News on the CO 2 cooling developments at CERN DT CMS Tracker Upgrade Cooling and Mechanics meeting Bart Verlaat 13 October

Status of the current CO 2 systems: Blow system Joao’s blow system: –Blow system was upgraded with a 2 nd blow branch to create the ability to have more latent heat or sub cooling. 2 Liquid Vapor 2-phase Pressure Enthalpy Liquid Vapor 2-phase Pressure Enthalpy Internal sub cooling External sub cooling

Status of the current CO 2 systems: Cryo lab 2PACL Operational status: –Operational status discussed in Thorsten’s presentation. Some modifications done by Joao: –The system had problems with small flows (Large heat leak & low flows = high temperature differences or unwanted boiling) –System was modified to run always at high flow, small flows to experiments are obtained by a metering valve in the experiment feed line. 3 Dummy heater was placed in a 2nd by-pass. Metering valves were installed in the by-passes to create more pump pressure. –The R404a compressor unit works stable under high heat loads. The dummy heater in the by-pass can now be used to increase the cooling load for a stable chiller operation (=stable evaporator with current accumulator). –Accumulator was ready but had problems with certification. End flanges were made from a wrong steel grade: ~303 instead of 316L. (certificate showed the 316L). Error was found during the final material sample analyses. Accumulator is remanufactured. Delay is unknown up to now.

New developments in CO 2 cooling A few new CO 2 cooling developments are ongoing in CERN-DT. –Development of a 2 multipurpose CO 2 coolers for general use based on the 2PACL principle (LHCb and AMS systems). A “portable” air-cooled 100Watt system A “not so portable” water cooled 1kW system Operational temperature range of both systems: -40°C to +25°C evaporative temperature. –Development of new concepts Making the system simpler (portable system) To reduce accumulator volume (important for large scale systems) –Contribute to concepts for future systems CMS pixel / upgrade Atlas IBL / upgrade (SR1-cooling plant) 4

The 1kW “xxxxx” system Development of the kW system is in close cooperation with Nikhef. Nikhef is developing a CO 2 cooler for the XFEL detector at DESY. A common design is made as specs are (almost) identical. Concept is to make them from a user stand point as simple as possible. Basic CO 2 cooling knowledge required. –3 user input variables: Evaporative temperature Mass flow Enthalpy (sub cooling or vapor quality for user) –4 operation states: Connecting experiment Disconnecting experiment Cooling experiment (re) filling CO 2 –User interface via integrated touch screen, connection of PVSS is optional but not required –This is all you can do with it! …… but must be enough to cool your won bottle of wine. 5 We are still looking for a name. 1 bottle of wine if you come up with the winning name!

6 xxxxx system

Set-Point Controls 7 Accumulator control (Pressure) Tsub = -50°C => Enthalpy=135 kJ/kg (Experiment sub cooling request) Pump sub cooling control Taccu+Tsub-10 => = -40°C Pump sub cooling control Taccu+Tsub-10 => = -30°C 3 3 Heater = (Enth request - Enth 3) x Massflow Taccu = 20°C Taccu = -20°C VQ = 20% => Enthalpy=210 kJ/kg (Experiment vapor quality request) Tsub = -50°C 10°C

Accumulator design and control Similar to VELO accumulator but with hot gas by-pass for chiller capacity control. Temperature set-point with pressure control. Volume ca. 5 liter (PED class II) Discussion with CERN central workshop and safety for designing and construction of accumulators at CERN following the PED rules. 8

CO 2 condenser design and control Alfa-laval AXP10-20 high pressure heat exchanger (120 bar) CO 2 sub cooled liquid control with R404a injection Temperature set point of PID controller determined by system. T pumpinlet = T accu + T subcooling – 10°C 9

Pump mass flow control Two pumps in series to boost pressure drop Gather 1m-J/12-11/x-ss/s/q/k200/DLC gear pumps with integral DC drive Massflow controlled with Rheonik massflow meter 10 Single pump Dual pump

Condensing unit Water cooled R404a or CO 2 chiller Frequency controlled compressor to minimize base load. Investigating Sanyo 2-stage CO 2 compressor with inverter for xxxxx cooler. Frequency controlled Maneurop compressor selected for XFEL cooler. Test chiller is ordered for condenser control and hot gas by-pass tests. 11

