Analytical solutions for pipe flow of a fourth grade fluid with Reynold and Vogel's models of viscosities

In this paper, the steady incompressible flow of a fourth grade fluid down a vertical cylinder with variable viscosity and heat transfer analysis are considered. The governing equations of motion of fourth grade fluid in cylindrical coordinates have been derived. The complete analytic solutions of momentum and energy equations have been obtained by homotopy analysis method (HAM). The entropy generation number for two cases of viscosities namely (i) Reynold's model and (ii) Vogel's model have also been computed. The results are compared with the available finite difference and perturbation solutions of third grade fluid. At the end the pressure gradient for the fourth grade fluid has also been calculated. (C) 2008 Elsevier B.V. All rights reserved.