Thermal shock maximum temperature change

O ance of a material, is valid for relatively low rates of heat transfer. When the rate is high, then, upon cooling of a body, the maximum temperature change allowable without thermal shock, ATp is given by approximately... 

Thermal Shock. Multilayer ceramic capacitors may crack if exposed to thermal transients exceeding 4°C/s. These cracks are usually invisible, but may be the sites for dendritic growth in service, when the assembly is exposed to moisture under applied bias. Capacitors with high values and larger thicknesses are most susceptible. These failures can be avoided by following the manufacturer s requirements for maximum temperature excursion and rate of temperature change. 

Seal pots are nonmechanical valves that use controlled wata- levels to regulate the flow of gas to the CO boiler. The refractory lining can change from a water-saturated condition at near-ambient temperatures to 700°C (1300°F) in less than 90 sec when the water level drops and hot flue gas starts into the CO boUer. The condition will reverse when water is put back into the poL In this environment, materials with extremely good thermal shock resistance must be used to ensure maximum service life. Often, fused silica-based castables provide the best overall service. 

On the basis of thermal shock fracture theory, the basic equation to predict thermal shock resistance is a well-known triaxial modification of Hooke s law to account for thermal strains during rapid cooling (Equation 38) (Zimmermann et al., 2008). The critical change in temperature, R, can be expressed in terms of the strength of the material (o). Young s modulus (E), Poisson s ratio (v) and coefficient of thermal expansion (a). The critical temperature difference, R, to represent thermal shock resistance predicts the maximum change in temperature that can occur without the initiation of cracks ... 

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