Study on the thermodynamic characteristic matching property and limit design principle of general flat plate solar air collectors (FPSACs)

Based on a typical single pass flat plate solar air collector (FPSAC) model, the collector thermodynamic characteristic matching property between the air-side heat transfer and total heat losses is analyzed in terms of unified air-side heat transfer coefficient Ub-f and total heat loss coefficient U-L. Then the limit design principle of FPSACs is discussed in order to obtain high collector efficiency intercepts. The results show that, both lower and upper limit values of UL exist for obtaining an expected efficiency intercept (eta(0)) which is lower than the maximum realizable intercept ((eta(0))(max)) with specific collector components. The case of maximum realizable intercept (eta(0))(max) can be obtained by the minimum realizable total heat loss coefficient (UL)(min) and a high convective heat transfer coefficient Ub-f (Ub-f = 200 W/(m(2).K) is argued to be good collector air-side thermal performance and is considered in the present study), resulting in a minimum thermodynamic characteristic coefficient zeta(min). And the maximum realizable intercepts for different component combination cases of FPSACs are obtained by numerical calculation. Besides, for FPSACs with specific airflow channels, the cases of minimum realizable (UL)(min) represent the limit design.