1. 3M Novec 649 as alternative to C6F14 for single-phase cooling
Petr GORBOUNOV
CERN PH-LBO and ITEP (Moscow)
Why seeking alternative fluids?
Why Novec 649?
Why does it need to be validated?
Validation objectives
What is the current status?
What do we need?

2. —— Why seeking alternatives to PFCs?
PFCs are GHG and poor single-phase coolants, but have unique properties that justified their wide use at the LHC: inertness, non-flammability, low pour point, quartz- like electrical resistivity, water-like pumpability at low temperatures, volatility and cleanness. Regarded as “rad-hard”…
As HTFs, widely used in ATLAS, CMS, LHCb
KYOTO Protocol, in force since 2005, commits its Parties to reduce GHG emissions
From
GWP: PFC vs other commercial refrigerants
Novec 649
(C6K)
PFCs
CERN: the program to monitor and reduce the emissions of PFCs, alternative technologies for new developments are promoted
LHCb SciFi photodetector cooling (-40°C): alternative baseline coolant, M Novec 649
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3. —— Why 3M Novec 649 (fluoroketone C6K)?
Only fluorinated fluids match the low-temperature single-phase DC requirements [6]
Apart from PFC, only Novec fluids – FKs (C6K and C7K) and segregated HFE – are commercially available. HFEs: contain H and have GWP of ~300; FKs: no H, GWP=1
C6K was in use since long time as a “clean fire suppressing agent”, very well studied and covered by extensive literature (atmospheric sink, safety)
As Novec 649, C6K is now positioned by 3M as a HTF. It is one of very few conceptually new HTFs since KYOTO’2005.
Thermo-physical properties: C6K is very similar to C6F14 (drop-in replacement?)
Slighty lower boiling point (49°C vs 56°C)
Lower electrical resistivity (104 GOhm-cm, like dry air, vs 106 GOhm-cm)
Slightly lower viscosity and better heat conductivity at low temperatures
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4. —— Single-phase cooling: coolants comparison
From Ref. [6]
N649
N649
The higher, the better
C6F14: FH=1
The lower, the better
C6F14: FP=1
Thermally and hydraulically, Novec fluids (both FK and HFE) are better than PFCs
HFEs are significantly better than C6F14: by ~20% higher HTC and by ~15% less pressure drop at -40°C
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5. —— Novec 649/1230 facts Known as “waterless water” or “dry water”
As HTF, intended for full immersion 2-phase cooling (e.g. in data centers) and ORC (low-temperature Rankine Cycle electrical generators)
Sustainable alternative to halons, PFCs and HFCs in clean agent apps
Non-toxic, NOAEL > 10% v/v, certified for use in occupied areas
The low GWP is due to the photolysis under UVB at ~305 nm (4.04 eV) causing the C6K molecule scissions into short-lived compounds and radicals
C6K
(3M “Novec 649”)
Chemically not as inert, as PFCs: it’s a ketone (contains carbonyl C=O group)
Price ≈ C6F14 (Q quotation)
iso-C6F14
(F2 “Flutec PP1”)
n-C6F14
(3M “PF-5060”)
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6. —— Why do we need to validate Novec 649 for DC?
Weakly reactive with
liquid water, producing an organic acid PFPrA and HFC-227ea (~ neutral gas).
alumina and alumino-silicates (used in filters for C6F14)
Nothing is known about radiolytical properties of C6K (“radiation resistance”)
less critical for zero- or low-dose applications
Limited published data on the compatibility of C6K with materials (mostly 3M)
Requires new methods of fluid purification (drying, acid removal) and monitoring
Novec 649 is proposed as the baseline coolant in LHCb SciFi Tracker [1] and in the BGV project of BE/BI [2]. It will be also evaluated by the ATLAS DC group [3]
Of potential interest to other CERN projects?
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7. —— Chemical reactivity of N649: hydrolysis
Most significant hazard for low-dose applications
Little if any reaction is observed in C6K in equilibrium with moist air.
C2F5C(O)CF(CF3)2 + H2 ↔ HOC(O)C2F5 (aq) C2HF7
C6K Perfluoropropionic HFC-227ea
Fluoroketone Acid (PFPA)
Water addition to C=O is a reversible reaction, won’t occur with water dissolved in the fluid
Liquid water is required for the hydrolysis to proceed
PFPA will be accumulating in the aqueous phase
In practice, the problem is expected if liquid water gets inside the cooling circuit and in the case of a leak and a prolonged contact with condensation water. SS 316 is safe!
Like with any chemical reaction, the hydrolysis rate will drop at low temperatures
Initial concentration of PFPA in Novec 649 is < 5 ppm (3M)
Water solubility in N649 is small: 20 ppm at 25°C (expected to decrease at low T)
Both moisture and acid levels in the coolant have to be monitored during the service
Corrosion of Ni-plated brass drain valve of the chiller
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8. —— Chemical reactivity of N649: hydrolysis
Most significant hazard for low-dose applications
Little if any reaction is observed in C6K in equilibrium with moist air.
