Experimental Investigation of Performance on A PCM Assisted Solar Water Heater

Abstract

Latent heat thermal energy storage is one of the most efficient ways to store thermal energy for heating water by receiving energy from sun. This paper summarizes the investigation and analysis of thermal energy storage incorporating with and without Phase Change Materials (PCM) for use in solar water heaters .This energy is utilized to heat water for domestic purposes during night time. This ensures the hot water availability throughout the day. The system consists of two simultaneously functioning heat-absorbing units. One of them is a solar flat plate collector and the other a heat storage unit consisting of PCM (paraffin). The water heater functions normally and supplies hot water during the day. The storage unit stores the heat in PCMs during the day which supplies hot water during the night. The storage unit utilizes cylindrical tubes made of copper and curved cylindrical tubes made of steel filled with paraffin wax as the heat storage medium. The performance of both the geometries are analyzed and compared in this work. The water in the storage unit receives heat form the heating panel and transfers it to the PCM. The PCM undergoes a phase change by absorbing latent heat, excess heat being stored as sensible heat. During night hours the stored energy is transferred to cold water again by the phase changing process till the liquid phase of paraffin become solid phase. The present experiment focuses to maintain 60 liters of water at a temperature of around 70oC during the day time with a flow rate of 5 ml/sec through a flat plate collector. Copper is used for the collector plate and the runner tube and the storage tank is of stainless steel material. The melting point of Paraffin is 56oC. By the application of PCM the hot water availability can be extended up to 4 hours than the normal condition. Keywords:-Solar water heater , Latent heat thermal energy storage, Phase Change Materials, phase changing process. I. INTRODUCTION The primary energy sources in the earth are eliminating day by day due to the higher consumption rates .The increasing population and the human comfort level standards speedup the crises level and it leads to the effective utilization of secondary energy sources. The large scale application of fossil fuels causes atmospheric pollution by the evolution of harmful gasses in large scale like nitrogen oxides (NOx), sulphur oxides(SO2),carbon monoxide and carbon dioxide(CO &CO2), hydrocarbons, suspended particles and fly ash. Due to these pollutants causes ozone layer depletion, health hazards, global climate change and global warming etc. The secondary sources are mainly of solar, wind, tidal, wave, hydro and geothermal energies. In which the main energy source is of the sun and these alternative sources are the manifestation of solar energy. The solar energy is freely available and is environmentally clean. So this energy is accepted as the most promising alternative energy. The effective utilization of solar energy is not at all popular and common in this modern scenario. The domestic hot water application consumes above 45% of energy produced worldwide. By the effective utilization of solar energy can control the energy crises and atmospheric pollution all over the world. The solar energy obtained only in day timings and the major requirement of hot water arises in the night hours and the morning. The major difficulties are the intermittent and variable supply due to the clouds and the large area requirement of the collector. The energy supplied by the sun keeps the temperature level of the Earth for the human beings, animals and all the species and the temperature level of ocean and land to cause the air circulations and the photosynthesis in plants. The solar energy incident over the atmosphere is 1017watts in which the incidence on the earth surface is 1016 watts. The total power demand all over the world is 1013watts.The solar radiation in a normal sunny day is around 1Kw/m2 [1].From this figures it is clear that the energy available is 1000 times more than that we required. If we can utilize 1% of this energy, it will be 10 times the total world will require. The diameter of sun is 1.39 x106 and the earth is of 1.27 x 104.The mean distance between the two is 1.50 x 108 km[1].The sun is a hydrodynamic spherical body of extremely hot ionized gases called plasma. The energy is produced by the process of thermonuclear fusion. The temperature inside the sun is estimated as 8 x106 K to 40 x 106 K.The energy is emitted by the fusion of hydrogen to helium [2].The radiated energy is in the form of electromagnetic waves in which 99 percent have wavelengths from .2 to 4. Micrometers. The solar energy reaching the top of the earth's atmosphere consists of about 6.4 to 8 per cent ultraviolet radiations (ƛ<0.38µm), 46 to 48 per cent visible light (0.38 µm <0.78µm) and 46 per cent infrared radiation (ƛ >0.78µm) of total energy [1, 2].The successful applications of solar energy are of solar water heating for domestic purposes, electric power generation, solar cookers, solar driers, heating and cooling of residential buildings, solar distillation, food refrigeration etc. A domestic solar water heater with latent heat thermal energy storage by phase change material is experimentally conducted and analyzed in this paper. The solar radiations incidents over a black collared copper flat plate collector is absorbed and converted to heat energy. Two thermocouples one at the right side bottom and another at the left side top is fitted for proper measurements below the flat plate collector.