Numerical investigation of the aerodynamic breakup of diesel droplets under various gas pressures

[EN] Abstract The present study investigates numerically the aerodynamic breakup of Diesel droplets for a wide range of ambient pressures encountered in engineering applications relevant to oil burners and internal combustion engines. The numerical model solves the Navier-Stokes equations coupled with the Volume of Fluid (VOF) methodology utilized for capturing the interface between the liquid and the surrounding gas. An adaptive local grid refinement technique is used to increase the accuracy of the numerical results around the interface. The Weber (We) numbers examined are in the range of 14 to 279 which correspond to bag, multimode and sheet-thinning breakup regimes. Model results are initially compared against published experimental data and show a good agreement in predicting the drop deformation and the different breakup modes. The predicted breakup initiation times for all cases lie within the theoretical limits given by empirical correlations based on the We number. Following the model validation, the effect of density ratio on the breakup process is examined by varying the gas density (or equivalently the ambient pressure), while the We number is kept almost constant equal to 270; ambient gas pressure varies from 1 up to 146bar and the corresponding density ratios (ε) range from 700 down to 5. Results indicate that the predicted breakup mode of sheet-thinning remains unchanged for changing the density ratio. Useful information about the instantaneous drag coefficient (Cd) and surface area as functions of the selected non-dimensional time is given. It is shown that the density ratio is affecting the drag coefficient, in agreement with previous numerical studies.Financial support from the MSCA-ITN-ETN of the European Union’s H2020 programme, under REA grant agreement n. 675676 is acknowledged.Stefanitsis, D.; Malgarinos, I.; Strotos, G.; Nikolopoulos, N.; Kakaras, E.; Gavaises, M. (2017). Numerical investigation of the aerodynamic breakup of diesel droplets under various gas pressures. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 1052-1059. https://doi.org/10.4995/ILASS2017.2017.4690OCS1052105

A review of key environmental and energy performance indicators for the case of Renewable Energy Systems when integrated with storage solutions.

During the last years a variety of numerical tools and algorithms have been developed aiming at quantifying and measuring the environmental impact of multiple types of energy systems, as those based on Renewable Energy Sources. Plenty of studies have proposed the use of a Life Cycle Assessment methodology, to determine the environmental impact of renewable installations when coupled with storage solutions, based on a pre-selected repository of Key Performance Indicators. The main scope of this paper is to propose a limited number of best fitting, and at the same time easily adaptable to various configurations, list of KPIs for the case of renewable energy systems. This is done by capitalizing on the environmental and energy performance KPIs tracked in the open literature (e.g. “Global Warming Potential”, “Energy Payback Time”, “Battery Total Degradation”, “Energy Stored on Invested”, “Cumulative Energy Demand”) and/or other proposing new simple, scalable and adaptable ones, (e.g. “Embodied Energy for Infrastructure of Materials and for the building system”, “Life Cycle CO2 Emissions”, “Reduction of the Direct CO2 emissions”, “Avoided CO2 Emissions”, “CO2 equivalent Payback Time”). Moreover, the proposed KPIs are distributed according to the individual phases of the entire life-cycle of a related component of a renewable energy system, each time the environmental impact refers to, i.e. manufacturing, operational and end-of-life. Apart from that, the current paper presents a necessary base grounded approach, which can be followed for a holistic approach in environmental point of view of renewable-based technologies, by addressing the potential competing interests of the relevant stakeholders (e.g. profit for the market operator in contrast to low-cost services for the consumer). All in all, the scalar quantification of the environmental impact of multiple energy systems, through a list of proposed assessment criteria, being evaluated in terms of the selected repository of KPIs, enables the comparison on a fair basis of the available energy systems, irrespective if they are fossil-fuel or RES based ones. As a typical example, a simple standard model of a photovoltaic integrated with an electric battery is selected, for which indicative indicators are provide

Intensive Care Management of The Critically Ill Elderly Population: The Case of ‘Sotiria’ Regional Chest Diseases Hospital of Athens, Greece

The aim of this study was to assess the characteristics and short-term outcome of elderly patients admitted to the ICU of ‘Sotiria’ Regional Chest Diseases Hospital of Athens. We examined retrospectively the records of 344 patients aged ≥70 years old admitted to the ICU of a tertiary hospital during a five-year period, from 2009-2013. We reported demographic and clinical data, length of ICU stay, need for mechanical ventilation and ICU mortality. Among 1730 admitted to the ICU during this period, the elderly comprised 344 (19.8%). The main causes of ICU admission were Chronic Obstructive Pulmonary Disease (COPD) exacerbation (n=169), postoperative respiratory failure (n=78), acute respiratory failure of various etiologies (n=76) and cardiogenic pulmonary edema (n=25). Overall mortality rate of elderly patients was 41.5%. According to age groups, 200 patients were 70-74 years old with a mortality rate of 47%, 42 patients were 80-84 years old presenting a mortality rate of 28.5%, while 14 patients aged over 85 years old, presented a mortality of 42.8%. The mean length of ICU stay (LOS) for the elderly patients was 11.2 days, while the corresponding LOS value for younger patients was 8.1 days. Elderly patients present highest mortality than younger population. However, mortality does not correlate exclusively with advancing age over 70 years, but mostly with the underlying disease. Therefore, age should not be the sole determinant of ICU admission

Effect of Steaming on Waste-Derived Zeolite ZSM-5 as Methanol-To-Hydrocarbons Catalyst

