The design and preliminary testing of a Venus Atmosphere Simulation System are described. The system was designed for testing a quadrupole mass spectrometer proposed for the Pioneer-Venus Experiment. The system is capable of providing programmed temperature cycles up to 550 C, and manually controlled pressure up to 100 atmospheres

Cridlin, M. S.

Munford, J. A.

English

NASA Technical Reports Server

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https://ntrs.nasa.gov/search.jsp?R=19740023633 2020-03-23T03:49:10+00:00Z
X-753-74-229
GSFC VENUS ATMOSPHERE SIMULATOR
M. S. Cridlin
J. A. Munford
Engineering Services Division
February 1974
GODDARD SPACE FLIGHT CENTER
Greenbelt, Maryland
GSFC VENUS ATMOSPHERE SIMULATOR
M. S. Cridlin
J. A. Munford
Engineering Services Division
ABSTRACT
The design and preliminary testing of a Venus Atmos-
phere Simulation System are described. The system
was designed for testing a quadrupole mass spectro-
meter proposed for the Pioneer-Venus Experiment.
The system is capable of providing programmed tem-
perature cycles up to 550 0 C, and manually controlled
pressure up to 100 atmospheres.
iii
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CONTENTS
Page
ABSTRACT . . . . . . . . . . . . . . . . . . . . . * .... iii
OBJECTIVE . . . . . . . . . . . . . . . . . . . . . . . . . 1
AUTHORIZATION ....................... 1
RESULTS. . . . . . . . . . .......................... 1
DESCRIPTION OF SYSTEM
Chamber . . .. . .. . . . .. . . . ... . . ... ... . 1
Gas Transfer System . ..... . . . . . . . . . . . . 2
Temperature Control System . ...... . . . . . . . 2
Thermocouple Assembly. . ........ . . . . . . ... 3
Insulation . . . . . . . . . . . . . . . . . . . . . . . 3
PRELIMINARY TESTING ................... 3
APPENDIX A PHOTOGRAPHS OF SYSTEM . ......... A-i
PRECEDING PAGE BLANK NOT FILMED
V
ILLUSTRATIONS
Figure Page
1 Test Chamber Assembly ............... 5
2 Schematic Diagram, Gas Transfer System . ...... 6
3 Schematic Diagram, Electrical . ........ . . . 7
4 Thermocouple Assembly . ............. . 8
5 Descent Temperature, Model and Result . ..... . 9
App. A Photographs of Venus Atmosphere Simulator . ..... A-1
vi
GSFC VENUS ATMOSPHERE SIMULATOR
OBJECTIVE
The goal of this program was to develop and construct an environmental sys-
tem capable of simulating the entry conditions expected to be experienced by a
proposed Pioneer-Venus experiment package. The simulation system was
designed for ground-based testing of a candidate quadrapole mass spectrometer
and its associated sampling mechanisms. The system is capable of simulating
the anticipated temperature-time and pressure-time profiles of entry.
AUTHORIZATION
The Engineering Services Division was authorized by Work Request No. 623-
76361-0052 of October 10, 1973, submitted by the Experiment Development and
Operations Branch, Laboratory for Planetary Atmospheres, to fabricate one
high temperature, high pressure reaction chamber. The task also required
design, engineering, and testing.
RESULTS
Laboratory test runs indicate that the simulation system is capable of simulat-
ing the temperature-time profile anticipated in a proposed Pioneer-Venus ex-
periment. The pressure-time profile can be maintained manually if a heated
gas source is employed. Minor gas leakage problems were encountered around
the main flange seal. High strength titanium bolts have been installed to pro-
vide more clamping force, but no further tests have been conducted.
DESCRIPTION OF SYSTEM
CHAMBER
The heart of the Venus Atmosphere Simulation system is a specially designed
stainless steel pressure vessel containing integral socketed heaters, provi-
sions for gas flow, and accessory feedthroughs to accommodate thermocouple
assemblies. The chamber is fabricated from an AISI 316 stainless steel
forging per Figure 1. The main sealing flange is a Hughes Aircraft Co. non-
rotatable blank flange Model VF 800-2. Two flanges are provided; one blank,
for testing and calibrating the simulation system, and a similar flange modified
to accept the Quadrupole Mass Spectrometer structural model. The pressure
vessel is jacketed to provide for cooling using liquid nitrogen.
The pressure chamber was designed jointly by the Fabrication Technology
