Can pulsation unsteadiness increase the convective heat transfer in a pipe flow? A systematic study

Abstract

Unsteady laminar and turbulent pipe flows subjected to a constant temperature gradient in axial direction are investigated based on asymptotic considerations. The thermal boundary condition is that of a constant wall heat flux for a steady flow. The unsteadiness is induced by a sinusoidal pressure gradient with different amplitudes and frequencies. The asymptotic analysis is performed with the help of selected CFD simulations. The simulation model is a pipe which is assumed to be infinitely long with an ideal condition of fully developed flow at the pipe entrance. For laminar flows there is no effect with respect to the time averaged heat transfer performance. For turbulent flows appreciable heat transfer enhancement only occurs with large amplitudes and low frequencies. The asymptotic analysis with CFD results are in accordance with the conclusions according to full CFD simulations. Their computational costs, however, are several orders lower. The study shows that, prior to expensive CFD simulations, an asymptotic analysis with CFD simulations at ideal conditions can be considered to find the trend with respect to the parameters of interest.