Laminar pulsed forced and mixed convection in a vertical isothermal tube

Numerical fluid now and heat transfer results were obtained for a pulsed laminar how through a vertical, isothermal-walled tube for Gr/Re = 0 (no buoyancy) and 30 (buoyancy) at a cyclic-averaged Reynolds number of 5 x 10(2). The pulsations resulted in cyclic-averaged Nusselt numbers Nu(av) that were greater than the steady, fully developed laminar Nusselt number, with Nu(av) increasing with increasing frequency. The Nusselt number also increased with increasing amplitude a for Gr/Re = 0, but it remained virtually constant beyond a = 0.1 for Gr/Re = 30. Although the Nu(av) values at Gr/Re = 30 were greater than at Gr/Re = 0, they were offset by relatively Large values of the cyclic-averaged dimensionless wall shear stress tau(av). For Gr/Re = 30, Nu(av)/tau(av), was either the same or less than that for steady, fully developed laminar pow Conversely, Nu(av)/ tau(av) increased by as much as 39% for Gr/Re = 0.