Using a sunrays trap in direct-absorption solar collector (DASC) to enhance the thermal efficiency of collector

Abstract

In this work, a new model of direct absorption solar collector (DASC) is presented, in which for the first time one sunrays trap is applied to capture as much solar energy as possible and consequently to enhance the efficiency of the collector. Also, the second innovation of the presented model is the sequential reflections of sunrays in the receiver tube which leads to the augmentation of sunrays path length and subsequently the reduction of the nanoparticles agglomeration based on Beer-Lambert law. The reduction of nanoparticles agglomeration can decrease the cost and higher operational stability. To achieve the higher efficiency and stability, as well as the reduced cost, the new-presented sunrays trap is comprised with an evacuated envelope surrounding the receiver tube as well as a compound parabolic concentrator (CPC) which swallows the sunrays. The walls of the receiver tube and envelope are reflective and insulated respectively which attenuate the heat losses from receiver tube in which Plasmonic nanofluid is applied to collect solar energy. The COMSOL software is applied to trace sunrays optically and then to simulate the internal space of receiver tube numerically. Using the validated simulation method, the effects of variables on collector efficiency are analyzed. These variables include the width of the CPC exit (w2), the outer diameter of receiver tube (do), absorption coefficient (α), the place of focus point, and inlet temperature (Ti). Finally, it was concluded that using presented collector not only results about 4% more efficiency than the conventional DASC, but also can significantly reduce the agglomeration of nanoparticles in the base fluid. These positive results can be achieved vesus Ti = 310 K, α.P=3.46, and do = 7 cm.