-
NASA TECHNICAL
MEMORANDUM
r-.tnCMI
x
NASA TM X-2574
CA LE^g^# &^^*-COPY
DESIGN AND PERFORMANCE EVALUATION
OF A CRYOGENIC CONDENSER
FOR AN IN-PILE EXPERIMENT
by Robert W, Graham, Richard J, Crum
and Yih-Ynn ffr//
Lewis Research Center
Cleveland, Ohio 44135
NATIONAL A E R O N A U T I C S AND S P A C E ADMINISTRATION •
WASHINGTON, D. C. • JUNE 1972
-
1. Report No.
NASA TM X-25742. Government Accession No. 3. Recipient's Catalog
No.
4. Title and Subtitle
DESIGN AND PERFORMANCE EVALUATION OF A CRYOGENICCONDENSER FOR AN
IN-PILE EXPERIMENT
5. Report DateJune 1972
6. Performing Organization Code
7. Author(s)
Robert W. Graham, Richard J. Crum, and Yih-Yun Hsu8. Performing
Organization Report No.
E-6868
9. Performing Organization Name and Address
Lewis Research CenterNational Aeronautics and Space
AdministrationCleveland, Ohio 44135
10. Work Unit No.
111-05
11. Contract or Grant No.
12. Sponsoring Agency Name and Address
National Aeronautics and Space AdministrationWashington, D. C.
20546
13. Type of Report and Period Covered
Technical Memorandum
14. Sponsoring Agency Code
15. Supplementary Notes
16. Abstract
An apparatus was designed to enable in-pile irradiation of
materials in liquid hydrogen atcryogenic temperatures. One of the
principal components of this apparatus was a horizontaltube
condenser. The performance of the condenser was evaluated by
running a liquid-nitrogenprototype of the apparatus at heat loads
comparable to or greater than those expected duringthe irradiation.
The tests showed that the condenser was capable of handling the
design heatload and that the design procedure was sound.
17. Key Words (Suggested by Author(s))
Cryogenic condenserCondenserLiquid nitrogen
18. Distribution Statement
Unclassified - unlimited
19. Security Classif. (of this report)
Unclassified20. Security Classif. (of this page)
Unclassified21. No. of Pages
11
22. Price'
$3.00
* For sale by the National Technical Information Service,
Springfield, Virginia 22151
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DESIGN AND PERFORMANCE EVALUATION OF A CRYOGENIC CONDENSER
FOR AN IN-PILE EXPERIMENT
by Robert W. Graham, Richard J. Crum, and Yih-Yun Hsu ' :
Lewis Research Center
' . . . ' . ' ' ' SUMMARY
. - ' . - ' " ' ' - • ' : '
An apparatus was designed to enable in-pile irradiation of
materials in liquid hydro-gen at cryogenic temperatures. One of the
principal components of this apparatus wasa horizontal tube
condenser. The performance of the condenser was evaluated by
run-ning a liquid-nitrogen prototype of the apparatus at heat loads
comparable to or greaterthan those expected during the irradiation.
The tests showed that the condenser wascapable of handling the
design heat load and that the design procedure was sound.
.INTRODUCTION ;
As the result of a proposal to do some material studies in pile
in liquid hydrogen,the design of a hermetically sealed test chamber
suitable for insertion in the Plum BrookReactor was inaugurated.
One of the design criteria to maximize safety of operation wasthat
the hydrogen coolant be confined in a welded, lead-free test
chamber and recycled;consequently, a.condenser was selected to be a
major constituent of the apparatus.
A survey of the design literature revealed that there was
practically no informationrelative to hydrogen condensing. What
little was found pertained to vertical condensertubes, and the
design of concern would have to involve horizontal tubes.
i.' ' ' ' . . , ' ' ' '
Of course, there is considerable literature pertaining to
condensers in general -primarily those involving steam.
Cpndensing-heat-transfer correlations do exist, buttheir
applicability to an.entirely different thermal domain must be
questioned. As ameans of evaluating the design procedure for
hydrogen, it was considered advisable, todesign and test a nitrogen
condenser prototype similar to the hydrogen one. Runningthis
nitrogen prototype condenser out of pile would yield valuable
information about theapplicability of the correlations and scaling
laws employed. This report contains anevaluation of the nitrogen
condenser performance with reference to its design. These
-
tests with the nitrogen condenser indicate that the design
equations and procedure can beapplied to the hydrogen condenser
with considerable confidence and the desired perform-ance of the
condenser will be achieved.
