ASTM C1043-24 PDF

SIGNIFICANCE AND USE 4.1 This practice describes the design of a guarded hot plate with circular line-heat sources and provides guidance in determining the mean temperature of the meter plate. It provides information and calculation procedures for: (1) control of edge heat loss or gain (Annex A1); (2) location and installation of line-heat sources (Annex A2); (3) design of the gap between the meter and guard plates (Appendix X1); and (4) location of heater leads for the meter plate (Appendix X2). 4.2 A circular guarded hot plate with one or more line-heat sources is amenable to mathematical analysis so that the mean surface temperature is calculated from the measured power input and the measured temperature(s) at one or more known locations. Further, a circular plate geometry simplifies the mathematical analysis of errors resulting from heat gains or losses at the edges of the specimens (see Refs (15, 16)). 4.3 The line-heat source(s) is (are) placed in the meter plate at a prescribed radius (radii) such that the temperature at the outer edge of the meter plate is equal to the mean surface temperature over the meter area. Thus, the determination of the mean temperature of the meter plate is accomplished with a small number of temperature sensors placed near the gap. 4.4 A guarded hot plate with one or more line-heat sources will have a radial temperature variation, with the maximum temperature differences being quite small compared to the average temperature drop across the specimens. Provided guarding is adequate, only the mean surface temperature of the meter plate enters into calculations of thermal transmission properties. 4.5 Care shall be taken to design a circular line-heat-source guarded hot plate so that the electric-current leads to each heater either do not significantly alter the temperature distributions in the meter and guard plates or else affect these temperature distributions in a known way so that appropriate corrections are applied. 4.6 The use of one o... SCOPE 1.1 This practice covers the design of a circular line-heat-source guarded hot plate for use in accordance with Test Method C177. Note 1: Test Method C177 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 is 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 for circular line-heat-source guarded hot plates having a single line-heat source in the meter plate is given in Refs (1-9).2 1.5 For high-temperature applications, the line-heat-source guarded hot plate has been used successfully over a mean temperature from 7 to 160°C, with circular metal plates and multiple line-heat sources in the meter plate. The chronological development for circular line-heat-...