Numerical and experimental study on mesoscopic stress and strain characteristics of printed circuit heat exchanger in gas-cooled nuclear reactors

Printed circuit heat exchanger (PCHE) possesses promising application prospects in high temperature gas-cooled nuclear reactors. It is important to analyze thermal–mechanical properties of PCHE under high temperature and high pressure conditions to ensure the safe operation of nuclear reactors. The homogenization method is able to obtain the macroscopic stress and strain distribution in PCHE, but it fails to provide accurate mesoscopic stress and strain. In this paper, equivalent mechanical properties of the minimum repetitive element of the PCHE core are calculated based on the homogenization method. The stress magnification matrix and strain magnification matrix of the unit cell are calculated, and the variation of the magnification matrix with temperature is studied. Tensile experiments of a specimen with characteristic periodic structures are conducted, and mesoscopic strain is obtained. Full-field strain distribution shows clear periodic characteristics. The strain distribution of the specimen along the path is less than 25 % deviated from the results of finite element analysis (FEA) and the magnification matrix. By establishing an actual model and an equivalent model of the PCHE core, the mesoscopic thermal stress calculated by traditional FEA and the magnification matrix are compared under mechanical and thermal loads. The relative error of both methods is lower than 10 %, while the calculation time of the magnification matrix is 80 % lower than that of traditional FEA. The above results prove the feasibility of using the magnification matrix to calculate the mesoscopic stress and strain in PCHE of gas-cooled nuclear reactors.