APPARATUS AND PROCEDURE
Figure 1 shows the design concept of the apparatus as it was
envisioned for theactual in-pile experiments where liquid hydrogen
was the coolant. The material speci-mens to be tested would be
placed in the liquid-hydrogen sump shown at the left side ofthe
drawing. The nominal liquid-hydrogen temperature in the sump is 30
K (54° R).The condenser part of the apparatus comprises 15
horizontal tubes in which helium flowsas a coolant. The helium is
to enter the condenser tubes at 24 K (43° R). The antici-pated heat
load to be dissipated by the condenser is approximately 845 watts
(2880Btu/hr). This heat load is the estimated gamma and neutron
heating that will be devel-oped in the test hole of the
reactor.
In carrying out the nitrogen prototype test program, electrical
heaters were in-stalled in the heat exchanger to simulate the gamma
and neutron heating that would beexperienced in pile. Sufficient
electrical heating capacity was installed in the nitrogenheat
exchanger to far exceed the anticipated design level. Since liquid
nitrogen was tobe used as the coolant in the prototype heat
exchanger instead of gaseous helium, thedesign-point heat flux for
the prototype should be higher than that of the actual in-pileheat
exchanger. The higher density and Prandtl number of the liquid
nitrogen wouldeffect a greater transport of heat for comparable
temperature differences and flow ve-locities. A number of ways of
establishing this prototype heat load could be used.Through
simulitude relations, one could compute the heat load on the
condensing sideand on the coolant side for various conditions. It
was decided that the most conserva-tive estimation would be to
operate the nitrogen prototype at the same value of the flood-ing
parameter
-
Exchanger
PrototypeHydrogen
Coolant tem-perature,
K
8023.8
Wall tem-perature,
K
9424.8
Estimated coolant-side heat-transfer
coefficient,W/(m2)(K)
30601300
Figure 2 shows the apparatus and how it was instrumented for the
nitrogen experi-mental program. A liquid-level indicator was
installed in the sump to give an approxi-mate idea of the amount of
liquid nitrogen there. The instrument consisted of six
carbonresistor circuits located at different positions on the
probe. The sump was utilized asa convenient reference temperature
bath for the cold junctions of the thermocouple
in-strumentation.
The thermal conditions of the condenser coolant (liquid
nitrogen) were determinedfrom platinum resistor bulk temperature
measurements as the coolant entered the con-denser and when it
discharged. A turbine-type flowmeter was used to monitor the
flowrate. The liquid nitrogen pressures at the inlet and exit were
measured.
As is shown in figure 2, one of the condenser tubes was
instrumented with severaltypes of thermocouple sensors. The
temperature difference AT between the outsidewall and the vapor
surrounding the tube was measured at three axial stations, 14.
7,36. 8, and 61. 5 centimeters (5. 8, 14. 5, and 23. 2 in.) from
the inlet. Centerline ATthermocouples were installed at four
internal stations of the condenser tube. As shownin figure 2 they
were located at 14. 7, 29. 4, 44. 2, and 58. 8 centimeters (5. 8,
11. 6,17. 4, and 23. 2 in.) from the inlet.
During the course of the test program, some of these
thermocouples shorted oropened up and could not be repaired. Thus,
not all of the instrument stations of the con-denser tube were
available during the testing. However, a sufficient number
remainedintact to yield performance information.
HEAT-TRANSFER DESIGN CALCULATIONS
The correlations and important assumptions pertinent to the
design of the hydrogenapparatus and the nitrogen prototype are
outlined in this section. Most of these corre-lations, when taken
from their original references, were designated for use with U.
S.customary units. They will be cited in their original published
form. In cases wherethe predictions are dimensional, the conversion
factors necessary to list them in SI unitsare presented.
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Heat-Transfer Coefficient Inside Condenser Tubes
Hydrogen apparatus. - In the hydrogen apparatus, cold helium gas
was to be used asthe condenser coolant. A simple, forced-convection
correlation for gases obtained fromreference 1 was employed in
estimating the inside-tube heat-transfer coefficients:
h = KG°-8d-°-2V-^ (Dw
where
h heat-transfer coefficient, Btu/(ft2)(hr)(°F); to convert to
W/(m2)(K) multiply .by 5. 69
K proportionality constant which includes fluid properties as
well as Dittus-Boelterconstant, c(k°' 6Cp' 4/M°' 4); K = 0. 020 for
helium
G flow per unit area
d diameter or hydraulic diameter
Nitrogen prototype. - Liquid nitrogen was employed as the
condenser coolant. Aconventional forced-convection correlation for
liquids was utilized, namely,
' ' h = * CRe0' 8Pr°-25 (la)d
where Re is the Reynolds number, Pr is the Prandtl number, and C
is a coefficient.
