FS&T Template - Nasr Ghoniem's Matrix Laboratory - UCLA

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Sharafat et al. SiC-FOAM BASED FLOW CHANNEL INSERT FOR DCLL TBM W/m 2 -K, depending on the interface smoothness and contact pressure. For unpolished CVD SiC surfaces a heat transfer coefficient of 1500 W/m 2 -K is assumed, which translates into a thermal resistance of 6.67×10 -4 K-m 2 /W. The location of thermal resistance interfaces are indicated in Fig. 9. The FCI material properties used for the analyses are summarized in Table II. The CVD-SiC brackets, shown in Fig. 3 serve to secure adjacent FCI segments to each other and to provide a stand-off distance from the TBM wall structure. However, following thermo-mechanical analysis of the brackets it was decided brackets. Figure 8 shows the latest design of the bracket along with characteristic dimensions. outside of the bracket is maintained at about 450 o C. The majority areas of the FCI outside panels are between 470 and 480 o C, while the inside panels are closer to 510 o C. Fig. 7: Strength and modulus of SiC foam as a function of bulk density. 11 TABLE II: FCI material properties at room temperature* PROPERTY CVD-SiC (12) SiC-Foam (11) (100% dense) (20% dense) Thermal conductivity 48 2 (W/m-K) Thermal expansion 4.55 4.20 (10 -6 /K) Specific heat (J/kg-K) 1096 1096 Density (kg/m 3 ) 3210 630 Young's modulus (GPa) 430 11 Poisson's ratio 0.21 0.22 Tensile strength (MPa) 150 7.6 *un-irradiated properties Fig. 8: Solid model of 1/4th of a single FCI segment showing bracket details (dim. in mm); this model was used for thermo-mechanical analysis with top half of the bracket removed for symmetry BCs. Thus, the largest temperature difference between the inside and outside of the FCI exists near the brackets due to the thermal resistance between bracket and FCI panels. The corresponding von Mises stress contours are shown in Fig. 10. Average stress levels along the surface of the CVD-SiC brackets are of the order of 100 MPa, while those on the foam/CVD face sheets are below 80 MPa. IV.A. FCI Segment Thermo-Mechanical Response To model typical ITER conditions, the response of the FCI segment with a uniform through the thickness gradient of 40 o C was analyzed. Results of this thermal analysis are shown in Fig. 9. The high thermal resistance between the bracket and the FCI panels results in the maximum temperatures inside the top and bottom of the FCI panels near the brackets of about 550 o C, while the Fig. 9: Temperature contours of the SiC Foam-based FCI segment; insert shows thermal resistance surfaces between bracket and FCI panels (inner FCI w MW/m 2 ; outer FCI wall: cooled with PbLi at 450 o C and h=10,000 W/m 2 -K). The stresses are highest along the outside of the SiC brackets, for two reasons: (1) the bracket is assumed to be 888 FUSION SCIENCE AND TECHNOLOGY VOL. 56 AUG. 2009
Sharafat et al. 100% dense CVD SiC with a high modulus of 412 GPa (high stiffness), and (2) the FCI foam panels exert stresses due to their thermal expansion which concentrates along the upper and lower edges of the foam panels. The high thermal resistance between the bracket and the foam panel causes the highest temperature gradients to occur near the FCI foam panel edges. This exacerbates the stresses in the brackets. This analysis indicates that improved thermal heat transfer coefficient between the bracket and the FCI foam panels are desirable to reduce temperature gradients near the support brackets. Figure 10 also plots the detailed localized stress levels along the inside edge between bracket and FCI foam panel. Stress levels in the FCI foam/CVD structure are above the tensile stress limit (~120 MPa) for unirradiated CVD SiC materials, with stresses in the bracket material being about 10 MPa to 20 MPa higher. These results indicate that the bracket design has to be modified in order to reduce stresses. Potential reduction in stress levels may be achieved, by rounding of all edges and changes and by changing bracket geometry. SiC-FOAM BASED FLOW CHANNEL INSERT FOR DCLL TBM in Figure 11 (Ref. 5). The maximum temperatures along the FCI structure occurs toward the top (exit) of the FCI, in addition, the temperature distributions are not symmetrical nor are the uniform. Fig. 11: Temperature contour maps of FCI surfaces: (a) behind FW (inside the FCI); (b) behind FW (outer); (c) back of the FCI (inner); (d) back of the FCI (outer). Fig. 10: Thermal stress contours of the SiC-Foam Based FCI segment; also shown are the stresses along the edge between the SiC bracket and CVD SiC face sheet. IV.B. Full-length FCI Thermo-Mechanical Response Based on 3-D magnetohydrodynamic calculations, detailed temperature distributions along the inside and outside faces of the entire 1.3 m long FCI structure were developed for typical ITER operations, which are shown This results in non-uniform thermal gradients across the FCI structure, which differ significantly from the simple uniform temperature conditions used to investigate a single segment (Fig. 8 Fig. 10). Figure 12 shows the results of the thermal analysis of the full length FCI structure. Temperatures along the FCI range from a low of 343 o C at the inlet to 427 o C at the outlet. The temperature gradient across the FCI structure at the exit is between 30 o C and 40 o C, while at the bottom the gradient is less than 15 o C. In calculating the stress distributions, we considered as a primary load the pressure head of PbLi along the 1.3 m height of the FCI. The maximum pressure load is of the order of 0.1 MPa exerted at the bottom and from the inside of the FCI. We did not include any pressure difference between the inside and outside of the FCI structure, because these estimates were not available. The von Mises stress contours of the combined thermal plus pressure loads are shown in Fig. 13. The maximum stresses of about 66 MPa occur above the mid-plane of the FCI on the FCI panel and behind the bracket. The stresses do not vary greatly as a function of FCI height, in fact most of the FCI structure experiences relatively uniform stress levels, ranging between 20 MPa and 50 MPa, with the lowest stresses occurring at the brackets. The combined von Mises stresses in the FCI structure made of SiC-foam sandwiched between CVD SiC face sheets and supported by CVD SiC brackets are below the allowable stress levels of for CVD SiC (~120 MPa). FUSION SCIENCE AND TECHNOLOGY VOL. 56 AUG. 2009 889
Page 1 and 2: DEVELOPMENT STATUS OF A SiC-FOAM BA
Page 3 and 4: Sharafat et al. given in reference.
Page 5: Sharafat et al. for 65 and 100 pore
Page 9: We presented here the design, the t

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