A small and light weight heat exchanger used for small helium refrigerator has been developed by Sumitomo Heavy Industries, Ltd. This heat exchanger is a laminated metal heat exchanger which consists of perforated aluminum metal plates and glassfiber reinforced plastic separators. The size is from 100 mm to 28 mm in diameter and about 300 mm in length. The weight is from 2.5 kg to 0.6 kg. Also it can be used between room temperature and liquid helium temperature. The thermal efficiency obtained has been more than 96%. The heat exchanger has been practically used for on-board helium refrigerator in Japanese National Railways' superconducting magnetic levitated trains

Kanazawa, Y.

Koizumi, T.

Suzuki, M.

Takahashi, M.

Uchida, T.

English

NASA Technical Reports Server

A SMALLANDLIGHTWEIGHTHEATEXCHANGER
FORON-BOARDHELIUMREFRIGERATOR
T. Koizumi, M. Takahashi, T. Uchida,
Y. Kanazawa,and M. Suzuki
Hiratsuka Research Laborat@ry,
SumitomoHeavy Industries, Ltd., Japan
ABSTRACT
A small and light weight heat exchanger used for small helium refri-
gerator has been developed by Sumitomo Heavy Industries, Ltd.. This heat
exchanger is a laminated metal heat exchanger which consists of perforated
aluminum metal plates and glassfiber reinforced plastic separators. The
size is from I00 mm to 28 mm in diameter and about 300 mm in length. The
weight is from 2.5 kg to 0.6 kg. Also it can be used between room tempera-
ture and liquid helium temperature. The thermal efficiency obtained has
been more than 96%. The heat exchanger has been practically used for
on-board helium refrigerator in Japanese National Railways' superconducting
magnetic levitated trains.
INTRODUCTION
Counterflow heat exchanger of high thermal efficiency is required for
refrigeration and liquefaction systems. In recent years, many type heat
exchangers, for example, Hampson, Collins and Plate-fin type have been
developed. But these heat exchangers do not fit in with small refrigerators
because the heat transfer area per unit volume of these heat exchanger is
not large enough.
The small refrigerator, for example, on-board refrigerator in super-
conducting magnetic levitated trains, requires very small and high thermal
efficient heat exchanger. Such heat exchanger must possess the following
characteristics [1],[2].
i. Large heat transfer surface area per unit volume and per
unit weight.
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2. Very small longitudinal heat conduction through the walls in
the exchanger.
3. Uniform distribution of flow throughout any cross section of
exchanger.
4. High resistance to shock and vibration.
Wehave developed the small and light weight heat exchanger which
fulfilled above requirements and applied it to on-board helium refrigerator
in JapaneseNational Railways' superconducting magnetic levitated trains.
This paper describes the development of the laminated metal heat
exchanger and its application for small refrigerator use.
CONSTRUCTION
The construction of laminated metal heat exchanger is illustrated in
Fig. i. This heat exchanger consists of a large number of parallel perfor-
ated aluminum metal plates, plastic separators and epoxy adhesives.
The perforated metal plates and separators are alternately stacked and bonded
with adhesives to build up the multilayer-body, lleaders made of aluminum
are bonded to both faces of the multilayer-body. Then, headers and
multilayer-body are inserted into a thin walled stainless steel vessel with
pipe fittings. One end of the fitting is welded to the stainless steel
vessel and the other end is bonded to the header. Therefore, there is
no gas leakage to the vaccum space, when the heat exchanger is installed in
a vaccum space.
In this exchanger, gas flow passages are divided into eight sections
and gas flows longitudinally in counterflow pattern. Heat transfers latera-
lly from hot gas to cold gas through the perforated plates. The perforated
heat transfer plate is made of aluminum which has high thermal conductivity
and is 0.3 mm in thickness, with 0.5 mm diameter holes.
A thickness-to-diameter ratio is 0.6 in this perforated plate.
