I.

Project Research
Project 13

PR13

Development on Neutron Imaging Application

Y. Saito
Research Reactor Institute, Kyoto University
1. Objectives and Allotted Research Subjects
Neutron imaging provides valuable information whichcannot be obtained from an optical or X-ray imaging. The
purpose of this project is to develop the imaging method
itself and also the experimental environment for expanding the application area of the neutron imaging. The allotted research subjects are as follows:

ARS-1 Measurements of Multiphase Dynamics by Neutron Radiography (Y. Saito et al.)ARS-2 Visualization and Measurement of Flow Behavior
in Industrial Equipment (N. Takenaka et al.)
ARS-3 Visualization and Measurement of Adsorption/Desorption Process of Ethanol in ActivatedCarbon Adsorber for Adsorption Heat Pump (N.
Asano et al.)
ARS-4 Neutron Radiography on Tubular Flow Reactor
for Supercritical Hydrothermal Synthesis ofNanoparticles (T. Tsukada et al.)
ARS-5 Characteristics of the Void Fraction under Transient Condition (H. Umekawa et al.)
ARS-6 Estimation of the Frosting and Defrosting Phenomena by Using Neutron Radiography (R.
Matsumoto et al.)
ARS-7 Neutron imaging and optics development using
simulation of VCAD Systems (Y. Yamagata etal.)
ARS-8 Water and Salt Distribution in a Rice Hull Medium under Sodium Chloride Solution Culture(U. Matsushima et al.)
ARS-9 Measurement of Water Content in Hardened
Cement Paste by Neutron Imaging (T. Numao etal.)
ARS-10 In-situ Neutron Radiography Investigation on
the Hydraulic Behavior of High Strength Cement Paste under High Temperature (M.
Kanematsu et al.)
ARS-11 Evaluation of coolant distribution in a flat
heat-pipe type heat spreader (K. Mizuta et al.)
ARS-12 Visualization of Organic Materials for Development of Industrial Applications (A. Uritani etal.)
ARS-13 Visualization of Coolant Flow in a Micro-Structured Wick (Y. Tsuji et al.)2. Main results and the contents of this report
Due to the termination of KUR, no neutron imaging
has been performed for fiscal 2016. However, some results have been obtained by analyzing existing experi-28P13

mental results or by performing X-ray imaging as follows:
ARS-2 applied X-ray imaging to two-phase flow acrosshorizontal tube bundles of in-line and staggered. X-ray
radiography was employed for the measurement of void
fraction distributions. The transmitted X-ray was converted to visible rays using an image intensifier, and the10-bit gray-scale radiographs were taken using ahigh-speed camera (MotionPro Y-4 Lite, IDT Inc.) withan array of 1024 × 1024 pixels and with a pixel size of
170 μm. The flame rate was set at 30 fps and 450 radiographs which correspond to 15 s were taken in each condition. The X-ray was generated at 80 kV and 5 mA.
From X-ray visualization, two-dimensional void fraction
profiles were obtained varying gas- and liquid-superficial
velocities. Heat transfer characteristics in two-phase flow
across horizontal tubes are clarified also from heat transfer experiments. For bubbly flow condition, heat transfer
coefficient between±90 to ±180° was higher than that insingle-phase flow. Void fraction around upstream of thetube was higher than that in the others. Liquid flow agitation by bubbles motion improved the heat transfer
around the tube. Under intermittent flow condition, heattransfer coefficient flatten over the tube in comparison tothat in single-phase flow. Since the void fraction aroundthe tube was almost uniformly distributed, enhancementof the heat transfer could be obtained by bubbles motion
over the entire perimeter of the tube under the condition.
ARS-6 applied X-ray radiography to frosting behavior
in cooling heat exchange system. Frost layer was clearlyvisualized by the X-ray imaging system in the B-4 portof KUR. The X-ray generator was operated at 80kV and5mA similar to ARS-2. To estimate the frost profile
quantitatively, the mass attenuation coefficient of thewater and the ice were measured. Experimental results
indicate that the mass attenuation coefficient of the ice
shows higher value than that of the water. Finaly Abelinversion was applied to the X-ray image to reconstruct
the frost density profiles under the circularly symmetricfrost formation around the cylindrical surface. In addition,
3-dimensional measurement of the frost deposition wastried by using the newly developed X-ray CT system. On
the present step of this research, the 3-D frost density
distribution is not success due to the less attenuation by
the frost layer on the X-ray CT. In the next stage, theX-ray imaging conditions are modified.

