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Improvement of the flow rate distribution in quench tank by measurement and computer simulation
Materials Letters 60 (2006) 1659 – 1664 www.elsevier.com/locate/matlet
Improvement of the flow rate distribution in quench tank by measurement and computer simulation Nailu Chen a,b,⁎, Bo Liao a , Jiansheng Pan b , Qiang Li a , Changyin Gao c a
c
Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinghuangdao 066004, China b School of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200030, China Department of Mechanical and Electrical Engineering, Zhengzhou Institute of Aeronautical Industry Management, China Received 11 June 2005; accepted 28 November 2005 Available online 17 January 2006
Abstract In order to investigate the flow rate distribution and improve the flow rate uniformity of the quenchant in a quench tank, the ultrasonic Doppler velocimeter (UDV) was adopted to measure the flow rate of quenchant with agitation, and then computational fluid dynamics (CFD) simulation had been carried out to simulate the flow rate distribution without/with flow baffles. According to the CFD simulation results, the structure and positions of flow baffles in the draft-tube were optimized to obtain the uniformity of flow rate in the quench zone, which were verified by experiments as well. The simulation and measurement results show that the UDV is suitable for measuring the flow rate of a large size quench tank. This research will provide a foundation for optimizing the structure design of flow baffles in production quench tanks. © 2005 Elsevier B.V. All rights reserved. Keywords: Quench tank; Flow rate; Simulation; Measurement; Flow baffles
1. Introduction During the quenching operation, distortion and sometimes cracking can occur because of uneven cooling of a part, which in turns affect the quality of the produced part. One of the greatest contributors to non-uniform hardness, cracking and distortion during quenching is non-uniform fluid flow throughout the quenching zone in the production quench tank [1]. Therefore, it is vital to provide uniform flow rate distribution in the quench zone to avoid cracking and control distortion [2,3]. For a particular quench tank, the flow rate uniformity in the quench zone depends mainly on the manner of agitation and the structure of flow baffles. Quench tank agitation can be provided by various methods including the recirculation pump, submerged spray, impeller stirrer, ultrasonic, and actual movement
⁎ Corresponding author. School of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200030, China. Tel./fax: +86 21 54745922. E-mail address: [email protected] (N. Chen). 0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.11.102
of the part itself, etc. Among these agitation methods, the most common and cost-effective one is an impeller mixer. Recirculation pumps, as a rule, require approximately ten times the
Fig. 1. Principle of the UDV.
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N. Chen et al. / Materials Letters 60 (2006) 1659–1664
Fig. 2. The measurement system of the UDV. Fig. 4. The structures and positions of flow baffles in quench tank.
power to drive the same amount of quenchant to reach the same flow rate as that of an impeller mixer, and at the same time the impeller agitation can drive large flux of quenchant to create the high turbulence necessary for uniform quenching cooling of a part. Generally the mixing impellers used for quenching operations are either open-impeller or draft-tube one. In the absence of a baffle to redirect flow into the quenching region of the tank, the open-impeller mixer does not have a flow directing surface encasing the impeller, which depends on the impeller itself. Thus, the draft-tube agitation is often used to provide directional fluid flow around the part being quenched. Totten and Lally [4] introduced the design principle of the draft-tube mixer, especially about the structures of the impeller and flow baffles. Because of the limitations of flow rate measurement
under turbulence, the structure of the draft-tube mixer is empirically designed by experiments up to now. Although some integral (sealed) quench furnaces also employ quench tanks with the draft-tube agitation, flow baffles, and overflow weir [5], the effect of the structures and positions of flow baffles in quench tank with draft-tube on flow rate distribution has not yet been investigated. The turbine velocimeter, Pitot-static tube, streak photography and the hot-wire anemometer are used to measure the actual values of flow rates in order to evaluate the uniformity of flow rate distribution in the quench zone. Most of these methods are only suitable for the laminar flow measurement, but are not suitable for the turbulence flow measurement of quenchant under impeller agitation. In the documents [6] the laser Doppler velocimeter with the Doppler frequency shift as its operating principle has been adopted to measure flow rates in a laboratory-scale mixing vessel. Since it is difficult to receive the reflected laser light in the quench tank with a relative greater size, flow rates of quenchants that occupies only one seventh volume of quench tank were measured, and the flow rates distribution of quenchants in the whole quench tank were then inferred by computer simulation. With the development of computer technology, CFD has been employed to simulate the flow rate distribution in a quench tank [7–10]. But the research on the flow rate distribution in a complex quench tank with flow baffles has not yet been reported, and the papers about improving the structures and
Table 1 The flow rate measurements by UDV at n = 371 rpm without flow baffles
Fig. 3. Schematic diagram of the quench tank with impeller agitation (X100 mm).
