CubeSat Thermal Vacuum

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CubeSat Thermal Vacuum



By



James Jang

Jonathan Wang









ECE 345, SENIOR DESIGN PROJECT


FALL 2003






TA: Jing Tang




December 10, 2003



Project No. 13














ii

ABSTRACT


For our Senior Design project, we decided to complete an auxiliary
project under the

UIUC

CubeSat
Mission
:
to
design and build a thermal vacuum chamber

for environmental testing
.

Our
goal for the
thermal vacuum chamber
was

simulate the harsh temperature conditions of space, from its extreme low
(absence of heat) to its e
xtreme high (full effects of the sun). This will allow the CubeSat team to
properly test the durability and functionality of the satellite in the environment it will be launched into.

The pressure
-
less conditions of space will be reached using a
n

existin
g vacuum chamber.


Once at
vacuum, t
he
deep
-
space conditions
are

simulated using a coil reservoir filled with liquid
n
itrogen
surrounding the spacecraft
.

The heat from
is

simulated using a properly calibrated halogen bulb in
conjunction with a parabolic re
flector.

Testing
and simulations are

done
by

monitoring the temperature
with
thermal couples

using Lab
VIEW
.






































iii

TABLE OF CONTENTS



1.

INTRODUCTION

................................
................................
................................
....................
1


1.1
Motivation

................................
................................
................................
...........................
1


1.2
Project Goals

................................
................................
................................
.......................
1


1.3 Subprojects

................................
................................
................................
.........................
1


1.4 Block Diag
ram

................................
................................
................................
....................
2


2.

DESIGN PROCEDURE

................................
................................
................................
...........
3


2.1 Cryogenics Simulator

................................
................................
................................
.........
3


2.2 Solar Simulator

................................
................................
................................
...................
3


2.3 LabVIEW Data Logging

................................
................................
................................
.....
3


2.4

Current Control

................................
................................
................................
...................
4



3.

DESIGN DETAILS

................................
................................
................................
..................
5


3.1 Cryogenics Simulator Components

................................
................................
....................
5



3.1.1 Inherited Reservoir

................................
................................
................................
....
5



3.1.2 Designed Reservo
ir

................................
................................
................................
....
5



3.1.3 Implemented

................................
................................
................................
..............
6


3.2 Solar Simulator Design

................................
................................
................................
.......
6



3.2.1
Choice of Reflector

................................
................................
................................
....
6



3.2.2
Choice of Halogen Bulb

................................
................................
............................
7



3.2.3
Wattage to Temperature Conversion

................................
................................
.........
7



3.2.4
Current Needed to Drive Bulb

................................
................................
...................
8


3.3 LabVIEW Data Logging

................................
................................
................................
.....
8


4.

DESIGN VERIFICATION

................................
................................
................................
.......
9


4
.1 Testing

................................
................................
................................
................................
9



4.1.1 Cryogenics Simulations

................................
................................
.............................
9



4.1.2 Solar Simulations

................................
................................
................................
.....
11


4.2
Simulation
Conclusions

................................
................................
................................
....
12


5.

COST

................................
................................
................................
................................
......
13


5.1 Parts

................................
................................
................................
................................
..
13


5.2 Labor

................................
................................
................................
................................
.
14


5.3 Total

................................
................................
................................
................................
..
14


6.

CONCLUSIONS

................................
................................
................................
....................
15



APPENDIX

1



VACUUM CHAMBER OPERA
TI
NG DIRECTIONS
...............................
16



APPENDIX

2



LIQUID NITROGEN SAFE
TY & CONCERNS

................................
........
17



REFERENCES

................................
................................
................................
.......................
18





1


1. INTRODUCTION


1.1


Motivation


As an auxiliary team of the CubeSat Satellite Environmental Testing team, we are working on a thermal
vacuum chamber for the testing of

the Satellite to be launched this upcoming summer. Our work will
provide the environment that will simulate the harsh conditions of outer space. This will allow the
CubeSat team to properly test the durability and functionality of the satellite in the e
nvironment it will
be launched into.


We are excited about this project because we get to be part of a select group of students that will have
helped to design, build and ensure the success of the UIUC CubeSat satellite.



