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Numerical investigation of heat transfer enhancement in ribbed channel for the first wall of DFLL-TBM in ITER
Fusion Engineering and Design 87 (2012) 974–978
Contents lists available at SciVerse ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Numerical investigation of heat transfer enhancement in ribbed channel for the first wall of DFLL-TBM in ITER Qiang Jin a,c,∗ , Songlin Liu b,c , Min Li a,c , Weihua Wang a,b a b c
Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences, Hefei, Anhui, 230031, China Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui, 230031, China School of Nuclear Science and Technology, University of Science and Technology of China, Hefei, Anhui, 230027, China
a r t i c l e
i n f o
Article history: Available online 13 March 2012 Keywords: DFLL-TBM First wall Transverse rib Heat transfer enhancement
a b s t r a c t As an important component of Dual Functional Lithium Lead-Test Blanket Module (DFLL-TBM), the first wall (FW) must withstand and remove the heat flux from the plasma (q = 0.3 MW/m2 ) and high nuclear power deposited in the structure at normal plasma operation scenario of ITER. In this paper the transverse ribs arranged along the plasma facing inner wall surface were used to enhance the heat transfer capability. After the validation compared with empirical correlations the Standard k–ω model was employed to do the numerical simulation using FLUENT code to investigate the heat transfer efficiency and flow performance of coolant in the ribbed channel preliminarily. The perforation on the bottom of rib was proposed near the lower heat transfer area (LHTA) to improve the heat transfer performance according to results of analyses. © 2012 Elsevier B.V. All rights reserved.
1. Introduction China Liquid LiPb breeder blanket for DEMO [1] was defined according to a series of LiPb breeder blanket concepts [2–9] designed and evaluated by FDS team. Based on definition of DEMO blanket, a DFLL-TBM [10–13] was developed by China as one of the candidate concepts which is expected to be installed and operated in half of an ITER equatorial port. FW structure is one of the key elements for DFLL-TBM. It is designed to withstand the heat flux from the plasma chamber and the volumetric nuclear heat while it needs to maintain structure temperature and stress below the allowable limits, and to keep DEMO-blanket FW relevant. Thus, the heat transfer capability between the coolant and FW structural is critical to ITER-TBM development. As one of the well-developed technologies in the heat transfer enhancement, the transverse rib arrays are used inside the internal channel to enhance heat transfer by restarting the boundary layer after flow reattachment between two neighboring ribs. In order to evaluate the thermal and fluid performance of rib design in the coolant channel of FW, more detailed analysis of local values of heat transfer and friction loss should be investigated. It is also useful to anticipate the LHTA where the effect of heat transfer is contra deteriorated compared with the corresponding smooth channel.
∗ Corresponding author. Tel.: +86 551 5591397; fax: +86 551 5591397. E-mail address: [email protected] (Q. Jin). 0920-3796/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2012.02.072
This paper presents a physical model of FW coolant channel in DFLL-TBM where the solid rib geometries design is similar to the design in Chandra’s work [14]. Three turbulent models in prediction of heat transfer and friction loss were validated by the empirical correlations and an appropriate turbulent model was employed to make the Computational Fluid Dynamics (CFD) modeling of fluid flow and heat transfer in the coolant channel. A perforation was proposed to reduce the LHTA according to results of analyses.
