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?

—— 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 http://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=04509386 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, 3M Novec 649 P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— 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 P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— 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 P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— 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 (Q2 2015 quotation) iso-C6F14 (F2 “Flutec PP1”) n-C6F14 (3M “PF-5060”) P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— 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? P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— 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 P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— 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 P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— 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 P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— “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 P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— “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 99.8- 99.9%. 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. P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— “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 2006-2007 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 P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— “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 P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— 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 22.12.2014: Titanium gr. 5 and stainless steel 316 are being “incubated” in different Novec fluids (including the 649), with or without water Dynamic test bench? P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— 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) P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— N649 validation project at CERN (I) Draft WP EDMS 1489771 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?) P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— 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 P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— 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 ! P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— 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! P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

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 P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

References P.G., “Cooling for the LHCb Upgrade SciFi Tracker”, presented at TIPP’14 “Detector Cooling for the BGV Demonstrator in the LHC”, EDMS 1439028 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 1489771 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 804849 and 842110 P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

Backup slides P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

—— 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! P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN

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: C6F14 (3M™ FC-72, F2™ PP1) very well studied, used in 13 LHC systems deprecated, GWP=7400 P. Gorbounov (PH-LBO) Alternatives to liquid fluorocarbons for detector cooling at CERN 10 June 2015 CERN