Transcript Vorkurs Mathematik 2002

Design considerations for a CMS CO2 cooling system
CMS specials:
50 kW cooling system at -40 0C (see below)
Difficulties: membrane pumps to -250C, condensors at low pressure
No high pressure allowed (max. 70 bar, preferred <35 bar)
Difficulties: have to separate room temperature storage cylinders (70 bar)
from operating system (extra pump or cooled storage cylinders)
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Why -40 0C?
25 W/10x10 cm sensor at -25 0C, factor 1.5 reduction/5 0C
Hybrids for strixel design of 2.2 cm: 2 W
Want to reduce by factor 8: from -25 to -40 0C -> x3.4
Additionally: reduce V by factor 1.5-> factor 2.3 in power=VxI
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Temperature profile for 25W in 10x10 Si sensor
Cooling: 240 K at edge-> 40 K increase
towards middle for 25 W (Si = SEMI-conductor!)
High risk of thermal run away for such high gradients !
Have to run at lower voltage or still lower temperature.
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Choices for evaporative cooling systems
Condensor
Liquid pump
Compressor (gas)
Chiller
Pressure
regulator
Pressure
regulator
Evaporator
Evaporator
Condensor at high pressure,
Do not need external chiller.
Have to avoid that liquid
enters compressor, so need
heaters in case heat load drops
or TEV (Thermal expansion valve)
which regulates flow.
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Condensor
Condensor at low pressure,
Need external chiller
Have to avoid evaporation in
or before pump, so need subcooled
liquid, which need to be heated before
evaporator to have well defined temp.
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Need pressure reduction
between condensor and evaporator
3 methods: a) capillary
b) expansion valve
c) pressure reducer
a) Capillary pressure drop flow dependent, so need
additional pressure control (accumulator in LHC-b)
b) Expansion valve usual method in commercial
cooling systems, but different for different fluids.
Not available for CO2 (as far as we know)
c) Simple pressure reducer used on bottles work excellent
(but not used as such, as far as we know)
Pressure reduction by temperature
controlled expansion valve
Pressure reduction by pressure
sensitive valve (used on bottles)
Tested to work very well for controlling
temperature of CO2 two phase mixture.
Can avoid complicated accumulator used in LHC-b
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Choices from ATLAS and LHCb
From B. Verlaat, NIKHEF
Atlas method:
Direct expansion into detector with C3F8 compressor
Warm transfer lines
Boil-off heater and in detector
Temperature control by back-pressure regulator
Vapor compression system
•Always vapor needed
•Dummy heat load when switched off
•Oil free compressor, hard to find
Heater
Compressor
BP. Regulator
Warm transfer over distance
Liquid
Vapor
Pressure
Detector
Cooling plant
2-phase
Enthalpy
LHCb method:
CO2 liquid pumping
Cold concentric transfer line
No components in detector
Temperature control by 2-phase accumulator
Pumped liquid system
•Liquid overflow, no vapor needed
•No actuators in detector
•Oil free pump, easy to find
•Standard commercial chiller
Compressor
Detector
Pump
Chiller
Liquid circulation
Cold transfer over distance
Cooling plant
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Vapor
Pressure
Liquid
2-phase
Enthalpy
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LHCb-VTCS Overview (B. Verlaat)
A 2-Phase Accumulator Controlled Loop
Accessible and a friendly
environment
Accumulator
Inaccessible and a
hostile environment
Cooling plant area
Transfer lines
(~50m)
VELO area
8
R404a
R507a
chiller
Chiller
2-phase
1
2-phase
2-phase
6
Evaporators
Pump
liquid
Cooling plant:
• Sub cooled liquid CO2 pumping
• CO2 condensing to a R507a
chiller
• CO2 loop pressure control using
a 2-phase accumulator
2
liquid
Concentric tube
liquid
3
Restriction
gas
Condenser
7
5
2-phase
4
liquid
Evaporator :
• VTCS temperature ≈ -25ºC
• Evaporator load ≈ 0-1600 Watt
• Complete passive
LHCb-VTCS Overview (B. Verlaat)
A 2-Phase Accumulator Controlled Loop
Accessible and a friendly
environment
Accumulator
Inaccessible and a
hostile environment
Cooling plant area
Transfer lines
(~50m)
VELO area
8
R404a
R507a
chiller
Chiller
2-phase
1
2-phase
2-phase
6
Evaporators
Pump
liquid
Cooling plant:
• Sub cooled liquid CO2 pumping
• CO2 condensing to a R507a
chiller
• CO2 loop pressure control using
a 2-phase accumulator
2
liquid
Concentric tube
liquid
3
Restriction
gas
Condenser
7
5
2-phase
4
liquid
Evaporator :
• VTCS temperature ≈ -25ºC
• Evaporator load ≈ 0-1600 Watt
• Complete passive
The simplest CO2 cooling system you can image
AND IT WORKS!
