scholarly journals NUMERICAL STUDY OF THE EFFECT OF MUTUAL ORIENTATION OF OLIGOMER MACROMOLECULES ON THEIR DESTRUCTION UNDER ULTRASONIC CAVITATION

2021 ◽  
pp. 281-287
Author(s):  
Р.Н. Голых ◽  
В.Н. Хмелёв ◽  
В.Д. Минаков ◽  
И.А. Маняхин ◽  
Д.А. Ильченко
Keyword(s):  
Relative Velocity ◽  
High Pressures ◽  
Fractional Composition ◽  
Complete System ◽  
Numerical Study ◽  
Critical Value ◽  
Ultrasonic Cavitation ◽  
Mutual Orientation ◽  
System Of Equations ◽  
Molecular Weights

Исследование механизма разрушения макромолекул под действием ультразвуковой кавитации представляет собой важную задачу. На сегодняшний день известен механизм разрушения макромолекул, основанный на том, что в условиях ультразвуковой кавитации создаются микроскопические зоны экстремально высоких давлений, в которых повышается вероятность актов разрыва макромолекулы. Разрыв происходит тогда и только тогда, когда относительная скорость при соударении макромолекул между собой превышает критическое значение. За счёт кавитации доля макромолекул, относительная скорость которых превышает критическое значение, увеличивается. В статье описана предложенная численная модель, которая предназначена для выявления молекулярных весов образуемых фрагментов при соударении. Предложен способ уменьшения количества неизвестных функций в 4 раза по сравнению с полной системой уравнений механики мономерных звеньев, основанный на симметрии в предлагаемой постановке задачи. Численно исследовано влияние взаимной ориентации макромолекул олигомеров на количество образуемых фрагментов. Полученные результаты могут служить ориентиром для развития макроскопической кинетической модели эволюции фракционного состава мономерных звеньев (эволюции концентраций мономерных звеньев различных типовых весов). The study of the mechanism of destruction of macromolecules under the action of ultrasonic cavitation is an important task. To date, the mechanism of destruction of macromolecules is known, based on the fact that microscopic zones of extremely high pressures are created in the conditions of ultrasonic cavitation, in which the probability of acts of rupture of the macromolecule increases. A rupture occurs if and only if the relative velocity when macromolecules collide with each other exceeds a critical value. Due to cavitation, the proportion of macromolecules whose relative velocity exceeds the critical value increases. The article describes the proposed numerical model, which is designed to identify the molecular weights of the fragments formed during collision. A method is proposed to reduce the number of unknown functions by 4 times compared to the complete system of equations of mechanics of monomeric links, based on symmetry in the proposed formulation of the problem. The effect of the mutual orientation of oligomer macromolecules on the number of fragments formed has been numerically investigated. The results obtained can serve as a guideline for the development of a macroscopic kinetic model of the evolution of the fractional composition of monomeric units (the evolution of concentrations of monomeric units of various typical weights).

Research of stamping of unequal channel bars. Part 3. Force parameters and shape change of the billet when extruding channels. 1. Kinematic and stress states of the billet

2021 ◽  
pp. 65-71
Author(s):  
A.L. Vorontsov
Keyword(s):  
Plastic Flow ◽  
Complete System ◽  
Shape Change ◽  
Plane Deformation ◽  
System Of Equations ◽  
Flow Rates ◽  
Die Forging ◽  
The Matrix ◽  
Stress States ◽  
Theory Of Plastic Flow

On the basis of the complete system of equations of the theory of plastic flow, the kinematic and stress states of the billet are determined when the channels are extruded under conditions of plane deformation of the misaligned position of the punch and the matrix. Keywords: die forging, extrusion, misaligned position, punch, matrix, plane deformation, plastic flow rates, stresses. [email protected]

Vortex synchronization in the cylinder wake due to harmonic and non-harmonic perturbations

2016 ◽  
Vol 804 ◽  
pp. 248-277 ◽  
Author(s):  
Efstathios Konstantinidis ◽  
Demetri Bouris
Keyword(s):  
Relative Velocity ◽  
Numerical Study ◽  
Vortex Formation ◽  
Phase Portraits ◽  
Cylinder Wake ◽  
Frequency Space ◽  
Flow Past A Cylinder ◽  
Harmonic Perturbation ◽  
Perturbation Frequency ◽  
Vortex Patterns

