High Global Warming Potential Research Articles

Study of spatiotemporal variation and annual emission of CH4 in Shaoxing Yangtze River Delta, China, Using a portable CH4 detector on the UAV

Methane (CH4) is the second greenhouse gas and has a profound impact on global climate change due to its high global warming potential and concentration. By 2022, the CH4 concentration was approximately 1.9 ppm, which was 264% of the pre-industrial level. The spatiotemporal distribution of CH4 was investigated by a portable CH4 detector on an unmanned aerial vehicle and electric bicycles in Shaoxing, a city situated in the Yangtze River Delta, China. The vertical distribution revealed CH4 concentration generally decreased slowly with height. However, the inversion condition and low atmospheric boundary layer height (ABLH) leaded to the enhancement of CH4 with height. The highest CH4 concentration (2.2 ± 0.1 ppm, n = 1428) was observed in winter and the lowest (2.0 ± 0.2 ppm, n = 1530) in spring. Regarding the daily variation, CH4 concentration peaked at 5:00 local time (LT) and reached its lowest level at 14:00 LT, which was attributed to the daily variation of ABLH, lowest in the early morning and highest in the noon. In urban areas, CH4 concentrations showed higher levels near restaurants, natural gas stations and sewerage well, with a maximum value of 13.1 ppm, which was caused by CH4 emission and natural gas leakage from these places. The annual CH4 emission in Shaoxing were estimated to be approximately 69 ton/(km2·year) by the mass balance approach. Compared with other cities in the world, the CH4 emission is in higher level which imply some control measures should be conducted to reduce CH4 emission in Shaoxing.

A comprehensive phenomenological model for unburned fuel emission simulation applied to natural gas engines

The development of lean-burn concepts for internal combustion engines, utilizing a homogeneous air/fuel charge, aims to improve multiple aspects simultaneously, including thermal efficiency, fuel consumption, nitric oxide, and carbon monoxide emissions. However, the adoption of this technology may result in a notable increase in the emission of unburned hydrocarbons (uHC) compared to stoichiometric engines. The sources of uHC are diverse and their relative significance depends on fuel characteristics, engine operating conditions, and geometric features of the combustion chamber. This concern becomes more pronounced when considering engines fueled with natural gas, as methane has a high global warming potential compared to other pollutant emissions. This research proposes an enhancement to an existing simulation model that describes the primary mechanisms involved in uHC formation, which are filling/emptying of the piston top-land crevice volume and the flame wall quenching, with subsequent uHC post-oxidation. The improvements include the calculation of flame penetration into crevice volumes, the description of uHC production from non-piston crevices, and the introduction of a novel scavenging model. The uHC model is integrated into commercial software (GT-Power) as a “user routine”. Validation of the model is conducted with reference to three large bore engines (W31DF, W31SG, and W46SG) with bore sizes of 31 cm and 46 cm, fueled with natural gas, and operated under lean mixtures (λ > 2), employing different ignition methods (dual fuel mode or pre-chamber device). The uHC model is validated against engine-out measurements, exhibiting an average error of 10.0 % for W31DF, 19.4 % for W31SG, and 14.0 % for W46SG engines, respectively. The reliability of the uHC model is demonstrated by the absence of case-specific adjustments to its tuning constants, even when there are significant variations in engine load and geometric design of the crevice volumes.

Seasonal performance assessment and experimental investigation of R32 drop-in and BPHX size in an R410A chiller when using two compressor modulation strategies

The decrease in fossil fuel reserves and high energy consumption by HVAC&R equipment require the use of compressors with better efficiencies and capacity modulation strategies. Usually, seasonal performance studies focus on compressor capacity modulation methods, however the current study explores the idea of improving the seasonal performance of two compressor modulation techniques: a two-stage and a variable speed compressor with different capacity modulation ranges by using larger condensers in an R410A water ethylene glycol chiller system. The analysis shows that oversizing the heat exchangers has larger benefits with the compressor modulation strategy with lower range. Additionally, the seasonal performance estimated according to AHRI 551/591 (2020) of a two-stage compressor with oversized condenser is higher than a basic single speed compressor with a better motor indicating that oversizing brazed plate heat exchanger (BPHX) might yield higher performance than improving the compressor motor efficiency. Due to the high global warming potential (GWP) of R410A, there is a focus on replacing it with low GWP refrigerants such as R32 to reduce CO2 emissions. This study would also compare the performance when using R32 as a drop-in refrigerant in the two different R410A compressor capacity modulation strategies with comparable cooling capacity. When the refrigerant was changed from R410A to R32, the integrated part load value (IPLV.SI), an efficiency metric for variable speed compressor remains relatively constant at 5.5 while it increases from 3.9 to 4.4 for the two-stage compressor. It is hypothesized that low refrigerant mass flow rate (m˙ref) provided by the variable speed compressor when matching the load at the lower part load conditions leads to refrigerant maldistribution in BPHX and reduced IPLV.SI.