Coordinate (X/Y/Z)
Flow rates (m s− 1)
Z (mm) Y (mm) X (mm)
300 0 0.42 0.45 0.59
0 200 400
250 0.42 0.56 0.54
500 0.47 0.45 0.59
600 0 0.33 0.37 0.48
250 0.35 0.37 0.30
500 0.27 0.34 0.25
N. Chen et al. / Materials Letters 60 (2006) 1659–1664 Table 2 The flow rate measurements by UDV at n = 371 rpm with flow baffles Coordinate (mm)
Flow rates (m s− 1)
Z (mm) Y (mm) X (mm)
300 0 0.45 0.48 0.39
0 200 400
250 0.41 0.48 0.43
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3. Simulation of the flow rate distribution 3.1. Boundary conditions
600 500 0 0.32 0.32 0.45 0.33 0.41 0.36
250 0.32 0.36 0.30
500 0.30 0.33 0.28
positions of flow baffles by means of flow rate measurement or simulation are also not available. In order to highlight the effect of flow baffles on the flow rate in a quench tank, the CFD simulation has been carried out for the flow rate distribution without/with flow baffles, and the flow rates were measured by a UDV to verify the simulation results as well. Finally, the design of the structures and positions of the flow baffles are optimized. 2. Flow rate measurement In this study, the UDV was adopted to measure the flow rate of the quenchant in a quench tank by impeller agitation. The UDV operates on the Doppler shift principle. The transmitted frequency is altered linearly by being reflected from particles and bubbles moving in the fluid, as illustrated in Fig. 1. Since acoustic wave can be transmitted in liquid, the emitting and collecting sensors of the UDV can be directly immersed in the quenchant to measure the local flow rate of the quenchant. Fig. 2 shows the flow rate measurement system in a quench tank. The structure of the quench tank is illustrated in Fig. 3, which has a total capacity of 1 m3. The quenching system consists of a variable speed trifoliate impeller of diameter 350 mm used in vessel, two J-shaped flow baffles and an overflow weir, etc. Water was chosen as quenchant for the test. The structure of the flow baffles and those positions in the draft-tube are shown in Fig. 4. Table 1 lists the values of flow rate measured by the UDV without the flow baffles at rotate speeds of impeller n = 371 rpm, and the values with the flow baffle are shown in Table 2.
Fig. 5. The flow rate distribution in the x–z plane of y = 250 mm without flow baffles at n = 371 rpm.
In the quench tank, water is driven through the draft-tube by a rotating impeller. Dynamic viscosity of water at 20 °C is 1.002 e− 3 N s/m2. In the computational model, the initial flow rate leaving the impeller needs to be set. If the rotational component of impeller agitation is ignored, the boundary condition is regarded as a uniform velocity from the impeller down to the bottom of the draft-tube: n = 371 rpm: Vz = −1.113 m/s Vx = Vy = 0 m/s n = 566 rpm: Vz = −1.698 m/s Vx = Vy = 0 m/s n — rotate speeds of impeller
The free surface of the quenchant that works as the interface between quenchant and air is complex and unsteady. For simplification, the surface is simulated as a rigid lid with slip. The rigid lid implies that the surface is flat. A slip surface is impermeable for the flow, but it does not resist its tangential motion. 3.2. Results of CFD simulation Using the finite element method, the flow rate distributions in the quench tank at n = 371 rpm and n = 566 rpm are obtained. Fig. 5 shows the flow rate distribution in the x–z plane at the coordinate y of 250 mm without flow baffles at n = 371 rpm, while Fig. 6 represents the flow rate distribution in the same plane with flow baffles (in Fig. 4) at n = 371 rpm. 4. Distribution of flow rate with improved flow baffles As shown in Fig. 5, the flow rate distribution in the production-quenching zone is not uniform. In order to obtain the uniform flow rate distribution, CFD simulations had been performed for many design cases with different structures and positions of the flow baffles in the quench tank. Based on the simulation results, the structures and positions of the
Fig. 6. The flow rate distribution in the x–z plane of y = 250 mm with flow baffles at n = 371 rpm.
