Similarity theory of solar water heater with natural circulation

The similarity theory of solar thermosyphon collector is developed in the present paper. Ten dimension-less groups or system characteristic parameters which uniquely determine the performance of the collector are derived. The solution shows that the mean efficiency generally increases with increasing incident solar radiation and relative height of the tank. For the frictional parameters N_e and N_f higher than 10⁵, the efficiency appears to be independent of the incident radiation and the relative height of the tank. Therefore, for parallel plate absorber, the tank may be designed to sit on the floor without sacrificing the efficiency since the values of N_e and N_f are usually larger than 10⁵ in most designs.