Enthalpy heater control User input –yy to +xx -yy = subcooling ( ºC), +xx = vapor quality (%) 0 = saturation line Set points translated to enthalpy with respect accumulator pressure. Heater power is calculated by input condition (Enthalpy point 3 and mass flow) -> No PID control. DC-power for smooth heating (pulse heater influences mass flow and thus the heater control itself) 12

xxxxx versus XFEL cooler 13 CERN-DT xxxxx system Nikhef/Desy XFELDifference in the design Temperature range-40 ºC to +25ºC -15 ºC to +20ºC Different chiller Cooling power1kW1.2kWDifferent chiller Pump pressure head 10 bar5 bar2 serial pumps versus 1 pump Fluid conditionSub cooled liquid to X=0.5 X=0, Saturated liquid Heater instead of heat exchanger Enthalpy CERN-DT xxxxx system Liquid Vapor 2-phase Pressure Enthalpy Nikhef/Desy XFEL system Liquid Vapor 2-phase Pressure

14 Heater vs heat exchanger 2 vs 1 pump ºC vs 1.2 xxxxx system XFEL system Differences will be designed to be interchangeable: 1 common mechanical (and control?) design Designer from Krakow will arrive 1 st of November at CERN. Nikhef has also assigned 1 FTE.

The portable 100W “Mini -xxxxx” system Development of the 100W system will be a simplified concept wrt the 1kW xxxxx system. Controls are reduced to a minimum. (Goal is no PLC). Collaboration with LHCb for the VELO upgrade development. Raphael is working on design. Volume is small so everything fits in the lowest PED class (Article 3.1). The goal is to have -40°C, and a temperature range between 25°C and -40°C. Same pump and heat exchanger type as xxxxx system, but smallest in range. 15

Future developments Future systems will have a large increase of power and volume. Especially large volume pipes (reuse of CMS pipes) will demand for large volume accumulators. The CMS low pressure requirement, requires emptying of the system at standstill. This demands for even larger accumulators. Therefore room temperature accumulation is under study. 16

2PACL State point model in Matlab To support future system development a simulation is developed in Matlab to study state point values of a full loop. At each state point the pressure and enthalpy are calculated iteratively according to the properties at the given state-points. Integrated Refprop database Model can be sub divided in small sections of dL to accurately calculate the fluid state at any place in the loop. Environmental heat is included. General configuration file as input giving tube information (lengths, diameter and isolation), flow restrictions (Cv), heat exchange(external or internal), pump performance. 17

Matlab state point model 18 P x,H x P x+1 = P x - dP x H x+1 = H x + dH x Q x = Q applied + Q environment +Q exchanged dP x = f(D,Q 1,MF,VQ,P,T) or f(Cv) dH x = Q tot /MF or pump work dP pump =∑dP all dH condenser = ∑dH all T x,VQ x and properties derived from Refprop Q x+1 dP x+1 dH x+1 P x+2,H x+2 Current status: All latest Thome models (dP, HTC) are being implemented Model currently works with old models (Friedel & Kandlikar from the LHCb-velo stone ages)

Typical state point model input Excel configuration file 19 State point Identifier Identifier numberPressure reference Temperature reference L(m) DO(") DO(m) DI(m) Dh(m) Qty of paralel tubes Crossectional Area Per tube (m2) Vol tubes (m3) Vol rest (m3) Volume total (m3) Wetted area Per tube (m2) Outside area per tube(m2) Isolation thickness (m)Lambda pipe (W/mK) Lambda Isolation (W/mK) Applied heat (W) Volume flow (m3/s) Cv-value Exchange heat with node# Co-currentflow (1), Contercurrentflow (-1) 1tube111 1/ E E pump E E-06 3tube12 1/ E E E E tube / E tube12 1/ E E E E restriction tube11 1/ E E tube E E E E E tube E E E E E tube13 3/ E E tube E E E E tube113 3/ E E condenser4 3.00E E

Typical state-point model output (LHCb-VELO) 20 State points in PH-diagram Subdivision details of transfer line Tsub=-40°C, Taccu=26°C Tsub=-40°C, Taccu=-10°C Tsub=-40°C, Taccu=-30°C

Summary 2 operational CO 2 CERN 2 new laboratory CO 2 systems under development -40°C & -40°C) Scaling up 2PACL for the future Prototyping of different concepts Development of a state point model with latest Thome models to investigate new cycles 21

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