solar desalination device are 0.023 $/L and 3.42 years, respectively.