Enhancement in energy and exergy efficiency of a solar receiver using suspended alumina nanparticles (nanofluid) as heat transfer fluid

An experimental and theoretical energy and exergy analysis was conducted for a cylindrical cavity receiver employed in a parabolic dish collector. Based on simultaneous energy and exergy analysis, the receiver average wall temperature and overall heat transfer coefficient were determined. A simplified Nusselt number for heat transfer fluid (HTF) through the receiver as a function of Reynolds and Prandtl numbers was proposed. Based on correlated Nusselt number, the effects of two nanofluids of alumina nanoparticles in water and ethylene glycol as base fluid on the performance of system were investigated. When nanofluids are employed as HTF through the receiver, the energy and exergy efficiency are greater compare to pure water. The minimum enhancement in receiver thermal efficiency is 25% and enhancement greater than 60% is attainable. The results indicate that, by increasing only 5% volume in nanoparticle concentration in water, the receiver thermal efficiency is increased greater than 20%. The effect of nanoparticles volume fraction on exergy efficiency for small HTF mass flow rates is greater than larger mass flow rates. By selecting only 5% volume of alumina nanoparticle in water, for small HTF mass flow rates, enhancement in exergy efficiency greater than 10% is attainable.