An Inverse Method for Determining Thermal Load History Which Reduces Transient Thermal Stress

Abstract

When high temperature fluid flows into a pipe, a temperature distribution in the pipe induces a thermal stress. It is important to reduce the thermal stress for managing and extending the lives of plants. In this problem heat conduction, elastic deformation, heat transfer, liquid flow should be considered, and therefore the problem is of multidisciplinary nature. In this paper an inverse method is proposed for determining the optimum thermal load history which reduces transient thermal stress considering the multidisciplinary physics. As a typical problem, transient thermal stress in a thin pipe during start-up was treated. It was assumed that the inner surface was heated by liquid flow and the outer surface was insulated for simplicity. The multidisciplinary complex problem was decomposed into a heat conduction problem with given internal wall temperature history, thermal stress problem with given temperature distribution, and heat transfer problem with given heat flux on an inner surface. An analytical solution of the temperature distribution of the radial thickness and the thermal hoop stress distribution was obtained. The maximum inner hoop tensile stress was minimized for the case where inner surface temperature Ts(t) was expressed in terms of the 3rd order polynomial function of time t. Finally, from the temperature distributions, the optimum fluid temperature history was obtained for reducing the transient thermal tensile stress.