1、Designation: C168 18Standard Terminology Relating toThermal Insulation1This standard is issued under the fixed designation C168; 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 ind
2、icates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope1.1 This standard provides definitions, symbols, units, andabbreviations of terms used in ASTM standards pertaining tothermal insulating materials, and to materials
3、 associated withthem.1.2 This terminology is not intended to be used to classifyinsulation materials as having particular properties. Rather,classification of insulation materials is to be done by thematerial standards themselves.1.3 This standard does not purport to address all of thesafety concern
4、s, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety, health, and environmental practices and deter-mine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accor-dance with int
5、ernationally recognized principles on standard-ization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recom-mendations issued by the World Trade Organization TechnicalBarriers to Trade (TBT) Committee.2. Referenced Documents2.1 ASTM Standards:2D35
6、74 Test Methods for Flexible Cellular MaterialsSlab,Bonded, and Molded Urethane FoamsE456 Terminology Relating to Quality and StatisticsE2282 Guide for Defining the Test Result of a Test Method2.2 ISO Standard:ISO 7345 Thermal InsulationPhysical Quantities andDefinitions33. Terminology3.1 Definition
7、s:absorptance, nthe ratio of the radiant flux absorbed by abody to that incident upon it.absorption, ntransformation of radiant energy to a differentform of energy by interaction with matter.apparent thermal conductivity, a, ka, na thermal conduc-tivity assigned to a material that exhibits thermal t
8、ransmis-sion by several modes of heat transfer resulting in propertyvariation with specimen thickness, or surface emittance. Seeconductivity, thermal.DISCUSSIONThermal conductivity and resistivity are normally con-sidered to be intrinsic or specific properties of materials and, as such,should be ind
9、ependent of thickness. When nonconductive modes ofheat transfer are present within the specimen (radiation, free convec-tion) this may not be the case. To indicate the possible presence of thisphenomena (for example, thickness effect) the modifier “apparent” isused, as in apparent thermal conductivi
10、ty.DISCUSSIONTest data using the “apparent” modifier must be quotedonly for the conditions of the measurement. Values of thermal conduc-tance (material C) and thermal resistance (material R) calculated fromapparent thermal conductivity or resistivity, are valid only for the sameconditions.DISCUSSION
11、Test data labeled with “apparent” shall not include anyequipment related measurement errors induced due to measurementattempts beyond an apparatus range or calibration.DISCUSSIONUse of the “apparent” modifier with system C or systemR measurements is not permitted.apparent thermal resistivity, ra, na
12、 thermal resistivityassigned to a material that exhibits thermal transmission byseveral modes of heat transfer resulting in property variationwith specimen thickness, or surface emittance. Seeresistivity, thermal.DISCUSSIONSee entire discussion under apparent thermal conduc-tivity.area weight, nweig
13、ht per unit area for a specified sample, inunits of lb/ft2(kg/m2).aerogel, na homogeneous, low-density solid phase materialderived from a gel, in which the liquid component of the gelhas been replaced with a gas.DISCUSSIONThe resulting material has a porous structure with anaverage pore size below t
14、he mean free path of air molecules at standardatmospheric pressure and temperature.batt, nblanket insulation manufactured to dimensions asrequired by a specific application.1This terminology is under the jurisdiction of ASTM Committee C16 onThermal Insulation and is the direct responsibility of Subc
15、ommittee C16.94 onTerminology.Current edition approved April 15, 2018. Published April 2018. Originallyapproved in 1941. Last previous edition approved in 2017 as C168 17.DOI:101520/C0168-18.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Service at serv
16、iceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.3Available from American National Standards Institute (ANSI), 25 W. 43rd St.,4th Floor, New York, NY 10036, http:/www.ansi.org.Copyright ASTM International, 100 Barr Harb
17、or Drive, PO Box C700, West Conshohocken, PA 19428-2959. United StatesThis international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for theDevelopment of International Standards, Guides and Recommendati
18、ons issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.1blackbody, nthe ideal, perfect emitter and absorber ofthermal radiation. It emits radiant energy at each wavelengthat the maximum rate possible as a consequence of itstemperature, and absorbs all incident radianc
