Heat Transfer From a Heated Flat Surface Due to Swirling Coaxial Turbulent Jet Impingement

Abstract

Heat transfer from an isothermally hot flat surface due to swirling coaxial turbulent jet impingement is investigated numerically. The coaxial jet construction consists of implanting a thin-walled round tube inside a coaxial outer pipe. Two different fluid streams or jets, having different average velocities, flow through the inner tube, and the annular space between the inner tube and the outer pipe. The ratio of the average velocities of the jets, the ratio of the pipe diameters, the jet exit Reynolds number, the strength of the swirl, and the separation distance from the jet exit to the impingement surface are the main parameters for this flow configuration. The effects of the swirl strength on the jet impingement heat transfer at the target surface are investigated by computing the flow and thermal fields for various combinations of the problem parameters. The presented results contain the plots of the flow streamlines, the contours of the temperature, the contours of the swirl velocity, as well as the distribution of the local and average Nusselt number on the impingement surface. It is found that, compared to the single round jet, the coaxial jet produces enhanced and more uniform heat transfer at the heated surface. The jet-spreading and mixing are affected by the imposed jet swirl which modifies the heat transfer process. Thus, the heat transfer compared to a non-swirling jet is either enhanced or diminished depending on the combination of the problem parameters.

Coaxial Circular Jets—A Review

“…Their aim was to achieve uniform heat transfer coefficients by inverse optimization. A recent numerical simulation based on the RANS equations [50], studying both the effects of center jet swirl as well as annular jet swirl, reached the same conclusions as those by Markal [49]. However, they mentioned that heat transfer may either be enhanced or reduced depending on the combination of the problem parameters.…”

“…While there is quite some information on the flow field characteristics in the near-field of coaxial jets (as discussed in Sections 2 and 3), impinging coaxial jets have barely been studied [6,7,[49][50][51][52]. This is surprising in light of the expected potential for enhancing heat and mass transfer especially for impingement at relatively small stand-off distances (H/D ≤ 4 − 5).…”

“…Due to the complex flow dynamics of impinging coaxial jets, only few numerical studies have been published [50,62]. Bijarchi and Kowsary [62] used the finite volume method to solve the Navier-Stokes equations and the energy equation for a laminar axisymmetric, steady flow.…”