ASTM C108-1946(2004) Standard Symbols for Heat Transmission《热传导用符号》.pdf

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1、Designation: C 108 46 (Reapproved 2004)Standard Symbols forHeat Transmission1This standard is issued under the fixed designation C 108; the number immediately following the designation indicates the year oforiginal adoption or, in the case of revision, the year of last revision. A number in parenthe

2、ses indicates the year of last reapproval. Asuperscript epsilon (e) indicates an editorial change since the last revision or reapproval.SPECIAL PRACTICES RELATING TO HEAT FLOWTERMSTerms Ending in “ivity”Terms ending in “ivity” designatecharacteristics of materials, normally independent of size orsha

3、pe, sometimes called “specific properties.”Examples: Conductivity and resistivity.Terms Ending in “ance”Terms ending in “ance” designateproperties of a particular object, depending not only on thematerial, but also upon size and shape, sometimes called“total quantities.”Examples: Conductance and tra

4、nsmittance.Terms Ending in “ion”Terms ending in “ion” designatetime rate of the process of transfer; flux, flow rate.Examples: Conduction and transmission.Transmission“Transmission,” “transmissivity,” “transmit-tance” usually refer to transfer by one or more of theprocesses of conduction, convection

5、, and radiation.Conduction“Conduction,” “conductivity,” “conductance”usually refer to transfer within a medium, and without bodilydisplacement as occurs with convection, and without transferat a distance as occurs with radiation.HEAT FLOW SYMBOLSA = areap = density; pounds, kilograms, etc., per unit

6、 of volumeL = length of path of heat flowQ = total quantity of heat transferred (with subscripts for particular casesand to distinguish for Q for volume rate)Q = volume rate; discharge by volume; fluid rate of flow by volume.(There also is used q with a subscript to distinguish from heat flowrate.)c

7、 = specific heatT = temperature on absolute scalet = temperature, degrees Celsius or Fahrenheitt, t = timeW = weight; quantity of matter measured in pounds, kilograms, etc.w = flow rate; pounds, kiliograms, etc., per unit of timeq = heat flow rate; time rate of heat transferred for a particular setu

8、pwith any value of area Aq is in general the time derivative of total quantity of heattransferred. For steady-state heat flow, q is total quantity of heatdivided by time.k = thermal conductivity; heat flow rate, per unit of area, per “degreeper unit of length”dq/dmathitA = k (dt/dL) general expressi

9、on giving value at eachpointk=(q/A)/(Dt/L) for substantially uniform and steady-state heat flowthrough a homogeneous medium of thickness L, with plane parallelfaces of area A, and a constant temperature difference Dt appliedto the faces1/k = thermal resistivity; reciprocal of conductivityR = thermal

10、 resistance; degrees, per unit of heat flow rate, for aparticular body or setup (where the area may not be known)R=Dt/q for substantially uniform and steady-state heat flow,generallyR = L/kA for substantially uniform and steady-state heat flowthrough a homogeneous medium of thickness L with plane pa

11、rallelfaces of area A1/R = thermal conductance; reciprocal of thermal resistance (C is alsoused)1/RA = thermal conductance per unit of area; heat flow, rate, per unit ofarea, per degreeRA = thermal resistance of unit area; degrees, per “unit of heat flow rateper unit of area.” R is used for resistan

12、ce for a setup with aparticular area (which may not be known) and RA for resistance ofunit area. In some British texts R is used for thermal resistance ofunit area, here called RAh = surface coefficient of heat transfer; heat flow rate, per unit of area,per degree, across a boundary surfacedq/dA=hDt

13、 general expression giving value at each pointhm= (q/A)/Dtmfor substantially uniform and steady-stateheat flow, where hmand Dtmare constant over the area A or whereone (but not both) of them varies but may substantially berepresented by a mean value. h is an average property of aparticular boundary

14、condition or film and is not necessarily inverselyproportional to film thickness. Dtmis the mean absolute differencebetween the temperature tsof the surface and t, the bulktemperature of the ambient fluid, or the temperature of the surfaceof an adjacent solid.U = overall coefficient of heat transfer

15、; sometimes called thermaltransmittance per unit of area; heat flow rate, per unit of area, perdegree, for a particular setup of one or more bodies and films.Thenfor substantially uniform and steady-state heat flowU = (q/A)/Dt Some particular area in the setup, A, may be chosenas a reference. Then f

16、or a setup of homogeneous bodies, area Ax,and adjacent films, area Afx, where the corresponding values of hand k are substantially constant over the areas considered,1/U 5 (L/kAxA! 1 (1/hAfx/A!#1These symbols are under the jurisdiction of ASTM Committee C08 onRefractories and are the direct responsi

17、bility of Subcommittee C08.02 on ThermalProperties.Current edition approved March 1, 2004. Published February 2005. Originallyapproved in 1934. Last previous edition approved in 1998 as C 10846 (1998).These symbols for heat transmission are identical with those appearing in theAmerican National Stan

18、dard Letter Symbols for Heat and ThermodynamicsIncluding Heat Flow (ANSI Y10.4) of the American National Standards Institutes.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.For parallel walls,1/U 5 (L/k! 1 (1/h! or,1/U 5 (RA 1 (1/h!

19、S = shape factor of a structure; heat flow rate, divided by equivalentthermal conductivity and by the temperature difference betweeninner and outer surfaces,S 5 q/kDtse = total emissivity; ratio of radiant flux from a source to that for ablackbody of the same size and shape,at the same temperature,

20、according to the Stefan-Boltzmann lawwhich is,F5seAT4F = radiant flux; radiant energy per unit of time, for any area Aa = thermal diffusivity; thermal conductivity divided by heat capacity perunit volume,a5k/crG = flow rate in pounds per unit of time, per unit of area of crosssection; called weight

21、velocity, or mass velocity,G 5 VrD = difference between values, often taken as positive when it is thatdifference causing flow.ASTM International takes no position respecting the validity of any patent rights asserted in connection with any item mentionedin this standard. Users of this standard are

22、expressly advised that determination of the validity of any such patent rights, and the riskof infringement of such rights, are entirely their own responsibility.This standard is subject to revision at any time by the responsible technical committee and must be reviewed every five years andif not re

23、vised, either reapproved or withdrawn. Your comments are invited either for revision of this standard or for additional standardsand should be addressed to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of theresponsible technical committee, which you

24、may attend. If you feel that your comments have not received a fair hearing you shouldmake your views known to the ASTM Committee on Standards, at the address shown below.This standard is copyrighted by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959,United States. Individual reprints (single or multiple copies) of this standard may be obtained by contacting ASTM at the aboveaddress or at 610-832-9585 (phone), 610-832-9555 (fax), or serviceastm.org (e-mail); or through the ASTM website(www.astm.org).C 108 46 (2004)2