Thermodynamic Analysis of the Absorption of Common Refrigerants in Fluorinated Deep Eutectic Solvents

The potential to decrease the negative environmental impact of greenhouse gases in terms of global warming potential (GWP) is a current challenge. Apart from CO2, fluorinated greenhouse gases (F-gases), which are human-made chemicals used in refrigeration and other industrial applications, have a huge environmental impact due to their high GWPs. In this regard, the design of units to capture and recover these gases would contribute to their reuse, avoiding the negative impact of their final emission or incineration. Fluorinated Deep Eutectic Solvents (FDESs) have been considered as promising solvents for the absorption and the selective separation of F-gases. However, the complex and expensive experimental labour to fully characterize FDESs delays its study and development. In this work, a computational approach is applied to develop accurate thermodynamic models of the gas solubility of several F-refrigerants in DESs. The molecular-based equation of state (EoS) soft-SAFT is used to assess the absorption of three F-gases (1,1,1,2-tetrafluoroethane (R-134a), difluoromethane (R-32), and pentafluoroethane (R-125)) at different temperatures in five DESs derived from fluorinated salts and perfluorinated acids. New molecular models are developed through the soft-SAFT approach for FDESs in good agreement with experimental data, and the solubility of F-gases is also calculated at varying temperatures with high accuracy. Then, an in-depth analysis of the characteristics of the refrigerants, and of the FDESs affecting the F-gases absorption is performed, and the enthalpy and entropy of absorption and the selectivity are calculated. It has been encountered that the best FDESs for each particular F-gas separation can be obtained by modifying the composition of DES and the operating temperature. Finally, an assessment based on the selectivity obtained from the soft-SAFT model is carried out to choose the most adequate solvent to separate the studied F-gases.

Life cycle assessment of n-caproic acid production via chain elongation from food waste: Comparison of shunting and staged technology

n-Caproic acid is a widely used biochemical that can be produced from organic waste through chain elongation technology. This study aims to evaluate the environmental impacts of n-caproic acid production through chain elongation by two processes (i.e., shunting and staged technology). The Open-life cycle assessment (LCA) model was used to calculate the environmental impacts of both technologies based on experimental data. Results showed that the shunting technology had higher environmental impacts than the staged technology. Water and electricity made bigger contribution to the environmental impacts of both technologies. Reusing chain elongation effluent substituting for water and using electricity produced by wind power could reduce the environmental impacts of water and electricity effectively. Using ethanol from food waste had higher global warming potential than fossil ethanol, which suggested that a cradle-to-grave LCA is needed to be carried out for specific raw materials and chain elongation products in the future.

Reducing the carbon footprint of operating rooms through education on the effects of inhalation anesthetics on global warming: A retrospective study.

Environmental concerns, especially global warming, have prompted efforts to reduce greenhouse gas emissions. Healthcare systems, including anesthesia practices, contribute to these emissions. Inhalation anesthetics have a significant environmental impact, with desflurane being the most concerning because of its high global warming potential. This study aimed to educate anesthesiologists on the environmental impact of inhalation anesthetics and assess changes in awareness and practice patterns, specifically reducing desflurane use. This study included data from patients who underwent surgery under general anesthesia 1 month before and after education on the effects of inhalation anesthetics on global warming. The primary endpoint was a change in inhalational anesthetic use. Secondary endpoints included changes in carbon dioxide equivalent (CO2e) emissions, driving equivalent, and medical costs. After the education, desflurane use decreased by 50%, whereas sevoflurane use increased by 50%. This shift resulted in a reduction in the overall amount of inhalational anesthetics used. The total CO2e and driving-equivalent values decreased significantly. The cost per anesthesia case decreased, albeit to a lesser extent than expected. Education on the environmental impact of inhalation anesthetics has successfully altered anesthesiologists' practice patterns, leading to reduced desflurane usage. This change has resulted in decreased CO2e emissions and has had a positive effect on mitigating global warming. However, further research is required to assess the long-term impact of such education and the variability in practice patterns across different institutions.

