Numerical Investigation on Simultaneous Effects of Surface Roughness and Variable Properties on Laminar Flow in Annular Tubes

A comprehensive study is conducted to evaluate the heat transfer characteristics of laminar nanofluid flow in an annular tube. Thermo-physical properties of the nanofluid is considered to be variable and for the inner and outer walls, there exists serrated surface roughness. The study focuses on the velocity distribution, friction factor and Nusselt number. All results are compared with those for the smooth channel and constant property nanofluid as well. The results show that the tube with serrated wall experiences greater maximum velocity. Moreover, decrease in velocity gradient and some other thermal characteristics result in decrease in average Poiseuille and Nusselt numbers for the rough tube with variable-property fluid.