Experimental investigation of the thermal behavior a single-cavity and multiple-orifice synthetic jet impingement driven by electromagnetic actuator for electronics cooling

ABSTRACT

Present experimental study reports the thermal and flow measurement of multiple-orifice synthetic jet involving circular, square, and rectangular orifice shapes. Here, an infrared camera and constant temperature anemometer are used for measurement of surface temperature and flow velocity, respectively. Reynolds number and the dimensionless axial distance is varied within 1689–4670 and 1–25. The average Nusselt number for the multiple-orifice jet is found to be 60% higher compared to single orifice jets. The power spectral density of the velocity signal is analyzed to understand the vortex dynamics.

KEYWORDS:

• Synthetic jet
• multiple-orifice
• heat transfer
• power spectral density
• electronics cooling

Nomenclature

$A_s$	=	Surface area of test foil (m2)
$A_h$	=	Heated surface area (m2)
$A_o$	=	Orifice area (m2)
$d_h$	=	Hydraulic diameter of center orifice (m)
$f$	=	Frequency (Hz)
$h_{avg}$	=	Average heat transfer coefficient (W/m2K)
$H$	=	Depth of cavity (m)
$I$	=	Input current (A)
$k$	=	Thermal conductivity of air (W/m K)
$L$	=	Orifice plate length (m)
$N{u}_{avg}$	=	Average Nusselt number (havgdh/k)
$Re$	=	Reynolds number $\left(\frac{U_{0d_h}}{\vartheta }\right)$
$r$	=	Radial distance (m)
$S$	=	Stokes number $\left(S=\sqrt{\frac{2\pi f{d}^2}{\gamma }}\right)$
St	=	Strouhal number
$t$	=	Orifice plate thickness (m)
$T_w$	=	Surface temperature (oC)
$T_a$	=	Ambient temperature (oC)
$U_0$	=	Average jet centerline velocity (m/s)
$U_m$	=	Mean velocity (m/s)
$U_{max}$	=	Maximum Um value (m/s)
$q_{conv}$	=	Net heat flux convected to impinging jet (W/m2)
$q_{gen}$	=	Ohmic heat flux (W/m2)
$q_{loss}$	=	Free convection heat loss (W/m2)
$q_{\left(rad\right)t}$	=	Radiation loss from the top surface (W/m2)
$q_{\left(rad\right)b}$	=	Radiation loss from the bottom surface (W/m2)
$V$	=	Input voltage (V)
$z$	=	Axial distance between jet and surface (m)
$z/d_h$	=	Nozzle-to-surface distance
Greek symbols	=
$\mu$	=	Dynamic viscosity of jet fluid (kg/m-s)
$\vartheta$	=	Kinematic viscosity of jet fluid (m2/s)
	=	Density of air (kg/m3)
$\tau$	=	Period of actuation of jet generation (s)
Abbreviations	=
$AR$	=	Aspect ratio
$avg$	=	Average
$CJ$	=	Continuous jet
DSJ	=	Dual synthetic jet
$max$	=	Maximum
m	=	Mean
$PR$	=	Pitch ratio
rad	=	Radiation
rms	=	Root mean square
SJ	=	Synthetic jet