This paper reports a numerical study of two-dimensional periodically perturbed flow past a cylinder. Both harmonic and non-harmonic perturbation waveforms of the inflow velocity are considered for a maximum instantaneous Reynolds number of 180. Phase portraits of the lift force are employed to identify the dynamical state of the cylinder wake and determine the range of kinematical parameters for which primary synchronization occurs, that is the regime where vortex formation is phase-locked to the subharmonic of the perturbation frequency. The effect of different perturbation waveforms on the synchronization range and on patterns of vortex formation is examined in detail over the normalized amplitude–frequency space. It is shown that systematic shifts of the synchronization range, towards either higher or lower frequencies, can be attained by imposing different perturbation waveforms. As a consequence, in certain regions of the parameter space it is possible to obtain multiple periodic and/or quasi-periodic wake states for waveforms of exactly the same amplitude and frequency. For the range of parameters where synchronization occurs, different vortex patterns are attained in the wake involving the shedding of solitary and binary vortices, or mixtures thereof, which can be controlled by the perturbation waveform. The phenomenology of these patterns, which result from modification of the basic Kármán mode in the unperturbed wake, is discussed and explained in terms of the generation of circulation that is induced by perturbations in the relative velocity. Vortex patterns from cylinders oscillating either in line with or transverse to a free stream are recast in the framework of the relative velocity.

scholarly journals Numerical Predictions of a Swirl Combustor Using Complex Chemistry Fueled with Ammonia/Hydrogen Blends

Energies ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 288 ◽  
Author(s):  
Marco-Osvaldo Vigueras-Zuniga ◽  
Maria-Elena Tejeda-del-Cueto ◽  
José-Alejandro Vasquez-Santacruz ◽  
Agustín-Leobardo Herrera-May ◽  
Agustin Valera-Medina
Keyword(s):  
Boundary Conditions ◽  
High Pressures ◽  
Numerical Study ◽  
High Energy ◽  
Combustion Efficiency ◽  
Heat Losses ◽  
High Hydrogen ◽  
Numerical Predictions ◽  
Combustion Systems ◽  
Complex Chemistry

Ammonia, a chemical that contains high hydrogen quantities, has been presented as a candidate for the production of clean power generation and aerospace propulsion. Although ammonia can deliver more hydrogen per unit volume than liquid hydrogen itself, the use of ammonia in combustion systems comes with the detrimental production of nitrogen oxides, which are emissions that have up to 300 times the greenhouse potential of carbon dioxide. This factor, combined with the lower energy density of ammonia, makes new studies crucial to enable the use of the molecule through methods that reduce emissions whilst ensuring that enough power is produced to support high-energy intensive applications. Thus, this paper presents a numerical study based on the use of novel reaction models employed to characterize ammonia combustion systems. The models are used to obtain Reynolds Averaged Navier-Stokes (RANS) simulations via Star-CCM+ with complex chemistry of a 70%–30% (mol) ammonia–hydrogen blend that is currently under investigations elsewhere. A fixed equivalence ratio (1.2), medium swirl (0.8), and confined conditions are employed to determine the flame and species propagation at various operating atmospheres and temperature inlet values. The study is then expanded to high inlet temperatures, high pressures, and high flowrates at different confinement boundary conditions. The results denote how the production of NOx emissions remains stable and under 400 ppm, whilst higher concentrations of both hydrogen and unreacted ammonia are found in the flue gases under high power conditions. The reduction of heat losses (thus higher temperature boundary conditions) has a crucial impact on further destruction of ammonia post-flame, with a raise in hydrogen, water, and nitrogen through the system, thus presenting an opportunity of combustion efficiency improvement of this blend by reducing heat losses. Final discussions are presented as a method to raise power whilst employing ammonia for gas turbine systems.

