Transient behavior of thermally developing laminar flow within offset plates confined in a channel heated by radiation for integrated photovoltaic solar thermal collector applications

Abstract Experimental and numerical investigations were conducted on the transient behavior, following power activation, of laminar flow forced-convection heat transfer for air traversing offset plates within a two-parallel-plate channel heated by radiation, which is pertinent to integrated photovoltaic/thermal air heater solar collector applications. In the numerical simulation, a two-dimensional transient model was used, and the temperature boundary conditions were determined at each time step. The experimental data showed a range of 990 to 4050 seconds for the time to reach equilibrium, depending on Re. It also revealed that the heat-transfer mechanism undergoes dynamic changes, characterized by a minimum in the convective heat-transfer coefficient, before stabilizing at a steady state, a critical factor in understanding the system's heat-transfer efficiency. Experimental and numerical findings indicated that offset plates attain steady-state temperatures that depend on plate location, ranging from 40°C to 100°C, with equilibrium times varying from 4050 seconds at Re=650 to 990 seconds at Re=2550. The transient Nusselt number initially peaks during the transition period, then stabilizes between 5 and 15 seconds, indicating that the heat-transfer mechanism undergoes dynamic changes that stabilize more quickly at higher Reynolds numbers. The model's velocity field and isothermal contour maps provide a physical explanation of the experimental results.