1.1 This practice covers the design of a circular line-heat-source guarded hot plate for use in accordance with Test Method C 177. Note 1—Test Method C 177 describes the guarded-hot-plate apparatus and the application of such equipment for determining thermal transmission properties of flat-slab specimens. In principle, the test method includes apparatus designed with guarded hot plates having either distributed- or line-heat sources.

1.2 The guarded hot plate with circular line-heat sources is a design in which the meter and guard plates are circular plates having a relatively small number of heaters, each embedded along a circular path at a fixed radius. In operation, the heat from each line-heat source flows radially into the plate and is transmitted axially through the test specimens.

1.3 The meter and guard plates are fabricated from a continuous piece of thermally conductive material. The plates are made sufficiently thick that, for typical specimen thermal conductances, the radial and axial temperature variations in the guarded hot plate are quite small. By proper location of the line-heat source(s), the temperature at the edge of the meter plate can be made equal to the mean temperature of the meter plate, thus facilitating temperature measurements and thermal guarding.

1.4 The line-heat-source guarded hot plate has been used successfully over a mean temperature range from 10 to + 65°C, with circular metal plates and a single line-heat source in the meter plate. The chronological development of the design of circular line-heat-source guarded hot plates is given in Refs (1-9).

1.5 This practice does not preclude ( 1) lower or higher temperatures; (2) plate geometries other than circular; (3) line-heat-source geometries other than circular; (4) the use of plates fabricated from ceramics, composites, or other materials; or ( 5) the use of multiple line-heat sources in both the meter and guard plates.

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 and health practices and determine the applicability of regulatory limitations prior to use.