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Emmons Problem
In combustion, Emmons problem describes the flame structure which develops inside the boundary layer, created by a flowing oxidizer stream on flat fuel (solid or liquid) surfaces. The problem was first studied by Howard Wilson Emmons in 1956. The flame is of diffusion flame type because it separates fuel and oxygen by a flame sheet. The corresponding problem in a quiescent oxidizer environment is known as Clarke–Riley diffusion flame. Burning rateWilliams, F. A. (2018). Combustion theory. CRC Press. Consider a semi-infinite fuel surface with leading edge located at x=0 and let the free stream oxidizer velocity be U_\infty. Through the solution f(\eta) of Blasius equation f+ff''=0 (\eta is the self-similar Howarth–Dorodnitsyn coordinate), the mass flux \rho v (\rho is density and v is vertical velocity) in the vertical direction can be obtained :\rho v = \rho_\infty \mu_\infty \sqrt \left(f'\rho \int_0^\eta \rho^ \ d\eta - f\right), where :\xi = \int_0^x \rho_\infty \mu_\in ... [...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 produced. A ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Howard Wilson Emmons
Howard Wilson Emmons (1912–1998) was an American professor in the department of Mechanical Engineering at Harvard University. During his career he conducted original research on fluid mechanics, combustion and fire safety. Today he is most widely known for his pioneering work in the field of fire safety engineering. He has been called "the father of modern fire science" for his contribution to the understanding of flame propagation and fire dynamics. He also helped design the first supersonic wind tunnel, identified a signature of the transition to turbulence in boundary layer flows (now known as "Emmons spots"), and was the first to observe compressor stall in a gas turbine compressor (still a major item of research today). He initiated studies on diffusion flames inside a boundary layer, and Emmons problem is named after him. He was eventually awarded the Timoshenko Medal by the American Society of Mechanical Engineers and the 1968 Sir Alfred Egerton Gold Medal from The Combusti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Diffusion Flame
In combustion, a diffusion flame is a flame in which the oxidizer and fuel are separated before burning. Contrary to its name, a diffusion flame involves both diffusion and convection processes. The name diffusion flame was first suggested by S.P. Burke and T.E.W. Schumann in 1928, to differentiate from premixed flame where fuel and oxidizer are premixed prior to burning. The diffusion flame is also referred to as nonpremixed flame. The burning rate is however still limited by the rate of diffusion. Diffusion flames tend to burn slower and to produce more soot than premixed flames because there may not be sufficient oxidizer for the reaction to go to completion, although there are some exceptions to the rule. The soot typically produced in a diffusion flame becomes incandescent from the heat of the flame and lends the flame its readily identifiable orange-yellow color. Diffusion flames tend to have a less-localized flame front than premixed flames. The contexts for diffusion may ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clarke–Riley Diffusion Flame
In combustion, Clarke–Riley diffusion flame is a diffusion flame that develops inside a naturally convected boundary layer on a hot fuel surface with quiescent oxidizer environment, first studied and experimentally verified by John Frederick Clarke and Norman Riley in 1976.Clarke, J. F., & Riley, N. (1976). Free convection and the burning of a horizontal fuel surface. Journal of Fluid Mechanics, 74(3), 415-431. This problem is an extension of Emmons problem. See also *Emmons problem *Liñán's diffusion flame theory Liñán diffusion flame theory is a theory developed by Amable Liñán in 1974 to explain the diffusion flame structure using activation energy asymptotics and Damköhler number asymptotics.Liñán, A., Martínez-Ruiz, D., Vera, M., & Sánchez, A. ... References Fluid dynamics Combustion {{combustion-stub ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Blasius Equation
In physics and fluid mechanics, a Blasius boundary layer (named after Paul Richard Heinrich Blasius) describes the steady two-dimensional laminar boundary layer that forms on a semi-infinite plate which is held parallel to a constant unidirectional flow. Falkner and Skan later generalized Blasius' solution to wedge flow (Falkner–Skan boundary layer), i.e. flows in which the plate is not parallel to the flow. Prandtl's boundary layer equations Using scaling arguments, Ludwig Prandtl argued that about half of the terms in the Navier-Stokes equations are negligible in boundary layer flows (except in a small region near the leading edge of the plate). This leads to a reduced set of equations known as the boundary layer equations. For steady incompressible flow with constant viscosity and density, these read: Mass Continuity: \dfrac+\dfrac=0 x-Momentum: u \dfrac + v \dfrac = - \dfrac \dfrac + \dfrac y-Momentum: 0= - \dfrac \dfrac Here the coordinate system is chosen wi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Howarth–Dorodnitsyn Transformation
In fluid dynamics, Howarth–Dorodnitsyn transformation (or Dorodnitsyn-Howarth transformation) is a density-weighted coordinate transformation, which reduces compressible flow conservation equations to simpler form (in most cases, to incompressible form). The transformation was first used by Anatoly Dorodnitsyn in 1942 and later by Leslie Howarth in 1948. The transformation of y coordinate (usually taken as the coordinate normal to the predominant flow direction) to \eta is given by :\eta = \int_0^y \frac \ dy, where \rho is the density and \rho_\infty is the density at infinity. The transformation is extensively used in boundary layer theory and other gas dynamics problems. Stewartson–Illingworth transformation Keith Stewartson and C. R. Illingworth, independently introduced in 1949, a transformation that extends the Howarth–Dorodnitsyn transformation. The transformation reads asN. Curle and HJ Davies: Modern Fluid Dynamics, Vol. 2, Compressible Flow :\xi = \int_0^x \frac\f ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Density
Density (volumetric mass density or specific mass) is the substance's mass per unit of volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' can also be used. Mathematically, density is defined as mass divided by volume: : \rho = \frac where ''ρ'' is the density, ''m'' is the mass, and ''V'' is the volume. In some cases (for instance, in the United States oil and gas industry), density is loosely defined as its weight per unit volume, although this is scientifically inaccurate – this quantity is more specifically called specific weight. For a pure substance the density has the same numerical value as its mass concentration. Different materials usually have different densities, and density may be relevant to buoyancy, purity and packaging. Osmium and iridium are the densest known elements at standard conditions for temperature and pressure. To simplify comparisons of density across different s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Liñán's Diffusion Flame Theory
Liñán diffusion flame theory is a theory developed by Amable Liñán in 1974 to explain the diffusion flame structure using activation energy asymptotics and Damköhler number asymptotics.Liñán, A., Martínez-Ruiz, D., Vera, M., & Sánchez, A. L. (2017). The large-activation-energy analysis of extinction of counterflow diffusion flames with non-unity Lewis numbers of the fuel. Combustion and Flame, 175, 91-106. Liñán used counterflowing jets of fuel and oxidizer to study the diffusion flame structure, analyzing for the entire range of Damköhler number. His theory predicted four different types of flame structure as follows, * ''Nearly-frozen ignition regime'', where deviations from the frozen flow conditions are small (no reaction sheet exist in this regime), * ''Partial burning regime'', where both fuel and oxidizer cross the reaction zone and enter into the frozen flow on other side, * ''Premixed flame regime'', where only one of the reactants cross the reaction zone, in ... [...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 time. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
