1、Designation: C 680 08Standard Practice forEstimate of the Heat Gain or Loss and the SurfaceTemperatures of Insulated Flat, Cylindrical, and SphericalSystems by Use of Computer Programs1This standard is issued under the fixed designation C 680; the number immediately following the designation indicat
2、es 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.1. Scope1.1 This practice provides the algorithms and cal
3、culationmethodologies for predicting the heat loss or gain and surfacetemperatures of certain thermal insulation systems that canattain one dimensional, steady- or quasi-steady-state heattransfer conditions in field operations.1.2 This practice is based on the assumption that the thermalinsulation s
4、ystems can be well defined in rectangular, cylindri-cal or spherical coordinate systems and that the insulationsystems are composed of homogeneous, uniformly dimen-sioned materials that reduce heat flow between two differenttemperature conditions.1.3 Qualified personnel familiar with insulation-syst
5、emsdesign and analysis should resolve the applicability of themethodologies to real systems. The range and quality of thephysical and thermal property data of the materials comprisingthe thermal insulation system limit the calculation accuracy.Persons using this practice must have a knowledge of the
6、practical application of heat transfer theory relating to thermalinsulation materials and systems.1.4 The computer program that can be generated from thealgorithms and computational methodologies defined in thispractice is described in Section 7 of this practice.The computerprogram is intended for f
7、lat slab, pipe and hollow sphereinsulation systems.1.5 The values stated in inch-pound units are to be regardedas standard. The values given in parentheses are mathematicalconversions to SI units that are provided for information onlyand are not considered standard.1.6 This standard does not purport
8、 to address all of thesafety concerns, if any, associated with its use. It is theresponsibility of the user of this standard to establish appro-priate safety and health practices and determine the applica-bility of regulatory limitations prior to use.2. Referenced Documents2.1 ASTM Standards:2C 168
9、Terminology Relating to Thermal InsulationC 177 Test Method for Steady-State Heat Flux Measure-ments and Thermal Transmission Properties by Means ofthe Guarded-Hot-Plate ApparatusC 335 Test Method for Steady-State Heat Transfer Proper-ties of Pipe InsulationC 518 Test Method for Steady-State Thermal
10、 TransmissionProperties by Means of the Heat Flow Meter ApparatusC 585 Practice for Inner and Outer Diameters of RigidThermal Insulation for Nominal Sizes of Pipe and Tubing(NPS System)C 1055 Guide for Heated System Surface Conditions thatProduce Contact Burn InjuriesC 1057 Practice for Determinatio
11、n of Skin Contact Tem-perature from Heated Surfaces Using a MathematicalModel and Thermesthesiometer2.2 Other Document:NBS Circular 564 Tables of Thermodynamic and TransportProperties of Air, U.S. Dept of Commerce3. Terminology3.1 DefinitionsFor definitions of terms used in this prac-tice, refer to
12、Terminology C 168.3.1.1 thermal insulation systemfor this practice, a thermalinsulation system is a system comprised of a single layer orlayers of homogeneous, uniformly dimensioned material(s)1This practice is under the jurisdiction of ASTM Committee C16 on ThermalInsulation and is the direct respo
13、nsibility of Subcommittee C16.30 on ThermalMeasurement.Current edition approved Aug. 1, 2008. Published September 2008. Originallyapproved in 1971. Last previous edition approved in 2004 as C 680 - 044.2For referenced ASTM standards, visit the ASTM website, www.astm.org, orcontact ASTM Customer Serv
14、ice at serviceastm.org. For Annual Book of ASTMStandards volume information, refer to the standards Document Summary page onthe ASTM website.1Copyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.intended for reduction of heat transfer betw
15、een two differenttemperature conditions. Heat transfer in the system is steady-state. Heat flow for a flat system is normal to the flat surface,and heat flow for cylindrical and spherical systems is radial.3.2 SymbolsThe following symbols are used in the devel-opment of the equations for this practi
16、ce. Other symbols willbe introduced and defined in the detailed description of thedevelopment.where:h = surface transfer conductance, Btu/(hft2F) (W/(m2K) hiat inside surface; hoat outside surfacek = apparent thermal conductivity, Btuin./(hft2F) (W/(mK)ke= effective thermal conductivity over a presc
17、ribed tem-perature range, Btuin./(hft2F) (W/(mK)q = heat flux, Btu/(hft2) (W/m2)qp= time rate of heat flow per unit length of pipe,Btu/(hft) (W/m)R = thermal resistance, Fhft2/Btu (Km2/W)r = radius, in. (m); rm+1 rm= thicknesst = local temperature, F (K)ti= inner surface temperature of the insulatio
