LHCb-VELO Microchannel fracture

safety system and evaporator concept

26 June 2015

Bart Verlaat 1

Microchannel volume (1)

• The minimum volume which we can shut-off is 1 u-channel including the in and outlet pipes.

• The worst case is a filling of cold liquid – T-30ºC liquid (1076 kg/m3)

used in analyses– Under normal circumstances

vapor is present and less CO2 is present.

• Assuming a 0.5mm inlet and 1.2mm outlet (1m long)– See quick CoBra analyses 2

0 0.5 1 1.5 2-35

-30

-25

-20

-15

Velo Upgrade thermal profileMF=0.3 g/s, Tsp=-25ºC, Q

app=40 W, Q

env=0 W, x

end=0.45 dP=4.62 bar

Branch length (m)

Tem

pera

ture

(ºC

)

1 23 4 5

1x, D

=0.5

mm

19x,

D=0

.06m

m

19x,

D=0

.15m

m

1x, D

=1.2

mm

¯T

ur R

e=50

21

v

=1.4

5 m

/s

¯T

ur R

e=50

22

v

=1.4

5 m

/s

¯T

ur R

e=50

23

v

=1.4

5 m

/s

¯T

ur R

e=50

24

v

=1.4

5 m

/s

¯A

nnu

x=0

.18

¯A

nnu

x=0

.45

¯A

nnu

x=0

.45

¯A

nnu

x=0

.45

¯A

nnu

x=0

.45

¯A

nnu

x=0

.45

0

10

20

30

40

Pre

ssur

e(B

ar)

T Structure

T Tube wall (ºC)

Tsat Fluid (ºC)T Fluid (ºC)

P Fluid (Bar)

Microchannel volume (2)

• Module volumes and CO2 content @ -30ºC liquid (1076 kg/m3):– Inlet: D0.5mm x 1m = 0.2 ml

• 0.21 gram

– μ-channel: 19x (60μm* 60μm*30mm+120μm*200μm*267mm) = 0.12 ml• 0.13 gram

– Outlet: D1.2mm x 1m = 1.1 ml• 1.2 gram

– Total module volume: • 1.6 gram CO2 total

• Vacuum volumes (Eddy Jans memo, 5 November 2009) :– Secondary: 450 liter– Primary: 1715 liter– Maximum dP=10 mbar

• Loosing 1.6 gram of CO2 in the secondary volume gives a density of 1.6 g / 450 l = 3.5 g/m3– 3.5 g/m3 density after warming up to 20’C gives a pressure of 1.9mbar– Direct expansion without heat pick-up is

• Conclusion: 1 μ-channel leak is not critical! But a proper module shut-off mechanism is needed

3

Venting CO2 in vacuum

4

3.5 g/m3 => v=285 m3/kg

Far off scale

Ca 350 kJ/kg*1.6 g = 560 J to heat it up to ambient.

Condition of -30 C liquid ⁰

Condition of +20 C ⁰low pressure gas

How can we isolate 1 μ-channel?

• 3 module shut-off options:

– Place no-return valves at each module inlet and outlet• Will add the inlet manifold volume to the leaking volume• 1 critical active common inlet valve• No risk of liquid trapping• Need a reliable miniature no return valve

– Place a shut-off valve at the inlet and protect the outlet return flow with a no-return valve

• No risk of liquid trapping• Need a reliable miniature no return valve• Many active valves in the vacuum

– Place shut-off valves at each module inlet and outlet• Risk of liquid trap• Many active valves in the vacuum• For safe operation:

– A relieve: risk of leak or an atmospheric back flow.– A safety gas volume: need a small heat source to keep it filled with gas (might be ambient) 5

No return valve option

• This concept requires small passive no return valves.• Actuator can be out of the tertiary vacuum • Inlet manifold will be leaked into the vacuum as well:

– Assuming a 4x0.7 tube & 1m long– Extra Volume: 5.3 ml = 5.7 gram– Pressure in secondary vacuum @ 20’C = 8.9 mbar 6

1 Active NC valve needed and many miniature no return valves

Red volume will leak in vacuum

Green volume can stay pressurized. An additional pressure relieve can be included

Ambient Tertiary vacuum Secondary Vacuum

Valve is NC and actuated when a pressure increase in the Velo is detected. Eg. 1e-3mbar

Individual inlet shut-off

• This concept requires small passive no return valves.• 26 actuators in the tertiary vacuum

– Pneumatic valves very complex in a vacuum– Electrical valves NC have a constant heat load on the

CO2 inlet• Small volume leaked into vacuum

– Pressure in secondary vacuum @ 20’C = 1.9 mbar7

26 Active NC valves needed in vacuum and 26 miniature no return valves

Red volume will leak in vacuum

Green volume can stay pressurized. An additional pressure relieve can be included

Ambient Tertiary vacuum Secondary Vacuum

Valves are NC and actuated when a pressure increase in the Velo is detected. Eg. 1e-3mbar