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Fig. 9. Distribution of simulated flow rates at n = 371 rpm (water, Y = 250 mm, Z = 300 mm). Fig. 7. The structures and positions of flow baffles after improved in the quench tank.
Fig. 10. Distribution of simulated flow rates at n = 371 rpm (water, Y = 250 mm, Z = 600 mm). Fig. 8. The flow rate distribution in the x–z plane of the y = 250 mm with improved flow baffles at n = 371 rpm.
flow baffles were designed to obtain the optimum flow rate distribution in the quenching zone, as illustrated in Fig. 7. The flow rate distribution simulated with improved flow baffles at the x–z plane of coordinate y of 250 mm at n = 371 rpm is shown in Fig. 8. To verify the simulation results, the actual values of flow rates were measured, and are listed in Table 3.
Table 3 The flow rates measured at n = 371 rpm with improved flow baffles Coordinate (mm)
Flow rates (m s− 1)
Z (mm) Y (mm) X (mm)
300 0 0.30 0.40 0.37
0 200 400
250 0.36 0.41 0.38
500 0.36 0.38 0.35
600 0 0.28 0.32 0.29
250 0.30 0.35 0.32
500 0.30 0.33 0.31
Fig. 11. Distribution of simulated flow rates at n = 566 rpm (water, Y = 250 mm, Z = 300 mm).
N. Chen et al. / Materials Letters 60 (2006) 1659–1664
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5. Discussion 5.1. Effect of the flow baffles In the practical experiment, the impeller is driven to force the quenchant of water down and across the bottom along the drafttube. So, the angular momentum is inevitably imparted to the fluid, which has an effect on the uniformity of the flow rate, especially on the flow rates in the direction along the x axis, see Tables 1 2 and 3. Figs. 9–12 show the change of flow rates along the coordinate x axis in the quench tank without flow baffles, with flow baffles and with improved flow baffles at the coordinate z of 300 and 600 mm at n = 371 rpm and n = 566 rpm, respectively. The effect of flow baffles is to redirect the flow and to remove great mass of the swirl from the impeller. The datum shown in (Figs. 5, 6, and 8) indicate that the uniformity of flow rate gradually increases as the structures and position of the flow baffles are adjusted. Therefore, by improving the structures and positions of the flow baffle in the draft-tube effectively, the uniformity of flow rates in the quench tank will be increased significantly. 5.2. Effective quenching zone (Figs. 5, 6, and 8) show the change of the flow rate distribution in the x–z plane of the y = 250 mm in the quench tank without flow baffles, with flow baffles and with improved flow baffles, respectively. It can be seen that the uniformity of flow rate increases from the bottom of the quench tank to its top, especially in the region from the coordinate z of 300 to 700 mm. This implies that a quenching zone exists in which the flow rate distribution is uniform, and its dimension increases as the flow baffles improved. For the experimental quench tank with improved flow baffles, the dimensions of the effective quenching zone are 400 mm(x) × 500 mm(y) × 400 mm(z) from the coordinate z of 300 to 700 mm. This information is important for steel quenching. The uniform cooling of a part in this zone can obviously reduce the distortion.
Fig. 13. Comparison of the flow rates of simulation and measurement at y=0.25 m, z=0.3 m along the coordinate x axis at n=371 rpm with improved flow baffles.
5.3. Effect of the rotate speeds of impeller At this research, the flow rates distribution had been measured and simulated at two rotate speeds of impeller. The simulated results, Figs. 9–12, show that the degree of uniformity of flow rate decreases with increase in the rotate speeds of impeller. So moderate rotate speeds of impeller is necessary to reduce the distortion of a part. 5.4. Analysis of simulation error Fig. 13 shows the comparison between the flow rates calculated by simulation and measured by actual experiment. Although the discrepancy exists, the CFD simulation can exhibit the actual tendency of the flow rate distribution in the quenching zone to some extent. 6. Conclusions 1) The flow rates of the quenchant in the quench tank are measured by using UDV. The experimental results prove that this method is suitable for measuring the flow rates of quenchants in a quench tank. 2) According to the CFD simulation results, the structures and positions of flow baffles are adjusted to obtain the uniform distribution of flow rates in the quenching zone. This research will guide the structure design of the flow baffles in a quench tank. 3) The simulation of flow rate in the quench tank indicates an effective quenching zone with uniform flow rate exists, and its dimensions depend on the structures and positions of flow baffles. References
Fig. 12. Distribution of simuilated flow rates at n = 566 rpm (water, Y = 250 mm, Z = 600 mm).
