Experimental study of the effects of quadrupole magnetic field and hydro-thermal parameters on bubble departure diameter and frequency in a vertical annulus

ABSTRACT

The effects of input parameters such as pressure, mass flux, and inlet subcooling on bubble departure diameter, frequencies, and quadrupole magnetic field have been investigated. It was observed that process of changes in diameter and bubble departure frequency was similar with and without magnetic field, and the bubbles proved a regulated growth in the presence of a magnetic field. Compared to alike working conditions without a magnetic field, with subcooled, mass flux and pressure increase, the bubble departure diameters decreased by an average of 9.55%, 15.18% and 15%, and the bubble departure frequencies increased by 45.45%, 30.38% and 21.71%, respectively.

KEYWORDS:

• Flow boiling
• inlet subcooling
• magnetic field
• bubble departure diameter
• bubble departure frequency

Nomenclature

q”	=	heat flux [Kw m−2]
$I$	=	electrical current [A]
$u$	=	fluid velocity [m s−1]
G	=	mass flux [kg m−2 s−1]
V	=	voltage [v]
R	=	electrical resistance ($\mathrm{\Omega }$)
$G$	=	mass flux [kg m−2s−1]
$X$	=	vapor quality
$D$	=	channel internal width [m]
$D_h$	=	hydraulic equivalent diameter[m]
Pr	=	prantel number
Ja	=	Jacob number
$u^{\ast }$	=	friction velocity [m s−1]
h	=	heat transfer coefficient [w m−2°C]
B	=	magnetic induction field [T]
$h_{lv}$	=	heat of vaporization (latent heat) [$J$]
dw	=	bubble contact diameter with surface[m]
$k_l$	=	thermal conductivity [w m−2°C]
$C_{pl}$	=	specific heat [$J$kg−1°C]
$C_f$	=	friction coefficient
$r_r$	=	bubble contact radius with surface[m]
$r_b$	=	bubble separation radius [m]
$f_d$	=	separation frequency [Hz]

Greek symbols

$\sigma$	=	surface tension [N m−1]
${\vartheta }_l$	=	kinematic viscosity [m2 s]
${\mu }_l$	=	dynamic viscosity of bulk fluid [kg m−1s−1]
${\tau }_w$	=	shear stress of the wall [N m−2]
${\rho }_l$	=	water density [kg m−3]
${\rho }_v$	=	vapor density [kg m−3]
$\delta$	=	liquid film thickness [m]

Subscripts

x	=	x-direction
y	=	y-direction
$l$	=	liquid
$v$	=	vapor
W	=	wall
sat	=	saturation