Section, Fabrication Engineering Branch and the Experiment Development and
1
Operations Branch. In order to avoid time consuming developmental problems,
the chamber was designed employing the following principles:
1. Avoiding mechanical feedthroughs, and minimizing gas stratification
with adequate gas flow, using internal baffling where required.
2. Eliminating gas-heater contact. Hot heaters contaminate the gas,
and the heaters may be chemically attacked by the hot gases.
3. Avoiding dependence upon internal insulation.
4. Avoiding hot electrical feedthroughs for heaters and thermocouples.
5. Minimizing the mass to be heated.
6. Avoiding welds in the pressure vessel.
7. Allowing maximum flexibility for other potential applications.
GAS TRANSFER SYSTEM
A schematic diagram of the gas transfer system is shown in Figure 2. The
simulation system was designed for use with bottled carbon dioxide or mix-
tures of carbon dioxide and other gases. All high pressure tubing is AISI 304
stainless steel, 0. 25 inch O. D., 0. 065 inch wall thickness. The vacuum pump,
vacuum gauge tube, and low pressure transducer are isolated from the high
pressure by a manually operated valve. Exhaust gas flow rate is controlled by
a high pressure micrometer needle valve. All valves and controls, with the
exception of the gas bottle regulator, are mounted on the front panel; the
pressure vessel and high pressure lines are located behind a safety shield.
TEMPERATURE CONTROL SYSTEM
The temperature control system is described schematically in Figure 3. The
temperature-time profile is controlled automatically by a solid state power
controller whose set point is varied by a curve-following programmer. Twelve
Chromalox Model CIR-2080 cartridge heaters, inserted into sockets in the
pressure vessel, are capable of supplying up to 8400 watts at 240 VAC, or 6300
watts at 208 VAC.
The temperature control system consists of a Research, Inc. Series 625,
Model 6000 Thermac Controller with 60 ampere capacity integral phaser. The
controller has the capability for operation in manual, set point, or program
2
modes. The programmer is a Dbata-Trak Model 5110 electrostatic curve
follower with a 100 ohm potentiometric output.
The thermocouple range card installed in the controller is calibrated from
-185Co (-3000 F) to 6500C (1200 0 F) with an iron-constantan thermocouple.
Any temperature within this range may be automatically maintained in the set
point mode.
THERMOCOUPLE ASSEMBLY
The thermocouple assembly, illustrated in Figure 4, consists of two pairs of
B&S No. 24 gauge iron-constantan wire, insulated with 1. 5mm O. D. glass
pipet tubing, encased in a stainless steel sheath. The pressure seal was made
with Hysol 151 epoxy adhesive at the end of the sheath most distant from the
chamber, where the temperature remains practically ambient. The assembly
was designed to permit ease of removal and replacement by disconnecting a
compression fitting. Each thermocouple assembly was hydrostatically tested
to 2000 psi at 75 0 F before installation into the simulation chamber.
INSULATION
External insulation was provided to reduce heat losses from the pressure
vessel. The insulation was cast in two half-cylindrical sections approximately
one inch thick using a mixture of powdered asbestos cement, calcined calcium
sulfate (plaster of paris), and water. The two halves were clamped onto the
pressure vessel outer jacket with modified worm gear clamps.
PRELIMINARY TESTING
Four preliminary test runs were made with a blank main flange. The first
three were performed while awaiting delivery of the thermocouple range card,
so automatic temperature control was not possible. Also, nickel gaskets for
the main seal were not yet fabricated, so readily available copper gaskets were
substituted, and some seal leakage was expected.
Run No. 1 was performed beginning at room temperature and a pressure of 100
microns of mercury. The evacuated system was backfilled to 500 psig with
bottled carbon dioxide. The temperature-power controller was operated in the
manual mode, and was arbitrarily set at an output current of 15 amperes.
Thermocouples were located on the inner surface of the pressure vessel and
in the center of the vessel. The pressure was allowed to rise naturally as the
