Experimental Study on a Coiled Tube Solar Receiver under Variable Solar Radiation Condition

This article presents an experimental investigation of the heat transfer characteristics as well as energy and exergy performance for a coil type solar dish receiver under variable solar radiation conditions. During a 4.5 h period of continuous operation in the morning, the solar irradiance fluctuates in the range between 160 W/m2 and 650 W/m2, and the concentrated solar flux is approximately 1000 kW/m2 at aperture. Experimental results show that: (1) the efficiency of the solar receiver is found to be over 58% and the highest efficiency can be reached to 64%. Generally, the efficiency is maintained at around 60% under steady state condition. (2) A very low value of the heat loss factor (0.035 kW/K) could be achieved during steady state operation. (3) The highest value of the exergy rate is approximately 7.3 kW, whereas the maximum energy rate can reach 16.2 kW. (4) The highest exergy efficiency is approximately 23%, whereas the highest energy efficiency is around 64%.