Project Research
Project 2

PR2

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 of
Nanoparticles (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 Netron 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 et
al.)ARS-10 Hydrazine Thickness Measurement by NeutronRadiography at a Catalyst Bed during Operation(H. Kagawa et al.)
ARS-11 In-situ Neutron Radiography Investigation on
the Hydraulic Behavior of High Strength Cement Paste under High Temperature (M.
Kanematsu et al.)
ARS-12 Evaluation of coolant distribution in a flat
heat-pipe type heat spreader (K. Mizuta et al.)
ARS-13 Visualization of Organic Materials for Development of Industrial Applications (A. Uritani
et al.)
ARS-14 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 2015. However, some results have been obtained by analyzing existing experimental results or by performing X-ray imaging.
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 the
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.
heat transfer study on an adsorption refrigerator. In this
ARS, visualization of adsorption amount distributions of
ethanol in an activated carbon powder bed. Experimental
results show that transient behaviors of adsorption
amount distribution could be clearly observed by neutron
radiography.
ARS-3 visualized transient change of adsorbed refrigerant amount during an adsorption process by using neutron imaging. From the measurement results effect of themetallic fins was investigated for improvement of heatdiffusion in adsorption process.
In ARS-4, flow behavior of heavy oils in a packed-bed
reactor was investigated by using B-4 neutron imaging
facility. In this work, it was revealed that the visualization of flow behaviors of heavy oils in the packed-bed
reactor at high temperature and high pressure is feasible
by neutron radiography.
ARS-5 conducted frosting and defrosting experiments
by using neutron/X-ray imaging. On the cooled surface
of a heat exchanger, the frost grows with a spatial distribution that is determined by the temperature and humidity profiles of the air and the flow pattern in the heat exchanger. This means that the mass transfer coefficient for
frost formation has both temporal and spatial distribution.
However, in conventional methods of measuring the frost
accumulation rate, the frost is scraped from the surface,or the frost accumulation is estimated from the difference
between the absolute humidity before and after the heatexchanger. In the present study, the frost formation anddefrosting process was estimated by the two ways byneutron and X-ray radiographies at KUR B-4 radiation
port.

27P2

- 11 -

PR2-1

Void Fraction Distritbution around a Tube in Two-phase Flows
Across Horizontal Tube Bundles

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. The void
fraction in the flow channel are important parameters forpredicting the flow characteristics, fluid oscillation andheat transfer. To clarify the two-phase flow structures,
many experimental studies have been carried out in arectangular channel with the tube bundle [1-4]. However,many of these investigation evaluate local void fraction atseveral measurement positions in the tube bundles, andthe two-dimensional void fraction distributions in thebundles has not been sufficiently carried out.
In this study, two-dimensional void fractions were measured by using X-ray radiography in two-phase flow
across horizontal tube bundles of in-line and staggered.
Difference of void fraction distribution in each flow regime and bundle arraignment were compared.

termittent flow regime, large bubble intermittently passthrough the tubes. As a result, void fraction around the
maximum gap and vertical minimum gap increased. The
maximum void fraction around maximum and verticalminimum gaps were almost the same. However, void
fraction around the horizontal minimum gap is slightly
lower than that around maximum and vertical minimum
gaps.
For staggered tube bundle, the void fraction around upstream of tubes is slightly high in comparison with thehorizontal tube side. Tendency of the void fraction distribution is almost the same with that in in-line tube bundle, however, the void fraction around the bottom oftubes are slightly higher than that in the other region. Atintermittent flow, void fraction around bottom of tubes
became much higher than the other region. Therefore, it
can be confirmed that large bubbles tend to be stagnant
around the bottom of tubes. As a result, void fraction haslarge distribution in comparison with that in in-line tube
bundle. Furthermore, the maximum void fraction in
staggered tube bundle was higher than that in in-line tube
bundle.
Void fraction [-]0

