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.
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.
•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.
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A dendrite-free and ultra-stable potassium metal composite anode has realized by infusing metallic potassium into a 3D potassiophilic α-MoC modified carbon cloth. Both the density ...functional theory (DFT) calculations and COMSOL Multiphysics demonstrate that the potassiophilic 3D host not only can facilitate fast molten potassium wetting and reduce nucleation overpotential but also homogenize the distribution of current density and inhibit potassium dendrite growth.
•Dendrite-free K metal anode has realized by potassiophilic α-MoC modified host.•3D potassiophilic host reduces nucleation overpotential and inhibits dendrite.•3D potassiophilic host homogenizes the distribution of current density.•DFT and COMSOL demonstrate the effectiveness of 3D potassiophilic host.
Potassium metal anodes are desirable for the advantages of low price, high abundance, and similar standard redox potential with metallic lithium. However, dendritic growth and large volume changes impede its practical application. Herein, a dendrite-free and stable potassium metal composite anode has realized by infusing metallic potassium into an α-MoC modified carbon cloth (α-MoC@CC). The prepared α-MoC@CC as a 3D host exhibits an intrinsic potassiophilicity based on experimental investigations and density functional theory (DFT) calculations, which not only facilitates fast molten potassium wetting but also reduces nucleation overpotential. In addition, the current density distribution of the composite anode carried out by COMSOL Multiphysics reveals that the 3D host can effectively reduce current density and inhibit dendrite growth. Consequently, the K@α-MoC@CC composite anode displays stable plating/stripping profiles for more than 2000 h with low polarization in symmetric batteries. As a practical device application, the K@α-MoC@CC composite anode demonstrates superior suitability when paired with Prussian blue cathode in a full battery. Significantly, this work represents an effective pathway to regulate potassium metal anode towards practical applications.
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.
Analysis of Shell and Tube Heat Exchanger Type Tanujaya, Harto; Riza, Abrar
IOP conference series. Materials Science and Engineering,
12/2020, Letnik:
1007, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The stationary-head prototypes unusually are designed using low cost manufacture and simple construction, without bolt or nut to join both the stationary-head and shell. The shell has four holes to ...supply hot/cold fluid, and next to the tube-sheet hole to supply cold/hot fluid, the position both of them are inside the stationary-head. The calculation of the dimensions of the heat exchanger aims to determine the quality of the heat exchanger based on the overall heat transfer coefficient, impurity factor, and the pressure drop that will occur.Calculations using the LMTD method, obtained that receive heat released has a large unity with time Q, then the heat received by cold fluid is Q = 4565.16 W, LMTD produced also shows the number 20, with a proven factor (F) is 1. Comparison obtained from the calculation of the tube side and shell side is the value of Re generated is greater than the value of Re on the shell side.
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•COMSOL Multiphysics reveal the electric field distribution of synthetic samples.•Discharge channel developed along the magnetite edge and retains the complete form.•Magnetite alters ...the distribution state of electric field within synthetic samples.•Quartz particles hinders the development of certain discharge channels.
Herein, COMSOL Multiphysics is proposed to discuss the electric field distribution of synthetic sample during the high voltage pulse discharge crushing. The pulses number required for high voltage pulse discharge to crush the synthetic sample filled with magnetite is lower than that required for quartz-filled samples. The embedding mode that the magnetite is located on the central line between the high voltage electrode and the grounding electrode of the synthetic sample is most conducive to electrical breakdown of synthetic sample. The discharge channel developed along the magnetite edge and retains the complete crystal form of magnetite. Differences in dielectric constants are responsible for variations in electric field distribution. Magnetite alters the distribution state of electric field within synthetic samples to derive higher electric field intensity and more extensive areas with high electric field intensity. The peak electric field intensity at the interface of magnetite particles is higher than that of quartz. The presence of quartz particles hinders the development of certain discharge channels.
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.
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