18、n, F (K)t1= inner surface temperature of the systemto= temperature of ambient fluid and surroundings, F(K)x = distance, in. (m); xm+1 xm= thickness = effective surface emittance between outside surfaceand the ambient surroundings, dimensionlesss = Stefan-Boltzmann constant, 0.1714 3 10-8Btu/(hft2R4)
19、 (5.6697 3 10-8W/(m2K4)Ts= absolute surface temperature, R (K)To= absolute surroundings (ambient air if assumed thesame) temperature, R (K)Tm=(Ts+ To)/2L = characteristic dimension for horizontal and verticalflat surfaces, and vertical cylindersD = characteristic dimension for horizontal cylinders a
20、ndspherescp= specific heat of ambient fluid, Btu/(lbR) (J/(kgK)hc= average convection conductance, Btu/(hft2F) (W/(m2K)kf= thermal conductivity of ambient fluid, Btu/(hftF)(W/(mK)V = free stream velocity of ambient fluid, ft/h (m/s)y = kinematic viscosity of ambient fluid, ft2/h (m2/s)g = accelerati
21、on due to gravity, ft/h2(m/s2)b = volumetric thermal expansion coefficient of ambientfluid, R-1(K-1)r = density of ambient fluid, lb/ft3(kg/m3)DT = absolute value of temperature difference betweensurface and ambient fluid, R (K)Nu = Nusselt number, dimensionlessRa = Rayleith number, dimensionlessRe
22、= Reynolds number, dimensionlessPr = Prandtl number, dimensionless4. Summary of Practice4.1 The procedures used in this practice are based onstandard, steady-state, one dimensional, conduction heat trans-fer theory as outlined in textbooks and handbooks, Refs(4,5,20,21,22,30). Heat flux solutions ar
23、e derived for tempera-ture dependent thermal conductivity in a material. Algorithmsand computational methodologies for predicting heat loss orgain of single or multi-layer thermal insulation systems areprovided by this practice for implementation in a computerprogram. In addition, interested parties
24、 can develop computerprograms from the computational procedures for specificapplications and for one or more of the three coordinatesystems considered in Section 6.4.1.1 The computer program combines functions of datainput, analysis and data output into an easy to use, interactivecomputer program. B
25、y making the program interactive, littletraining for operators is needed to perform accurate calcula-tions.4.2 The operation of the computer program follows theprocedure listed below:4.2.1 Data InputThe computer requests and the operatorinputs information that describes the system and operatingenvir
26、onment. The data includes:4.2.1.1 Analysis identification.4.2.1.2 Date.4.2.1.3 Ambient temperature.4.2.1.4 Surface transfer conductance or ambient windspeed, system surface emittance and system orientation.4.2.1.5 System DescriptionMaterial and thickness foreach layer (define sequence from inside ou
27、t).4.2.2 AnalysisOnce input data is entered, the programcalculates the surface transfer conductances (if not entereddirectly) and layer thermal resistances. The program then usesthis information to calculate the heat transfer and surfacetemperature. The program continues to repeat the analysisusing
28、the previous temperature data to update the estimates oflayer thermal resistance until the temperatures at each surfacerepeat within 0.1F between the previous and present tempera-tures at the various surface locations in the system.4.2.3 Program OutputOnce convergence of the tempera-tures is reached
29、, the program prints a table that presents theinput data, calculated thermal resistance of the system, heatflux and the inner surface and external surface temperatures.5. Significance and Use5.1 Manufacturers of thermal insulation express the perfor-mance of their products in charts and tables showi
30、ng heat gainor loss per unit surface area or unit length of pipe. This data ispresented for typical insulation thicknesses, operating tempera-tures, surface orientations (facing up, down, horizontal, verti-cal), and in the case of pipes, different pipe sizes. The exteriorsurface temperature of the i
31、nsulation is often shown to provideinformation on personnel protection or surface condensation.However, additional information on effects of wind velocity,jacket emittance, ambient conditions and other influentialparameters may also be required to properly select an insula-tion system. Due to the la
32、rge number of combinations of size,temperature, humidity, thickness, jacket properties, surfaceemittance, orientation, and ambient conditions, it is not prac-tical to publish data for each possible case, Refs (31,32).5.2 Users of thermal insulation faced with the problem ofdesigning large thermal in
33、sulation systems encounter substan-tial engineering cost to obtain the required information. ThisC680082cost can be substantially reduced by the use of accurateengineering data tables, or available computer analysis tools, orboth. The use of this practice by both manufacturers and usersof thermal in
