Evaluation of Thermophysical Properties of Menthol-Based Deep Eutectic Solvent as a Thermal Fluid: Forced Convection and Numerical Studies

Concentrated solar power (CSP) is one of the emerging renewable energy technology, where sunlight is concentrated from a large area and is stored in a collector filled with heat-transfer fluid (HTF). The current work reports the synthesis of novel HTF based on menthol-based deep eutectic solvents (DESs). DES consisting of a hydrogen bond acceptor, namely, DL-menthol and a hydrogen bond donor (oleyl alcohol), has been prepared and explored to evaluate its effectiveness as a thermal fluid. The thermal properties, namely, viscosity, density, thermal conductivity (TC), and heat capacity, are measured and compared with both conventional and commercial solvents within the temperature range T = 298.15-353.15 K. The density of DES was found to decrease with increase in temperature, while the rheological measurements suggest a Newtonian fluid with its shear viscosity decreasing exponentially with increasing temperature. The TC of the DES was found to be similar to 0.161 W/m K, which decreases linearly with temperature, while a contrary was observed for heat capacity. Further, the performance of these solvents has been evaluated in a forced convective heat-transfer configuration under laminar flow conditions with N-Re = 105, 155, and 260. The convective heat-transfer experiments demonstrated the fact that the thermal entrance length of the DES is very large because of its high viscosity and low TC. The convective heat-transfer data, namely, heat-transfer coefficient and Nusselt number, were compared with the in-house AnuPravaha CFD simulator under laminar conditions. From the obtained thermophysical properties, it is confirmed that the synthesized DES can be used as a next-generation heat storage media in the CSP plant.