Modeling Formic Acid Combustion

Nowadays, the knowledge of the gas-phase chemistry of formic acid is paramount for several industrial sectors, including energy supply and the production of bulk chemicals. In this work, a simplified kinetic mechanism and a detailed kinetic mechanism deriving from a rate-based selection algorithm were developed and tested against experimental data available in the literature. The former contains 141 species and 453 reactions, whereas the latter comprises 90 species and 1047 reactions. A focus on a low initial temperature (i.e., up to 500 K) was provided by comparing the numerical estimations with laminar burning velocity and jet-stirred measurements at several conditions. A good agreement among numerical predictions and experimental data was observed, especially for the simplified kinetic mechanism. The accuracy of the generated mechanism allowed for further analysis of the chemistry of the system, enlightening some determining aspects of the chemistry of formic acid. The produced mechanism can be also intended as per seed mechanism for the generation of kinetic models focused on the chemistry of biofuels. Indeed, the characterization of chemical aspects of formic acid occurring in an oxidative environment is crucial due to its relevance as an energy vector as well as an intermediate compound in the decomposition of larger hydrocarbons and bio-oil

Hydrogen Refueling Stations: Prevention and Scenario Management. Large Scale Experimental Investigation of Hydrogen Jet-Fires

Hydrogen is becoming an attractive alternative for energy storage and transportation, because of the elevated energy content per unit of mass and possibility to have zero carbon-emission vehicles. For these reasons, hydrogen's share in global market is expected to grow substantially in the coming years. Today, hydrogen-fueled buses and cars are already available, and several refueling stations are operating in different countries around the world. A key role of the deployment of hydrogen fueled-vehicles is the presence of a widespread network of refueling stations, especially close to residential and industrial areas. This fact poses attention to the safety aspects related to hydrogen, with particular interest to its high flammability that can lead to catastrophic consequences for personnel and equipment. As a matter of fact, hydrogen is a comparatively less safe fuel compared to conventional fuels such as gasoline and diesel. Hydrogen infrastructures are characterized by operating pressure up to 1000 bar that, in case of an unintended loss of containments, produce a highly under expanded turbulent jet. If ignited, this hydrogen jet may give rise to very severe scenarios, mainly related to high temperatures and the oriented flows. As recently suggested by Moradi and Groth (Moradi and Groth, 2019), there is a lack of experimental and on-site data for almost all of the storage and delivery technologies relevant to the hydrogen infrastructures. Experimental data is vital to support model validation, especially in the case of the very peculiar combustion process of hydrogen. In this way, a real-scale experimental campaign is proposed to investigate the main characteristic of the hydrogen jet fire resulting from its rapid fired depressurizations. Focus of the experimental campaign is evaluation of safety distance for person and device (i.e. pressurized tanks) in order to avoid critical conditions and domino effects in real refueling station. Different initial conditions, i.e., storage pressures, are exploited, and the resulting jet across specified orifice is investigated. More specifically, temperatures at various locations are measured through an arrangement of thermocouples. Values up to 1200 °C were obtained in the core of the jet. Moreover, it was found that the recorded temperatures, especially those at the outer portion of the jet, are very sensitive to the initial conditions

Shedding light on typical species : implications for habitat monitoring

Habitat monitoring in Europe is regulated by Article 17 of the Habitats Directive, which suggests the use of typical species to assess habitat conservation status. Yet, the Directive uses the term “typical” species but does not provide a definition, either for its use in reporting or for its use in impact assessments. To address the issue, an online workshop was organized by the Italian Society for Vegetation Science (SISV) to shed light on the diversity of perspectives regarding the different concepts of typical species, and to discuss the possible implications for habitat monitoring. To this aim, we inquired 73 people with a very different degree of expertise in the field of vegetation science by means of a tailored survey composed of six questions. We analysed the data using Pearson's Chi-squared test to verify that the answers diverged from a random distribution and checked the effect of the degree of experience of the surveyees on the results. We found that most of the surveyees agreed on the use of the phytosociological method for habitat monitoring and of the diagnostic and characteristic species to evaluate the structural and functional conservation status of habitats. With this contribution, we shed light on the meaning of “typical” species in the context of habitat monitoring

