University of Sistan and Baluchestan, Iranian Society Of Mechanical Engineers Challenges in Nano and Micro Scale Science and Technology 2821-000X 14 2 2026 09 01 Investigation of Friction Factor and Nusselt Number Distributions for Zno-water Nanofluid under Forced, Mixed and Free Convection with Varying Eckert Numbers 16 30 9848 10.22111/cnmst.2026.55029.1290 EN Tohid Adibi University of Bonab Journal Article 2026 04 05 This study investigates the behavior of the friction factor and Nusselt number in fluid flow across forced, mixed, and free convection regimes, with a specific emphasis on the influence of the Eckert number. Numerical simulations were performed for a moving lid configuration, maintaining a constant Reynolds number (Re=100) while systematically varying the Grashof numbers (Gr=103,104,105) and Eckert numbers. The analysis reveals distinct trends: In forced (Gr=103) and mixed (Gr=104) convection, the mean friction factor remains largely constant across different Eckert numbers, while the mean Nusselt number shows a significant increase with Eckert number. This suggests that viscous dissipation primarily enhances heat transfer without substantially altering wall shear stress in these regimes. Conversely, under free convection (Gr=105), both mean friction factor and Nusselt number exhibit a substantial increase with rising Eckert number, highlighting the dominant role of buoyancy forces and viscous dissipation in governing both heat transfer and energy losses. Detailed friction factor distribution profiles further illustrate these phenomena, revealing unique behaviors, particularly the emergence of a near-zero slope region in free convection at higher Eckert numbers. https://chal.usb.ac.ir/article_9848_c4f6fcdcd2555a77fa5cbb5bf7bd7ce0.pdf