2. Physical model In basic version, the structure of DFLL-TBM consisted of a 484(Tor.) mm × 1660(Pol.) mm × 585(Rad.) mm rectangular steel box. As shown in Fig. 1, the FW was a U-shaped structure made of China Low Activation Martensitic (CLAM) steel [15,16] cooled by helium coolant gas. After the scheme optimization of the FW channel, each coolant sub-circuit consisted of 5 interconnected channels (Fig. 2), i.e. the frequency of channel passing through FW was 5. The adjoining two channels remained counter-flowing arrangement in order to achieve a uniform temperature distribution across the FW surface. The physical model used in this paper is shown in Fig. 3. Considering the heat flux from the plasma facing side (q = 0.3 MW/m2 ) was highest in all the region of the FW, the ribs were arranged (AR = 1) facing inner wall surface to obtain a larger augmentation of heat transfer coefficient with a lower friction loss. Considering the limitation of compute resources, the periodic boundary condition was used for a small section of the FW channel assumed
Q. Jin et al. / Fusion Engineering and Design 87 (2012) 974–978
975
Nomenclature AR Dh e f h H k L Nu p P Pr q Re T um W y+ ω
aspect ratio = W/H hydraulic diameter (m) 15 mm rib height (m) friction factor heat transfer coefficient (W/(m2 K)) channel height (m) 15 mm thermal conductivity (W/mK) channel length of test section (m) Nusselt number static pressure (Pa) pitch of rib (m) Prandtl number heat flux (MW/m2 ) Reynolds number temperature, K bulk mean velocity (m/s) channel width (m) 15 mm dimensionless wall distance density (kg/m3 ) thermal enhancement factor turbulent specific dissipation (s−1 )
the heat transfer and fluid flow were fully developed. Because the characteristics of fluid flow and heat transfer were symmetrical to the central plane of the channel, only half of the ribbed domain was shown. The height-to-hydraulic diameter ratio e/Dh was 0.0625 and rib pitch-to-height ratio P/e was kept at 8. 3. Data reduction To describe the fluid flow and heat transfer performances, three important dimensionless parameters of interest are presented: (1) friction factor, (2) Nusselt number, and (3) thermal enhancement factor.
Fig. 2. He flow scheme in sub-circuits.
The friction factor can be defined by: f =
(p/L)Dh
(1)
2u2m
Heat transfer coefficient used is defined by: h = q /(Tw − Tb )
(2)
where Tw is the wall temperature of the channel surface adjacent to the fluid and Tb is the fluid bulk mean temperature in the channel. The heat transfer effect measured by local Nusselt number can be obtained by: Nu =
hDh k
(3)
The enhancement effect on heat transfer in channels with ribs is always accompanied by large increase of pressure drop. The thermal enhancement factor is used to evaluate the enhanced heat transfer performance: =
Nu/Nus (f/fs )
(4)
1/3
where Nus is the Nusselt number and fs is the friction factor for the fully developed flow in the smooth channel, they can be defined by Dittus–Boelter correlations (3000 ≤ Re ≤ 5 × 106 , 0.5 ≤ Pr ≤ 200): Nus =
(fs /2)(Re − 1000)Pr
1 + 12.7
fs /2(Pr 2/3 − 1)
fs = 0.25 × (1.82 log Re − 1.64)−2
Fig. 1. 3D view of the DFLL-TBM.
Fig. 3. The physical model of the transverse ribs.
(5)
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Q. Jin et al. / Fusion Engineering and Design 87 (2012) 974–978
4. Numerical simulation method The governing equations are the three-dimensional incompressible steady-state Reynolds-averaged Navier–Stokes equations. The thermophysical properties of fluid are assumed to be constant. Three turbulent models with the potential predictive ability including the Renormalized Group (RNG) k–ε model, the Realizable k–ε model and the Standard k–ω model were used for the closure of the Reynolds Stress terms in momentum equation. More details of each model can be found in Ref. [17], including the transport equations and meanings of each term in the equations. 4.1. Computational procedure Enhanced wall treatment was adopted at adjacent wall region to resolve the laminar sub-layer. To obtain grid independence solution, the number of cells was varied by changing the y+ value respectively. The numerical results of Nu indicated slightness when the boundaries near the ribbed walls was treated with y+ < 2. The governing equations were solved using the commercial CFD code Fluent 12.1. The SIMPLE algorithm was used for the velocity–pressure coupling. A second-order upwind scheme was chosen for energy and momentum equations. 4.2. Performance evaluation of turbulent models Based on the similarity law of momentum and heat respectively developed by the Nikuradse [18] and Dipprey/Sabersky [19], it was analogous in the flow and temperature field if the boundary conditions in the FW channel were the same as that in the work of Chandra et al. [14]. The empirical correlations derived by Chandra et al. [14] could be used to verify the predictive ability of the turbulent models. It is reasonable when the range of Reynolds number is Re > 1.2 × 104 . When working substance is air, all the turbulent models underestimate the values compared with the results from the empirical correlation (Fig. 4(a)). It has been observed that the relative differences between the turbulent models and empirical correlations are less than 6% and 9% for Standard k–ω model and RNG k–ω model, respectively. The Realizable k–ε model has the most deviation from empirical correlation. It has been seen that the friction factor decreases with increasing Reynolds number due to the suppression of viscous sub-layer (Fig. 4(b)). But the relative deviations in the RNG k–ε model are generally approximately 25% compared with 15% in the Standard k–ω model. It was acceptable that the Standard k–ω model could be employed to investigate the heat transfer and flow performance of coolant (He) in the ribbed channel of FW taking into account that the thermophysical properties of Air and He were similar. 5. Numerical results and discussions
Fig. 4. Validation of results in terms of (a) Nusselt number and (b) friction factor.
