Heat transfer enhancement by using pulsating flows

摘要

The paper presents a theoretical model of convective heat exchangers working with internal pulsating flows. It aims for a better physical understanding of the processes leading to a heat transfer enhancement inside these devices. When the frequency of the pulsation is increased, some geometries exhibit a maximum response, measured by its temperature rise, similar to those obtained in some dynamical resonant systems. The work explains the nature of this characteristic behavior and produces a simplified theoretical model that isolates the main physical features of the fluid dynamics involved. Two characteristic frequencies, measured by its Strouhal numbers, are theoretically found. The first one is associated with the spatial-averaged thermal response of the fluid near the wall and the second with the response of the velocity field. It is found, for a general device, that both Strouhal numbers and the maximum enhancement are mainly defined by the geometry of the device. Finally, the heat transfer enhancementrn of a straight channel, a backward facing step channel, and a two heated blocks inside an adiabatic channel are used to validate the model. Enhancements calculated with the present model are compared with the results reported in the scientific literature showing a good agreement for the tested cases.