The valorization of low-grade industrial residues into valuable materials has been a way to reduce the impact of the industry on planetary boundaries. Silicon-rich wastes have been used for zeolite synthesis while the impurities originating from wastes have a vital role in the physicochemical properties and the catalytic performance of waste-derived zeolites. Here, the effect of steaming and the impact of impurities on waste-derived zeolites were investigated. Steamed waste-derived zeolite ZSM-5 maintained their structure while their Brønsted acidity was decreased significantly due to dealumination. Electron paramagnetic resonance revealed that steaming of the samples resulted in the re-dispersion of Fe impurities phases. The waste-derived zeolites exhibited a high amount of weak and intermediate acidity upon steaming. Interestingly, the waste-derived sample with a higher amount of impurities had an increase in Lewis acidity upon steaming, while catalytic testing in the Methanol-to-Hydrocarbons reaction exhibited 10 % higher conversion and 4 % in propylene yield

Simulation of a CFB Boiler Integrated With a Thermal Energy Storage System During Transient Operation

In the current work, a transient/dynamic 1-dimensional model has been developed in the commercial software APROS for the pilot 1 MWth CFB boiler of the Technical University of Darmstadt. Experiments have been performed with the same unit, the data of which are utilized for the model validation. The examined conditions correspond to the steady-state operation of the boiler at 100, 80, and 60% heat loads, as well as for transient conditions for the load changes from 80 to 60% and back to 80%. Fair agreement is observed between the simulations and the experiments regarding the temperature profiles in the riser, the heat extracted by the cooling lances, as well as the concentration of the main species in the flue gases; a small deviation is observed for the pressure drop, which, however, is close to the results of a CFD simulation run. The validated model is extended with the use of a thermal energy storage (TES) system, which utilizes a bubbling fluidized bed to store/return the particles during ramp up/down operation. Simulations are performed both with and without the use of TES for the load path 100–80–60–80–100%, and the results showed that the TES concept proved to be superior in terms of changing load flexibility, since the ramp up and down times proved to be much faster, and lower temperature drops between the loads are observed in this case

Alumina binder effects on the hydrothermal stability of shaped zeolite-based catalyst bodies

The development of shaped zeolite-based catalyst bodies with high performance for the production of fuels and chemicals requires the addition of binder materials. Thus, alumina binder effects and their impact on the hydrothermal stability are crucial for shaped catalyst bodies and their catalytic performance in the methanol-to-hydrocarbon (MTH) reaction. Here, a side-by-side comparison of zeolite powder and zeolite-alumina catalyst extrudates is made to elucidate the effect of the extrusion process and/or the hydrothermal treatments in combination with the binder effects. Characterization of the acidic properties was carried out with Fourier-transform infrared (FT-IR) spectroscopy to understand the role of the binder material. It was found that the alumina binder increases the Lewis acidity, while it protects the zeolite material from dealumination during the hydrothermal treatments. Testing of the samples, before and after steaming, showed that the extrusion and steaming lead to a more stable and selective catalyst material, while altering the physicochemical properties of the alumina binder plays a crucial role in achieving the optimal ethylene-to-propylene ratio. Operando UV-vis diffuse reflectance spectroscopy (DRS) revealed the higher formation of conjugated polyaromatic species for the technical catalyst bodies. This study illustrates the impact of the extrusion process and the binder material in combination with the hydrothermal treatments and the major effect of the binder properties on the physicochemical properties and the product distribution

Impact of the location of magnesium in zeolite-based shaped catalyst bodies on the methanol-to-hydrocarbons process

One of the main challenges for the chemical industries is finding new ways to produce lower olefins, such as propylene and ethylene, to satisfy the increase in demand for e.g., polymers, namely polypropylene and polyethylene. The Methanol-to-Hydrocarbons (MTH) process is an alternative manufacturing process that can help to address this increasing demand for these important chemical building blocks. It has been proposed that the addition of magnesium to zeolites, in the form of powdered catalyst materials, enhances the selectivity towards light olefins. In this work, the impact of the location of magnesium (present as Mg2+ and MgO) in zeolite-based shaped catalyst bodies on their physicochemical properties and catalytic performance in the MTH reaction has been studied. By adjusting one of the preparation steps of the overall extrusion process in which magnesium is added tuning the location of magnesium, higher interaction between magnesium and the zeolite material could be achieved. Pre-extrusion modification showed the most favorable results in terms of physicochemical properties and catalytic activity. We found that the magnesium location could be crucial for altering molecular transport, coke formation, and catalyst deactivation during the MTH reaction due to its pronounced effects on the acidity as well as porosity of the shaped catalyst bodies. These new insights can be applied to other zeolite-based extrudate materials and other acid-catalyzed reactions as it can be crucial for the design of better and more efficient catalyst materials in their industrially shaped form

Role of Titanium in Ti/SiO2-Supported Metallocene-based Olefin Polymerization Catalysts. Part 2: Particle Fragmentation

A commercial SiO2 modified by the addition of a TiO2 layer on its surface and pore walls offers a support for metallocene-based ethylene polymerization catalysts with a 35 % improved catalytic activity. The effect of such support modification on the catalyst particle fragmentation during polymerization reactions were assessed. This was performed by exposing the internal cross-section of several SiO2 and Ti/SiO2-based metallocene catalyst particles, polymerized at a wide range of reaction conditions, with a Focused-Ion Beam Scanning Electron Microscope (FIB-SEM), followed by a semi-quantitative analysis of polymer, catalyst and macropores of each 2D image obtained. The titanation of the SiO2 lead to a support framework that fractures earlier and more efficiently. This was evidenced by the presence of several empty (polymer-free) cracks along the support dense-shell, found more extensively in the Ti-modified polymerized catalyst particle, which also resulted in a more sustained polymerized particles macroporosity during the course of the reaction