Control Volume Method Research Articles

Magnetohydrodynamic mixed convection and entropy generation analysis of Al2O3-water nanofluid past a confined circular cylinder

Numerical simulations are carried out for transient magnetohydrodynamic mixed convective heat transfer of alumina–water nanofluid flow past an isothermal circular cylinder confined in an electrically insulated rectangular duct in the presence of a uniform transverse magnetic field. A control volume method is used to solve the governing equations on a nonuniform Cartesian grid, and the cylinder is imposed using the immersed boundary method. Numerical experiments are performed for a Reynolds number based on the cylinder diameter of ReD=200, blockage ratio of BR=0.2, Richardson numbers of (Ri=−1;0;2), nanoparticle volume fractions of (φ=0.0;0.1;0.2), and Hartmann numbers in the range 0≤Ha≤13. In this work, mean and instantaneous flow and thermal distributions are analyzed graphically, and their corresponding sensitivity to the nanoparticle volume fraction has been determined. Numerical predictions demonstrate the impact of buoyancy and magnetic parameters regarding the spatial development and shedding characteristics of the near wake, and we explore their potential use to selectively excite or suppress vortex shedding, augmentation of heat transfer, and entropy generation minimization in nanofluid flow. The results reported herein indicate that depending on the parametric set, linear and nonlinear flow response to magnetic excitation is observed with bifurcations between different states. The outcome of the study shows that vortex shedding is completely suppressed when a critical value of the Hartmann number is reached, and that the threshold value of the Hartmann number strongly depends on the value of the buoyancy parameter and nanoparticle volume fraction. Based on the entropy distributions, we show that for all values of the nanoparticle volume fraction and in the range of buoyancy and magnetic parameters considered in this work, the entropy generation is dominated by irreversibilities due to heat transfer and the relative contributions of entropy generation due to fluid friction and magnetic effect are not preponderate.

Effects of membrane polarization, steric repulsion and ion-solvent interactions on electroosmosis through a conical nanopore

The impact of solid polarization of a dielectric membrane on ion transport in a conical nanopore drilled through a membrane is studied by considering ions as finite-sized dielectric charged spheres. The excess polarization of the hydrated ions creates a dielectric decrement. A mean-field-based approach is adopted by modifying the Nernst-Planck equation to incorporate the ion steric interactions, the Born force, and the dielectrophoretic force arising due to the spatial variation of electrolyte permittivity. The viscosity of the medium is considered to vary with the local ionic concentration through the Bachelor-Green equation, which leads to a reduction in the mobility of ions near a charged surface. Governing equations are solved numerically through the control volume method along with a pressure-correction-based iterative algorithm. The solid polarization of the membrane, which is often neglected in existing studies, is found to have a strong impact on the volume flux, conductance, selectivity, and ion current rectification in the conical nanopore. The ion saturation in the vicinity of the charged surface, as governed by the present modified model, creates a pronounced alteration in the electrokinetics compared to that predicted by the standard Poisson-Nernst-Planck (PNP-model) based on the point charge consideration of ions. This discrepancy due to ion steric repulsion and ion-solvent interactions is pronounced at a higher ionic concentration as well as a highly polarizable surface. A close agreement between the predictions of the present modified model and the existing experimental data, compared with that of the standard PNP model, is encouraging. The present modified model provides an accurate analysis of the electroosmotic flow and ion transport in a dielectric charged conical nanopore beyond the low charge density and dilute solution limits.

Валидация технологии прогнозирования гидродинамических характеристик судовых движителей в пакете программ «ЛОГОС»

