Group Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Title: 3.3.4 - Flow visualization of refrigerant behaviors in a self-vibration heat pipe
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 Material Information
Title: 3.3.4 - Flow visualization of refrigerant behaviors in a self-vibration heat pipe Industrial Applications
Series Title: 7th International Conference on Multiphase Flow - ICMF 2010 Proceedings
Physical Description: Conference Papers
Creator: Sugimoto, K.
Murakawa, H.
Kamata, Y.
Yoshida, T.
Asano, H.
Takenaka, N.
Mochiki, K.
Publisher: International Conference on Multiphase Flow (ICMF)
Publication Date: June 4, 2010
 Subjects
Subject: heat pipe
self-vibration
neutron radiography
flow visualization
two-phase flow
 Notes
Abstract: Heat generation density of electric elements increases close to the limit of forced air-cooling. New cooling technology is required and a self-vibration heat pipe is proposed for the electric elements cooling. The self-vibration heat pipe which has a meandering capillary channel can operate for vertical and horizontal heat removal without gravity effects. However, the behaviors of the working fluid in the pipe have not been well studied. The purpose of this study is to clarify the working fluid phenomena in the heat pipe. The working fluid in the pipe was visualized by neutron radiography system in Japan Atomic Energy Agency. The liquid columns in the meandering channel of the heat pipe were recorded by a high speed camera. The obtained images were segmentated and the meandering capillary channel was uncoiled by image processing methods to show the temporal vibration of the liquid columns in the stretched channel. Periods of the column oscillation were about 0.2 to 0.6 second. The oscillation of the columns was analyzed by a mass-spring model. The periods and the phase speed of the oscillation were obtained and compared with the experiment results. It was showed that the analytical values agreed fairly with the experimental ones.
General Note: The International Conference on Multiphase Flow (ICMF) first was held in Tsukuba, Japan in 1991 and the second ICMF took place in Kyoto, Japan in 1995. During this conference, it was decided to establish an International Governing Board which oversees the major aspects of the conference and makes decisions about future conference locations. Due to the great importance of the field, it was furthermore decided to hold the conference every three years successively in Asia including Australia, Europe including Africa, Russia and the Near East and America. Hence, ICMF 1998 was held in Lyon, France, ICMF 2001 in New Orleans, USA, ICMF 2004 in Yokohama, Japan, and ICMF 2007 in Leipzig, Germany. ICMF-2010 is devoted to all aspects of Multiphase Flow. Researchers from all over the world gathered in order to introduce their recent advances in the field and thereby promote the exchange of new ideas, results and techniques. The conference is a key event in Multiphase Flow and supports the advancement of science in this very important field. The major research topics relevant for the conference are as follows: Bio-Fluid Dynamics; Boiling; Bubbly Flows; Cavitation; Colloidal and Suspension Dynamics; Collision, Agglomeration and Breakup; Computational Techniques for Multiphase Flows; Droplet Flows; Environmental and Geophysical Flows; Experimental Methods for Multiphase Flows; Fluidized and Circulating Fluidized Beds; Fluid Structure Interactions; Granular Media; Industrial Applications; Instabilities; Interfacial Flows; Micro and Nano-Scale Multiphase Flows; Microgravity in Two-Phase Flow; Multiphase Flows with Heat and Mass Transfer; Non-Newtonian Multiphase Flows; Particle-Laden Flows; Particle, Bubble and Drop Dynamics; Reactive Multiphase Flows
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Bibliographic ID: UF00102023
Volume ID: VID00082
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: 334-Sugimoto-ICMF2010.pdf

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7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


Flow visualization of refrigerant behaviors in a self-vibration heat pipe


Katsumi Sugimoto*, Hideki Murakawa*, Yohei Kamata*, Takehisa Yoshida*,
Hitoshi Asano* Nobuyuki Takenaka* and Koichi Mochiki**

*Department of Mechanical Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501, Japan
**Department of Nuclear Safety Engineering, Tokyo City University, 1-28-1 Tamazutsumi, Setagaya,
Tokyo 158-8557, Japan
sugimoto @mech.kobe-u.ac.jp


Keywords: Heat pipe, Self-vibration, Neutron radiography, Flow visualization, Two-phase flow




