Convective heat transfer from a billet due to an oblique impinging circular jet within the spray forming process

An experimental investigation was performed to study the heat transfer process from the surface of a billet due to an oblique impinging circular gas jet. The gas stream was generated by a circular array of 24 single jets within an atomizer nozzle. The application of this heat transfer condition can be found in the spray forming process during the cooling of the sprayed billet. At several positions on the billet surface the local heat transfer coefficients were measured. The measurement technique was based on the cooling of a surface mounted sensor having a sufficiently small Biot number. A comparison between published data and a test case had been carried out successfully. The distance between the atomizer and the billet, the gas mass flow rate, and the rotation angle of the billet were varied. Velocity measurements were executed to characterise the gas flow in the confined jet in the absence of the billet, while numerical flow field simulations were used to calculate the flow around the billet. The heat transfer coefficient distribution showed a significant peak at the stagnation point and decreased with increasing atomizer to billet distance and also with decreasing gas mass flow. The heat transfer coefficients averaged over the circumference of the billet were correlated empirically. (C) 2003 Editions scientifiques et medicales Elsevier SAS. All rights reserved.