1. Design of the thermosiphon Test Facilities 2nd Thermosiphon Workshop
A. MORAUX
PH Dpt / DT Group
CERN
October 1st 2009

2. Summary Proposal overview and objectives Thermodynamic cycle
Operating scenarios
Design parameters
Services
Conclusion
Condenser
Evaporator

3. Interests and Objectives
Provide a natural circulation of the fluid
Avoid working components in the main circuit
Access refrigeration units in the surface and make maintenance easier
Validate gravity driven system design
Achieve cooling at low temperature (-40 C)
Compensate pressure drops in cooling channels by low temperature condensation on surface

4. Process Diagram SURFACE PIT 70 m CAVERN 0.59 Bar -48.0 C 11.5 Bar

5. Cycle of the cooling system
Operation at -40°C (evaporation temperature in the boiling channel)
T = -25C
P = 11.5 bar
m’ = 60 g/s
T = 20C
P = 11.5 bar
m’ = 60 g/s

6. Operating Scenarios Purging and filling the system Start-up
Nominal operating conditions with 0.1 kW loop
Nominal operating conditions with full power

7. Design parameters: Test sections and Mass flow (1/4)
Evaporation temperature [°C]
Nominal power load
[kW]
Outlet quality
Inlet quality
Latent heat
[kJ/kg]
Mass flow rate
[g/s]
-40
2.0
0.9
0.58
106.3
58.8
-25
0.48
100.8
47.2
0.24
90.3
33.5
0.1
2.3
-35
0.55
104.5
2.7
Nominal operation
mass flow rate baseline under different operating conditions

8. Transfer lines (1/2) Material: Stainless Steel 304L
70m Liquid transfer line characteristics
Nominal diameter / pressure: DN25 / PN25
Insulation: 25mm ARMAFLEX A/F
Weight (for sizing wall support)
Mass without fluid (pipe + insulation): 145 kg
Mass with fluid (density = 1600 kg/m3): 220 kg
Thermal expansion
From 20 C to -40 C → Length change = m
70m Gas transfer line characteristics
Nominal diameter / pressure: DN50 / PN10
No insulation
Weight: 205 kg
70 m

9. Transfer lines (2/2) Liquid transfer line Gas transfer line
Outlet temperature (Inlet temperature = -48 C)
-25 C with mass flow = 60 g/s (ΔT = 18 C)
+12 C with mass flow = 6 g/s (ΔT = 60 C)
Pressure drops (taking into account density change along pipe)
Frictional pressure drop is in the order of 5 mbar
Hydrostatic pressure = 9.6 bar with mass flow = 6 g/s
Hydrostatic pressure = 10.9 bar with mass flow = 60 g/s
Outlet pressure
10.2 bar with mass flow = 6 g/s
11.5 bar with mass flow = 60 g/s
Gas transfer line
Calculated pressure drop (hydrostatic + frictional + singular) = 90 mbar
Condensation temperature is designed for ΔP = 300 mbar

10. Transfer line to test section
Approximate required length : 15 m (DN 25)
Equipment
Thermal tapes
H2O Filters
Mass flow meter ( g/s)
C3F8 bulk temperature measurements
Heating the liquid up to 20 C
Maximum required power: 3kW
Thermal tapes switched on according to the test sections in use
Temperature control by PWM

11. Bypass line (1/2) Approximate required length : 4 m
Pipes nominal diameter
Inlet DN15
Outlet DN25
Equipment
Valves (shut-off and control)
Evaporator
Mass flow meter ( g/s)
Instrumentation
Bypass control
Flow control or Bottom temperature control
Evaporation pressure
Water glycol bath temperature PT FT TT PT

12. Bypass line (2/2) - Evaporator
Objectives
Heat the liquid up to 20 C
Evaporate the fluid at 20C
Design height: 1.5 m
Design external diameter: 0.4 m
Required power: 1.25 kW (10 g/s)
Internal spiral
Pipe nominal diameter: DN15
Spiral nominal diameter: 0.3 m
Approximate height: 1.2 m
Water/Glycol bath
Maintain at constant temperature by electrical heater
Simulations performed
by A. Romanazzi

13. Storage vessel Storage vessel size and volume Heat loads
Useful volume 600 L
Approximate internal diameter: 1 m
Approximate internal length: 1.5 m
Heat loads
Insulation: 25mm ARMAFLEX A/F
Heat pickup in the tank: °C
Flanges, feedthroughs and instrumentation
2 Temperature sensors
1 High and 1 low pressure gauges
1 Level gauge and 1 low level switch
Safety valves
Connections to gas (DN50) and liquid (DN25) transfer lines
Connection to purging valve
Connection to degassing tank
Flanges for condensing + subcooling coils

14. Design parameters: Chiller (3/4)
Required power for 0.1 kW loop operation: around °C
Evaporation temperature
[°C]
+15
+10
-10
-20
-25
-30
-40
Condensation temperature [°C]
13.4
8.2
-2.3
-13
-24.1
-29.7
-34.7
-48.6

15. Design parameters: Chiller (4/4)
Required power for 2x 1 kW loop operation: around °C
Evaporation temperature
[°C]
+15
+10
-10
-20
-25
-30
-40
Condensation temperature [°C]
13.4
8.2
-2.3
-13
-24.1
-29.7
-34.7
-48.6

16. Service requirements Surface Cavern Water distribution
Electrical power (chiller + control system)
Compressed Air
Ethernet Network
Cavern
Electrical power (heaters + control system + test sections evaporator)
Compressed air

17. Critical issues
Low pressure in part of the system (return gas pipe + vessel)
Very low leak rate requirements
Avoid evaporation in the liquid line
Avoid elbows on the pipes

18. Status for test with blends (C3F8 / C2F6)
Interests for a gravity driven cooling process
Achieve higher pressure evaporation in the cooling loops
Operate at higher pressure temperature in the surface
Reach higher pressure at the bottom of the liquid column
Nominal pressure of piping can remain the same (PN25)
Instrumentation, valves and heaters can approximately remain the same
Issues (under study)
Blend composition needs to be carefully monitored
Additional instrumentation has to be installed
Additional equipment to control the mixture composition

19. Conclusion and Next steps
Gravity-driven cooling systems are appealing but the feasibility needs to be demonstrated first and requires precise study and a high level of materials quality
Next actions
Build the 1:8 scale test facility in autumn to perform test with C3F8
Finalize integration study
Sharp component selection, and market survey for the large scale system
Preparation for project Readiness Review