EXPERIMENTS: The test section was 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. Two different tube bundles
were employed for the measurements. One was an in-line
tube bundle with 8 rows of three full tubes and two half
tubes. And the other was a staggered tube bundle with 8
rows. The tube in both bundles were 90 mm long and theouter diameter, d, was 15 mm. The tubes pitch, p, was22.5 mm and the pitch-to-diameter ratio, p/d, was 1.5.
The experiments were performed at 20–25 ºC.
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 mass flux, G, is
200 kg/m2s, and the superficial gas velocity, JG, is 0.36
and 0.86 m/s. The measurement area is around centertube at 4th row from the inlet of the bundles.
For in-line tube bundle, many bubbles pass travel along
the vertical tube gaps, and the void fraction became
higher than that at the other region in bubbly flow. Some
bubbles passing through the bottom of tubes. As a result,void fraction around the upstream of each tube becomes
higher than that around downstream of the tubes. In in-

In-line0.65
Staggered

Bubbly flow (JG = 0.36 m/s)

Intermittent flow (JG = 0.86 m/s)
Fig. 1. Two-dimensional void-fraction distributions in
in-line and staggered tube bundles.
REFERENCES:[1] R. Dowlati et al., AIChE Journal, 36 (1990) 765-772.
[2] R. Dowlati et al., Tras. ASME, 114 (1992) 450-456.
1992.
[3] D.A. McNeil et al., Int. J. Multiphase Flow, 45 (2012)53-69.
[4] G.R. Noghrehkarm et al., Int. J. Multiphase Flow, 25(1999) 857-874.

27P2-2- 12 -

Quantitative Measurement of Adsorbed Ethanol Amountin Activated Carbon Adsorber for Adsorption Heat Pump

Department of Mechanical Engineering, Kobe University
1
Research Reactor Institute, Kyoto University

INTRODUCTION: Adsorption refrigerator is one of
the efficient tools for waste heat utilization at low
temperature. In the refrigerating cycle, adsorption anddesorption processes are alternately repeated in batch
operation. Since heat removal of latent heat of adsorbed
refrigerant is necessary during the adsorption process,
improvement of heat diffusion in adsorption layer.
Although metallic fins are usually used for theenhancement in the heat diffusion, the amount of inserted
fins should be minimized from the standpoint of thedownhold of the heat capacity. It is important for the
improvement of adsorber to clarify the distribution ofadsorbed refrigerant amount in an adsorbent bed duringtransient conditions of adsorption/desorption. Neutron
radiography was applied to visualize the adsorption
amount distribution of ethanol in an activated carbon
particle bed, and the effect of aluminum fins were
evaluated from the measured results.

the valve. Just after the start, the adsorbent temperature
rapidly increased, and reached around 70 °C due to thestrong adsorption. Then, adsorbed refrigerant amountgradually increased with a gradual decrease in theadsorbent temperature due to heat diffusion. The
difference in the temperature of the adsorbent between
Tad2 and Tad3 was little. The adsorption amounts in thearea of 5, 7, and 8 near the heat transfer surfaces werelarger than the amounts in the area of 6 during thetransient condition. The fact means that the phenomenon
is dominated by heat conduction in the adsorbent bed.

EXPERIMENTS: Activated carbon and ethanol wasused as the adsorbent and refrigerant, respectively. The
activated carbon MAXSORB® III produced by Kansai
Coke and Chemical Co., Ltd. was used as the adsorbent.
Activated carbon was packed in an aluminum frame
shown in Figure 1. The container was connected to an
ethanol reservoir. The vapor pressure in the container
could be maintained by the temperature of the reservoir.
The front and back wall was made of thin stainless steel
plates to avoid heat diffusion through the walls. The
adsorber could be cooled in adsorption process or heatedin desorption process by water through a channel in thebottom wall. Two aluminum fins with the thickness of 1
mm were inserted in the adsorbent bed to enhance theheat diffusion. The mass attenuation coefficient of
ethanol against thermal neutron was measured as 3.86
g/cm2 in our preliminary experiment.
RESULTS: Transient change of adsorbed refrigerant
amount during an adsorption process was measured
quantitatively by the umbra method using a checked-type
neutron absorber. Figure 2 (a) shows a visualized image
with the neutron absorber grid. The inside wall including
the fins are indicated by white lines. The measured
adsorbed amounts in the center section and temperaturein the adsorption bed are shown in Fig. 2 (b) and (c),respectively. At the initial condition, the adsorbent wasdry and vacuated. Then, by opening a valve between theethanol reservoir and the test section, vapor ethanol was
supplied to the test section. The horizontal axis of Fig. 2(a) and (b) shows the elapsed time from the opening of

27P2-3- 13 -

Fig. 1 Configuration of the test section.

