Aachen Status Report: CO2 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 2010 MEC Upgrade Meeting

Outline Test System at RWTH Aachen University Results 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 Jennifer Merz

R&D at RWTH Aachen University Ongoing: Gain experience with a closed recirculating CO2 system Determine lowest operating temperature Find out ideal operating conditions ( stable system), depending on heat load and CO2 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 Jennifer Merz

System Specifications Maximum cooling power: 500W CO2 temperature in detector: -45°C to +20°C Precise flow and temperature control Continuous operation Safe operation (maximum pressure:100bar) Jennifer Merz

Schematic View of CO2 System Chiller 1: Chiller temp.  vapour pressure  system temp. Expansion Vessel: Saturated mixture of CO2 liquid and vapour pressure, bar Enthalpy, kJ/kg Heat Exchanger: Subcooling of incoming CO2 (only liquid in pump) Dissipation of detector heat load Up to 500 W heat load Heat Exchanger: Warm incoming CO2 to nominal temperature ( given by chiller 1) Partial condensation of returning CO2 Jennifer Merz 5

CO2 Test System (I) CO2-Bottle CO2-Flasche Expansion Vessel 16cm CO2 Detector 42cm 7.6cm Heat Exchanger 19cm Jennifer Merz

Electrical connections CO2 Test System (II) Thermistors CO2-Bottle CO2-Flasche Users panel Electrical connections 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) Box for insulation Jennifer Merz

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

Dryout Measurement Dryout: pipe walls not in touch with liquid anymore  No heat dissipation by evaporating CO2 Rise in detector temperature x: vapour quality x=0 x=1 liquid gas Temperature distribution over detector 14 12 10 8 6 4 2 14 thermistors along pipe CO2 temperature: +20°C Heat load: 100W Detector temperature, °C 13 11 9 7 5 3 1 Keep heat load constant Decrease flow step by step Determine where detector temperature rises over nominal value Decrease flow Time, s Jennifer Merz

Dryout Measurement - Results 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 -20°C +20°C Heat Load, W Flow, g/min Jennifer Merz

Temperature Distribution CO2 @ +20°C CO2 @ -20°C CO2 @ -40°C 100W 80W 60W Detector Temperature, °C Pipelength, m CO2 @ -20°C 100W 80W 60W Detector temperature almost constant with applied heat load Effect bigger at lower temperatures Comparison with theory still needs to be done Detector Temperature, °C Pipelength, m Jennifer Merz

Pressure Drop along Detector Pipe 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 di = 1.7mm -20°C, 100W -20°C, 80W -20°C, 60W +20°C, 100W +20°C, 80W +20°C, 60W Pressure Drop, bar Pressure sensor from “Aplisens” Flow, g/min Pressure drop measurement with dedicated pressure sensors Results comparable with old results (Δp from ΔT) Jennifer Merz

Parallel Cooling Branches 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  We plan to operate parallel cooling branches with our test system L=5.8m di = 1.7mm Flow, g/min -20°C, Δ=1.0bar +20°C, Δp=0.3bar Heat Load, W Jennifer Merz

Summary CO2 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) Jennifer Merz

Outlook 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 Jennifer Merz