Object and purpose of research. The objects of research are models of propeller and impeller of a water jet. The purpose of the work is to validate the new calculation module LOGOS of domestic software complex for engineering analysis and the technology for its use in predicting the hydrodynamic performance of ship propulsion based on comparison with experimental research data and reference calculations in foreign commercial software. Materials and methods. Methods of computational fluid dynamics are used to determine the hydrodynamic performance of ship propulsion systems. The characteristics of the viscous fluid flow are obtained from the solution of non-stationary Reynolds equations (RANS (Reynolds averaged Navier-Stokes equations)) by control volume method. The Reynolds equations are closed by a two-parameter semi-empirical turbulence model. To validate the results of numerical modeling in the LOGOS software package, data from experimental studies and reference calculations performed at the Krylov Center are used. Main results. Validation of the new calculation module of LOGOS software complex, performed on the basis of comparison with the results of experimental studies and reference calculations, demonstrates the high accuracy of modern domestic software in the field of computational fluid dynamics in solving problems of determining the hydrodynamic performance of propellers. Conclusion. The paper shows that the determination of hydrodynamic performance of ship propulsion models in a uniform viscous fluid flow can be performed using the domestic software package LOGOS. The accuracy of predicting the hydrodynamic performance of propellers in the meantime compares favourably to leading foreign software products and is confirmed by the results of experimental studies carried out in the deepwater towing tank of Krylov Center. At the same time, further development of the LOGOS software package is required for the correct solution of more complex tasks related to ship propulsion.

Non-Newtonian Fluid Flow Modeling in the Inertial Viscometer with a Computer Vision System

Purpose of research. Development of theoretical premises for the new inertial viscometer, as well as the development of an approximate model of the viscosity fluid flow using convolutional neural networks and laser speckle contrast imaging data.Methods. The study consists of two parts. The first is devoted to a theoretical study of viscosity fluid flow in the toroidal channel of еру new inertial viscometer. The mathematical model of the flow includes the dimensionless equations of Navier-Stokes and convective heat conduction, the analysis of which made it possible to estimate the conditions for the uniformity of pressure and temperature fields. The numerical solution of the simplified Navier-Stokes equation was obtained by the control volume method. The computational experiment made it possible to identify additional operating conditions for the viscometer. The second part of the research is aimed at solving the problem of predicting the values of the shear strain rate on the tour surface and the flow rate. The approximate flow model is based on an ensemble of convolutional neural networks trained on data from laser speckle-contrast visualization of a fluid flow in a transparent tube.Results. The recommendations on the operating parameters of the inertial viscometer for the studied types of liquids in a given viscosity range are obtained. An approximate model has been developed in the form of an ensemble of deep neural networks, which makes it possible to determine the volumetric flow rate and the shear strain rate on the flow surface based on fluid flow images.Conclusion. The approximate Navier-Stokes equation obtained as a result of theoretical analysis for the flow of a viscous fluid in a toroidal channel can be used to numerical determination the kinematic viscosity. So, the necessary flow characteristics, such as volumetric flow rate and shear strain rate on the flow surface, can be found using the developed and pretrained convolutional neural network based on laser speck contrast imaging data. The test fluid can be any non-Newtonian fluid capable of reflecting coherent radiation. In particular, it can be physiological fluids, including blood.

Utjecaj perforacija i proreza na higrotermalna svojstva EPS-a

This paper presents the results of research on the influence of perforation and slits on the water vapour diffusion of expanded polystyrene (EPS) and the influence of the size and number of perforations and slits on the thermal conductivity of EPS board. The research was conducted using numerical models (control volume methods) with varying sample thickness, slit spacing, and depth and diameter of perforations. The numerical model showed that it is possible to obtain up to 42.18 % better water vapour diffusion compared to EPS board without perforation with an increase in thermal conductivity of 9.02 %. Also, the results of this study show that the effective vapour diffusion coefficient depends on the thickness of the perforated EPS samples.

Numerical Simulation and Experimental Research of Oil-free Scroll Air Compressor Based on CFD

