Thermohydraulic performance analysis of absorber tube with coiled wire turbulators in small aperture parabolic trough collector

Three-dimensional (3D) simulation using computational fluid dynamics (CFD) has been performed to investigate the impact of a coiled wire turbulator (CWT) on heat transfer and fluid flow in the absorber tube of a small aperture parabolic trough collector (PTC) under a turbulent flow regime. The PTC was modeled with a projected aperture area of 0.64 m² and an optimized value of rim angle 90 degrees using the ray tracing tool SolTrace based on an optimum value of average heat flux (8.58 kW/m²), and this optimum average heat flux was used as one of the boundary conditions in CFD simulation. The CFD-simulated findings for the smooth absorber tube of the PTC model are compared with the Dittus-Boelter equation for heat transfer and the Filonenko equation for friction factor. The simulated result showed an average deviation of 2.54% and 14.68% in the Nusselt number and friction factor, respectively. The effect of a wall-detached type of CWT (Dm = 10 mm) on thermohydraulic performance with coil pitch ratios (P/dh) of 1, 1.5, and 2 and height ratios (e/dh) of 0.053, 0.063, and 0.074 is considered for the analysis in the Reynolds number (Re) range of 4000-12000. The optimal value of thermohydraulic performance (ηthp) is obtained 1.56 for P/dh = 2, e/dh = 0.053, and Re = 4000, corresponding to which enhancement ratio of Nusselt number (Nur/Nus) and friction factor (fr/fs) are 2.28 and 3.14, respectively.