temperature increased. Both temperature locations were monitored using a
Leeds and Northrup temperature potentiometer, and the pressure was read
from a 0-2000 psig pressure gauge. Leaks around the copper gasket on the
main seal developed as the temperature began to increase. The leaks were
3
stopped by tightening the flange bolts, but enough gas was lost to prevent the
system from reaching the desired 100 atmospheres.
The second trial run was performed at a constant heater current of 20 amperes,
using a copper gasket. The temperature-time data indicated that the heating
rate at 20 amperes input more closely resembled the desired rate than the first
run. Again, pressure leaks developed as the temperature began to increase.
The pressure reached a maximum of 78. 5 atmospheres at the end of the heat-
ing cycle.
The third run was performed under the same conditions as the second, except
that the chamber was backfilled to full bottle pressure, 965 psig, before the
temperature was elevated. Only small leaks developed, again around the
copper gasket. No significant loss of gas occurred, and the pressure climbed
to 100 atmospheres and was maintained by bleeding off excess gas through the
needle valve. Leaks occurred late in the run but the pressure remained near
95 atm.
It should be noted that the pressure leaks occurred during temperature eleva-
tions; leaks occurred in all three temperature runs during the first 55 0 C (100 0 F)
rise.
Test run number 4 was performed using an annealed nickel gasket instead of
copper; the thermocouple range card was received and installed in the con-
troller, permitting a programmed temperature profile for the first time. The
temperature control system functioned satisfactorily, however, the tempera-
ture of the chamber remained a constant 33 0 C (60 0 F) below the apparent set
point throughout the test run, indicating the need for calibration. No pressure
leaks occurred and the starting bottle pressure of 64 atmospheres quickly
reached 100 atmospheres, at which time the pressure was maintained by bleed-
ing off gas through the needle valve.
A fifth test run was performed after calibration of the temperature programmer.
A structural model of the quadrupole mass spectrometer housing was installed
in the modified main flange. A temperature-time curve was plotted from data
recorded and was compared to a target curve. Both curves are illustrated in
Figure 5. A gas leak occurred early in the test and a sufficient quantity of gas
was lost such that the target pressure of 100 atmospheres was not attained.
If a warmed carbon dioxide bottle is employed for pressure regulation in
future testing, the pressure profile can be restored as small leaks are sealed.
4
3.00 -3.00- .376 DIA THRU
2-PLACES
.063 WALL TUBES X 2" LONG
2-PLACES
20-HOLES EQ. SP. 1/4 PIPE TAP
7.128 DIA B.C. 4 PLACES EQ. SP.
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Figure 1. Test Chamber Assemby164.00 DIA $ .187 6.00
9.00 DIA 1.0
6.850 7.00 NO. 8 - 32 X I/. DEEP
6.6000 2-PLACES
1O 13HALF SECTION 
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TEST CHAMBER
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VIEW-A
SECTION A-A
Figure 1. Test Chamber Assembly
PRESSURE LN2 SUPPLY
GAUGE
THERMOCOUPLE
GAUGE TUBE
BLEED
VALVE
VENT
MANIFOLD VALVE
OSOLATiON 
VALVE
MECH.
TEST PUMP
CHAMBER
GAS
SUPPLY
Figure 2. Schematic Diagram, Gas Transfer System
6
117 VAC
MECH. PUMP
4 TC/1 WALL
TC/2 WALL
TC/3 CHAMBER
CENTER
THERMOCOUPLE 117 VAC
GAUGE (TEMP.)
', TC/4 CHAMBER
CENTER
PROGRAMMER
TEMPERATURE 208 VAC/10/30A
CONTROLLER
12 HEATERS
525 WATTS-EACH
THERMOCOUPLE TUB
GAUGE
(PRESSURE) 117 VAC
Figure 3. Schematic Diagram, Electrical
7
STADNLESS STEEL
TUBiNG-SWAGED END
GLASS PIPET TUBE
4-PIECES
BARE THERMOCOUPLE
WWIE NO. 24 B&S 8-C
TYPE J
EPOXY-HYSOL 151
FABRUC INSULATION
Figure 4. Thermocouple Assembly
8
550
500
450
400 - TEST PROFILE
350 -
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200 -
150
100 -
50 -
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0 10 20 30 40 50 60 70 80
TIME (minutes)
Figure 5. Descent Temperature, Model and Result
9
APPENDIX A
Photographs of
Venus Atmosphere Simulator
A-i
Front View
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GSFC Venus atmosphere simulator

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