Transient theoretical model for the assessment of three heat exchanger designs in a large-scale salt gradient solar pond: Energy and exergy analysis

Abstract

This paper deals with transient modelling of a large-scale salt gradient solar pond (SGSP – 50000 m2) located in a semi-arid climate region. Precisely, the pond was exposed to meteorological data of the Agafay site (located 30 km south of Marrakesh-Morocco) covering the period from January 2015 to May 2017. We considered three different heat extraction technics (HET) including the reference one (R-HET) that limits the heat draw to the heat storage zone using horizontal tubes. The other two methods consider an additional heat draw from the intermediate non-convective zone using horizontal (HT-HET) and vertical (VT-HET) tubes. We elaborated a transient mathematical model based on energy balance equations for the pond (including the ground) and the extraction’s tubes. This model was solved using a MATLAB code based on the fully implicit finite-difference scheme that has been developed for this purpose. The study focuses on the examination of the thermal performances of the considered SGSP for each of the three heat extraction methods based on energetic and exergetic analysis. The obtained results reveal that the third method of heat extraction (VT-HET) provides higher energy and exergy efficiencies by reducing the total heat losses towards the pond’s surroundings and saving exergy from destruction. The amount of energy/exergy extraction improvement recorded is around 22.5%/30% compared to the reference heat extraction technic (R-HET) against an improvement of only 1.7%/0.6% for the HT-HET.