Reverse conduction on a rotating cylinder: Case of convective boiling induced by the impact of a water jet.

Summary In the framework of this thesis, we are interested in the problem of cooling by jet impact of a moving surface carried at high temperature. The aim is to better understand the boiling mechanisms resulting from the interaction between the jet and the wall. The targeted industrial application is related to the metallurgical industry. It concerns the hot rolling process, during which steel plates brought to temperatures between 750 and 1000°C undergo a quenching (jets at about 75°C) whose kinetics condition the microstructure of the steel product and consequently determine its mechanical properties. Our objective is to develop a methodology to measure the fluxes extracted during the impact of a jet on a running surface. Providing this type of measurement over a wide range of temperatures corresponding to boiling requires the development of a stable estimation method, closely associated with a bench and a specific experimental procedure. The proposed method consists in analyzing temperature responses measured on a solid cylinder in rotation and impacted by a jet. A Fourier transformation is applied to the Laplace transform of the signals provided by several thermocouples implanted in the near wall. In the case where the problem is considered as linear, an explicit relation between the Laplace-Fourier transform of the internal temperature and the Fourier transform of the temporal distribution of the parietal heat flux can be found. The inversion of this relationship provides an explicit algorithm to easily estimate the spatial and temporal distributions of parietal heat flux. Simulations of the inversion as well as real measurements are presented: they show the robustness of the inversion technique and allow to study the influence on the transfers of parameters such as the velocity, the temperature of the jet and the speed of the wall.