Progress on the Development of a Quench Boiling Model for CFD

Heat treating, including a liquid or gas quenching step, is an integral component of the production of most metal components. The rapid cooling that occurs during quenching largely defines the phase distribution, microstructure, residual stress, and distortion in the as-quenched part. Improvements in liquid quenching performance through analysis and simulation have proven difficult due to the complexities of boiling heat transfer. While extensive water boiling models have been developed for nuclear reactors, those models are focused on nucleate boiling, omitting the film and transition boiling that are critical to quenching processes.

Development of accurate boiling models for use in CFD simulations requires a solid foundation of boiling heat flux data for the quenchant in question. Anecdotal data are available based on the quenching of instrumented parts, with surface temperatures and heat fluxes determined through inverse analyses. That approach can provide solutions that are non-unique, and may not represent that actual transient surface heat fluxes.

In order to provide the high quality data needed to develop boiling models for CFD analyses, a flow boiling test fixture has been developed that can collect steady-state data for surface temperatures up to 1600 F, eliminating many of the pitfalls of previous test methods. Using that data, a preliminary model has been developed to represent the boiling heat fluxes of that quench oil. A CFD simulation of the quenching of a simple part is presented along with comparison to thermocouple data and inverse-generated surface heat fluxes.