Assessment of the design effects on the structural performance of the Printed Circuit Heat Exchanger under very high temperature condition

Abstract

The Printed Circuit Heat Exchanger (PCHE) is an important candidate to be used as Intermediate Heat Exchangers (IHX) in High Temperature Gas-cooled Reactor (HTGR) due to its advantages in terms of heat transfer and compactness. However, the complex operating conditions that include fluid temperatures around 1173 K and pressures higher than 7 MPa, cause the structural integrity of the device must be investigated in depth. In this work, a computational model of a PCHE with two-dimensional specification was developed using computational fluid dynamics and finite element method to evaluate the thermal and mechanical stresses. The simplification of the geometric domain was done considering the sensitivity of the stresses in the channels wall. The influence of the temperature gradient and the geometric parameters on the thermal stress is presented. The mechanical stress caused by pressure was evaluated for different geometric designs in the channel wall. The temperature gradient between channels was changed in a range from 10 K to 250 K, and the design was studied by means of parameters as channel diameter, plate thickness, ridge thickness and rounded tip radius. The isochronous strain–stress curves presented in the Draft ASME BPVC for use of the Alloy 617 (UNS N06617) at high temperature, were used to develop a multilinear plasticity material model. A proportional relationship between the thermal stress and the thermal gradient between channels was found. Opposite effects of the plate thickness and the ridge thickness on the thermal and mechanical stresses were evidenced. The increase of these produced a maximum thermal stress increment while the mechanical stress was reduced. The rounded tip radius was found as the main dimension to reduce both stresses reducing the stress concentration in this region. Based on the allowable stress of the structural material, safety ranges of the geometric parameters in the PCHE design were proposed. The plastic strain was also reduced with the roundness, but this displacement showed a great affectation with the time of service at high temperature condition.