Fire-Extinguishing Dibromomethane Mixtures with Fluorinated Alkanes for Fire and Explosion Protection of Oil and Gas Industry Facilities

The high fire hazard level is specific to the oil and gas industry due to the circulation of large volumes of flammable gases and liquids. To ensure fire protection at the oil and gas industry facilities, automated gaseous fire extinguishing is widely used. The main fire-extinguishing agents in automated gaseous fire-extinguishing systems are refrigerants HFC 23, 125, 227еа, FC 318c, and fluorinated ketone FK 5-1-12. Upon the adoption of the international agreements on combating global warming, most fluorinated gaseous fire-extinguishing agents currently used for fire extinguishing fell under restrictions. The article indicates the importance of refrigerants HFC 23, 125, 227еа, and FC 318c, whose production volume must be reduced by 85 % by 2036 to ensure the required level of fire and explosion protection of oil and gas industry facilities. A method to reduce the volumes of used fluorinated alkanes by producing highly efficient fire-extinguishing mixtures, one of the components of which is an agent of high global warming potential (GWP) and the other is a chemical compound with a short atmospheric lifetime, has been proposed. Dibromomethane, which fully meets the latest environmental requirements, is to be considered a short-lived component. Based on the well-known kinetic data, the rates of elementary chemical reactions generated in the flame of the methane-oxygen mixture when contacting with refrigerants HFC 23, 227еа, and dibromomethane, have been calculated and compared. The efficiency of using dibromomethane to increase the fire-extinguishing efficiency of refrigerants HFC 23 and 227еа has been substantiated. An experimental determination of the minimum fire-extinguishing efficiency of the generated mixed compositions is conducted to confirm the correctness of theoretical calculations. The obtained mixed gaseous fire-extinguishing agents enable the reduction of the volume of high global warming potential refrigerants by 1.5–2 times. It has been also demonstrated that the obtained mixed compositions have no toxic impact on a human.

An evaluation of energy and carbon budgets in diverse cropping systems for sustainable diversification of rainfed uplands in India's eastern hill and plateau region

With increasing cost and use of energy in agriculture, the traditional practice of mono-cropping of rice in upland is neither sustainable nor eco-friendly. It is necessary to identify crop diversification options with high energy efficiency, productivity, and low global warming potential (GWP). In this experiment, an inclusive system analysis was accomplished for 3 years (2016–2019) of five mono-cropping production (MCP) systems namely rice (R), finger millet (FM), black gram (BG), horse gram (HG), pigeon pea (PP), and four intercropped systems viz. R+BG, R+HG, FM+ BG, and FM + HG. The key objective was to evaluate the flow of energy, carbon balance, and GWP of these varied production systems. Puddled rice was recorded as an energy-exhaustive crop (27,803 MJ ha−1), while horse gram was noted to have the lowest energy use (26,537 MJ ha−1). The total energy output from pigeon pea (130,312 MJ ha−1) and diversified intercropped systems (142,135 MJ ha−1) was 65.3% and 80.3% higher than mono-cultured systems, respectively. Rice and rice-based intercropping production systems showed higher carbon footprints (1,264–1,392 kg CO2 eq. ha−1). Results showed that R+BG and R+HG were the most energy-efficient production systems, having higher energy ratio (5.8 and 6.0), higher carbon efficiency (7.41 and 8.24), and carbon sustainability index (6.41 and 7.24) as against 3.30, 3.61, and 2.61 observed under sole cropping production systems. On average, rice and rice-based production systems had 7.4 times higher GWP than other production systems. In productivity terms, pigeon pea and FM+HG had higher rice equivalent yields of 8.81 and 5.79 t ha−1 and benefit-cost ratios of 2.29 and 1.87, respectively. Thus, the present study suggests that pigeon pea and finger millet-based intercropping systems were the most appropriate crop diversification options for the rainfed upland agro-ecosystem of the eastern region of India.