Evolving trends in the management of acute appendicitis during COVID-19 waves. The ACIE appy II study

Background: In 2020, ACIE Appy study showed that COVID-19 pandemic heavily affected the management of patients with acute appendicitis (AA) worldwide, with an increased rate of non-operative management (NOM) strategies and a trend toward open surgery due to concern of virus transmission by laparoscopy and controversial recommendations on this issue. The aim of this study was to survey again the same group of surgeons to assess if any difference in management attitudes of AA had occurred in the later stages of the outbreak. Methods: From August 15 to September 30, 2021, an online questionnaire was sent to all 709 participants of the ACIE Appy study. The questionnaire included questions on personal protective equipment (PPE), local policies and screening for SARS-CoV-2 infection, NOM, surgical approach and disease presentations in 2021. The results were compared with the results from the previous study. Results: A total of 476 answers were collected (response rate 67.1%). Screening policies were significatively improved with most patients screened regardless of symptoms (89.5% vs. 37.4%) with PCR and antigenic test as the preferred test (74.1% vs. 26.3%). More patients tested positive before surgery and commercial systems were the preferred ones to filter smoke plumes during laparoscopy. Laparoscopic appendicectomy was the first option in the treatment of AA, with a declined use of NOM. Conclusion: Management of AA has improved in the last waves of pandemic. Increased evidence regarding SARS-COV-2 infection along with a timely healthcare systems response has been translated into tailored attitudes and a better care for patients with AA worldwide

How future surgery will benefit from SARS-COV-2-related measures: a SPIGC survey conveying the perspective of Italian surgeons

COVID-19 negatively affected surgical activity, but the potential benefits resulting from adopted measures remain unclear. The aim of this study was to evaluate the change in surgical activity and potential benefit from COVID-19 measures in perspective of Italian surgeons on behalf of SPIGC. A nationwide online survey on surgical practice before, during, and after COVID-19 pandemic was conducted in March-April 2022 (NCT:05323851). Effects of COVID-19 hospital-related measures on surgical patients' management and personal professional development across surgical specialties were explored. Data on demographics, pre-operative/peri-operative/post-operative management, and professional development were collected. Outcomes were matched with the corresponding volume. Four hundred and seventy-three respondents were included in final analysis across 14 surgical specialties. Since SARS-CoV-2 pandemic, application of telematic consultations (4.1% vs. 21.6%; p < 0.0001) and diagnostic evaluations (16.4% vs. 42.2%; p < 0.0001) increased. Elective surgical activities significantly reduced and surgeons opted more frequently for conservative management with a possible indication for elective (26.3% vs. 35.7%; p < 0.0001) or urgent (20.4% vs. 38.5%; p < 0.0001) surgery. All new COVID-related measures are perceived to be maintained in the future. Surgeons' personal education online increased from 12.6% (pre-COVID) to 86.6% (post-COVID; p < 0.0001). Online educational activities are considered a beneficial effect from COVID pandemic (56.4%). COVID-19 had a great impact on surgical specialties, with significant reduction of operation volume. However, some forced changes turned out to be benefits. Isolation measures pushed the use of telemedicine and telemetric devices for outpatient practice and favored communication for educational purposes and surgeon-patient/family communication. From the Italian surgeons' perspective, COVID-related measures will continue to influence future surgical clinical practice

Ultra-Low Temperature Partial Oxidation: Detailed Kinetics, Safety, and Environmental Issues