the solid rib ( = 1.01) are better than that in the basic design ( = 1) and ( = 0.89) integrally. Figs. 7 and 8 exhibit the streamlines and fluid velocity in the symmetry plane of ribbed-channel. As shown in Figs. 7 and 8, the stronger vortex and fluid stagnation were generated by the added solid rib compared with by the added perforated rib. 5.2. Discussion Above two schemes were investigated, the heat transfer could be significantly enhanced in ribbed channel compared with in smooth channel because the stronger vortex was generated by restarting the boundary layer after flow reattachment between two neighboring ribs, which contributed to the increase of the Nu. But
5.1. Numerical results The minimum flow velocity needed to keep the FW temperature within the limit value (550 ◦ C) was 45 m/s (Re = 1.265 × 105 ). Take this situation for example, the normalized Nu (Nu/Nus ) is higher than 1 at most part of the FW (Fig. 6(a)). The augmentation of heat transfer is significantly high on the upwind side and the top of the rib at the price of higher friction factor ratio (f/fs = 6.2). But the LHTA behind the rib can also be observed (Fig. 6(b)). A perforation had been made at the center and bottom of the solid rib to reduce the LHTA (Fig. 5). The friction factor ratio (f/fs = 4) is reduced with the decrease in the normalized Nu at the front wall (Fig. 6(c)) compared with that in the solid rib. It is observed that LHTA is reduced (Fig. 6(d)). The thermal and fluid performances in
Fig. 5. Spanwise shape of perforated rib vertical to flow direction.
Q. Jin et al. / Fusion Engineering and Design 87 (2012) 974–978
977
Fig. 6. Heat transfer distribution in terms of normalized Nu for the front wall (a) and (b) solid rib; (c) and (d) perforated rib.
the pressure drop was higher due to the increase of the friction factor. The LHTA appeared behind the rid due to fluid stagnation. The transfer heat effect in the perforated rib scheme was lower than that in the solid rib one, but the LHTA and the pressure drop was significantly reduced. The main reasons were the variation of the flow separation/reattachment point and reduction in the intensity of vortex so as to improve the velocity magnitude of fluid while a part of fluid can escape the perforation. As a compromise between transfer heat and pressure drop and LHTA, the perforated rib scheme might be suitable for heat transfer enhancement in ribbed channel for the FW. However, the thermal and fluid performance for rib scheme should be studied extensively to obtain the optimum parameters. Fig. 7. Streamlines of symmetry plane in a single pitch (a) solid rib; (b) perforated rib.
6. Conclusions In present investigation, a numerical prediction has been conducted to study heat transfer and flow behaviors in ribbed coolant channel in the FW of DFLL-TBM. The heat transfer could be enhanced although higher pressure loss of the fluid flow was obtained. After the perforation was made, the pressure drop and the LHTA were reduced at the price of heat transfer effect decreased. As next step, the thermal and fluid performance at different rib geometry including the angle, size, and spacing should be studied extensively to obtain the optimum parameters. The detailed thermal structural analysis should be investigated and analyzed after the rib added in the future work. Acknowledgments
Fig. 8. Velocity magnitude of symmetry plane in a single pitch (a) solid rib; (b) perforated rib.
This work was supported by National Special Project for Magnetic Confined Nuclear Fusion Energy (No. 2009GB109001); and by the National Natural Science Foundation of China (No.10975157 and No. 11175207).
