Hybrid nanofluid flow and heat transfer in a parabolic trough solar collector with inner helical axial fins as turbulatorMohammad Zaboli, Seyed Soheil Mousavi Ajarostaghi, Seyfolah Saedodin and Behnam KianiEur. Phys. J. Plus, 136 8 (2021) 841DOI: https://doi.org/10.1140/epjp/s13360-021-01807-z