Oscillatory flow and heat transfer characteristics in a pipe and a packed column

Abstract

The fluid flow and heat transfer characteristics in a pipe subjected to a periodically oscillatory and reversing flow have been investigated numerically and experimentally. An examination of the governing equations and boundary conditions shows that the governing similarity parameters for the oscillatory flow in a pipe of finite length are the kinetic Reynolds number, the dimensionless oscillation amplitude of the fluid, and the length to diameter ratio of the pipe. An experimental study on the onset of turbulence found that the changes in the sign of the pressure gradient are directly responsible for the occurrence of instability in an oscillatory and reversing pipe flow. Friction coefficients of a fully developed laminar oscillating and reversing pipe flow were investigated analytically and experimentally. The numerical simulation of a sinusoidally oscillatory and reversing flow in a pipe of finite length shows that, at any instant of time, there exist three flow regimes in the pipe: an entrance regime, a fully developed regime, and an exit regime. Based on the numerical results, a correlation equation of the space-cycle averaged friction coefficient was obtained. For forced heat convection in an oscillatory flow, it was found that the Prandtl number is the additional similarity parameter, besides the kinetic Reynolds number, the dimensionless oscillation amplitude of the fluid, and the length to diameter ratio of the heated pipe. The numerical results of the associated heat transfer problem reveal that annular effects also exist in the temperature profiles of an oscillatory flow at high kinetic Reynolds numbers near the entrance and exit locations of the pipe. The space-cycle averaged Nusselt numbers of air oscillating in a pipe heated at constant temperature and uniform heat flux were obtained based on either the numerical results or the experimental data. The related problem of pressure drop in an oscillatory flow through a woven-screen packed column has also been investigated experimentally.