Study of the Interaction Between a High-Pressure Jet and Horizontal Tanks using CFD

Accidental high-pressure flammable gas releases are among the most relevant hazards in the process safety, and consequences could be severe. In the recent decades, there have been numerous efforts to study high-pressure jets in open field (i.e., free jets). Easy-to-use mathematical models have been developed, to rapidly assess the main physical variables involved in safety evaluations. However, in a realistic scenario, the accidental leak may involve either the ground or a piece of equipment. As demonstrated by recent works, when a jet interacts with an obstacle, its behavior can significantly change. Therefore, the mathematical models extrapolated for the free jet scenario could be a source of incorrect predictions. Focusing on the scenario of an accidental high-pressure unignited flammable jet, this work shows how the presence of one or two obstacles, placed at a different distance from the source of the leak, can influence the lower flammability limit cloud extent of methane. Varying the height of the source term, the effect of the interaction among the jet, both the obstacles, and the ground was systematically studied through a Computational Fluid Dynamics analysis

Modelling of indoor air pollutants dispersion: New tools

Ventilation systems are used for create a thermally comfortable environment and good indoor air quality. It is therefore essential to have adequate tools for predicting the performance of these systems. Among the various approachs, the computational fluid dynamics could be a useful tool for the design of the ventilation system. When dealing with pollutants dispersion problems, a steady state averaged simulation can be misleading because it is not able to properly predict and model peak concentrations, which can be relevant even if temporary. An interesting approach is the use of LES (Large Eddy Simulations) simulations to obtain a better description of concentrations oscillations. In this framework, the aim of this work is the validation of simulation carried out using the FDS (Fire Dynamic Simulator) software with an actual case study, already studied with a mock-up. Secondly, two new configurations of the ventilation system are proposed, in order to stress the capacity of the software to describe complex and different features, classical of HVAC (Heating, Ventilation and Air Conditioning) systems. Interesting conclusions about efficiency are drawn from the comparison, highlighting the potentiality of the software

Virtual Support for Real-World Movement:Using Chatbots to Overcome Barriers to Physical Activity

Conversational agents (CAs, aka chatbots) for behavioral interventions have great potential to improve patient engagement and provide solutions that can benefit human health. In this study, we examined the potential efficacy of chatbots in assisting with the resolution of specific barriers that people frequently encounter when doing behavioral interventions for the purpose of increasing physical activity (PA). To do this, six common barriers (i.e., things that stand in the way of increasing PA) were targeted (e.g., stress and fatigue), we adopted domain knowledge (i.e., psychological theories and behavioral change techniques) to design six interventions aimed at tackling each of these six barriers. These interventions were then incorporated into consultative conversations, which were subsequently integrated into a chatbot. A user study was conducted on non-clinical samples (n=77) where all participants were presented with three randomly but equally distributed chatbot interventions and a control condition. Each intervention conversation addressed a specific barrier to PA, while the control conversation did not address any barrier. The outcome variables were beliefs in PA engagement, attitudes toward the effectiveness of each intervention to resolve the barrier, and the overall chatbot experience. The results showed a significant increase in beliefs of PA engagement in most intervention groups compared to the control group, and positive attitudes toward the effectiveness of the interventions in reducing their respective barriers to PA, and positive chatbot experience. The results demonstrate that theory-grounded interventions delivered by chatbots can effectively help people overcome specific barriers to PA, thereby increasing their beliefs in PA engagement. These promising findings indicate that chatbot interventions can be an accessible and widely applicable solution for a larger population to promote PA.</p

Multi-obstacles Influence on High-Pressure Methane Jets

Accidental high-pressure unignited jets of methane are one of the most dangerous scenarios investigated in industrial risk analysis. Considering a typical industrial plant, it is common that during the dispersion of a flammable gas cloud it interacts with one or more obstacles like buildings or equipment (e.g., columns, tanks, pipe rack, etc.); such interaction could significantly change the relevant damage areas. Due to this, in the industrial safety framework, empirical integral models elaborating only the free jet scenario could resolve in unreliable evaluations. Assuming the importance to correctly approach the scenario of a jet interacting with a series of obstacles the only numerical model able to properly evaluate any obstacle influence is the Computational Fluid Dynamics (CFD). The aim of this work is to investigate how a series of obstacles, in different configurations, can influence the jet cloud extent. Realistic case-studies of industrial plant are analysed: a stationary jet at various pressure impinging a series of cylindrical vertical tanks placed along the axis release. Sensitivity investigation on the obstacles size and distance is performed with CFD simulations through the software ANSYS® CFX®

Unignited High-Pressure Methane Jet Impinging a Pipe Rack: Practical Tools for Risk Assessment

Although the diffusion of its storage and transport under liquefied conditions, nowadays it is common to have methane in gaseous form in several industrial applications. This leads to safety implications to be considered: hazards are linked to both the high-pressure at which the gas is kept and to its flammability. Scenarios where flammable jets impact an obstacle are of paramount importance because of their possible occurrence. Following a numerical approach, literature shows up that their assessment can be reliably performed by means of only Computational Fluid Dynamics tools. However, despite the improvements of computing power, Computational Fluid Dynamics costs still limit its use in daily risk analysts’ activities. Therefore, considering an accidental jet-obstacle scenario of industrial interest, the present work investigates how a pipe rack can influence the development of a high-pressure methane jet. Based on a Computational Fluid Dynamics analysis, main achievements of this work are a simple criterion able to identify the situations where the pipe rack does not influence the high-pressure methane jet behavior, therefore allowing to identify the scenarios where simpler models can be used (i.e., analytical correlations known for the free jet situation), and, if present, a simple analytical relationship that roughly predicts the influence of the pipe rack without the need of performing complex Computational Fluid Dynamics simulations

