J. Deng et al./Ceramics international 36(2010)299-306 329.947 150.509 28.929 208368 Fig. 14. Thermal stresses in the LN3 layered nozzle (MPa). Fig. 11. Finite element method gridding model of the nozzle. 口 N5 stress-free nozzle ■LN3 layered nozzle 日 LNI layered nozzle 362449 8013 11838 5663 Fig. 15. Comparison of maximum thermal stress at the exit in different nozzles 2275 13751 (MPa) Fig. 12. Temperature gradients in the LN3 layered nozzle (C/m). The temperature gradient in LN3 layered nozzle is shown in Fig. 12. It was found that there is greater temperature gradient used in a Cws boiler, three-dimensional finite element method inside the CWS nozzles, and the highest temperature gradient is (FEM) was used. Owing to the symmetry, an axisymmetric 17576C/, and is located at the nozzle exit. Fig 13 shows the calculation was preferred and steady state boundary conditions comparison of maximum temperature gradient of LNl, LN2, were invoked. Details on the FEM model approach and the LN3, layered nozzles and N5 stress-free nozzle at the exit. It is boundary conditions employed are described in Refs. [1, 21]. indicated that the maximum temperature gradient of N5 stress- The materials constants are listed in Table 1. Fig. 1 l shows the free nozzle is much higher than that of the Lnl, lN2, and LN3 FEM gridding model of the nozzle. layered nozzles. Fig. 14 shows the thermal stress distribution in LN3 layered 18500 N5 stress-free nozzle nozzle. As can be seen. there are higher thermal stresses inside the ■LN3 layered nozzle CWS nozzles, and the highest thermal stress is located on the exit 日LN2 layered nozzle of the nozzle and the maximum value is 477. 525 MPa. Fig. 15 E 18000 DLNI layered nozzle shows the comparison of thermal stress of LNl, LN2, and LN3 <6 ered nozzles and N5 stress-free nozzle at the exit. Itis indicated As calculated above, there are higher temperature gradient 17500 (Figs. 12 and 13)at the exit of the nozzle, which lead to large hermal stresses(Figs. 14 and 15) during the Cws burning processes. These thermal stresses can lower the fracture strength of the ceramic material, which, in some cases, may be sufficient to cause considerable damage or even catastrophic Nozzles failure of cws ceramic nozzles Fg. S 13. Comparison of maximum temperature gradients at the exit in different There may be several factors that affect the erosive wear les (C/m) resistance of the cws nozzles One is the hardness of the cwsused in a CWS boiler, three-dimensional finite element method (FEM) was used. Owing to the symmetry, an axisymmetric calculation was preferred and steady state boundary conditions were invoked. Details on the FEM model approach and the boundary conditions employed are described in Refs. [1,21]. The materials constants are listed in Table 1. Fig. 11 shows the FEM gridding model of the nozzle. The temperature gradient in LN3 layered nozzle is shown in Fig. 12. It was found that there is greater temperature gradient inside the CWS nozzles, and the highest temperature gradient is 17576 8C/m, and is located at the nozzle exit. Fig. 13 shows the comparison of maximum temperature gradient of LN1, LN2, LN3, layered nozzles and N5 stress-free nozzle at the exit. It is indicated that the maximum temperature gradient of N5 stress￾free nozzle is much higher than that of the LN1, LN2, and LN3 layered nozzles. Fig. 14 shows the thermal stress distribution in LN3 layered nozzle. As can be seen, there are higher thermal stresses inside the CWS nozzles, and the highest thermal stress is located on the exit of the nozzle, and the maximum value is 477.525 MPa. Fig. 15 shows the comparison of thermal stress of LN1, LN2, and LN3 layered nozzles and N5 stress-free nozzle at the exit. It is indicated that the layered nozzles possess lower maximum thermal stresses. As calculated above, there are higher temperature gradient (Figs. 12 and 13) at the exit of the nozzle, which lead to large thermal stresses (Figs. 14 and 15) during the CWS burning processes. These thermal stresses can lower the fracture strength of the ceramic material, which, in some cases, may be sufficient to cause considerable damage or even catastrophic failure of CWS ceramic nozzles. There may be several factors that affect the erosive wear resistance of the CWS nozzles. One is the hardness of the CWS Fig. 12. Temperature gradients in the LN3 layered nozzle (8C/m). Fig. 13. Comparison of maximum temperature gradients at the exit in different nozzles (8C/m). Fig. 15. Comparison of maximum thermal stress at the exit in different nozzles (MPa). Fig. 11. Finite element method gridding model of the nozzle. Fig. 14. Thermal stresses in the LN3 layered nozzle (MPa). J. Deng et al. / Ceramics International 36 (2010) 299–306 305