Volume 6, Issue 4 (April 2009)
Quenching Homogeneity and Intensity Improvement in Batch Mode High Pressure Gas Quenching
Modern high pressure gas quenching processes are favorable for certain cases compared to conventional liquid media quenching, because of their advantages like, e.g., pure convective heat transfer and a lower impact of the process on the environment. But, typical gas quenching facilities may exhibit inhomogeneous flow conditions through the quench load and the parts, resulting in a scattering of the quenching result. The upstream gas flow profile of the load has been identified as one key factor that determines the local flow conditions and the heat transfer distribution from the specimen. This incoming gas velocity distribution results from the interaction between upstream placed entities, as global flow guidance, baffles, and heat exchangers. The global intensity of the quenching process is determined on one side by the pressure drop that results from the flow resistance of the quench load inside the chamber and the total volumetric flow rate in the system. On the other side, a significant part of the gas flow goes in the gap between the load and the chamber walls and does not contribute to the quenching process of the load. The first part of the investigation addresses the modeling and simulation of the flow structure inside a commercial high pressure gas quenching chamber. A multi-scale simulation model on different detailed levels is performed leading to fast convergence of the simulation. For validation of the simulation, the second part describes an experimental analysis of the gas flow inside a model quenching chamber. Here, gas velocity measurements and flow visualizations are performed. Finally, a quenching run with cylindrical parts in a double-chamber vacuum furnace is described in order to confirm the model results. Different upstream velocity profiles to the load are adjusted to demonstrate their influence on the quenching result.