Understanding ligand-protein interactions in affinity membrane chromatography for antibody purification

Affinity chromatography with Protein A beads is the current standard for the primary capture of monoclonal antibodies. The high cost of Protein A activated supports, ligand leakage and the limited production capabilities of the bead-based chromatographic process are at the origin of the current research efforts towards feasible alternatives. Synthetic ligands, that mimic the interaction between Protein A and the Fc portion of immunoglobulins, have been immobilized on membrane supports. In this work, regenerated cellulose membranes with immobilized synthetic A2P have been characterized and tested for binding and elution performance using pure polyclonal human IgG solutions as a feed and several buffers for the elution step. A2P is a synthetic ligand obtained from a triazine scaffold, which binds the Fc region of the antibody. The effects of the membrane support and of the spacer arm on the ligand-ligate interaction have been studied in detail. The experimental results have been interpreted on the basis of molecular dynamics simulation of the interaction between IgG and the supported ligand. Molecular models offer in fact the possibility to investigate the nature of the interaction between protein and ligand from an atomistic standpoint, thus supplying information that can be hardly accessed following experimental procedures. MD simulations were performed in explicit water, modelling the membrane as a matrix of overlapped glucopyranose units. Electrostatic charges of the ligand and spacer considered were calculated through ab initio methods to complete the force field used to model the membrane. The simulations enabled to elucidate how the conjunct interactions of surface, spacer and ligand with IgG contribute to the formation of the bond between protein and affinity membrane

Effect of large obstacles on high momentum jets dispersion

Dispersion of toxic and flammable materials from Chemical industries represents a major issue in Risk Analysis; presently, integral models are generally used to assess dispersion consequences, due to the low CPU and time requirements connected to the use of these tools. Nevertheless, they are mainly developed and tuned for releases in open field (open spaces without relevant obstacles), and therefore they cannot properly account for the geometrical features of the dispersion domain. Computational Fluid Dynamic, on the other hand, allows a full 3D analysis, thus accounting for all the obstacles influence on the flow field, but it involves large computational requirements. In case of gas discharge directed towards nearby large obstacles, an impinged jet is expected: if the jet hits a nearby obstacle, the gas velocity suddenly drops, minimizing the inertial dispersion phase, thus reducing the relevant air entrainment and generally increasing the damages distances. Impinged release models are included in some commercial integral models for consequences assessment even if a clear method to decide when to use them is often missing. The aim of this work is to provide a comparison between the two approaches (CFDs vs. integral tools) in predicting damage thresholds for both impinged and non impinged jets. A realistic case-study of industrial interest was set-up and the fine tuning of all the involved models and parameters (turbulence modeling, geometry description, mesh independence, etc.) was finalized

Consequences assessment of an accidental toxic gas release through a cfd tool: Effect of the terrain and major obstacles

The main aim of this study is the establishment of a new methodology for the assessment of terrain and structures geometry effects on gas dispersion. Significant obstacles (such as the plant structures, buildings, or the terrain elevation) play a major role in gas dispersion, due to the eddies, wakes, stagnation and recirculation points they can introduce. A comparison between CFD simulations and integral model predictions have been worked out for a realistic case-study in order to point geometry role in gas dispersion. Moreover, obstacles and terrain geometries are often not available in a suitable format. The proposed methodology uses easy-accessible data (such as SRTM data and geo-referenced aerial photography) to work out the required inputs, to reduce the time and cost associated to CFD modelling and make it practically applicable in industrial cases (design of new installations or assessment of existing ones)

Safety of LPG rail transportation

none6The risk due to the road and rail transportation of liquefied petroleum gas (LPG) is well known. The analysis of historical records evidences that severe scenarios were caused by road or rail accidents involving LPG pressurized tank cars. Consolidated approaches exist for the analysis, the prevention and the mitigation of risk due to the transportation of hazardous materials (HazMat) by road or rail. On June 29th, 2009, an extremely severe transportation accident involving LPG took place in the station of Viareggio, in Italy. A tanker was punctured, releasing its entire content, that ignited causing an extended and severe flash-fire, that set on fire several houses, causing extended damage and 31 fatalities. The present study focused on the analysis of the consequences of the event and on the evaluation of the effectiveness of the safety barriers now present along the railway. Once the accident has been simulated and the CFD model validated with the actual damage map, the same approach has been used to test the effectiveness of the safety wall that has been built, after the accident, by Viareggio’s municipality to protect the houses near to the railway line.mixedV. Busini; M. Pontiggia; M. Derudi; G. Landucci; V. Cozzani; R. RotaV. Busini; M. Pontiggia; M. Derudi; G. Landucci; V. Cozzani; R. Rot

Comparison of CALPUFF and AERMOD models for odour dispersion simulation

Different types of models can be used to simulate the odour dispersion into the atmosphere. This work aims to compare two dispersion models that are widely used for regulatory purposes (Dresser and Huizer, 2011): the steady-state, U.S. Environmental Protection Agency (EPA) model AERMOD, and the non-steady-state puff model CALPUFF. The comparison focuses on how meteorological conditions (i.e., stable vs. instable conditions) and source type (i.e., point vs. area source) affect the modelling results, thereby allowing to analyse the differences based on the characteristic dispersion equations of the two above mentioned models