CERN
CH1211 Geneva 23
Switzerland
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Date : 2012-04-12
Integration Document
Full Scale Thermosyphon
Cooling Plant Description
DOCUMENT PREPARED BY:
J.A. Botelho Direito / EN
DOCUMENT CHECKED BY:
M. Battistin / EN
J. Godlewski / PH
DOCUMENT APPROVED BY:
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HISTORY OF CHANGES
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DATE
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All
DESCRIPTIONS OF THE CHANGES
First version
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TABLE OF CONTENTS
1.
INTRODUCTION ....................................................................................................................................................................... 4
2.
FULL SCALE THERMOSYPHON DETAILED DESCRIPTION......................................................................................... 5
2.1.
2.2.
2.3.
THERMOSYPHON CIRCUIT ...................................................................................................................................................................... 5
BRINE CIRCUIT ......................................................................................................................................................................................... 8
CHILLER CIRCUIT ..................................................................................................................................................................................... 8
3.
PROCESS AND INSTRUMENTATION DIAGRAM AND ITS COMPONENTS ............................................................. 9
4.
ELECTRICAL POWER........................................................................................................................................................... 10
5.
INTEGRATION ....................................................................................................................................................................... 11
6.
REFERENCES .......................................................................................................................................................................... 12
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1. Introduction
The Thermosyphon Project 1 concerns the cooling of the Inner Detector of ATLAS experiment, in LHC Point 1
(Switzerland).
The silicon part of the Inner Detector (ID) of the ATLAS experiment is presently cooled by a fluorocarbon
evaporative system, keeping -25 °C in the in the detector and the inlet and outlet tubes at 20 °C. The heat
load is 62.4 kW while the evaporation temperature in the boiling channels is -25 °C.
A 95m high two-phase thermosyphon shall replace the present system.
The Thermosyphon Project has three separated circuits: the main Thermosyphon circuit, the Brine circuit
and the Chiller one:
•

•
The Thermosiphon circuit uses C3F8. Its basic working principle consists on condensing the
C3F8 at the surface. This produces a liquid column from the surface to the cavern, increasing
the pressure due to the height difference. Then the C3F8 evaporates in the detector while
cooling it and goes back to the surface as gas by differential pressure.
The Brine circuit uses liquid Perfluorohexane C6F14. This circuit removes the heat from the
Thermosyphon circuit via a heat exchanger that will be then transferred to the chiller circuit.
The Chiller circuit uses a cascade refrigeration circuit to cool down the Perfluorohexane
circuit.
A general overview of the Thermosyphon cooling plant is presented in Figure 1.
Chiller Circuit
Brine Circuit
Thermosyphon Circuit
New Plant: Thermosyphon
2-Stage
Redundant
Chiller
(-70°C)
- Natural circulation of the fluid
- No working components
- Low maintenance (filters)
P1
G
F
H
I
K
ATLAS Surface
J
M N
P2 > P3 > P1
O
L
I‘
ΔH
E
P
B
A
D
C
12/10/2010
P2
To detector
Liquid Supply
PX15
ATLAS I.D.
Pin Tin
x204 lines
Vapour Return
Dummy Load
60kW Thermosyphon
6
P3
From detector
Present Plant:
- High circuit pollution risk
- Risk of oil free compressor failure
- Frequent compressor maintenance
Pout
x204 lines
UX15
USA15
Figure 1. Full Scale Thermosyphon scheme in LHC Point 1.
The main components of the Thermosyphon cooling plant: the Condenser, the Brine circuit and the Chiller
circuit are located at the surface level where all the heat is removed from the system.
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The existing evaporative cooling system can be switched to the Thermosyphon, once it is fully
commissioned, by operating two valves on the supply and return distribution lines.
2. Full Scale Thermosyphon Detailed Description
In order to reach and to decrease even more the detector’s working temperature with this new cooling
system, the return pressure (that will set the evaporation pressure at the detector) at the return line needs
to be decreased. In order to do so, the condenser of the Thermosyphon will need to condense the return
vapour at -60 °C and to sub-cool it to -65 °C (to allow a stable performance of the Thermosyphon cooling
plant). The correspondent saturation pressure of the C3F8 at this temperature on the condenser is 0.31
bar(a).
In order to keep the condenser at -65°C, the chiller will have to cool the Brine circuit to -70 °C. The heat
load on the detector is 62.4 kW and the cooling channels use approximately 50 % of the total available
latent heat of the C3F8, therefore, the total required mass flow rate is 1.2 kg/s. The required chiller power
to condense and sub-cool the C3F8 from 20 °C to -65 °C on the Thermosyphon Condenser is then 170.5
kW.
