Numerically Predicted Burning Velocities of C1 and C2 Hydrofluorocarbon Refrigerant Flames with Air

Due to their high global warming potentials, many existing working fluids for heating, cooling and refrigeration equipment are being phased out. Their replacements will often be flammable or slightly flammable, and the burning velocity of refrigerant-air mixtures is being used as a metric to rank their flammability. To allow industry to estimate the flammability of new blends of agents, predictive tools for the burning velocity of refrigerants are being developed, and calculating burning velocity requires a kinetic mechanism. The National Institute of Standards and Technology hydrofluorocarbon (HFC) mechanism was developed 20 years ago to describe hydrocarbon-air flames with added trace amounts of hydrofluorocarbon fire retardants (primarily CH2F2, CF3H, CF4, C2H2F4, C2HF5, and C2F6). In the present work, the mechanism has been updated slightly to include new HFC compounds, more recent rate data, and rate data for new species. The modified mechanism is used to predict steady, planar, 1D, unstretched burning velocities for mixtures of air with each of the one- and two-carbon saturated HFC compounds R41 (CH3F), R32 (CH2F2), R161 (C2F5H), R152 (CH2F-CH2F), R152a (CH3-CHF2), R143 (CH2F-CHF2), R143a (CH3-CF3), R134 (CHF2-CHF2), and R134a (CH2F-CF3), for which existing experimental data were available. Simulation results are present for a range of fuel-air equivalence ratio ϕ, for comparison with the available experimental data. Agreement is reasonable, and major kinetic pathways and radical populations are explored to uncover the general reaction properties of these new flames

An Empirical Model For Refrigerant Flammability Based On Molecular Structure and Thermodynamics

Screening methods for refrigerant blend flammability using metrics that can be easily calculated are of great interest to the refrigerant industry. Existing flammability metrics such as heat of combustion are not adequate for hydrofluorocarbon blends. Alternative metrics are needed that can be used to assess the flammability of refrigerant blends without requiring time-consuming experimental measurements. In this work we study the combination of the maximum adiabatic flame temperature and the fluorine-substitution ratio as metrics for characterizing the flammability of refrigerant blends. The combination of these metrics yields an estimate of the flammability class of refrigerants (both blends and pure fluids) containing hydrofluorocarbon and hydrocarbon components. The calculations of adiabatic flame temperature are carried out with the open-source chemical kinetics software package Cantera using a mechanism available in the literature

Evaluation of binary and ternary refrigerant blends as replacements for R134a in an air-conditioning system

We investigated refrigerant blends as possible low-GWP (global warming potential) alternatives for R134a in an air-conditioning application. We carried out an extensive screening of the binary and ternary blends possible among a list of 10 pure refrigerants comprising three hydrofluoroolefins (HFOs), six hydrofluorocarbons (HFCs), and carbon dioxide. The screening was based on a simplified cycle model, but with the inclusion of pressure drops in the evaporator and condenser. The metrics for the evaluation were nonflammability, low-GWP, high COP (coefficient of performance), and a volumetric capacity similar to the R134a baseline system. While no mixture was ideal in all regards, we identified 12 best blends that were nonflammable (based on a new estimation method by Linteris, et al., presented in a companion paper at this conference) and with COP and capacity similar to the R134a baseline; the tradeoff, however, was a reduction in GWP of, at most, 56% compared to R134a. An additional seven blends that were estimated to be marginally flammable (ASHRAE Standard 34 classification of A2L) were identified with GWP reductions of as much as 90%. These 19 best blends were then simulated in a more detailed cycle model

Fluorinated halon replacement agents in explosion inerting

The US Federal Aviation Administration (FAA) observed during explosion tests that at a low concentration of agent, some candidate halon replacement agents increased the explosion severity instead of mitigating the event. At UTC Aerospace Systems a test program was developed to assess the behaviour of alternative agents at values below inerting concentration. Two agents were selected, C2HF5 (Penta- fluoroethane, HFC-125) and C6F12O (FK-5-1-12, Novec™1230). Baseline tests were performed with unsuppressed C3H8 (propane)/air mixtures and C3H8/air mixtures with CF3Br (Halon 1301) and N2 (nitrogen). Using CF3Br or N2 at below inerting concentrations mitigated the explosion. C2HF5 was tested against C3H8 at stoichiometric (4 vol%) and lower explosion limit (LEL) (2 vol%). Against 4 vol% C3H8 the combustion was mitigated, proportional to agent concentration; however, low concentrations of C2HF5 with 2 vol% C3H8 enhanced the explosion. Tests with N2 against a volatile mixture of C3H8 with C2HF5 showed that N2 mitigated the events. Final tests were performed with low concentrations of C6F12O against C3H8/air mixtures. This showed similar behaviour to that observed with the C2HF5 tests. Normally during qualification tests for new agents the stoichiometric concentration of a fuel is deemed to be the worst case scenario and the baseline against which agents are tested. The above described test results show that this assumption may need to be reconsidered. This work shows that contrary to common assumption the agents investigated are unlikely to have acted chemically at the flame front, but most likely, mainly cooled the flame and changed the stoichiometry, i.e. the ratio of components of the flammable mixture

Η εξέλιξη της ελληνικής νομοθεσίας για την αποκατάσταση [αντιμετώπιση] των επιπτώσεων από φυσικές καταστροφές. Μελέτη περίπτωσης: Από καταστροφικό σεισμό της Θεσσαλονίκης του 1978 έως το σεισμό του Αρκαλοχωρίου Κρήτης το 2021.