Void Fraction and Heat Transfer Characteristics in Two-Phase Flow across a
Horizontal Tube Bundle

H. Murakawa, M. Baba, T. Miyazaki, K. Sugimoto,
H. Asano, N. Takenaka, D. Ito1 and Y. Saito1
Department of Mechanical Engineering, Kobe University
Research Reactor Institute, Kyoto University

1

INTRODUCTION: Heat exchangers such like shelland tube type are commonly used in process industry,
chemical industry, and geothermal power plant. To clarify
the two-phase flow structures, many experimental studies
have been carried out in a rectangular channel with thetube bundle [1-3]. However, many of these investigation
evaluate local void fraction at several measurement positions in the tube bundles, and the measurement of thetwo-dimensional void fraction distributions in the bundles has not been sufficiently carried out.
In this study, two-dimensional void fractions around a
tube were obtained by using X-ray radiography. Local
heat transfer coefficients were measured by using anelectrode made of platinum wire placed on a tube, and theinteraction between the void fraction and heat transfer
coefficient distributions were investigated.
EXPERIMENTS: The test section was a vertical ductwith a cross-section of 90 × 90 mm2. Air was injected
into the test section through two porous tubes located at
the bottom of the test section. Tube arraignment was anin-line tube bundle with 8 rows of three full tubes andtwo half tubes. The tubes were 90 mm long and the outer
diameter, d, was 15 mm. The tubes pitch, p, was 22.5 mm
and the pitch-to-diameter ratio, p/d, was 1.5. The experiments were performed at 20–25 ºC under atmosphericpressure condition.
X-ray radiography was employed for the measurement ofvoid fraction distributions. The transmitted X-ray wasconverted to visible rays using an image intensifier, andthe 10-bit gray-scale radiographs were taken using ahigh-speed camera (MotionPro Y-4 Lite, IDT Inc.) withan array of 1024 × 1024 pixels and with a pixel size of
170 μm. The flame rate was set at 30 fps and 450 radiographs which correspond to 15 sec were taken in eachcondition. The X-ray was generated at 80 kV and 5 mA.
RESULTS: Results of two-dimensional void fraction
distributions are shown in Fig. 1. The superficial liquid
velocity, JL, is 0.2 m/s, and the superficial gas velocity, JG,
is 0.12 and 0.77 m/s. The flow regimes are bubbly andintermittent flows, respectively. The measurement area isaround center tube at the 4th row from the inlet of thebundles. Figure 2 shows the heat transfer coefficientsaround the tube. 0° indicates at the bottom of the tube,
and the counterclockwise rotation is defined as positivedegree.
Heat transfer coefficient under liquid single-phase flow
increases from 0° and takes the maximum values near ±90°, thereafter takes the minimum values around ± 135°.

28P13-2For bubbly flow condition, heat transfer coefficient between ± 90 to ± 180° was higher than that in single-phaseflow. Void fraction around upstream of the tube washigher than that in the others. Liquid flow agitation by
bubbles motion improved the heat transfer around thetube. Under intermittent flow condition, heat transfer
coefficient flatten over the tube in comparison to that insingle-phase flow. Since the void fraction around the tube
was almost uniformly distributed, enhancement of theheat transfer could be obtained by bubbles motion overthe entire perimeter of the tube under the condition.

Void fraction [-]00.65

Intermittent flow
Bubbly flow
(JG = 0.77 m/s)
(JG = 0.12 m/s)
Fig. 1. Time-average two-dimensional void-fraction distributions in in-line tube bundle.

Single-phase flow
Bubbly flow (JG = 0.12 m/s)
Intermittent flow (JG = 0.77 m/s)

2h / 
hL, In-line [-]PR13-1

10-180-900θ [degree]

90180

Fig. 2 Heat transfer coefficient around a tube in eachflow.
REFERENCES:[1] R. Dowlati et al., AIChE Journal, 36 (1990) 765-772.
[2] D.A. McNeil et al., Int. J. Multiphase Flow, 45 (2012)53-69.
[3] G.R. Noghrehkarm et al., Int. J. Multiphase Flow, 25(1999) 857-874.