The innovation in several industrial sectors has been recently characterized by the need for reducing the operative temperature either for economic or environmental related aspects. Promising technological solutions require the acquisition of fundamental-based knowledge to produce safe and robust systems. In this sense, reactive systems often represent the bottleneck. For these reasons, this work was focused on the integration of chemical (i.e., detailed kinetic mechanism) and physical (i.e., computational fluid dynamics) models. A theoretical-based kinetic mechanism mimicking the behaviour of oxygenated fuels and their intermediates under oxidative conditions in a wide range of temperature and pressure was developed. Its validity was tested against experimental data collected in this work by using the heat flux burner, as well as measurements retrieved from the current literature. Besides, estimations deriving from existing models considered as the benchmark in the combustion field were compared with the newly generated mechanism. The latter was found to be the most accurate for the investigated conditions and fuels. Most influential species and reactions on the combustion of butyl acetate were identified. The corresponding thermodynamic parameter and rate coefficients were quantified through ab initio calculations. A reduced detailed kinetic mechanism was produced and implemented in an open-source computational fluid dynamics model to characterize pool fires caused by the accidental release of aviation fuel and liquefied natural gas, at first. Eventually, partial oxidation processes involving light alkenes were optimized following the quick, fair, and smoot (QFS) paradigm. The proposed procedure represents a comprehensive and multidisciplinary approach for the construction and validation of accurate models, allowing for the characterization of developing industrial sectors and techniques

Accidental Combustion Phenomena at Cryogenic Conditions

The presented state of the art can be intended as an overview of the current understandings and the remaining challenges on the phenomenological aspects involving systems operating at ultra-low temperature, which typically characterize the cryogenic fuels, i.e., liquefied natural gas and liquefied hydrogen. To this aim, thermodynamic, kinetic, and technological aspects were included and integrated. Either experimental or numerical techniques currently available for the evaluation of safety parameters and the overall reactivity of systems at cryogenic temperatures were discussed. The main advantages and disadvantages of different alternatives were compared. Theoretical background and suitable models were reported given possible implementation to the analyzed conditions. Attention was paid to models describing peculiar phenomena mainly relevant at cryogenic temperatures (e.g., para-to-ortho transformation and thermal stratification in case of accidental release) as well as critical aspects involving standard phenomena (e.g., ultra-low temperature combustion and evaporation rate)

Comparison and validation of detailed kinetic models for the oxidation of light alkenes

The increasing interest in light alkenes oxidation for the development of detailed kinetic model is mainly due to their relevance in the combustion chemistry of most common fuels and their formation in the oxidation of higher alkanes. This study analyses the detailed kinetic mechanisms for the oxidation of linear lighter alkenes, ethylene, propylene and 1-butene, through the comparison of several combustion kinetic models retrieved from current literature with respect to the experimental data for the laminar burning velocity in air, and for the ignition delay time, by varying either reactant concentration or initial temperature. The mechanisms by University of California, San Diego (UCSD), Konnov group (KOM), University of Southern California (USC), Saudi Aramco 2.0 (SAM), Lawrence Livermore National Laboratory (LLNL), and Politecnico of Milano (CRECK) have been evaluated through a unified statistical analysis. A sensitivity analysis for the laminar burning velocity was also performed to assess and compare the reactions described in the studied models and sort by relevance. Best fits are produced by the LLNL and the UCSD model even if the optimal results can depend on the specific hydrocarbon. We then produced a new mechanism by adding the UCSD for C3 and LLNL for C4 or more, which resulted to work better

Numerical simulation of multi-component LNG pool fire

The release of large amount of liquefied natural gas from fixed or mobile equipment may induce to pool fire when immediate ignited. The prediction and simulation of this phenomenon is very complex because several premixed, convective and diffusive burning phenomena, and rapid phase evaporation, are involved simultaneously. Nevertheless, the use of Reynolds-averaged Navier-Stokes (RANS) equations with k-\u3b5 model for turbulence and classical models are still adopted, although strong uncertainties and over-simplifications with respect to the real scenario. More recently large-eddy simulation (LES) modeling, as adopted in some codes as FLUENT or FDS, has been adopted. LES methodology is able to introduce more detailed information on the chemical kinetic of the oxidation reactions. Again, however, poor kinetic combustion mechanisms suitable for the implementation in computational fluid dynamic (CFD) codes, and simplified composition for the LNG - often treated as pure methane - are typically adopted. In this work, the simulation of a LNG pool fire was performed by detailed (reduced) kinetic model validated for multi-component LNG compositions by using FDS. Results were compared with both experimental and numerical analyses retrieved from literature. This approach has the potential to correctly estimate the heat radiation and the production rates of the main reaction products, including soot. Copyright \ua9 2019, AIDIC Servizi S.r.l