# Mechanical Integrity Analysis of a Printed Circuit Heat exchanger with Channel Misalignment
## 1 Introduction  
Heat exchangers are devices that facilitate the exchange of heat between two fluids at different temperatures while keeping them from mixing together [1, 2]. Heat exchangers are mostly used in processing, power, petroleum, air conditioning, refrigeration, alternate fuels, and other industries. Heat transfer in a heat exchanger usually involves convection in each fluid and conduction through the wall separating the two fluids. In general industry, heat exchangers can be classified according to their construction, transfer process, degree of surface compactness, flow arrangement, pass arrangement, phase of the process fluids, and heat transfer mechanism. The shell-tube type is the most popular heat exchanger for industry. However, printed circuit heat exchangers (PCHE) have shown promise because of their advantages, such as having large area density and good pressure and temperature capabilities [3, 4, 5]. High-efficiency compact heat exchangers are being widely developed and becoming increasingly important for the nuclear industry. The main target of such development is improvement of the efficiency, economics, and safety. Depending on the intended scale and application, different types are being considered, using fluids such as helium, supercritical carbon dioxide (SCO2), mixed nitrogen andhelium nitrogen, liquid metals, and molten salts. All of these reactors are operated at high temperature. For example, sodium fast-cooled reactors (SFRs) and supercritical carbon dioxide (S CO2) reactors are operated at maximum temperatures of 550 \({}^{\circ}\)C. The only difference is the working pressures, which are 0.1 and 20 MPa, respectively, for these reactor types [6]. For these reasons, safety is an important feature of PCHEs because some critical issues can occur. Additionally, the development of high-efficiency plate heat exchangers is also important for thermal energy storage in alternative energy. Alternative technologies are being developed in order to save fossil resources and reduce air pollution by capturing and using renewable sources of energy, such as solar, wind, and hydropower, or geothermal heat. Thermal energy storage (TES) is a technology that stocks thermal energy by heating or cooling a storage medium, so that the stored energy can be used at a later time for heating and cooling applications and power generation. One of the issues with this is the thermo-structural fatigue, as observed by [PERSON] et al. [7]. The thermal stresses have been found to be more dominant than stresses due to pressure cycles. This is due to the higher temperature gradient. Hence, safety has a strong relationship with high mechanical integrity and long operating life. Much effort has been given to studying the thermo-hydraulic characteristics of PCHE channels. The thermo-hydraulic performance of PCHEs for SCO2, which contains helium as the fluid, was studied by [PERSON] et al. [8]. There was a difference in the critical Reynold numbers due to the difference in the shape of the cross-section between the circular and semi-circular ducts. The thermo-hydraulic performance of a newly developed PCHE, which had a longitudinal corrugation flow channel, was studied by [PERSON] et al. [9]. The friction factors tended to be greater when the PCHE had a smaller hydraulic diameter and a larger angle of inclination. [PERSON] et al. conducted a study on heat exchangers for thermoelectric power generation. The shape of the cross-section was a combined rectangular and circular shape, with a developed tangled channel. The obtained result showed the increase of the heat transfer at a relatively lower Reynold number [10]. [PERSON] et al. conducted an assessment study of straight, zigzag, s-shape, and airfoil PCHEs for intermediate heat exchanger (IHX) of high temperature gas reactors (HTGR) and sodium-cooled fast reactors (SFR). The study suggests a best option named the Kalimer-600 IHX, which is a straight PCHE [11]. For this reason, improvement of the cross-section shape may enhance the thermo-hydraulic performance.