978
Q. Jin et al. / Fusion Engineering and Design 87 (2012) 974–978
References [1] [2] [3] [4] [5] [6] [7] [8] [9]
C.H. Pan, Y.C. Wu, K.M. Feng, et al., Fusion Eng. Des. 3 (2008) 877. Y.C. Wu, Fusion Eng. Des. 81 (2006) 2713. Y.C. Wu, Fusion Eng. Des. 83 (2008) 1683. T. Ihli, T.K. Basu, L.M. Giancarli, et al., Fusion Eng. Des. 83 (2008) 912. P. Sardain, D. Maisonnier, the PPCS team, et al., Fusion Eng. Des. 81 (2006) 2673. Y.C. Wu, J. Nucl. Mater. 386 (2009) 122. Y.C. Wu, Nucl. Sci. Eng. 133 (1999) 350. Y.C. Wu, X. Zhong, U. Fischer, Fusion Eng.Des. 84 (2009) 1987. H. Hu, Y.C. Wu, M. Chen, et al., Fusion Eng. Des. 82 (2007) 2867.
[10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
Y.C. Wu, Nucl. Fusion 47 (2007) 1. Y.C. Wu, W.H. Wang, S.L. Liu, et al., Nucl. Fusion 47 (2007) 1533. Y.C. Wu, Fusion Eng. Des. 25 (2005) 347. Y.C. Wu, Fusion Eng. Des. 82 (2007) 1893. P.R. Chandra, C.R. Alexander, J.C. Han, J. Heat Mass Transfer 46 (2003) 481. Q.Y. Huang, C.J. Li, Y. Li, et al., J. Nucl. Mater. 367 (2007) 142. Q.Y. Huang, C.J. Li, Q.S. Wu, et al., Fusion Eng. Des. 85 (2009) 2192. ANSYS Fluent-12, User Manual, ANSYS-Fluent, 2009. J. Nikuradse, Laws for Flow in Rough Pipes, NACA TM, 1950, p. 1292. D.F. Dipprey, R.H. Sabersky, J. Heat Mass Transfer 6 (1963) 3.
Contents lists available at SciVerse ScienceDirect
Fusion Engineering and Design journal homepage: www.elsevier.com/locate/fusengdes
Numerical investigation of heat transfer enhancement in ribbed channel for the first wall of DFLL-TBM in ITER Qiang Jin a,c,∗ , Songlin Liu b,c , Min Li a,c , Weihua Wang a,b a b c
Institute of Nuclear Energy Safety Technology, Chinese Academy of Sciences, Hefei, Anhui, 230031, China Institute of Plasma Physics, Chinese Academy of Sciences, Hefei, Anhui, 230031, China School of Nuclear Science and Technology, University of Science and Technology of China, Hefei, Anhui, 230027, China
a r t i c l e
i n f o
Article history: Available online 13 March 2012 Keywords: DFLL-TBM First wall Transverse rib Heat transfer enhancement
a b s t r a c t As an important component of Dual Functional Lithium Lead-Test Blanket Module (DFLL-TBM), the first wall (FW) must withstand and remove the heat flux from the plasma (q = 0.3 MW/m2 ) and high nuclear power deposited in the structure at normal plasma operation scenario of ITER. In this paper the transverse ribs arranged along the plasma facing inner wall surface were used to enhance the heat transfer capability. After the validation compared with empirical correlations the Standard k–ω model was employed to do the numerical simulation using FLUENT code to investigate the heat transfer efficiency and flow performance of coolant in the ribbed channel preliminarily. The perforation on the bottom of rib was proposed near the lower heat transfer area (LHTA) to improve the heat transfer performance according to results of analyses. © 2012 Elsevier B.V. All rights reserved.
