Simulation of an enhanced flat-plate solar liquid collector with wire-coil insert devices

Solar liquid collectors are potential candidates for enhanced heat transfer, but there are just a few studies focused on this topic. However, enhancement techniques can be applied to thermal solar collectors to produce more compact and efficient designs. This work presents the study of heat transfer enhancement in a tube-on-sheet solar panel with wire-coil inserts, using TRNSYS as the simulating tool. The numerical simulation methodology predicts the thermohydraulic flow behaviour of enhanced and standard tube-on-sheet solar collectors, evaluating the local losses, friction coefficients and Nusselt numbers as functions of the operating parameters. The standard and the enhanced collectors have been simulated under the same ambient, radiant and operating conditions. The standardized efficiency curves according to the standard UNE-EN 12975-2 are provided. The enhanced collector increases the thermal efficiency values by 4.5%. A parametric study was performed to relate the fluid and flow characteristics with the heat transfer enhancement by wire-coil inserts. The simulations were performed for different working fluids (water and propylene glycol/water mixtures) in a mass flow rate range from 15 to 120 l/h m2.