Viscous effects on Kelvin–Helmholtz instability in a channel

2011 ◽  
Vol 680 ◽  
pp. 398-416 ◽  
Author(s):  
H. KIM ◽  
J. C. PADRINO ◽  
D. D. JOSEPH
Keyword(s):  
Slug Flow ◽  
Kinematic Viscosity ◽  
Relative Velocity ◽  
Viscosity Ratio ◽  
Critical Value ◽  
Helmholtz Instability ◽  
Viscous Effects ◽  
Velocity Difference ◽  
Neutral Curves ◽  
Gas Fractions

The effects of viscosity on Kelvin–Helmholtz instability in a channel are studied using three different theories; a purely irrotational theory based on the dissipation method, an exact rotational theory and a hybrid irrotational–rotational theory. These new results are compared with previous results from a viscous irrotational theory. An analysis of the neutral state is conducted and its predictions are compared with experimental results related to the transition from a stratified-smooth to a stratified-wavy or slug flow. For values of the gas fraction greater than about 0.20, there is an interval of velocity differences for which the flow is unstable for an interval of wavenumbers between two cutoff wavenumbers, k− and k+. For unstable flows with a velocity difference above that interval or with gas fractions less than 0.20, k− = 0. The maximum critical relative velocity that determines the onset of instability can be found when the kinematic viscosity of the gas and liquid are the same. This critical value is surprisingly achieved when both fluids are inviscid. The neutral curves from the analyses of potential flow of viscous fluids and the hybrid method, the only theories that account for the viscosity of both fluids in this work, indicate that the critical velocity does not change with the viscosity ratio when the kinematic viscosity of the liquid is greater than a critical value. For smaller liquid viscosities, the critical relative velocity decreases.

Natural Convection in a Cylindrical Enclosure Filled With Heat Generating Anisotropic Porous Medium

2001 ◽  
Vol 124 (1) ◽  
pp. 203-207 ◽  
Author(s):  
M. R. Dhanasekaran ◽  
Sarit Kumar Das ◽  
S. P. Venkateshan
Keyword(s):  
Porous Medium ◽  
Natural Convection ◽  
Thermal Diffusivity ◽  
Aspect Ratio ◽  
Numerical Study ◽  
Critical Value ◽  
Permeability Ratio ◽  
Anisotropic Permeability ◽  
Anisotropic Porous Medium ◽  
Diffusivity Ratio

A numerical study has been made to analyze the effects of anisotropic permeability and thermal diffusivity on natural convection in a heat generating porous medium contained in a vertical cylindrical enclosure with isothermal wall and the top and bottom perfectly insulated surfaces. The results show that the anisotropies influence the flow field and heat transfer rate significantly. The non-dimensional maximum cavity temperature increases with increase in permeability ratio. For aspect ratio greater than or equal to two, the nondimensional maximum cavity temperature increases with an increase in the thermal diffusivity ratio. For aspect ratio equal to unity, there exists a critical value of thermal diffusivity ratio at which the maximum cavity temperature is a minimum. This critical value increases with an increase in the value of anisotropic permeability ratio. Based on a parametric study correlations for maximum cavity temperature and average Nusselt number are presented.

Numerical Study on the Migration of Two Spheres in Upward Pipe Flow

2018 ◽  
Author(s):  
Lei Liu ◽  
Haining Lu ◽  
Jianmin Yang ◽  
Xinliang Tian ◽  
Tao Peng ◽  
...  
Keyword(s):  
Flow Velocity ◽  
Poiseuille Flow ◽  
Pipe Flow ◽  
Deep Sea ◽  
Numerical Study ◽  
Critical Value ◽  
Dynamic Responses ◽  
Phase Flow ◽  
Two Phase ◽  
Offshore Engineering

Migration of particles in pipe flow is commonly seen in offshore engineering, such as vertical transport of ores in deep sea mining. As the basis of the investigation on fluid-particle two-phase flow, the interaction of two spheres in upward pipe flow is studied by direct numerical simulations in this paper. The pipe flow is set as Poiseuille flow; the Reynolds number is no more than 1250. The dynamic responses of the spheres and the flow pattern are analyzed at different flow velocity. When compared to the sedimentation of two spheres in quiescent flow, the trailing sphere in Poiseuille flow will never surpass the leading one in Poiseuille flow. As the flow velocity increases in the pipe, the spheres are easier to separate after collision. When the flow velocity exceeds a critical value, the spheres will never collide.

scholarly journals Experimental and Numerical Study of an Automotive Component Produced with Innovative Ceramic Core in High Pressure Die Casting (HPDC)