1. Introduction China Liquid LiPb breeder blanket for DEMO [1] was defined according to a series of LiPb breeder blanket concepts [2–9] designed and evaluated by FDS team. Based on definition of DEMO blanket, a DFLL-TBM [10–13] was developed by China as one of the candidate concepts which is expected to be installed and operated in half of an ITER equatorial port. FW structure is one of the key elements for DFLL-TBM. It is designed to withstand the heat flux from the plasma chamber and the volumetric nuclear heat while it needs to maintain structure temperature and stress below the allowable limits, and to keep DEMO-blanket FW relevant. Thus, the heat transfer capability between the coolant and FW structural is critical to ITER-TBM development. As one of the well-developed technologies in the heat transfer enhancement, the transverse rib arrays are used inside the internal channel to enhance heat transfer by restarting the boundary layer after flow reattachment between two neighboring ribs. In order to evaluate the thermal and fluid performance of rib design in the coolant channel of FW, more detailed analysis of local values of heat transfer and friction loss should be investigated. It is also useful to anticipate the LHTA where the effect of heat transfer is contra deteriorated compared with the corresponding smooth channel.
∗ Corresponding author. Tel.: +86 551 5591397; fax: +86 551 5591397. E-mail address: [email protected] (Q. Jin). 0920-3796/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.fusengdes.2012.02.072
This paper presents a physical model of FW coolant channel in DFLL-TBM where the solid rib geometries design is similar to the design in Chandra’s work [14]. Three turbulent models in prediction of heat transfer and friction loss were validated by the empirical correlations and an appropriate turbulent model was employed to make the Computational Fluid Dynamics (CFD) modeling of fluid flow and heat transfer in the coolant channel. A perforation was proposed to reduce the LHTA according to results of analyses.
2. Physical model In basic version, the structure of DFLL-TBM consisted of a 484(Tor.) mm × 1660(Pol.) mm × 585(Rad.) mm rectangular steel box. As shown in Fig. 1, the FW was a U-shaped structure made of China Low Activation Martensitic (CLAM) steel [15,16] cooled by helium coolant gas. After the scheme optimization of the FW channel, each coolant sub-circuit consisted of 5 interconnected channels (Fig. 2), i.e. the frequency of channel passing through FW was 5. The adjoining two channels remained counter-flowing arrangement in order to achieve a uniform temperature distribution across the FW surface. The physical model used in this paper is shown in Fig. 3. Considering the heat flux from the plasma facing side (q = 0.3 MW/m2 ) was highest in all the region of the FW, the ribs were arranged (AR = 1) facing inner wall surface to obtain a larger augmentation of heat transfer coefficient with a lower friction loss. Considering the limitation of compute resources, the periodic boundary condition was used for a small section of the FW channel assumed
Q. Jin et al. / Fusion Engineering and Design 87 (2012) 974–978
975
Nomenclature AR Dh e f h H k L Nu p P Pr q Re T um W y+ ω
aspect ratio = W/H hydraulic diameter (m) 15 mm rib height (m) friction factor heat transfer coefficient (W/(m2 K)) channel height (m) 15 mm thermal conductivity (W/mK) channel length of test section (m) Nusselt number static pressure (Pa) pitch of rib (m) Prandtl number heat flux (MW/m2 ) Reynolds number temperature, K bulk mean velocity (m/s) channel width (m) 15 mm dimensionless wall distance density (kg/m3 ) thermal enhancement factor turbulent specific dissipation (s−1 )
the heat transfer and fluid flow were fully developed. Because the characteristics of fluid flow and heat transfer were symmetrical to the central plane of the channel, only half of the ribbed domain was shown. The height-to-hydraulic diameter ratio e/Dh was 0.0625 and rib pitch-to-height ratio P/e was kept at 8. 3. Data reduction To describe the fluid flow and heat transfer performances, three important dimensionless parameters of interest are presented: (1) friction factor, (2) Nusselt number, and (3) thermal enhancement factor.
Fig. 2. He flow scheme in sub-circuits.
The friction factor can be defined by: f =
(p/L)Dh
(1)
2u2m
Heat transfer coefficient used is defined by: h = q /(Tw − Tb )
(2)
where Tw is the wall temperature of the channel surface adjacent to the fluid and Tb is the fluid bulk mean temperature in the channel. The heat transfer effect measured by local Nusselt number can be obtained by: Nu =
hDh k
(3)
The enhancement effect on heat transfer in channels with ribs is always accompanied by large increase of pressure drop. The thermal enhancement factor is used to evaluate the enhanced heat transfer performance: =
Nu/Nus (f/fs )
(4)
1/3
where Nus is the Nusselt number and fs is the friction factor for the fully developed flow in the smooth channel, they can be defined by Dittus–Boelter correlations (3000 ≤ Re ≤ 5 × 106 , 0.5 ≤ Pr ≤ 200): Nus =
(fs /2)(Re − 1000)Pr
1 + 12.7
fs /2(Pr 2/3 − 1)
fs = 0.25 × (1.82 log Re − 1.64)−2
Fig. 1. 3D view of the DFLL-TBM.