Pressure reducer
regulates temperature
nylon tube
to see boiling
of CO2
Flowmeter
long nylon
regulates flow, i.e. tube to air
cooling power
Relief
valve
Advantage:
Initial pressure reduced
by cooling of CO2 to 12 bar
(instead of 70 bar at room temp)
No heat exchanger needed
CO2 bottle in
household freezer
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Whole system <500 Euro
Standard Swagelock connectors
Fast cooldown since liquid
has already detector temperature
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Some pictures
Flow
meters
hybrid with
heater and
T-sensor
Cold liquid sent through ladder.
Blue temperature curve shows
position of liquid.
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Regulating temperature with pressure
30
20
10
temperature [°C]
0
0
10
20
30
40
50
-10
60
time [min]
sensor1
-20
sensor2
sensor4
-30
-40
-50
-60
CO2 pressure
in [bar]
11,5bar
8bar
6,5
5,5
-70
very easy to set and hold temperature: just keep pressure constant
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Test results
flow was tested up to 3,7
kg/hour (max. of
flowmeters) with
negligible pressure drop
Even much bigger flow
seems possible with
tolerable pressure drop
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beginning dry-out
total heating power [W]
easy to cool large powers
with little flow of CO2,
300
250
200
150
100
50
0
0
0,5
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1,5
2
2,5
3
flow in kg/hour (both tubes)
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Why CMS cannot use any of these systems
CMS cannot use high pressure CO2 closed system, since 1 mm Cu cooling
pipes should have max. 70 bar.
CMS has large varying heat loads (detectors cannot be switched on
during cooldown) and 50 kW heaters are a nightmare in cooling circuit
For sLHC we would like to cool down to -40C to avoid risk of thermal
run away.
Possible solution: try liquid pump down to -40C
and design low pressure CO2 system.
A recirculating CO2 system
Commercial condensor
Chiller -50 C
Pump for
subcooled
CO2
9 bar
10 bar

25 bar
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Pressure
reducer
regulates
temperature
to 10 bar=-40C
<25 bar fill line

70 bar shut
down line with
high pressure
pump
Vacuum
pump for
leaktests
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Detector=evaporator
Transferline 60m as
concentric heat exchanger
to heat up subcooled liquid
and reduce pressure in outlet
Heat exchangers: www.geawtt.com.
Double Wall
For extra protection against leakage a special double wall system is developed. This system
consists of two stainless steel plates instead of one. In case of internal damage, due to strong
pressure variations for example, the chance of fluid contamination is prevented
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GEAWTT Condensors
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Safety Chamber™
The patented Safety Chamber™, the Non-Plus-Ultra for big brazed heat exchangers is the industrial
standard for GEA WTT heat exchanger types 7, 8, 9 and 10. The contact points (brazing points), which
are responsible to take off the stress in the port area, are separated. Overloading of these contact points
and cracking of the material do not lead to a mix with the other side - a maximum of safety for the user
The Full-Flow-System™
special developed for GEA WTT nickel brazed heat exchangers. To avoid freezing problems in the port
area when using nickel brazed heat exchangers as an evaporator GEA WTT has developed the Full-FlowSystem™. Continuous flow without stagnation around the port avoids "Port Freezing".
XCR
the plates consist of high grade corrosion resistant stainless steel, named SMO 254. XCR series has been
developed for special applications, such as pool heating, ground water heat pumps, etc. Depend on the
particular application we offer XCR models either copper brazed or nickel brazed
Delta-Injektion™...Distribution System
The Delta-Injektion™ distribution system on Advanced Evaporator AE models is made from AISI 316L
stainless steel and provides precise allocation of refrigerant to the channels
Double Wall
For extra protection against leakage a special double wall system is developed. This system consists of
two stainless steel plates instead of one. In case of internal damage, due to strong pressure variations for
example, the chance of fluid contamination is prevented.
