|
Markstein Number
In combustion engineering and explosion studies, the Markstein number characterizes the effect of local heat release of a propagating flame on variations in the surface topology along the flame and the associated local flame front curvature. The dimensionless Markstein number is defined as: :\mathcal = \frac where \mathcal is the Markstein length, and \delta_L is the characteristic laminar flame thickness. The larger the Markstein length, the greater the effect of curvature on localised burning velocity. It is named after George H. Markstein (1911—2011), who showed that thermal diffusion stabilized the curved flame front and proposed a relation between the critical wavelength for stability of the flame front, called the Markstein length, and the thermal thickness of the flame. Phenomenological Markstein numbers with respect to the combustion products are obtained by means of the comparison between the measurements of the flame radii as a function of time and the results of the a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion does not always result in fire, because a flame is only visible when substances undergoing combustion vaporize, but when it does, a flame is a characteristic indicator of the reaction. While the activation energy must be overcome to initiate combustion (e.g., using a lit match to light a fire), the heat from a flame may provide enough energy to make the reaction self-sustaining. Combustion is often a complicated sequence of elementary radical reactions. Solid fuels, such as wood and coal, first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them. Combustion is often hot enough that incandescent light in the form of either glowing or a flame is prod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Zel'dovich Number
The Zel'dovich number is a dimensionless number which provides a quantitative measure for the activation energy of a chemical reaction which appears in the Arrhenius exponent, named after the Russian scientist Yakov Borisovich Zel'dovich, who along with David A. Frank-Kamenetskii, first introduced in their paper in 1938. In 1983 ICDERS meeting at Poitiers, it was decided to name after Zel'dovich.Clavin, P. (1985). Dynamic behavior of premixed flame fronts in laminar and turbulent flows. Progress in energy and combustion science, 11(1), 1-59. It is defined as :\beta = \frac \cdot \frac where *E_a is the activation energy of the reaction *R is the universal gas constant *T_b is the burnt gas temperature *T_u is the unburnt mixture temperature. In terms of heat release parameter \alpha, it is given by :\beta = \frac \alpha For typical combustion phenomena, the value for Zel'dovich number lies in the range \beta\approx 8-20. Activation energy asymptotics Activation energy asy ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fluid Dynamics
In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids— liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) and hydrodynamics (the study of liquids in motion). Fluid dynamics has a wide range of applications, including calculating forces and moments on aircraft, determining the mass flow rate of petroleum through pipelines, predicting weather patterns, understanding nebulae in interstellar space and modelling fission weapon detonation. Fluid dynamics offers a systematic structure—which underlies these practical disciplines—that embraces empirical and semi-empirical laws derived from flow measurement and used to solve practical problems. The solution to a fluid dynamics problem typically involves the calculation of various properties of the fluid, such as flow velocity, pressure, density, and temperature, as functions of space and ti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Dimensionless Numbers Of Fluid Mechanics
A dimensionless quantity (also known as a bare quantity, pure quantity, or scalar quantity as well as quantity of dimension one) is a quantity to which no physical dimension is assigned, with a corresponding SI unit of measurement of one (or 1), ISBN 978-92-822-2272-0. which is not explicitly shown. Dimensionless quantities are widely used in many fields, such as mathematics, physics, chemistry, engineering, and economics. Dimensionless quantities are distinct from quantities that have associated dimensions, such as time (measured in seconds). Dimensionless units are dimensionless values that serve as units of measurement for expressing other quantities, such as radians (rad) or steradians (sr) for plane angles and solid angles, respectively. For example, optical extent is defined as having units of metres multiplied by steradians. History Quantities having dimension one, ''dimensionless quantities'', regularly occur in sciences, and are formally treated within the field o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Combustion
Combustion, or burning, is a high-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, usually atmospheric oxygen, that produces oxidized, often gaseous products, in a mixture termed as smoke. Combustion does not always result in fire, because a flame is only visible when substances undergoing combustion vaporize, but when it does, a flame is a characteristic indicator of the reaction. While the activation energy must be overcome to initiate combustion (e.g., using a lit match to light a fire), the heat from a flame may provide enough energy to make the reaction self-sustaining. Combustion is often a complicated sequence of elementary radical reactions. Solid fuels, such as wood and coal, first undergo endothermic pyrolysis to produce gaseous fuels whose combustion then supplies the heat required to produce more of them. Combustion is often hot enough that incandescent light in the form of either glowing or a flame is prod ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Schmidt Number
Schmidt number (Sc) is a dimensionless number defined as the ratio of momentum diffusivity ( kinematic viscosity) and mass diffusivity, and it is used to characterize fluid flows in which there are simultaneous momentum and mass diffusion convection processes. It was named after German engineer Ernst Heinrich Wilhelm Schmidt (1892–1975). The Schmidt number is the ratio of the shear component for diffusivity ''viscosity/density'' to the diffusivity for mass transfer ''D''. It physically relates the relative thickness of the hydrodynamic layer and mass-transfer boundary layer. It is defined as: :\mathrm = \frac = \frac = \frac where: * \nu is the kinematic viscosity or (/\,) in units of (m2/s) * D is the mass diffusivity (m2/s). * is the dynamic viscosity of the fluid (Pa·s or N·s/m2 or kg/m·s) * \rho is the density of the fluid (kg/m3). The heat transfer analog of the Schmidt number is the Prandtl number (Pr). The ratio of thermal diffusivity to mass diffusivity is the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Prandtl Number
