MODEL OF HEAT-TRANSFER DURING QUENCHING IN SODIUM POLYACRYLATE SOLUTIONS

A model is proposed to describe heat transfer during the later stages of a quench in sodium polyacrylate solutions. These quenchants exhibit characteristics similar to those of an oil quench, with a maximum rat e of heat transfer at temperatures much higher than that normally obta ined from aqueous quenchants. This is associated with a pronounced ran ge of temperature (400-100 degrees C) where the surface heat transfer coefficient is very low and the surface of the component is covered wi th a viscous slurry laden with almost stationary bubbles. The present work demonstrates that the heat transfer during this stage of the quen ch may be explained in terms of a heat conduction model, with heat flo w through the vapour layer similar to that found during the vapour bla nket stage at the start of the quench. Thus, in both instances the vap our acts a a layer of insulation, in contrast to the nucleate boiling stage, where rapid heat flow is associated with the release of individ ual bubbles.