Experimental investigation of metal foam embedded surface thermal characteristics using air-jet impingement with different orifice geometry

ABSTRACT

Present study reports the influence of various orifice shapes (circular, square, triangular, and elliptical) on the local and average heat transfer properties of a metal foamed surface for a varied range of Reynolds number (Re = 10000 –30,000) and plate to nozzle distances (z/d = 1–10) by employing thermal imaging techniques. A copper open-cell metal foam (OCMF) with a porosity of 90% and a pores per inch (PPI) value of 20 is attached to the flat plate. The thermal behavior of the thin foil in conjunction with the OCMF employing various orifices is observed to be better than that of the smooth foil. The enhancement in heat transfer at the stagnation point for circular, elliptical, square, and triangular orifices with metal foamed plate is observed to be around 76%, 64%, 54%, and 55%, respectively, for Re = 10000. The hot surface integrated with metal foam exhibits improvements in the local thermal characteristics with distinct orifice configurations. A dimensionless foam enhancement factor was defined to assess the influence of foam on jet impingement heat transfer. The foam effect is particularly noticeable in the impingement zone compared to the wall jet region. Compared to other parameters, the nozzle-to-plate distance has a significant effect on the enhancement factor. For z/d ≤4, the improvement in local heat transfer is observed in the stagnation region (x/d ≤2); while, for a higher value of nozzle to plate distance (z/d $>$6), a uniform augmentation in thermal performance is noted across the entire heated surface. Elliptical and circular orifices exhibit better thermal performance compared to square and triangular orifices. The findings demonstrate that the foam-integrated foil significantly enhances heat transfer performance, particularly at increasing impinging distances.

KEYWORDS:

• Air-jet impingement
• metal foam
• orifice
• Reynolds number
• Nusselt number
• heat transfer characteristics

Nomenclature

$A_s$	=	Surface area
$\mathit{d}$	=	Orifice equivalent diameter
$\mathit{D}$	=	Orifice pipe diameter
$\mathit{h}$	=	Convective heat transfer coefficient
I	=	Current
$\mathit{k}$	=	Thermal conductivity of coolant
$\mathit{l}/\mathit{D}$	=	Length-to-orifice pipe diameter ratio
$\dot{\text{m}}$	=	Quantity of air supplied per second
$\mathit{Nu}$	=	Nusselt number
$\mathit{Re}$	=	Reynolds number
$\mathit{t}$	=	Orifice plate thickness
$\mathit{t}/\mathit{d}$	=	Orifice plate thickness to diameter ratio
$\mathit{x}/\mathit{d}$	=	Dimensionless distance from point of impingement
$q_{\mathit{conv},\mathit{i}}$	=	Convective heat flux
$q_{\mathit{gen},\mathit{i}}$	=	Plate generated heat per unit area (W/m2)
$q_{\mathit{loss},\mathit{i}}$	=	Atmospheric heat loss per unit area (W/m2)
$T_s$	=	Target surface temperature
$T_{\mathit{aw}}$	=	Adiabatic wall temperature
$\mathit{z}/\mathit{d}$	=	Dimensionless distance from orifice exit
Abbreviations	=
FEF	=	Foam enhancement factor
AR	=	Aspect ratio
OCMF	=	Open-cell metal foam
PPI	=	Pores per inch fps frames per second
fps	=	Frames per second

Disclosure statement

No potential conflict of interest was reported by the author(s).