Theoretical Investigation of Low Global Warming Potential Blends Replacing R404A: The Simple Refrigeration Cycle and Its Modifications

Abstract R404A refrigerant is one of the most widely used hydrofluorocarbons in the commercial refrigeration industry for low and medium temperatures. However, this refrigerant contributes negatively to the environment due to its high global warming potential (GWP = 3943), and for several years, it has been labeled as one of the refrigerants that should be phased out. The present study theoretically evaluates low-GWP refrigerants as a replacement alternative to R404A, including R407H, R442A, R449A, R454A, R454C, R455A, R459B, and R465A. The analysis focuses on the comparison between relative differences in the volumetric flow in the compressor suction and the coefficient of performance for four configurations of the vapor compression cycle, such as the basic cycle, the cycle with an internal heat exchanger, the cycle with direct injection, and the cycle with a sub-cooler. According to the proposed operating conditions of evaporation temperature (−10 °C and −40 °C) and condensation temperature (40 °C and 55 °C), R454A could be the best long-term replacement option for its low GWP, energy performance, and direct fit for any configuration. R459B could also be considered a viable option, but with certain design modifications. On the contrary, the refrigerants R465A, R455A, and R454C would be discarded because they present a greater non-adaptation to the compressor in each configuration analyzed.

Analysis of Plasma and Gas Characteristics According to the Recovery Process Using a New Alternative Gas

Perfluorocarbon (PFC) gas, which is predominantly used in the etching and chamber cleaning processes of semiconductor manufacturing, is very stable and remains on Earth for long periods. Moreover, it has a high global warming potential because it blocks the emission of radiant heat from the Earth and contributes to global warming. To mitigate these effects, the waste PFC gas can be recovered and reused, which also limits the unnecessary waste of resources. In this study, the liquid fluorocarbon C6F6, which has a high C/F ratio and exists as a liquid at room temperature, was selected as an alternative to PFC gas, and adsorption and recovery were performed through an adsorption module during the plasma process. To characterize the recovered gas, residual gas analysis was performed on the gases recovered during etching. In addition, optical emission spectroscopy and printed circuit board probes were used to characterize the plasma. Finally, the feasi-bility of the gas recovery process was evaluated by comparing the thicknesses of the CF polymers produced in Si and SiO2 using an ellipsometer. The results revealed that the C6F6 had similar characteristics before and after recovery, confirming that this gas can be reused and is suitable for use in semiconductor manufacturing as a green alternative.

Capture Fluorocarbon and Chlorofluorocarbon from Air Using DUT-67 for Safety and Semi-Quantitative Analysis.

Fluoro- and chlorofluorocabons (FC/CFCs) are important refrigerants, solvents, and fluoropolymers in industry while being toxic and carrying high global warming potential. Detection and reclamation of FC/CFCs based on adsorption technology with highly selective adsorbents is important to labor safety and environmental protection. Herein, the study reports an integrated method to combine capture, separation, enrichment, and analysis of representative FC/CFCs (chlorodifluoromethane(R22) and 1,1,1,2-tetrafluoroethane (R134a)) by using the highly stable and porous Zr-MOF, DUT-67. Gas adsorption and breakthrough experiments demonstrate that DUT-67 has high R22/R134a uptake (124/116 cm3 g-1) and excellent R22/R134a/CO2 separation performance (IAST selectivities of R22/CO2 and R134a/CO2 ranging from 51.4 to 33.3, and 31.1 to 25.8), even in rather low concentration and humid conditions. A semi-quantitative analysis protocol is set up to analyze the low concentrations of R22/R134a based on the high selective R22/R134a adsorption ability, fast adsorption kinetics, water-resistant utility, facile regeneration, and excellent recyclability of DUT-67. In situ single-crystal X-ray diffraction, theoretical calculations, and in situ diffuse reflectance infrared Fourier transform spectra have been employed to understand the adsorption mechanism. This work may provide a potential adsorbent for purge and trap technique under room temperature, thus promoting the application of MOFs for VOCs sampling and quantitative analysis.

Proper C/N ratio enhances the effect of plant diversity on nitrogen removal and greenhouse effect mitigation in floating constructed wetlands.