Background: Compared with other types of compressors, although the scroll compressor has a simple structure and low noise, due to the limitation of the structure, it has defects such as excessively high discharge temperature, and has extremely high requirements on the machining accuracy of parts. The oil-free scroll compressor is a new type of scroll machine, which does not contain oil during the working process; it can be applied to cases with low displacement requirements and a high-pressure ratio. Objective: Taking a scroll compressor with a rated displacement of 0.6 m3/min as the research object, the analysis and research of the working performance parameters of the scroll compressor in actual work provide a certain theoretical basis for the improvement and optimization of the test prototype. Methods: The thermodynamic model of the scroll compressor in the actual working process is established by the variable-mass system thermodynamics and the control volume method. Based on the CFD method, a three-dimensional unsteady-state numerical simulation of the flow characteristics of the working fluid in the scroll compressor's working chamber is carried out in order to verify the thermodynamic model. Considering the accuracy of numerical simulation, a test platform with air as the working fluid is set up. Results: Through the thermodynamic model and numerical simulation, the changes of temperature, pressure and velocity in the working chamber of the scroll compressor with the orbiting angle of the main shaft as well as the gas force and torque acting on the orbiting scroll tooth are obtained. Through experiments, the law of volume flow and shaft power of the scroll compressor with the speed of change, and the law of the change of discharge temperature with pressure at different speeds are obtained. Conclusion: At the same time, the thermodynamic model established by considering heat transfer and leakage is more in line with the actual working process of the compressor; the mass exchange between adjacent working chambers of the scroll compressor has a greater impact on the temperature and pressure in the working chamber. Due to internal leakage and irreversible loss, such as heat transmission, there is a deviation between the theoretical volume flow and the actual volume flow.

Numerical simulation of forced acoustic gas oscillations with large amplitude in closed tube

Nonlinear acoustic oscillations with large amplitude created in gas-filled closed tube by piston oscillating according to the harmonic law near three natural resonant frequencies are numerically studied. The movement of the medium is described by the Navier–Stokes equations for viscous compressible fluid, which are approximated through the control volume method using the OpenFoam library. The influence on the maximum pressure drop of the excited piston oscillation frequency at large amplitudes near the first resonant frequency is studied. The used numerical model allows to achieve good agreement with the experimental data for intensive gas oscillations with breaking waves. The dynamics of changes in pressure and velocity during a single period of oscillations at different natural frequencies are studied in detail. Nonlinear features for intensive shock oscillations of viscous gas in a closed tube at higher harmonics have been detected. In particular, oscillations in the pressure nodes with a frequency equal to the doubled frequency of forced oscillations of the piston at the first and higher modes resonance frequencies were found. For non-linear gas oscillations with a shock front of pressure changes in the nodes for the velocities of gas particles inside the tube, the large amplitudes of the change in particle velocities over a very short period of time are observed. The received results show that the used numerical approach is a suitable method for modeling highly nonlinear acoustic oscillations and related problems.

Size and Shape Effects on Fatigue Behavior of G20Mn5QT Steel from Axle Box Bodies in High-Speed Trains

In this paper, the axial loading fatigue tests are at first conducted on specimens ofG20Mn5QT steel from axle box bodies in high-speed trains. Then, the size and shape effects on fatigue behavior are investigated. It is shown that the specimen size and shape have an influence on the fatigue performance of G20Mn5QT steel. The fatigue strength of the hourglass specimen is higher than that of the dogbone specimen due to its relatively smaller highly stressed region. Scanning electron microscope observation of the fracture surface and energy dispersive X-ray spectroscopy indicate that the specimen size and shape have no influence on the fatigue crack initiation mechanism. Fatigue cracks initiate from the surface or subsurface of the specimen, and some fracture surfaces present the characteristic of multi-site crack initiation. Most of the fatigue cracks initiate from the pore defects and alumina inclusions in the casting process, in which the pore defects are the main crack origins. The results also indicate that the probabilistic control volume method could be used for correlating the effects of specimen size and shape o the fatigue performance of G20Mn5QT steel for axle box bodies in high-speed trains.

