Standard Practice for Measurement of the Steady-State Thermal Transmission Properties of Small Specimens Using the Heat Flow Meter Apparatus

Importancia y uso:

5.1 Thermal conductivity measurements on small insulation specimens are important during new product development processes or when larger specimens cannot be collected during forensic investigation (that is, failure analysis) (1, 2).

5.2 Numerous research projects have recently been initiated to develop insulation materials that have very high thermal resistivities (greater than 83 (m K)/W). Projects ranging from coatings to improve the thermal performance of single pane/layer glazing systems to the development of novel insulation products for building envelopes are being undertaken (1-4). All these projects have struggled in the development of new material technologies due to the difficulty associated with the measurement of thermal conductivity of small sections (approximately 0.025 m by 0.025 m) of high thermal resistance materials. As new materials are being developed, the size of each test specimen impacts the cost of development. Most of the existing test equipment and the methods do not align with the researcher’s need; the equipment requires a large specimen size is time consuming, and expensive to produce.

5.3 This practice provides a standardized procedure to enable the thermal characterization of small specimens of insulation materials. Accurate, and reliable thermal metrology to assess thermal properties of new insulation materials, such as novel very low thermal conductivity (< 0.01 W/ (m K)) nanomaterials or bio-based foam insulations, in small material sample sections, and minimal data analysis requirements is the desired outcome of this practice.

5.4 The ratio of the area of the specimen and the heat flux transducer has a significant impact on the uncertainty of the results obtained from this practice. As the specimen area decreases this ratio decreases, a smaller percentage of the total heat flow is associated with the unknown specimen. Information from the literature (4) shows that some heat-flow-meter apparatus, generally not available commercially and used by the research laboratories only, can be modified to change out the heat flux transducer so that transducers of varying sizes can be deployed. The observations presented in Fig. 2 were obtained from the measurements done by such a heat-flow-meter apparatus that was modified to change out the heat flux transducer. Fig. 2 demonstrates the significance of the ratio of the area of the specimen and the heat flux transducer on the accuracy of the thermal conductivity measurement using this Practice. This exercise is not a required part of this Practice and Fig. 2 is for information only.

FIG. 2 Example of a data set obtained from 0.010 m² (that is, 0.10 m × 0.10 m) heat flux transducer (heat flow) exploring the uncertainty (that is, difference between full size XPS specimen and smaller XPS specimen placed inside the mask) of varying thicknesses, 0.005 m, 0.010 m, and 0.020 m

Subcomité:

C16.30

Volúmen:

04.06

Número ICS:

91.120.10 (Thermal insulation of buildings)

Palabras clave:

heat flow meter apparatus; heat flux; instrument; small specimens; thermal conductivity; thermal resistance; thermal testing;