The Identification Algorithm Of Temperature Dependent Thermophysical Properties Of Material And Verification

Inverse heat transfer problems(IHTPs) are widely used to identify thermal physical parameters of material and surface heat flux for experimental simplicity and practicability. But the ill-posed property makes them hard to solve; therefore, the research of calculation method of IHTPs is of much importance. There are many different way to solve IHTPs, of which t he conjugate gradient method(CGM) and Levenberg-Marquardt method(LMM) are most frequently used iterative regulation methods. This thesis proposes a subsection identification method by analyzing the algorithm of CGM and LMM, researches the calculation accuracy, calculation efficiency, the dependency of initial guess and th e stability of temperature measuring error of the proposed method, and verifies its feasibility by experiment.Firstly, by Kirchhoff transformation, the nonlinear heat transfer control equation is linearized. The calculation method of direct heat transfer problems is established taking advantage of implicit finite difference method, whose effectiveness is verified by comparing the results with that of finite element method, laying a foundation for the solution of inverse heat transfer problems.Secondly, the subsection identification method is proposed on the base of analyzing obstacle of the algorithm of CGM and LMM in identification of temperature dependent thermal physical parameters.The calculation accuracy, calculation efficiency, the dependency of in itial guess and the stability of temperature measuring error of CGM, LMM and the subsection identification method is contrasted by numerical method, showing that the subsection identification method preforms better in calculation accuracy, calculation efficiency and has less dependency of initial guess. The effectiveness of multi temperature dependent thermal physical parameters identification and surface heat flux identification is also verified by numerical method.Finally, an experiment is designed to verify the feasibility of the proposed method for temperature dependent thermal physical parameter identification by real temperature history. Using collected temperature history, the thermal conductivity of oxygen-free copper is identified by the subsection identification method and compared with that of laser flash diffusivity apparatus test, indicating that the identified results are completely in the error range of test results with the same variation tendency, proving the validity of the proposed method for real temperature signal. In addition, by loading a step heat flux on the surface of material and collecting the temperature history inside, the surface heat flux is identified by the subsection identification method, verifying the effectiveness of heat flux identification, and the feasibility of the calculation method of the direct heat transfer is also verified in the meantime.