Radiation damages to genes and cells occur at the DNA level, and therefore they are directly related to the spatial distribution of events caused by radiation at nanometer scale. Nanodosimetry ...introduces new quantities to correlate the initial features of radiation interactions and the likelihood of late radiobiological effects by means of Monte Carlo codes and, experimentally, with gas-detectors operating at low pressure.
Within this context, the aim of this work is to develop a numerical approach based on the implementation of different simulation tools to accurately describe the low energy electron transport processes within nanodosimetric devices. This approach was directly applied to perform a proof-of-concept study of the response of the electron collector of the STARTRACK nanodosimeter. Garfield++ was used to simulate the primary track structure of 5.8 MeV He-4 particles, while COMSOL Multiphysics was used to model the geometry and the electrostatic field of the electron collector. Available experimental data, measured with the STARTRACK nanodosimeter, were used to validate Garfield++ nanodosimetric spectrum before proceeding with the simulation of the electron transport stage in the drift volume, again performed with Garfield++. In order to verify the performance and reliability of the implemented codes, the nanodosimetric distributions were studied with the threefold objective of characterizing the time, space, and energy distributions of particles collected at the end of the drift volume. These results can offer a valuable insight into the overall working principle of nanodosimeters: this understanding can be pivotal in optimizing and refining the design of such devices, ultimately extending their effectiveness in particle track characterization during radiation therapy.
•Development of numerical tools for electron transport in low-density gases.•The developed tools are applied to experimental nanodosimetry.•Garfield++ is capable of simulating the track structure of alpha particles.•The results offer an insight to the working principle of the gas electron nanodosimeters.
A new mathematical model for spheroidal droplet heating and evaporation is proposed. This model takes into account the effect of liquid finite thermal conductivity and is based on the previously ...obtained analytical solution for the vapour mass fraction at the droplet surface and a new correlation for the convective heat transfer coefficient incorporated into the numerical code. The heat transfer equation in the liquid phase is solved numerically using the finite-element heat transfer module of COMSOL Multiphysics. It is shown that the lifetime of spheroidal (prolate and oblate) droplets is shorter than that of spherical droplets of the same volume. The difference in the lifetimes of spheroidal and spherical droplets, predicted by the new model, is shown to increase with increasing aspect ratios for prolate droplets and decreasing aspect ratios for oblate droplets. As in the case of stationary spherical droplets, the d2-law is shown to be valid for spheroidal droplets after the completion of the heat-up period. The predictions of this model agree with experimental observations. The duration of the heat-up period is shown to decrease with increasing aspect ratios for prolate droplets and decreasing aspect ratios for oblate droplets. The maximal surface temperatures are predicted near the regions where the surface curvature is maximal. The aspect ratios are shown to be weak functions of time, in agreement with experimental observations.
•A new mathematical model for spheroidal droplet heating and evaporation.•Effect of non-uniform surface temperature on droplet heating and evaporation.•The effect of liquid finite thermal conductivity is considered using COMSOL.•An analytical solution for the vapour mass fraction at the droplet surface is used.•A new correlation for the convective heat transfer coefficient is obtained and used.
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•Energy conversion in a horn type sonicator was investigated under batch and continuous flow.•Acoustic power was varied depending on the liquid properties at a fixed nominal power of ...transducer.•A power relation was proposed for acoustic power prediction as a function of dimensionless groups.•Temperature, Pr and Oh numbers are the mains factors affecting acoustic to nominal power ratio.•Lower thermal energy conversion was obtained in continuous flow compared to batch configuration.
The level of knowledge on the non-thermal contribution of ultrasonic wave’s energy to perform physico-chemical phenomena is one of the bottlenecks for the commercialization purposes. Under constant nominal power of transducer (Pn), the input electrical power (Pin) is less and sensitive to the medium’s physical properties. This study attempts to assess the conversion of acoustic to thermal power experimentally and numerically using COMSOL Multiphysis@ for a 24 kHz horn-type sonicator through a medium without any sono-chemical effect. Single- and homogeneous two-phase Newtonian mixtures of sunflower oil and water (o/w) with a relatively wide range of density (914–998 kg/m3) and viscosity (0.5–63.5 mPa.s) were irradiated in a lab-scale vessel (1 L) under batch and continuous flow configuration. The direct influence of Pn (80–400 W) and o/w ratio (0–1) on temperature rise and subsequent thermo-physical properties of liquid and the indirect influence on Pin and thermal energy conversion (TEC) were investigated employing calorimetric method. A new engineering concept including a power factor correlation was proposed and validated for prediction of Pin as a function of liquid space velocity (ϑ), temperature, Prandtl (Pr) and Ohnesorge (Oh) dimensionless groups. The results showed that under constant temperature and Pn, increasing Pr and Oh increased Pin with a similar trend for both modes of operation. An increase in temperature directly led to a decrease in Pin with a power factor closed to “-1”. The Pin in continuous flow was higher compared to batch configuration at similar temperature, liquid properties, and Pn. This effect was more significant with increasing ϑ. An increase in ϑ at constant Pn led to a decrease in the inlet/outlet temperature difference in continuous flow and an increase in Pin. Increasing Pn resulted in higher TEC for both configurations; however, TEC was relatively lower in continuous flow than batch configuration indicating more efficient sonication in continuous flow.
