5.1 Factors that may influence the thermal-transmission properties of a specimen of material are described in Practice C1045 and the Precision and Bias section of Test Method C177.
5.2 Because of the required test conditions prescribed by this test method, it shall be recognized that the thermal properties obtained will not necessarily apply without modification to all conditions of service. As an example, this test method normally provides that the thermal properties shall be obtained on specimens that do not contain moisture, although in service such conditions may not be realized. Even more basic is the dependence of the thermal properties on variables such as mean temperature and temperature difference.
5.3 When a new or modified design of apparatus is evolved, tests shall be made on at least two sets of differing material of known long-term thermal stability. Tests shall be made for each material at a minimum of two different mean temperatures within the operating range of each. Any differences in results should be carefully studied to determine the cause and then be removed by appropriate action. Only after a successful verification study on materials having known thermal properties traceable to a recognized national standards laboratory shall test results obtained with this apparatus be considered to conform with this test method. Periodic checks of apparatus performance are recommended.
5.4 The thermal transmission properties of many materials depend upon the prior thermal history. Care must be exercised when testing such specimens at a number of conditions so that tests are performed in a sequence that limits such effects on the results.
5.5 Typical uses for the thin-heater apparatus include the following:
5.5.1 Product development and quality control applications.
5.5.2 Measurement of thermal conductivity at desired mean temperatures.
5.5.3 Thermal properties of specimens that are moist or close to melting point or other critical temperature (see Note 1).
5.5.4 Determination of thermal properties of relatively high R value insulation samples with large apparatuses. In the case of the metal-screen heater apparatus, samples with thicknesses up to 15 cm can be measured.
1.1 This test method covers the determination of the steady-state thermal transmission properties of flat-slab specimens of thermal insulation using a thin heater of uniform power density having low lateral heat flow. A thin heater with low lateral thermal conductance can reduce unwanted lateral heat flow and avoid the need for active-edge guarding.
1.2 This primary test method of thermal-transmission measurement describes a principle, rather than a particular apparatus. The principle involves determination of the thermal flux across a specimen of known thickness and the temperatures of the hot and cold faces of the specimen.