Abstract

Heat generation density of electric elements increases close to the limit of forced air-cooling. New cooling technology is
required and a self-vibration heat pipe is proposed for the electric elements cooling. The self-vibration heat pipe which has a
meandering capillary channel can operate for vertical and horizontal heat removal without gravity effects. However, the
behaviors of the working fluid in the pipe have not been well studied. The purpose of this study is to clarify the working fluid
phenomena in the heat pipe. The working fluid in the pipe was visualized by neutron radiography system in Japan Atomic
Energy Agency. The liquid columns in the meandering channel of the heat pipe were recorded by a high speed camera. The
obtained images were segmentated and the meandering capillary channel was uncoiled by image processing methods to show
the temporal vibration of the liquid columns in the stretched channel. Periods of the column oscillation were about 0.2 to 0.6
second. The oscillation of the columns was analyzed by a mass-spring model. The periods and the phase speed of the
oscillation were obtained and compared with the experiment results. It was showed that the analytical values agreed fairly with
the experimental ones.


Nomenclature


A self-vibration heat pipe consists of a meandering
capillary channel between heated and cooled area. The
working fluid in it generates self-vibration due to
differential pressure between the high and the low
temperature area. The vibrating working fluid transports
heat from the high to the low temperature area. This heat
pipe can operate in any configuration since the effects of
gravity are much smaller than the vibration force. The
vibration phenomena have not been understood well.
Several researchers have built portions or entire heat pipe
out of glass or plastic to visualize the working fluid flow
(Miyazaki 2001, Nishio 2003, Nagasaki 2005). However,
transient temperature measurements on glass or plastic heat
pipe are difficult due to the material's low thermal
diffusivity compared to metal. One way to visualize fluid
within metal heat pipe is using neutron radiography with
hydrogen rich fluids. Researcher have built metal heat pipe
with meandering copper tube to visualize the working fluid
flow (Wilson 2008). However, product type heat pipe made
the plate type.
The purpose of this study is to clarify the phenomena
of the working fluid in the heat pipe. This experiment was
use difference of filling ratio the product type heat pipe. The
working fluid in the heat pipe was visualized by the neutron
radiography system at JRR-3 in Japan Atomic Energy
Agency.


A cross-section area (m2)
L length (m)
P pressure (Pa)
t time(sec)
T temperature(C), period (sec)
Q heat input (W)
Greek letters
p filling ratio ( -)
K specific heat ratio ( -)
X thermal conductivity (W/mK)
p density (kg/m3)
o radial frequency(-)

Subscripts
cal calculation
ex experiment
L liquid phase
G vapor phase
h heating area
c cooling area


Experimental apparatus

The working fluid in the self-vibration heat pipe (the
plate) was visualized by the real time neutron radiography


Introduction






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


system at JRR-3 in Japan Atomic Energy Agency.
A schematic diagram of the experimental setup is
shown in Fig. 1. The test section is placed between the
neutron source and the neutron image intensifier (Mochiki
2006). The neutrons arrive at the plate in nearly a parallel
beam and are projected through the plate. Neutrons easily
travel through most metals, however they are greatly
attenuated by hydrogen. Therefore, hydrogen rich butane
block most neutrons from reaching the image sensor. The
density difference between liquid and vapor phases is also
visible due to the much higher concentration of hydrogen in
liquid phase than in vapor phase. These dark liquid area and
light vapor area can be seen in Fig. 2(b). Liquid
fluorocarbon in the chiller circulated through the cooling
plate. The fluorocarbon is transparent to the neutron beam.
The electric power is supplied to the heater through the
variable transformer with the electric power meter. The
cooling plate was installed on the upper area of the plate to
be cooled by circulating fluorocarbon in the cooling plate
and the two cartridge heaters were installed on the lower
area.


(a) Picture image of plate


(b) Neutron radiography
image of plate


2


Neutron beam




Test section


1. Power supply 2. Variable transformer
3. Wattmeter 4. Chiller 5. Cooling plate
6. Heating block 7. Neutron image intensifier

Figure 1: Schematic diagram of experimental apparatus.
The test section is shown in Figs. 2. The plate was
made of aluminium, 200 mm in height, 50 mm in width, and
2 mm in thickness. The plate had a meandering channel with
41 turn in it the depth and the width of the channel were
about 0.8 mm. Butane was injected as a working fluid in the
evacuated channel. The filling ratio in the channel was from
0.2 to 0.6 for the neutron radiography visualization.
The plate was covered with ceramic fiber insulation
and nine K-type thermocouples were placed directly on the
plate as shown in Fig. 2(c). Temperature readings were
collected at 1 Hz with a data logger. The heat input limit is
100 W. The limit operating temperature is 130 C of heating
area. The fluorocarbon temperature is 25 C constant.
The movies of the liquid behavior in the plate were obtained
by C-MOS camera (200frames per sec, 8bit) with a neutron
image intensifier.

