Mass Fraction Distribution Research Articles

Effect of different exhaust parameters on NO conversion efficiency enhancement of a dual-carrier catalytic converter in the gasoline engine

The high NO2 concentration in the gasoline engine exhaust gas is beneficial to improve the regenerative equilibrium performance of the catalytic particulate filter regeneration system. In this work, the effect of exhaust parameters on NO conversion efficiency of a dual-carrier catalytic converter is simulated. The reliable operating temperature range and NO2 mass fraction distribution of dual-carrier catalytic converter under different exhaust parameters are analyzed and the simulation results are verified by the experimental values. The main results are presented as follows: (1) The maximum of NO conversion efficiency is 68% when the exhaust gas temperature is 600 K. (2) The maximum value of NO conversion efficiency is increased by 30% when the exhaust gas flow is reduced from 0.025 kg/s to 0.01 kg/s (3)The maximum value of NO conversion efficiency is increased by 14% when the oxygen concentration from the exhaust is increased from 1.4% to 5%. (4) The orthogonal experimental results show that when the exhaust gas temperature is constant at 600 K, the exhaust gas flow has the most significant influence on the NO conversion efficiency. Finally, some guidelines are proposed to improve the NO conversion efficiency of the dual-carrier catalytic converter.

Tracing water mass fractions in the deep western Indian Ocean using fluorescent dissolved organic matter

The meridional distributions of fluorescent dissolved organic matter (FDOM) and various hydrologic properties were investigated along 67°E in the western Indian Ocean. Our results showed that the highest fluorescence of the humic FDOM (FDOMH) was discovered in the Indian Deep Water (IDW), and relatively lower values were observed in the intruding water masses from the upper layer (e.g., Circumpolar Deep Water (CDW), Antarctic Intermediate Water (AAIW), and South Indian Central Water (SICW)). The deep FDOMH was robustly correlated with apparent oxygen utilisation (AOU), as suggested by previous studies. In particular, the slopes of the regression line AOU on FDOMH varied for different water masses and the two humic components. In this study, to identify the factor inducing the variations of the slope, we estimated the relative water mass fraction of different water masses using a three-end-member mixing model with a salinity-FDOMH diagram. The distribution of water mass fractions was in good agreement with water mass distribution from the conventional method from temperature and salinity distribution and previous studies. The FDOMH components were positively correlated with the aged water mass fraction (i.e., IDW; r = 0.93) and negatively correlated with fresher ones originating from the upper water (r = −0.93, −0.51, and − 0.95 for CDW, AAIW, and SICW, respectively). The fluorescence ratio between the two FDOMH components was also observed to be linked to the water mass fractions. The results indicate that the distribution of FDOMH is attributed to the mixing of various deep-water masses during the global ocean circulation.

A Computational Modeling of the Influence of Different Oxy-fuel Combustion Environment on Combustion Characteristics and Particles Temporal History

ABSTRACT In the present article, CFD simulation of various oxy-fuel combustion cases has been performed to find out the influences of oxy-fuel combustion environment on temperature distribution, char consumption, radiative properties and temporal variation of particle phase variables such as particle temperature, volatile and char mass fraction. The oxy-fuel combustion cases are obtained by varying O2 and CO2 concentrations while keeping the total volume flow rate constant. Four oxy-fuel cases are considered in the present work having oxygen concentration 21%, 25%, 30%, and 35%. The present article also investigates the influence of char gasification reactions on temperature distribution, species concentration and temporal profile of particle char mass fraction. The predicted temperature distribution and radiative properties under oxy-fuel cases are compared with the corresponding values obtained under air-fired combustion as for retrofit existing power plants comparable values are desirable. The oxy-30 case having 30% oxygen has almost identical temperature and radiative profiles. With an increase in oxygen concentration in oxy-fuel cases leads to an increased peak temperature and surface incident radiation due to the rise in local stoichiometry, which results in enhanced reaction kinetics and burning rate. The peak temperature obtained in oxy-25, oxy-30 and oxy-35 cases is around 10%, 18%, and 24% higher than the oxy-21 case. Reduced char burnout time is obtained due to the presence of gasification reactions.