34、sulation will provide standardized engineeringdata of sufficient accuracy for predicting thermal insulationsystem performance. However, it is important to note that theaccuracy of results is extremely dependent on the accuracy ofthe input data. Certain applications may need specific data toproduce m
35、eaningful results.5.3 The use of analysis procedures described in this practicecan also apply to designed or existing systems. In the rectan-gular coordinate system, Practice C 680 can be applied to heatflows normal to flat, horizontal or vertical surfaces for all typesof enclosures, such as boilers
36、, furnaces, refrigerated chambersand building envelopes. In the cylindrical coordinate system,Practice C 680 can be applied to radial heat flows for all typesof piping circuits. In the spherical coordinate system, PracticeC 680 can be applied to radial heat flows to or from storedfluids such as liqu
37、efied natural gas (LNG).5.4 Practice C 680 is referenced for use with Guide C 1055and Practice C 1057 for burn hazard evaluation for heatedsurfaces. Infrared inspection, in-situ heat flux measurements,or both are often used in conjunction with Practice C 680 toevaluate insulation system performance
38、and durability ofoperating systems. This type of analysis is often made prior tosystem upgrades or replacements.5.5 All porous and non-porous solids of natural or man-made origin have temperature dependent thermal conductivi-ties. The change in thermal conductivity with temperature isdifferent for d
39、ifferent materials, and for operation at a relativelysmall temperature difference, an average thermal conductivitymay suffice. Thermal insulating materials (k tUwhere a1, a2, a3, b1, b2, b3 are constants, andtLand tUare, respectively, the lower and upperinflection points of an S-shaped curveAddition
40、al or different relationships may be used, but themain program must be modified.8. Report8.1 The results of calculations performed in accordancewith this practice may be used as design data for specific jobconditions, or may be used in general form to represent theperformance of a particular product
41、 or system. When theresults will be used for comparison of performance of similarproducts, it is recommended that reference be made to thespecific constants used in the calculations. These referencesshould include:8.1.1 Name and other identification of products or compo-nents,8.1.2 Identification of
42、 the nominal pipe size or surfaceinsulated, and its geometric orientation,8.1.3 The surface temperature of the pipe or surface,8.1.4 The equations and constants selected for the thermalconductivity versus mean temperature relationship,8.1.5 The ambient temperature and humidity, if applicable,8.1.6 T
43、he surface transfer conductance and condition ofsurface heat transfer,8.1.6.1 If obtained from published information, the sourceand limitations,8.1.6.2 If calculated or measured, the method and signifi-cant parameters such as emittance, fluid velocity, etc.,8.1.7 The resulting outer surface temperat
44、ure, and8.1.8 The resulting heat loss or gain.8.2 Either tabular or graphical representation of the calcu-lated results may be used. No recommendation is made for theformat in which results are presented.9. Accuracy and Resolution9.1 In many typical computers normally used, seven signifi-cant digits
45、 are resident in the computer for calculations.Adjustments to this level can be made through the use of“Double Precision;” however, for the intended purpose of thispractice, standard levels of precision are adequate. The format-ting of the output results, however, should be structured toprovide a re
46、solution of 0.1 % for the typical expected levels ofheat flux and a resolution of 1F (0.55C) for surface tempera-tures.FIG. 2 Thermal Conductivity vs. Mean TemperatureC680089NOTE 1The term “double precision” should not be confused withASTM terminology on Precision and Bias.9.2 Many factors influence
47、 the accuracy of a calculativeprocedure used for predicting heat flux results. These factorsinclude accuracy of input data and the applicability of theassumptions used in the method for the system under study.The system of mathematical equations used in this analysis hasbeen accepted as applicable f
48、or most systems normally insu-lated with bulk type insulations. Applicability of this practiceto systems having irregular shapes, discontinuities and othervariations from the one-dimensional heat transfer assumptionsshould be handled on an individual basis by professionalengineers familiar with thos
49、e systems.9.3 The computer resolution effect on accuracy is onlysignificant if the level of precision is less than that discussed in9.1. Computers in use today are accurate in that they willreproduce the calculated results to resolution required ifidentical input data is used.9.4 The most significant factor influencing the accuracy ofclaims is the accuracy of the input thermal conductivity data.The accuracy of applicability of these data is derived from twofactors. The first is the accuracy of the test method used togener