Results and Discussion
Results of thermal conductivity

The thermal conductivity results were compiled at
different heating area and cooling area temperatures. The


X: Thermocouple
1. Plate 2. Cooling plate
3. Heating block
(c) Test section
Figure 2: Picture image of plate and test section.

resulting thermal conductivity of the plate is,



4000-

A a


L0. o
g

| V 0 p,10.2
8 A 0.25
10 0.4
V 0.5
0 0.6

0 20 40 60 80 100
Heat input [W]


Figure 3: Effective thermal conductivity.





7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010

























(a) BL=0.2 (b) 1L=0.25 (c) BL=0.4 (d) PL=0.5 (e) BL=0.6

Figure 4: Examples of visualized images.


1 '






(a) 3L=0.2


(b) PL=0.25


(c) BL=0.4


(d) 3L=0.5


(e) BL=0.6


Figure 5: Examples of binarized images.


L=
A Th-T)

Where Q is heat input, A is cross-section area (2x50 mm2), L
is length of between the measurements heating area and
cooling area, Th is the average thermocouples temperature in
the heating area, Tc is the average thermocouples


temperature in the cooling area.
The thermal conductivity are shown in Fig. 3. Each
filling ratio has peak of the thermal conductivity. The
maximum effective thermal conductivity of the plates were
about 20 times of aluminum.






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


A B A


B A


Figure 6: Image processing methods
behaviors of the liquid columns.


A A
r- r-.


show the temporal


8


7-


P
..- ... .....






I llll .. ..................




0 5 10
t [s]
(a) BL=0.2


4


m- ~ "/" .. .


S | -- -- I


L I I
0 5 10
t [s]
(b) PL=0.25


Visualized results


Figs. 4 show examples of the movie frame obtained
by the C-MOS camera. The frame rate was 200 frames per
second. The black lines in the images indicate liquid phase.
The visualized movies showed that the liquid concentrated
near the cooling area and the liquid vibration moved
horizontally like waves. The liquid sometimes entered the
heating area and cooled there. It was shown that the
vibration was strong and the effects of the gravity were
small.
The visualized images were binarized to make the
images clear. Examples of the binarized images are shown
in Figs. 5. Black lines are liquid phase and white lines are
vapor phase in the images. The amount of the working fluid
found of the difference of filling ratio.
The plate heat pipe used in this study had meandering
channels in the plate. This plate heat pipe is topologically
the same as a heat pipe with a single straight channel. The
meandering channel was stretched to one straight channel
by image processing methods as shown in Fig.6. The
stretched images are lined in the time series.
The stretched images of heat input 60 W are shown in
Figs. 7. The abscissa is time and the ordinate is distance in
the channel. White areas are the vapor and black areas are
the liquid in the time-distance space. The vibration
phenomena looked like very complex in the movie.


t [s]
(c) BL=0.4


8II~~ eIY~Y~~~


t [s]
(d) PL=0.5


I I I
0 5 10
t [s]
(e) BL=0.6


Figure 7: Examples of stretched images (Heat input 60W).


Time
T, ~






7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


8


7 r -



c --A-
6



MPA
5 --



4
4 J ae~dN
6<^ies
p-.-^a "^^


0 5
t [s]
(a) Q=20W


8- 8


7 --- 7



6 -'W,-. l 6



5 5



4 '4 -- V' 4
.04.


10 0 5
t [s]
(b) Q=40W


8


-7



_ -'2,! t 6







S 4



-. .-- 3


-4-- -



. .. .1
a-I


1 o il I I
10 0 5 10
t [s]
(c) Q=60W


8


7



;6



.......... ... i 5



^-- 4



- ~3


2
- ................ .. ..



1


I I I 0
0 5 10
t [s]
(d) Q=80W


-i
I ...... ..... I
























0 5 10
t [s]
(e) Q=100W
_ i I..












0 5 10
t [s]
(e) Q=100w


Figure 8: Examples of stretched images (Filling ratio PL=0.25).


Filling ratio [-]

Figure 9: Mapping of the flow patterns.