Inward and Outward Opening Properties of One-Sided Windcatchers: Experimental and Analytical Evaluation

Vernacular measures, such as courtyard, wind catcher “Malqaf”, wooden lattice “Mashrabia”, and lantern—which can help buildings to depend on natural energy from the sun and the wind—have started to be abandoned in the last decades. However, wind pressure and stack effects are becoming more popular in modern buildings design and the primary method in most domestic buildings to achieve the desired cross ventilation and minimize the air temperature to reach the required cooling loads. This paper aims to revive one of the vernacular measures “the windcatcher”, quantifying the effectiveness of the inward/outward opening properties on the air temperature and airflow inside the buildings. Analytical literature review, context analysis, and numerical simulations are performed. The computer fluid dynamics (CFD) is utilized to simulate both the temperature distribution and the flow field within the windcatcher model. Simulations are carried out in the fluent environment, which uses the control volume method for solving the conservation law. The Reynolds-averaged Navier–Stokes (RANS) and energy equation with the realizable k-ϵ turbulent model are employed. The research uses a parametric analysis to test different scenarios of windcatcher designs in terms of dimensions, proportions, and opening ratios. The results of this study confirm that windcatcher has a significant effect in lowering the air temperature inside the different floors. However, it is recommended to use a wind-catcher for not more than two floors, increase the area of the outward opening to 200% relative to the inward opening and apply side opening in the upper floors.

EFFECT OF CORRUGATED PIPE ON LAMINAR CONVECTIVE HEAT TRANSFER BY USING SWCNT NANOFLUID: A NUMERICAL STUDY

Extension of the tube wall’s heat transfer area and mixing nanoparticles with working fluids are the most effective and potential techniques to enhance the heat transfer rate, which is required to remove the excessive load of heat from the heat transfer apparatus. These extreme loads are dangerous threats for heat transfer equipment, which may cause several damages. Therefore, a corrugated pipe was studied numerically along with SWCNT-water nanofluid, to determine the improvement of laminar convective heat transfer rate. Ansys fluent software and steady-state control volume method were applied for simulation purposes. Hence, different volume fractions (1% - 5%) of nanoparticles were considered to mix with water to produce nanofluid. A range of Reynolds numbers from 500 to 1200 with a constant wall heat flux of 1000 W/m2 was considered to calculate the heat transfer rate. Additionally, the corresponding pumping power requirement for such improvements was also calculated. The result demonstrated that by increasing the Reynolds number, the Nusselt number and heat transfer coefficient were raised significantly for corrugated pipe compared to a plain pipe. Consequently, the presence of nanoparticles in the working fluid also showed more enhancement. For the corrugated pipe, at Re =500, SWCNT-water nanofluid showed a maximum 56.52% enhancement of Nusselt number and heat transfer coefficient. Furthermore, SWCNT-water nanofluid showed pumping power advantage (92% for 5% volume fraction). Additionally, correlations to calculate the Nusselt number and heat transfer coefficient of nanofluid were also developed, which showed good agreement with numerical results. However, it can be concluded that corrugated channels, along with nanofluid, provide enhancement of heat transfer rate, Nusselt number, and pumping power advantage for the laminar developed region of a pipe.

Mathematical Modeling of Large Forest Fires Initiation and Spread

It is presented mathematical model for description of heat and mass transfer processes at crown and large forest fires initiation and spread, taking into account their mutual influences. Mathematical model of forest fire was based on an analysis of experimental data and using concepts and methods from reactive media mechanics. The paper suggested in the context of the general mathematical model of forest fires give a new mathematical setting and method of numerical solution of a problem of a forest fire modeling. The boundary-value problem is solved numerically using the control volume methods and method of splitting according to physical processes. In this context, a study - mathematical modeling - of the conditions of forest fire initiation and spreading that would make it possible to obtain a detailed picture of the change in the velocity, temperature and component concentration fields with time, and determine as well as the conditions of forest fires initiation and spread is of interest.

Validation of the thermal-hydraulic thunder code and application for PWR core in transient conditions

