GB 8722-1988 Determination of thermal conductivity of graphite materials at medium temperature
Some standard content:
National Standard of the People's Republic of China
Method for the determination of thermal conductivity of graphite materials at median temperatureThis standard applies to the determination of thermal conductivity of graphite products at 100～800℃. 1 Method Principle Summary
UDC 661. 666
:620.179.13
GB 8722—88
The direct current longitudinal heat flow method is adopted. When direct current passes through the cylindrical sample, the heat generated is mainly conducted along the longitudinal direction of the sample to both ends. After reaching the thermal stability state, it is considered that the sample is a one-dimensional longitudinal heat flow, and the heat exchange between the sample and the lateral environment is corrected. 2 Instruments and Equipment
2.1 Instruments
2.1.1 Micrometer: accuracy 0.01mm.
2.1.2 Vernier caliper: accuracy 0.02mm.
2.1.3 Nickel-chromium-nickel-silicon armored thermocouple: exposed type. Thermocouple wire diameter 0.4 ~ 0.5mm, its performance conforms to the provisions of GB2614-85 "Nickel-chromium-nickel-silicon thermocouple wire and graduation table", and should be corrected according to the standard thermocouple. 2.1.4 Precision digital temperature display: resolution 0.1℃, accuracy ±1.3%. 2.1.5 DC digital voltmeter: resolution 0.001mV, accuracy ±0.006%. 2.1.6 Fixed value shunt: 500A/75mV, 0.2 level, equipped with a DC millivoltmeter of corresponding accuracy, or a digital voltmeter specified in Article 2.1.6.
2.2 EquipmentwwW.bzxz.Net
2.2.1 Split-tube heat-proof furnace: The furnace membrane specification is 50±2mm in diameter and 135~~140mm in length. A metal heat-saturating tube of corresponding size is added in the furnace, with a thickness of 0.8~~1.5mm. The longitudinal temperature on it should be close to the secondary parabola distribution, and the temperature difference between each point on the cross section of the heat-saturating tube is less than 5℃;
Soft insulation materials such as aluminum silicate fiber felt are filled between the heat-saturating tube and the sample. 2.2.2 Precision temperature controller: temperature control accuracy ±1℃. 2.2.3 Sample heating power supply equipment
2.2.3.1 Electronic AC voltage stabilizer: 5kVA. 2.2.3.2 Auto-coupling voltage regulator: 5kVA.
2.2.3.3 Transformer: primary 220V/23A, secondary 12V/411A. Rectifier cabinet: maximum current 500A, filtered current ripple factor less than 0.65%, current stability greater than ±0.3%. 2. 2. 3. 4
Sample heating and measuring device as shown below: Ministry of Metallurgical Industry of the People's Republic of China approved on February 2, 1988 292
Implementation on March 1, 1989
AC Electronics
Auto-coupling voltage regulator
Transformer
GB 8722—88
Fixed value shunt
Millivoltmeter
2.2.4 Vacuum system: including vacuum pump, diffusion pump and vacuum furnace cover, the vacuum degree is 0.133Pa. 2.2.5 No electromotive force conversion switch.
3 Sample
3.1 Sampling: According to the provisions of Article 1.1.3 of GB1427-88 "Sampling Method for Carbon Materials", but the length of the specimen shall not be less than 190mm. +0.0%mm, length 160±1mm, and no obvious knife marks on the surface of the specimen are required. 3.2 Specifications: Diameter 16+
3.3 Sample working range: 30.640mm.
3.4 Drill 3 temperature measuring holes with a diameter of 1.5mm and a depth of 1mm on the coaxial section, and at the same time require that the difference in the distance from the two end holes to the center hole is less than 0.3mm.
3.5 Quantity: Take 1 each at the furnace head, furnace middle, and furnace tail. 4 Test conditions
4.1 When the sample temperature changes by no more than 2℃ within 5 minutes, it is considered that the system under test has reached a thermally stable state, and the measured data is valid at this time.