50

100

150

(a) Visualized image with neutron absorber grid0.4

rr [g/cm2]

H. Asano, K. Murata, N. Takenaka, H. Murakawa, K.
Sugimoto, Y. Saito1 and D. Ito1

0.3
0.2

5
6
7
8

0.1
0

0

50

100
150
Time [min]200(b) Adsorbed refrigerant amount
Adsorbent temperature [℃]

PR2-2

80
Tad1
Tad2
Tad3
Tw

70
60

Tad1

9
10
11
12

Tad2

50

Tad3

40
30
20

Tw
0

50

100

150
Time [min]200(c) Temperature in adsorption layer
Fig. 2 Transient change during adsorption process.

PR2-3

Neutron Radiography on Flow Behavior of Heavy Oils in Packed-Bed Reactor

T. Tsukada, K. Sugioka, M. Kubo, Y. Mukawa, S. Takami
1, T. Adschiri2, K. Sugimoto3, N. Takenaka3, Y. Saito4 and
Y. Kawabata4

through the packed bed. From the figures, it is found thatthe temperature in the reactor, i.e., the viscosity of thesample, and the diameter of packed materials affect theflow behaviors. The sample spreads to the radial direction
as the temperature decreases or the diameter of particles
in the reactor decreases.
.
CONCLUSIONS: In this work, it was revealed thatthe visualization of flow behaviors of heavy oils in thepacked-bed reactor at high temperature and high pressure
is feasible by neutron radiography.

Dept. of Chemical Engineering, Tohoku University
1
IMRAM, Tohoku University
2
WPI-AIMR, Tohoku University3
Dept. of Mechanical Engineering, Kobe University
4
RRI, Kyoto University

INTRODUCTION: With the increase of the demandfor petrochemical feedstock and middle distillate, it isdesired to utilize heavy crude oils and residues as new
resources. However, as heavy oils have high viscosityand poor quality, the upgrading and refining processes ofheavy oils are indispensable. For instance, a trickle-bed
reactor is commonly used as the residue hydrodesulfurization unit of heavy oils, and thus, it is important to understand the flow behavior of heavy oils through apacked bed of catalyst pellets at high temperature andhigh pressure for design and optimization of the process.
However, because of the reactor which is made of metal
and the high-temperature and high-pressure processing, it
is impossible to visualize directly the flow behavior inside the reactor. Therefore, we are going to use neutron
radiography to visualize the flow behavior of heavy oils
in a trickle-bed reactor. In this work, as a first step ofsuch visualization, the flow behavior of bitumen througha packed bed were observed at atmospheric pressure using neutron radiography.

REFERENCES:[1] K. Sugioka et al., AIChE J., 60, (2014) 1168.

Figure 1 Schematic diagram of the apparatus

EXPERIMENTS: Fig.1 shows the schematic diagramof a packed-bed reactor, which was made of a SUS316
tube with outer diameter of 1/2 inch and contained alumina particles with 1 or 3 mm diameter. Heavy oil was
fed to the reactor through SUS316 1/16 inch tube by using a high-pressure pump. The fourth of five fractions
fractionated by vacuum distillation of bitumen was used
as a sample. Here, the viscosity of the sample was adjusted by varying the temperature between 40 and 80℃.
Neutron radiography of the packed-bed reactor, i.e.,
the flow behavior of the sample through the packed bed,
was carried out, where the neutron radiographs were taken by an image intensifier and a high speed camera. A
thermal neutron beam emitted from the B4 port in KUR
was used. The imaging method of neutron radiography
and subsequent analysis of the images were almost similar to those in our previous work [1].
RESULTS:
Figs. 2 (a) to (c) show the neutron radiographs of flow behaviors of packed-bed reactor, where(a) the temperature T = 69.8℃, the flow rate Q = 0.6
mL/min, and the diameter of particles D = 1 mm, (b) T =73.0℃, Q = 0.6 mL/min, D = 3 mm, and (c) T = 44.2℃,
Q = 0.6 mL/min and D = 3 mm. In the images, the darkpart corresponds to the sample flowing downward

Figure 2 Neutron radiographs of flow behaviors of bitumen through the packed-bed.

