|
View Factor
In radiative heat transfer, a view factor, F_, is the proportion of the radiation which leaves surface A that strikes surface B. In a complex 'scene' there can be any number of different objects, which can be divided in turn into even more surfaces and surface segments. View factors are also sometimes known as configuration factors, form factors, angle factors or shape factors. Summation of view factors Because radiation leaving a surface is conserved, the sum of all view factors ''from'' a given surface, S_i, is unity: :\sum_^n = 1 For example, consider a case where two blobs with surfaces ''A'' and ''B'' are floating around in a cavity with surface ''C''. All of the radiation that leaves ''A'' must either hit ''B'' or ''C'', or if ''A'' is concave, it could hit ''A''. 100% of the radiation leaving ''A'' is divided up among ''A'', ''B'', and ''C''. Confusion often arises when considering the radiation that ''arrives'' at a ''target'' surface. In that case, it generally does n ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Radiative Heat Transfer
Thermal radiation is electromagnetic radiation generated by the thermal motion of particles in matter. Thermal radiation is generated when heat from the movement of charges in the material (electrons and protons in common forms of matter) is converted to electromagnetic radiation. All matter with a temperature greater than absolute zero emits thermal radiation. At room temperature, most of the emission is in the infrared (IR) spectrum. Particle motion results in charge-acceleration or dipole oscillation which produces electromagnetic radiation. Infrared radiation emitted by animals (detectable with an infrared camera) and cosmic microwave background radiation are examples of thermal radiation. If a radiation object meets the physical characteristics of a black body in thermodynamic equilibrium, the radiation is called blackbody radiation. Planck's law describes the spectrum of blackbody radiation, which depends solely on the object's temperature. Wien's displacement law dete ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
1 (number)
1 (one, unit, unity) is a number representing a single or the only entity. 1 is also a numerical digit and represents a single unit of counting or measurement. For example, a line segment of ''unit length'' is a line segment of length 1. In conventions of sign where zero is considered neither positive nor negative, 1 is the first and smallest positive integer. It is also sometimes considered the first of the infinite sequence of natural numbers, followed by 2, although by other definitions 1 is the second natural number, following 0. The fundamental mathematical property of 1 is to be a multiplicative identity, meaning that any number multiplied by 1 equals the same number. Most if not all properties of 1 can be deduced from this. In advanced mathematics, a multiplicative identity is often denoted 1, even if it is not a number. 1 is by convention not considered a prime number; this was not universally accepted until the mid-20th century. Additionally, 1 is ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Convex Function
In mathematics, a real-valued function is called convex if the line segment between any two points on the graph of a function, graph of the function lies above the graph between the two points. Equivalently, a function is convex if its epigraph (mathematics), epigraph (the set of points on or above the graph of the function) is a convex set. A twice-differentiable function of a single variable is convex if and only if its second derivative is nonnegative on its entire domain. Well-known examples of convex functions of a single variable include the quadratic function x^2 and the exponential function e^x. In simple terms, a convex function refers to a function whose graph is shaped like a cup \cup, while a concave function's graph is shaped like a cap \cap. Convex functions play an important role in many areas of mathematics. They are especially important in the study of optimization problems where they are distinguished by a number of convenient properties. For instance, a st ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Concave Function
In mathematics, a concave function is the negative of a convex function. A concave function is also synonymously called concave downwards, concave down, convex upwards, convex cap, or upper convex. Definition A real-valued function f on an interval (or, more generally, a convex set in vector space) is said to be ''concave'' if, for any x and y in the interval and for any \alpha \in ,1/math>, :f((1-\alpha )x+\alpha y)\geq (1-\alpha ) f(x)+\alpha f(y) A function is called ''strictly concave'' if :f((1-\alpha )x + \alpha y) > (1-\alpha) f(x) + \alpha f(y)\, for any \alpha \in (0,1) and x \neq y. For a function f: \mathbb \to \mathbb, this second definition merely states that for every z strictly between x and y, the point (z, f(z)) on the graph of f is above the straight line joining the points (x, f(x)) and (y, f(y)). A function f is quasiconcave if the upper contour sets of the function S(a)=\ are convex sets. Properties Functions of a single variable # A differentiab ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
View Factor Two Differential Areas Illustration
A view is a sight or prospect or the ability to see or be seen from a particular place. View, views or Views may also refer to: Common meanings * View (Buddhism), a charged interpretation of experience which intensely shapes and affects thought, sensation, and action * Graphical projection in a technical drawing or schematic ** Multiview orthographic projection, standardizing 2D images to represent a 3D object * Opinion, a belief about subjective matters * Page view, a visit to a World Wide Web page * Panorama, a wide-angle view * Scenic viewpoint, an elevated location where people can view scenery * World view, the fundamental cognitive orientation of an individual or society encompassing the entirety of the individual or society's knowledge and point-of-view Places * View, Kentucky, an unincorporated community in Crittenden County * View, Texas, an unincorporated community in Taylor County Arts, entertainment, and media Music * ''View'' (album), the 2003 debut album by ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Differential Area
