1. Re-circulating CO2 Test System
Lutz Feld, Jennifer Merz, Michael Wlochal
(RWTH Aachen University)
3rd HGF Annual Meeting, DESY

2. Why a new Tracker Cooling System for SLHC?
increased radiation damage can be compensated by lower sensor temperature leakage current ~ irradiation fluence leakage current doubles every 7°C
CMS aims for silicon temperature around -25°C: out of reach with current mono-phase C6F14 system
reduction of cooling material budget
Need to guarantee operational reliability and safety!
Lutz Feld (RWTH Aachen University)

3. Lutz Feld (RWTH Aachen University)
Why CO2
heat removal through evaporation is factor ~100 more efficient than through heat capacity  small coolant quantities
low temperatures down to -45°C
uniform temperature controlled by equilibrium vapor pressure
evaporative CO2 cooling systems run at high pressure (10…50 bar)  significant pressure drops along pipes can be tolerated  thin pipes (1…2 mm diameter)
low density of CO2 + thin pipes  small contribution to material budget example: CMS Strip Tracker End-Caps -8% on total material budget
CO2 is environmentally friendly and cheap
Lutz Feld (RWTH Aachen University)

4. Lutz Feld (RWTH Aachen University)
Issues with CO2
high pressure (at least 50 bar + safety margin)
need to stay in annular flow regime (cooling will turn from very good to very bad when pipe wall falls dry)
heat transfer into small diameter pipes
no commercial cooling plants available (only very big refrigeration systems)
CO2 is toxic
Lutz Feld (RWTH Aachen University)

5. Specifications for our CO2 Cooling Test System
load: 500 W maximum
CO2 temperature at detector: -45°C … +20°C
precise temperature control
precise flow measurement
continuous operation
safe operation (100 bar max.)
Lutz Feld (RWTH Aachen University)

6. CO2 Enthalpy Pressure Diagram: Re-Circulating System
liquid
liquid + gas
gas
dry ice 1 2 4 5 6
4 -> 5: detector load DQ 3
Lutz Feld (RWTH Aachen University)

7. Design of Re-Circulating CO2 Cooling Test System1 4 ΔQ 5 6 3 2
Chiller 1: Chiller temperature  vapoure pressure  temperature in system
Expansion Vessel:
Filled with saturated mixture of CO2 liquid and vapour
-45°C
Vacuum
Pump
Heat Exchanger 1:
Heats liquid CO2 to appropriate temperature
CO2
Bottle
Chiller 2: Heat removal p 6 5
Detector:
500 W
heat load
Heat Exchanger 2
-50°C
Heat Exchanger 1 3 4
Heat Exchanger 2:
Removes heat from the system
Cooles ingoing CO2 down to about -50°C 1
Flow Meter p
CO2 Pump 2
Jennifer Merz
Jennifer Merz 7
Lutz Feld (RWTH Aachen University)

8. Implementation of Re-Circulating CO2 Cooling Test System
Components Chiller 1: Huber Unistat 815 (1.2 Chiller 2: (Huber CC-505) see below Expansion Vessel: Swagelok 304LHDF4-1Gal Levelmeter: Rechner Sensors KFS PEEK-VA-3/4“ Heat Exchangers: SWEP B16DWx8/1P-SC-U Pump: GATHER 1MX-X/12-11/X-SS/S/Q/K200/HDT/DS2D50 Flow Meter: Rheonik RHM015-T2-P1-SM0-M0-G1-N Piping, fittings etc.: Swagelok Frame: ITEM Temperature Probes: various
Lutz Feld (RWTH Aachen University)

9. Fotos of the Re-Circulating CO2 Cooling Test System
Expansion Vessel
Chiller 2
Heat Exchanger
System
Chiller
(to be exchanged)
5 m pipe with thermistors and contacts for electrical heating
CO2-Pump
Lutz Feld (RWTH Aachen University)

10. First Measurements at Room Temperature
vary CO2 flow
keep heat load constant
determine at which point temperature rises over certain level 8 9 10 11 12 13 14 7 6 5 4 3 2 1
25W
33W
41W
53W
63W
73W
Liquid CO2 at room temperature
Dry-Out: Pipe walls are not in touch with liquid anymore  no power dissipation by evaporating CO2
temperature rises
revolutions of CO2 pump
Lutz Feld (RWTH Aachen University)

11. Lutz Feld (RWTH Aachen University)
Status & Plans
re-circulating CO2 cooling test system has been commissioned at room temperature
second chiller missing for operation below room temperature
first measurements show basic functionality of the system
perform tests of the cooling system itself
test the system under variation of load and temperature
test reliability and failiure modes
then perform thermal and hydraulic measurements of
pipes
interfaces
detector modules
super-modules
Lutz Feld (RWTH Aachen University)