1. UT cooling discussion 3 december 2014
Bart Verlaat

2. System summary Standard:
TABLE 1. PARAMETERS OF THE UT COOLING SYSTEM
Property
Value
Units
Comments
GENERAL
Cooling system –
2-PACL
Cooling power
5000 W
total plus margin (see est. Table 3)
Fluid
CO2
Fluid filtration
need
accessible, replaceable in technical stop
Emergency redundancy
Temporary share with VELO system
UPS connection
want entire system, minimally controls
Component design pressure, max
100
bar
max pressure
Component test pressure, max
150
max pressure = 1.5*Pvap(CO2)
DT_evap on stave
0.5 °C
stability
OPERATIONAL MODES
T_evap, nominal, data-taking, cold
-40 to -20
max power 5 kW
T_evap, standby, cold
From 1 to 2 kW
T_evap, beam pipe bake-out
Amb temp
Cooling off
T_evap, installation mode, cold
0.5 kW-1 kW (1 half-plane operating)
DISTRIBUTION AND MANIFOLD
Number of individual loops 68
one loop per stave
Control of loops
TBD
remote ot local ON/OFF control (?)
Manifold
in BOX
local, in UT BOX, connected to loops
Connection to manifold
flexible
needs to move with UT as it retracts
CONTROL
Continuous T_evap control
remotely
controlled by 2PACL design
T_evap Set point
common (?), range (?)
T_evap Monitoring
stave input
all stave inputs, plus module T readback
Plant to DSS output signals ?
no idea what this means !
Env. gas to DSS output signals
DSS to plant input signals
ENVIRONMENTAL GAS
Gas
dry N2, Air
gas in UT BOX
max dew point
safety
several
over-pressure valves at strategic points
Standard:
MDP=110 bar (for large volumes = safety valves)
MDP=130 bar (for small volumes = burstdisc)
Test pressure: 1.43x => 157 bar or 186 bar.
If a 2 PACL is designed for -40’C all other temperatures can easily be selected above up to 20’C
Not clear what this means and why it is considered

3. PED Classification (1) (Pressure Equipment Directive)
PED classification for CO2 systems.
Stored energy = MDP x Volume
MDP = Relieve pressure
MDP= TenvMax or P+dPpump)x110%
PTP = 1.43 x MDP
MDP = Maximum design pressure, PTP = Proof Test Pressure
Stored energy of accumulator in case of fluid storage (worst case).
Find minimum for stored energy
(Not necessarily at lowest pressure)

4. PED Classification (2)
Category
Design
Fabrication
Commis-sioning
PED Module
Applicable to MDP=110bar
Art. 3.3
Good practice
V≤0.45 Liter
Dn≤ø32 mm I A
0.45<V≤1.8 L
DN≤ø100mm II
Notified Body control
A+A1
1.8<V≤9.1 L
DN≤ø250mm
III
Approved fabrication procedure
B1+F
9.1<V≤27.2L
DN>ø250mm IV G
V>27.2L
The higher the PED class, the larger notified body involvement

5. Trapped liquid
Trapped cold liquid is a real danger in a cooling system.
Be careful with introducing too many valves
Don’t use valves with dead volumes
Every volume needs a relieve
AMS-TTCS has no valves, only liquid trap possible in frozen condenser
MDP=3000 bar for condenser!
LHCb-VTCS and Atlas IBL have burst discs at each volume or relieve valves. + controlled valves to avoid liquid trap
MDP=130 bar (Swagelok burst disc)
Ball valve with T-hole

6. System summary Standard:
TABLE 1. PARAMETERS OF THE UT COOLING SYSTEM
Property
Value
Units
Comments
GENERAL
Cooling system –
2-PACL
Cooling power
5000 W
total plus margin (see est. Table 3)
Fluid
CO2
Fluid filtration
need
accessible, replaceable in technical stop
Emergency redundancy
Temporary share with VELO system
UPS connection
want entire system, minimally controls
Component design pressure, max
100
bar
max pressure
Component test pressure, max
150
max pressure = 1.5*Pvap(CO2)
DT_evap on stave
0.5 °C
stability
OPERATIONAL MODES
T_evap, nominal, data-taking, cold
-40 to -20
max power 5 kW
T_evap, standby, cold
From 1 to 2 kW
T_evap, beam pipe bake-out
Amb temp
Cooling off
T_evap, installation mode, cold
0.5 kW-1 kW (1 half-plane operating)
DISTRIBUTION AND MANIFOLD
Number of individual loops 68
one loop per stave
Control of loops
TBD
remote ot local ON/OFF control (?)
Manifold
in BOX
local, in UT BOX, connected to loops
Connection to manifold
flexible
needs to move with UT as it retracts
CONTROL
Continuous T_evap control
remotely
controlled by 2PACL design
T_evap Set point
common (?), range (?)
T_evap Monitoring
stave input
all stave inputs, plus module T readback
Plant to DSS output signals ?
no idea what this means !
Env. gas to DSS output signals
DSS to plant input signals
ENVIRONMENTAL GAS
Gas
dry N2, Air
gas in UT BOX
max dew point
safety
several
over-pressure valves at strategic points
Standard:
MDP=110 bar (for large volumes = safety valves)
MDP=130 bar (for small volumes = burstdisc)
Test pressure: 1.43x => 157 bar or 186 bar.
If a 2 PACL is designed for -40’C all other temperatures can easily be selected above up to 20’C
Not clear what this means and why it is considered

7. 2PACL temperature freedom
IBL set-point tests
All temperature levels can be selected
Today
Detector off
Detector on
As long as sub cooling level is sufficient (>10’C)
CO2 liquid in plant

8. Power requirements
Is depending on temperature, so better to give the T0 and I0 values
What about the electronics?
Purpose not understood

9. More modes…

10. Thermal chain in detectors
The design of the cooling is the whole chain between heat source and heat sink
Typical example for IBL
Heatload
Th. paste
Glue
Glue
HTC ΔP
CO2 in tube
Silicon
CF-sheet
C-foam
Pipe wall
Manifold

11. Thermal chain in detectors
The design of the cooling is the whole chain between heat source and heat sink
Typical example for IBL
Heatload
Th. paste
Glue
Glue
HTC ΔP
CO2 in tube
Silicon
CF-sheet
C-foam
Pipe wall
Manifold
Load variations give gradients w.r.t the common sink => Outlet manifold!