4.2 The current through the sample should make the temperature of the midpoint of the sample close to the midpoint temperature of the heat-proof furnace, and ensure that the absolute value of the function of the temperature difference between the sample and the lateral environment is less than 5℃.
4.3 By adjusting the cooling water flow of the water-cooled electrodes at both ends of the sample, the temperature difference at both ends of the sample is close, and the difference between the midpoint of the sample and the average temperature at both ends is not less than 9℃ and not higher than 120℃. 5 Test steps
5.1 Sample loading: The sample is required to be in close contact with the water-cooled electrode. 5.2 The thermocouple measuring the temperature of the sample is inserted into the temperature measuring hole so that its contact resistance is as consistent as possible. At the same time, the position of the thermocouple measuring the lateral environment temperature is adjusted to correspond to it, and its hot spot is inserted into the insulation layer about 5 mm, and the distance from it to the axis of the sample is 18~22 mm. 5.3 The vacuum degree of the entire test is maintained above 13.3Pa. 5.4 Power on the heat-proof furnace, and when the system under test reaches thermal equilibrium, measure and record the temperature of the sample and the lateral environment. Then the sample is heated to the corresponding temperature through power supply. When thermal equilibrium is reached again, the temperature at each point, the current flowing into the sample, and the voltage in the working range are measured and recorded. 5.5 Each measurement is repeated 3 to 5 times, and the average value is taken for calculation. 6 Calculation of test results
6.1 The thermal conductivity of the sample (^) is calculated according to the following formula: IVL
= 6. 36 × (4,e)× 10-
GB 8722--88
Wherein: a-——thermal conductivity of the sample, J/(cm·s·℃); --average length of the working interval of the sample, mm;
current passed through the sample, A,
-average voltage drop in the working interval of the sample, mV; d-diameter of the sample, mm;
-average temperature difference between the midpoint and the two end points of the working interval of the sample, ℃, 4,
coefficient reflecting the size of lateral heat exchange;
N—function of the temperature difference between the marking sample and the lateral environment, ℃; 4., &, N are calculated by the following formulas:
4r - t -
4, = tz -
N=t t+
4 to2
to + to
s, = ta, -- -
N. = to toz +
Wherein: t, t2, $--the temperature of the end point, midpoint and other end point of the sample when the sample is energized, ℃, t, t2, t,
the temperature of the end point, midpoint and other end point of the lateral environment when the sample is energized, ℃; to, o2, to--the temperature of the end point, midpoint and other end point of the sample when the sample is not energized, C; t,,--the temperature of the end point, midpoint and other end point of the lateral environment when the sample is not energized, ℃; 4: the average temperature difference between the midpoint and the two end points of the sample when the sample is not energized, ℃; 4--the average temperature difference between the midpoint and the two end points of the sample in the lateral environment when the sample is not energized, ℃; 4,--the average temperature difference between the midpoint and the two end points of the sample in the lateral environment when the sample is energized, ℃; N. — Function of the temperature difference between the marked sample and the lateral environment when the sample is not energized, ℃; the average temperature of the sample (), is determined by the following formula: t = t
...........( 4 )
（７）
（9）
6.2 Substitute the measured average value into formulas (1) to (9) to obtain the actual thermal conductivity of each experimental point. 6.3 Based on the measured value of thermal conductivity at each temperature, use the graphical method to calculate the relationship between temperature and thermal conductivity, and obtain the thermal conductivity value corresponding to a certain temperature from this relationship, and issue a formal result report. 7 Experimental error
Experimental error: ±6%.
8 Test report
The test report should include the following contents:
Commissioning unit;
b. Test name and number;
Test results;
Test unit,
Test personnel;
Test date.
Additional notes:
This standard was drafted by Jilin Carbon Factory.
The main drafter of this standard is Xia Shuxun.
This standard was first issued on February 22, 1988. GB8722-88
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