ASTM C745-92(1999)
Standard Test Method for Heat Flux Through Evacuated Insulations Using a Guarded Flat Plate Boiloff Calorimeter
- Standard No.
- ASTM C745-92(1999)
- Release Date
- 1992
- Published By
- American Society for Testing and Materials (ASTM)
- Status
- 2008-09
- Latest
- ASTM C745-92(1999)
- Scope
The thermal performance of multilayer insulations will vary from specimen to specimen due to differences in the material properties, such as the emittance of the reflective shields. In addition, it can vary due to environmental conditioning and the presence of foreign matter such as oxygen or water vapor. Finally, it can vary due to aging, settling, or exposure to excessive mechanical pressures which could wrinkle or otherwise affect the surface texture of the layers. For these reasons, it is imperative that specimen materials be selected carefully to obtain representative samples. It is recommended that several specimens of any one material be tested and no less than four data points obtained for each. For specimens where heat transfer measurements under high-vacuum conditions are required, a preconditioning procedure should be employed to remove water vapor and other outgas components from the multilayer materials.
1.1 This test method covers the determination, from cryogenic to near room temperatures, of heat flux through evacuated insulations (Note 1) within the approximate range from 0.3 to 30 W/m . Heat flux values obtained using this method apply strictly only to the particular specimens as tested.
Note 1-This test method is primarily intended for use to assess heat flux through evacuated multilayer insulations which are highly anisotropic by nature. Characteristically, multilayer insulations exhibit apparent thermal conductivity values one or two orders of magnitude lower than the best available powder, fiber, or foam insulations. Although this test method is also technically applicable to these latter insulations, other ASTM methods with less stringent requirements are equally applicable and much more economical and practical for such materials.1.2 This shall be a primary test method for measuring heat flux through evacuated insulations (Note 2), since calibration of the apparatus depends on measurement standards traceable to the National Institute of Standards and Technology (NIST) for length, force, temperature, time, etc. Traceable standards are not yet available for heat flux through standard evacuated reference specimens or transfer standards.
Note 2-Values of heat flux for the same materials and environments specified in this method may also be obtained by measuring electrical energy dissipation using a guarded hot plate (Test Method C177) (1, 2) or a guarded cylindrical apparatus (3, 4), or by measuring transient thermal response (5).1.3 Specimens to be tested using this method shall be flat and may be either a circular or a rectangular configuration, as appropriate for the particular apparatus being used (Note 3). Contoured specimens or those of other shapes must be tested by other methods which are outside the scope of this standard. Specimen sizes and thicknesses shall conform to the limitations specified in Section 7.
Note 3-Existing guarded flat plate boil-off calorimeters require circular specimens. For highly anisotropic multilayer insulations, this configuration somewhat simplifies heat transfer calculations, since the resulting heat flow is two-dimensional rather than three-dimensional as it would be for a rectangular specimen.1.4 Environmental and other parameters that can be varied in the application of this method are ( ) the hot and cold boundary temperatures, ( ) the boundary temperature at the exposed edge of the specimen, ( ) the mechanical compressive pressure to be imposed on the specimen, and ( ) the species and partial pressure of the gas occupying the interlayer cavities of the specimen and the test chamber (Note 4). Hot boundary temperature can be varied within the approximate range from 250 to 670 K, while cold boundary temperature can be varied from approximately 20 to 300 K (Note 5). Selection of boundary temperatur......
ASTM C745-92(1999) Referenced Document
- ASTM C177 Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus*， 1997-04-19 Update
ASTM C745-92(1999) history
- 1992 ASTM C745-92(1999) Standard Test Method for Heat Flux Through Evacuated Insulations Using a Guarded Flat Plate Boiloff Calorimeter
