Wyniki wyszukiwania - Biblioteka Nauki

1

Heat and mass transfer mechanism on three-dimensional flow of inclined magneto Carreau nanofluid with chemical reaction

100%

Rao B. M. , Gopal D. , Kishan N. , Ahmed S. , Prasad P. D.

Archives of Thermodynamics

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2020

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tom Vol. 41, no 2

223--238

EN

The characteristic of nano sized particles mass flux conditions are engaged in this investigation. Here we assume that the nano sized particle flux is zero and the nano sized particle fraction arranged itself on the boundary layer. With this convincing and revised relation, the features of Buongiorno relation on three-dimensional flow of Carreau fluid can be applied in a more efficient way. The governing partial differential equations of continuity, momentum, energy and concentration equations which are transmitted into set of pair of nonlinear ordinary differential equations utilizing similar transformations. The numeric solutions are acquired by engaging the bvp4c scheme, which is a finite-difference code for solving boundary value problems. A parametric study is accomplished to demonstrate the impact of Prandtl number, Weissenberg numbers, radiation parameter, chemical reaction parameter, thermophoresis parameter, Brownian motion parameter and Lewis number on the fluid velocity, temperature and concentration profiles as well skin friction coefficient, Nusselt number and Sherwood number within the boundary layer. From this we find the way in which magnetic parameter contributes to the increase in local skin fraction, and the decrease in the Nusselt and Sherwood numbers in these cases. The effects of the velocity temperature and concentration profile are obtained and presented graphically.

2

Chemiczna synteza oligorybonukleotydów

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Milecki J.

Wiadomości Chemiczne

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2002

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tom [Z] 56, 3-4

255-277

EN

Basic issues and problems of chemical synthesis of oligoribonucleotides are presented. The paper describes three methods for construction of oligonucleotide chains: (1) a triester method which involves activation of nucleoside phosphodiesters with different azole sulfonates, and currently widely used methods employing PIII synthetic intermediates: (2) a phosphoramidite method which makes use of activation of nucleoside phosphoramidites by weakly acidic azoles or azole salts, (3) an H-phosphonate method, which uses nucleoside H-phosphonates activated by acid chlorides, both PIII intermediates are applied mainly in solid-support synthetic methodology. Problems of choosing appropriate protecting group for the synthesis are discussed. The article presents properties of basic types of protecting groups for lactam, exo-amino (base-labile protection), and hydroxyl groups (acid-labile for 5' protection, acid- or specific reagent-labile for 2' protection). The problem of 2'OH protection is described in detail. In this respect acid-labile groups and alkylsilyl groups are compared and their advantages and disadvantages are discussed. More detailed discussion is devoted to the phenomenon of the silyl group migration during the synthesis of monomeric units for oligonucleotide chain assembly. Basing on the NMR study of the isomerisation reaction it was possible to determine limits of safety of the reaction conditions.

3

Czynniki wpływające na przebieg reakcji Cu0 + Cu2+ = 2 Cu+ w roztworach chlorkowych.

100%

Malinowska K.

Rudy i Metale Nieżelazne

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2003

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tom R. 48, nr 12

585-589

PL

Omówiono wyniki badań nad przebiegiem reakcji Cu0 + Cu2+ = 2 Cu+ w roztworach chlorkowych. Określono wpływ stosunku Cu0 /Cu +, czasu, pH i temperatury, a także stężenia roztworów na stopień przebiegu reakcji. Wyniki badań wskazują na różnice w stopniu przebiegu reakcji liczonym w oparciu o zmianę stężenia jonów chlorkowych i miedziowych. Stwierdzono niekorzystny wpływ wzrostu temperatury na wydajność reakcji. Wyniki badań pozwoliły ustalić najkorzystniejsze warunki do jej przebiegu.

EN

Results of the investigation into the course of Cu0 + Cu2+ = 2 Cu+ reaction taking place in the chloride solutions have been described. An effect of Cu0/Cu2+ ratio, time, pH, temperature and concentration of solutions on the extent of reaction course has been determined The results indicate that there are differences in the extent of reaction course, the measure of which is concentration change of the chloride and copper ions. It was found that temperature increase has disadvantageous effect on the reaction yield. The most beneficial conditions for the reaction to proceed have been determined.

4

Changes in physical structure during calcination of carbonate rocks

100%

Turek P. , Hycnar E. , Bajda T.