Treating wastewater with low carbon-to-nitrogen (C/N) ratios by constructed wetlands (CWs) is still problematic. Adding chemicals is costly and may cause secondary pollution. Configuring plant diversity in substrate-based CWs has been found to be a better way to treat low-C/N wastewater, but wastewater treatment in floating CWs needs to be studied. In this study, wastewater with C/N ratios of 5 and 10 were set in simulated floating CWs, and 9 combinations with plant species richness (SR) of 1, 3, and 4 were configured. The results showed that (1) increasing SR improved the total N mass removal (NMR) by 29% at a C/N ratio of 5 but not 10; (2) the presence of Oenanthe javanica in the microcosms increased the NMR by 13% and 20% with C/N ratios of 5 and 10, respectively; (3) increasing SR mitigated the net global warming potential (GWP) by 120% at a C/N ratio of 5 but not 10; and (4) a Hemerocallis fulva × O. javanica × Echinodorus parviflours × Iris hybrids mixture resulted in a high NMR and low net GWP. In summary, assembling plant diversity in floating CWs is an efficient and clean measure during the treatment of wastewater with a C/N ratio of 5.

Operation of a low resistivity glass MRPC at high rate using ecological gas

The Multigap Resistive Plate Chamber (MRPC) is a gaseous detector that has low building costs and excellent timing performances. It is usually operated using a mixture of C2F4H2 and SF6, which have very high Global Warming Potential (GWP) values (1430 and 23,900 respectively). The ecological HFO-1234ze (C3F4H2), GWP <7, was investigated if it could be a viable alternative to the standard gas mixture. In this work, we present the performances of an MRPC with 10 gaps of 235μm width, built using 0.5 mm thick plates of low resistive glass. This detector was also operated using the standard gas mixture for comparison. At low particle rate, this detector reaches an efficiency of 98% and a time resolution of around 70 ps for the two mixtures of gases. We observed no degradation of its performances when a limited size of its active area is exposed to particle rates up to 63 kHz/cm2.

Non-CO2 greenhouse gas separation using advanced porous materials.

Global warming has become a growing concern over decades, prompting numerous research endeavours to reduce the carbon dioxide (CO2) emission, the major greenhouse gas (GHG). However, the contribution of other non-CO2 GHGs including methane (CH4), nitrous oxide (N2O), fluorocarbons, perfluorinated gases, etc. should not be overlooked, due to their high global warming potential and environmental hazards. In order to reduce the emission of non-CO2 GHGs, advanced separation technologies with high efficiency and low energy consumption such as adsorptive separation or membrane separation are highly desirable. Advanced porous materials (APMs) including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), hydrogen-bonded organic frameworks (HOFs), porous organic polymers (POPs), etc. have been developed to boost the adsorptive and membrane separation, due to their tunable pore structure and surface functionality. This review summarizes the progress of APM adsorbents and membranes for non-CO2 GHG separation. The material design and fabrication strategies, along with the molecular-level separation mechanisms are discussed. Besides, the state-of-the-art separation performance and challenges of various APM materials towards each type of non-CO2 GHG are analyzed, offering insightful guidance for future research. Moreover, practical industrial challenges and opportunities from the aspect of engineering are also discussed, to facilitate the industrial implementation of APMs for non-CO2 GHG separation.

Life cycle assessment of fluorinated gas recovery from waste refrigerants through vacuum swing adsorption

The refrigeration industry is facing a challenge due to stricter regulations on the use of fluorinated gases (F-gases) with high Global Warming Potential (GWP). In many cases, the design of alternative refrigerants requires the recycling of low and moderate GWP compounds from existing refrigerant blends, but currently there is no a standardized technology available to recover them, and finally most gases are incinerated at the end of the equipment's life cycle. Recently, Vacuum Swing Adsorption (VSA) has been proposed as a possible solution for the complex separation of F-gas mixtures. The environmental sustainability of the recovery of R-32 from R-410A blend using a VSA process (circular economy scenario), was analysed through a life cycle assessment (LCA) approach, and it was compared to the conventional R-32 production (benchmark scenario). The results show that the VSA technology can achieve a 30.9% recovery of 97 mol% R-32 suitable for further reuse, with a reduction in the environmental loads ranging from 58 to 99% compared to industrial R-32 production. The carbon footprint of the recovery process is 4.81 kg CO2 equiv., while for the industrial production of R-32 is 10.9 kg CO2 equiv. This study proves that the development of adsorption-based technologies for F-gas recovery can improve the environmental impact of these compounds from a circular economy perspective.