It is represented that the desirable ratio is in the range 0.5 to 1.0 because
thermal and hydrodynamic boundary layers are broken up before they have a
chance to become fully developed, which results in high heat transfer
surface coefficients [i].
The separator is made of glassfiber reinforced plastic which has low
thermal conductivity and its thickness is 0.4 mm. Therefore, the longitudi-
nal heat conduction through the walls in the heat exchanger is very samll.
Figure 2 is a photograph of this heat exchanger. This is applied to
first stage heat exchanger for on-board refrigerator. The size is 80 mm
180
in diameter and 250 mm in length and the weight is about 2.2 kg. The heat
transfer area per unit volume in this heat exchanger is about i000 ma/m 3.
PERFORMANCE
TEST APPARATUS
The heat transfer and friction loss performance test apparatus is
shown in Fig. 3. The test has been performed by using helium gas between
room temperature and the liquid nitrogen temperature. The pressure of the
high pressure line and low pressure line are 1.57 MPa and 0.I MPa respec-
tively.
High pressure helium gas flows through test heat exchanger and is
throttled to low pressure by throttle valve and flows back to helium com-
pressor through the heat exchanger. The temperature of gas flow is
measured by copper-constantan thermocouple. The pressure drop is measured
by differential pressure gage.
EXPERIMENTAL DATA
The heat exchanger shown in Fig. 2 has been tested. The hole diameter
of perforated plate is 0.5 mm and open area ratio of the high pressure
passage is 15% and low pressure is 30%. The gap between perforated plates is
about 0.6 mm. The effectiveness and pressure drop versus the mass flow rate
of helium are plotted in Fig. 4. It shows that when helium gas flow rate is
1 g/sec, 96.5% effectiveness is obtained and pressure drop is 0.008 MPa.
Another type laminated metal heat exchanger which we have fabricated is
shown Fig. 5. The size of this heat exchanger is 28 mm in diameter and
300 mm in length. Headers and multilayer-body are inserted into the stain-
less steel vessel and their weight is about 0.6 kg. Obviously, it is much
small and light in weight compared with the heat exchanger shown in Fig. 2.
RELIABILITY
ADHESIVE
The construction of laminated metal heat exchanger which we have des-
cribed above is very simple. But for heat exchanger it is important to
possess the effective adhesive strength, gas tight and good durability,
because this exchanger is constructed with adhesive bonding.
181
So, we have selected manykinds of adhesives and tested their adhesive
strength and gas leakage at low temperature to choose the best adhesive among
them. The test results of epoxy adhesive which we applied to fabricate
the heat exchanger is explained in the following.
ADHESIVESTRENGTH
Wemeasuredthe strength of two different test specimens, one is
aluminum-aluminumadhesive bonded joint, the other is aluminum-GFRP-aluminum
adhesive bonded joint.
The shearing strength versus temperature is shownin Fig. 6. The
results indicate that the shearing strength increases as the temperature
decreases. The shearing strength of AI-GFRP-A1at liquid nitrogen tempera-
ture is about 15 MPaand the specimens failed in the adhesive. Also shearing
strength denoted by triangles showsthe test results after 7 thermal cycles
between room temperature and liquid nitrogen temperature.
Fig. 7 presents the tensile strength versus temperature. The tensile
strength of AI-GFRP-AI specimensat liquid nitrogen temperature is about
50 MPa. Somespecimensdenoted by squares were cycled 235 times between
room temperature and liquid nitrogen temperature after one year has passed
since they were bonded. Their tensile strength were nearly equal to the
other specimens. Also the failed surface displayed a cohesive failure in
adhesive.
EFFECTOFTHERMALCOOLING
The heat exchanger is also requested to have high reliability for gas
leakage. The thermal cycle test of the heat exchanger has been performed
and examinedits reliability. The thermal cycle test apparatus is Fig. 8.
The test was conducted by cooling the exchanger between room temperature