The two stage chiller will be responsible for the heat removal at the desired temperature. In between the
Chiller circuit and the Thermosyphon circuit is the Brine circuit. The Brine circuit allows the precise regulation
of the temperature on the Thermosyphon Condenser.
In order to keep the detector cold even when its electronics are switched off, the Thermosyphon cooling
plant has a “warm operation” mode that provides 50 kW of cooling power at -20 °C. This mode can be
independent from the supply of the cooling water from the cooling towers, by using an air cooled condenser
on the first stage of the chiller.
The control software for the Thermosyphon, Brine, Chiller, and Water circuits is conforming to the CERN’s
UNICOS framework (UNified Industrial COntrol System). The human-machine interface will be based on a
SCADA built on PVSS.
2.1. Thermosyphon Circuit
The liquid C3F8 at the outlet of the condenser is at -65 °C and will fall to the bottom of the circuit, at the
USA15 service cavern, increasing its pressure until the required 15 bar(a). The liquid supply line going to the
detector requires a fluid temperature of 20 °C. So the liquid C3F8 needs to be heated to this temperature.
Two electrical heaters and one recuperation heat exchanger where then added to the main liquid line at the
bottom of the thermosyphon circuit. The recuperation heat exchanger heats the liquid C3F8 by the use of
the return vapour. Cooling the return vapour will also reduce the required power for the condensation.
In order to allow a stable performance of the thermosyphon a by-pass that keeps a minimum load on the
system is used. The by-pass contains a Dummy Load that consists on heat exchanger and electrical heaters
submerged in a water-glycol bath. To keep an easy access to the system’s components the by-pass and all
the electrical heaters and heat exchangers on the liquid and vapour line are located at the same place: in
the USA15 service cavern.
A scheme of the cooling system and its thermodynamic diagram is shown in Figure 2. Table 1 shows the
thermodynamic conditions on all the points of the system and Table 2 shows the power evaluation on all the
system’s components.
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C
G
F
H
I
K
D
J
E
M N
F
O
L
G
B
H
I‘
A
E
P
B
A
D
C
I
12/10/2010
60kW Thermosyphon
6
Figure 2. Scheme of the Thermosypnon cooling system
(left) and thermosynamic
diagram (right).
Table 1. Thermodynamic conditions on all the points of the Thermosyphon circuit.
Operating point
A
B
C
D
E
F
G
H
I
I’
Pressure
(bar)
Temperature
(°C)
0.5
20
0.51
-20
0.309
-25
0.309
-60
0.4
-65
16.1
-62
16.1
-51
16
-20
16
20
0.5
-51
Density
(kg/m3)
Thermodynamic State
3.90
Superheated Vapour
4.65
Superheated vapour
2.85
Superheated vapour
1699
Saturated liquid
1717
Sub-cooled liquid
1712
Sub-cooled liquid
1672
Sub-cooled liquid
1552
Sub-cooled liquid
1365
Sub-cooled liquid
7.89
Two-phase 66% vapour
Table 2. Power evaluation on all the Thermosyphon circuit’ components.
Operation
line
Description
Power
[kW]
Component
Point A to B
Cooling of return vapour
36.2
Vapour Cooling HX
Point B to C
Expansion on the return line
4.5
Return Pipe
Point C to D
Condensation
165
Condensing Coil
Point D to E
Sub-Cooling
5.5
Sub-Cooling Coil
Point C to E
Condensation & Sub-cooling
170
Condenser
Point E to F
Heating along the liquid line
4
Supply Pipe
Point F to G
Heating from -62 to -51°C
12.2
Electrical Heater
Point G to H
Heating the liquid with the return vapours
36.2
Sub-Cooling HX
Point H to I
Heating from -20 to 20°C
51.1
Electrical Heater
Point I’ to A
Evaporation and super heating to 20°C
107
Dummy Load
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An important parameter for the FTS is the design pressure. This pressure is dependent of the maximum
condensation temperature/pressure combined with the hydrostatic pressure difference due to the height of
the condenser. Figure 3 shows the variation of the pressure (condensation pressure plus the pressure
correspondent to the hydrostatic pressure difference) for different condensation temperatures for pure C3F8.
Maximum Pressure [bar]
25
20
15
10
5
0
-80
-60
-40
-20
0
20
40
60
Condensation Temperature [°C]
Figure 3. Maximum pressure as a function of the condensation temperature for pure C3F8.
For the maximum condensation temperature of 35°C, the maximum pressure at the bottom of the plant is
less than 25 bars. So, for pure C3F8 the plant components would be PN25.