The THUNDER computer code allows performing thermal-hydraulic core analysis of pressurized water reactors aiming at the design and safety analysis of power and naval reactors in steady state and transient conditions. It uses the subchannel and control volume methods to perform a tridimensional analysis of the nuclear reactor core. The conservation equations are solved simultaneously for each control volume based on geometric and operation conditions. The Integral Momentum Method is used for solving the conservation equations decoupling the momentum equation from the mass and energy conservation equations. The drift-flux model is adopted to treat the two-phase flow condition. The analysis is performed in two-stages: first, a macroscopic analysis is conducted with subchannel equivalent to a fuel assembly (bundle), and second, with a subchannel equivalent to an individual coolant channel. Only the hottest fuel assembly is analyzed with detail. To validate the THUNDER code we used the experimental data from the NUPEC PWR benchmark (subchannel and bundle tests), in which we verify the accuracy of the coolant temperature at steady-state in 4 different void fraction conditions and the accuracy of the void fraction at transients initiated by four different conditions: core power increase, reduction of inlet mass flow rate, increase of inlet coolant temperature and depressurization of the inlet coolant. At steady-state conditions, the mean relative discrepancy for the coolant temperature was 0.09. At transient conditions, the void fraction mean absolute discrepancy for power increase was 0.045, for mass flow reduction was 0.079, for inlet coolant depressurization was 0.032 and for temperature increase was 0.092. The code was applied for the Brazilian 1350 MW nuclear power plant ANGRA 2 for evaluating the thermal-hydraulic safety parameters at steady-state, as well as the operational transients of loss of one or several primary coolant pumps. The THUNDER code results showed that the safety limits were not exceeded in concordance to the Final Safety Analysis Report of the plant. These results indicate that the THUNDER code is sufficiently accurate to perform thermal-hydraulic analyses for PWR power plants at steady-state and transient conditions.

Numerical analysis of vacuum drying of a porous body in the integrated domain

AbstractIn the present study, the vacuum drying process of an apple slice is numerically modeled based on a control volume method. Transient two‐dimensional Navier–Stokes, energy, moisture, and Luikov equations are solved by numerical coding (Fortran) to simulate the simultaneous heat and mass transfer in the ambient and apple slice, respectively. The privilege of using Luikov's model is that the capillary forces are considered, and a differentiation between air, vapor, liquid, and solid is made. Luikov described the two phenomena associated with the transport of air, vapor, and liquids through the porous media as molecular transport and molar transport. The ambient pressure linearly reduced within a minute until it reached a constant value. One of the intellectually demanding preoccupations among researchers is how to simulate the sample and its surroundings with high accuracy of boundary conditions, which enables to avoid the use of empirical transfer coefficients. This study can be scrutinized from various dimensions, among which nonuse of boundary condition between a porous sample and its surroundings is the most conspicuous novelty. Results showed that although at 50 s, isothermal and iso‐moisture lines inside the sample are symmetric, they are not symmetric at 100, 200, and 400 s. In addition, at first minute, pump operation leads to vary the density of the isothermal and iso‐moisture lines around the sample, but at 100, 200, and 400 s, higher temperature and moisture gradients have been achieved at the right and top of the sample surface.Practical ApplicationsDrying is the main technique of food preservation, so that it reduces the humidity of crops and is the most crucial procedure for safeguarding agricultural crops because it has a considerable impact on the condition of parched goods. In this study, some assumptions of drying including using empirical transfer coefficients between sample and its surrounding and vacuum drying under constant pressure have been eliminated. To achieve this goal, computational fluid dynamics (CFD), plays a crucial role to simulate the parameters inside the sample and its ambient without using boundary condition.

Investigation of the impact of pipe geometric form on earth-to-air heat exchanger performance using Complex Finite Fourier Transform analysis. Part I: Operation in cooling mode

