1、Designation: C108 46 (Reapproved 2018)Standard Symbols forHeat Transmission1This standard is issued under the fixed designation C108; 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 parenthese
2、s indicates the year of last reapproval. Asuperscript epsilon () 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 orshape,
3、 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 transm
4、ittance.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, a
5、nd 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 of
6、 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 is also q with a subscript to distinguish from heat flow rate.)c = spec
7、ific heatT = temperature on absolute scalet = temperature, degrees Celsius or Fahrenheitt, = timeW = weight; quantity of matter measured in pounds, kilograms, etc.w = flow rate; pounds, kilograms, etc., per unit of timeq = heat flow rate; time rate of heat transferred for a particular setupwith any
8、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/dA52ksdt/dLd general expression giving value at
9、 eachpointk5sq/Ad/st/Ld for substantially uniform and steady-stateheat flow through a homogeneous medium of thickness L,with plane parallel faces of area A, and a constant tempera-ture difference t applied to the faces1/k = thermal resistivity; reciprocal of conductivityR = thermal resistance; degre
10、es, per unit of heat flow rate, for a particu-lar body or setup (where the area may not be known)R5t/q for substantially uniform and steady-state heat flow,generallyR5L/kA for substantially uniform and steady-state heat flowthrough a homogeneous medium of thickness L with planeparallel faces of area
11、 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 resistance for a setup with
12、 a particu-lar area (which may not be known) and RA for resistance of unitarea. In some British texts R is used for thermal resistance of unitarea, here called RA1These symbols are under the jurisdiction of ASTM Committee C08 onRefractories and are the direct responsibility of Subcommittee C08.02 on
13、 ThermalProperties.Current edition approved Feb. 1, 2018. Published February 2018. Originallyapproved in 1934. Last previous edition approved in 2013 as C108 46 (2013).DOI: 10.1520/C0108-46R18.These symbols for heat transmission are identical with those appearing in theAmerican National Standard Let
14、ter Symbols for Heat and ThermodynamicsIncluding Heat Flow (ANSI Y10.4) of the American National Standards Institute.Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internati
15、onally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1h = surface coefficient of heat transfer; heat flow
16、rate, per unit of area,per degree, across a boundary surfacedq/dA5ht general expression giving value at each pointhm5sq/Ad/tmfor substantially uniform and steady-state heatflow, where hmand tmare constant over the area A orwhere one (but not both) of them varies but may substan-tially be represented
17、 by a mean value. h is an average prop-erty of a particular boundary condition or film and is notnecessarily inversely proportional to film thickness. tmisthe mean absolute difference between the temperature tsofthe surface and t, the bulk temperature of the ambient fluid,or the temperature of the s
18、urface of an adjacent solid.U = overall coefficient of heat transfer; sometimes called thermal trans-mittance per unit of area; heat flow rate, per unit of area, perdegree, for a particular setup of one or more bodies and films.Then for substantially uniform and steady-state heat flowU5sq/Ad/t Some
19、particular area in the setup, A, may bechosen as a reference. Then for a setup of homogeneousbodies, area Ax, and adjacent films, area Afx, where the cor-responding values of h and k are substantially constant overthe areas considered,1/U 5osL/kAxAd1of1/shAfx/AdgFor parallel walls,1/U 5osL/kd1os1/hd
20、 or,1/U 5oRA1os1/hdS = shape factor of a structure; heat flow rate, divided by equivalentthermal conductivity and by the temperature difference betweeninner and outer surfaces,S 5 q/kts = total emissivity; ratio of radiant flux from a source to that for ablackbody of the same size and shape, at the
21、same temperature,according to the Stefan-Boltzmann law which is, 5 AT4 = radiant flux; radiant energy per unit of time, for any area A = thermal diffusivity; thermal conductivity divided by heat capacity perunit volume, 5 k/cG = flow rate in pounds per unit of time, per unit of area of cross sec-tio
22、n; called weight velocity, or mass velocity,G 5 V = 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 thi
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26、8-2959,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). Permission rights to photocopy the standard may also be secured from the Copyright Clearance Center, 222Rosewood Drive, Danvers, MA 01923, Tel: (978) 646-2600; http:/ 46 (2018)2
