Small-scale linear Fresnel collector using air as heat transfer fluid: Experimental characterization

Abstract

Linear Fresnel collectors offer great potential for producing solar heat for industrial processes, both on a small and large scale. Thermal oil, pressurized water, or steam are used as heat transfer fluid in most applications, due to their suitable thermal properties. A heat exchanger is required for thermal power delivery to the user unless the heat transfer fluid is directly used as a medium in the industrial process. For those industrial applications using hot air as a process fluid, direct air heating inside linear Fresnel collectors can be an interesting solution aiming at simplification, cost reduction, and environmental and safety benefits.In this experimental study air is heated inside a commercial small-scale Linear Fresnel collector row of 79.2 m2 active surface, demonstrating the viability of direct air heating up to 500 °C at its outlet. A commercial turbocharger pressurizes the air and reduces the blowing power. The purposely designed test campaign carried out in Madrid (Spain) during spring and summer seasons allowed the experimental contrast of a detailed 1D opto-thermal numerical model. Both static and purposely developed dynamic models of the receiver tube have been scrutinized and tested. The models and the experimental information allowed for the accurate characterization of both thermal losses and optical efficiency.