Condensing Heat-Transfer Coefficient Outside Tubes
Jakob (ref. 2, p. 673) suggests the following correlation for
condensation with mul-tiple,horizontal tubes:
*/ 2 3= 0.725V P Xk g
V nMd(tf - th = 0. 725't/ P AK g (2)
where .
h heat-transfer coefficient, Btu/(hr)(ft2)(°F); convert to
W/(m2)(K) by multiplyingb y 5.69 ' . - . • • • • • ;
p density, lbm/ft3
4
-
A heat of vaporization, Btu/lb .- . : ..
k thermal conductivity, Btu/(ft)(hr)(°F) ' •2
g gravity, ft/sec
n number of tubes • --. . •' /•
p. viscosity, lb/(ft)(hr)
d tube diameter, ft
to .saturation temperature,. °F . , . . . . ; . : . . . -
t surface temperature, °Fo
; ' ' • - • - . / •
' l Flooding or Holdup Estimation
Perhaps the most critical and questionable estimation in the
entire design proce- 'dure is the one pertaining to the prediction
of possible "flooding" in the condenser. By"flooding" we mean that
the condensate is inhibited from returning to the sump by themoving
vapor. A flobding criterion expressly developed for vertical
condenser tubeswas used (ref. 3). No criterion for horizontal tubes
was found in the literature. Theflooding criterion is : " ' '•
.0, ... (3)O
i n which - ' - - . . . . . .
where
j upward gas flow, ft/sec 'O .
• • ' ' • . .•
p density of vapor& • ' ' • " • » •
g local gravity . . .
d horizontal spacing between tubessp, density of liquid
j downward liquid flow, ft/sec
-
In using this criterion, we assumed that at the holdup
condition, no liquid condensate.*was dropping, or jf = 0.
RESULTS AND DISCUSSION
Twenty-four runs were made with the nitrogen prototype heat
exchanger. The elec-trical heat input to simulate the gamma and
neutron heating ranged from 500 to 6000watts. The design heat load
for the nitrogen prototype was approximately 2400 watts.
A computer code was developed incorporating the correlations
discussed in the lastsection. The output of the code was the heat
extracted in the condensing process. Ta-ble I summarizes the
principal operating conditions, including the calculated and
meas-ured electrical heat to the apparatus. Generally, when the
calculated and experimentalheat inputs are compared, they are in
relatively good agreement. One can conclude thatthe design analysis
is fairly accurate as long as steady-state operation takes
place.There remains the question of flooding or holdup, which would
make the condenser in-operative.
It was estimated by the analysis of reference 3 that the
threshold of flooding wouldnot be encountered until heat rates 2,,
times the design value were realized. The unusualgeometry of the
heat exchanger quadrant did raise some doubts whether the
floodingcriterion was meaningful. It was suggested that a kind of
horizontal flow holdup couldoccur. This speculation meant that the
condensate accumulated in the bottom of thesmaller diameter shell
(fig. 1, right side of drawing) could be backed up by a
counter-flow of the vapor. This situation could result in a
flooding excursion and an inoperativecondenser. To test this idea,
a clear plastic model of the apparatus was built, and thevapor flow
was simulated by a series of air jets and the liquid flow by water
jets. Overa wide range of conditions (gas and liquid flow rates)
there was no evidence for the be-ginning of a holdup transient. The
volumetric rates of the gas and liquid were compara-ble to the
actual ones in the heat exchanger. From this test and from the
analysis doneon estimating holdup, it is concluded that holdup is
not a likely possibility.
As was mentioned in the section APPARATUS AND PROCEDURE, some
difficultywas incurred with several of the thermocouples in the
instrumented condenser tube.Only two of the internal centerline
thermocouples remained operable throughout the en-tire testing
program. However, from knowledge of the inlet and exit coolant
tempera-tures it was possible to gain valuable information about
the bulk temperature distribu-tion along the length of the
instrumented tube.
