الفهرس 
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Abstract
The continuous increase in the level of greenhouse gas emissions and the increase in fuel prices are the main driving force to utilize various source of renewable energy. Among the clean and renewable energy technologies, solar energy is one of the most important alternatives to conventional power generation methods because it is free and provides clean and environmentally friendly energy. Solar cookers are used nowadays extensively especially in developing countries due to the shortage and high costs of traditional sources of energy, i.e. fossil fuels. The objective of this research is to improve the heating capabilities of evacuated tubes solar cookers that operates based on a closed loop thermosyphon action, and utilize thermal oil as the heating medium.Two identical evacuated tube solar cookers have been designed and built to study the influence of inserting metallic wires or nanographene particles on the thermal performance of the cooker.
The metallic wires and the nanographene particles are inserted inside the evacuated tube, which is filled with the heat exchange oil.one cooker is always tested without an modifications, i.e. taken as a reference, the other cooker is the developed cooker, i.e. with wires or particles. Steel, aluminum and copper wires have been examined, and the number of wires has been varied between 5, 10 and 15. It has been found that the copper wires improve the rate of heat transfer compared to steel wires, aluminum wires and the nanographene particles. It has been also found that there are a critical number of wires, i.e. 10 wires, above which the rate of heat transfer by natural convection decreases and that is due to the increased friction which resists the natural convection currents. Adding nanographene particles increases the viscosity of the oil, which increases the resistance to natural convection currents and consequently decreases the rate of heat transfer by natural convection.