PSI - Issue 42

Ricardo Pires et al. / Procedia Structural Integrity 42 (2022) 639–646 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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2. Materials and methods In Fig. 3, one can see the two subdomains considered in the computational fluid dynamical simulations (CFD) carried out using SolidWorks® Flow Simulation. On the left, the exhaust gas domain is visible, while on the right figure it is shown the coolant domain, circulating outside the heat exchanger system, which is composed of water and ethylene glycol ( C 2 H 4 ( OH ) 2 ), both at 50% by volume, since this mixture prevents the boiling phenomenon from occurring. In addition, several working variables were defined considering the maximum functioning regimes, namely: • For the exhaust gases: a pressure of 2 bar, a mass flow of 50 kg/h and an inlet temperature of 650 ºC. • For the coolant fluid: a pressure of 4 bar, a flow of 1.5 m 3 /h and an inlet temperature of 90 ºC. For the CFD analyses carried out, the fluid and the solid domains were discretized with millions of finite volumes (cells), with very refined meshes, mainly in the transition regions at the boundary layer (Fig. 3). Hence, the total number of cells increase d with the increase on the fin’s length, being about 7 million for each analysis (in average). Moreover, the various non-linear thermomechanical analyses were carried out with the parameters then calculated from the CFD analyses. As a result, the EGR components were discretized with solid type finite elements, approximately 5 million per analysis, and a fixed boundary condition was defined at the bolt through-holes of one of the EGR flanges. In Fig. 3, it is also shown a representative image of the temperatures and fluids circulating inside the EGR, which was obtained in one of the CFD analyses carried out.

Fig. 3 Subdomains considered in the computational fluid dynamical simulations (CFD) carried out. As for the material selection, given the fact that the EGR will be exposed to thermal fatigue, oxidation at high temperatures, and corrosive condensation when operating at low loads, an AISI 304L annealed steel was selected. This is an austenitic stainless steel offering an interesting combination of cost, corrosion resistance, strength, and ductility, with low carbon content (L), a characteristic that aims to avoid intergranular/pitting corrosion, i.e., the formation of chromium carbides at grain boundaries, Martins and Branco (2004), while increasing its weldability, Prasad et al. (2014).