Laminar Forced Convection of Liquids in Tubes With Variable Viscosity

Analytical solutions for laminar forced convection of liquids flowing in circular tubes with temperature-dependent viscosity are obtained for both step change in tube-wall temperature and step change in wall heat flux by using an improved integral procedure. The accuracy of this analytical procedure is demonstrated by comparing results for the isothermal problems with that from the exact solutions. Results for the nonisothermal cases are presented in graphical forms in terms of Nusselt numbers, velocity variations at tube center line, and friction factors. Tabulated Nusselt numbers are also given.