NOTE AMS-TRD GAS #1
Procedure of CO2 Transfer
Feng Zhou，MIT
CC: Martina Green
February 23, 2005
In this write up, we discuss the procedure on how to transfer CO2, to a designed gas
storage vessel that supplies CO2 to the TRD for AMS-02. Our goal is to have the desired
final gas density in the target vessel to be 9.9 mole/L but not to exceed this value for safety
reasons. In our setup, we used a 150 ml vessel, which simulates a ten-day life cycle of the
gas supply to the TRD. The purpose of this write up is to serve as a guide for future
filling of the space qualified CO2 vessel in Box S of the TRD.
1. General Description
The Transition Radiation Detector (TRD) for the AMS-02 detector requires a detection
medium containing a mixture of xenon and carbon dioxide gas at a ratio of 80:20 by
volume [1]. About 48.4 kg (109lbs) of xenon and 5.8 kg (11 lbs) of CO2[2] in carbon
fiber over-wrapped lightweight stainless steel vessels of 27.5 L and 13.3 L, respectively are
needed for a full mission of more than 3 years. These vessels will be filled on ground
prior to launch.
Our goal at MIT is to perform ten-day life cycle simulations of the gas supply system
with the Engineering Module, both manually and with the electronics developed at CERN
and in Rome. Each ten-day cycle simulation will represent about 1% volume of Xe and
CO2. To this end, we have set up a CO2 transfer system and have successfully filled two
150 mL bottles of CO2 for our initial tests. A detailed discussion of the gas transfer
system and the transfer procedure is presented below.
2.
Requirements
Transfer CO2 from source bottle to a store bottle to the density of 9.9mol/L.
Process should be controllable and safe.
Considering the safety issue, we should not overfill it.
3.
Properties of CO2
The main properties of CO2 are
Molecular weight:
44.01 g/mol
Boiling point:
-78.5°C (sublimation)
Critical density:
464 kg/m3
Critical temperature:
31 °C
Critical pressure:
1070.74 psi
NOTE AMS-TRD GAS #1
Following Fig.1 describe the isothermal property of CO2[3]
Fig. 1 Isothermal curves of CO2
4. Transfer System
The Fig. 2 and Fig. 3 below show the scheme of the transfer system.
Fig. 2 Scheme of CO2 transfer system
NOTE AMS-TRD GAS #1
V2
To
vacuum
V3
pump
Source
V7
bottle
V4
V1
V6
Heater
Scale 2
PEEK
tubing
Store
bottle
For Xe
use only
Scale 1
Fig. 3
Experiment setup of CO2 transfer system
We use 1/4 inch copper tube as transmission line and the parameters of main parts are
listed below.
Scale 1
Scale 2
Heater
Store bottle
Source bottle
Pressure Gauge
Polymer tubing
Maximum: 3100g
Accuracy: 0.01g
Maximum: 21kg
Accuracy: 2g
Used on AMS -01
U=120 V
W=20 Watt
V=150.6 ml
Mnet=716.40 g
V=7 L
P~900 psia as initial pressure
Mechanical
Maximum: 2000psi
Can hold high pressure and flexible, greatly reduce the spring force
We need fill 65.60 g CO2 in this store bottle to reach the density up to 9.9mol/L.
5. Procedure of Transfer
Corresponding to above scheme, we separate the procedure into 4 stages.
1. Evacuate C1 and transmission lines
1)
Measure the net mass of store bottle C1
NOTE AMS-TRD GAS #1
2)
3)
4)
5)
6)
Connect store bottle C1 with circuit to the supply bottle C2
Turn on heater on C2, Whenever the pressure reach as 1000 psi, stop heating
Open V1, V3, V4 and V6
Turn on vacuum pump down to 1.81 Torr （99.999% purity）
Close V4 and V3, turn off pump
2. Preparation for transfer
1)
2)
Open V2
Turn on scales and zero both scales with the "tare" button.
3. Begin transfer
1)
2)
3)
4)
Open V3 partway (2.1 turn) to start transfer
When C1 has gained the desired mass* of gas, close V3 and V1
Turn off heaters and then close V2 and V6
Turn on vacuum pump and open V7 to vent the rest gas in connection to C1
and then turn off pump and close V7
Disconnect the store bottle and measure the mass increase
5)
End
4.
1)
2)
Open V3 and V5 to vent out all CO2 in the gas line
Close all valves and turn off main power
*Even we have used polymer tubing to cut the string force, we still need transfer about
4g more CO2 to remedy the residual one in the connection part to C1 that will be show
on scale but can not be counted to the whole mass of CO2 in the bottle C1.
6. Sample of transfer procedure data
One sample of transfer data is listed below.
Time (min)
Accumulate
mass (g)
0
3
5
10
15
20
30
35
40
50
55
59
60
0
24.42
29.23
32.26
33.42
35.4
39.35
43.98
48.72
58.98
64.28
68.47
69.12
905
900
900
900
900
905
910
920
920
930
940
940
940
24.5
24.6
24.6
24.5
24.5
24.8
25.2
25.6
25.8
26.2
26.3
26.4
26.5
Pressure of source
bottle (psi)
Temperature of
source bottle (℃)
Table 1.
CO2 transfer data
NOTE AMS-TRD GAS #1
Initial Status:
MC1net=716.37 g
Troom=21.5℃
PC2=905psi
TC2=24.5℃
MCO2=65.33g
PC2=940psi
TC2=26.4℃
Final Status:
MC1total=781.70g
Error: 0.4%
7. Summary
It usually takes about 60 minutes to transfer 70g gas. Transfer velocity is very high at the
beginning and drop down quickly. Near the end the velocity is steady and almost 1g per
second. Since the vapor pressure of CO2 is sensitive to the temperature like Fig. 4, we can
easily hold the pressure difference by heating the source bottle to several degrees higher
than that of store bottle. For instance, in this sample we only need to heat the source
bottle to 27℃ when the store bottle is at room temperature. The pressure is usually
below 1000 psi, so the whole process is safe and controllable. We can monitor the mass
increase during the process with accurate scale, this real time control could secure we never
overfill the store bottle.
Fig. 5 Vapor Pressure of CO2 versus temperature
NOTE AMS-TRD GAS #1
Reference
[1]
“The construction of the Alpha Magnetic Spectrometer (AMS) for the International Space Station”.
AMS-02 Homepage
[2]
U. Becker, J. Burger and P. Fisher, “TRD Gas system Summary and Specifications”. AMS-02
Homepage
[3] R. Span and W. Wagner,
“A New Equation of State for Carbon Dioxide Covering the Fluid Region
from the Triple-Point Temperature to 1100 K at Pressures up to 800 Mpa”, J. Phys. Chem. Ref.
Data, 1996, 25, 6, 1509-1596.