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Physics Procedia 43 ( 2013 ) 264 – 268
1875-3892 © 2013 The Authors. Published by Elsevier B.V.Selection and/or peer-review under responsibilty of ITMNR-7doi: 10.1016/j.phpro.2013.03.030
The 7th International Topical Meeting on Neutron Radiography
Application of neutron radiography to flow visualization in supercritical water
N.Takenaka a*, K.Sugimoto a, S.Takami b, K.Sugioka c, T.Tsukada c,
T.Adschiri b,d, Y. Saito e a. Department of Mechanical Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
b. Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan
c. Department of Chemical Engineering, Tohoku University, 6-6-07 Aramaki, Aoba, Sendai 980-8579, Japan d. WPI Advanced Institute for Materials Research, Tohoku University, 2-1-1 Katahira, Aoba, Sendai 980-8577, Japan
e. Department of Nuclear Science and Engineering, Research Reactor Institute, Kyoto University, Kumatori, Sennann, Osaka 590-0494, Japan
Abstract
© 2013 The Authors. Published by Elsevier Ltd. Selection and/or peer-review under responsibility of ITMNR-7
* Corresponding author. E-mail address: [email protected] .
Available online at www.sciencedirect.com
© 2013 The Authors. Published by Elsevier B.V.Selection and/or peer-review under responsibilty of ITMNR-7
Open access under CC BY-NC-ND license.
Open access under CC BY-NC-ND license.
N. Takenaka et al. / Physics Procedia 43 ( 2013 ) 264 – 268 265
Keywords: neutron radiography,visualization supercritical water, subcritical water, mixing process, nano-particles
1. Introduction
Supercritical water is used in various chemical reaction processes including hydrothermal synthesis of metal oxide nano-particles, oxidation, chemical conversion of biomass and plastics. The critical temperature Tc and pressure Pc of water are 374 oC and 22 MPa, respectively. Density of the supercritical water depends much on its temperature and pressure as shown in Fig. 1 and much less than that of the subcritical water.
Adschiri et al. [1] had proposed a hydrothermal synthesis by mixing subcritical metal solution and supercritical water in a T-junction to make nano-particles of metal oxide. It was estimated that sizes of the metal oxide were small since the chemical reaction velocity was high and the solubility was low in the supercritical water. It was reported that the particle sizes depend much on the mixing method and the hydrothermal conditions of pressure, temperature and flow rate of supercritical and subcritical water. However, the conditions to obtain appropriate particle sizes were determined by try and error since mechanism of the mixing process was not known and its visualization in high temperature and pressure conditions was difficult.
Applications of neutron radiography to flow visualization of supercritical water have already reported. Peterson et al. have studied salt precipitation processes in supercritical water [2, 3] and the flow pattern in a reverse-flow vessel for salt precipitation [4], and Balaskó et al. have revealed the behavior of supercritical water in a container [5].
The neutron radiography was applied to the flow visualization of the supercritical and subcritical water mixture in a T-junction made of stainless steel pipes for high pressure and temperature conditions to investigate their mixing process. Still images by a CCD camera were obtained by using the neutron radiography system at B4 port in Kyoto University Reactor (KUR).
Fig.1 Density of water near the supercritical point
200 300 400 500
Temperature [ ]
0
200
400
600
800
1000
Den
sity
[kg/
m3 ]
25 MPa
30 MPa
35 MPa
25 200 300 400 500
Temperature [ ]
0
200
400
600
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Den
sity
[kg/
m3 ]
25 MPa
30 MPa
35 MPa
25
266 N. Takenaka et al. / Physics Procedia 43 ( 2013 ) 264 – 268
2. Experimental apparatus and methods
Fig. 2 shows a schematic diagram of the present experimental apparatus. The subcritical water at room temperature simulating the metal solution and the supercritical water at around 390 oC are supplied to the T junction made of 1/4 inch stainless steel pipes and a Swagelock tee under pressure of 25 MPa.
Thermal neutrons were irradiated to the observation area at the T-junction. The 6LiF converter and a cooled-CCD, 1024x1024 in pixel numbers, about 50 m in pixel size and 16 bits in dynamic range were used to obtain still images with exposure time of 60 sec. Horizontal L/D was about 1000 by using a slit 1mm in horizontal width.
The present experimental conditions were shown in Table 1. They are in the range of the hydrothermal conditions when the nano-particles are made.
3. Visualized results
Figs. 3 (a), (b) show original neutron radiography images of the Swagelock tee filled with the supercritical and the subcritical water, respectively. It can be seen that the neutron attenuation by the supercritical water is much lower than that by the subcritical water and they could be clearly distinguished..
Effects of the subcritical water flow rate on the mixing state with the constant super critical flow rate are shown in Fig. 4. It can be seen that the downwards supercritical water penetrates to the subcritical water in the horizontal pipe with decreasing the subcritical flow rates.
Fig. 2 Schematic diagram of experimental apparatus
1. Pump 2. Tank 3. Pump 4. Tank 5. AC Electrical source 6. Heater 7. Insulator 8. Cooling zone 9. Chiller unit 10. Inline filter 11. Back pressure valve
N. Takenaka et al. / Physics Procedia 43 ( 2013 ) 264 – 268 267
Run No.
Supercritical water temperature
[oC]
Supercritical water flow rate [cc/min]
Subcritical water flow rate [cc/min]
1 398 4 0 2 396 4 2 3 396 4 5 4 395 4 10 5 398 4 20 6 384 8 1 7 385 8 2 8 392 6 0 9 395 6 1.5
10 395 6 3 11 396 6 4 12 396 6 10
Table 1 Experimental conditions
(a) filled with supercritical water (b) filled with subcritical water
268 N. Takenaka et al. / Physics Procedia 43 ( 2013 ) 264 – 268
Fig. 3 Neutron radiography images at T-jumction
subcritical water flow rate
2 cc/min 5 cc/min 10 cc/min 20 cc/min
Fig. 4 Mixing of supercritical and subcritical water, supercritical water flow rate 4 cc/min
4. Conclusion
Visualization of the mixing process of the supercritical and the subcritical water were conducted by using the neutron radiography. It was shown that the supercritical and the subcritical water could be clearly distinguished. It is expected that the neutron radiography is applicable to chemical process researches using the supercritical water..
References
[1] T. Adschiri et al., J. American Ceramic Society, 75, (1992) 1019 [2] A.A. Peterson, P. Vontobel, F. Vogel, J.W. Tester, Supercritical Fluids 43 (2008) 490–499. 378 [3] A.A. Peterson, P. Vontobel, F. Vogel, J.W. Tester, J. Super-critical Fluids 49 (2009) 71–78. [4] A.A. Peterson, J.W. Tester, F. Vogel, J. Supercritical Fluids 43 (2010) 250–257. [5] M. Balaskó, L. Horváth, Á. Horváth, P. Tóth, Nuclear Instruments and Methods in Physics
Research A 605 (2009) 138–141.