Geology, Geophysics and Environment

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2014

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tom Vol. 40, no. 1

133--134

EN

Limestone and other carbonate rocks are commonly used as sorbents for removing sulfur oxides from coal combustion flue gases. The process is based on chemical reaction between calcium oxide CaO and sulfur dioxide SO2, which results in formation of anhydrite CaSO4. CaO required for the reaction is produced by thermal dissociation of calcite CaCO3 which is the major constituent of each limestone. Calcite during calcination is decarbonized according to the reaction CaCO3 → CaO + CO2. The quality of such sorbent is usually being related to its total uptake of sulfur dioxide, which is frequently considered to depend mainly on chemical composition of the sorbent, especially CaCO3 content. However, there are premises that the rate of desulphurization of contaminated gases depends more on the structure of the products of limestone calcination than on CaCO3 content. Exceptionally significant is the surface area of CaO which results from its high porosity. The formation of such structure can be affected by several factors among which the structure of the raw material, its porosity and pore distribution along with crystallinity and the size of crystals are considered to be the most important issues. The current study demonstrates that the size of calcite crystals plays a key role in developing high porosity during limestone calcination in spite of calcium carbonate content in raw material. Four samples of different carbonate rocks were investigated: 1.crystalline limestone with well-developed calcite crystals of size 1-2 mm; 98.75 wt. % CaCO3; 2. micrite limestone with calcite crystals of size not exceeding 2 (im and 94.08 wt. % CaCO3; 3. limestone with calcite crystals of size up to 50 (μm dispersed in a micrite background; 94.75 wt. % CaCO3; 4. marble with crystals up to 1 mm; 96.08 wt. % CaCO3. The samples were ground to 0.125-0.250 mm particle size and calcined in the fixed bed at 850°C for 1 hour. The observation for differences in morphology of raw and calcined samples were conducted using Scanning Electron Microscopy (SEM). The particles and pore size distribution were characterized by BET analysis using low-temperature nitrogen adsorption technique. The content of CaCO3 in raw samples was calculated using total Ca content which was determined by titration with EDTA after digestion of samples with hot hydrochloric acid. SEM images revealed a regular system of cracks in the sample 1. The whole surface of calcite grains fractured and became very rough and porous. Sample 2, which was cryptocrystalline, did not show such behavior. Cracks and fractures did not occur, but under large magnification a slight porosity could be observed. Large crystals of the third sample cracked in a similar way to sample 1. Noteworthy is also the fact of creating little voids on the grain contact. Calcite crystals in sample 4 fractured along wide cracks into large fragments. Smaller clefts also occurred but they created irregular pattern, in contrast to sample 1. BET analysis confirmed foregoing SEM data. The calcination process increased the porosity and surface area of the investigated samples which was more evident with respect to more crystalline samples. Moreover, the pore distribution changed significantly. Calcination was followed by formation of the new porosity of samples, especially in mesoporous and macroporous range. Cracks in coarse calcite crystals enhance calcination by creating fast diffusion ways for CO2 escape. They could play similar role in sorption of SO2, hence the structure of raw sorbent becomes more significant issue with respect to flue gases desulphurization problem.

5

Generation of vorticity motion by sound in a chemically reacting gas and inversion of acoustic streaming in the non-equilibrium regime

100%

Perelomova A. , Wojda P.

Open Physics

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2011

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tom 9

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nr 3

740-750

EN

Nonlinear stimulation of the vorticity mode caused by losses in the momentum of sound in a chemically reacting gas is considered. The instantaneous dynamic equation for the vorticity mode is derived. It includes a quadratic nonlinear acoustic source, which reflects the fact that the reason for the interaction between sound and the vorticity mode is nonlinear. Both periodic and aperiodic sound may be considered as the origin of the vorticity flow. The equation governing the mean flow (the acoustic streaming) in the field of periodic sound is also derived. In the non-equilibrium regime of a chemical reaction, there may exist streaming vortices whose direction of rotation is opposite to that of the vortices in the standard thermoviscous flows. For periodic sound, this is illustrated by an example. The theory and the example describe both equilibrium and non-equilibrium chemical reactions.

6

Numerical solution through mathematical modelling of unsteady MHD flow past a semi-infinite vertical moving plate with chemical reaction and radiation

100%

Bhandari A.

Studia Geotechnica et Mechanica

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2018

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tom Vol. 40, nr 4

270--281

EN

In the present manuscript, unsteady magnetohydrodynamic (MHD) flow over a moving porous semi-infinite vertical plate with time-dependent suction has been studied in the presence of chemical reaction and radiation parameters. Time-dependent partial differential equations in the dimensionless form are solved numerically through mathematical modelling in COMSOL Multiphysics. The results are obtained for velocity, temperature and concentration profiles at different times. Steady state results are also presented for different values of physical parameters. The parameters involved in the problem are useful to change the characteristics of velocity, heat transfer and concentration profiles. The numerical solution of partial differential equations involved in the problem is obtained without sacrificing the relevant physical phenomena.

