Thermal mixing and dispersion in a confined swirling flow

Abstract

We present a swirl chamber with an embedded heating coil where the swirl flow is generated by a tangential entry of water into a cylindrical chamber. This apparently simple setup, as we show here, provides a rapid thermal mixing and thereby endorses a quick attainment of an asymptotic steady temperature rise at the outlet. However, the interplay between the incipient momentum and energy transport is far from being trivial. Here, we present a thermal dispersion-based paradigm that is found to capture this asymptotic behavior satisfactorily with respect to the experimental observations. The combined experimental observations and the theoretical analysis reveal that the asymptotic behavior is due to a near perfect mixing that is promoted by the stirring ability of the incipient swirling flow. The dispersion model, for the present scenario, conforms to an effective thermal diffusivity that varies linearly with the flow rate; this contrasts with the conventional dispersion model where the effective diffusivity varies quadratically with the flow rate. The asymptote of the temperature rise is found to be inversely proportional to the flow rate. The time to reach this asymptotic behavior, or equivalently the pre-asymptotic duration, is also found to be inversely proportional to the flow rate.