Investigation on thermal energy storage of evacuated tube solar water heater using nano enhanced phase change material

Abstract

This modern era, the demand for energy is interminably increasing day by day in a faster pace due to the rapid growth in urban population and industrial sectors. Specifically, energy consumed for hot water requirements is a major concern which estimates around one-fourth of the global energy end-use. It clearly indicates the potential of solar water heaters for satisfying hot water requirements to substantiate the energy demand in an economical and an eco-friendly manner. It is estimated that the solar water heaters are having around 90% of market shares for domestic requirements. Earlier days, thermosyphonic circulation flat plate solar water heaters were used in the majority of the households; however, all-glass evacuated tube solar water heaters are becoming popular in recent times due to their comparative advantages such as improved efficiency, simple construction, reliable operation and competitive price. In spite of the advantages solar water heaters are suffered with certain setbacks chiefly due to their weather dependent operating condition. Primarily, they are deficient in regulating their total stored heat energy for properly meeting supply-demand requirements, especially if there is a need of different withdrawals during the day of operation and in the following morning. Further, they lack in storing maximum possible thermal energy and retain it effectively, owing to their intrinsic losses. In this work, an attempt has made to address the aforementioned setbacks related the domestic solar water heaters with the help of phase change materials (PCM) and further with the help of a specially prepared nano-enhanced phase change materials (NEPCM)Phase change materials (PCM) are the constituents having ability to absorb and release a significant amount of heat energy in terms of latent heat within a small volume. Paraffin is one among the PCM which possesses superior thermo-physical properties to be used as thermal energy storage material for the variety of applications. Nonetheless, they have a shortfall with their inherent low thermal conductivity which affects the rate of heat transfer within this material. Among the different proposed methods, the dispersion of appropriate nanoparticles within the phase change materials seems to be the effective method for improving their thermal conductivity. In this present study, an experimental setup of thermosyphonic flow based all-glass evacuated tube solar water heater with an integrated water storage tank has been fabricated and installed in Coimbatore which is located in Tamilnadu, the southern part of India. The investigations have been piloted on the installed solar water heater (SWH) in eleven different cases namely, without PCM, with paraffin as PCM and with nine different combinations of NEPCMs consisting three varieties of nanoparticles, each with three different mass fractions. The nanoparticles used in this study are SiO2 nanoparticles, CeO2 nanoparticles and the hybrid nanoparticles having equal mass of SiO2 and CeO2 nanoparticles. The nine combinations of NEPCMs have been prepared by dispersing each of the mentioned nanoparticles in paraffin with three different mass percentages such as 0.5%, 1.0% and 2.0%, respectively using two-step method. newline