Measuring Thermal Conductivity of Carbon Felts and Other Insulation Materials Below 1600 ℃ Using a Vacuum High-Temperature Conductivity Meter

Thermal conductivity is a key parameter for evaluating the physical properties of materials. Aerospace, nuclear energy, construction, and non-metal industries all require either accurate prediction or direct measurement of thermal conductivity. For carbon-based insulation materials such as carbon felts, testing commonly follows a steady-state or transient approach. In this method, a heat-flow principle combined with a water-flow guarded hot plate is applied. Using an imported high-temperature heat flux sensor in a high-temperature vacuum chamber (with optional protective gas atmosphere), measurements are automated by computer with digital readouts at each state point. Manual operation is also possible. This setup meets high-precision requirements for research institutes and carbon material manufacturers when determining thermal conductivity. Reference standards: GB/T 10295-2008 and YB/T 4130-2005. Instrument and setup specifications: - Hot-face or furnace temperature: 600 ℃ to 1600 ℃ - Thermal conductivity range: 0.01–5 W/m·K - Sample count per test: 1 piece - Total sample thickness: 35–45 mm - Sample diameter: hard felt 118 mm; soft felt 119 mm - Measurement accuracy: ±3% - Repeatability: ≤3%; fully automated analysis software - Heating: 1800 W silicon-molybdenum rod - Test chamber atmosphere: fill with protective gas or evacuate; vacuum level: 200 Pa Operating procedure: 1) Power-up After confirming all external cables are correctly connected, close the main power breaker and turn on the instrument. The power indicator (red) illuminates and instruments perform self-checks. Start the thermostatic water bath and set it near ambient temperature by referencing the cold-side reading; the display icons (sun/snowflake/fan) indicate normal status and can be adjusted by long-pressing the circulation and cooling keys. Check the vacuum gauge reading; if it does not show 1 E 5, open the vent (intake solenoid) to release the furnace vacuum. 2) Load the sample Use the rise/stop/fall control to open the furnace (adjust lift speed as needed). Trim the specimen to approximately 119 mm diameter and place it in the sample frame; control thickness within 40–50 mm. Close the furnace. Turn on cooling water and the bath circulation. 3) Evacuate and/or fill protective gas Turn on the vacuum function and open the manual vacuum valve (inside the control box). When the vacuum display reaches 2.0 E 2 (200 Pa) or lower, close the manual valve and stop the pump. If protective gas is needed, open the intake valve and cylinder/line valve, set the flow, and fill the chamber. When the pressure gauge approaches ambient pressure, open the exhaust valve; when chamber pressure exceeds ambient, it will vent automatically. 4) Start the test Press Start on the instrument, open the software, enter the sample thickness (other fields optional), and begin the test. Monitor the ammeter: if current exceeds 180 A for more than 8 seconds, press and hold STOP for 3 seconds, wait 10 seconds, then press and hold RUN for 3 seconds. Repeat until the indicated current is below 180 A. 5) Data acquisition Once the target temperature is reached, you may stop the test manually or allow it to stop automatically at the predefined terminal temperature. Save the detailed data to the specified location. Open the test report to view results; you can input target temperature points to retrieve corresponding data and then save or print the report (printing requires a connected printer; otherwise save the digital report). Press the Stop button on the instrument panel. For isothermal measurements: configure the heating profile as per the supplemental heating curve (Table 4.3) and set the software terminal temperature to 1555 or 1558. This workflow enables repeatable, high-accuracy thermal conductivity measurements on carbon felts and similar insulation materials up to 1600 ℃ under vacuum or protective atmospheres.

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