7

Conditions for a steady state in different type reaction

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Głowiński J. , Tylus W. , Baczyńska T.

Polish Journal of Applied Chemistry

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2000

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tom Vol. 44, nr 1

1-6

EN

The behavior of the chemical affinity at the stage of intermediate product formation was analyzed in a three different schemes of a composite reaction involving one intermediate. It was derived expressions defining the validity of the assumption that the rate formation and the rate of decay of the intermediate are equal. These relations become a quantity criterion of the well - known Bodenstein approximation. The method by which the criterion had been derived was given and examples of application were provided. The approach has a general character and can be used with reference to any composite reaction.

8

Second law analysis of flow, heat and mass transfer past a nonlinearly stretching permeable wedge with temperature jump and chemical reaction

89%

Dalir N. , Dalir N.

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9

Radiative heat and mass transfer effects on moving isothermal vertical plate in the presence of chemical reaction

88%

Muthucumaraswamy R. , Chandrakala P. , Antony Raj S.

International Journal of Applied Mechanics and Engineering

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2006

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tom Vol. 11, no 3

639-646

EN

The effect of thermal radiation on the unsteady free convective flow over a moving vertical plate with mass transfer in the presence of homogeneous first order chemical reaction is considered. The fluid considered is a gray, absorbing-emitting radiation but a non-scattering medium. The plate temperature is raised to and the concentration level near the plate is also raised to . The dimensionless governing equations are solved using the Laplace transform technique. The velocity and skin-friction are studied for different parameters like the radiation parameter, chemical reaction parameter, Schmidt number, thermal Grashof number, mass Grashof number and time. It is observed that the velocity increases with decreasing radiation parameter or chemical reaction parameter.

10

Cross-diffusion effects on MHD mixed convection over a stretching surface in a porous medium with chemical reaction and convective condition

88%

Bhuvaneswari M. , Eswaramoorthi S. , Sivasankaran S. , Hussein A. K.

Engineering Transactions

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2019

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tom Vol. 67, iss. 1

3--19

EN

In this paper, we investigate the Dufour and Soret effects on MHD mixed convection of a chemically reacting fluid over a stretching surface in a porous medium with convective boundary condition. The similarity transformation is used to reduce the governing non-linear partial differential equations into ordinary differential equations. Then, they are solved analytically by using the homotopy analysis method (HAM) and are solved numerically by the Runge-Kutta fourth-order method. The analytical and numerical results for the velocity, temperature, concentration, skin friction, Nusselt number and Sherwood number are discussed.

11

Transfer effects on an unsteady MHD mixed convective flow past a vertical plate with chemical reaction

88%

Raju R. S.

Engineering Transactions

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2017

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tom Vol. 65, iss. 2

221--249

EN

An attempt is made to study the effects of chemical reaction and combined buoyancy effects on an unsteady MHD mixed convective flow along an infinite vertical porous plate in the presence of hall current. A uniform magnetic field is applied in a direction normal to the porous plate. The governing coupled non-linear partial differential equations are solved using an efficient Galerkin finite element method. With the help of graphs, the effects of the various important parameters entering into the problem on the velocity, temperature, and concentration fields within the boundary layer are discussed. Also the effects of the pertinent parameters on the skin-friction coefficient and rates of heat and mass transfer in terms of the Nusselt number and Sherwood number are presented numerically in a tabular form. The results obtained show that the velocity, temperature, and concentration fields are appreciably influenced by the presence of chemical reaction, hall current, heat, and mass transfer. It is observed that the effect of Schmidt number and chemical reaction parameter is to decrease the velocity and concentration profiles in the boundary layer while the velocity profiles are increasing with increasing of hall parameter, Grashof numbers for heat and mass transfer. There is also considerable effect of hall current and chemical reaction on skin-friction coefficient and Nusselt number. In the present analysis various comparisons with previously published work are performed and the results are found to be in a good agreement.

12

A reliable treatment of the homotopy analysis method for viscous flow over a non-linearly stretching sheet in presence of a chemical reaction and under influence of a magnetic field

88%

Dinarvand S.