12. Design of cooling: From source to sink
So the reference should not be at a pipe wall, nor at the liquid temperature as it is generally approached.
This is similar then taking a reference in the middle of the structure.
Loaded stave temperature: -24.4°C
(0.72 W/cm2)
Stave conductance ~61%
Atlas IBL
example
Heat transfer ~ 19%
Unloaded stave temperature: -39°C
Pressure drop ~20%
Inlet
manifold
Outlet Manifold = temperature reference

13. First we need to understand what happens inside a cooling tube
First we need to understand what happens inside a cooling tube? Heating a flow from liquid to gas

14. Cooling method used in detector cooling:
The 2-Phase Accumulator Controlled Loop (2PACL)
2-Phase Accumulator
Shielding wall P7
Evaporator inside detector (4-5)
Heat in
Long distance (50-100m)
P4-5
HFC Chiller 5
Condenser 6
Detector heat 2 3 1
Capillaries (3-4)
for flow distribution
Pump
Transfer line
(Heat exchanger) 4
2PACL principle ideal for detector cooling:
Liquid overflow => no mass flow control and good heat transfer
No local evaporator control, evaporator is passive in detector.
System not sensitive for heat load changes
Very stable evaporator temperature control at a distance (P4-5 ≈ P7)
Large operational temperature range (+20’C to -40’C)

15. Understanding detector evaporator tubes
Outlet manifold: Pressure = fixed
Inlet manifold: Temperature = fixed
In a 2PACL the capillary inlet temperature is a function of the outlet saturation pressure.
The detector inlet is close to saturation.
But can be liquid due to pressure drop
Usually ambient heating is enough to overcome sub cooled entry state
Detectors with high dP have to be designed to cope with liquid at the inlet
FE: pre heating by electronics (CMS pixel)
Pressure drop of the evaporator tube and outlet tube is part of the thermal resistance chain from heat source to sink!
Inlet manifold
Inlet capillary dP
Detector dP
Outlet line dP
outlet manifold
Temperature exchange

16. Long branch thermal profile
Liquid
2-Phase
Inlet tube
Evaporator tube
Outlet tube
HTC
Temperature gradient inside detector due to pressure drop and heat transfer dP
Offset of evaporator temperature due to outlet pressure drop
Liquid entry into evaporator
Manifold temperature = common reference of all branches
Inlet: 2mm x 4m, Detector: 2mm x 4m, Outlet: 2mm x 4m
Heatload on detector: 200 Watt

17. Flow distribution: Inlet tube reduction
Which flow do we need when 200 Watt to a single stave is applied?
Inlet: 2mm x 4m
Stave: 2mm x 4m
Outlet: 2mm x 4m
Inlet: 1mm x 4m
Stave: 2mm x 4m
Outlet: 2mm x 4m
Pressure drop and dry-out calculated using CoBra
Pumping energy is flow x dP. Adding capillaries can save pumping power (in example 1.61*3.54/2.18*3.75=0.70 => 30% saving)
Figures from: DESIGN CONSIDERATIONS OF LONG LENGTH EVAPORATIVE CO2 COOLING LINES
Bart Verlaat and Joao Noite, GL-209, 10th IIF/IIR Gustav Lorentzen Conference on Natural Working Fluids, Delft, The Netherlands 2012

18. Influence of the in and outlet-lines on thermal performance
Inlet: 2mm x 4m
Stave: 2mm x 4m
Outlet: 2mm x 4m
Inlet: 1mm x 4m
Stave: 2mm x 4m
Outlet: 2mm x 4m
Inlet: 1mm x 4m
Stave: 2mm x 4m
Outlet: 3mm x 4m
Figures from: DESIGN CONSIDERATIONS OF LONG LENGTH EVAPORATIVE CO2 COOLING LINES
Bart Verlaat and Joao Noite, GL-209, 10th IIF/IIR Gustav Lorentzen Conference on Natural Working Fluids, Delft, The Netherlands 2012

19. Dealing with environmental heat pick-up
Three important statements:
Expose return tube to ambient heating
There is usually enough cooling power left
Connect as much as possible the inlet to the outlet
Outlet boils first (lower P), so will take care of heat absorption
Avoid boiling before the inlet manifold
Flow separation will feed some channels with vapor only!
Capillary dP makes manifold liquid
Pre capillary heat pickup
Inlet manifold
outlet manifold
Manifold boiling
Outlet transfer line
outlet manifold
Outlet transfer line
Remaining cooling power for ambient
To keep this problem simple: Have the manifold right after the heat exchanging transfer line.

20. IBL: A detector with very long in and outlet lines
The IBL detector is only 800mm long, but has about 15m long in and outlets.
dT due outlet line pressure drop significantly (ca 3ºC)
Ambient heat load in same order as detector load
Atlas IBL
example
Inlet
Outlet 2 12
Heat exchange
Ambient
Ambient heating 9 4 6 7
IBL