ASTM-E457:08(R2020) pdf free download – Standard Test Method for Measuring Heat-Transfer Rate Using a Thermal Capacitance (Slug) Calorimeter.
4.3 In the evaluation of high-temperature materials, slug calorimeters are used to measure the heat transfer rate on various parts of the instrumented models, since heat transfer rate is one of the important parameters in evaluating the performance of ablative materials.
4.4 Regardless of the source of thermal energy to the calorimeter (radiative, convective, or a combination thereof) the measurement is averaged over the calorimeter surface. If a significant percentage of the total thermal energy is radiative, consideration should he given to the emissivity of the slug surface. If non-uniformities exist in the input energy, the heat transfer rate calorimeter would tend to average these variations: therefore, the size of the sensing element (that is, the slug) should be limited to small diameters in order to measure local heat transfer rate values. Where large ablative samples are to be tested, it is recommended that a number of calorimeters be incorporated in the body of the test specimen such that a heat transfer rate distribution across the heated surface can be determined. In this manner, more representative heat transfer rate values can be defined for the test specimen and thus enable more meaningful interpretation of the test. The slug selection may he determined using the nomogram as a guide (see Appendix Xl).
5. Apparatus
5.1 General—The apparatus shall consist of a thermal capacitance (slug) calorimeter and the necessary instrumentation to measure the thermal energy transferred to the calorimeter. All calculations should use only those data taken after the heat source has achieved steady-state operating conditions. Wherever possible. it is desirable that several measurements be made of the required parameters.
5.2 Back-Face Temperature Measurement—The method of temperature measurement must be sufficiently sensitive and reliable to ensure accurate temperature rise data for the back-face thermocouple. Procedures should he adhered to in the calibration and preparation of the thermocouples. Attachment of the thermocouples should be such that the true back-side temperatures are obtained. Although no standardized procedures arc available, methods such as resistance welding (small spot) and peening have been successfully used. The error in measurement of temperature difference between the initial and final times should not exceed ±2 %. The temperature measurements shall he recorded continuously using a conimercially available recorder whose frequency response is at least ten times the expected frequency response of the slug to provide the accuracy required. During the course of operation of the plasma arc or other heat source, care must he taken to minimize deposits on the calorimeter surface.
5.3 Data Acquisition—The important parameter, back-face temperature rise, shall he automatically recorded throughout the calibration period. Recording speed will depend on the heat transfer rate level such that the time range shall approach the temperature rise displacement on the recording paper. Timing marks shall be an integral part of the recorder output.
6. Procedure.