A coupled numerical model for tube-on-sheet flat-plate solar liquid collectors. Analysis and validation of the heat transfer mechanisms

A 3D numerical model for flat-plate liquid solar collectors has been developed. This model is envisioned for predicting the efficiency curve of the collector, for which the different heat transfer mechanisms involved are simultaneously taken into account: solar radiation absorption, transmission and reflection; natural convection in the air cavity; heat conduction across the tube-absorber welded junction; mixed convection flow in the risers; and heat losses by convection and radiation to the ambient. To ensure the reliability of the model, the heat transfer results inside the risers and in the air cavity were contrasted with well-known experimental correlations available in the open literature.