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翻訳と辞書　辞書検索 [ 開発暫定版 ] スポンサード リンク Heat transfer coefficient ： ウィキペディア英語版 Heat transfer coefficient The heat transfer coefficient or film coefficient, in thermodynamics and in mechanics is the proportionality constant between the heat flux and the thermodynamic driving force for the flow of heat (i.e., the temperature difference, Δ''T''): :$h\; =\; \backslash frac$ where: :q: amount of heat transferred (heat flux), W/m2 i.e., thermal power per unit area, ''q'' = ''d$\backslash dot$''/''dA'' :''h'': heat transfer coefficient, W/(m2•K) :Δ''T'': difference in temperature between the solid surface and surrounding fluid area, K. It is used in calculating the heat transfer, typically by convection or phase transition between a fluid and a solid. The heat transfer coefficient has SI units in watts per squared meter kelvin: W/(m2K). Heat transfer coefficient is the inverse of thermal insulance. This is used for building materials (R-value) and for clothing insulation. There are numerous methods for calculating the heat transfer coefficient in different heat transfer modes, different fluids, flow regimes, and under different thermohydraulic conditions. Often it can be estimated by dividing the thermal conductivity of the convection fluid by a length scale. The heat transfer coefficient is often calculated from the Nusselt number (a dimensionless number). There are also (online calculators ) available specifically for heat transfer fluid applications. Experimental assessment of the heat transfer coefficient poses some challenges especially when small fluxes are to be measured (e.g. ). == Composition == A simple method for determining an overall heat transfer coefficient that is useful to find the heat transfer between simple elements such as walls in buildings or across heat exchangers is shown below. Note that this method only accounts for conduction within materials, it does not take into account heat transfer through methods such as radiation. The method is as follows: :$1/(U\; \backslash cdot\; A)\; =\; 1/(h\_1\; \backslash cdot\; A\_1)\; +\; dx\_w\; /(k\; \backslash cdot\; A)\; +\; 1/(h\_2\; \backslash cdot\; A\_2)$ Where: * $U$ = the overall heat transfer coefficient (W/(m2•K)) * $A$ = the contact area for each fluid side (m2) (with $A\_$ and $A\_$ expressing either surface) * $k$ = the thermal conductivity of the material (W/(m·K)) * $h$ = the individual convection heat transfer coefficient for each fluid (W/(m2•K)) * $dx\_w$ = the wall thickness (m). As the areas for each surface approach being equal the equation can be written as the transfer coefficient per unit area as shown below: :$1/U\; =\; 1/h\_1\; +\; dx\_w\; /k\; +\; 1/h\_2$ or :$U\; =\; 1/(1/h\_1\; +\; dx\_w\; /k\; +\; 1/h\_2)$ It is to be noted that often the value for $dx\_w$ is referred to as the difference of two radii where the inner and outer radii are used to define the thickness of a pipe carrying a fluid, however, this figure may also be considered as a wall thickness in a flat plate transfer mechanism or other common flat surfaces such as a wall in a building when the area difference between each edge of the transmission surface approaches zero. In the walls of buildings the above formula can be used to derive the formula commonly used to calculate the heat through building components. Architects and engineers call the resulting values either the U-Value or the R-Value of a construction assembly like a wall. Each type of value (R or U) are related as the inverse of each other such that R-Value = 1/U-Value and both are more fully understood through the concept of an overall heat transfer coefficient described in lower section of this document. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Heat transfer coefficient」の詳細全文を読む スポンサード リンク 翻訳と辞書 : 翻訳のためのインターネットリソース Copyright(C) kotoba.ne.jp 1997-2016. All Rights Reserved.