【国外标准】 Standard Practice for Using a Guarded-Hot-Plate Apparatus or Thin-Heater Apparatus in the Single-Sided Mode

4.1 This practice provides a procedure for operating the apparatus so that the heat flow, Q′, through the meter section of the auxiliary insulation is small; determining Q′; and, calculating the heat flow, Q, through the meter section of the specimen.4.2 This practice requires that the apparatus have independent temperature controls in order to operate the cold plate and auxiliary cold plate at different temperatures. In the single-sides mode, the apparatus is operated with the temperature of the auxiliary cold plate maintained at the same temperature of the hot plate face adjacent to the auxiliary insulation.NOTE 4: In principle, if the temperature difference across the auxiliary insulation is zero and there are no edge heat losses or gains, all of the power input to the meter plate will flow through the specimen. In practice, a small correction is made for heat flow, Q′, through the auxiliary insulation.4.3 The thermal conductance, C’, of the auxiliary insulation shall be determined from one or more separate tests using either Test Method C177, C1114, or as indicated in 5.4. Values of C’ shall be checked periodically, particularly when the temperature drop across the auxiliary insulation less than 1 % of the temperature drop across the test specimen.4.4 This practice is used when it is desirable to determine the thermal properties of a single specimen. For example, the thermal properties of a single specimen are used to calibrate a heat-flow-meter apparatus for Test Method C518.1.1 This practice covers the determination of the steady-state heat flow through the meter section of a specimen when a guarded-hot-plate apparatus or thin-heater apparatus is used in the single-sided mode of operation.1.2 This practice provides a supplemental procedure for use in conjunction with either Test Method C177 or C1114 for testing a single specimen. This practice is limited to only the single-sided mode of operation, and, in all other particulars, the requirements of either Test Method C177 or C1114 apply.NOTE 1: Test Methods C177 and C1114 describe the use of the guarded-hot-plate and thin-heater apparatus, respectively, for determining steady-state heat flux and thermal transmission properties of flat-slab specimens. In principle, these methods cover both the double- and single-sided mode of operation, and at present, do not distinguish between the accuracies for the two modes of operation. When appropriate, thermal transmission properties shall be calculated in accordance with Practice C1045.1.3 This practice requires that the cold plates of the apparatus have independent temperature controls. For the single-sided mode of operation, a (single) specimen is placed between the hot plate and the cold plate. Auxiliary thermal insulation, if needed, is placed between the hot plate and the auxiliary cold plate. The auxiliary cold plate and the hot plate are maintained at the same temperature. The heat flow from the meter plate is assumed to flow only through the specimen, so that the thermal transmission properties correspond only to the specimen.NOTE 2: The double-sided mode of operation requires similar specimens placed on either side of the hot plate. The cold plates that contact the outer surfaces of these specimens are maintained at the same temperature. The electric power supplied to the meter plate is assumed to result in equal heat flow through the meter section of each specimen, so that the thermal transmission properties correspond to an average for the two specimens.1.4 This practice does not preclude the use of a guarded-hot-plate apparatus in which the auxiliary cold plate is either larger or smaller in lateral dimensions than either the test specimen or the cold plate.NOTE 3: Most guarded-hot-plate apparatus are designed for the double-sided mode of operation (1).2 Consequently, the cold plate and the auxiliary cold plate are the same size and the specimen and the auxiliary insulation will have the same lateral dimensions, although the thicknesses need not be the same. Some guarded-hot-plate apparatus, however, are designed specifically for testing only a single specimen that is either larger or smaller in lateral dimensions than the auxiliary insulation or the auxiliary cold plate.1.5 This practice is suitable for use for both low- and high-temperature conditions.1.6 This practice shall not be used when operating an apparatus in a double-sided mode of operation with a known and unknown specimen, that is, with the two cold plates at similar temperatures so that the temperature differences across the known and unknown specimens are similar.1.7 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.8 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.