In the present work, a parabolic trough solar (PTC) collector with inner helical axial fins as swirl generator or turbulator is considered and analyzed numerically. The three-dimensional numerical simulations have been done by finite volume method (FVM) using a commercial CFD code, ANSYS FLUENT 18.2. The spatial discretization of mass, momentum, energy equations, and turbulence kinetic energy has been obtained by a second-order upwind scheme. To compute gradients, Green-Gauss cell-based method has been employed. This work consists of two sections where, first, four various geometries are appraised, and in the following, the selected schematic of the collector from the previous part is selected, and four various pitches of inner helical fins including 250, 500, 750 and 1000 mm are studied. All the numerical results are obtained by utilizing the FVM. Results show that the thermal performance improvement by 23.1% could be achieved by using one of the proposed innovative parabolic trough solar collectors compare to the simple one. Additionally, the minimum and maximum thermal performance improvement (compare to the case without fins) belong to the case with P = 250 mm by 14.1% and, to the case with P = 1000 mm by 21.53%, respectively.

This paper reviews the impacts of employing inserts, nanofluids, and their combinations on the thermal performance of flat plate solar collectors. The present work outlines the new studies on this specific kind of solar collector. In particular, the influential factors upon operation of flat plate solar collectors with nanofluids are investigated. These include the type of nanoparticle, kind of base fluid, volume fraction of nanoparticles, and thermal efficiency. According to the reports, most of the employed nanofluids in the flat plate solar collectors include Al₂O₃, CuO, and TiO₂. Moreover, 62.34%, 16.88%, and 11.26% of the utilized nanofluids have volume fractions between 0 and 0.5%, 0.5 and 1%, and 1 and 2%, respectively. The twisted tape is the most widely employed of various inserts, with a share of about one-third. Furthermore, the highest achieved flat plate solar collectors’ thermal efficiency with turbulator is about 86.5%. The review is closed with a discussion about the recent analyses on the simultaneous use of nanofluids and various inserts in flat plate solar collectors. According to the review of works containing nanofluid and turbulator, it has been determined that the maximum efficiency of about 84.85% can be obtained from a flat plate solar collector. It has also been observed that very few works have been done on the combination of two methods of employing nanofluid and turbulator in the flat plate solar collector, and more detailed work can still be done, using more diverse nanofluids (both single and hybrid types) and turbulators with more efficient geometries.

The present study aims to investigate the effects of the pin on flow and heat transfer from pulsating jet impinging on a heated flat surface. A row of cylindrical pins has been applied on a flat plate with a constant heat flux of 2000 W/m². The experiments have been performed for two jet to target surface distances, frequency range from 50 Hz to 100 Hz and jet Reynolds number from 7000 to 15000. The effect of presence of pin, pulse frequency, Reynolds number, and jet to target surface distance have been investigated. Results of the numerical simulations indicate that the RNG k-ε model can predict the distribution of Nusselt number in good agreement with the experimental data. Results of the present study showed that the presence of pin changes the coherent vortical of the flow structure at both upstream and downstream of the pins. It is shown that at Re = 10000 and H/d = 5 the pulsed jet with frequencies of 50 Hz, 80 Hz, and 100 Hz increases the heat transfer from the pinned surface by 21%, 30%, and 36%, respectively, in comparison the steady jet. Finally, experimental observation indicated that the Nusselt number increases with increasing the pulse frequency and Reynolds number and decreases with increasing the jet to target surface distance.