Novel approach for adaptive coefficient tuning for the simulation of evaporating high-speed sprays injected into a high-temperature and high-pressure environment

Producing reliable in-cylinder simulations for quick-turnaround engine development for industrial purposes is a challenging task for modern computational fluid dynamics, mostly because of the tuning effort required for the sub-models used in the various frameworks (the Reynolds-averaged Navier–Stokes and large eddy simulation). Tuning is required because of the need for modern engines to operate under a wider range of conditions and fuels. In this article, we suggest a novel methodology based on automated simulation parameter optimisation that is capable of delivering a priori a coefficient matrix for each operating condition. This approach produces excellent results for multiple comparison metrics like liquid and vapour penetration lengths, radial and axial mass fraction and temperature distributions. In this article, we also show for the first time that input model coefficients can potentially be linked to ambient boundary conditions in a physically consistent manner. Changes in injection pressure, charge pressure and charge density are considered. This paves the way for the tabulation of the constants in order to eliminate lengthy tuning iterations between operating conditions and move towards adaptive simulations as the piston moves changing the in-cylinder conditions. An additional discussion is performed for the validity range of existent models given that in recent years there has been a shift towards more extreme thermodynamic conditions in the injection stage (reaching the limits of transcritical flows). Although in this work the framework was implemented in the Reynolds-averaged Navier–Stokes context because this is the tool of preference of digital engineering currently by automotive industries, the approach can be easily extended in large eddy simulation.

Failure mechanism of thermal barrier coatings of an ex-service aero-engine combustor

Failure mechanism analysis of thermal barrier coatings (TBCs) on an ex-service aero-engine combustor is carried out. Microstructure, chemical composition, phase composition, and Young's modulus of TBCs are detected for three typical spallation areas as well as an as-sprayed sample for reference. A fluid-structure interaction simulation for the turbulent combustion is conducted to obtain the working temperature, fuel impurities mass fraction and dust particles erosion rate distribution on the TBCs surface. Results show that the maximum working temperature, the impurity mass fraction, and the sucked-in dust erosion rate correspond to the spallation at the outer liner complementary combustion zone (CCZ), the outer liner primary combustion zone (PCZ), and the inner liner of CCZ respectively. It is found the failure of TBCs at outer liner of CCZ is caused by high-temperature sintering, the infiltration of deposits is the main reason for the failure of TBCs at outer liner of PCZ, and the combination of sintering and particles impact is responsible for the failure of TBCs at inner liner of CCZ. Besides, the accumulation of inelastic strain in the vicinity of thermally growth oxide (TGO) caused by thermal stress may lead to formation and propagation of cohesive interfacial cracks.

Enhancement of the melting process in the thermal energy storage system by using novel geometry

Latent heat thermal energy storage systems (LHTESS) store more considerable heat than sensible heat thermal energy storage systems in the same volume due to the phase change. However, latent heat storage systems suffer from low thermal conductivity. In this work, a novel geometry is used to enhance the heat transfer and reduce the melting process time in the LHTESS by increasing the interface area between the HTF and PCM. The numerical method by using ANSYS Fluent software is used to study the melting rate and the distribution of temperature, velocity, and mass fraction. Also, the convective heat transfer is considered in the melt PCM. The results show that the PCM in the novel system melts during the first 900 seconds, whereas the state-of-the-art LHTESS needs 2,700 seconds. Therefore, the required melting time for the novel system is one-third that for the currently used one.

