Thermal Performance Study of Helically Grooved Absorber Tubes for Parabolic Trough Solar Collector

In this work, a computational study on four different types of helically grooved absorber tubes namely, semi-circular, rectangular, trapezoidal, and triangular has been carried out for their possible application in parabolic trough solar collector. In order to conduct the work, absorber tube of 2 m length with 19 mm inner and 25 mm outer diameter is selected. Flow velocities have been calculated by fixing the Reynolds number of the flow as 4000 i.e., turbulent flow. A constant heat flux of 818.5 W/m² is provided at the lower surface of the absorber tube, facing the reflector. The simulation is performed using the finite volume based tool ANSYS FLUENT 17.1. The standard k-ε RNG turbulence model is used for simulation. The values of friction factors for semi-circular, rectangular, trapezoidal, and triangular absorber tube are 0.0511, 0.0889, 0.0929, and 0.0352, respectively. Nusselt numbers for these tubes are calculated as 68.91, 65.69, 72.05, and 85.49. Hence, it can be concluded from the present study that the thermal performance of the absorber tube with triangular groove is superior to the other groove types. The pressure drop for the same tube is also lowest.