[1] G.E. Totten, G.E. Webster, N. Gopinath, Quenching fundamentals: effect of agitation, Advanced Materials & Processes 2 (1996) 73–76. [2] H.M. Tensi, G.E. Totten, G.M. Webster, Proposal to Monitor Agitation of Production Quench tanks, 17th ASM Heat Treating Society
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[3]
[4]
[5] [6]
N. Chen et al. / Materials Letters 60 (2006) 1659–1664
Conference Proceedings including the 1st International induction Heat Treating Symposium.Indianpolis, Indiana, USA, September 15–18 1998, pp. 423–431. Canale, C.F. Lauralice, G.E. Totten, Elimination of quench cracking by controlling agitation uniformity, Proceedings of the 14th IFHTSE Congress, October 26-28 2004, Transactions of Materials and Heat Treatment, vol. 25 (5) (2004), pp. 457–461, Shanghai, China. G.E. Totten, K.S. Lally, Proper agitation dictates quench success, Heat Treating, 9 (1992) 12–17; G.E. Totten, K.S. Lally, Proper agitation dictates quench success, Heat Treating, 10 (1992) 28–30. G.E. Totten, C.E. Bates, N.A. Clitton, Handbook of Quenchants and Quenching Technology[M], ASM International, Cleveland, 1993, p. 384. D.R. Garwood, J.D. Lucas, R.A. Wallis, J.D. Ward, Modeling of the flow distribution in an oil quench tank, Journal of Materials Engineering and Performance, 1 (6) (1992) 781–787.
[7] A.J. Baker, Potential for CFD in heat treating, Advanced Materials and Processes, 10 (1997) 44O–44T. [8] N. Bogh, Quench tank agitation design using flow modeling, in: G.E. Totten, R.A. Wallis (Eds.), Heat Treating: Equipment and Processes (Conference Proceedings), ASM International, Materials Park, Ohio, 1994, pp. 51–54. [9] R.A. Wallis, D.R. Garwood, J. Ward, The use of modeling techniques to improve the quenching of components, in: G.E. Totten, R.A. Wallis (Eds.), Heat Treating: Equipment and Processes (Conference Proceedings), ASM International, Materials Park, Ohio, 1994, pp. 105–116. [10] A.J. Baker, P.D. Manhardt, J.A. Orzechowski, On a FEM platform for simulation of quenching/heat treating operations, in: G.E. Totten, M.A.H. Howes, S.J. Sjostron, K. Funatani (Eds.), Proceeding of the Second International Conference on Quenching and the Control of Distortion, ASM International, Cleveland. Ohio, November 4–7 1996, pp. 283–290.
