Jet Array Design for the Physical Tempering Process of Ultrathin Glass

A high heat transfer rate and excellent heat transfer uniformity are crucial to the physical tempering manufacturing of glass. In the current study, numerical simulations were conducted to evaluate the influence of nozzle shape (circular, square, or triangular) on the transient heat transfer rate and uniformity during jet impingement heating using a square-array configuration at low nozzle-to-plate distances. The Reynolds number (Re) was varied between 2000 and 10000, the nozzle-to-plate distance to nozzle diameter ratio (H/D) was varied between 0.2 and 2, and the nozzle-to-nozzle spacing to nozzle diameter ratio (S/D) was set to values of 4, 5, and 7. The properties of heat transfer rate and uniformity are evaluated by the surface Nusselt number distribution, the average Nusselt number, and the coefficient of variation of temperature. The results revealed that a higher heat transfer rate and good heat transfer uniformity could be obtained only at H/D = 0.2 or 2. Furthermore, square and triangular nozzles afforded superior heat transfer rates and uniformity to the corresponding circular nozzles in specific jet configurations. Moreover, at low H/D values, non-circular nozzles can obtain a higher local maximum Nusselt number than circular nozzles, and significant axis switching occurs around the impingement hole in the center of the jet impingement wall.