Fig. 3. The physical model of the transverse ribs.
(5)
976
Q. Jin et al. / Fusion Engineering and Design 87 (2012) 974–978
4. Numerical simulation method The governing equations are the three-dimensional incompressible steady-state Reynolds-averaged Navier–Stokes equations. The thermophysical properties of fluid are assumed to be constant. Three turbulent models with the potential predictive ability including the Renormalized Group (RNG) k–ε model, the Realizable k–ε model and the Standard k–ω model were used for the closure of the Reynolds Stress terms in momentum equation. More details of each model can be found in Ref. [17], including the transport equations and meanings of each term in the equations. 4.1. Computational procedure Enhanced wall treatment was adopted at adjacent wall region to resolve the laminar sub-layer. To obtain grid independence solution, the number of cells was varied by changing the y+ value respectively. The numerical results of Nu indicated slightness when the boundaries near the ribbed walls was treated with y+ < 2. The governing equations were solved using the commercial CFD code Fluent 12.1. The SIMPLE algorithm was used for the velocity–pressure coupling. A second-order upwind scheme was chosen for energy and momentum equations. 4.2. Performance evaluation of turbulent models Based on the similarity law of momentum and heat respectively developed by the Nikuradse [18] and Dipprey/Sabersky [19], it was analogous in the flow and temperature field if the boundary conditions in the FW channel were the same as that in the work of Chandra et al. [14]. The empirical correlations derived by Chandra et al. [14] could be used to verify the predictive ability of the turbulent models. It is reasonable when the range of Reynolds number is Re > 1.2 × 104 . When working substance is air, all the turbulent models underestimate the values compared with the results from the empirical correlation (Fig. 4(a)). It has been observed that the relative differences between the turbulent models and empirical correlations are less than 6% and 9% for Standard k–ω model and RNG k–ω model, respectively. The Realizable k–ε model has the most deviation from empirical correlation. It has been seen that the friction factor decreases with increasing Reynolds number due to the suppression of viscous sub-layer (Fig. 4(b)). But the relative deviations in the RNG k–ε model are generally approximately 25% compared with 15% in the Standard k–ω model. It was acceptable that the Standard k–ω model could be employed to investigate the heat transfer and flow performance of coolant (He) in the ribbed channel of FW taking into account that the thermophysical properties of Air and He were similar. 5. Numerical results and discussions
Fig. 4. Validation of results in terms of (a) Nusselt number and (b) friction factor.
the solid rib ( = 1.01) are better than that in the basic design ( = 1) and ( = 0.89) integrally. Figs. 7 and 8 exhibit the streamlines and fluid velocity in the symmetry plane of ribbed-channel. As shown in Figs. 7 and 8, the stronger vortex and fluid stagnation were generated by the added solid rib compared with by the added perforated rib. 5.2. Discussion Above two schemes were investigated, the heat transfer could be significantly enhanced in ribbed channel compared with in smooth channel because the stronger vortex was generated by restarting the boundary layer after flow reattachment between two neighboring ribs, which contributed to the increase of the Nu. But
5.1. Numerical results The minimum flow velocity needed to keep the FW temperature within the limit value (550 ◦ C) was 45 m/s (Re = 1.265 × 105 ). Take this situation for example, the normalized Nu (Nu/Nus ) is higher than 1 at most part of the FW (Fig. 6(a)). The augmentation of heat transfer is significantly high on the upwind side and the top of the rib at the price of higher friction factor ratio (f/fs = 6.2). But the LHTA behind the rib can also be observed (Fig. 6(b)). A perforation had been made at the center and bottom of the solid rib to reduce the LHTA (Fig. 5). The friction factor ratio (f/fs = 4) is reduced with the decrease in the normalized Nu at the front wall (Fig. 6(c)) compared with that in the solid rib. It is observed that LHTA is reduced (Fig. 6(d)). The thermal and fluid performances in
Fig. 5. Spanwise shape of perforated rib vertical to flow direction.