Figure 3 shows these bulk temperature distributions for ranges
of flow rates andheat fluxes. It is evident that the distributions
are not linear, especially near the rearof the heat exchanger where
the sump is located. However, if one did assume a
lineardistribution of bulk temperatures between the inlet and exit
stations, it would not be a
6
-
bad approximation and would yield fairly good overall results.
Such an assumption wouldnot reveal that the rear section of the
condenser above the sump is doing most of thecondensing, as would
be anticipated from an examination of the geometry.
CONCLUSION
*The main conclusion from a design and performance evaluation is
that a heat ex-
changer with a horizontal condenser bank can be designed by
using standard heat-transfer correlations and that the condenser
will operate stably without holdup over aconsiderable heating
range. The condenser described in this report handled 4. 6
watts
2 1per square centimeter (30 W/in. ), which was approximately 2^
times its design ca-pacity.
Lewis Research Center,National Aeronautics and Space
Administration,
Cleveland, Ohio, April 7, 1972,111-05.
REFERENCES
1. Simoneau, R. J.; and Hendricks, R. C.: A Simple Equation for
Correlating Turbu-lent Heat Transfer to a Gas. Paper 64-HT-36,
ASME, Aug. 1964.
2. Jakob, Max: Heat Transfer. Vol. 1. John Wiley & Sons,
Inc., 1949.
3. Wallis, Graham: One-Dimensional Two-Phase Flow. McGraw-Hill
Book Co.,Inc., 1969.
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TABLE I. - SUMMARY OF NITROGEN-HEAT-EXCHANGER PERFORMANCE
Flow
m3/hr
'17.018.2
17.0
14.712.3
2. 5
2 .45.0
2.82.7
4.92.7
2.5
2.4 >" 2. 3 '
1. 11.03.5
3.5
3.4
2.7
gal/miri
74. 479. 8 -
74.4
64.454.0
11.0
10.4
21.912.5
12.0
21.7
11.6
10.910.610.2
5.0
4. 515.4
15.2
14.8
11.9
Chamber pressure
N/cm2
'12.0512.36
14.09
18.2921.77
29.94
59. 1445. 1429. 27
55.44
49.2328.47
43. 50
55.6472.39
42.6854.05
24.33
44.81
58.6727.64
Ib/in. 2 abs
17.48' ' 17.93;
20.44
26.53
31.58
43.43
85.7865.4842.46
80.41
71.4141.30
63. 10
80.70105.00
61.90
78.4035.3065.00
85. 1040. 10
Chamber satura-tion temperature
K
78. 9779 .20 '
80.39
82.89
84.68
88.01
97.96
92.6887.79
95.24
93.74
87.48-
92.2995. 4699.02
92.01
95.0785.79
92.68
96.0787. 18
• °R
142. 05142. 45
144.60
149. 10152.30
158.. 30
176.20166.70157.90
171.30
168.60
157. 35
166.00174. 70178. 10
165. 50
171.00154.30
166.70
172.80156.80
Heat, Q, W
Actual
5001000
2000
4000
4000
2500
50006000
2500
5500
60002500
4000
5000.6000
2500
30002500
5000
60002500
Calcu-
lated
445940
1825
35283612
2863
56076592
2933
5228
6771
2747
406849545791
2340
26072720
5238
63582733
^calculated ,', ^QQ
^actual ''
percent
' 8994
91
8890
115112110
117
95
113110
102
9997
94
87109
105
106109
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-Condenser tubes
Discharge line (two)-
Fill line
Vacuum vessel '..
-VCoolant
Figure 1. - Schematic of apparatus.
^Platinumresistancethermometer(T2)
Vapor temperature • (/ ) Pressure gagethermocoupleT ^ '
^Condenser tubes
Discharge line (two)
-—Referencejunctionblock-
^Inside bulktemperaturethermocouple Fj|| ,,ne
Vacuum vessel
Figure 2. - Instrumentation of condenser tube.
- Platinumresistancethermometer
yCoolant
^Turbineflowmeter
.9
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Flow,m3/hr (gal/min)
2.6 (11.6)(10.9)(15.4)(15.2)
2.53.53.5
Heat flux,W
2500400025005000
(a) High flow rates.
12
10
Flow,m^/hr (gal/min)
o 2.4 (10.6)
Heat flux,W
20 40 60 8Length of tube, cm
100 120
10 14 18 22Length of tube, in.
(b) Low flow rates.
26 30
Figure 3. - Nitrogen coolant temperature rise tube-in-shell
cryogenic con-denser.
10 A-Langley, 1972 33 E -6868
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