Development of a Facility for High Cycle Thermal Fatigue Testing in Pure Water and Measurement of Heat Transfer Coefficient in an Annular Gap between Rotating Inner and Stationary Outer Cylinders

摘要

Temperature fluctuations in power plants may cause thermal fatigue in structures. In order to maintain integrity of structures, the thermal fatigue life has to be evaluated. Although a Coffin type thermal fatigue testing apparatus induces a homogeneous thermal strain in a specimen, high cycle thermal fatigue with strain distribution under the specimen surface can not be performed by it. In this study, a facility for high cycle thermal fatigue testing in pure water was developed. High and low temperature water are continuously supplied into an autoclave with a rotating cylindrical fatigue specimen, so that the specimen surface is simultaneously surrounded by high and low temperature water. Since the specimen is driven by a motor outside of the autoclave, the specimen suffers from the rotation synchronized thermal fatigue. Using the developed facility, heat transfer coefficients on the specimen surface of type 304 stainless steel were measured at various revolution frequency. The heat transfer coefficients were found to increase with the revolution frequency and were greater than 50 kW/m~2 K at the frequency higher than 5 Hz. High cycle thermal fatigue cracks are expected to be initiated since higher stress than the fatigue limit of mechanical fatigue can be initiated with this facility.