ASTM_C_108_-_46_2013.pdf

Designation:C10846(Reapproved 2013)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 parentheses 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,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 transmittance.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,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 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=specific 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 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/dLdgeneral expression giving value at eachpointk5sq/Ad/st/Ldfor 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;degrees,per unit of heat flow rate,for a particu-lar body or setup(where the area may not be known)R5t/qfor substantially uniform and steady-state heat flow,generallyR5L/kAfor substantially uniform and steady-state heat flowthrough a homogeneous medium of thickness L with planeparallel faces 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 resistance for a setup with 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 ThermalProperties.Current edition approved Sept.1,2013.Published September 2013.Originallyapproved in 1934.Last previous edition approved in 2009 as C10846(2009).DOI:10.1520/C0108-46R13.These symbols for heat transmission are identical with those appearing in theAmerican National Standard Letter 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 States1 h=surface coefficient of heat transfer;heat flow rate,per unit of area,per degree,across a boundary surfacedq/dA5htgeneral 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 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 surface 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/tSome particular area in the setup,A,may bechosen as a reference.Then fo