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Heat transfer enhancement of impinging jets with fractal-generated turbulence

Cafiero, G., Discetti, S. and Astarita, T. (2014) Heat transfer enhancement of impinging jets with fractal-generated turbulence International Journal of Heat and Mass Transfer, 75. pp. 173-183.

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A new passive method for the heat transfer enhancement of circular impinging jets is proposed and tested. The method is based on enhancing the mainstream turbulence of impinging jets using square fractal grids, i.e. a grid with a square pattern repeated at increasingly smaller scales. Fractal grids can generate much higher turbulence intensity than regular grids under the same inflow conditions and with similar blockage ratio, at the expense of a slightly larger pressure drop. An experimental investigation on the heat transfer enhancement achieved by impinging jets with fractal turbulence promoters is carried out. The heated-thin foil technique is implemented to measure the spatial distribution of the Nusselt number on the target plate. The heat transfer rates of impinging jets with a regular grid and a fractal grid insert are compared to that of a jet without any turbulator under the same condition of power input. A parametric study on the effect of the Reynolds number, the nozzle-to-plate distance and the position of the insert within the nozzle is carried out. The results show that a fractal turbulence promoter can provide a significant heat transfer enhancement for relatively small nozzle-to-plate separation (for a distance equal to 2 diameters an increase of 63% at the stagnation point, and 25% if averaged over an area of radius equal to 1 nozzle diameter, are respectively found with respect to the circular jet, against 9% and 6% for the regular grid in the same conditions of power input).

Item Type: Article
Divisions : Faculty of Engineering and Physical Sciences > Mechanical Engineering Sciences
Authors :
Discetti, S.
Astarita, T.
Date : August 2014
DOI : 10.1016/j.ijheatmasstransfer.2014.03.049
Uncontrolled Keywords : Convective heat transfer; Fractal turbulence; Heat transfer enhancement; Heated thin foil; Impinging jet; Thermography; Ceramic membranes; Heat transfer coefficients; Nozzles; Reynolds number; Thermography (temperature measurement); Turbulence; Convective heat transfer; Experimental investigations; Heat Transfer enhancement; Impinging jet; Mainstream turbulence; Nozzle-to-plate distance; Thin foil; Turbulence promoters; Fractals
Depositing User : Clive Harris
Date Deposited : 12 May 2020 18:03
Last Modified : 12 May 2020 18:03

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