GB/T 32981-2026Test method for the effective thermal conductivity of wall materials (English PDF)

5.2 Cold Box

5.2.1 The internal space of the cold box should be large enough to accommodate refrigeration, heating and airflow organization equipment.

5.2.2 Adjust the air velocity parallel to the specimen surface using a deflector. The airflow direction should be the same as the natural convection direction, and the airflow velocity should be adjustable. The wind speed should be between

0.1 m/s and 10 m/s.

5.3 Protective Heat Box

5.3.1 The protective heat box shall be composed of homogeneous materials and shall have good sealing performance, with a thermal resistance of not less than

5.3.2 The protective heat box is placed outside the metering box, completely enclosing it. The distance between the inner surface of the protective heat box and the outer surface of the metering box is not less than [amount missing]. 150mm.

5.3.3 The temperature control system in the protective heat chamber is used to balance the temperature changes between the metering chamber and the protective heat chamber, thereby reducing heat loss in the metering chamber. Loss, in order to achieve a stable experimental state.

5.4 Metering box The metering box is made of thermal insulation material and is required to be structurally free of cold bridges and have good sealing performance, with a thermal resistance of not less than

3.5 m2·K/W. The space should be able to accommodate the heating device and the flow guiding device.

5.5 Specimen Frame The specimen frame is a device for mounting specimens. The opening size of the specimen frame is 500mm × 500mm, and the maximum thickness of the specimen mounted in the specimen frame is [not specified]. It is 400mm.

5.6 Control and Data Acquisition and Processing System

5.6.1 Cold Box Temperature Control System It consists of a cold box refrigeration compressor, a cold box temperature balancing electric heater, temperature control instruments, and temperature sensors. The temperature sensors measure... The uncertainty should not exceed 0.25K, and the quantity should be at least 5 pieces. At least two measurement points should be located in the gap between the flow guide and the specimen, and they should be horizontal. Setup. The cold box temperature setting range is -20°C to -10°C.

5.6.2 Temperature control system for the protective thermal chamber It consists of a protective heat chamber refrigeration compressor, a protective heat chamber temperature balancing electric heater, temperature control instruments, and temperature sensors. The measurement uncertainty of the instrument is no greater than 0.25K. Measurement points are located on the outer surface of the measuring chamber, with at least one measurement point on each surface. Heat protection is provided. The chamber temperature setting range is 20°C~30°C.

5.6.3 Metering Box Temperature Control System It consists of an electric heater, a temperature control instrument, and a temperature sensor. The heating power meter has an accuracy class of no less than 0.5.The temperature sensor... The measurement uncertainty is no greater than

0.25 K. Measurement points are located on the inner wall surface of the metrology chamber, with at least one measurement point on each wall surface. Metering chamber temperature. The set value is consistent with the temperature set value of the protective heat box.

5.6.4 Data Acquisition and Processing System It consists of a computer and data acquisition instruments. The data acquisition instruments can be used in conjunction with temperature control instruments or independently. It is used for data... The temperature sensors used for data acquisition should not be digital temperature sensors; thermocouples or platinum resistance thermometers should be selected according to different temperature measurement scenarios. Control software. The temperature changes at various measuring points can be displayed in real time by observing the temperature changes within the reaction chamber.

5.7 Performance Check Before the measuring device is put into use, at least two items with different thermal conductivity and stable thermal properties should be tested and calibrated in a nationally accredited laboratory. Materials must be tested, and only those with consistent results can be used. In subsequent use, the testing device should be checked periodically using the same method.

6.1 Environmental Conditions

6.1.1 The temperature fluctuation of the test chamber air during the test should not exceed 2.0°C.

6.1.2 Standard environmental conditions. Conducted according to the Class 23/50 standard environmental conditions in GB/T 2918.

6.2 Preparation of filler Molded polystyrene foam boards with an insulation performance grade of

0.33 as specified in GB/T 10801.1 should be used as the filling material. Materials. Based on the dimensions of the test piece, two pieces with dimensions of (500×500×d) mm (d) were prepared on the same piece of filler material produced in the same batch. The test sample consists of a filler (thickness in the heat transfer direction), one piece for testing the heat flow through the filler, and another piece with a cutout at its center. Holes of the same size as the sample being tested are used for sample testing.

6.3 Sample Preparation

6.3.1 When the length and width dimensions of a homogeneous wall material sample or a non-homogeneous wall material sample are no greater than 500mm × 500mm, a whole sample should be taken. Tests were conducted on materials such as porous bricks, hollow bricks, and composite blocks. Homogeneous wall material samples and samples with dimensions greater than 500mm × For non-homogeneous material specimens with a length and width of 500mm, whose thermal properties remain consistent with those of the original specimen after cutting, the specimens are classified according to their length and width. It is prepared by cutting 500mm×500mm, such as composite wall panels. If the sample has a tenon and mortise structure, the tenon structure should be completely cut to ensure that... Use mortar or caulking material to bond it to the joint, ensuring that the test sample is a regular hexahedron.

6.3.2 All test samples shall be dried at a temperature that does not affect the properties of any of their constituent materials until constant weight (using a graduation value not greater than 5g). Weighing should be performed on a platform scale, with a time interval of no less than 24 hours between two weighings, and the difference in weighing values should not exceed 0.2%.

6.4 Determination Methods

6.4.1 The length, width, and thickness of the specimen shall be in accordance with the relevant national (or industry) standards.

6.4.2 Install the filler onto the specimen frame, and seal and fix the filler to the specimen frame with sealant (neutral adhesive) around the perimeter, ensuring no voids are left. The gap should be filled and cured under standard environmental conditions for no less than 24 hours.

6.4.3 Start the device, set the hot box temperature to 25°C and the cold box temperature to -15°C, and monitor the temperature changes at each control point. When the temperature of the hot box is measured... When the absolute values of the hourly average temperature changes of the cold box and the average temperature change of the cold box are no greater than 0.1K and 0.3K respectively, it indicates that the heat transfer process has reached a steady state.

6.4.4 After the heat transfer process stabilizes, the heat flow rate QT through the filling material is measured every 30 minutes for a total of 6 measurements.

6.4.5 Seal and embed the test sample in the center of the filler, with the sample thickness direction aligned with the filler thickness direction, using a neutral sealant. Seal and fix the sample and filler around the perimeter with adhesive, leaving no gaps, and repeat the test steps

6.4.2 and 6.4.3.

6.4.6 After the heat transfer process stabilizes, the heat flow rate QS through the filler and the sample is collected every 30 minutes for a total of 6 times.

6.5 Calculation Method

6.5.1 The parameters QT and QS obtained from the data collection are taken as the arithmetic mean of 6 data collections.

6.5.2 The equivalent thermal conductivity of the sample is calculated according to formulas (1) to (4).