Analytical and numerical studies of mass flux dispersed from tapered swirl atomizer with various nozzle cut profiles

Spraying dispersed fluid by swirl atomizer into a main gas stream in order to obtain homogeneous blended flow within a restricted distance from the atomizer position is a significant issue. The dispersal of sprayed fluid mass-flux from the atomizer should be correlated to mass flux distribution of the main flow gas. Consequently, it is essential to control the distribution of liquid mass flux from the injector to match the distribution of main gas flux to attain perfect mixing with identical liquid/gas mass flux ratio all over the pipe. The present study examines the liquid mass flux pattern injected from tapered swirl atomizer having various cut shapes. A mathematical approach to circumferentially evaluate the outlet mass fraction distribution from generalized tapered nozzle cut was analyzed. The derived mass fraction distribution equation is dependent on the flow-angle, the cut-angle, and the arc-angle. A CFD simulation was performed to evaluate the flow angle at the outlet from the nozzle cut. The finding of the present work delivers a guide for researchers and engineers to the preferred injector cut profile to give the best mass flux uniformity. The simulated spray pattern relied on circumferential mass flux at nozzle outlet has been in great coincidence with what depicted by imaging. More studies could be performed to have the most appropriate cut shape of the injector with various flow profiles of the main gas stream.

Multi-Scale Modeling of Anode-Supported Solid Oxide Fuel Cell

Three-dimensional comprehensive model of micro-scale transport in positive electrode/ electrolyte/negative electrode(PEN) and macro-scale transport in gas channel of anode supported SOFCs (solid oxide fuel cells) is developed in object-oriented CFD code Open Field Operation and Manipulation (OpenFOAM). The numerical procedure consists of calculations of complex phenomena which are fully coupled together with electrochemical reaction kinetics, mass balance, and energy balance, interacting between porous PEN structure and fluid gas channel. Computational fluid dynamics (CFD) was performed in flow channels with calculations of mass balance and continuum micro-scale model were used to predict the electrochemical characteristics in PEN. The distributions of current density and mass fraction are employed to suggest a dependency. To validate our numerical model, we compare the simulated results with experimental data at intermediate temperatures. This study provides detailed information of heat and mass transport phenomena with electro-chemical characteristics for intermediate temperature SOFCs.

Numerical Simulation and Optimization of Staged Combustion and NOx Release Characteristics in Precalciner

In order to study the combustion characteristics in a precalciner, the temperature and composition field in a typical Trinal-sprayed calciner were numerically analysed. The results obtained by simulation were compared to actual measurements and the simulated results were in good agreement with the measured ones. The results indicated that the aerodynamic flow field in the precalciner is satisfactory, and a symmetrical reflux occurs in the shrinkage zone of the precalciner because of air staging, which can increase the residence time of the solid particles. The temperature distribution in the furnace is uniform, and the average temperature is greater than 1200 K, which can satisfy the conditions for the pulverised coal combustion and raw material decomposition. The mass fraction distribution of oxygen, carbon monoxide, and carbon dioxide in the precalciner is closely related to the temperature distribution. The concentration of nitrogen oxides (NOx) exhibits a trend of increasing, decreasing and then increasing, and finally tending to a stable level. Within a certain velocity range, the average temperature in the precalciner and the decomposition efficiency of the raw material increase as the flue gas velocity increases. When the flue gas velocity is 24 m/s, the overall performance of the precalciner is optimal.

Numerical and experimental investigation on hybrid rocket motor with two-hole segmented rotation grain

This paper investigates the effect of rotation angles on the fuel regression rate and the motor combustion efficiency in hybrid rocket motor with two-hole segmented grains. In this research, the propellant combination of 90% hydrogen peroxide (H2O2) and polyethylene (PE) is adopted, and two two-hole grains with the same configuration are used to conduct both numerical and experimental tests. A 3D simulation model is established to obtain combustion efficiency, fuel regression rate, temperature distribution and species mass fraction distribution. Meanwhile, in order to achieve the motor combustion efficiency and the average regression rate, 20 firing tests were conducted on a lab-scale hybrid rocket motor. The numerical and experimental results agree well and demonstrate that the rotation of after-section grain has no influence on the fore-section grain regression rate, while the after-section grain regression rate arises, compared with the no rotation case. Regression rates are fitted with the following empirical equation, r˙=aGoxn(1−e−D‾pm), in which the regression rate coefficients a and n of after-section grain changed with the rotation angle. The motor combustion efficiency is higher than the base operation condition. It increases gradually with the increase of rotation angle, and the increasing rate becomes slower. The combustion efficiency can reach to the maximum when the rotation angle is 45°, after which it drops slowly, and the rate of descent is slower than that of ascent.

