Abstract:
The criterion for the movement of the wetting front (visible leading edge of a moving
wetting area) on a hot solid surface due to impingement of liquid jet is important for
clear understanding of quenching / cooling phenomenon by jet impingement
quenching. No complete understanding of this important criterion has yet cited in
literature. A comprehensive study on this phenomenon is essential at the moment for
obtaining a model of jet quenching. The present study represents the wetting front
movement criterion during free jet impinging quenching on a heated surface by
impinging circular water jet. The water jet struck with jet force on the heated surface
and wanted to move towards the circumference of the heated plate but during the
movement, some other forces produced against the driving jet force and resisted the
movement of the wetting front. These resisted forces are; shear force, bubble
detaching force and the bubble explosion pressure force. When the fluid flows over
the stationary surface, the velocity of the fluid adjacent to the stationary surface
becomes zero and this layer effects the velocity of the adjacent layer and so on. This
phenomenon occurs due to the viscosity of the fluid. This force varies with the
viscosity of the fluid and traveled distance. When the water comes into contact with
super heated surface, boiling occurs. The continuous bubbles form on the surface
which resists the water flow due to surface tension. The temperature of the heated
surface during quenching at various position and time is estimated by many
researchers. The bubbles burst continuously and create a stream of vapor, this stream
of vapor resist the water flow. If the driving jet force is greater than the summation of
these three resistance forces, the wetting front will move, if equal the wetting front
will stagnant and if less, then the wetting front will not reached there. The occurring
of maximum heat flux is the most desirable event during quenching process which
always occurs after the movement of the wetting front. Therefore, the criterion for the
movement of the wetting front can be regarded as a criterion for the maximum heat
flux and ultimately maximum cooling.