The Prandtl number (Pr) or Prandtl group is a dimensionless number, named after the German physicist Ludwig Prandtl, defined as the ratio of momentum diffusivity to thermal diffusivity. The Prandtl number is given as: : \mathrm = \frac = \frac = \frac = \frac where: * \nu : momentum diffusivity ( kinematic viscosity), \nu = \mu/\rho, ( SI units: m2/s) * \alpha : thermal diffusivity, \alpha = k/(\rho c_p), (SI units: m2/s) * \mu : dynamic viscosity, (SI units: Pa s = N s/m2) * k : thermal conductivity, (SI units: W/(m·K)) * c_p : specific heat, (SI units: J/(kg·K)) * \rho : density, (SI units: kg/m3). Note that whereas the Reynolds number and Grashof number are subscripted with a scale variable, the Prandtl number contains no such length scale and is dependent only on the fluid and the fluid state. The Prandtl number is often found in property tables alongside other properties such as viscosity and thermal conductivity. The mass transfer analog of the Prandtl number is t ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
G Equation
In Combustion, G equation is a scalar G(\mathbf,t) field equation which describes the instantaneous flame position, introduced by Forman A. Williams in 1985 in the study of premixed turbulent combustion. The equation is derived based on the Level-set method. The equation was studied by George H. Markstein earlier, in a restrictive form. Mathematical descriptionWilliams, Forman A. "Combustion theory." (1985). The G equation reads as :\frac + \mathbf\cdot\nabla G = U_L , \nabla G, where *\mathbf is the flow velocity field *U_L is the local burning velocity The flame location is given by G(\mathbf,t)=G_o which can be defined arbitrarily such that G(\mathbf,t)>G_o is the region of burnt gas and G(\mathbf,t) Local burning velocity The burning velocity of the[...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lewis Number
The Lewis number (Le) is a dimensionless number defined as the ratio of thermal diffusivity to mass diffusivity. It is used to characterize fluid flows where there is simultaneous heat and mass transfer. The Lewis number puts the thickness of the thermal boundary layer in relation to the concentration boundary layer. The Lewis number is defined as :\mathrm = \frac = \frac . where \alpha is the thermal diffusivity and D the mass diffusivity, \lambda the thermal conductivity, \rho the density, D_ the mixture-averaged diffusion coefficient, and c_p the specific heat capacity at constant pressure. In the field of fluid mechanics, many sources define the Lewis number to be the inverse of the above definition. The Lewis number can also be expressed in terms of the Prandtl number and the Schmidt number : :\mathrm = \frac. It is named after Warren K. Lewis (1882–1975), who was the first head of the Chemical Engineering Department at MIT. Some workers in the field of combustion assum ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Heat Release Parameter
In combustion, heat release parameter (or gas expansion parameter) is a dimensionless parameter which measures the amount of heat released by the combustion process. It is defined as :\alpha = \frac where *T_b is the burnt gas temperature *T_u is the unburnt mixture temperature. In typical combustion process, \alpha\approx 0.7-0.9. For isobaric combustion, using ideal gas law, the parameter can be expressed in terms of density,Clavin, P. (1985). Dynamic behavior of premixed flame fronts in laminar and turbulent flows. Progress in energy and combustion science, 11(1), 1-59. i.e., :\alpha = \frac = \frac. The ratio of burnt gas to unburnt gas temperature is :\frac = \frac=\frac. See also *Zel'dovich number The Zel'dovich number is a dimensionless number which provides a quantitative measure for the activation energy of a chemical reaction which appears in the Arrhenius exponent, named after the Russian scientist Yakov Borisovich Zel'dovich, who along ... References {{Reflist, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Explosion
An explosion is a rapid expansion in volume associated with an extreme outward release of energy, usually with the generation of high temperatures and release of high-pressure gases. Supersonic explosions created by high explosives are known as detonations and travel through shock waves. Subsonic explosions are created by low explosives through a slower combustion process known as deflagration. Causes Explosions can occur in nature due to a large influx of energy. Most natural explosions arise from volcanic or stellar processes of various sorts. Explosive volcanic eruptions occur when magma rises from below, it has very dissolved gas in it. The reduction of pressure as the magma rises and causes the gas to bubble out of solution, resulting in a rapid increase in volume. Explosions also occur as a result of impact events and in phenomena such as hydrothermal explosions (also due to volcanic processes). Explosions can also occur outside of Earth in the universe in events su ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Forman A
Forman may refer to: Places: *Forman, North Dakota, city in Sargent County, North Dakota, United States * Forman, West Virginia, unincorporated community in Grant County, West Virginia, United States * Forman Glacier between Mount Franke and Mount Cole, in the Queen Maud Mountains of Antarctica * Forman Park, in Syracuse, New York Surname: * A. G. Forman CBE (1910–1967), Chief of Naval Staff of the Ghana Navy * Al Forman (1928–2013), baseball umpire * Alexander A. Forman (1843–1922), American soldier in the American Civil War *Alison Forman (born 1969), Australian soccer player *Andrew Forman (1465–1521), Scottish diplomat and Archbishop *Arthur Forman (1850–1905), English schoolmaster and cricketer * Bill Forman (1886–1958), baseball player * Bruce Forman (born 1956), American jazz guitarist *Carol Forman (1918–1997), American actress * Charles William Forman (1821–1894), Presbyterian missionary in Pakistan *Christine Jones Forman, American astrophysicist *Craig Fo ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