PR13-2

Estimation of Frosting Formation on the Heat Exchanger byUsing X-ray Radiography

R. Matsumoto, K. Kagebayashi1, T. Uechi1, Y. Nagasawa1, D. Ito2 and Y. Saito2
Faculty of Engineering Science, Kansai University
Graduate School of Science and Engineering, KansaiUniversity
2
Research Reactor Institute, Kyoto University
13-D FROST DENSITY PROFILE ON THE HEATEXCHANGER ESTIMATED BY X-RAY COMPUTED TOMOGRAPHY: The three dimensional
distribution of the frost deposition on the plate-fin tube
heat exchanger was tried to estimate by the X-ray CT.
Fig.4 shows a schematic of the experimental setup withrotating stage. On the present step of this research, the 3D frost density distribution is not success due to the lessattenuation by the frost layer on the X-ray CT. In the nextstage, the X-ray imaging conditions are modified.

28P13-6-ln{(S-O)/(S0-O)/}0.5
0.45 Water Exp.
The.
0.4
Exp.
0.35 Ice
0.3
20.25 m,ice= 0.4018 [cm /g]
0.20.150.1
m,w= 0.1835 [cm2/g]
0.05
00 0.1 0.2 0.3 0.4 0.5 0.6
0.7 0.8 0.9 1
 [g/cm2]

Fig.2 Mass attenuation coefficient of water and ice.
3

MEASUREMENT OF FROST DENSITY PROFILEBY X-RAY RADIOGRAPHY: The photograph of thefrost formation at 180 min of the frosting time on the cylindrical cooling surface at -14.0 deg.C. is shown inFig.1(a). The frost layer was clearly shown by the X-ray
beam attenuation in the radiography image, Fig.1(b). The
X-ray generator was operated at 80kV and 5mA.
To estimate the frost density profile quantitatively, themass attenuation coefficients of the water and the ice
were measured by the calibration test. The gradient ofFig.2 corresponds to the mass attenuation coefficient.
Experimental results of the water was close agreementwith the reference value. The mass attenuation coefficient of the ice shows higher value than that of the water.
The mass attenuation coefficient for the frost density estimation was used that of the ice.
Abel inversion was applied to the X-ray image to reconstruct the frost density profiles under the circularly
symmetric frost formation condition around the cylindrical surface [1]. The frost density profile is shown in Fig.
3 at the 16 mm from the reading edge of the cylindricalcooling surface. The experimental result is almost thesame density profiles with the previous researches [1],[2]. High frost density is appeared near the cooling surface. Frost density increased with the frosting time. At
180 min after frosting, the density profile shows a relative maximum at a distance about 3 mm from the coolingsurface.

(a) Digital camera image (b) X-ray radiography image
Fig.1 Frost layer on the cylindrical cooling surface at
180 min of frosting time.

Frost density  [kg/m ]INTRODUCTION: Heat exchangers which are operated at below 0 °C are subjected to the frost deposition
and its growth. Frost is the porous material of the crystal
ice and air. The low thermal conductivity of the frost
causes the low heat transfer performance. The frost density profile of the frost layer is the important property forthe frost formation estimation. The frost density profiles
were measured by the X-ray radiography on the cylindrical cooling surface. The three dimensional distribution ofthe frost deposition on the plate-fin tube heat exchanger
was tried to estimate by the X-ray computed tomography
at KUR B-4 radiation port.

1200

m,ice= 0.4018 [cm22/g]
m,w= 0.1835 [cm /g]

1000

ShimomuraCremers

800
600
400
200020212223
Radius r [mm]24Fig. 3 Distributions of frost density profiles.

Fig. 4 Experimental setup for estimation the 3-D frost
density distributions.
REFERENCES:[1] C. J. Cremers, et al., Advances in Cryogenic Eng.,23 (1978), 371-375.
[2] N. Shimomura, et al., Trans. of the JSRAE, 19(3)(2002), 245-254.