Open Physics

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2009

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tom 7

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nr 1

114-122

EN

The similarity solution for the steady two-dimensional flow of an incompressible viscous and electrically conducting fluid over a non-linearly semi-infinite stretching sheet in the presence of a chemical reaction and under the influence of a magnetic field gives a system of non-linear ordinary differential equations. These non-linear differential equations are analytically solved by applying a newly developed method, namely the Homotopy Analysis Method (HAM). The analytic solutions of the system of non-linear differential equations are constructed in the series form. The convergence of the obtained series solutions is carefully analyzed. Graphical results are presented to investigate the influence of the Schmidt number, magnetic parameter and chemical reaction parameter on the velocity and concentration fields. It is noted that the behavior of the HAM solution for concentration profiles is in good agreement with the numerical solution given in reference [A. Raptis, C. Perdikis, Int. J. Nonlinear Mech. 41, 527 (2006)].

13

Heat and mass transfer from a convectively heated vertical surface with chemical reaction and internal heat generation

88%

Seini I. Y.

Engineering Transactions

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2019

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tom Vol. 67, iss. 1

101--118

EN

A numerical approach has been adopted to investigate the steady chemically mixed convection boundary layer flow from the right face of a vertical plate of finite thickness. Cold fluid flowing over the right face of the plate contains a heat generation that decays exponentially with a dimensionless distance from the surface. The left face of the plate is in contact with a hot flowing fluid. The heating process on that side is characterized by a convective boundary condition that takes into account the conduction resistance of the plate as well as a possible contact resistance between the hot fluid and the left face of the plate. Using a pseudo similarity approach, the governing equations for the mixed convective flow over the right face of the plate are transformed into a set of coupled ordinary differential equations which give local similarity solutions. The effects of local Grashof numbers (defined to represent a mixed convection parameter), Prandtl number, and the internal heat generation parameter on the velocity, temperature and concentration profiles are illustrated and interpreted in physical terms.

14

Two–Phase Flow in Porous Bed with Chemical Reaction

88%

Niegodajew P. , Asendrych D. , Drobniak S. , Elsner W.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

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2013

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tom z. 101

75--76

EN

Continuous growth of CO2 emission is one of the most important threats of today’s power industry. Among the alternatives allowing to solve that problem, carbon capture and storage (CCS) technology seems to be a very promising option. With this method the flue gases are being sent through the absorber where CO2 is captured by aqueous amine solution flowing countercurrently. Both phases pass through the packed bed where most of the chemical reaction occurs due to the enlarged contact area between phases. The research performed so-far included investigations with the use of laboratory or pilot installations as well as numerical modelling by means of simplified 0D or 1D models. These methods have, however, limited capabilities as they do not allow to have an insight into the details of the process.

15

Effect of thermal radiation, chemical reaction and viscous dissipation on MHD flow

75%

Zigta B.

International Journal of Applied Mechanics and Engineering

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2018

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tom Vol. 23, no. 3

787--801

EN

This study examines the effect of thermal radiation, chemical reaction and viscous dissipation on a magnetohydro- dynamic flow in between a pair of infinite vertical Couette channel walls. The momentum equation accounts the effects of both the thermal and the concentration buoyancy forces of the flow. The energy equation addresses the effects of the thermal radiation and viscous dissipation of the flow. Also, the concentration equation includes the effects of molecular diffusivity and chemical reaction parameters. The gray colored fluid considered in this study is a non-scattering medium and has the property of absorbing and emitting radiation. The Roseland approximation is used to describe the radiative heat flux in the energy equation. The velocity of flow transforms kinetic energy into heat energy. The increment of the velocity due to internal energy results in heating up of the fluid and consequently it causes increment of the thermal buoyancy force. The Eckert number being the ratio of the kinetic energy of the flow to the temperature difference of the channel walls is directly proportional to the thermal energy dissipation. It can be observed that increasing the Eckert number results in increasing velocity. A uniform magnetic field is applied perpendicular to the channel walls. The temperature of the moving wall is high enough due to the presence of thermal radiation. The solution of the governing equations is obtained using regular perturbation techniques. These techniques help to convert partial differential equations to a set of ordinary differential equations in dimensionless form and thus they are solved analytically. The following results are obtained: from the simulation study it is observed that the flow pattern of the fluid is affected due to the influence of the thermal radiation, the chemical reaction and viscous dissipation. The increment in the Hartmann number results in the increment of the Lorentz force but a decrement in velocity of the flow. An increment in the radiative parameter results in a decrement in temperature. An increment in the Prandtl number results in a decrement in thermal diffusivity. An increment in both the chemical reaction parameter and molecular diffusivity results in a decrement in concentration.