Improvement of the flow rate distribution in quench tank by measurement and computer simulation Nailu Chen a,b,⁎, Bo Liao a , Jiansheng Pan b , Qiang Li a , Changyin Gao c a
c
Key Laboratory of Metastable Materials Science and Technology, Yanshan University, Qinghuangdao 066004, China b School of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200030, China Department of Mechanical and Electrical Engineering, Zhengzhou Institute of Aeronautical Industry Management, China Received 11 June 2005; accepted 28 November 2005 Available online 17 January 2006
Abstract In order to investigate the flow rate distribution and improve the flow rate uniformity of the quenchant in a quench tank, the ultrasonic Doppler velocimeter (UDV) was adopted to measure the flow rate of quenchant with agitation, and then computational fluid dynamics (CFD) simulation had been carried out to simulate the flow rate distribution without/with flow baffles. According to the CFD simulation results, the structure and positions of flow baffles in the draft-tube were optimized to obtain the uniformity of flow rate in the quench zone, which were verified by experiments as well. The simulation and measurement results show that the UDV is suitable for measuring the flow rate of a large size quench tank. This research will provide a foundation for optimizing the structure design of flow baffles in production quench tanks. © 2005 Elsevier B.V. All rights reserved. Keywords: Quench tank; Flow rate; Simulation; Measurement; Flow baffles
1. Introduction During the quenching operation, distortion and sometimes cracking can occur because of uneven cooling of a part, which in turns affect the quality of the produced part. One of the greatest contributors to non-uniform hardness, cracking and distortion during quenching is non-uniform fluid flow throughout the quenching zone in the production quench tank [1]. Therefore, it is vital to provide uniform flow rate distribution in the quench zone to avoid cracking and control distortion [2,3]. For a particular quench tank, the flow rate uniformity in the quench zone depends mainly on the manner of agitation and the structure of flow baffles. Quench tank agitation can be provided by various methods including the recirculation pump, submerged spray, impeller stirrer, ultrasonic, and actual movement
⁎ Corresponding author. School of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200030, China. Tel./fax: +86 21 54745922. E-mail address: [email protected] (N. Chen). 0167-577X/$ - see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.matlet.2005.11.102
of the part itself, etc. Among these agitation methods, the most common and cost-effective one is an impeller mixer. Recirculation pumps, as a rule, require approximately ten times the
Fig. 1. Principle of the UDV.
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N. Chen et al. / Materials Letters 60 (2006) 1659–1664
Fig. 2. The measurement system of the UDV. Fig. 4. The structures and positions of flow baffles in quench tank.
power to drive the same amount of quenchant to reach the same flow rate as that of an impeller mixer, and at the same time the impeller agitation can drive large flux of quenchant to create the high turbulence necessary for uniform quenching cooling of a part. Generally the mixing impellers used for quenching operations are either open-impeller or draft-tube one. In the absence of a baffle to redirect flow into the quenching region of the tank, the open-impeller mixer does not have a flow directing surface encasing the impeller, which depends on the impeller itself. Thus, the draft-tube agitation is often used to provide directional fluid flow around the part being quenched. Totten and Lally [4] introduced the design principle of the draft-tube mixer, especially about the structures of the impeller and flow baffles. Because of the limitations of flow rate measurement
under turbulence, the structure of the draft-tube mixer is empirically designed by experiments up to now. Although some integral (sealed) quench furnaces also employ quench tanks with the draft-tube agitation, flow baffles, and overflow weir [5], the effect of the structures and positions of flow baffles in quench tank with draft-tube on flow rate distribution has not yet been investigated. The turbine velocimeter, Pitot-static tube, streak photography and the hot-wire anemometer are used to measure the actual values of flow rates in order to evaluate the uniformity of flow rate distribution in the quench zone. Most of these methods are only suitable for the laminar flow measurement, but are not suitable for the turbulence flow measurement of quenchant under impeller agitation. In the documents [6] the laser Doppler velocimeter with the Doppler frequency shift as its operating principle has been adopted to measure flow rates in a laboratory-scale mixing vessel. Since it is difficult to receive the reflected laser light in the quench tank with a relative greater size, flow rates of quenchants that occupies only one seventh volume of quench tank were measured, and the flow rates distribution of quenchants in the whole quench tank were then inferred by computer simulation. With the development of computer technology, CFD has been employed to simulate the flow rate distribution in a quench tank [7–10]. But the research on the flow rate distribution in a complex quench tank with flow baffles has not yet been reported, and the papers about improving the structures and
Table 1 The flow rate measurements by UDV at n = 371 rpm without flow baffles
Fig. 3. Schematic diagram of the quench tank with impeller agitation (X100 mm).