Experimental Calibration of a Biohydrogen Production Estimation Model

Abstract A dynamic physics-based model developed for the prediction of biohydrogen production in a compact tubular photobioreactor (PBR) was calibrated experimentally. The spatial domain in the model was discretized with lumped control volumes and the principles of classical thermodynamics, mass, species, and heat transfer were combined to derive a system of ordinary differential equations, whose solution was the temperature and mass fraction distributions across the entire system. Two microalgae species, namely, Acutodesmus obliquus and Chlamydomonas reinhardtii strain cc125, were cultured in triplicate with different culture media via indirect biophotolysis. Measured biomass and hydrogen concentrations were then used to adjust the specific microalgae growth and hydrogen production rates in the model based on residual sum of squares (RSS) and the direct search method. Despite its simplicity, the presented volume element model was verified to well predict both hydrogen and biomass concentration over time. The microalgae growth rate for each species was determined as 2.16 μalga,0 s−1 and 0.91 μalga,0 s−1 for A. obliquus and C. reinhardtii strain cc125, respectively, where μalga,0 is the specific growth rate of Scenedesmus almeriensis for given temperature and irradiance. The adjusted maximum hydrogen production rates for the local nonmutant A. obliquus and for C. reinhardtii strain cc125 were 1.3 × 10−7 s−1 and 4.1 × 10−7 s−1. Consequently, these hydrogen production rates were 59 times and 19 times smaller, respectively, than that for the mutant C. reinhardtii strain cc849.

A hydrodynamic analogy based modelling approach for zero-gravity distillation with metal foams

Zero-gravity distillation (ZGD) is one of the few ways to establish a small-scale distillation process. In contrast to conventional distillation columns, capillary forces, e.g. induced by metal foams, are exploited to ensure liquid flow in ZGD units. In order to strengthen the knowledge basis necessary for the ZGD equipment design, understanding of the relevant transport phenomena is necessary. In this work, a model for the description of ZGD processes was developed. It includes momentum, heat and species transport in both liquid and vapour phases. Evaporation and condensation influence on momentum transfer is captured in a simplified manner, allowing an approximate local flow velocity determination. The developed model was implemented in the OpenFOAM® software and used to numerically simulate methanol/ethanol distillation processes in 2D approximation. In particular, the model was applied to investigate the influence of the metal foam porosity and thickness as well as the length of the foam-free compartment on the velocity, temperature and mass fraction distributions.

Numerical Modeling of Anode-Supported Solid Oxide Fuel Cell Using Openfoam

Three-dimensional comprehensive model of micro-scale transport in PEN (positive electrode/ electrolyte/negative electrode) and macro-scale transport in gas channel of anode supported SOFCs (solid oxide fuel cells) is developed in object-oriented CFD code Open Field Operation and Manipulation (OpenFOAM). The numerical procedure consists of calculations of complex phenomena which are fully coupled together with electrochemical reaction kinetics, mass balance, and energy balance, interacting between porous PEN structure and fluid gas channel. The Computational fluid dynamics (CFD) was performed in flow channels with calculations of mass balance and continuum micro-scale model were used to predict the electrochemical characteristics in PEN. The temperature distributions, temperature profiles, and standard deviations are investigated at different average current densities to evaluate the uniformity. The distributions of current density and mass fraction are employed to suggest a dependency. This study provides detailed information of heat and mass transport phenomena with electro-chemical characteristics for intermediate temperature SOFCs

