Heat transfer performance of flag vortex generators in rectangular channels

Abstract

© 2018 Elsevier Masson SAS This experimental work investigated the heat transfer characteristics of rectangular channels equipped with a flapping flag as a vortex generator. Specifically, it aimed to determine the influences of channel geometry, flag material properties and flow conditions on the resulting heat transfer behaviour of the system. Results showed that the inclusion of a flapping flag in the channel enhanced the flow unsteadiness and turbulence levels, leading to Nusselt number enhancement by as high as 1.34 to 1.62 times bare channel levels. As the turbulence decays in the streamwise direction, so does the thermal enhancement. The turbulence and heat transfer enhancements are accompanied by an increase in pressure drop due to the periodic blockage imposed by the flag during flapping. The friction factor, which is governed by the flag oscillation mode and frequency, was found to be as high as 1.39 to 3.56 times bare channel levels. The thermal enhancement benefit of the flag vortex generator varies with streamwise distance: a thermal enhancement factor as high as 1.14 was observed near the flag's free end. The blockage may be minimised through the use of a thicker flag which assumes a simpler oscillation mode that reduces the contact between the flag and the channel walls. The size of the channel (aspect ratios of 0.2–1.0) relative to the flag has profound effects on flag dynamics, turbulence levels and heat transfer. Wider channels allow wider flapping amplitudes and more complex oscillation modes, which lead to the creation of stronger vortices that decay slower inside the channel. Due to stronger vortices and delayed turbulence decay, thermal enhancement in wider channels are higher and sustained for longer distances.

Source or Periodical Title

International Journal of Thermal Sciences

ISSN

12900729

Page

26-44

Document Type

Article

Subject

Flag flutter, Fluid-structure interaction, Heat transfer enhancement, Rectangular channels, Turbulence, Vortex generators

This document is currently not available here.

Share

COinS