Thermal modeling and exergetic analysis of a thermoelectric assisted solar still

Abstract

The present study is devoted to a comprehensive thermodynamic modeling of a novel portable solar still through the first and second laws analysis. In this new solar still, a thermoelectric module is employed to elevate the temperature difference between evaporating and condensing zones. Energy and exergy balance equations have been written for all components of the solar still including glass cover, thermoelectric module, saline water, and basin-liner. A new approach is used to evaluate evaporative heat transfer coefficients. Comparison of distilled water calculated by the present approach and the results obtained by employing various semi-experimental models proved the accuracy of the proposed thermodynamic modeling. It is also found that the exergy stored within the body of saline water, which was neglected in the most previous studies, is important and should be considered.It is shown that the daily average energy and exergy efficiencies of the solar still are 19.8% and 0.95%, respectively. It is seen that the exergy efficiency is much lower than the energy efficiency. Furthermore, it is found that the rate of exergy destructions in solar still components is proportional to the incident solar intensity. The largest exergy destruction belongs to the thermoelectric module, which is 63.4% of the total exergy destruction, while the glass cover has the smallest share. It is concluded that although the energy efficiency associated with this type of thermoelectrically assisted solar still is higher than its counterpart simple passive solar still one, however, its exergy efficiency is lower.