1986 Volume 19 Issue 1 Pages 20-26
An experimental apparatus was constructed to experimentally verify the numerical analysis used for determining convective heat transfer for laminar flow in a vertical pipe with variable viscosities and under cooling conditions.
Both temperature and velocity profiles are found to be readily determined by values of X+ (= z/(Re • Pr •D)) and viscosity ratio (μi/μw) based on the inlet and wall temperatures. The maximum velocity deviation from Poiseuille flow is observed clearly at X+ ≅ 0.02 for all viscosity ratios covered in this work. For smaller values of (μi/μw), the Nusselt number decreases, reaches a minimum and then increases with increasing X+. On the basis of numerically calculated Nusselt numbers, a more reliable semiempirical equation is proposed to predict Nusselt numbers for a highly viscous fluid.
To cool a highly viscous fluid, it is recommended to gradually cool the fluid under conditions where there is a small viscosity variation with the surface temperature of the heated section.