19、e.blanket, nflexible insulation product, supplied rolled or flat.blanket insulation, na relatively flat and flexible insulationin coherent sheet form furnished in units of substantial area.blanket insulation, metal mesh, nblanket insulation cov-ered by flexible metal-mesh facings attached on one or
20、bothsides.block insulation, nrigid insulation preformed into rectangu-lar units.board insulation, nsemirigid insulation preformed into rect-angular units having a degree of suppleness particularlyrelated to their geometrical dimensions.calcium silicate, ninsulation composed principally of hy-drous c
21、alcium silicate, and which usually contains reinforc-ing fibers.cellular elastomeric, ninsulation composed principally ofnatural or synthetic elastomers, or both, processed to form aflexible, semirigid, or rigid foam which has a predominantlyclosed-cell structure.cellular glass, ninsulation composed
22、 of glass processed toform a rigid foam having a predominantly closed-cellstructure.cellular polyimide, ninsulation composed of the reactionproduct in which the bonds formed between monomersduring polymerization are essentially imide units forming acellular structure.cellular polystyrene, ninsulatio
23、n composed principally ofpolymerized styrene resin processed to form a rigid foamhaving a predominantly closed-cell structure.cellular polyurethane, ninsulation composed principally ofthe catalyzed reaction product of polyisocyanate and poly-hydroxy compounds, processed usually with fluorocarbongas
24、to form a rigid foam having a predominantly closed-cellstructure.cellulosic fiber, ninsulation composed principally of cellu-lose fibers usually derived from paper, paperboard stock, orwood, with or without binders.cement, finishing, na mixture of dry fibrous or powderymaterials, or both, that when
25、mixed with water develops aplastic consistency, and when dried in place forms a rela-tively hard, protective surface.cement, insulating, na mixture of dry granular, flaky,fibrous, or powdery materials that when mixed with waterdevelops a plastic consistency, and when dried in placeforms a coherent c
26、overing that affords substantial resistanceto heat transmission.cladding, nSee jacket (as related to insulation jacketing).closed cell foam, na material comprised predominantly ofindividual non-interconnecting cellular voids.coating, na liquid or semiliquid that dries or cures to form aprotective fi
27、nish, suitable for application to thermal insula-tion or other surfaces in thickness of 30 mils (0.76 mm) orless, per coat.conductance, film, nthe time rate of heat flow from a unitarea of a surface to its surroundings, induced by a unittemperature difference between the surface and the environ-ment
28、.DISCUSSIONThe environment is a fluid (liquids or gases). h dependson the nature of fluid motion past the surface (laminar or turbulent). (hin SI units: W/m2K).conductance, thermal, C, nthe time rate of steady state heatflow through a unit area of a material or construction inducedby a unit temperat
29、ure difference between the body surfaces.C 5 q/TA conductance (C) associated with a material shall bespecified as a material C. A conductance (C) associated witha system or construction of materials shall be specified as asystem C.(C in SI units: W/m2K.) (C in inch-pound units:(Btu/h)/ft2/F = Btu h
30、ft2F.)DISCUSSIONThe average temperature of a surface is the area-weighted temperature of that surface.DISCUSSIONWhen the surfaces of a mass type thermal insulation arenot of equal areas, as in the case of thermal transmission in the radialdirection, or are not of uniform separation (thickness), the
31、surface areaand thickness to which the conductance is assigned must be defined.DISCUSSION“Total” or “areal” thermal conductance are often usedas synonyms for thermal conductance.DISCUSSIONThermal conductance and thermal resistance are recip-rocals of one another.DISCUSSIONSee Discussion under resist
32、ance, thermal.conductivity, thermal, or k, nthe time rate of steady stateheat flow through a unit area of a homogeneous materialinduced by a unit temperature gradient in a directionperpendicular to that unit area. ( or k in SI units: (W/m2)/(K/m) = W m K.) ( or k in inch-pound units: (Btu/h)/ft2/(F/
33、ft) = Btu h ft F) or (Btu/h)/ft2/(F/in.) = Btu in./h ft2F.) (Seediscussion under apparent thermal conductivity.)DISCUSSIONThermal conductivity testing is usually done in one oftwo apparatus/specimen geometries: flat-slab specimens with parallelheat flux lines, or cylindrical specimens with radial he
34、at flux lines. Theoperational definitions of thermal conductivity for these two cases aregiven as follows:Flat 2 slab geometry 5QALT(1)where:Q = heat flow rate,A = area through which Q passes, andL = thickness of the flat-slab specimen across which thetemperature difference T exists.The T/L ratio ap
