Simulation of quenching process with liquid jets

摘要

Liquid quenching media are often utilized during heat treatment to provide the high heat transfer rates necessary to achieve the desired specimen properties (high hardness while distortion is low). Evaporation occurs close to the hot workpiece and parts of the surface might be covered by a vapor film leading to low local heat transfer rates. At Leidenfrost temperature, the boiling film collapse commonly starts at the specimen's edges followed by a movement of the rewetting front(s) towards the surface's center. In the rewetted areas, nucleation boiling enables very high heat transfer rates. The local cooling rates shall be adopted through an adjustable jet nozzle field by locally impinging the hot surface with high liquid flow velocities. In the flow's stagnation zone, the dynamic pressure accelerates the collapsing of the vapor film significantly or the vapor film formation might even be completely suppressed.A suitable numerical model is developed to calculate the heat transfer coefficients (HTC) and the flow and temperature field around the specimen during all boiling phases. Time-dependent interactions of the vapor phase with the jet-flow field are included. For a metallic plate quenched with jets arranged perpendicularly to the surface, the time-dependent cooling is calculated and compared to experimental results. The influence of flow rate, liquid temperature, nozzle arrangement and nozzle distance to the plate is analyzed.Material simulations using the calculated heat transfer rates are conducted to predict the metallic phase fractions and the hardness as the final result of the quenching process.