27P2-4- 14 -

PR2-4 Estimation of the Frosting and Defrosting Phenomena by Using Netron Radiography
R. Matsumoto, K. Kagebayashi1, T. Uechi1, D. Ito2 and Y.
Saito2
Faculty of Engineering Science, Kansai University
Graduate School of Science and Engineering, Kansai
University
2
Research Reactor Institute, Kyoto University
1

INTRODUCTION:
Heat exchangers which are operated at below 0 °C
are subjected to the frost deposition and its growth.
Frost formation on heat exchangers has a serious impact on the heat transfer performance in two ways; oneis a thermal resistance between the cold surface and thehumid ambient air, the other is an air-side pressure dropby the blockage effect of the frost layer. In spite of therelatively large number of articles, there are still gaps
between the analytical model and the experimental results. One of the reasons is the difficulty to evaluate themass transfer coefficient for the frost deposition.
On the cooled surface of a heat exchanger, the frost
grows with a spatial distribution that is determined by
the temperature and humidity profiles of the air and theflow pattern in the heat exchanger. This means that themass transfer coefficient for frost formation has both
temporal and spatial distribution. However, in conventional methods of measuring the frost accumulation rate,
the frost is scraped from the surface, or the frost accumulation is estimated from the difference between theabsolute humidities before and after the heat exchanger.
In the present study, the frost formation and defrostingprocess was estimated by the two ways by neutron and
X-ray radiographies at KUR B-4 radiation port.

formation estimation. The frost formation process wasmeasured by the X-ray radiography (XRG) on the cylindrical cooling surface.
The frost density profiles is shown in Fig. 3 at the
22.5mm from the reading edge of the cylindrical cooling surface. The experimental results clearly shows thedevelopment of the frost layer density.
CONCLUSIONS:
The neutron and X-ray radiographies are effectivenessfor the frost layer measurement.

Fig.1

ESTIMATION DEFROSTING PROCESS BY
NEUTRON RADIOGRAPHY:
The frost layer with defrosting process was measured
by using a neutron radiography in the defrosting process on the aluminum finned-tube heat exchanger under
the forced-convection. The heat exchanger is shown in
Fig.1. Fins have dimensions of 60mm in height, 28mm
in width and 0.12mm in thickness.
The water deposition distributions were estimatedquantitatively in every 5 seconds for 10 minutes of thedefrosting period. The melting water behavior was investigated by comparing the water deposition distribution before defrosting. The initial stage of the defrosting
was referred to as the melting progressing period, inwhich the melting water penetrated into the water permeation layer in the frost thickness direction, as shownin t=140sec. of Fig.2. After 180sec from starting thedefrosting process, the frost at the fin front edge and thesurrounding the tubes were melted, then, the water
permeation layer was saturated by the melting water.
The neutron radiography images, as shown at t=380 sec.
of Fig.2, indicated the melting water penetration into
the spanwise direction of the fins. The total migration
volume of the melting water into the spanwise direction
was about 30% of the total frost deposition.

Plate-fin tube heat exchanger.

t =140 sec.

t =380 sec.
(a) Digital camera image (b) Water deposition mw
Fig.2 Water deposition profiles on the fins.

3

Frost density  [kg/m ]1200

MEASUREMENT OF FROST DENSITY PROFILE BY X-RAY RADIOGRAPHY:
Frost is the porous material of the crystal ice and air.
The low thermal conductivity of the frost causes thelow heat transfer performance. The frost density profileof the frost layer is the important property for the frost

800
600
400
200
0
20

Fig.3

27P2-6- 15 -

10min.
60min.
180min.
Shimomura

1000

21

22
23
Radius y [mm]24Distribution of frost density with height.