Movement of the Wetting Front during Water Jet Impingement Quenching on Hot Solid Surface

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.