This paper deals with the impact of the geometric form of pipe section upon the performance of earth-to-air heat exchangers operating in cooling mode. For this purpose, three different configurations, namely circular, rectangular and elliptical were selected. Based on the heat balance analysis, a transient two-dimensional model was developed for the disturbed soil around the buried pipe. The discretization of the partial differential equation by applying the Finite Control-Volume Method yields a new generalized heat equation valid for all kinds of cylinders. Then, the resulting set of ordinary differential time-equations was linearized by using the technique of Complex Finite Fourier Transform. After successfully validating the model against available data in the literature, a thorough sensitivity analysis was carried out for assessing the impact of geometric and operating parameters including pipe length and cross-section and air speed. Further, the effect of pipe flatness relating to the rectangular and elliptical configurations was also considered through the geometric aspect ratio.The results show that the rectangular and elliptical buried pipes are more effective because they possess large exchange surfaces compared to the circular (conventional) one. For instance, at a pipe cross-section of 0.07 m2 and a geometric aspect of 9, the exchange surface between the flowing air and pipe wall in the rectangular and elliptical exchangers are larger of 88.3% and 93.6% than that of the conventional system, respectively. Moreover, at a geometric aspect of 4 and a pipe length of 60 m, the outlet temperatures supplied by the rectangular and elliptical systems are of 1.5 and 1.3 °C less than that obtained with the conventional one. Regarding the influence of pipe dimensions, it is shown that the effect of pipe length is dominant compared to that of pipe section and the performance of the system is proportional to the pipe length. Likewise, the EAHE performance increases with the increasing of the pipe geometric aspect, but a value of 4 is found to be a good compromise. Though, the performance of EAHE is found to drop dramatically at high speeds of air.

Instantaneous optimal control of inflatable folded structures

The inflatable folded membrane structure is mainly made of flexible materials, so it has the advantages of simple structure, high folding efficiency, small launch volume, light weight, low production cost, and high reliable, and it has broad application prospects in large space structures such as space antennas, solar panels. In order to overcome the shortcoming that the traditional constant rate inflation cannot take into account the folded structure development time and stability at the same time, this paper proposes a method of variable inflation rate, which combines the inflation rate with the optimal control, so that the folded structure can deploy quickly and stably. The paper uses extended position-based dynamics method (XPBD) and control volume (CV) method to establish the inflatable folded membrane structure simulation system, and derive its instantaneous optimal control expression with inflation rate as control variable. The simulation of the four-fold tube and the comparison with the constant inflation rate show that the present method is more stable and less kinetic energy than the fast inflation rate, and takes less time than the slow inflation rate. To prove the effectiveness of the proposed control algorithm for complex folded inflatable structure, the paper uses origami to design a sunshield model and simulate the deployment process.

Influence of the number of holes and two types of PCM in brick on the heat flux passing through the wall of a building on a sunny day in Medina, Saudi Arabia

In this article, the impact of using two types of phase change material (PCM) in brick on a summer day according to the climate of Medina, Saudi Arabia is studied numerically. Bricks with square holes filled with PCM are used for the inner sidewall. For this purpose, PCMs P116 and n-Eicosane are used to fill the bricks and are compared with the case without PCM to determine its effect on the amount of heat flux passing (HEFP) through the wall. The effect of the different number of holes (1–4) is also studied. Two-dimensional numerical simulations are performed using the control volume method. The results show that the maximum HEFP through the wall occurs in the afternoon. Examination of the melting front of PCMs indicates that the melting front moves from the hot wall toward the cold wall and the type of PCM are important during the completion of the melting process. In general, the usage of PCM minimizes the amount of HEFP through the wall. The usage of PCM n-Eicosane results in a greater decrease in the quantity of heat flux going through the wall. At midday, the biggest drop in heat flow occurs. Using additional holes, particularly when the bricks are filled with PCM n-Eicosane, dramatically lowers the HEFP through the wall. The kind of PCM used to decrease flux going through the wall is determined by the temperature of the building.

Numerical investigation on water entry of a three-dimensional flexible bag of an air cushion vehicle

The water entry of a three-dimensional (3D) flexible bag near the corner of an air cushion vehicle (ACV) was studied by combining the control volume and arbitrary Lagrangian Eulerian methods. The accuracy of the numerical procedure was validated against the available drop tests of an airbag. A detailed investigation of the water entry process, internal pressure of the flexible bag, maximum deformations, and maximum principal stresses was performed. The results from the 3D numerical simulation were compared with those from the two-dimensional numerical simulation to clarify the 3D effects. The results provide a useful reference for designing the flexible bags located near the corners of the ACVs.

