Principle and Operating Guide for Measuring Thermal Conductivity of Pipe-Insulation Shells

This guide describes a measurement system for determining the heat transfer coefficient and thermal conductivity of pipe-type insulation shells in accordance with GB/T 10296-2008 (steady-state heat transfer properties by the guarded hot pipe method) and ISO 8497:1994 (measurement of steady-state thermal transmission properties of thermal insulation for circular pipes). The apparatus is suitable for elastomeric and extruded polymer tubes, as well as rock wool, glass wool, and other pipe-shell insulation materials. It employs virtual-instrument technology for data acquisition and analysis related to surface heat transfer and conduction on circular pipes. Principle The apparatus consists of a heated test pipe together with temperature control and measurement instruments. It regulates and measures the temperatures of the test pipe and the surrounding air, and records the average electrical power supplied to the metering-section heater. Unless only overall heat transfer rate is required, instrumentation is included to measure the outer surface temperature of the insulation specimen. The test pipe is uniformly heated by an internal electric heater, with resistance wire wound on an internal, separate tube to promote uniformity. A calibrated end-guard arrangement is used at both ends of the metering section to minimize axial heat flow. Insulated end caps are applied to each end; their heat losses are corrected by direct calibration under test conditions. Auxiliary end heaters near the metering section help maintain uniform axial heat flux. The end caps are designed to have the same cross-sectional area and similar heat-transfer characteristics as the test specimen. Each end cap includes a cavity dimensioned to match the radius of the test pipe, ensuring continuity of heat flow and accurate correction for end effects. Operating Procedure 1) Remove one end cap from the specimen tube and sleeve the insulation sample onto the test pipe. 2) Affix the temperature sensors to the sample along the designated positions (three-point placement along the circumference), then reinstall the end cap. 3) Switch on the instrument power. 4) Launch the test software on the computer, set the test parameters, and start data acquisition. 5) Set the target test temperature and start heating. 6) Once the temperature reaches the setpoint, execute the calculation routine. 7) When the readings stabilize, end the test and save the results.

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