1.2


Project Goals



The ability t
o sustain a constant cold (50K) and hot (1.35 kW/m
2
) temperature from the liquid nitrogen
and solar lamps, respectively, is the basis
of

our thermal vacuum project. The need to sustain these
temperatures is to emulate the deep
-
space environment needed to
thoroughly test the Cube Satellite.
Without temperature control in the vacuum chamber, the satellite cannot be fully tested before launch.


As supplementary goals, we may implement a LabVIEW data logging system and a duty cycle for the
solar simulator.
T
he labview implementation would allow the user to view the
data
graphically,
temperature versus time. The automated duty cycle for turning the solar simulator on and off would
simulate the conditions of space while in
orbit. Combining these two supplemen
tary goals, we would
then be able to log data for a full day simulation. However, environmental testing on the spacecraft can
still be done manually without these functions, and therefore these tasks will only be started once the
basi
c goals

of our therma
l vacuum
project
are completed.



1.3


Subprojects


Our
thermal vacuum chamber

consists of four subprojects.


Cryogenics Simulator

The key to the cold simulator is the liquid nitrogen

reservoir. Right now, there is an L
-
shaped reservoir
attached to the vacuu
m chamber door. This reservoir will surround the space craft on 2 sides, and it will
hold the liquid nitrogen.

Once we pour in the liquid nitrogen, we want to see how quickly it takes the
chamber to cool down to desired space low temperature. This is im
portant because we will need to
know this information for the actual space simulation testing of the Satellite. We will want to know how
long it takes to reach the low temperature before we start the testing so that the test is as accurate as
possible and
so that we do not collect unrelated data.

The desired low temperature is 50K.


Solar Simulator

We need to find a solar simulator lamp that will emit the proper amount of heat onto the spacecraft. The
lamp must have the correct solar output, 1.35 kW/m
2
.
We must research all available lamps and choose
the correct one taking cost and function into account.

The light must be focused directly on the craft so
that none of the bulb’s light energy is wasted, and so
t
hat it does not evaporate the liquid nitrogen

in the
surrounding reservoir
.


2


LabVIEW Data Logging

The logging and reading of temperature is extremely important. This will be done using LabVIEW. We
will also look into the other features of LabVIEW and see what else can be done. We hope to have
auto
mated as many features and functions as possible.

The temperature of the spacecraft will be
determined by strategically placed
thermal couples

on the craft.


Current Control

A current control will be implemented to turn the lamp on/off. This lamp duty cy
cle will emulate the
presence of the sun in outer space orbit.

This control may be implemented through LabVIEW.



1.4

Block Diagram


Our block diagram, shown in Figure 1, displays the flow of data between the components of our vacuum
chamber. More speci
fic details of each
block will be described later.
























Figure
1
: Block Diagram of Thermal Vacuum Chamber





3


2. DESIGN PROCEDURE



2.1

Cryogenics

Simulator


Our initial test required us to fill the L
-
shaped reservoir with liquid nitr
ogen to determine if the welds
throughout the reservoir would hold. The reservoir completely failed. The stress caused by the liquid
nitrogen created leaks all along the weld of the reservoir.


There were a couple problems with the original L
-
shaped desi
gn: there were too many welds and the
shape of the reservoir didn’t allow it to conform to the enormous stress caused by the drastic
temperature change
from the addition of liquid Nitrogen
(stress would build up along the edges of the
entire reservoir
, eve
ntually causing the weld to crack
).


Thus, we needed a new reservoir: coil implementation. Professor Swenson came up with this idea and it
was perfect for our needs. A coil reservoir would provide many advantages: it would completely
surround the spacecr
aft; virtually eliminate the need for any welding (only 1 weld needed); and the
rounded coils would allow the stress to distributed throughout the coil.



2.2


Solar Simulator


We needed to decide on a heat source to emulate the heat from the sun. We came up

with two very
good choices: a
halogen

bulb or the use of hot plates. The best advantage of the use of hot plates is that
it would allow us to simulate the rotation of the sun. If we placed an array of hot plates along one side
of the spacecraft, we coul
d turn them on and off in a row in such a way to represent the position of the
sun as t
he craft travels its orbit. A halogen

bulb would require much less energy to power to 1.35
kW/m
2

because we could focus the light directly onto the spacecraft using a p
arabolic reflector.

Also, it
was considerably less than hotplates (mere cents compared to hundreds of dollars.)


