1. Aachen Status Report: CO 2 Cooling for the CMS Tracker at SLHC Lutz Feld, Waclaw Karpinski, Jennifer Merz and Michael Wlochal RWTH Aachen University, 1. Physikalisches Institut B 13 October 2010MEC Upgrade Meeting

2. Outline 2Jennifer Merz  Test System at RWTH Aachen University  Goals and specifications  Schematic design  Set-up  Results  Temperature distribution over detector pipe  Pressure drop  Dryout, heat from environment  Parallel cooling branches  Summary and Outlook

3. 3Jennifer Merz Ongoing:  Gain experience with a closed recirculating CO 2 system  Determine lowest operating temperature  Find out ideal operating conditions (  stable system), depending on heat load and CO 2 temperature Midterm plans:  Operation of parallel cooling branches  Measurements on pipe routing inside the tracker (number of bendings, bending radius, inner diameter,...)  Determine optimal cooling contact between cooling system and heat dissipating devices (different materials, different types of thermal connections,...)  Contribute to final module design for tracker at SLHC R&D at RWTH Aachen University

4. Maximum cooling power: 500W CO 2 temperature in detector: -45°C to +20°C Precise flow and temperature control Continuous operation Safe operation (maximum pressure:100bar) 4Jennifer Merz System Specifications

5. 55 Expansion Vessel: Saturated mixture of CO 2 liquid and vapour Up to 500 W heat load pressure, bar Enthalpy, kJ/kg Heat Exchanger:  Subcooling of incoming CO 2 (only liquid in pump)  Dissipation of detector heat load Heat Exchanger:  Warm incoming CO 2 to nominal temperature ( given by chiller 1)  Partial condensation of returning CO 2 Jennifer Merz Chiller 1: Chiller temp.  vapour pressure  system temp. Schematic View of CO 2 System

6. CO2-FlascheCO2-Bottle 6Jennifer Merz Heat Exchanger Expansion Vessel Detector CO 2 Bottle 19cm 7.6cm 16cm 42cm CO 2 Test System (I)

7. CO2-FlascheCO2-Bottle 7Jennifer Merz  6m stainless steel pipe, 1.7mm inner diameter  14 Thermistors along the pipe: Measurement of temperature distribution  Simulation of uniform heat load, by current through pipe (  ohmic losses) Thermistors Electrical connections Box for insulation Users panel CO 2 Test System (II)

8. CO2-FlascheCO2-Bottle 8Jennifer Merz Improved CO 2 Test System Aluminum vacuum box currently under construction New detector pipes for parallel piping Connection to detector pipes Flanges for electrical feed through Mount for detector pipes

9. 9 Temperature distribution over detector  Keep heat load constant  Decrease flow step by step  Determine where detector temperature rises over nominal value CO 2 temperature: +20°C Heat load: 100W Jennifer Merz Decrease flow liquidgas x=0 x=1 x: vapour quality Dryout: pipe walls not in touch with liquid anymore  No heat dissipation by evaporating CO 2  Rise in detector temperature Time, s Detector temperature, °C Dryout Measurement 2468101214 1357 91113 14 thermistors along pipe

10. 10Jennifer Merz -We observed high heat input from environment -Amount can be estimated from dryout measurements -Corrections are rather big (60, 80, 100 W applied with power supply) -Needs crosscheck in vacuum box Heat Load, W Flow, g/min -20°C +20°C Dryout Measurement - Results

11. 11 100W 80W 60W 100W 80W 60W CO 2 @ -20°C Pipelength, m Temperature Distribution CO 2 @ +20°C CO 2 @ -20°C CO 2 @ -40°C Detector Temperature, °C -Detector temperature almost constant with applied heat load -Effect bigger at lower temperatures -Comparison with theory still needs to be done Pipelength, m Jennifer Merz

12. 12Jennifer Merz -Pressure drop measurement with dedicated pressure sensors -Results comparable with old results (Δp from ΔT) Pressure Drop, bar Flow, g/min -2-phase flow: pressure drop = temperature drop -Measure pressure gradient  precise control of detector temperature -Determine Δp between inlet and outlet of detector pipe L=5.8m d i = 1.7mm Pressure Drop along Detector Pipe -20°C, 100W -20°C, 80W -20°C, 60W +20°C, 100W +20°C, 80W +20°C, 60W Pressure sensor from “Aplisens”

13. 13Jennifer Merz -Keep pressure drop constant -Apply heat load and determine flow -High heat load  low mass flow -Influence on parallel piping  Insert restrictions in each branch Parallel Cooling Branches Flow, g/min Heat Load, W -20°C, Δ=1.0bar +20°C, Δp=0.3bar L=5.8m d i = 1.7mm  We plan to operate parallel cooling branches with our test system

14. 14Jennifer Merz  CO 2 test system fully commissioned and operational  Measurements down to low temperatures show: reasonable cooling power at -40°C  Pressure drop measurements: comparable with “old” results, need comparison with theory  Dryout Measurements: estimate for heat input from environment (needs crosscheck in vacuum box) Summary

15. 15Jennifer Merz  Improvements of test system ongoing: - Vacuum box for detector pipe: minimize heat input from environment - New heat exchanger: less massive, should allow faster measurements  Perform more measurements on pressure and temperature drop along different pipes: - Vary inner diameter and form/bending - Operation of parallel cooling branch  Comparisons with theory  Repeat measurements with improved system Outlook