Heat transfer coefficient suitable for thermal fatigue assessment at a T-junction

Abstract

Thermal fatigue cracks have been found at T-junctions where high and low temperature fluids flow in. In this study, the heat transfer coefficient at a T-junction was investigated. The obtained heat transfer coefficient was then validated by estimating the temperatures on a pipe inner surface. The temperatures of the fluid and the pipe inner surface were measured by mock-up tests in which high and low temperature water was mixed. The fluid temperature fluctuation near the boundary between the hot jet flow and the cold main flow caused the temperature on the pipe inner surface to fluctuate. The heat transfer coefficient was obtained by the power spectrum method for the pipe inner surface where the temperature fluctuation was relatively large. The estimated heat transfer coefficient was 3.3 times larger than that calculated by the Dittus-Boelter equation. The temperature on the pipe inner surface was successfully estimated using the obtained heat transfer coefficient and the measured fluid temperature in the vicinity of the inner surface. The prediction error was less than ±20% for the temperature fluctuation range.