Study on behaviour of thermal energy storage materials under conventional and solar heating systems (original) (raw)

Milk is a highly perishable commodity and needs quick processing to prevent growth of microorganisms. Milk processing mainly contains heating and cooling operations and for most of the heating operations, steam is used as a heat transfer fluid. But the increasing energy demand leads to search for alternative renewable energy resources. Sun energy is highly efficient, free to use and does not harm the environment. A comparative study was done to select best heat transfer material for heating operations in milk processing. During the study, different energy storage materials viz. thermal fluids and phase changing material (PCM) in the form of salts were investigated to check their thermal profile, engineering characteristics viz. thermal expansion, melting point, smoke point etc. were evaluated. Sensible heat energy storage of thermal fluids namely; paraffin oil (light), silicon oil and phase changing salts namely; acetamide, magnesium chloride hexahydrate were analyzed for their heat absorption and thermo-physical properties. Among these four materials, paraffin oil was found as highest thermal energy absorbing material. The phase changing salts has more heat storage density as they absorb the heat in the form of latent heat. This leads to the storage of thermal energy for a longer period, once the salts are charged by heating but maximum heat energy was absorbed by paraffin oil (276˚C276˚276˚C) surging ahead of silicon oil (260˚C260˚260˚C). Peak temperature achieved by these oils is more than sufficient to cover the entire range of heating operations required in dairy process industries. Introduction With increasing population, there is a huge increase in energy demand which is fulfilled with both renewable and non-renewable energy sources. In India, only 28% of energy demand is met with renewable energy resources and rest is met from non-renewable sector which automatically results in huge emission of carbondioxide. Shortage of fossil fuels, associated ill effects of use of fossil fuels on environment and ever increasing demand for energy compels us to shift towards renewable energy resources like solar energy, wind energy, geothermal energy, tidal energy, biomass etc. as these energy resources are free, anti-polluting and anti-toxic to the environment. Among these energy resources, solar energy has a great scope in a country like India where sun shines in abundance. India gets around 5-7 KW/m 2 of sunshine for about 300-320 days per year (Desai et al. 2013, Sharma et al. 2012) [5, 12]. In addition, energy storage can help to save the premium fuels and also reduces the wastage of conventional energy.