Οι φυσικές καταστροφές έχουν πολλαπλασιασθεί σε όλες τις περιοχές της γης τα τελευταία έτη. Οι φυσικές καταστροφές που έπλητταν την Ελλάδα διαχειρίζονταν με επιδερμικό τρόπο από το κράτος και μόνο οι σεισμοί λαμβάνονταν πιο σοβαρά υπ΄όψιν. Ο σεισμός των 6.5R της 20.06.1978 στη Θεσσαλονίκη αποτέλεσε κομβικό χρονικό σημείο, από το οποίο άρχεται η ψήφιση νόμων για την αποκατάσταση των βλαβών των κτιρίων. Η αρμοδιότητα λήψης των ενδεικνυομένων μέτρων δίδεται στο Υπουργείο Δημοσίων Έργων που σήμερα έχει μετονομασθεί σε Υπουργείο Υποδομών και Μεταφορών. Ιδρύεται η Υπηρεσία Αποκατάστασης Σεισμοπλήκτων Βορείου Ελλάδος (Υ.Α.Σ.Β.Ε.) που σήμερα έχει μετονομασθεί σε Διεύθυνση Αποκατάστασης Επιπτώσεων Φυσικών Καταστροφών (Δ.Α.Ε.Φ.Κ). Από τα άτοκα στεγαστικά δάνεια και μόνο της αρχικής περιόδου, στην δωρεάν απόκτηση προκατασκευασμένης ή με τυποποιημένο σχέδιο κατοικίας έως 60μ2 του σεισμού Γρεβενών-Κοζάνης το 1995 και στη Στεγαστική Συνδρομή αποτελούμενη κατά 1/3 Δωρεάν Κρατική Αρωγή και κατά 2/3 Άτοκο Δάνειο του σεισμού της Αθήνας το 1999, με ταυτόχρονη επιδότηση ενοικίου ή συγκατοίκησης, ή στη δωρεάν διαμονή πληγέντων σε ξενοδοχειακές μονάδες και Σ.Σ. αποτελούμενη κατά 40% Δωρεάν Κρατική Αρωγή και κατά 60% Άτοκο Δάνειο του σεισμού του Ρεγγίνιου Φθιώτιδας το 2013. Μετά τις φονικές πυρκαγιές του 2018 σε Ανατολική και Δυτική Αττική νομοθετήθηκαν ειδικότερα μέτρα για τους πυρόπληκτους όπως και μετά τις πλημμύρες του 2020 ειδικότερα μέτρα για τους πλημμυρόπληκτους. Στην παρούσα εργασία γίνεται μια προσπάθεια παρουσίασης της εξέλιξης της νομοθεσίας σχετικής με την αποκατάσταση των επιπτώσεων φυσικών καταστροφών.Natural disasters have multiplied in all parts of the world in recent years. The natural disasters that struck Greece were managed superficially by the state and only earthquakes were taken more seriously. The 6.5R earthquake of 20.06.1978 in Thessaloniki was a pivotal point in time, from which begins the passing of laws for the restoration of damage to buildings. The responsibility for taking the appropriate measures is given to the Ministry of Public Works, which today has been renamed the Ministry of Infrastructure and Transport. The Earthquake Rehabilitation Service of Northern Greece (YASVE) is established, which today has been renamed the Directorate for the Rehabilitation of the Impact of Natural Disasters (DAEFK). From the interest-free mortgages of the initial period only, to the free acquisition of a prefabricated or standard housing plan up to 60m2 of the Grevena-Kozani earthquake in 1995 and to the Housing Assistance consisting of 1/3 Free State Aid and 2/3 Interest-free Loan of the earthquake of Athens in 1999, with a simultaneous subsidy for rent or cohabitation, or the free accommodation of victims in hotel units and SS. consisting of 40% Free State Aid and 60% Interest-free Loan of the earthquake of Reginio Fthiotida in 2013. After the deadly fires of 2018 in Eastern and Western Attica, special measures were legislated for the fire victims as well as after the floods of 2020, special measures for the affected . In the present work, an attempt is made to present the evolution of the legislation related to the restoration of the impacts of natural disasters