and liquid nitrogen temperature. The test vessel in which test heat
exchangers are put is immersedin liquid nitrogen and the heat exchangers
are cooled to liquid nitrogen temperature. Then, the vessel movesto up
and heat exchangers are heated up to roomtemperature by the heater.
The temperature of the heat exchanger is measuredby copper-constantan
thermocouple. Also one thermal cycle between room temperature and liquid
nitrogen temperature takes about 2 hours. During the test, high pressure
and low pressure passagesare pressurized with 1.57 MPaand 0.i MPahelium
respectively. Helium gas leakage flow is measuredwith a soap bubble flow
meter attached to the low pressure side.
182
Table 1 summarizesresults of the thermal cycle test. Before cooling
the heat exchanger, helium gas leakage flow high pressure passages to low
pressure passageswas measuredto be less than 1X iO4Pa m3/sec. After 235
cycles, helium gas leakage was constantly less than 1X iO 4 Pa m3/sec.
CONCLUSION
From these test results, it is confirmed that this heat exchanger
can meet the requirements and fulfill the characteristics for " on-board
refrigerator "
A photograph of on-board helium refrigerator which we have developed
is shown in Fig. 9. This refrigerator is Claude Cycle and consists of two
reciprocating expantion engines and five laminated metal heat exchangers.
The refrigerator capacity is 5 W at 4.4 K. The size is 300 mm in
diameter and 800 mm in length and the weight is about 40 kg. This refrigera-
tor has been installed in the test vehicle and is presently being tested
at Miyazaki Test Track in Japanese National Railways.
REFERENCES
I. R.B.Fleming, " A Compact Perforated-Plate Heat Exchanger " ; Adv.
Cry. Eng., vol. 14, 197-204 (1968)
2. G.Vonk, " A Compact Heat Exchanger of High Thermal Efficiency " ;
Philips Technical Review, vol. 29, no. 5, 158-162 (1968)
DISCUSSION
Question by W.L.Swift, Creare P_D; Have you tested shear strength,
tensile strength and leakage of epoxy adhesive joints below liquid nitrogen
temperature?
Answer by author; No, I have not.
Question by F.J.Kadi, Air Products & Chemical Inc.; Would you comment
on any potential leakage of helium into vaccum space?
Answer by author; There is no leakage of helium into vaccum space,
because headers and multilayer-body of heat exchanger are inserted into
a thin walled stainless steel vessel.
183
Hot gas inlet
Cold gas outlet .I.
,f
L_
Cold gas i_
Hot gas outlet
,8O
Cold gas passage
Hot gas pass_ '_
Header
(At)
P[astic separator
(FRP)
Multilayer
Epoxy adhesive
c
Cold gas passage Perforated heat
Stainless
_vessel transfer prate
(A[)
Hot gas passage
_Header
(At)
Epoxy adhesive
Fig. 1 The construction of laminated metal heat exchanger.
Fig. 2 laminated metal heat exchanger.
184
He Compressor _7
Mass flow meter
1.57MPQ (_
Boi Iof'{ "_1 _,,
flow met erl _J._.
pump -_l
®
I
®
r
r
r
Ill
P ; Pressure gage
dP ; Differential
Pressure gage
(E)_(_) ; Thermocouple
.__J
\ Heaf exchanger
/Dewar(Liquid Nitrogen)
/Vaccum Vessel
Fig. 3 Schematic diagram of heat transfer and
friction loss performance test.
100
;_ 95
I/1
L/I
r
>
w
90
Fig. 4
0.015
0
Hole diam_
Open area rdtio ¢
High press, passage 15% J
L
o.'25 0.% o:7_ l lo 1._5 i.5
Mass flow rate (g/sec)
Performance of laminated metal heat exchanger.
CL
0.01
CL
O
I,-
"El
L.
D
I/1
I/1
P
13_
3.005
185
Fig. 5 Laminated metal heat exchanger.
Table i. Result of thermal cycle test.
!tern
Heat exchanger
A
Heat exchanger
B
Number
of cyc I es
Pressure(MPa)
High pressure
passage
Low pressure
passoge
Helium gas leakage(Pom_sec)
(from high pressure passage
to tow pressure passage)
0 1.57 0.1 tess than lx10 "4
1.57 0.1 less than lx10.4
235
2.30 0.1 tess than 1 x 10 -4
0 1.57 0.1 less than 1 x 10 .4
1.5'7 0.1 less than 1 x10.4
235
2.30 0.1 less than 1 x 10 -=
186
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Dewor(Liquid Nitrogen)
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Fig. 8 Schematic diagram of thermal cycle test.
Fig. 9 Refrigerator
188


A small and light weight heat exchanger for on-board helium refrigerator

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