Water addition to C=O is a reversible reaction, won’t occur with water dissolved in the fluid
Liquid water is required for the hydrolysis to proceed
PFPA will be accumulating in the aqueous phase
In practice, the problem is expected if liquid water gets inside the cooling circuit and in the case of a leak and a prolonged contact with condensation water. SS 316 is safe!
Like with any chemical reaction, the hydrolysis rate will drop at low temperatures
Initial concentration of PFPA in Novec 649 is < 5 ppm (3M)
Water solubility in N649 is small: 20 ppm at 25°C (expected to decrease at low T)
Both moisture and acid levels in the coolant have to be monitored during the service
Corrosion of Ni-plated brass drain valve of the chiller
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9. —— Chemical reactivity of N649: alumina, zeolytes
3M reported a weak reactivity of N649 with alumina and zeolytes (tested down to 25°C). Quite cursory study!
The most important consequence, which will be central to the validation study, is that the MS- and alumina-based filters currently found in the C6F14 cooling systems will be not usable with N649, at least at moderate temperatures
3M recommends to use alternative desiccants, like silicagel (or metal sulfites for deep drying to < 1 ppm)
Reactivity of N649 with Alumina of different acidity, quantified by HFC-227ea evolution
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10. —— “Radiation hardness” (I): can fluids be “rad. hard”?
Remark: the notion of “radiation hardness” is mostly applied to solids and not very well defined for liquids. The effect of radiation for liquids is limited to radiolysis
Radiolysis (dissociation of the molecules under radiation) alters the chemical composition and, at elevated doses, might lead to undesirable macroscopic effects: change in viscosity, loss of dielectric strength, polymerization, increase of acidity, evolution of toxic gases etc. 2-phase cooling is more sensitive to all that
For single-phase applications (typically, large tubes), the most important effect is the formation of HF (in presence of water and other H-containing compounds) and CF2O
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11. —— “Radiation hardness” (II): expectations for N649
Fluoroketones (e.g. N649) can be expected to be less “radiation hard” than C6F14 because of the lower energy of the weakest C-C bond: ~4 eV (~8 eV in C6F14). Moreover, the presence of oxygen in the molecule might favor the CF2O formation. Does that all prohibit the use of N649? Answer: a priori NO!
The exact extent of the radiation damage to N649 for typical irradiation doses still has to be experimentally determined (in collaboration with 3M!)
For moderate total doses (like for SciFi: 200 Gy/5 dilution) the expected effect is microscopic [5]. Like for zero-dose applications, the hydrolysis remains the dominant potential issue.
Stricter requirements on the initial coolant purity! Commercial N649 purity is %. It can be further improved either by initial purification (like with C6F14 in ALICE RICH) or by requesting a special “rectified” grade from 3M
Inline (service time) purification can become a bit more sophisticated than just a couple of changeable cartridges. For example, a closed-loop N2-purging for HF and CF2O extraction may has to be arranged in the expansion tank.
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12. —— “Radiation hardness” (III) : a word on C6F14
2002 simplified tests by M.Atac et al. indicated that C6F14 resisted well the 20 kGy γ-dose.
Further comprehensive study of radiolytical properties of C6F14 was made in at CERN by S.Ilie et al. [10], provide guidelines for N649 validation!
“The induced acidity and the fluorine ion content, the presence of polymers or prepolymers, the appearance of new chemical species were the main radiation induced effects and these parameters were used to characterize the radiation hardness of the fluids…”
Air, moisture and other H-containing contaminants caused “detrimental effects” like CF2O formation, corrosion (mainly for Al) and the appearance of polymeric deposits
Branched iso-C6F14 was found to be more radiation-resistant than n-C6F14 (NB: C6K is branched!)
The higher the liquid purity, the better its radiation resistance
The detrimental radiolysis products could be effectively removed by inline cleaning. The cleaning agents , as well as the filter composition, were recommended (activated charcoal, alumina and MSs)
Initial deoxygenation and dehydration is recommended
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13. —— “Radiation hardness” (IV) : summary
Radiation damage for fluids is limited to radiolysis
Irradiation tests at O(102), O(103), O(104) Gy, to assess the radiation damage to N649, are required (initially with γ-source, later with hadrons)
Detrimental radiolysis products: acids (primarily HF), (pre-)polymers, toxic gases (eg CF2O). Moisture, HCs and oxygen are main enemies!
No important structural effects are expected for intended N649 applications, so the focus must be on cleaning (initial and online)
Need to find efficient cleaning agents alternative to zeolites and alumina
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14. —— Compatibility with materials
3M: Novec and PFC fluids have similar compatibility with metals, hard plastics and elastomers. De facto proof: pool boiling and ORC applications
An independent long-term (or accelerated) compatibility test with typical materials is desirable
LHCb SciFi, since : Titanium gr. 5 and stainless steel 316 are being “incubated” in different Novec fluids (including the 649), with or without water
Dynamic test bench?
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15. —— Purification for N649 Desiccants (regenerable) Acid removal
CaSO4 (“Drierite”)
Silicagel (used in pool boiling)
Ion-exchange resins (acid, Na+ form)
Acid removal
IER (eg Dowex M-43), non-regenerable
General (HCs, pre-polymers, low-mol-w)
Activated carbon (acid washed!)
