This method is a longitudinal heat flow method with direct current passing through the sample, which is suitable for measuring the thermal conductivity of metals at temperatures without phase change within the temperature range of 80~900℃. GB/T 3651-1983 Method for measuring thermal conductivity of metals at high temperatures GB/T3651-1983 Standard download decompression password: www.bzxz.net

National Standard of the People's Republic of China
Measuring method for thermal conductivity of metal at high temperatureUDC 689 : 586.6
GB 3651-83
This method is a longitudinal heat flow method with direct current passing through the sample. It is applicable to the measurement of thermal conductivity of metal at no phase change temperature within the temperature range of 80~900℃. 1 Principle of method and calculation formula
1.1 When a direct current is passed through a rod-shaped sample, the generated Joule heat is mainly conducted to both ends along the longitudinal direction of the sample. After reaching the thermally stable state, it is considered that there is a one-dimensional longitudinal heat flow on the sample, and the heat exchange between the sample and the lateral environment is corrected. The thermal conductivity of the sample is determined by the following formula: 1.521IV
d2 (A-eN)
-thermal conductivity of the sample, Cal/cm·s·℃, where: 一
1——average length of the working section of the sample 1=+22
I——direct current passing through the sample, AV
-average voltage drop in the working section of the sample, V=一d——diameter of the sample, mm,
（1）
V and V are the voltage drops on, mvsA and 2 respectively, the temperature difference between the midpoint and the end point of the working section of the sample, ℃, the coefficient reflecting the size of the lateral heat exchange:
N——function marking the temperature difference between the sample and the lateral environment, ℃. t+
Figure 1 Schematic diagram of measurement method
1-heatproof furnace, 2-temperature tube, 3-insulating material, 4-sample, 5-thermocouple for measuring ambient temperature, 6-thermocouple for measuring sample temperature i, e, N are determined by the following formulas:
Af =t2
National Bureau of Standards1983-05-02Published
(2))bZxz.net
(3)
1984-08-01Implementation
Where: ti, t2, t3
, silk, t3
to1, t02, t03
toyto2. ti3
GB3651-83
ton+tos
tot+t'o3
No= t oz - t oz +
The temperature of the end point, midpoint and other end point of the sample when the sample is energized, °C, The temperature of the end point, midpoint and other end point of the lateral environment when the sample is energized, °C, The temperature of the end point, midpoint and other end point of the sample when the sample is not energized, °C, The temperature of the end point, midpoint and other end point of the lateral environment when the sample is not energized, °C, The temperature difference between the midpoint and the end point of the sample when the sample is not energized, °C - The temperature difference between the midpoint and the end point of the lateral environment when the sample is not energized, °C, 49
- The temperature difference between the midpoint and the end point of the lateral environment when the sample is energized, °C, 42 -
The function of the temperature difference between the marked sample and the lateral environment when the sample is not energized, °C. 1.2 The average temperature of the sample is determined by the following formula: t = t2
2 Sample
The wrestling sample shall comply with the requirements of Figure 2 (a) or Figure 2 (6). 220
Figure 2 Specifications and dimensions of rod-shaped specimens
Φ14~5±0.01mmz3~5±0.01mm, Li—100~140mm, L280~120mm
The diameter d of the wire-shaped specimen is 13mm.
The working section of the specimen is 20～45mm.
Number of specimens: more than 2.
（5）
（9）
3 Measuring equipment and instruments
3.1 Measuring equipment
GB 3651-83
3.1.1 Use a special tubular heatproof furnace to make the sample side have an ambient temperature close to the sample temperature to reduce the heat exchange between the sample and the lateral environment. A metal heat-saturating tube is added in the heatproof furnace, and the longitudinal temperature distribution on it should be close to the secondary parabola distribution. The heat-proof furnace can be split-type, and the temperature difference between each point on the cross-section circumference of the heat-scaling tube should be less than 5°C. The temperature of the heat-proof furnace is automatically controlled with a temperature control accuracy of ±0.5~1.0°C. 3.1.2 The space between the sample and the heat-scaling tube is filled with insulation material. When using hard insulation material, such as foamed aluminum oxide, soft fiber insulation material should be evenly filled between the insulation material and the heat-scaling tube. The thermocouple for measuring the ambient temperature is welded on a long metal sheet, and the metal sheet is placed in the soft fiber insulation material, and has good thermal contact with the insulation material. The distance between the metal sheet and the center line of the sample should be less than 0.6! . The thermal conductivity and size of the insulation material must ensure that e is less than 1. 3.1.3 The thermocouple for measuring the sample temperature must be spot welded on the sample to ensure good thermal and electrical contact between the thermocouple and the sample to ensure the reliability of temperature measurement. At the same time, the |2" should be less than 0.01. 3.1.4 The experimental vacuum degree should not be less than 5×10-4mmHg. 3.1.5 The stability of the DC current passing through the sample should be higher than ±0.1%, and the ripple factor should be less than 0.5%. 3.2 Temperature measuring components, instruments, and measuring tools.