However, and despite the fact that the actual plant uses pure C3F8 as a cooling medium, blends with other
fluorocarbons may be required in the future to improve the cooling performance on the detector. It is
therefore possible that a mixture of C3F8/C2F6 is used to increase the evaporation pressure at the same
evaporation temperature. For a given temperature, a higher the concentration of C2F6 implies a higher
saturation pressure of the blend. So, it would be possible to decrease the evaporation temperature without
decreasing the evaporation pressure.
Taking the blends into account, the Full Scale Thermosiphon is PN40. This means that it would be capable of
using a high concentration (up to 40%) of C2F8 in C3F8, corresponding to a higher condensation and
hydrostatic pressures.
2.1.1. Condenser
The condenser of the Thermosyphon is the most important component of the Thermosyphon loop, being
responsible for maintaining the detector’s evaporation pressure. It will also be capable of storing all the fluid
in the system. The total mass of C3F8 in the Thermosyphon is 2750 kg: 1565 for the liquid line, 645 kg for
the vapour line, and 540 kg for the leak compensation. The construction drawing of the Condenser is shown
in Figure 4.
Figure 4. Construction drawing of the FSTS Condenser.
The Condenser has an approximate volume of three cubic meters, a length of seven meters, and a weight of
4750 kg. It is made in stainless steel 316L and 316Ti and it is insulated with a layer of FOAMGLASS. In order
to minimize its weight and cost, because of its large size, the design pressure is 25 bar.
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A triangular steel structure placed on the top of the building 3184 is used to place the condenser.
2.1.2. Pipes
The thermosyphon supply and return pipes are seamless stainless steel 304L with the following dimensions:
- Supply pipe DN50: ID = 56.3mm; OD = 60.3mm (2mm thickness).
- Return pipe DN200: ID = 211.56mm; OD = 219.08mm (3.76mm thickness).
The design pressure for both supply and return pipes is PN40. The design temperature range for the supply
and return pipes are -70 °C to 35 °C and -35 °C to 35 °C, respectively.
Both the supply and return pipes are covered with an insulation layer of FOAMGLAS with a thickness of 80
mm and 75 mm, respectively.
The pipe route has the 3DModel Number: ST0322617_01 and can be found on the EDMS document number
1142340.
The piping and piping supports stress analysis including the calculations for the earthquake resistance
following the Eurocode 8 has been done 3, 4.
The pipe welds are 100% X-ray inspected.
2.2. Brine Circuit
The Brine circuit is placed between the Thermosyphon circuit and the Chiller circuit. It is responsible for
removing the heat removal from the Thermosyphon Condenser to the Chiller. The cooling fluid of the Brine
circuit is the Perfluorohexane C6F14.
The circuit consists on the use of a liquid pump that sends the C6F14 at -70 °C to the Thermosyphon
Condenser on the top of the building 3184 that then goes back to the Chiller, located at the ground floor.
After the pump there is an electrical heater of 40 kW of power that is responsible for the fine tuning of the
supply temperature, allowing also a fast increase of the C6F14 temperature when needed. The expansion
vessel of the Brine circuit is placed on the roof of building 3184, in same structure of the Thermosyphon
Condenser.
The brine circuit pipes are DN125 (ID = 134.5 mm; OD = 139.7 mm; 2.6 mm thickness). They are designed
for a temperature range of -75 °C to 35 °C. The design pressure for both the return and supply pipes is
PN16. The pipes are covered with an insulation layer of 70 mm of FOAMGLAS. Like the Thermosyphon pipes,
the Brine circuit pipes and their supports, a stress analysis including the calculations for the earthquake
resistance following the Eurocode 8 has been done5.
2.3. Chiller Circuit
The Chiller circuit is responsible for the heat removal of the Thermosyphon. It has a cooling power of 170
kW at a temperature of -70 °C. It is cooled by the cooling water circuit that is cooled by water from cooling
towers.
The chiller consists on a two stage vapour compression cycle using R404a on the first stage (high
temperature) and R23 on the second stage (low temperature). It can run from 20 to 100 % of its cooling
capacity at all temperature set points: from 20 to -70 °C. The first stage is equipped with an air cooled
condenser that is capable of providing 50 kW of cooling power at -20°C. The first stage can work
independently of the cooling water. For the operation of the control valves it uses a 6 bar pneumatic dry air
supply.
Figure 5 shows the chiller configuration scheme.
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Figure 5. Chiller configuration scheme.
The chiller unit has 12 meters of length, 2.5 meters width, and three meters height. The total weight is 15
tons. It has two connections for the inlet and outlet of the brine circuit and two connections for the inlet and
outlet of the cooling water. During normal operation the Chiller consumes 101.4 m 3/h of cooling water.