Effect of CF3H and CF3Br on laminar diffusion flames in normal and microgravity

Chemical inhibition of diffusion flames through addition of halogenated inhibitors is a problem of significant practical and scientific interest. Extensive studies on diffusion flames in microgravity have shown that these flames have significantly different characteristics than those under normal gravity. However, the mechanisms through which inhibitors reach the reaction zone to suppress combustion in diffusion flames and the effectiveness of these compounds under reduced gravity have yet to be investigated. This study reports preliminary results of investigations on the behavior of laminar jet diffusion flames upon the addition of bromotrifluoromethane (CF3Br) and trifluoromethane (CF3H) to the surroundings under normal and microgravity conditions. The results show that the flame structure in microgravity is significantly different from that under normal gravity conditions, and more importantly, that conditions for flame stability are less stringent under microgravity. Experiments show that flames that cannot be stabilized under normal gravity are quite stable under microgravity conditions. In addition, normal gravity experiments at reduced pressure (low buoyancy) did not reproduce the structure or stability limits of inhibited flames in microgravity

The effect of gas phase flame retardants on fire effluent toxicity

Standard industry formulations of flame retarded aliphatic polyamides, meeting UL 94 V-0, have been burned under controlled conditions, and the yields of the major asphyxiants, carbon monoxide (CO) and hydrogen cyanide (HCN) have been quantified. Although both the combination of aluminium phosphinate and melamine polyphosphate, and the combination of brominated polystyrene and antimony oxide, inhibit combustion reactions in the gas phase, this study shows that the phosphorus causes a much smaller increase in the CO and HCN yields than antimony-bromine. The mechanisms of CO and HCN generation and destruction are related to the flame inhibition reactions. Both CO and HCN form early in the flame, and the OH radical is critical for their destruction. Crucial, in the context of the flame inhibition mechanism, is the observation that the phosphorus system reduces the H and O radical concentrations without a corresponding decrease in the OH radical concentration; conversely, the bromine system reduces all three of the key radical concentrations, H, O and OH, and thus increases the fire toxicity, by inhibiting decomposition of CO and HCN. Moreover, while the phosphorus flame retardant is effective as an ignition suppressant at lower temperatures (corresponding to early flaming), this is effect “switches off” at high temperatures, minimising the potential increase in fire toxicity, once the fire develops. Since flame retardants are most effective as ignition suppressants, and at the early stages of flaming combustion, while most fire deaths and injuries result from toxic gas inhalation from more developed fires, it is clearly advantageous to have an effective gas phase flame retardant which only causes a small increase in the toxic product yield

Structure and soot properties of nonbuoyant ethylene/air laminar jet diffusion flames

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77080/1/AIAA-1998-568-769.pd

The Leeds Evaluation of Efficacy of Detoxification Study (LEEDS) project: An open-label pragmatic randomised control trial comparing the efficacy of differing therapeutic agents for primary care detoxification from either street heroin or methadone [ISRCTN07752728]

BACKGROUND: Heroin is a synthetic opioid with an extensive illicit market leading to large numbers of people becoming addicted. Heroin users often present to community treatment services requesting detoxification and in the UK various agents are used to control symptoms of withdrawal. Dissatisfaction with methadone detoxification [8] has lead to the use of clonidine, lofexidine, buprenorphine and dihydrocodeine; however, there remains limited evaluative research. In Leeds, a city of 700,000 people in the North of England, dihydrocodeine is the detoxification agent of choice. Sublingual buprenorphine, however, is being introduced. The comparative value of these two drugs for helping people successfully and comfortably withdraw from heroin has never been compared in a randomised trial. Additionally, there is a paucity of research evaluating interventions among drug users in the primary care setting. This study seeks to address this by randomising drug users presenting in primary care to receive either dihydrocodeine or buprenorphine. METHODS/DESIGN: The Leeds Evaluation of Efficacy of Detoxification Study (LEEDS) project is a pragmatic randomised trial which will compare the open use of buprenorphine with dihydrocodeine for illicit opiate detoxification, in the UK primary care setting. The LEEDS project will involve consenting adults and will be run in specialist general practice surgeries throughout Leeds. The primary outcome will be the results of a urine opiate screening at the end of the detoxification regimen. Adverse effects and limited data to three and six months will be acquired

Experimental review of oxygen content at mixing layer in cone calorimeter

This work aims to elucidate whether the hypothesis of zero oxygen at the mixture layer when flame takes place is assumable for every kind of material. For that purpose, we investigated the oxygen concentration there by cone calorimeter tests. A modified holder was developed in order to collect oxygen in this mixture layer. In addition, thermogravimetric tests were carried out so as to relate the possible effects of the presence of oxygen in the atmosphere where the pyrolysis process takes place, since the cone calorimeter does not allow to control the oxygen level of the atmosphere during the experiment. The reaction rates and per cent of residue in the cone calorimetric tests were measured and compared with the results from thermogravimetric tests. Six products were analysed which can be classified in three main groups: lignocellulosic, thermoplastic polymers and thermoset polymers. Cone calorimetric results showed that for some of the materials analysed (PET, Nylon and PUR foam) the oxygen level at mixture layer decreased until values close to zero. The comparison of reaction rates between cone calorimetric and thermogravimetric tests revealed the char layer created in cone calorimetric tests over the exposed face for brushed fir, Nylon and PET established an important heat barrier that modifies the thermal behaviour of these materials.Authors would like to thank to the Spanish Ministry of Economy and Competitiveness for the PYRODESIGN Project grant, Ref.: BIA2012-37890, financed jointly by FEDER funds