Metals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 217 ◽  
Author(s):  
Giovanna Cornacchia ◽  
Daniele Dioni ◽  
Michela Faccoli ◽  
Claudio Gislon ◽  
Luigi Solazzi ◽  
...  
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Numerical Study ◽  
Die Casting ◽  
High Volume ◽  
Form Complex ◽  
High Pressure Die Casting ◽  
High Volume Production ◽  
Critical Components ◽  
Pressure Die Casting

Weight reduction and material substitution are increasing trends in the automotive industry. High pressure die casting (HPDC) is the conventional casting technology for the high volume production of light alloys; it has recently found wide application in the manufacturing of critical components, such as complex and thin geometry automotive parts. However, the major restriction of this affordable technology is the difficulty to design and realize hollow sections or components with undercuts. An innovative way to further increase the competitiveness of HPDC is to form complex undercut shaped parts through the use of new lost cores that are able endure the high pressures used in HPDC. This paper investigates the use of innovative ceramic lost cores in the production of a passenger car aluminum crossbeam by HPDC. Firstly, process and structural simulations were performed to improve the crossbeam design and check the technology features. The results led to the selection of the process parameters and the production of some prototypes that were finally characterized. These analyses demonstrate the feasibility of the production of hollow components by HPDC using ceramic cores.

Investigation of ammonia and hydrogen as CO2-free fuels for heavy duty engines using a high pressure dual fuel combustion process

2020 ◽  
pp. 146808742096787
Author(s):  
Stephanie Frankl ◽  
Stephan Gleis ◽  
Stephan Karmann ◽  
Maximilian Prager ◽  
Georg Wachtmeister
Keyword(s):  
High Pressure ◽  
High Pressures ◽  
Numerical Study ◽  
Combustion Process ◽  
Combustion Efficiency ◽  
Dual Fuel ◽  
Parameter Study ◽  
Fuel Injector ◽  
Cfd Model ◽  
Pilot Fuel

This work is a numerical study of the use of ammonia and hydrogen in a high-pressure-dual-fuel (HPDF) combustion. The main fuels (hydrogen and ammonia) are direct injected and ignited by a small amount of direct injected pilot fuel. The fuels are injected using a dual fuel injector from Woodward L’Orange, which can induce two fuels independently at high pressures up to 1800 bar for the pilot fuel and maximum 500 bar for the main. The numerical CFD-model gets validated for of hydrogen-HPDF with experimental data. Due to safety issues at the test rig it was not possible to use ammonia in the experiments, so it is modelled using the numerical model. It is assumed that the CFD-model also gives qualitative correct results for the use of ammonia as main fuel, so a parameter study of ammonia-HPDF is made. The results for the hydrogen-HPDF show, that hydrogen can be used in the engine without any further modifications. The combustion is very stable, and the hydrogen ignites almost immediately when it enters the combustion chamber. The results of the ammonia combustion indicate, that the HPDF combustion mode can handle ammonia effectively. It seems beneficial to inject the ammonia at higher pressures than hydrogen. Also pre-heating the ammonia can increase the combustion efficiency.

scholarly journals Phase Behaviour of the System Propene/Polypropene at High Pressure

2011 ◽  
Vol 2011 ◽  
pp. 1-5
Author(s):  
Oliver Ruhl ◽  
Gerhard Luft ◽  
Patrick Brant ◽  
John Richard Shutt
Keyword(s):  
Cloud Point ◽  
High Pressures ◽  
Weight Fraction ◽  
Phase Behaviour ◽  
Critical Weight ◽  
Molecular Weights ◽  
Metal Bellows ◽  
Similar Density ◽  
Increasing Temperature ◽  
Good Agreement

The phase behaviour of mixtures of supercritical propene and a number of polypropenes, which have a similar density but significantly different molecular weights and tacticities, was investigated in a broad range of polymer weight fractions and temperatures at high pressures. The cloud-point pressures were measured optically, using a view cell which was equipped with two windows made of synthetic sapphire and a metal bellows to accurately adjust the pressure. The cloud-point pressures were found in the range from 29 to 37 MPa decreasing with increasing polymer weight fraction and increasing with increasing temperature and polymer molecular weight. The critical weight fraction was found below 2 to 6 wt.-%. Whereas the cloud-point pressures of atactic and syndiotactic samples were high and very similar, the isotactic species exhibit distinctly lower values. The results, extrapolated to lower temperatures, show good agreement with the literature data.

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