Enhancing the performance of a salt gradient solar pond using a coiled flow inverter heat exchanger with nanofluids

A Solar Gradient Solar Pond (SGSP) is a simple and reliable technology to collect solar energy that can be storage as thermal energy for long periods of time. The heat losses from the pond to the surroundings are reduced because of the salinity gradient that inhibit the mixing of the fluid. The appropriate extraction of this thermal energy is required in order that this technology can be competitive to be used for processes that demand heat of low temperature (below 100°C). In this work, an innovative method of heat extraction of a SGSP using a Coil Flow Inverter Heat Exchanger (CFI-HE) with nanofluids is investigated. Experiments were conducted in the SGSP to evaluate the thermal performance of the CFI-HE for two types of nanofluids (Al2O3/H2O and TiO2/H2O) at different volume concentrations. The overall heat transfer coefficient of the CFI-HE increased for both nanofluids with the nanoparticle concentration with a maximum increase of 32 % and 25 % for the Al2O3/H2O and TiO2/H2O nanofluid, respectively. Results of the mathematical model and the experiments agree well with a maximum error of 12 % for the overall heat transfer coefficient. Maximum thermal efficiencies of 63 %, 61 %, and 58 % were achieved for the CFI-HE system in the SGSP with Al2O3/H2O, TiO2/H2O, and water, respectively. These results showed that the CFI-HE with nanofluids is a heat extraction method that increases the potential of SGSP to provide thermal energy for industrial and commercial applications.