1.1 This test method describes the continuous measurement of the hemispherical heat flux to one or both surfaces of an uncooled sensor called a directional flame thermometer (DFT). 1.2 DFTs consist of two heavily oxidized, Inconel 600 plates with mineral insulated, metal-sheathed (MIMS) thermocouples (TCs, type K) attached to the unexposed faces and a layer of ceramic fiber insulation placed between the plates. 1.3 Post-test calculations of the net heat flux can be made using several methods The most accurate method uses an inverse heat conduction code. Nonlinear inverse heat conduction analysis uses a thermal model of the DFT with temperature-dependent thermal properties along with the two-plate temperature measurement histories. The code provides transient heat flux on both exposed faces, temperature histories within the DFT, as well as statistical information on the quality of the analysis. 1.4 A second method uses a transient energy balance on the DFT sensing surface and insulation, which uses the same temperature measurements as in the inverse calculations to estimate the net heat flux. 1.5 A third method uses inverse filter functions (IFFs) to provide a near real-time estimate of the net flux. The heat flux history for the front face (either surface exposed to the heat source) of a DFT can be calculated in real time using a convolution type of digital filter algorithm. 1.6 Although developed for use in fires and fire safety testing, this measurement method is quite broad in potential fields of application because of the size of the DFTs and their construction. It has been used to measure heat flux levels above 300kW/m2 in high-temperature environments, up to about 1250C, which is the generally accepted upper limit of Type K or N thermocouples. 1.7 The transient response of the DFTs is limited by the response of the MIMS TCs. The larger the thermocouple the slower the transient response. Response times of approximately 1-2 s are typical for 1.6 mm diameter MIMS TCs attached to 1.6 mm thick plates. The response time can be improved by using a differential compensator. 1.8 The values stated in SI units are used in this standard. The values stated in parentheses are provided for information only.
DFTs have been used in fire testing related to certification of hazardous material shipping containers for over 30 years. These test procedures are specified by US-DOT, US-NRC, and IAEA. DFTs are specified in in fire-resistance testing related to commercial buildings and petrochemical facilities.
Keywordsdirectional flame thermometers; DFTs; thermocouple; MIMS; mineral insulated, metal sheathed; heat flux; measurement; net heat flux; incident heat flux; convective heat flux; inverse heat conduction method; inverse filter function method;energy storage method:
The title and scope are in draft form and are under development within this ASTM Committee.Back to Top