3. Process and Instrumentation Diagram and its Components
The Process and Instrumentation Diagram (P&ID) contains all the Thermosyphon cooling plant circuits
designed at CERN: the Thermosyphon, the Brine, and the Water circuits. The P&ID diagram is shown in
Figure 6.
Figure 6. Full Scale Thermosyphon Process and instrumentation Diagram 2.
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In general, on all the circuits of the thermosyphon cooling plant pressure and temperature transmitters
where placed each time the thermodynamic change on the specific location. When the temperature of the
circuit can reach low values, the pressure transmitters are connected to line throughout a capillary tube. The
temperature transmitters are installed inside a “Doit de Gant” allowing its removal from the line without the
need of stopping the plant or draining the circuit line.
Shutoff valves have also been installed in strategic parts of the circuit in order to allow the separation of the
different parts of the circuit in case any intervention is needed to be done. All the valves are pneumatically
actuated and its closing time can be controlled.
On the liquid lines, in between two shutoff valves a double safety valve has been installed to release the
pressure in case of cold liquid trap. The safety valves are connected after a three-way valve to allow the
switch between them when its recalibration is required.
On the thermosyphon and brine circuits the perfluorocarbons are filtered by particle filters and dehydrators,
installed in double parallel circuits. Differential pressure transmitters are placed between the filters to
monitor their performance. On the water circuit, differential pressure transmitters have also been placed
between the inlet and outlet of all the heat exchangers due to the risk of fouling on these components.
The plant is equipped with flow meters on the thermosyphon and water circuits.
The electrical heaters on the Thermosyphon and Brine circuits are protected with thermal switches.
In general, for the Brine and Thermosyphon circuits, where perfluorocarbons are used, the leak tightness
requirement of all the mechanical components is lower than 10-7 mbar.lt/s.
4. Electrical Power
For the two operation modes of the Thermosyphon cooling plant, the normal and the warm operations,
there are two different power supplies: the standard and he emergency one. The required emergency power
supply is also available as standard power during the normal operation.
The FSTS requires electrical power on the surface and underground areas. The electrical cupboards for the
power supply at the surface area are located in building 3185 and for underground the electrical cupboard is
located in USA15 service cavern. All control cupboards are secured by an UPS power supply.
The Table 3 two shows the required electrical power for the different components of the FSTS cooling
plant6.
Table 3. Full Scale Thermosyphon Electrical Power Consumption.
Component
Connection
Location
Standard Installed Power
[kW]
Emergency Power
[kW]
UPS Power
[kW]
Chiller I
Blg. 3185
231
237
-
Chiller II
Blg. 3185
231*
237*
-
Brine pumps
Blg. 3185
-
2x30
-
Brine Heater
Blg. 3185
40
-
-
Water Pumps
Blg. 3185
2x10
-
-
Thermosyphon Heater I
USA 15
15.5
-
-
Thermosyphon Heater II
USA 15
-
56
-
Thermosyphon Dummy Load
USA 15
100*
25
-
Thermosyphon and Chiller I Control
Cupboard (surface)
Blg. 3185
-
-
5
Brine and Water Control Cupboard
Blg. 3185
-
-
5
Chiller II Control Cupboard
Blg. 3185
-
-
5*
USA 15
-
-
5
TOTAL Blg. 3185
291
297
10+5*
TOTAL USA 15
115.5
81
5
Thermosyphon Control Cupboard
(underground)
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5. Integration
The FSTS components are located in separated areas, demanding different integration requirements 7. Figure
7 shows the detailed location for the FSTS main components.
Condenser Location
SDX1
Bld 3184
Location of the FSTS Electrical
and Control Cupboards
SH1
USA 15 Level 3
Thermosyphon Condenser
Thermosyphon by-pass components
Brine pipe routing
Blg. 3184 (SH1)
Underground Gallery
Brine Station
Chiller
Water pumps location
(inside SH1)
Brine Station
Chiller 1
Service Hole
Underground gallery
(dashed line)
Primary water HX
(inside the underground gallery)
Figure 7. Location schemes of the FSTS main components.
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6. References
[1] General Description of the Full Scale Thermosiphon Cooling System for Atlas SCT and Pixel.
Thermosyphon Project Technical Note. EDMS 1083852.
[2] FSTS P&ID. EDMS 1101188.
[3] FSTS Piping System Report. EDMS 1148755.
[4] FSTS C3F8 Pipe Stress Analysis. EDMS 1163494.
[5] FSTS Brine pipe calculation specification. EDMS 1164132.
[6] FSTS Electrical Power Requirement. EDMS 1159012.
[7] FSTS Integration folder: https://edms.cern.ch/nav/P:CERN-0000076703:V0/P:CERN0000090874:V0/TAB3.