16

Zastosowanie komputera w procesie przyswajania wiadomości o przebiegu reakcji chemicznych

75%

Čipera J. , Bilek M. , Gmoch R.

Prace Naukowe. Chemia / Wyższa Szkoła Pedagogiczna w Częstochowie

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1998

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tom Vol. 2

35--41

PL

Omówiono możliwości wykorzystania komputera w procesie przyswajania wiadomości o przebiegu reakcji chemicznych na przykładzie reakcji siarczanu miedzi (II) z zasadą sodową. Scharakteryzowano program komputerowy składający się z dwóch podprogramów, pozwalający na kierowanie umiejętności intelektualnych i sensomotorycznych uczniów w procesic dobierania przez nich współczynników stechiometrycznych do w/w reakcji. Opisano jeden z wariantów zastosowania programu w praktyce szkolnej.

EN

Possibilities of app1ying a computer to the process of acquiring knowledge about courses of chemical reactions, for example about the reaction of copper(Il) sulfate with sodium base, are discussed. A computer program consisting of 2 sub-programs, allowing control of intellectual and sensomotor skills of pupils during the process of selecting stoichiometric coefficients for the above reaction is characterized. A possibility of application of the program in school practice is described.

17

Effect of homogeneous chemical reaction on solutal analog of Rayleigh-Benard convection in a micropolar fluid

75%

Siddheshwar P. G. , Desseaux A.

International Journal of Applied Mechanics and Engineering

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2002

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tom Vol. 7, no 2

513-525

EN

The solutal analog of the Rayleigh-Benard convection in a reactive micropolar fluid is studied numerically using the Rayleigh-Ritz method. The solute concentration is assumed to disappear at a rate which is linearly proportional to the concentration. It is observed that the critical solutal Rayleigh number for this fluid system with homogeneous kinetics is greater than that of a non-reactive fluid system. The results have possible industrial applications.

18

Diffusion with chemical reaction – assessment of the accuracy of an approximate kinetic model for spherical pellets

75%

Gwadera M. , Kupiec K.

Technical Transactions

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2017

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tom Vol. 3(114)

19--30

EN

Diffusion with a first-order chemical reaction in a spherical pellet of a catalyst with third-type boundary conditions was considered; such a process can be described by a kinetic model based on the continued fraction approximation. Results of calculations obtained from an approximate kinetic model were compared with the exact solution. It was found that the application of this approximate model provides a good level of accuracy and requires short calculation times.

PL

Rozważono dyfuzję z reakcją chemiczną I rzędu w kulistym ziarnie katalizatora z warunkami brzegowymi III rodzaju. Taki proces można opisać modelem kinetycznym opartym na aproksymacji ułamkami łańcuchowymi. Wyniki obliczeń uzyskane z przybliżonego modelu kinetycznego porównano z rozwiązaniem ścisłym. Stwierdzono, że stosowanie przybliżonego modelu zapewnia dobrą dokładność wyników oraz krótkie czasy obliczeń.

19

Numerical study on flow past an oscillating plate with variable temperature and uniform mass diffusion under chemical reaction

75%

Vijayalakshmi A. R. , Selvajayanthi M.

International Journal of Applied Mechanics and Engineering

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2014

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tom Vol. 19, no. 1

181--193

EN

An numerical study on an unsteady flow past an oscillating semi-infinite vertical plate with variable temperature and uniform mass diffusion under the influence of a first order chemical reaction has been carried out. The dimensionless governing equations are solved by an unconditionally stable and fast converging implicit finite difference scheme. The effects of velocity and temperature for different physical parameters such as the chemical reaction parameter, thermal Grashof number, mass Grashof number and time are analysed. It is observed that due to the presence of first order chemical reaction, the velocity increases during a generative reaction and decreases in a destructive reaction.

20

Some free convection flows over a stretching cone embedded in porous media

75%

Mansour M. A. , Aly A. M. , El-Anssary N. F.

International Journal of Applied Mechanics and Engineering

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2009

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tom Vol. 14, no 3

799-812

EN

Laminar free convection from a stretching cone embedded in porous media with the effects of pressure work and chemical reaction is considered. The governing partial differential equations have been transformed by a similarity transformation into a system of ordinary differential equations, which are solved numerically using a fourth order Runge-Kutta scheme with the shooting method. The results are displayed graphically to illustrate the influences of the parameters characterizing the chemical reaction parameter, pressure work parameter and buoyancy ratio on the velocity, temperature and concentration fields for boundary conditions, namely an isothermal surface, a uniform heat surface and a vertical adiabatic surface.