Operating Procedure for a High-Temperature Thermal Conductivity Analyzer

This is a general operating outline for a high-temperature thermal-conductivity analyzer. Apply the stated settings only to a verified instrument configuration, its supplied procedure, and trained operators. A high-temperature thermal conductivity analyzer measures heat-transfer properties under controlled conditions. The procedure covers instrument preparation, specimen handling, measurement, data processing, maintenance, and safety. Instrument preparation Operate the instrument in a temperature-controlled laboratory at 23 ± 2 °C and below 60% humidity. Place it on a stable vibration-isolated platform at least 50 cm from the wall. Use a stable 220 V ± 10%, 50 Hz AC supply. Check cooling-water circulation at 8–10 L/min and water temperature at 20 °C ± 1 °C. Preheat for about 2 hours until thermal equilibrium, and inspect heater, specimen, and ambient-temperature readings. Verify the system with reference materials such as fused quartz or stainless steel and record the temperature–heat-flow curve. Specimen preparation Machine specimens to a diameter of 12.7 mm or 25.4 mm and thickness of 2–6 mm. Keep parallelism deviation below 0.02 mm and surface roughness at Ra ≤ 1.6 μm. Store machined specimens in a desiccator for at least 24 hours. Grind or polish the measurement surfaces and clean them ultrasonically in acetone for 10 minutes. For special materials, apply a graphite coating 1–3 μm thick and check visually for a uniform dark-gray surface without gaps or buildup. Measure each dimension five times with a digital caliper and record uncertainty. Measurement procedure At constant temperature, install the lower heater, place the specimen, and install the upper heater. Use the centering tool to keep coaxiality deviation below 0.1 mm. Monitor contact pressure at 0.5–1.0 MPa and allow 30 minutes for thermal equilibrium after installation. Set start temperature, final temperature, heating rate, and hold time. Use a heating rate of 3–5 °C/min, reducing it for special specimens where required; hold for 3–5 minutes per millimeter of specimen thickness. Set the acquisition frequency and confirm that sensors and recording are ready. Control and processing Use segmented PID temperature control and reduce the heating rate near transformation points. Keep the temperature difference between the upper and lower specimen surfaces within 1 °C. Automatically compensate contact-pressure changes caused by thermal expansion and keep pressure fluctuation within ±5% of the set value. Maintain an inert-gas atmosphere at 20–50 ml/min and monitor oxygen below 10 ppm. Overtemperature, pressure, and power-loss protections should place the system in a safe state and record the event. Preprocess data by removing abnormal points and applying a moving-average filter. Calculate thermal conductivity, thermal diffusivity, and specific heat capacity with a one-dimensional steady-state heat-conduction model, including heat-loss and boundary corrections. Evaluate dimensional, temperature, and heat-flow uncertainties, calculate combined and expanded uncertainty, and fit temperature dependence with a polynomial whose stated goodness-of-fit target is R² > 0.99. Compare results with literature values or reference specimens. After each test, clean the specimen chamber and inspect heaters and sensors. Check cooling-water quality monthly, calibrate temperature and pressure sensors quarterly, inspect the electrical and heat-dissipation systems every six months, and have a service engineer replace seals and calibrate the measurement system annually. Maintain spare parts and equipment records. Grounding resistance should be below 4 Ω. During high-temperature testing, the specimen-chamber surface may reach 1,500 °C; use dedicated tools and guards. Ventilate when using inert gas, secure gas cylinders, and maintain procedures and equipment for fire, leakage, and electrical emergencies. Only trained and assessed operators may work independently.