Improvement of Heat Transfer in a Parabolic Trough Collector Receiver Tube with Hollow Cylindrical Inserts: A CFD Study

The thermal performance of a parabolic trough receiver (PTR) with hollow cylindrical inserts (HCIs) is numerically investigated. The HCIs are coupled in an axial manner and also radially joined to the interior of the PTR. Totally, eleven different internally hollow cylindrical receivers are examined and compared with the plain tube (PT). The lengths, thicknesses, and numbers of HCIs are tested at varied values, and all these tubes are examined under a constant inlet temperature of 300 K and mass flow rates in the range of 0.6-1.0 kg/s. ANSYS Fluent is the simulation software in this work. The developed model is validated with experimental correlations for PT case. The simulation findings demonstrated that the addition of HCIs may greatly enhance the uniformity of the temperature gradient between the wall of the PTR and the water. The optimum case of the HCIs has a length of 40 mm, a thickness of 2 mm, and a number of 15 inserts. This model recoded the higher ranges of Nusselt number (132-296), fraction factor (0.301-0.064), and thermal efficiency (41-79%). Also, the outlet temperatures of the PT and modified tube are increased from 300 K to 325.5 K and 339.7 K, respectively. As a result, this approach provides advantages over the utilization of interior fins, as it can be applied on the parabolic trough collector (PTC) without requiring any modifications to the PTR, which are associated with numerous operational challenges.