STUDY OF THE EFFECT OF SUNFLOWER OIL AND WATER ON THERMAL STORAGE PROPERTIES OF A FLAT PLATE SOLAR WATER HEATING COLLECTOR

Abstract

Solar collectors can convert the solar radiation energy to thermal energy when it hits a surface. A flat plate solar collector is a medium-temperature glazed plate heater manufactured to warm water or air to 80 Cmaximum. The simplest and effective way of tapping solar energy is by domestic water heating. Weather changes also have a big effect on the solar heater output water temperature. Behaviour, complexity and size of a solar water heating system are largely affected by the changes of ambient temperature and solar radiation in different weather conditions. Therefore, there is the necessity to use thermal storage fluids such as sunflower oil that has been documented to be an excellent heat transfer fluid (HTF) in addition to the heat storage fluid also necessitating the use of heat storage fluids such as sunflower oil since it is easily accessible, non-corrosive and non-poisonous. The main objective of the study was to compare the thermal storage capacity parameters of a flat plate solar water heater using sunflower oil versus water as thermal storage fluids. Specific objectives were to: determine instantaneous receiver heat gain by solar collector and compare the thermal storage effect of water and sunflower oil on output temperatures from a flat plate solar collector, evaluate the effect of both fluids on heat loss and heat exchange parameters of a flat plate solar collector, compare the overall system efficiency when using water versus sunflower oil as thermal storage media compare and analyse the KOLEKTOR 2.2 simulation results with the experimental data. Flat plate solar water heating collectors containing sunflower oil, and water as thermal storage fluids were designed and constructed for this study. The absorber plate was made of mild steel welded on galvanized iron riser pipes. The stated objectives were achieved by applying appropriate equations and measuring parameters affecting the thermal storage of a solar water heater such as area of the receiver, incident solar radiation, mass flow rate, wind speed, humidity, ambient temperature, fluid inlet and outlet temperatures. The efficiency of solar water heating systems was deduced by considering the incident solar energy on the collectors and the useful energy output from the systems. This takes into account conductive, convective and radiative thermal losses. The experimental measurements were done using k-type thermocouples connected to a data logger and a computer. Simulation and theoretical modeling were done using KOLEKTOR 2.2 software while experimental data computation and analysis were done using MATLAB. Research findings showed that sunflower oil and air attained a peak temperature of 75℃, while that of water was 65℃ from 12 noon to 3.30 pm. Overall heat loss coefficients for air, water and sunflower oil as -38.40 W/m2K, -20.94 W/m2K and -15.80 W/m2K respectively Sunflower oil has the longest stagnation (steady) temperature duration.FR of 0.8934, 0.846 and 0.785 for sunflower oil water and air respectively. However, from the KOLEKTOR 2.2 model, the heat removal factor for sunflower oil is 0.937, while water and air have heat removal factors of 0.918, and 0.910 respectively. Both experimental and theoretical results showed that sunflower oil has a higher removal factor FR and efficiency factor F1 than water. From the KOLEKTOR model, efficiency factor F1 values of sunflower oil, water and air 0.922, 0.916 and 0.818 respectively. Sunflower oil is also a better thermal storage fluid than water since has a lower heat loss coefficient than water. Other studies have also shown that sensible heat storage media improve efficiency by reducing thermal losses. The information from this study would be useful for effective utilization of intermittent solar energy for heating applications. Thus reducing water heating expenses, and conserving our environment.