Examination of top and bottom inlet position in horizontal mantle heat exchanger solar thermosiphonic circuits

The present work deals with the examination of two different configurations of inlet mantle connections, on a solar thermosiphon of indirect heating type. In the first configuration, the heat transfer fluid enters the upper side of the mantle heat exchanger, while in the second it enters the lower side of the mantle. The outlet is always placed at the bottom of the mantle, oppositively to the inlet. Diurnal tests have been carried out by monitoring the inlet and outlet mantle temperatures, as well as thermosiphonic flow rates. Also, draw-offs measurements were performed, according to ISO 9459-2 and EN 12976-2 standards, at the end of each test day. The final achieved water temperatures of the first configuration are in general higher, than those of the second one, which means a better quality of the delivered energy. Also, the first configuration appears to pick up greater performance, under high solar energy gain (high insolation rate – low thermal losses).