Optimized strategies for nitrogen fertilizer application in Populus plantations in the context of climate change mitigation

Nitrogen (N) fertilizer application increases biomass volume and enhances the carbon sequestration of forest stands. However, overused N fertilizers induce nitrous oxide (N2O), a greenhouse gas with a higher global warming potential than CO2. This study estimates the growth function of Populus stands based on field data, based on which the revised Faustmann model is used to evaluate the optimal rotation and the N fertilizer application rate under different scenarios. Results show that the stand volume is an increasing logarithmic-reciprocal function of the age and N fertilizer rate, and the increment by age is more significant and lasting. When the cost of N2O emissions is considered, the fertilization rate is substantially reduced; a higher carbon price decreases the fertilization rate but prolongs the optimal rotation. Overall, participation in forest carbon projects is economically beneficial even when the costs of greenhouse gas emissions are considered. The research outcomes provide insights into the interplays between the benefits and costs of N fertilizer applications and forest owners' behavior. The conclusions support the accounting of N2O emissions in protocols of forest carbon projects and a more ambitious mitigation goal to push the carbon price on a national scale market.

A Cyclic Etching Process Using HFE-347mcc3 as a Lower-GWP Alternative to Perfluorocarbons for High-Aspect-Ratio SiO2 Features

As circuits continue to integrate at higher levels, the critical dimensions of DRAM and 3D-NAND are decreasing, leading to an increase in aspect ratios of various features such as contact holes and via holes in DRAM, and channel holes of stack layers in 3D-NAND. This trend has made the process of etching high-aspect-ratio SiO2 features more challenging. To achieve this, it is necessary to satisfy specific conditions including high selectivity to the mask or the underlayer film and the anisotropic etch profiles.Perfluorocarbons (PFCs) such as CF4 and c-C4F8 are commonly used for SiO2 etching. PFCs form a thicker steady-state fluorocarbon film on Si than SiO2, leading to high SiO2/Si selectivity. In addition, PFCs enable anisotropic etching since a passivation layer is formed on the sidewall, preventing lateral etching of the sidewall by chemical etchants.However, PFCs are a representative greenhouse gas with a high global warming potential (GWP) compared to CO2, causing significant adverse effects on global warming. Therefore, there have been efforts to reduce greenhouse gas emissions, such as setting goals for greenhouse gas reduction by each country through the Paris Agreement in 2015. Semiconductor manufacturers have also committed to reducing greenhouse gas emissions per silicon substrate area by 30% compared to 2010. In this regard, various studies are being conducted to develop a SiO2 etching process using alternative materials with lower GWP than PFCs. Fluorinated ethers and fluorinated alcohols are potential substitutes due to their low GWPs and short lifetimes. For example, heptafluoropropyl methyl ether (HFE-347mcc3) has a GWP of ~530 and an atmospheric lifetime of 5.2 years, significantly lower than those of PFCs.During etching of SiO2, the mask is susceptible to damage and corrosion by ions, resulting in various pattern deformations such as bowing, necking, and striation. These deformations adversely affect the miniaturization of the DRAM structure by reducing the process margin between holes and have a negative influence on the electrical characteristics of the device, such as contact resistance, line edge roughness, and line width roughness.To prevent these pattern deformations, the cyclic etching process that repeats the passivation layer deposition step and SiO2 pattern etching step was devised. A fluorocarbon film is deposited on the mask to protect it, then SiO2 is etched. The fluorocarbon film is deposited again to reinforce the mask and damaged fluorocarbon film during the etching process, and then SiO2 etching step is repeated to achieve the high-aspect-ratio SiO2 features.In this study, the cyclic etching process was conducted using HFE-347mcc3 as a lower-GWP alternative to PFCs to etch SiO2 contact holes. The effect of the duration of each step on the etch profile was investigated by adjusting the duration of the deposition and etching steps. This work demonstrated the feasibility of using HFE-347mcc3 as a lower-GWP alternative to PFCs for cyclic etching of SiO2 contact holes to obtain anisotropic etch profiles.