Coordinate (X/Y/Z)
Flow rates (m s− 1)
Z (mm) Y (mm) X (mm)
300 0 0.42 0.45 0.59
0 200 400
250 0.42 0.56 0.54
500 0.47 0.45 0.59
600 0 0.33 0.37 0.48
250 0.35 0.37 0.30
500 0.27 0.34 0.25
N. Chen et al. / Materials Letters 60 (2006) 1659–1664 Table 2 The flow rate measurements by UDV at n = 371 rpm with flow baffles Coordinate (mm)
Flow rates (m s− 1)
Z (mm) Y (mm) X (mm)
300 0 0.45 0.48 0.39
0 200 400
250 0.41 0.48 0.43
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3. Simulation of the flow rate distribution 3.1. Boundary conditions
600 500 0 0.32 0.32 0.45 0.33 0.41 0.36
250 0.32 0.36 0.30
500 0.30 0.33 0.28
positions of flow baffles by means of flow rate measurement or simulation are also not available. In order to highlight the effect of flow baffles on the flow rate in a quench tank, the CFD simulation has been carried out for the flow rate distribution without/with flow baffles, and the flow rates were measured by a UDV to verify the simulation results as well. Finally, the design of the structures and positions of the flow baffles are optimized. 2. Flow rate measurement In this study, the UDV was adopted to measure the flow rate of the quenchant in a quench tank by impeller agitation. The UDV operates on the Doppler shift principle. The transmitted frequency is altered linearly by being reflected from particles and bubbles moving in the fluid, as illustrated in Fig. 1. Since acoustic wave can be transmitted in liquid, the emitting and collecting sensors of the UDV can be directly immersed in the quenchant to measure the local flow rate of the quenchant. Fig. 2 shows the flow rate measurement system in a quench tank. The structure of the quench tank is illustrated in Fig. 3, which has a total capacity of 1 m3. The quenching system consists of a variable speed trifoliate impeller of diameter 350 mm used in vessel, two J-shaped flow baffles and an overflow weir, etc. Water was chosen as quenchant for the test. The structure of the flow baffles and those positions in the draft-tube are shown in Fig. 4. Table 1 lists the values of flow rate measured by the UDV without the flow baffles at rotate speeds of impeller n = 371 rpm, and the values with the flow baffle are shown in Table 2.
Fig. 5. The flow rate distribution in the x–z plane of y = 250 mm without flow baffles at n = 371 rpm.
In the quench tank, water is driven through the draft-tube by a rotating impeller. Dynamic viscosity of water at 20 °C is 1.002 e− 3 N s/m2. In the computational model, the initial flow rate leaving the impeller needs to be set. If the rotational component of impeller agitation is ignored, the boundary condition is regarded as a uniform velocity from the impeller down to the bottom of the draft-tube: n = 371 rpm: Vz = −1.113 m/s Vx = Vy = 0 m/s n = 566 rpm: Vz = −1.698 m/s Vx = Vy = 0 m/s n — rotate speeds of impeller
The free surface of the quenchant that works as the interface between quenchant and air is complex and unsteady. For simplification, the surface is simulated as a rigid lid with slip. The rigid lid implies that the surface is flat. A slip surface is impermeable for the flow, but it does not resist its tangential motion. 3.2. Results of CFD simulation Using the finite element method, the flow rate distributions in the quench tank at n = 371 rpm and n = 566 rpm are obtained. Fig. 5 shows the flow rate distribution in the x–z plane at the coordinate y of 250 mm without flow baffles at n = 371 rpm, while Fig. 6 represents the flow rate distribution in the same plane with flow baffles (in Fig. 4) at n = 371 rpm. 4. Distribution of flow rate with improved flow baffles As shown in Fig. 5, the flow rate distribution in the production-quenching zone is not uniform. In order to obtain the uniform flow rate distribution, CFD simulations had been performed for many design cases with different structures and positions of the flow baffles in the quench tank. Based on the simulation results, the structures and positions of the
Fig. 6. The flow rate distribution in the x–z plane of y = 250 mm with flow baffles at n = 371 rpm.
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Fig. 9. Distribution of simulated flow rates at n = 371 rpm (water, Y = 250 mm, Z = 300 mm). Fig. 7. The structures and positions of flow baffles after improved in the quench tank.
Fig. 10. Distribution of simulated flow rates at n = 371 rpm (water, Y = 250 mm, Z = 600 mm). Fig. 8. The flow rate distribution in the x–z plane of the y = 250 mm with improved flow baffles at n = 371 rpm.
flow baffles were designed to obtain the optimum flow rate distribution in the quenching zone, as illustrated in Fig. 7. The flow rate distribution simulated with improved flow baffles at the x–z plane of coordinate y of 250 mm at n = 371 rpm is shown in Fig. 8. To verify the simulation results, the actual values of flow rates were measured, and are listed in Table 3.
