Evaluation of the heat transfer coefficient in thermal shock of alumina disks

Disks of a high-purity commercial alumina powder were fabricated by slip casting, pre-calcined, sintered and machined with SiC paper (120 and 320 grit). The specimens were tested in thermal shock conditions from several temperatures (Ti) between 870 and 980 C using a high-velocity air jet at room temperature (T0). The temperature differential between the disk and the air jet was incremented in 10 C until crack propagation was detected. During the air impinging, the temperature was recorded on the lower specimen surface at the central point and at a peripheral one. The coefficient governing the convective heat transfer on the specimen surface, h, was estimated by fitting the calculated temperature profiles with those measured during the test. Three alternative models were proposed for the temperature calculations using a finite element analysis. (orig.)