Performance evaluation of an existing solar concentrator

Abstract

The main sources of energy in the world are based on fossil fuels. However, these sources have several downsides such as causing damage to the environment and they are also sensitive to price changes. Due to the above shortcomings, solar energy is increasingly being utilized in different parts of the globe. One of the solar technologies being used is the parabolic trough concentrator (PTC). It produces high temperatures that may not be attained by open sun drying or flat plate collectors. High temperatures are appropriate for high rates of drying and in situations where the only limitation is the prevention of self-ignition. Typical cases are in drying of biomass. An orifice meter was fabricated at the Mechanical Engineering Workshop, University of Nairobi. It was used to measure the mass flow rate of air through the receiver tube of a PTC. A PTC designed and fabricated by Mr. Wilson Kariuki was used for the experimentation [16]. The experiments were carried out between 1000hrs and 1600hrs on selected days between 26rdFebruary and 02ndApril 2014. Throughout the experimentation, the PTC was covered with glass and a 50.8mm diameter receiver tube used. Mass flow rates of 0.001493kg/s, 0.002986kg/s, 0.004472kg/s, 0.00538kg/s, 0.006678kg/s, 0.007483kg/s, 0.008846kg/s were used. The highest temperature was recorded while using a mass flow rate of 0.001493kg/s and it was 105.6°C while that recorded while using a mass flow rate of 0.008846kg/s was 72.9°C. It was therefore evident that higher outlet temperatures were obtained at low mass flow rates. The maximum useful energy obtained from the PTC with a mass flow rate of 0.001493kg/s was 101.86J/s while that obtained with a mass flow rate of 0.008846kg/s was 395.05J/s. This indicated that useful energy is directly proportional to mass flow rate. Overall efficiencies calculated while using mass flow rates of 0.001493kg/s and 0.008846kg/s were 3.5% and 10.74% respectively. This implied that overall efficiency increases with increase in mass flow rate.