We decided to use the
halogen

bulb because it would be a much more reliable heat source during testing.
We would not be able to control the h
eat generated from the hot plates and it would require much more
energy to power than the light bulb.


We needed a light bulb that would emit the proper amount of heat onto the spacecraft
; it

must have the
correct solar output. Also, the type of lamp is v
ery important. We need
ed

a bulb that will be nearly
identical to the sun’s spectral radiant emittance (Sun: 6000K).



2.3


LabVIEW Data Logging


Much of the first few weeks were spent learning what p
revious

CubeSa
t groups had built, and what
devices/programs

we
had at our disposal. To our surprise, the chamber already had one working thermal
couple.
There was also an
existing LabVIEW program
. Using these two components, we had the ability
to log temperature data into a text file.



The temperature througho
ut the space craft will be determined by strategically placed
thermal couples

on the craft: on the surface closest to the cold/hot source; on the edge of the surface closest to the
cold/hot source; and
on the
inside the space craft.


4



2.4



Current Control


A
current control
design would need to be implemented in order to create a duty cycle
that would

simulate the satellite’s orbit.
This lamp duty cycle will emulate the presence (and lack thereof) of the
sun in outer space orbit.
This was to be accomplished
by adjusting the
voltage to change the power
emitted from the halogen bulb. However, given time constraints and later adjustment of the scope of our
project

(discussed further later)
, we did not implement this subproject.








5


3. DESIGN DETAILS



3.1 C
ryogenics Simulator Components


3.1.1 Inherited Reservoir


The vacuum chamber was built the summer prior to our term. Included in the design was an L
-
shaped
reservoir
, shown in Figure 2,

to hold the liquid nitrogen. The strengths of this design shape wer
e that it
maximized the surface area, could hold a large amount of liquid nitrogen, and allowed for concurrent
use of the solar simulator for testing.











Figure
2
: Inherited L
-
Shaped Reservoir


3.1.2 Designed Reservoir


There were too many welds i
n
the original design
, and the strength of the vacuum

along with the
addition of liquid Nitrogen

cracked the reservoir. A new design was needed that would limit the surface
area, adjust to the addition
al

stress caused by the vacuum

and liquid Nitrogen
, an
d transfer temperature
more quickly.















Figure
3
: Newly
-
Designed Reservoir


The new design
, shown in Figure 3,

only had one weld, used a coil system to adjust to stress, and
surrounded the satellite to transfer temperature quickly. However,

the implementation did not allow for
concurrent use of the solar simulator with the cryogenics simulator. Therefore, a duty
-
cycle was
implausible, and instead we
aimed

for two separate tests.
Thus,
the scope of our project changed.

The
current control
was placed as a last priority, given that the duty cycle was
not a necessity
.

90
o


A
dd
LN2


Chamber
Door

New Coil

Implementatio
n

Platform Where
Satellite Will Sit


½” tubing

satellite

7” diameter

coiling

Top View:



12 turns of
coil




25 feet of
tubing


6


3.1.3

Implemented Reservoir


Instead of using the circular coiling system, the ECE Machine Shop built a square coiling system

with
rounded corners
. This design was easier for the s
hop to build,
and

still had all of the advantages we
were aiming for.














Figure
4
: Implemented Reservoir


This design

shown in Figure 4

is the current setup in the vacuum chamber
.


3.2

Solar Simulator Desi
gn


3.2.1

Choice of Reflector


In order to
maximize the efficiency of the bulb’s output, we decided to implement a reflector.
The reflector would be able to concentrate a beam

of

light onto the desired surface of the

satellite. The diameter would have to be greater than the diagonal of the illumi
nated size of the
satellite. We decided to illuminate the smallest side of the satellite to minimize costs. The
smallest diagonal of the square side is


Side x (2)
.5

= 10 cm x (2)
.5

= 141.421 mm.




(1)



From Eq. 1, the smallest diameter of t
he satellite would be 141.421 mm. However, we would
obviously need extra room around the satellites perimeter. We chose the
Melles Griot Reflector
(Product # 02 RPM 008)
, shown in Figure 5, with a diameter of 152 mm. The focal length of
19.1 mm is impor
tant to note because this is where the filament of the halogen needs to be placed
to maximize the output efficiency of the bulb.











