Thermal performance of a parabolic trough receiver with perforated conical inserts for heat transfer enhancement

Heat transfer enhancement in receivers of parabolic trough collectors offers several benefits including reduction in absorber tube circumferential temperature differences, reduced emissivity of the absorber tube selective coating, thus improved thermal and thermodynamic performance of the receiver. In this work, heat transfer enhancement in a parabolic trough receiver using perforated conical inserts was numerically investigated. The analysis was carried out for dimensionless insert's cone angles in the range 0.40 -0.90, dimensionless insert spacing in the range 0.06 -0.18 and dimensionless insert size in the range 0.45 -0.91. The flow was considered fully developed turbulent with Reynolds numbers in the range 1.02×104 ≤ Re ≤ 7.38 × 105 depending on the temperature of the heat transfer fluid. The heat transfer fluid temperatures used were 400 K, 500 K, 600 K and 650 K. The numerical solution was obtained using the finite volume method together with the realizable κ-ε model for turbulence modeling. From the study, there is a range of Reynolds numbers and geometrical parameters for which the gain in performance is more than the increase in pumping power due to heat transfer enhancement. The use of perforated conical inserts in the receiver's absorber tube increases the thermal efficiency in the range 3-8% for some range of geometrical parameters.