However, the vibration of the liquid columns around the
cooling area could be clearly seen by the stretched images.
The periods of the liquid column vibration depend on the
liquid fraction. The periods of the liquid column vibration
becomes weak at distance of 0 and 8 m of channel.
The stretched images for various heat inputs at filling
ratio PL=0.25 are shown in Figs. 8. The movement of liquid
column is observed but is not period at heat input of 20 and
40W. The periodical vibration of liquid column is observed


I-


0.8-


0.6-
- 0
S0.4-
S -


I I I
60 80 100
Heat input [W]

Figure 10: Periods of the liquid column vibration.

at heat input of 60 and 80 W.
Fig. 9 shows the mapping of the flow patterns defined
by the stretched images data. The symbol O indicates
strong vibration of the liquid column. The symbol A is week
one. The periodical vibration is double lined symbol. The
horizontal solid line in shown by Fig. 7(a)-(e) and the
vertical solid line in Fig. 8(a)-(e) shows the experimental
conditions. No periodical vibration is observed at the heat
input lower than 40 W. Periodical vibration is observed at


Vibration ig. 8(a)-(e)
O no @ @
A weak
O strong
A periodical A @ @
@ periodical

-. A.@ @ @ Fig. 7(a)-(e)


A 0 0 A

0 & A A A


0 PL-0.2
A 0.25
O 0.4
0.5
0.6


V V



0









the heat inputs higher than 60 W.
Periods of the periodical liquid column vibration are
shown in Fig. 10 against the heat input. The periods of the
liquid column vibration were about 0.2~0.6 seconds.

Modeling of vibration phenomena

The vibration phenomena looked like very complex in
the movie. However, the visualization results suggested that
the liquid columns were vibrating near each cooling area.
An analysis was conducted by considering that the liquid
columns were mass points and the vapor phases were the
springs in a mass-spring model as shown in Fig. 11.


vapor column(spring) L


i 11 j+l
liqui column(mass)
Figure 11: Mass-spring model.


A simple analysis based on the mass-spring model predicts
the periods of the liquid column oscillation as follows
(Matsui 1979):

2 P _A P
C) =- -
PLLLG PLL2 -L L


T 2;T 2K OL L 2L-lI L)-8



where, L: length, P: pressure, T: period, P: filling ratio, K:
specific heat ratio, PL: liquid density and co: radial
frequency.

The periods of the oscillation were compared with the
experimental results Fig. 12. It is shown that the analytical
results fairly agree with the experimental results. It was
shown that the principle of the self-vibration heat pipe was
based on the simple mass-spring model.


Conclusions

The working fluid behaviors in the self-vibration heat
pipe was visualized by neutron radiography system.
Following results were obtained:

(1) It was visualized that the heat was transported by the
working fluid vibrating between the heating and the cooling
area.

(2) A technique to clarify the vibration phenomena of the
working fluid was developed by stretching the meandering
channel of the binary image and arranging the stretched
images in time series.


7th International Conference on Multiphase Flow
ICMF 2010, Tampa, FL USA, May 30-June 4, 2010


(3) Visualization results suggested that the liquid columns
were vibrating near each cooling area. The periods of the
vibration was predicted fairly well by the mass-spring
model.


I-


I I I I
0.2 0.4 0.6 0.8
Texp [sec]


Figure 12: Comparison of the oscillation periods between
the analytical and the experimental results..


References

Y. Miyazaki, H. Akachi, H.,th Natl. Heat Transfer Symp., III,
735-736 (2001)

S. Nishio, S. Nagata, Y. Tada, Y. Tachino, 40th Natl. Heat
Transfer Symp., I, 321-322 (2003)

T. Nagasaki, Y. Ito, T. Ishikawa, 42th Natl. Heat Transfer
Symp., 211-212 (2005)

K. Mochiki, K. Nittoh, Oyo Buturi, Vol.75, No.11,
1349-1 1 5 1li2"1 -)

C. Willson, B. Borgmeyer, R.A. Winholtz, H.B. Ma, Journal
of Thermophysics and Heat Transfer, Vol.22, No.2,
366-372(2008)

G. Matsui, M. Sugihara, S. Arimoto, Journal of the Japan
Society of Mechanical Engineers, Vol.45, No.391,
331-338(1979)


0 PL-0.2
A 0.25
5 0.4
0.5
0.6





OA n/




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