Figure
5
: Specifications of Chosen Reflector


7



3.2.2

Choice of Halogen Bulb


Our target output is that of the
Sun
, which

emits 1.3
5

kW/m
2
. With our solar setup, shown in
Figure 6, the wattage illuminated on the satellite’s surface is


1350 W / 1 m
2

= X / [pi (152 mm / 2)]
2






(2)


and solving for wattage needed, X, we find that we need roughly 25 Watts. Assuming
50%
ef
ficiency

(
due to

loss
from
the hole at the top of the reflector,
loss of energy at the surface of the
reflector),
we
need
a
50

W
att

halogen bulb
. Professor Swenson had many halogen bulbs at his
disposal, so we chose the Phillips 12V, 55W Halogen Bulb beca
use they were easily obtainable
and free.
















Figure
6
: Solar Simulator Setup


3.2.3

Wattage to Temperature Conversion


W
e needed to convert the target wattage to a target temperature reading

because we only had
thermal couples to log temperature read
ings
. With this
conversion
, we could use
the target
temperature to
establish

if the bulb was outputting the desire
d

wattage

and make appropriate
adjustments, if needed
.

The heat transfer equation is


q = esT
4
A






(3)


where q is heat transfer, e is t
he emissivity coefficient, s is the Stefan
-
Boltzmann constant, T is
the temperature in degrees Kelvin, and A is area

[3]
.
The emissivity of aluminum is e = 0.3

[4]
.
After rearranging Eq. 3 to determine the desired temperature, we get


T = [(q / A) / (e
s)]
.25







(4)


T = [(25 W/ (pi x (.0001 m)
2
) ) (5.6703E
-
8 x .3) ]
.25
= 377
o
K = 104
o
C


(5)


From Eq. 5, we find that our target temperature is 104
o
C
.


Cube

Satellite


Reflector


Solar Lamp



8

3.2.4

Current Needed to Drive Halogen Bulb


At first, we were unable to light the halogen b
ulb with the power supplies in Senior Design Lab
and CubeSat’s Talbot Lab. We later found that the current in those power supplies were
insufficient to power the bulb. We determined the current needed by


I = P/V:


55 W/
12V = 4.583 A






(6
)


Once we

determined the current needed was at least 4.583A, we went to the ECE Shop to find a
power supply that would fit our needs. We received a 15V, 10A power supply, and we adjusted
the voltage to fit our needs. With this, we were able to power the bulb with

consistency.



3.3

LabVIEW Data Logging


After we found the existing program on the CubeSat computer, we spend some time learning how
to
use it, and create a log into ASCII (
text
)

format.
From there we were able to use Excel to graph
the data we obtained [2
].
We were able to test whether or not the logging was operational by using
the one thermal couple we had.


After we determined how to use the LabVIEW program, we set out to build more thermal couples,
since one was too few for the readings we wanted. W
e went to the ECE Store and bought 2 sets of
female
-
male K
-
type thermal couples. No one in the shop knew how to assemble the couples, so we
had to determine the functionality ourselves using the lone working thermal couple. We found that
we had to solder

the ends of the wires together to get a reading. Once we did that finished building
the thermal couples, we had three functional temperature readings for data logging, as shown in
Figure 7.

























Figure 7: Screenshot of LabVIEW Temperat
ure Reading


9


4. DESIGN VERIFICATION


4.1 Testing


4.1.1 Cryogenics Simulations


Once we received our liquid nitrogen safety equipment, our first test was to see if the chamber would
hold vacuum at extremely low temperatures.
















Figure
8
: Init
ial Leak Test


From our Leak Test,
shown in Figure 8,
we learned many positives. The three thermal couples in the
chamber were working. We were able to use LabVIEW to log the temperature readings in a text format,
and then use Excel to adjust and graph t
he data.
Also
, the lowest temperature obtained was

180
o
C.


However, two negatives of the L
-
shaped design were also revealed. The significant amount of time
needed to transfer the cool temperature to the satellite needed to be addressed. Also, after 5.
5 hours, the
drastic low temperature fractured the welds on the reservoir, causing the chamber to lose vacuum.


After a month of design, adjustment, and construction of the newly designed reservoir, we were able to
try another cryogenics simulation
, shown
in Figure 9
.