Analyses of non-Fourier heat conduction in 1-D spherical biological tissue based on dual-phase-lag bio-heat model using the conservation element/solution element (CE/SE) method: A numerical study

Among the various numerical methods in solving the hyperbolic equation systems, methods that are simple, have higher accuracy, and avoid creating unwanted numerical oscillations along with having shorter runtime are preferred. In the present study, two numerical methods, space-time conservation element and solution element (CESE) as well as control volume (CV) method have been utilized to estimate temperature distribution in the spherical living tissue during laser irradiation. The results of the CESE method in simulating the non-Fourier thermal wave of the dual-phase-lag (DPL) model in spherical coordinates have been validated against the available semi-analytical results as well as the results obtained using the CV method. The good correlation between the results proved that the CESE method can be applied accurately in solving the DPL model thermal waves in spherical coordinates. In addition, the advantages of the CESE method over the CV method have been investigated. No numerical oscillations are detected in the temperature distribution obtained by the CESE method during and after exposure. Furthermore, in the same circumstances, in terms of radial grid size, a larger time step can be used in CESE method which reduces runtime. Examining the four non-Fourier models, hyperbolic, wavelike, diffusive, and over-diffusive, shows that the thermal wave occurs only in two of these models, hyperbolic and wavelike, when the phase lag of the heat flux is greater than the phase lag of the temperature gradient. After stopping laser irradiation, the maximum temperature is diffused from the surface of the tissue to its inner layers. The results proved that the speed of thermal wave progression is not only constant in hyperbolic and DPL models but also decreases in different tissues with the passage of time. Regardless of the type of tissue, the wave motion towards the center of the tissue in the hyperbolic model is greater than the DPL model. In addition, studying the thermal wave propagation speed in different tissues indicated that this parameter has a direct relationship with the thermal diffusivity of the tissues. The diffusion property caused by the temperature gradient phase lag in the DPL model is the reason why the wave expansion is greater than the hyperbolic model and why a wider range of the tissue is affected by the laser irradiation.

Simulation of Variable Magnetic Field Effect on Natural Convection Heat Transfer of Fe3O4/Graphite Slurry based on Experimental Properties of Slurries

Natural convective heat transfer of Fe3O4/graphite slurry in a square cavity is numerically examined. The slurry is assumed to be a non-Newtonian ferrofluid under a variable external magnetic field. The left and right walls of the cavity are assumed to be at a relatively low temperature (Tc), while the horizontal walls are thermally insulated. A heat source with a variable temperature distribution is located at the bottom of the enclosure. The non-Newtonian behavior of the graphite slurry (a mixture of ethylene glycol and graphite powder) has been modelled using experimental results. The control volume method and the SIMPLE algorithm were used to discretize and solve the governing equations considering the Ferro-hydrodynamics (FHD), the Magnetohydrodynamics (MHD) and the non-Newtonian fluid behavior. The heat transfer and fluid flow properties are determined for different locations of the magnetic field source, and different values of the magnetic number (Kelvin force), and the Hartmann number (Lorentz force). The results show that when the magnetic field source is located below the enclosure and near the heat source, the vortices are strengthened resulting in an increased heat transfer. The heat transfer rate is affected by FHD and MHD. When the magnetic field source is located at the corner points, the heat transfer rate is not significantly affected by the magnetic and Hartmann numbers. However, once the magnetic field source is located near the central point of the lower wall of the enclosure, the heat transfer rate is influenced by the increase of the magnetic number.

Numerical Simulation of the Nonstationary Process of the Shot Based on the Navier – Stokes Equations

This paper gives a spatial mathematical formulation of the problem of internal ballistics based on the Navier – Stokes equations, taking into account the swirl of the flow due to the rotation of the projectile. The k-e model of turbulent viscosity is used. The control volume method is used for the numerical solution of systems of equations. The gas parameters at the boundaries of the control volumes are determined by the method of S. K. Godunov using a self-similar solution to the problem of the decay of an arbitrary discontinuity. The MUSCL scheme is used to increase the order of approximation of the difference method. For equations written in a cylindrical coordinate system, an orthogonal difference grid is constructed using the complex boundary element method. A comparative analysis of the results obtained with different approaches to modeling the process of an artillery shot is given. Quantitative data are presented on the influence of factors not previously taken into account on the characteristics of the process.