3.2.1 Use nickel-chromium-nickel-silicon thermocouples to measure temperature. The diameter of the thermocouple wire is 0.15~0.3mm. The thermocouple wire material should comply with the requirements of GB2614-81 "New nickel-chromium-nickel-silicon thermocouple wire and graduation table". 3.2.2 Use the same polarity wire of the thermocouple measuring the sample temperature as the measurement Lead wires for measuring the potential of the working section of the sample. The minimum scale of the instrument for measuring the voltage drop in the working section of the sample and the thermoelectric potential of the thermocouple is 0.01mv. 3.2.3 The minimum scale of the instrument for measuring the DC current flowing through the sample is 0.01A. 3.2.4 Use a vernier caliper with a minimum scale of 0.02mm to measure the length l of the working section of the sample. Use a micrometer with a minimum scale of 0.01mm to measure the diameter d of the sample.
4 Experimental conditions and measurement steps
4.1 When the sample temperature changes by less than 0.5℃ within 10 minutes, it is considered that the system under test has reached Thermally stable state, the measured data is valid after reaching this state.
4.2 After the sample is passed through a direct current and reaches a thermally stable state, measure the temperature, current and voltage, then change the direction of the current and measure each quantity again. The average value of each quantity in the two directions of the current is the experimental value. 4.3 By using sample extension rods and direct current leads of different materials or sizes, or by adding a small electric furnace with adjustable power at both ends of the sample to control 4, its size is within the range of 10 to 50°C. 4.4 The size of the direct current passed through the sample should make |N" less than 5°C. 5 Data processing Processing and measurement results
5.1 Substitute the measured data into equations (1) to (9) to obtain the thermal conductivity of the metal material at the temperature without phase change. 5.2 Process the rounded data in accordance with the provisions of Appendix C of GB1.1-81 "General provisions for the preparation of standards in the guidelines for standardization work". 5.3 The measurement error of the thermal conductivity obtained by this method is generally less than ±5%. 5.4 According to the measured values ​​of the thermal conductivity at various temperatures, the relationship between temperature and thermal conductivity is obtained (graphic method can be used), and the thermal conductivity value corresponding to a certain temperature is obtained from this relationship. 58
GB 3651—88
Appendix A
Calibration of measuring equipment
(reference)
Use rolled DT7 pure iron and 1Cr18Ni9Ti stainless steel as calibration reference materials to calibrate the measuring equipment. The chemical composition of the materials complies with the provisions of YB200-—75 "Pure Iron for Electrical Use" and GB1220-75 "Technical Conditions for Stainless Acid-Resistant Steel". The sample is heated at 1000℃ and 1×10-4mmHg vacuum for two hours, and then slowly cooled to room temperature for annealing. The data in the following table are the recommended values ​​of thermal conductivity of the above samples. Temperature
Note: The data in brackets in the table are for reference.
Thermal conductivity
Cal/cm-s .C
1Cr18Ni9Ti
Thermal conductivity
Cal/cm·s.'℃
Within the temperature range of 80～900℃, the thermal conductivity values ​​measured for the above samples deviate from the recommended values ​​in the above table by less than ±5%, and the deviation at 900℃ is less than ±8%, and the measuring equipment is considered to be usable. Additional remarks:
This standard was proposed by the Ministry of Metallurgical Industry of the People's Republic of China. This standard was drafted by the General Research Institute of Nonferrous Metals and other units. The main drafters of this standard are Yao Longqing, Hua Guitai, Shen Yongjiang, etc. 59
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