Figure
9
: First Simulation after New Design


10



After 1.5 hours, we had to shut the chamber down. Once again the chamber leaked, this time at the
single weld inside the chamber as well as through the feed
-
throughs outside the ch
amber.


We would once again fix the weld, this time reinforcing it with silver welding. In order to reduce the
stress on the reservoir, we decided to use solely the mechanical pump (in the absence of the turbo pump)
for cryogenics testing. This would r
esult in the chamber being run at higher pressure, but would
drastically reduce the stress on
the reservoir. Two days later
we ran another simulation,
shown in Figure
10,
this time with Scott from the Machine Shop present to help determine possible leak p
oints.
















Figure
10
: Simulation after Silver Welding Reinforcement of Reservoir


Again the chamber leaked, but this time we believe that the leaks occurred at the seam of the door, not
from the reservoir. Scott believes the washers on the doo
r near the feed
-
throughs cannot withstand
temperatures below

40
o
C
. The reinforced silver welding on the reservoir seemed to hold well, and we
now await readjustments to strengthen the seal of the door.



11

4.1.2 Solar Simulations


Right from the start, w
e ran into problems with our solar simulator. The reflector order would be
delayed for six weeks, and we were unable to power the halogen bulb using the power supplies in both
Talbot and Senior Design Labs (this was before we realized the current was too
low to drive the bulb.)
Instead of waiting for the reflector, we decided to implement a makeshift setup for crude data.


Using the 4.5” reflector from the inside of a flashlight and two 6V batteries, we ran a simulation using
the alternate solar setup
, sh
own in Figure 11
.














Figure

11
: Simulation from Alternative Solar Setup


Before the hour was up, we had to stop the simulation. The makeshift reflector was made of plastic and
had started to melt from the high temperature of the bulb. Also, th
e batteries were nearly completely
drained from the short testing. While we waited for the reflector to arrive, we determined the current of
the power supplies in the labs were insufficient to drive the bulb.


After we got a power supply from the ECE Pa
rts Shop and the reflector arrived, we were able to run
another simulation
, shown in Figure 12
.














Figure

12
: Simulation with Burnt Alligator Clips








12

The simulation was stopped early because the plastic on the alligator clips began to melt.

We removed
the plastic and once again ran a simulation
, show in Figure 13
.

















Figure
13
: Simulation Held at High Temperature



4.2
Simulation
Conclusions


According to CubeSat’s Key Specifications, the satellite will need to survive between
-
100
o
C to 12
0
o
C.
From our simulations, we are confident that our cryogenics simulator will reach the low bound once the
seal has been reinforced. We have already been able to hold
-
50

o
C for a long period of time, thus
showing that we are able to susta
in a low temperature. We believe we can sustain far below our
-
50
o
C
if we can sustain vacuum. Our initial Leak Test already enforced the low temperature of
-
18
0
o
C that
can be reached once in vacuum.


Our solar simulator has already met our own requirem
ents as well as CubeSat’s specifications. We have
also yet to maximize our output. Once Scott fastens the bulb in the right location and creates a platform
to rest the reflector, we will easily exceed our current high temperature of
120
o
C

13


5. COST



5.
1 Parts


TABLE
1
: SAFETY EQUIPMENT L
IST

Description

Notes

Price ($)

Quantity

Cost ($)

Face Shield


headgear


11.40

2

22.80

Face Shield


visor


5.35

2

10.70

Acid Apron


31.02

2

62.04

18” glove

Priced per pair

8.50

2

17.00

SAFETY EQUIPMENT COST:

$ 112
.54



TABLE

2
: THERMAL VACUUM PAR
TS LIST

Description

Notes

Price ($)

Quantity

Cost ($)

Vacuum Chamber


12,000.00

1

12,000.00

Flask Vacuum Cylinder, 4.3L

Dewar, liquid Nitrogen container

191.87

1

191.87

12V Phillips Halogen bulb

Extra quantities for tes
ting
purposes

7.00

3

21.00

Melles Griot Parabolic
Reflector

Spare for testing and assembling
purposes

302.00

2

604.00

K
-
type Thermalcouples

Male + Female + wires

9.25

2

18.50

THERMAL VACUUM COST:

$ 12,835.37



TABLE

3
: TESTING PARTS LIST

Description

No
tes

Price ($)

Quantity

Cost ($)

