A Heat Transfer Comparison Between a Synthetic Jet and a Steady Jet at Low Reynolds Numbers

Abstract

A study has been carried out to compare steady jet and synthetic jet heat transfer distributions at low Reynolds numbers. Both jets issued from a 5mm diameter orifice plate with air for the steady jet being supplied by a compressor via a plenum chamber. Tests were conducted for Reynolds numbers ranging from 1000 to 4000, and for non-dimensional surface to jet exit spacings (H/D) from 1 to 6. Dimensionless stroke length (Lo/D) for the synthetic jet was held constant at 8. A significant difference was observed between the steady and synthetic jet Nusselt numbers at low Reynolds numbers and low H/D. In comparison to steady jets, the stronger entrainment of surrounding fluid and the vigorous mixing near the impingement surface are characteristics of synthetic jets that are beneficial to heat transfer. Nonetheless, the steady jet yields higher Nusselt numbers for all test conditions.

Comparing steady and unsteady rectangular jets issuing into a crossflow

“…Next, we consider the jet mixing, which can not only delay separation (Rediniotis et al 1999), but also enhance heat transfer (Farrelly et al 2008) and enhance turbulence (Compton & Johnston 1992). Here we represent mixing through the flow streamwise enstrophy…”

“…For non-axisymmetric unsteady jets in a boundary layer, the downstream vortex structure is highly dependent on the orifice orientation (Van Buren et al 2016b). Up to this point, no direct comparison of rectangular steady and unsteady jets in a crossflow has been made, and furthermore, there is no justification in literature for why the two jet types perform differently in preventing flow separation (De Giorgi et al 2015), in reducing drag (Cui et al 2015), and in heat transfer (Pavlova & Amitay 2006;Farrelly et al 2008).…”