ASTM_C_1774_-_13.pdf

Designation:C177413Standard Guide forThermal Performance Testing of Cryogenic InsulationSystems1This standard is issued under the fixed designation C1774;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.1.Scope1.1 This guide provides information for the laboratorymeasurement of the steady-state thermal transmission proper-ties and heat flux of thermal insulation systems under cryo-genic conditions.Thermal insulation systems may be com-posed of one or more materials that may be homogeneous ornon-homogeneous;flat,cylindrical,or spherical;at boundaryconditions from near absolute zero or 4 K up to 400 K;and inenvironments from high vacuum to an ambient pressure of airor residual gas.The testing approaches presented as part of thisguide are distinct from,and yet complementary to,otherASTM thermal test methods including C177,C518,and C335.Akey aspect of this guide is the notion of an insulation system,not an insulation material.Under the practical use environmentof most cryogenic applications even a single-material systemcan still be a complex insulation system(1-3).2To determinethe inherent thermal properties of insulation materials,thestandard test methods as cited in this guide should be con-sulted.1.2 The function of most cryogenic thermal insulationsystems used in these applications is to maintain large tem-perature differences thereby providing high levels of thermalinsulating performance.The combination of warm and coldboundary temperatures can be any two temperatures in therange of near 0 K to 400 K.Cold boundary temperaturestypically range from 4 K to 100 K,but can be much highersuch as 300 K.Warm boundary temperatures typically rangefrom 250 K to 400 K,but can be much lower such as 40 K.Large temperature differences up to 300 K are typical.Testingfor thermal performance at large temperature differences withone boundary at cryogenic temperature is typical and repre-sentative of most applications.Thermal performance as afunction of temperature can also be evaluated or calculated inaccordance with Practices C1058 or C1045 when sufficientinformation on the temperature profile and physical modelingare available.1.3 The range of residual gas pressures for this Guide isfrom 10-7torr to 10+3torr(1.33-5Pa to 133 kPa)with differentpurge gases as required.Corresponding to the applications incryogenic systems,three sub-ranges of vacuum are also de-fined:High Vacuum(HV)from 10-6torr to 10-3torr(1.333-4Pa to 0.133 Pa)free molecular regime,Soft Vacuum(SV)from 10-2torr to 10 torr(from 1.33 Pa to 1,333 Pa)transitionregime,No Vacuum(NV)from 100 torr to 1000 torr(13.3 kPato 133 kPa)continuum regime.1.4 Thermal performance can vary by four orders of mag-nitude over the entire vacuum pressure range.Effective thermalconductivities can range from 0.010 mW/m-K to 100 mW/m-K.The primary governing factor in thermal performance isthe pressure of the test environment.High vacuum insulationsystems are often in the range from 0.05 mW/m-K to 2mW/m-K while non-vacuum systems are typically in the rangefrom 10 mW/m-K to 30 mW/m-K.Soft vacuum systems aregenerally between these two extremes(4).Of particular de-mand is the very low thermal conductivity(very high thermalresistance)range in sub-ambient temperature environments.For example,careful delineation of test results in the range of0.01 mW/m-K to 1 mW/m-K(from R-value 14,400 to R-value144)is required as a matter of normal engineering applicationsfor many cryogenic insulation systems(5-7).The applicationof effective thermal conductivity values to multilayer insula-tion(MLI)systems and other combinations of diversematerials,because they are highly anisotropic and specialized,must be done with due caution and full provision of supportingtechnical information(8).The use of heat flux(W/m2)is,ingeneral,more suitable for reporting the thermal performance ofMLI systems(9-11).1.5 This guide covers different approaches for thermalperformance measurement in sub-ambient temperature envi-ronments.The test apparatuses(apparatus)are divided into twocategories:boiloff calorimetry and electrical power.Bothabsolute and comparative apparatuses are included.1.6 This guide sets forth the general design requirementsnecessary to construct and operate a satisfactory test apparatus.1This test method is under the jurisdiction ofASTM Committee C16 on ThermalInsulation and is the direct responsibility of Subcommittee C16.30 on ThermalMeasurement.Current edition approved Nov.1,2013.Published February 2014.DOI:10.1520/C1774-13.2The boldface numbers in parentheses refer to the list of references at the end ofthis standard.Copyright ASTM International,100 Barr Harbor Drive,PO Box C700,West Conshohocken,PA 19428-2959.United States1 A wide variety of apparatus constructions,test