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

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

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

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

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

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

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

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 = - 0.072 m 70m Gas transfer line characteristics Nominal diameter / pressure: DN50 / PN10 No insulation Weight: 205 kg 70 m

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

Transfer line to test section Approximate required length : 15 m (DN 25) Equipment Thermal tapes H2O Filters Mass flow meter (0 - 100 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

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 (0 - 20 g/s) Instrumentation Bypass control Flow control or Bottom temperature control Evaporation pressure Water glycol bath temperature PT FT TT PT

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

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: 250 W @ -48°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

Design parameters: Chiller (3/4) Required power for 0.1 kW loop operation: around 2 kW @ -48 °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

Design parameters: Chiller (4/4) Required power for 2x 1 kW loop operation: around 12 kW @ -48 °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

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

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

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

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