Effects of Non-Uniform Heat Transfer on Glass Quality in A Tempering Process

Importance of heat transfer control on created residual stresses is well-known. Tempering of thin glasses has given new challenges not only to uniformity of heat transfer but also to energy consumption because very high heat transfer coefficients are required. This is achieved by using arrays of high velocity small air jets located near the glass surface which create large variation of the local heat transfer coefficient. Simultaneously optical anisotropies which are seen as stripes or spots in glass panes are formed.

In the paper numerically calculated (CFD) local heat transfer results of impinging jets made with OpenFOAM-code are presented and compared with measurements. Local heat transfer results are used as an input in the numerical modelling of residual stresses using Ansys. It is not yet clear that can we predict on the basis of residual stress variation the degree of anisotropy until on- going experimental verification is ready.