•Theoretical confirmation of good BDD(·OH) generation in the novel pre-pilot batch reactor.•Faster degradation of ciprofloxacin in sulfate medium at higher j, concentration, and pH.•Degradation ...enhancement in chloride medium by additional attack of active chlorine.•Inhibitory effect of carbonate and humic acid, as well as in tap water and synthetic urine.•Formation of nitrate, nitrite, ammonia, and recalcitrant acetic, oxalic, and formic acids.
This paper presents the theoretical and experimental confirmation of the performance of a novel pre-pilot reactor design implementing a boron-doped diamond (BDD) anode to destroy emerging pollutants by electrochemical oxidation. Turbulent flow simulation and secondary current distribution modeling with a COMSOL Multiphysics software were used to assess the engineering capabilities of the reactor along with the oxidant BDD(·OH) electrogeneration at the anode. The antibiotic ciprofloxacin (CIP) was chosen as model molecule to assess the oxidation power achieved with the pre-pilot batch plant. In sulfate medium where BDD(·OH) was the main oxidant, faster degradation was determined by increasing current density, CIP content, and pH. The effect of pH was explained by the transformation of the cationic form of CIP in acidic medium into its more easily oxidizable anionic form in alkaline medium. In chloride medium, CIP was more rapidly removed by the faster attack of the generated active chlorine. The degradation was decelerated in carbonate medium by its scavenging effect and in the presence of humic acid by its competitive oxidation with BDD(·OH). The antibiotic abatement also dropped down in tap water and synthetic urine. An almost total mineralization was achieved with a constant energy cost per unit COD mass of 0.6 ± 0.1 kWh (g COD)−1. The initial N of CIP was pre-eminently converted into nitrate, alongside nitrite and ammonia to lesser extent. Recalcitrant acetic, oxalic, and formic acids were detected as final carboxylic acids.
This paper presents a comprehensive study on phase-field modelling in COMSOL MultiPhysics for simulating dynamic hydraulic fracturing in porous media based on Biot’s poro-elasticity theory. The focus ...is on addressing the challenges associated with crack width estimation in this context. A new strain-based crack width formulation is proposed, offering improved accuracy in predicting fracture permeability and ease of implementation in numerical approaches. The model’s capabilities are extended to consider dynamic crack propagation by incorporating the kinetic energy in the governing coupled hydro-mechanical-damage equations. The numerical implementations in COMSOL MultiPhysics are thoroughly explained, providing insights into the techniques used to solve the governing equations. Verification examples, including the benchmark KGD verification, are presented to demonstrate the model’s capabilities in simulating hydraulic fractures in porous media and validate its accuracy and reliability. A final numerical example focusing on the dynamics of crack propagation in a gravity dam is simulated, allowing for a comprehensive examination of the model’s performance. The proposed strain-based crack width formulation and consideration of dynamic crack propagation contribute to improved accuracy in predicting fracture permeability.
The present work deals with the development of a semi-transparent photovoltaic thermal (PV-T) solar collector (STPVT) through computational fluid dynamics (CFD) modelling using COMSOL Multiphysics. ...The study was carried out in three stages; firstly, the CFD model was developed for STPVT and validated with experimental data. Secondly, three different configurations of semi-transparent PV-T collector were investigated, i.e., single pass with PV module on top (SPC), double pass with PV module on top followed by glass cover and absorber plate (DPT), and double pass with PV module in between the glass cover and absorber plate (DPS). The absorber plate was incorporated with cross-flow baffles for improved thermal performance due to increased surface area and turbulence. The study found a thermal efficiency of 76.94 % for DPS configuration and a total heat utilisation of 289.63 W at 50 % transparency level, i.e., 2–4 times higher than other configurations. Furthermore, the DPS model was investigated for thermal and electrical performance with different PV module transparency levels (52,42,27,13 %). The DPS with 18 solar cells having 13 % transparency exhibited peak power density (8 %) at 717 W/m2 and 101.89 °C panel temperature, achieving superior thermal efficiency (84 %) and total heat utilisation (315.09 W), surpassing configurations with higher transparency.
