Numerical Analysis for Jet Impingement and Heat Transfer Law of Self-Excited Pulsed Nozzle

The nozzle is the key component of ultra-fast cooling equipment in hot-rolling steel industry, which is crucial for improving the cooling performance. In this paper, in order to optimize the TMCP ultra-fast cooling technology, a self-excited pulsed nozzle was applied into the ultra-fast cooling equipment, and its cooling performance of jet impingement was studied. The flow states and heat transfer characteristics on the surface of the 840°C steel plate, which were impinged by the conventional cylindrical convergent nozzle and self-excited pulsed nozzle formed by adding a Helmholtz oscillating chamber, were simulated by using ANSYS-Fluent under the same inlet pressure, respectively. The maximum jet velocities, dynamic pressures, outlet flow rates of the two nozzles, the temperatures and heat fluxes of the plate surface were monitored. The results showed that, under the pressure of 0.8 MPa, the average outlet flow of the self-excited pulse nozzle was lower than that of the cylindrical convergent nozzle, whilst the self-excited pulse nozzle had higher instantaneous outlet velocity and dynamic pressure. The self-excited pulsed jet could increase turbulence intensity and heat flux on the plate surface. Compared with continuous jet impingement, the self-excited pulsed jet impingement had a better heat transfer effect with lower energy input. The results of the study can provide data support for nozzle designing and better application of ultra-fast cooling equipment.