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This standard is developed in accordance with the rules given in GB/T 1.1-2009.
This standard replaces GB/T 10297-1998 Test method for thermal conductivity of nonmetal solid materials by hot-wire method. In addition to a number of editorial changes, the following main technical changes have been made with respect to GB/T 10297-1998:
——The “Introduction” is deleted;
——The thermodynamic temperature in the International System of Units is used for the temperature in this edition of this standard.
——The phrase "especially light isotropic homogeneous thermal insulation materials" in clause 1 “Scope” is deleted.
——The requirement "The accuracy of measuring heating power shall be better than ± 0.5%" in 5.3 is changed to "The error of measuring heating power shall be less than 0.5%".
——Annex A (Indicative) in GB/T 10297-1998 is changed to Annex A (Informative), to which the relevant data of building materials with safety and flame retardant characteristics, such as foamed phenolic plastics and glass fiber phenolic moulding plastics, are added. And products like asbestos insulation boards that do not meet the requirements of environmental protection and low carbon emissions are deleted.
This standard was proposed by China Building Materials Federation.
This standard is under the jurisdiction of SAC/TC 191 National Technical Committee on Insulation Materials of Standardization Administration of China.
The previous edition of GB/T 10297-1998 is as follows:
——GB 10297-1988.
Test method for thermal conductivity of nonmetal solid materials -
Hot-wire method
1 Scope
This standard is applicable to the test of thermal conductivity of isotropic homogeneous nonmetal solid materials with thermal conductivity less than 2 W/(m·K).
This standard is not applicable to conductive nonmetal materials like silicon carbide.
As a supplement to the steady-state method, the method in this standard is suitable for occasions like enterprise quality control and is not suitable for qualification or arbitration test.
2 Normative references
The following referenced documents are indispensable for the application of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.
GB/T 4132 Definitions of terms relating to thermal insulating materials
3 Terms and definitions
For the purposes of this document, the terms and definitions given in GB/T 4132 apply.
4 Theory
Hot-wire method is an unsteady-state method to test the thermal conductivity of materials. The theory is as follows: place a piece of resistance wire, namely the so-called "hot wire”, in an isotropic homogeneous specimen with uniform temperature. When the hot wire releases heat at a constant power, the temperature of the hot wire and the specimen nearby will increase with time. The thermal conductivity of the specimen may be determined according to the relationship between temperature and time. Because the thermal capacity of the hot wire is different from that of the specimen, the hot wire, when heated at a constant power, does not release heat at a constant power, and the heat release power is not equal to the heating power either, causing measurement error. For light thermal insulation materials, such error is nonnegligible and, in this standard, it is corrected according to the simplified method of assuming linear temperature rise of the hot wire.
5 Instruments
5.1 Test device
Test devices commonly used in hot-wire method are as shown in Figures 1 and 2. The distance from points A or B to the edge of the specimen shall not be less than 5 mm, and that from points A or B to the temperature thermocouple shall not be less than 60 mm.
5.2 Power supply
Stabilized current (or stabilized voltage) power supply with stable direct current (or alternating current) shall be adopted, of which the change in the output value shall be less than 0.5%.
5.3 Power meter
The error of measuring heating power shall be less than 0.5%.
5.4 Temperature instrument
The resolution of the instrument for measuring the temperature rise of the hot wire shall not be less than 0.02 K (equivalent to 1 μV for Type K thermocouples), and the time constant shall be less than 2 s.
Keys:
1——compensator;
2——recorder;
3——specimen;
4——measuring junction of thermocouple;
5——power supply;
6——voltmeter;
7——ampere meter;
Figure 1 Schematic diagram for test circuit with compensator
Dimensions in millimeters
Keys:
2——recorder;
3——specimen;
4——measuring junction 1 of thermocouple;
5——power supply;
6——voltmeter;
7——ampere meter;
8——measuring junction 2 of thermocouple.
Figure 2 Schematic diagram for test circuit with differential thermocouple
5.5 Measuring probe
5.5.1 The measuring probe consists of a hot wire and a thermocouple welded to it, as shown in Figure 3. In order to eliminate the interference of the heating current on the output of the thermocouple, the thermocouple is welded to the hot wire via a single "+" (or "-") pole wire. The distance between the thermocouple contact and the hot wire shall be about 0.3 mm to 0.5 mm.
Foreword i
1 Scope
2 Normative references
3 Terms and definitions
4 Theory
5 Instruments
6 Specimen
7 Test process
8 Result calculation
9 Measuring error
10 Test report
Annex A (Informative) Specific thermal capacity and density