Suggested by 3M, shown to be efficient above water freezing
Low temperatures? (online cleaning)
Practically no information
IER ?? (a good task to outsource!)
MS might be usable at ≤ -40°C !
Hybrid filters:
Warm service (silicagel, IER, Drierite, activated carbon)
Cold service (activated carbon + MS)
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16. —— N649 validation project at CERN (I)
Draft WP EDMS v.0.2 [7] , initiated by PH-LBO, supported by EN/CV
Endorced by the CERN DRC, 1 year FTE + ~65 KCHF budget
This meeting is intended as a formal presentation of this WP
Actual work started in ~ November 2014, after the thermal validation of N649 as a HTF for the SciFi
Initial intent: full characterization at CERN, à la C6F14
Correction: due to limited availability of the CERN chemical lab, the R&D program had to be downscaled and largely outsourced to external labs
Characterization for low-dose applications (hydrolysis & basic radiolysis studies)
Methods of initial and online cleaning
Evaluate other alternative liquids (Novec 7000 series?)
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17. —— N649 validation project at CERN (II)
Involved parties: PH/LBO, EN/CV, TE-VSC-SCC, PH/DT (cooling, e.g. ATLAS), external labs (e.g. 3M, Dynalene, CH academic labs)
Work plan (now – April 2016)
Market and literature review, contact with 3M developers – done
Early material compatibility test – ongoing
Containers for irradiation – done
Basic chemical analyses (water and PFPA uptake rates, cleaning methods) – in preparation, with Dynalene
Irradiation (CERN CHARM + GIF++ , or external facility) – in preparation
Submitting the irradiated samples to 3M for the chemical analysis – foreseen
Material compatibility (CERN and external labs)
2nd round of irradiations (hadrons, high-doses)
Reports
We are here
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18. —— N649 validation project at CERN (III): what do we need?
Support by CERN chemists (TE-VSC-SCC): consultations, sample prep, basic analyses:
Moisture content (eg, KF titration)
Acid contents (with protocols defined/developed by external labs)
(option): FTIR spectrometry
Support by CERN RP service
Assistance in transporting the irradiated samples to external labs
Support by CERN irradiation services
Forum for discussions! Can the DCP club be used for this?
“Umbrella”: … EN/CV !
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19. —— Summary
There is an interest at CERN to C6F14 alternatives for single-phase cooling
3M Novec 649 is a promising candidate
A project to validate 3M Novec 649 has been initiated by LH-LBO (for SciFi Tracker upgrade)
Work has started, some funding is secured
We need further support, forum for discussions
Thank you!
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20. Nomenclature HTF heat transfer fluid IER ion-exchange resen(s)
3M 3M Company
C6F14 perfluorohexane, popular DC fluid
C6K short for “6-carbon FK”
DC detector cooling
FK fluoroketone
FOM figure of merit
GHG greenhouse gas
GWP global warming potential
HFE hydrofluoroether(s)
HC hydrocarbon(s)
HTF heat transfer fluid
IER ion-exchange resen(s)
MS molecular sieve(s)
ORC Organic Rangine Cycle
PFC perfluorocarbons
SS stanless steel
WP work package
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21. References
P.G., “Cooling for the LHCb Upgrade SciFi Tracker”, presented at TIPP’14
“Detector Cooling for the BGV Demonstrator in the LHC”, EDMS
PH/DT ATLAS_NOVEC Project (see presentation by Dina)
P.G., “Project: 3M Novec 649 as a replacement of C6F14 in liquid cooling systems” (Note 1) – literature survey
P.G.,“Assessment of the radiation damage to the coolant in SCiFi tracker” (Note 2)
P.G., M.B., E.Th, “Comparison of liquid coolants for single-phase detector cooling” (Note 3)
P.G., M.B., E.Th, “Alternative to liquid PFC C6F14 for mono-phase detector cooling applications at CERN” – the Work Package , EDMS v 0.2
Annex 1 for the Work Package, “Commentaries to C6K validation tasks”
Annex 2 for the Work Package, “Questions to Novec 649 manufacturer”
S.Ilie et al., “ Chemical and radiolytical characterization of PFC liquids…”, EDMS and
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22. Backup slides
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23. —— Open bath liquid immersion cooling with N649
Navy research Lab
DC Washington
Extremely energy efficient (up to 150 kW per standard rack)
NB: serious players are involved!
No material compatibility concerns, even at >50°C!
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24. Refrigerant Baseline choice: 3MTM NOVEC 649 thermal management fluid
fluoroketone, C6F12O
thermophysical properties similar to C6F14
volatile, dielectric, low viscosity
inflammable
low toxicity (widely used as a clean fire extinguishing agent in occupied spaces, e.g. data centers)
GWP=1
Reactive with liquid water (not important for our application)
3M positions Novec fluids as a replacement for PFCs
Backup: C6F (3M™ FC-72, F2™ PP1)
very well studied, used in 13 LHC systems
deprecated, GWP=7400
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