CO 2 cooling pipe dimensioning Pixel Upgrade Local Supports and Mechanics R&D meeting

1. CO2cooling pipe dimensioningPixel Upgrade Local Supports and Mechanics R&D meeting Bart Verlaat CERN 29 September 2009

2. Introduction • For the Atlas IBL a CO2 cooling pipe was dimensioned and tested. Case is an example for pixel tube dimensioning. • Dimensioning of the IBL cooling tube and supply capillaries • Introduction to the Nikhef2PACL test facility • Preliminary results of the IBL cooling tube at room temperature tests.

3. Two IBL cooling scenarios have been analyzed: 150 Watt 150 Watt 800mm 800mm System A System B 150 Watt 75 Watt 75 Watt Single cooling tube Double (redundant) cooling tube • Fully redundant cooling of the IBL • -Two cooling pipes per stave, each connected to an individual cooling system. • Design cooling tube on half the power. • A failure of maintenance of 1 cooling system is not catastrophic, staves can be kept cold. • Cooling of a powered detector with 1 system is most likely possible due to included safety margins.

4. Temperature (ºC) Pressure (Bar) Tube inner diameter (mm) DCO2≈1.4 mm DC3F8≈3.6 mm IBL stave cooling tube sizing (1) • Traditional method: • Calculating dP & dT according to the Friedel correlation • - Set threshold for max. temperature gradient. Assumed threshold: 1ºC • IBL stave assumptions: • 800 mm long • 150 Watt power (Non redundant) • -25ºC cooling fluid temperature • 40% exit vapor quality dP according to Friedel

5. IBL stave cooling tube sizing (2) • IBL stave assumptions: • 800 mm long • 150 Watt power (Non redundant) • -25ºC cooling fluid temperature • 40% exit vapor quality DCO2 = 1.4 mm DC3F8 = 3.6 mm Heat Transfer coefficient (W/m2K) Temperature distribution (ºC) CO2 C3F8 CO2 Tube wall Heat transfer according to Kandlikar dT= ~3ºC C3F8 Fluid Tube length (m) Tube length (m)

6. Kandlikar IBL stave cooling tube sizing (3) Nowadays more fancy design tools are available: And guess, they do not comply at all! (Welcome in the magic world of 2-phase flow!) Corresponding zone Results of the 1.4 mm CO2 tube in the Thome flow pattern maps Thome predicts an early dry-out

7. IBL stave cooling tube sizing (4) Redundant stave (2 cooling tubes) 1.4mm ID Stave with 1 single cooling tube 2.1mm ID

8. Are these spikes from a LHCb VELO test the dry-out which Thome predicts?

9. Prototype Atlas IBL cooling tube. Q≈100 Watt Inlet Capillary 0.6mmID x 4m Outlet Capillary 2mmID x 4m IBL stave: 1.6mmID x 800mm • Hand bended 2.5x0.25 mm soft stainless tube • Capillaries should be flexible “so they can be handled as a cable” IBL cooling tube in the Nikhef test box

10. In and outlet capillary sizing Assumption: DpCapillary>10xDpoutlet dP outlet (Bar ) dP capillary (Bar ) dP (Bar) 0.5°C dT (°C ) D=0.2.38 mm D=0.1.85 mm dT outlet (°C ) D=0.88 mm D=0.68 mm Diameter (mm) Single tube stave 1.28 g/s (150 Watt) Redundant tube stave 0.64 g/s (75 Watt)

11. IBL tube summary • Pressure drop is no problem • (0.6 bar Friedel, 0.4 bar Thome) for 1.4mmID @ 150 Watt • dT < 1.0ºC over tube length • HTC needs testing, 2-phase flow HTC predictions too unsure. • 1.4mmID tube fits for both theories, but is critical for dry out in single tube stave design. 1.6mmID tube is chosen for testing.

12. Nikhef CO2 cooling test facility2PACL lab cooler and test box Siemens PLC Room temperature bottle as accumulator Room temperature evaporation in test tube Cold water condenser (8ºC) 2PACL CO2 circulator is operational for room temperature CO2 cooling. Will be upgrade to a cold cooler the coming months 2PACL lab cooler prototype at NIKHEF

13. CO2 2PACL Lab Cooler 2PACL with PLC Test box with experiment • Supplies: • Massflow • Enthalpy • Pressure • Supplies: • Cold Cryostat • Supplies: • Power • Supplies: • Temperature • Pressure • Voltage • Demand for: • Mass flow • Enthalpy • Pressure Power supply • Demand for: • Temperature • Demand for: • Power • Supplies data: • HTC • Pressure drop • CHF • Dry out PC with PVSS to control the cooler and experiment

14. CO2 heat transfer and pressure drop measurements • In HEP we are using CO2 in un unexplored area. • Mini channels (<2mm) • Low temperature (<-20ºC) • No commercial applications = limited research • Current prediction models are therefore not verified • Heat Transfer Coefficient (HTC) • Dry-out • Pressure drop • Critical Heat Flux (CHF) • Those properties depend on a lot of variables • Mass flux • Heat flux • Pressure (=Temperature) • Enthalpy (=Vapor quality) • Tube geometry • Automatic scanning of the properties with PVSS controlling the set-points of the 2PACL research plant. Heat load Dry-out response to increasing heat PVSS interface

15. IBL Tube cooling tests(Warm Cooler) Temperature versus Power flow 1.6 g/s Exceeding Critical Heat Flux Dry-out Saturation temperature Sub-cooled Tests by Auke-Pieter Colijn IR pictures: flow=1.5g/s; p=61bar; T saturation=24.5°C

16. IBL tube heat transfer resultsMF=1.6 g/s, T=24.6ºC Thome heat transfer 58 Watt (17222 W/m2) 95 Watt (28208 W/m2) Kandlikar heat transfer Tube in flow pattern diagram Measured heat transfer 140 Watt (41570 W/m2) 176 Watt (52349 W/m2)

17. Conclusions • 2PACL lab cooler under construction • Runs at room temperature evaporation • Will be upgrade to run cold the coming months • IBL cooling tubes: • Diameter for CO2 cooling: ~1.5mm ID • Flexible in and outlet capillaries, no joints inside. • Preliminary tests at room temperature: • Measured dry-out is more sudden than theory but last longer • Measured heat transfer more constant than theory => Good, less temperature gradients • Heat transfer test at cold conditions to be done. Waiting for 2PACL upgrade.