The “green” use of fluorocarbons in Cherenkov detectors and silicon tracker cooling systems: challenges and opportunities in an unfolding era of alternatives

Saturated fluorocarbons (SFCs) of form CnF(2n+2) are chosen for their optical properties as Cherenkov radiators, with C4F10 and CF4 currently used at CERN in the COMPASS and LHCb ring imaging Cherenkov detectors. Their non-conductivity, non-flammability and radiation-resistance also make SFCs ideal coolants: C6F14 liquid cooling is used in all LHC experiments, while C3F8 is used for the evaporative cooling of TOTEM and the ATLAS silicon tracker. These fluids, however, have high global warming potentials (5000–10000*GWPCO2), and represented around 36% of CERN’s CO2-equivalent emissions in 2018. There is thus an impetus to reduce their use, losses in purification and wastage through leaks, through improved monitoring and closed circulation system design. Newer spur-oxygenated fluoro-ketones, for example from the 3 M NOVEC® range, with CnF2nO structures, can offer similar performance to SFCs with but with very low, or zero GWP. Although these fluids do not yet exist in large quantities over the full CnF2 “matrix” the radiation tolerance and thermal performance of NOVEC 649 (C6F12O) was sufficiently promising for it to be chosen as a C6F14 replacement for cooling silicon photomultipliers. Additionally, subject to optical testing, NOVEC 5110 (C5F10O) could (if blended with nitrogen) replace both C4F10 and CF4 in Cherenkov detectors. Lighter molecules (for example C2F4O, with similar thermodynamics to C2F6)—if and when available in industrial quantities—might allow lower temperature operation than evaporative CO2 in future silicon trackers operated at very high luminosity. Ultrasonic gas mixture analysis is very sensitive to concentration changes of a heavy vapour in a light carrier, and is used—in the only such fluorocarbon coolant leak monitoring system operating at LHC—for real-time monitoring of C3F8 coolant leaks from the ATLAS pixel and SCT silicon trackers into their nitrogen-flushed environmental volumes. A typical C3F8 sensitivity of better than 10−5 is achieved. Advanced new ultrasonic algorithms allow measurement of the concentrations of a pair of gases of particular interest on top of a varying known baseline of other gases. The technique is thus of considerable value in leak monitoring and could be used to blend fluoro-ketones with nitrogen or argon to reduce the GWP “load” of large volume atmospheric pressure gas Cherenkov radiators without the recourse to higher-pressure noble gas approaches. This paper outlines an approach to GWP reduction with fluoro-ketone fluids and the blending of heritage SFCs or fluoro-ketones with lighter gases using ultrasonic monitoring and control. Possible avenues for the use of fluoro-ketones in liquid phase and evaporative cooling of silicon trackers are discussed.

Toward an environmental friendly operation of the CBM-TOF system

The future fixed target high-rate compressed baryonic matter (CBM) experiment is one of the experimental pillars of the Facility for Antiproton and Ion Research (FAIR) located in Darmstadt/Germany. In order to provide an excellent particle identification (PID) of charged hadrons, the CBM-time-of-flight (TOF) group has developed a concept of a 120 m2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^2$$\\end{document} large TOF wall with a system time resolution below 80 ps based on multi-gap resistive plate chambers (MRPC). Currently, timing MRPC systems are operated with a gas mixture based on tetrafluoroethane (R134a, C2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}H2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_2$$\\end{document}F4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document}) with additions of few vol% quencher gases, e.g., sulfur hexafluoride (SF6\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_6$$\\end{document}) or/and isobutane (i-C4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_4$$\\end{document}H10\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_10$$\\end{document}). Unfortunately, these gas mixtures have a high global warming potential (GWP) in the order of 1500, and therefore, strategies to reduce the environmental impact have to be developed. The various possibilities, including studies on eco-friendly gases, and the considered strategy by the CBM-TOF group will be elaborated in this article.

Advanced exergy analysis of a Reverse Brayton cycle using air as working fluid for cryogenic purposes

The global push to reduce greenhouse gas emissions has led to the ban of high global warming potential (GWP) refrigerants in the refrigeration sector, prompting the adoption of low-GWP alternatives. However, as regulations are expected to tighten, technologies like the Reverse Brayton cycles (RBC) are emerging. RBCs can operate with safe fluids and can reach very low temperatures through compressions, regeneration, and expansion, requiring only electricity. This research presents results from an RBC equipped with a radial turbine using natural air (R-729), a hazard-free fluid with zero ozone depletion potential (ODP) and emission potential. The cycle utilizes automotive components, offering a cost-effective, high-tech solution. The study evaluates the cycle COP at a design point and performs an exergetic analysis at 173K. Using a thermal and fluid dynamic model of the cycle, the critical components of the cycle influencing the COP are identified, and potential improvements are explored.