Research on the Dynamic Model of Plasma Ignition Process of Solid Propellant

In decades, the plasma ignition technology has drawn much attention due to its advantages. However, the numerical research on the plasma ignition of solid propellants is still limited. In this paper, a 1-D transient plasma ignition model of solid propellant is developed. A simplified chemical reaction mechanism of XM39 is employed in the model to explore the solid phase and gas phase chemical reactions and species transportations in the gas phase. The expansion process of the plasma jet is also investigated. The predicted surface pressure and ignition delay are compared to the experimental results. Good agreement with these data provides the necessary validation of the presented model. In the model, the calculated temperature profiles and the mass fraction distribution of the gas hexogen are used to characterize the reaction zone. In addition, the mass fraction distributions of CH2O and HCN are used to estimate the possibilities of different reaction paths.

Multicomponent Evaporation Characteristics of Biodiesel Sprays

The vapor mass fraction distribution of the multicomponent surrogate of diesel and biodiesel fuel is studied using multicomponent evaporation model at engine-relevant conditions. The numerical model is validated with experimental liquid tip penetration and vapor penetration for diesel and biodiesel. The vapor distribution for a multicomponent surrogate is significantly different than that of single-component fuel. The tetradecane, single-component surrogate for diesel has different vapor mass distribution unlike in multicomponent diesel fuel. The spatial mass fraction distribution profile of biodiesel is found to be the function of volatility differential of the pure components and their proportion in the composition. The vapor mass fraction distribution for biodiesel of palm and soybean is found to be similar to that of their single-component surrogate due to comparable volatility of components of these biodiesels. However, methyl laurate in coconut biodiesel has volatility differential with other components and also has a significant share of 40% to 50% in the coconut biodiesel composition. The change in percentage of methyl laurate in coconut composition is found to have strong impact on vapor distribution. The vapor mass fraction distribution is observed to be affected by the change in the biodiesel composition specifically volatile component.

Effect of Cooling Water Flow Path on the Flow and Heat Transfer in a 660 MW Power Plant Condenser

The effect of the cooling water flow path on the flow and heat transfer in a double tube-pass condenser for a 660 MW power plant unit was numerically investigated based on a porous medium model. The results were used to analyze the streamline, velocity, air mass fraction and heat transfer coefficient distributions. The simulations indicate that the cooling water flow path is important in large condensers. For the original tube arrangement, the heat transfer with the lower-upper cooling water flow path is better than that with the upper-lower cooling water flow path. The reason is that the steam cannot flow into the internal of upper tube bundle and the air fractions are higher in the upper tube bundle with the upper-lower cooling water flow path. An improvement tube arrangement was developed for the upper-lower cooling water flow path which reduced the back pressure by 0.47 kPa compared to the original scheme. Thus, the results show that the tube arrangements should differ for different cooling water flow paths and the condenser heat transfer can be improved for the upper-lower cooling water flow path by modifying the tube arrangement.

Improved hybrid model applied to liquid jet in crossflow

Spray formation in a liquid jet in air crossflow is investigated numerically using a hybrid approach for two cases: We=11 and We=53, where We is the air Weber number. The VOF method was used to solve the interaction between the liquid jet column and the air flow up to the primary breakup. The Eulerian liquid portion is converted to discrete Lagrangian drops by the use of source terms of mass and momentum and according to empirical correlations. The effects of two secondary breakup models, as well as two-way coupling with droplet-to-droplet collisions were evaluated in this work, in order to establish an improved hybrid model suitable to solve liquid jet in crossflow at low computational cost. The results were very satisfactory relating droplet velocity and mass fraction distribution for the lower Weber number case. For the higher Weber number case, the deviation of the numerical mass fraction distribution in comparison with the experimental one was less than 14×10−2. Improvement to the droplet size distribution was observed by using a new secondary breakup model, specially for the higher Weber number case.