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Choice of liquid pump
Pressure firm pump characteristic
membrane displacement pumps
flowrate
rotary positive
displacement pumps
centrifugal pumps
pressure
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LEWA diaphragm pumps (ECOFLOW)
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Diaphragm exchange simple
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Output pressure limited
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Flow adjustment
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CMS: Control and Monitoring System
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Q=
k1*n
flowrate Q
fowrate Q
Adjusting the flowrate
Q = k2*(hh0)
limiting stroke length
h0
h
0
frequency n
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stroke length h
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Flowrate Q
Pulsating flowrate
Vh
Vh
Vh
time t
Need either: a) 3 phase-shifted pump heads
b) pulsation damper
c) maybe pressure reducer does the
job to prevent temperature variations
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Flow regimes in small tubes
1mm diameter, 0.5 mm thick
pmax 550 bar
2mm diameter, 0.5 mm thick
pmax 367 bar
annular
bubble
slug
rho
kg/m3
flow
kg/s
velocity
m/s
diameter
m
viscosity Surface tension
mPas=cP
N/m
1138
22
0,0002
0,0002
0,22
11,58
0,001
0,001
0,15
0,011
1138
22
1138
22
1138
22
0,0002
0,0002
0,0002
0,00002
0,0002
0,00002
0,06
2,89
0,22
1,16
0,06
0,29
0,002
0,002
0,001
0,001
0,002
0,002
0,15
0,011
0,15
0,011
0,15
0,011
REG/RE
L
Reynold
Suratman
(x10^6)
0,012
0,012
1697,70
23150,49
0,61
CO2 liq -44
CO2 gas -44 13,64
0,012
0,012
0,012
0,012
0,012
0,012
848,85
11575,25
1697,70
2315,05
848,85
1157,52
1,21
CO2 liq -44
CO2 gas -44 13,64
CO2 liq -44
CO2 gas -44 1,36
CO2 liq -44
CO2 gas -44 1,36
0,61
1,21
To be verified
for CO2 at
low temp.
0.0002 kg/s=66W
Pressure drop in 1 mm tube still small enough, especially with heat exchange between
in- and output by the electrical connections pads, so almost no T-gradient on ladder
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Questions to be resolved
Diaphragm pump to be tested at -400C
Started collaboration with LEWA.
They will give us a pump and we will test
different diaphragms
Heat exchanger at low temperature and low pressure:
Started collaboration with GEA.
Their design program says it is possible for high flow of primary liquid
Accumulator:
Can one use large volume of return tubes as accumulator?
(It would act as pulsation damper! No need for triple, phase shifted pumps,
one pump with CMS control preferred? Price tag: 20 kEuro/pump, 20 kEuro/CMS)
Do we need accumulator above tracker to guarantee always liquid
in upper part of tracker?
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Summary
• low pressure CO2 system with STANDARD commercial pumps,
heat exchangers and pressure reducers seems feasible.
• Require cooling of sensors below -40 0C to get leakage
current noise down and limit risk of thermal runaway#
(main difficulty: find membrane material for low temp.)
• Strixels of 2.2 cm could then yield S/N similar as for LHC
(signal down by ¼, so capacitance down by ¼)
• All connections outside volume possible
by CO2 cooling, which allows 6m long cooling pipes
• Reduction of material budget possible by powering via
cooling pipes, since pure Al cold pipes have VERY low resistivity.
No need for DC/DC converters inside tracker
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Backup slides
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Summary of cooling liquids at LHC
300
Notes:
 Single phase cooling simplest, but large pumps needed
 Two-phase evaporation in principle much better, because
heat of evaporation much larger than specific heat, but
any pressure changes means a temperature change, so be
careful about tube bending, tube sizes etc.
 CO2 has largest heat of evaporation, is non-toxic,
non-flammable, industrial standard, liquid at room
temperature, but high pressure (73 bar at 31 0C)
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Supermarkets start to use CO2
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CO2 phase diagram
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