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•FE model was developed to predict thermal and electrical performance of hybrid solar collector.•Thermal efficiency of DPS was 48.05–75.32 % higher than STPVT, SPC, DPT.•The thermal and electrical efficiency of DPS-18 was found to be 84 % and 8.31 %.•Power density per unit area from DPS-18 was 15.44–43.19 % higher than DPS-10, DPS-12, DPS-15.
The light trapping performance of Si nanowire with different inclination angles were systematically studied by COMSOL Multiphysics. The inclined nanowires with inclination angles smaller than 60° ...show greater light trapping ability than their counterparts of the vertical nanowires. The Si solar cell with the inclined nanowires of the optimal parameters, whose θ=30°, P=400nm, D=140nm, can achieve a 32.395mA/cm2 short circuit photocurrent density and a 35.655% conversion efficiency. The study of the inclined nanowire provides an effective way for further utilization of the incoming light.
•Inclined nanowire improves Jsc and η.•Mechanism of it.•The Jsc and η is 33.311mA/cm2, 35.655% respectively.
Spark plasma sintering (SPS) is an efficient manufacturing method especially for ultra-high temperature ceramics (UHTCs) such as titanium carbides. Heating mechanism in SPS is a result of high ...electric current in the device including die, punch, and sample powder. Because the temperature distribution in the sintering process has considerable effect on the microstructure of the final sintered sample, in the present work, SPS of a cylindrical sample consist of a titanium carbide was investigated numerically. The governing equations of heat diffusion and electricity distribution in the whole device was solved using finite element method. In the heat diffusion equation, heat generation per volume was considered as a result of electric current in the device. Boundary conditions including radiation heat transfer and convective cooling by water flow were modelled by Stefan-boltzman and Newton cooling laws, respectively. The maximum temperature was observed at the center of the TiC sample. The radial temperature distribution in the sample showed considerable gradient as the minimum and maximum temperatures were 2000 °C and 1920 °C, respectively. Despite the radial direction, vertical temperature gradient was negligible in TiC sintering. Although the highest current density and consequent heat generation were observed at the die/punch interface with the minimum cross section, the maximum temperature of the whole apparatus was at the punch location.
CFD model for tubular SOFC directly fed by biomass Somano, Valentina; Ferrero, Domenico; Santarelli, Massimo ...
International journal of hydrogen energy,
05/2021, Letnik:
46, Številka:
33
Journal Article
Recenzirano
The coupling between biomass gasification and Solid Oxide Fuel Cells can represent a sustainable and efficient system for electricity production. This work aims to develop a preliminary model for the ...operation of a tubular, electrolyte-supported fuel cell (SOFC) fed by a syngas mixture. The fuel required by the SOFC system is produced inside the energy generator box from an integrated biomass gasification system. This study stems from the European DB-SOFC project, that proposed the exploitation of the abundant biomasses deriving from agricultural residues for energetic purposes (as from olive oil and wine production). In this study, the main processes have been simulated to find a possible configuration to obtain a power value of 200 W. 25 cells were used in the model to produce the required power. The results showed that at 0.7 V it is possible to achieve 12.3 W, when the biomass gasification was integrated into the SOFC box, while it was possible to achieve 9.6 W when the system was fed by externally produced syngas.
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•A direct biomass to SOFC system is modelled.•25 single tubular cells are fed by Olive kernel biomass producing 200 We.•12.3 W from single tubular cells are produced with an integrated biomass system.
The energy transition can also be promoted by the sustainable use of biomass. Residual biomass in the Mediterranean areas can be exploited to a greater extent through highly efficient fuel cell ...systems. The Direct Biomass-SOFC project is based on a direct coupling between biomass power supply and SOFC tubular cells. This research project stems from the need to cover the electricity demand, avoiding the use of non-renewable sources. It will be investigated the unused or little-used biomass sources that can be exploited from the Mediterranean area.
To this purpose, analyses were conducted to model a SOFC tubular cell stack by investigating the optimal configuration. The basic objective is to design a SOFC tubular cell stack, fed by syngas to produce at least 200 W. Two configurations were chosen: a square and a circular arrangement. Another objective of the study is to choose the best temperature control system. It have been selected a pressurised water system and an air system. The results show that the best performance is guaranteed by a square arrangement with an air temperature control system. The circular configuration provides less power than the square configuration, being limited by the multiple series connection to the lowest current value. The maximum electrical power produced with the square configuration is 225 W.
•The Direct Biomass SOFC system was developed numerically for 25 tubolar cells.•25 tubolar cells were able to produce 225 W from syngas.•The square tubolar cell arrangement showed better results.•The air temperature control system showed better results.
