Mist Cooling for Thermal Tempering of Glass

Abstract

This paper presents a feasibility study of glass tempering using mist cooling. First, transient tests of mist cooling were conducted to investigate the effects of the thermal properties of cooling surface. To do this, test plates were made of silver, nickel, stainless steel (SUS304), and fused quartz. The experimental conditions of mist flow were as follows : the air velocity was V_a=20 m/s, the temperature of the water droplets T_l=21°C, and the volumetric-droplet-flow-rate D=0.0003-0.01m³/m²s. The experimental data show that both the plate temperature corresponding to the minimum heat flux (T_M) and the heat transfer coefficients at wall temperatures above T_M increase for decreasing thermal conductance of the surface material. Second, tempering tests of soda-lime glass plates of 2.95 and 3.90 mm thicknesses were conducted using mist cooling. The initial temperature of glass plates was about 690°C. The plates were cooled only from one side. Test results indicate that thin and low-cost tempered glass plates can be made by mist cooling without fracture.