In mathematics, differential refers to several related notions derived from the early days of calculus, put on a rigorous footing, such as infinitesimal differences and the derivatives of functions. The term is used in various branches of mathematics such as calculus, differential geometry, algebraic geometry and algebraic topology. Introduction The term differential is used nonrigorously in calculus to refer to an infinitesimal ("infinitely small") change in some Variable (mathematics), varying quantity. For example, if ''x'' is a Variable (mathematics), variable, then a change in the value of ''x'' is often denoted Δ''x'' (pronounced ''Delta (Greek), delta x''). The differential ''dx'' represents an infinitely small change in the variable ''x''. The idea of an infinitely small or infinitely slow change is, intuitively, extremely useful, and there are a number of ways to make the notion mathematically precise. Using calculus, it is possible to relate the infinitely small cha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Etendue
Etendue or étendue (; ) is a property of light in an optical system, which characterizes how "spread out" the light is in area and angle. It corresponds to the beam parameter product (BPP) in Gaussian beam optics. Other names for etendue include acceptance, throughput, light grasp, light-gathering power, optical extent, and the AΩ product. ''Throughput'' and ''AΩ product'' are especially used in radiometry and radiative transfer where it is related to the view factor (or shape factor). It is a central concept in nonimaging optics.Roland Winston et al.,, ''Nonimaging Optics'', Academic Press, 2004 Matthew S. Brennesholtz, Edward H. Stupp, ''Projection Displays'', John Wiley & Sons Ltd, 2008 From the source point of view, etendue is the product of the area of the source and the solid angle that the system's entrance pupil subtends as seen from the source. Equivalently, from the system point of view, the etendue equals the area of the entrance pupil times the solid angl ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Wilhelm Nusselt
Ernst Kraft Wilhelm Nußelt (Nusselt in English; born November 25, 1882 in Nuremberg – died September 1, 1957 in München) was a German engineer. Nusselt studied mechanical engineering at the Munich Technical University (Technische Universität München), where he got his doctorate in 1907. He taught in Dresden from 1913 to 1917. During this teaching tenure he developed the dimensional analysis of heat transfer, without any knowledge of the Buckingham π theorem or any other developments of Lord Rayleigh. In so doing he opened the door for further heat transfer analysis. After teaching and working in Switzerland and Germany between 1917 and 1925, he was appointed to the Chair of Theoretical Mechanics in München. There he made important developments in the field of heat exchangers. He held that position until 1952, being succeeded in the job by another important figure in the field of heat transfer, Ernst Schmidt. The Nusselt number used in Fluid Mechanics and Heat Transfer ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Solid Angle
In geometry, a solid angle (symbol: ) is a measure of the amount of the field of view from some particular point that a given object covers. That is, it is a measure of how large the object appears to an observer looking from that point. The point from which the object is viewed is called the ''apex'' of the solid angle, and the object is said to '' subtend'' its solid angle at that point. In the International System of Units (SI), a solid angle is expressed in a dimensionless unit called a ''steradian'' (symbol: sr). One steradian corresponds to one unit of area on the unit sphere surrounding the apex, so an object that blocks all rays from the apex would cover a number of steradians equal to the total surface area of the unit sphere, 4\pi. Solid angles can also be measured in squares of angular measures such as degrees, minutes, and seconds. A small object nearby may subtend the same solid angle as a larger object farther away. For example, although the Moon is much smaller ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fish-eye Lens
A fisheye lens is an ultra wide-angle lens that produces strong visual distortion intended to create a wide panoramic or hemispherical image. Fisheye lenses achieve extremely wide angles of view, well beyond any rectilinear lens. Instead of producing images with straight lines of perspective ( rectilinear images), fisheye lenses use a special mapping ("distortion"; for example: equisolid angle, see below), which gives images a characteristic convex non-rectilinear appearance. The term ''fisheye'' was coined in 1906 by American physicist and inventor Robert W. Wood based on how a fish would see an ultrawide hemispherical view from beneath the water (a phenomenon known as Snell's window). Their first practical use was in the 1920s for use in meteorology to study cloud formation giving them the name "whole-sky lenses". The angle of view of a fisheye lens is usually between 100 and 180 degrees, although lenses covering up to 280 degrees exist (see below). Their focal lengths depe ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Hemispherical Photography
Hemispherical photography, also known as canopy photography, is a technique to estimate solar radiation and characterize plant canopy geometry using photographs taken looking upward through an extreme wide-angle lens or a fisheye lens (Rich 1990). Typically, the viewing angle approaches or equals 180-degrees, such that all sky directions are simultaneously visible. The resulting photographs record the geometry of visible sky, or conversely the geometry of sky obstruction by plant canopies or other near-ground features. This geometry can be measured precisely and used to calculate solar radiation transmitted through (or intercepted by) plant canopies, as well as to estimate aspects of canopy structure such as leaf area index. Detailed treatments of field and analytical methodology have been provided by Paul Rich (1989, 1990) and Robert Pearcy (1989). History The hemispherical lens (also known as a fisheye or whole-sky lens) was originally designed by Robin Hill (1924) to vi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
