Laminar Pulsed Flow Heat Transfer in a Vertical, Isothermal Tube With and Without Buoyancy

Numerical fluid flow and heat transfer results were obtained for a pulsed laminar flow through a vertical, isothermal-walled tube for Gr/Re = 0 (no buoyancy) and 30 (buoyancy) at a cyclic-averaged Reynolds number of 500. The pulsations resulted in cyclic-averaged Nusselt numbers, Nuav, that were greater than the steady, fully-developed laminar Nusselt number, with Nuav 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 Nuav 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 τav. For Gr/Re = 30, Nuav/τav was either the same or less than that for steady, fully-developed laminar flow. Conversely, Nuav/τav increased by as much as 39 percent for Gr/Re = 0.