35、proximates the temperature gradient.Cylindrical geometry 5Q2lTloger2r1(2)C168 182where:1 = length,r2= the outer radius, andr1= the inner radius of the cylinder.Eq 1 and Eq 2 are actually special-case simplifications of the more generaldefinition:thermal conductivity, a tensor property defined by the
36、 tensor equation:q 52T (3)where q is the heat flux vector, and T (grad T) is the temperature gra-dient vector. Except in theoretical discussions, this generalized form ofthe definition is seldom used. For experimental situations, the geometryof the testing apparatus and the specimen are chosen such
37、that Eq 3reduces to the one-dimensional scalar equation:Q 52AdTdu(4)where:Q = heat flow rate,A = area through which Q passes, = thermal conductivity, anddT/du = the temperature gradient in the direction of heatflow.At steady state, Eq 1 and Eq 2 are consistent with Eq 4 if T is sufficientlysmall. If
38、 T is not sufficiently small, then Eq 1 and Eq 2 define a meanthermal conductivity over the T range, and this range in addition to themean temperature should be stated.DISCUSSIONIf the measured thermal property indicates that otherthan conductive heat flows are present, as evidenced by dependence on
39、specimen thickness, air flow, or emittance of bounding surfaces, thenthis definition does not apply. See also, apparent thermal conductiv-ity.DISCUSSIONThermal conductivity and thermal resistivity are recip-rocals of one another.DISCUSSIONAs an additional reference and discussion along similarlines,
40、 see the International Standard ISO 7345 Annex.corrosion retarder (as related to insulation jacketing), nSeemoisture barrier (as related to insulation jacketing).coverage, nthe area to be covered per unit volume of coatingto obtain specified dry thickness and desired performance.covering capacity, d
41、ry, nthe area covered to a dry thicknessof 1 in. (25 mm) by 100 lb (45.4 kg) of dry cement whenmixed with the recommended amount of water, molded anddried to constant weight.covering capacity, wet, nthe area covered to a wet thicknessof 1 in. (25 mm) by 100 lb (45.4 kg) of dry cement whenmixed with
42、the recommended amount of water, and molded.density, nthe mass per unit volume of a material. ( in SIunits: kg/m3.) ( in inch-pound units: lb/ft3.)DISCUSSIONThe term mass is used and not weight, due to thebuoyancy effect of some low density closed cell insulations.density, apparent (of applied insul
43、ation), nthe mass perunit volume of in-place mass thermal insulation.dewpoint temperature, nthe temperature at which conden-sation of water vapor in a space begins for a given state ofhumidity and pressure as the vapor temperature is reduced;the temperature corresponding to saturation (100 % relativ
44、ehumidity) for a given absolute humidity at constant pressure.diatomaceous silica, ninsulation composed principally ofdiatomaceous earth with or without binders, and whichusually contains reinforcing fibers.diffusivity, thermal, nthe ratio of thermal conductivity of asubstance to the product of its
45、density and specific heat. (InSI units: (W/(mK)/(kg/m3)(J/(kgK) = m2/s.) (In inch-pound units: (Btu/(hrft) F)/(lb/ft3)(Btu/(lbF) = ft2/hr.)emittance, , nthe ratio of the radiant flux emitted by aspecimen to that emitted by a blackbody at the sametemperature and under the same conditions.emittance, d
46、irectional (; ), nthe ratio of the radiancefrom a surface in a particular direction to the radiance froma blackbody at the same temperature under the sameconditions.emittance, hemispherical Hor (2), nthe average direc-tional emittance over a hemispherical envelope covering asurface.emittance, spectr
47、al or (; ; ), nan emittance based onthe radiant energy emitted per unit wavelength interval(monochromatic radiant energy).DISCUSSIONWhere necessary to avoid confusion, emittances shouldbe designated by subscripts, for example: HT, H, N, , HT. Formost engineering purposes, the hemispherical total emi
48、ttance HTsuffices.emittance, total Tor (t), nan emittance that is anintegrated average over all wavelengths of radiant energyemitted.facer, nthe outermost adhered top or bottom, or both, sheet(or layer) of an insulation product, rigid or flexible, that iscomprised of a different material than the in
49、sulation itself.facing, na thin covering adhered to the surface of insulationprior to field installation.fibrous glass, nA synthetic vitreous fiber insulation made bymelting predominantly silica sand and other inorganicmaterials, and then physically forming the melt into fibers.DISCUSSIONCommonly referred to as fiber glass.DISCUSSIONTo form an insulation product, there are often othermaterials applied to the fibrous glass such as binders, oils, etc
