Strain Sensing for Compact Heat Exchanger Defect Detection

Abstract

The development of Compact Heat Exchangers (CHE) improves heat transfer efficiency with surface-to-volume ratios approaching 2500 m2/m3. In the applications such nuclear plants, CHE need to work for years in a harsh environment of high temperature up to 800 °C and high pressure up to 20 MPa. Any structural failure, i.e. cracks due to material fatigue or residual stress concentration in the CHEs, may result in safety problems and tremendous economy losses. Compared to the conventional heat exchangers, the non-destructive testing for CHE is challenging because the deformation of micrometer sized channels is hard to detect by the conventional means such as strain gauges or ultrasonic sensors. This paper presents a novel approach to detect the presence of cracks using fiber strain sensors embedded in the compact heat exchangers. The fiber sensors are proposed to install the heat exchanger with the microchannel plate stacks in the heat exchanger, measuring the strain distribution in the structure during the operation. Numerical and analytical models of CHE with and without cracks are built to learn crack size influence on strain variation. Sensors’ sensitivity to crack positions was calculated through simulation. A defect retrieval algorithm based on Tikhonov regularization is presented to achieve crack detection according to sensors’ outputs. A sample CHE section with 5x5 channels are simulated to quantitatively test the accuracy and validity of the proposed method.