Ladder

Safety purposes

22.00

1

22.00

Yard stick

Measure remaining liquid Nitrogen

1.00

1

1.00

Aluminum tape

Special tape to attach thermal
couple sensors to Aluminum case

4.00

1

4.00

Aluminum casing

Used to simulate the
CubeSat
spacecraft during testing

16.00

1

16.00

Flashlight

Disassembled plastic reflector for
rough solar simulation

8.97

1

8.97

Transparent Duct Tape


1.79

1

1.79

TESTING PARTS COST:

$ 53.76



Total Parts = $112.54 + $12,835.37 + $53.76 = $13,001.
67




14

5.2 Labor



TABLE

4
: LABOR


Coefficient

Ideal Salary ($/ hr)

Hours/week

Number of Weeks

Labor Cost

James Jang

2.5

35.00

12

13

13,650.00

Jonathan Wang

2.5

35.00

12

13

13,650.00

LABOR COST:

$ 27,300.00




5.3 Total


Total Parts:

$13,001.67

Total La
bor:

$27,300.00

Total Cost:

$40,301.67




















15


6. CONCLUSIONS



Our project turned out very well. We were able to reach our goal or get very close to it. In retrospect,
we were too ambitious with our original goals. It would be very difficul
t, given our conditions
(timeframe and self
-
imposed fiscal responsibility), for us to have replicated space conditions.


Our goal for the extreme low temperature was 50
o
K, or
-
223
o
C. It is extremely difficult to get this close
to 0
o
K. In fact, it is impo
ssible to do so with the use of liquid nitrogen. The temperature of liquid
nitrogen is only
-
197

o
C [1
]. The low temperature goal outlined in CubeSat’s key specifications is
-
100
o
C, or 173
o
K. Given our experimental results, we are confident that we can
reach and sustain this
low temperature for an extended period of time. We have shown that we can reach an absolute low
temperature within the chamber at vacuum of
-
180
o
C. Also, we were able to reach a low temperature of
-
50

o
C for an extended period of t
ime in the chamber near atmospheric pressure (when there were leaks,
and we couldn’t bring down the pressure to create a vacuum). These two results show that we would
have been able to reach
-
100
o
C in a vacuum chamber. A chamber at vacuum would significa
ntly
minimize the presence of heat outside the chamber and allow us to keep a much lower temperature than
we would be able to at atmosphere,
-
50
o
C in our case. This can be tested and confirmed once the
vacuum door is fixed.


We were able to reach our goal

for the extreme high temperature, 1.35 kW/m
2

or, in our case, 104
o
C.
Actually, we outperformed the target temperature. The last solar experiment that we ran showed a high
temperature of over 120
o
C. We held the surface of the spacecraft at this temperat
ure for two hours, and
we would have been able to do so for a longer period of time if needed. By increasing or decreasing the
distance between the parabolic reflector and the surface of the craft, we could have decreased or
increased the maximum temperat
ure. In our case, we would simply increase this distance by raising the
parabolic reflector causing the high temperature to steady at our goal of 104

o
C. However, our current
arrangement providing a steady maximum temperature of 120
o
C corresponds perfect
ly to the goal
outlined in Cubesat’s Key Specifications.


Thus, the only remaining task is to mechanically fix the chamber to eliminate the leaks that occurred
during our Cold Test, and to mechanically refine the Heat Test assembly. Scott from the Machine

shop
is currently working on this. He is constructing a fixed parabolic reflector + bulb assembly so that the
bulb won’t move around, and will always be positioned at the proper focal distance. In addition, he is
making

a platform that the
reflector + b
ulb
will sit on.

















16


APPENDIX 1



VACUUM CHAMBER OPERA
TING DIRECTIONS



Prior to turning the system on, the following things should be done:

1.

Make sure the gas tank is giving pressure to the valves (80 psi).

2.

Make sure all valves are closed (For

all valves except the forward valve
(FV), the light off on
the console represents the valve being closed. For the FV, the
light on represents the valve being
closed).

3.

Run the Mechanical Pump for approximately 30 minutes prior to any
operation, in order to

allow
adequate warming up.

Notes:

a.

Thermalcouple #1 is broken.

b.

The ion gauge must be turned off. Operation of the ion gauge prior to
that designated in
this document may result in breaking the Ionization
Gauge Tube (approximately $200
to replace).


