Experimental and numerical study of flow and heat transfer from a pulsed jet impinging on a pinned surface

ABSTRACT

The present study aims to investigate the effects of the pin on flow and heat transfer from pulsating jet impinging on a heated flat surface. A row of cylindrical pins has been applied on a flat plate with a constant heat flux of 2000 W/m². The experiments have been performed for two jet to target surface distances, frequency range from 50 Hz to 100 Hz and jet Reynolds number from 7000 to 15000. The effect of presence of pin, pulse frequency, Reynolds number, and jet to target surface distance have been investigated. Results of the numerical simulations indicate that the RNG k-ε model can predict the distribution of Nusselt number in good agreement with the experimental data. Results of the present study showed that the presence of pin changes the coherent vortical of the flow structure at both upstream and downstream of the pins. It is shown that at Re = 10000 and H/d = 5 the pulsed jet with frequencies of 50 Hz, 80 Hz, and 100 Hz increases the heat transfer from the pinned surface by 21%, 30%, and 36%, respectively, in comparison the steady jet. Finally, experimental observation indicated that the Nusselt number increases with increasing the pulse frequency and Reynolds number and decreases with increasing the jet to target surface distance.

KEYWORDS:

• Pulsed impinging jet
• pinned surface
• heat transfer
• Nusselt number

Nomenclature

cp	=	Specific heat (N. m. kg−1. K−1)
d	=	Diameter of nozzle (mm)
D	=	Diameter of Pin (mm)
f	=	Frequency of pulsed jet (s−1)
H	=	Nozzle-to-surface distance (mm)
k	=	Turbulence kinetic energy (m2. s−2)
L	=	Height of pin (mm)
Nu	=	Time averaged of local Nusselt number
Nuave	=	Time and area averaged of Nusselt number
P	=	Static pressure (Pa)
q”	=	Heat flux (W. m−2)
r	=	Radial distance from the center of pinned surface
Rejet	=	Reynolds number based jet diameter
T	=	Temperature (K)
Ts	=	Surface temperature (K)