Table 3 The flow rates measured at n = 371 rpm with improved flow baffles Coordinate (mm)
Flow rates (m s− 1)
Z (mm) Y (mm) X (mm)
300 0 0.30 0.40 0.37
0 200 400
250 0.36 0.41 0.38
500 0.36 0.38 0.35
600 0 0.28 0.32 0.29
250 0.30 0.35 0.32
500 0.30 0.33 0.31
Fig. 11. Distribution of simulated flow rates at n = 566 rpm (water, Y = 250 mm, Z = 300 mm).
N. Chen et al. / Materials Letters 60 (2006) 1659–1664
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5. Discussion 5.1. Effect of the flow baffles In the practical experiment, the impeller is driven to force the quenchant of water down and across the bottom along the drafttube. So, the angular momentum is inevitably imparted to the fluid, which has an effect on the uniformity of the flow rate, especially on the flow rates in the direction along the x axis, see Tables 1 2 and 3. Figs. 9–12 show the change of flow rates along the coordinate x axis in the quench tank without flow baffles, with flow baffles and with improved flow baffles at the coordinate z of 300 and 600 mm at n = 371 rpm and n = 566 rpm, respectively. The effect of flow baffles is to redirect the flow and to remove great mass of the swirl from the impeller. The datum shown in (Figs. 5, 6, and 8) indicate that the uniformity of flow rate gradually increases as the structures and position of the flow baffles are adjusted. Therefore, by improving the structures and positions of the flow baffle in the draft-tube effectively, the uniformity of flow rates in the quench tank will be increased significantly. 5.2. Effective quenching zone (Figs. 5, 6, and 8) show the change of the flow rate distribution in the x–z plane of the y = 250 mm in the quench tank without flow baffles, with flow baffles and with improved flow baffles, respectively. It can be seen that the uniformity of flow rate increases from the bottom of the quench tank to its top, especially in the region from the coordinate z of 300 to 700 mm. This implies that a quenching zone exists in which the flow rate distribution is uniform, and its dimension increases as the flow baffles improved. For the experimental quench tank with improved flow baffles, the dimensions of the effective quenching zone are 400 mm(x) × 500 mm(y) × 400 mm(z) from the coordinate z of 300 to 700 mm. This information is important for steel quenching. The uniform cooling of a part in this zone can obviously reduce the distortion.
Fig. 13. Comparison of the flow rates of simulation and measurement at y=0.25 m, z=0.3 m along the coordinate x axis at n=371 rpm with improved flow baffles.
5.3. Effect of the rotate speeds of impeller At this research, the flow rates distribution had been measured and simulated at two rotate speeds of impeller. The simulated results, Figs. 9–12, show that the degree of uniformity of flow rate decreases with increase in the rotate speeds of impeller. So moderate rotate speeds of impeller is necessary to reduce the distortion of a part. 5.4. Analysis of simulation error Fig. 13 shows the comparison between the flow rates calculated by simulation and measured by actual experiment. Although the discrepancy exists, the CFD simulation can exhibit the actual tendency of the flow rate distribution in the quenching zone to some extent. 6. Conclusions 1) The flow rates of the quenchant in the quench tank are measured by using UDV. The experimental results prove that this method is suitable for measuring the flow rates of quenchants in a quench tank. 2) According to the CFD simulation results, the structures and positions of flow baffles are adjusted to obtain the uniform distribution of flow rates in the quenching zone. This research will guide the structure design of the flow baffles in a quench tank. 3) The simulation of flow rate in the quench tank indicates an effective quenching zone with uniform flow rate exists, and its dimensions depend on the structures and positions of flow baffles. References
Fig. 12. Distribution of simuilated flow rates at n = 566 rpm (water, Y = 250 mm, Z = 600 mm).
[1] G.E. Totten, G.E. Webster, N. Gopinath, Quenching fundamentals: effect of agitation, Advanced Materials & Processes 2 (1996) 73–76. [2] H.M. Tensi, G.E. Totten, G.M. Webster, Proposal to Monitor Agitation of Production Quench tanks, 17th ASM Heat Treating Society
1664
[3]
[4]
[5] [6]
N. Chen et al. / Materials Letters 60 (2006) 1659–1664
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