To pump

down the chamber:


1.

Turn on the rear valve (RV).

2.

Make sure the door is properly sealed, and squeeze the door anywhere in which
air is seeping
through.

3.

Let thermocouple 2 (TC#2) get to the 200 millitorr region.

4.

Once at the 200 millitorr region turn off the
RV

5.

Turn on the FV

6.

Press the turbo pump start button on the ACT600T console.

Note:


During turbo pump start
-
up, make sure the display always reads less than
3.5 A.
Should the display exceed this, turn the turbo pump off, and continue
roughing the
chamber wi
th the mechanical pump until it is less than 200 millitorr.
Once below 200
millitorr, proceed once again with turbo pump operations.

7.

When the console reads "pump at speed," open the High Vacuum Valve
(HV).

Note:

TC#2 should decrease rapidly, and the Amps

should initially increase again.

8.

When the console reaches approximately 0.6 A, turn on the ion gauge with the green button on
the 843 Vacuum Ionization Gauge panel.

9.

At this point, no additional steps are necessary, just continue letting the turbo pump run
.

Note:
Do not let the turbo pump run for excessive amounts of time non
-
stop. i.e.
more
than a day or day and a half. (Approximately $4,000 to replace.)


To shut system down:


1.

Turn off the ion gauge ($200 to replace)

2.

Close the HV

3.

Turn off the turbo pump

4.

Le
ave the FV open

5.

Open the CV

6.

Close the CV as soon as chamber is at atm

7.

Close the FV

8.

Turn off the mechanical pump

Note:

you can leave the mechanical pump in this configuration or turn it off.


17


APPENDIX 2



LIQUID NITROGEN SAFE
TY & CONCERNS



A back of the
envelope calculation indicates that the entire contents of a 10 Liter dewar being spilled in
a unventilated 274 square foot room with an 8 foot ceiling would reduce oxygen levels below the 19.5%
level where Air Products recommends the use of a respirator.
Since most classrooms are larger than this,
suffocation does not represent a major danger. When transporting the liquid in a car, however, it is
probably a good idea to open a window.


The possibility of freeze burns represents a much more serious danger a
nd is therefore our first concern.
This does not mean that the demonstration itself is dangerous, but it does mean you must be careful.
Dangers include:


Nitrogen can spatter (possibly in eyes) while being poured.


Flying chunks of frozen objects could cau
se eye injury.


Students (being children) will want to reach out and touch nitrogen or other cold objects. As mentioned
above, contact with nitrogen can cause tissue damage, and this must be prevented.


Therefore specific safety precautions should include:


Teachers must stress to their students the importance of not touching frozen objects or nitrogen.


Wear goggles whenever pouring or dumping nitrogen. Nitrogen can spatter into the eyes, and potentially
blinding pieces of frozen things can fly around when

we drop it.


Use a glove and / or tongs to handle any object going into or out of nitrogen and to carry the nitrogen
dewar.


Teachers should familiarize themselves with the following first aid instructions (excerpted from the Air
Products Nitrogen Materia
l Safety Data Sheet) for cryogenic freeze burns just in case the worst happens:


If cryogenic liquid or cold boil off contacts a worker's skin or eyes, frozen tissues should be flooded or
soaked with tepid water (105
-
115F, 41
-
46C). DO NOT USE HOT WATER. Cr
yogenic burns which
result in blistering or deeper tissue freezing should be seen promptly by a physician.


Remember to stress the importance of not touching liq
uid nitrogen or frozen objects.




18


REFERENCES



[1]

Chemistry & Biochemistry University of Cal
ifornia Santa Barbara, “Station 3: Liquid Nitrogen,”
December 2003,
http://www.chem.ucsb.edu/~outreach/station3.htm
.



[2]

National Instruments,
Lab
VIEW
: Function and VI Reference Manual
, Na
tional Instruments
Corporation, 1995,
http://www.ni.com/pdf/manuals/321526b.pdf
.


[3]

The Engineering Toolbox, “Radiation Heat Transfer,”
http://www.engineeringtoolbox.com/36_431.html
.



[4]

The Engineering Toolbox, “Emissivity Coefficient for Several Materials,”
http://www.engineeringtoolbox.com/36_447.html
.