Full active shut-off

• This concept is very sensitive for trapping cold liquid– Each line needs a relieve mechanism– Open relieve mechanisms (Burst disc or safety valves) are a risk for the modules

(sudden cool down when activated)– A warm safety volume is an option

• 52 Actuators in the tertiary vacuum– Pneumatic valves very complex in a vacuum– Electrical valves NC have a constant heat load on the CO2 inlet

• Small volume leaked into vacuum– Pressure in secondary vacuum @ 20’C = 1.9 mbar

8

52 Active NC valves needed in vacuum

Red volume will leak in vacuum

Green volume can stay pressurized. An additional pressure relieve can be included

Ambient Tertiary vacuum Secondary Vacuum

Valves are NC and actuated when a pressure increase in the Velo is detected. Eg. 1e-3mbar

Safety volume always contains warm gas

All

Upgrade Velo cooling vs current Velo cooling

9

All inlet capillaries on 1 side. Return common (Manifold inside)

Electronics crates

Cable feedthrough

Tertiary vacuum with manifolds and safety valves

Cooling feed through with thermal stand-off

Out of the way space for cooling connector and flexible part

Cooling lines passing the module base on the side

Safety system continued

• The all no-return valve option seems optional and favorable (option 1)– Simplest from control point of view

• No active parts in vacuum

– Need to develop a reliable miniature no-return valve• A small leak rate still tolerable as the vacuum

pump continues pumping (Ca. 10 mg/s allowed)

• Other options require many active valves (26 or 52) all in vacuum.

10

CO2 pumping in secondary vacuum

11

10-2

10-1

100

101

102

103

10-4

10-3

10-2

10-1

100

101

Pressure (mbar)

Mas

sflo

w (

g/s)

ACP28 CO2 pumping capacity

Pressure (mbar)

Mas

s flo

w (

g/s

)

ACP 28 pumping capacity for CO2

A constant CO2 leak of 10 mg/s is tolerable

At least 1 ACP28 pump is active, sometimes 2 work in parallel

Concept Evaporator P&ID

12

PV110

nc

TT35036

To UT-Detector

30

30

60

52

EH39052TT39052

CV39052 EH30036 CV30038 PV30038

NV30142

NV30148

NV30242

NV30248

NV30342

NV30348

nc

nc

EH35036 CV35038 PV35038

NV35142

NV35148

NV35242

NV35248

NV35342

NV35348

PV35052

nc

PV35040

nc

PV35050nc

PV39060

nc

PV39030

nc

PV30040

nc

PV30050

PV59032PV59054

PV49060

PV49030

nc

nc nc

36

PT35052TT35052BD35052

52

PT35038TT35038

38

SA35052

SA30052

PT30038TT30038

38

Safety vent

By-pass with dummy load

Pre-heater

Safety vent

Pre-heater

nc

PV35052

52

PT30052TT30052BD30052

TT39032PT39032BD39032

32

TT30036

36

60

PT39058TT39058BD39058

58

VacuumAmbient

P&ID explained

• Labelling (QQxyyzz)– QQ=component

• PV=Pressure valve• CV=Control Valve• NV=No Return Valve• TT=Temperature transmitter• PT=Pressure Transmitter• EH=Electrical Heater• SA=Safety Accumulator

– x=System ID• 1=Chiller A• 2=Chiller B• 3=CO2 Velo • 4=CO2 UT• 4=CO2 Common• 6=Dry-air• 7=Tertiary Vacuum

– yy=Branch ID• 00 = Aside common• 01…26 = Evaporator 1 to 26, A side• 50 = C –side common• 51-76 = Evaporator 1 to 26, C side• 90 = General (Inlet, By-pass & return)

•

• UT and Velo can be connected at the level of the accumulator

– PV59054 & PV59032 open– Close the PV39030 & PV39058 incase of Velo failure or visa

versa

• Preheater EH30036 & EH35036 regulate TT30036 & TT35036

• The Pressure difference (PT39032-PT39058) is regulated constant with CV39052

– CV30038 & CV35038 are set constant for a certain evaporator flow

– The constant dP allow the sharing of the UT

• Safety procedure– If Pvacuum>10-3 mbar, then close PV30038, PV35038, PV30052 & ,

PV35052 – If PT30038 < PT39058 – 3bar, then open PV30040 & PV30050;

This means there is a leak in this section– If PT35038 < PT39058 – 3bar, then open PV35040 & PV35050;

This means there is a leak in this section– System remains running over by-pass, to stay active for safety

control and UT operation– The safety procedure is safe by default valve position (No

venting), Venting is done in addition to be more safe. A safe vent action requires NO valves, but than there is a high risk of unwanted venting which is a hazard for the modules as a cool down is a result.

• A safety accumulator in the module section must prevent accidental liquid trap. The SA has always a gas filling. 13