Experimental study of the effect of secondary flow on the efficiency of solar flat plate collector applied nanofluid

In this study in order to study the effect of secondary flow on the efficiency of solar collectors, a circular collector with helical tube and a regular collector is constructed and tested at the same time. The assessment was based on the ASHRAE standard and in southern Iran. Experiments were carried out based on different environmental conditions using normal water agent and zinc oxide/ water nanofluid. The results of this study show that with variation in ambient conditions as well as increasing the efficiency and increasing the efficiency of the efficiency of both the circular and rectangle flat plate solar collector performance, the main reason is the secondary flow effect on the enhancement of heat transfer from the tubes to the operating fluid. Also, while using nanofluid instead of water as a factor fluid, although the efficiency of both solar collector is increased, the secondary effect on heat transfer in the use of nanofluid is significantly enhanced due to the motion of particles particles in suspension. In addition, the maximum number of registered solar collector efficiency by using nanofluid was about 77.6% in circular collector.