Modeling of underexpanded hydrogen jets through square and rectangular slot nozzles

The development and revision of safety codes and standards for hydrogen infrastructure requires a solid scientific basis, including studies of unignited releases from high pressure systems for various scenarios. Most hydrogen releases are modeled as axisymmetric jets, but real leaks are more likely to be non-axisymmetric jets issuing from high aspect ratio cracks or slots. In the present study, underexpanded hydrogen jets from square and rectangular nozzles with aspect ratios of 1–16 were numerically modeled for stagnation pressures up to 20 MPa. The near and far flow fields were modeled separately using two sequential computational domains to accurately and efficiently capture the flow characteristics. The numerical models were first validated with experimental data from a previous experimental study and literature data. The mass fraction and velocity distributions show that the centerline decay rates increase as the nozzle aspect ratio increases, but this increase is dependent on the pressure. This means that the canonical decay law of round turbulent jets and plumes no longer applies to the slot nozzle jets for high pressures. The radial profiles collapse onto a Gaussian curve in the major axis plane, but neither collapse, nor are they Gaussian in the minor axis plane with peaks away from the jet centerline. Different shock patterns were identified along the major and minor axes and the axis switching phenomenon seen in the literature was also reproduced. The axis switching resulted in significantly wider flattened concentration distributions compared with the axisymmetric jet which may require consideration during safety analyses for non-circular nozzles. A scaling factor taking both the nozzle shape and pressure effects into account was then developed to better scale the centerline decay rates for jets from both the square and rectangular nozzles. The present study demonstrates that the nozzle shape effects on the jet spreading should not be overlooked and proper scaling factors are required to collapse the data and calculate decay rates.

Three-dimensional multiphase model of proton exchange membrane fuel cell with honeycomb flow field at the cathode side

The performance of a proton exchange membrane fuel cell (PEMEC) depends on appropriate design of the flow field, particularly at the cathode side of PEMEC. Uniform distribution of the parameters such as current density, temperature, and pressure, along with proper management of water and heat, enhances overall performance and durability of PEMFC. In this study, we proposed a comprehensive 3D multiphase CFD model of a PEMFC with a new flow field pattern at the cathode side. Honeycomb flow field is composed of a regular pattern of hexagonal pins which are categorized in pin-type flow fields. The behavior of such a field is numerically analyzed by solving a set of continuity, momentum, energy, species and electrochemical equations. The obtained results revealed that maximum pressure-drop across the cathode gas channel are 762 Pa, while the pressure and temperature distributions are uniform at the gas diffusion layer (GDL)-catalyst layer (CL) interface. Also, the results indicated that water content is less than 14 in the membrane, reducing the possibility of water flooding in the CL. It was also found that the possibility of hotspots and flooding phenomena in PEMFC decrease by increasing the uniformity of temperature, pressure, and oxygen mass fraction distributions.

Migration and Evaporation Characteristics of Kerosene Droplet in Supercritical Environment

A one-dimensional full transient droplet evaporation model was established under consideration of factors such as high pressure vapour-liquid equilibrium, high-pressure physical property corrections, gas phase dissolution, and shift of interface. The finite volume method was used for discretization to study the migration and evaporation characteristics of the surrogate fuel for kerosene, which was constituting of (mass fraction)80% n-decane and 20%1,2,4-trimethylbenzene, under supercritical conditions. The results show that, under supercritical conditions, the higher the temperature and the pressure, the easier and the sooner the supercritical migration occurs. Before the supercritical migration occurring, there was obvious boundary between the gas and liquid phases. The mass fraction of component was discontinuous, and the gradient of temperature near the interface was large. After the supercritical migration occurring, the surface of the droplet disappeared, there was no obvious boundary between the gas and liquid phases, and the distribution of the components mass fraction and temperature were continuously. With the increase of the initial temperature of the droplet, the time of the supercritical migration was greatly advanced, the rise rate of the droplet surface temperature increased, and the phenomenon of endothermic expansion no longer appeared.