Q. Jin et al. / Fusion Engineering and Design 87 (2012) 974–978
977
Fig. 6. Heat transfer distribution in terms of normalized Nu for the front wall (a) and (b) solid rib; (c) and (d) perforated rib.
the pressure drop was higher due to the increase of the friction factor. The LHTA appeared behind the rid due to fluid stagnation. The transfer heat effect in the perforated rib scheme was lower than that in the solid rib one, but the LHTA and the pressure drop was significantly reduced. The main reasons were the variation of the flow separation/reattachment point and reduction in the intensity of vortex so as to improve the velocity magnitude of fluid while a part of fluid can escape the perforation. As a compromise between transfer heat and pressure drop and LHTA, the perforated rib scheme might be suitable for heat transfer enhancement in ribbed channel for the FW. However, the thermal and fluid performance for rib scheme should be studied extensively to obtain the optimum parameters. Fig. 7. Streamlines of symmetry plane in a single pitch (a) solid rib; (b) perforated rib.
6. Conclusions In present investigation, a numerical prediction has been conducted to study heat transfer and flow behaviors in ribbed coolant channel in the FW of DFLL-TBM. The heat transfer could be enhanced although higher pressure loss of the fluid flow was obtained. After the perforation was made, the pressure drop and the LHTA were reduced at the price of heat transfer effect decreased. As next step, the thermal and fluid performance at different rib geometry including the angle, size, and spacing should be studied extensively to obtain the optimum parameters. The detailed thermal structural analysis should be investigated and analyzed after the rib added in the future work. Acknowledgments
Fig. 8. Velocity magnitude of symmetry plane in a single pitch (a) solid rib; (b) perforated rib.
This work was supported by National Special Project for Magnetic Confined Nuclear Fusion Energy (No. 2009GB109001); and by the National Natural Science Foundation of China (No.10975157 and No. 11175207).
978
Q. Jin et al. / Fusion Engineering and Design 87 (2012) 974–978
References [1] [2] [3] [4] [5] [6] [7] [8] [9]
C.H. Pan, Y.C. Wu, K.M. Feng, et al., Fusion Eng. Des. 3 (2008) 877. Y.C. Wu, Fusion Eng. Des. 81 (2006) 2713. Y.C. Wu, Fusion Eng. Des. 83 (2008) 1683. T. Ihli, T.K. Basu, L.M. Giancarli, et al., Fusion Eng. Des. 83 (2008) 912. P. Sardain, D. Maisonnier, the PPCS team, et al., Fusion Eng. Des. 81 (2006) 2673. Y.C. Wu, J. Nucl. Mater. 386 (2009) 122. Y.C. Wu, Nucl. Sci. Eng. 133 (1999) 350. Y.C. Wu, X. Zhong, U. Fischer, Fusion Eng.Des. 84 (2009) 1987. H. Hu, Y.C. Wu, M. Chen, et al., Fusion Eng. Des. 82 (2007) 2867.
[10] [11] [12] [13] [14] [15] [16] [17] [18] [19]
Y.C. Wu, Nucl. Fusion 47 (2007) 1. Y.C. Wu, W.H. Wang, S.L. Liu, et al., Nucl. Fusion 47 (2007) 1533. Y.C. Wu, Fusion Eng. Des. 25 (2005) 347. Y.C. Wu, Fusion Eng. Des. 82 (2007) 1893. P.R. Chandra, C.R. Alexander, J.C. Han, J. Heat Mass Transfer 46 (2003) 481. Q.Y. Huang, C.J. Li, Y. Li, et al., J. Nucl. Mater. 367 (2007) 142. Q.Y. Huang, C.J. Li, Q.S. Wu, et al., Fusion Eng. Des. 85 (2009) 2192. ANSYS Fluent-12, User Manual, ANSYS-Fluent, 2009. J. Nikuradse, Laws for Flow in Rough Pipes, NACA TM, 1950, p. 1292. D.F. Dipprey, R.H. Sabersky, J. Heat Mass Transfer 6 (1963) 3.