Research On Determination Of Temperature Fluctuation Of The Inner Wall Of A Pipe Elbow Based On The Inverse Heat Conduction Method

Thermal stratification can occur when hot and cold fluids mix inside the pipe elbows of chemical or nuclear plants. Temperature fluctuations with large amplitude and high frequency caused by the unstable thermal interface can lead to time-varying wall heat stress and even induce thermal fatigue in the pipe elbow. It is one of the hot spots in science and technology research to learn how to accurately get temperature fluctuations of the inner wall without damaging the whole structure of the pipe system.In this paper, the two-and three-dimensional numerical models were developed based on the strategy of inverse heat conduction problems (IHCP) to estimate the temperature distribution and fluctuation of the inner wall from the temperature measurements on the outer wall. The developed model can be used without any a priori information about the fluid and wall inside the pipe, without simulating the complicated mixture of the fluids.The two-and three-dimensional direct heat conduction problems (DHCP) model were both structured based on the finite element method (FEM). The inverse problem model was developed based on the conjugate gradient method (CGM) and was valided using the experimental data in the cases.Comparisons of the estimated and exact inner wall temperatures were made and show that the estimated temperature fluctuations agree well with the exact values in the two-dimensional IHCP. The analysis was performed about the influence of the number of measurement points on the calculated results. The rational number of measuring points was suggested.During the analysis of three-dimensional IHCP, an effective and accurative DHCP numerical mode was structured using the hexahedral isoparametric element based the FEM. The inverse problem was solved using the temperature measurements on the out wall. Comparisons of the estimated and exact values show that the developed numerical mode could calculate the inner wall temperature accurately. Finally, the influnce of the number of the measuring cross sections and the measuring points on the calculated results was investigated.