Nanofluids (CuO & TiO2) - water as heat transfer fluid in a thermal energy storage system for applications of solar heating: An experimental study

Abstract

The present work aims to exploit the thermal performance of a packed bed of combined sensible and latent heat of storage unit with an integrated solar heat source. A cylindrical insulated storage tank in the thermal energy storage (TES) unit is filled with spherical capsules separately which contains PCM as paraffin wax and stearic acid. The PCM usage has the benefits that it can be used as a thermal management tool and it reduces the cost and size of the system as it offers higher isothermal behavior and thermal storage capacity. The thermal conductivity of heat transfer fluid (HTF) can be enhanced by using nanoparticles mixed in water. Nanofluids are the more efficient fluids for the applications of heat-transfer. The water based nanofluids are used to transfer heat between the solar collector and storage tank which is a sensible heat storage material. The HTF materials are varied and experimental trials have been conducted separately. Experimentation was carried out first by considering only water as HTF and is extended by adding water with one of the nanomaterials i.e. The TiO2 and CuO, each in 3 HTF vol.% as 0.2, 0.5, and 0.8. The variable source of heat supply considered is solar flat plate collector. The study was transpired by varying the flow-rates of nanofluids as 2.0, 4.0, and 6.0 Lpm. The novelty of this work is to envisage the enhancement of heat transfer and to study the effects on the melting time of the PCM of these fluids which were carried out. The performance parameters like charging time and system efficiency, instantaneous stored heat, cumulative stored heat were studied for the different HTF and for the PCM-paraffin and stearic acid. The batch wise process experiments for discharging were carried out to recover the heat stored, and the results are presented.