Application of steady - state card method to the measurement of hematrix emissivity of thermal control data

Using the steady-state card method to design a test data hemispheric emissivity try to install, and continue to the uncertainty of its synthesis. The use of the installation of the secondary name mirror (OSR) at room temperature hemisphere emissivity to continue the test, the test results uncertainty is less than 2.00%. At the same time, the hemispheric emissivity between OSR and a new phase change data between 190 and 350K was tested using this installation. 1, At the same time, the hemispheric emissivity between OSR and a new phase change data between 190 and 350K was tested using this installation.the hemispheric emissivity between OSR and a new phase change data between 190 and 350K was tested using this installation.

2, the test principle

Measurement of hemispheric emissivity by steady - state calorimetry. If the hemispherical emissivity of the sample is equal to the hemispherical attraction rate, when the heat of the sample reaches thermal imbalance,

Where is the nominal value of the sample; Ts and Tw are the heat of the sample and the inner wall of the test chamber; Q is the heating power of the heater; Qw is the heat loss of the sample through the lead; Qg is the heat loss caused by the residual gas in the test chamber; Qr is the energy of the sample and the interior of the test chamber.Qr is the energy of the sample and the interior of the test chamber.

In the test, the test room to maintain high vacuum, and the test room name is far greater than the nominal product plot, therefore, Qg and Qr can be negligent; because the adoption of the heating wire and lead diameter are smaller, it can neglect the lead heat Loss Qw. After measuring the heating power Q of the heater, the heat of the sample Ts and the inner wall heat Tw of the test chamber and the nominal product of the sample, the formula (2) is used to calculate the hemispheric emissivity of the data.

3, try to install

Test system diagram shown in Figure 1. The system is mainly composed of external insulation with a test chamber, vacuum system, DC power supply, digital voltmeter, the sample unit and so on. The inner wall of the test room has a size of & lt; 250 mm & lt; / RTI & gt; 280 mm, with a layer of matte black paint (& lt; / RTI & gt; During the test, add refrigerant to the insulated container. The vacuum system consists of a rotary cup pump and an oil drain pump, and the vacuum degree is maintained at 1 × 10-3 Pa. The sample cells consisted of two opposing samples (40.0 mm x 40.0 mm x 0.5 mm) and one heater (40.0 mm x 40.0 mm x 0.2 mm) as shown in Fig. The diameter of the thermocouple and the heating wire is 0.16mm. Adopted by Changchun Electric Measuring Tool Factory WYJ DC power supply to provide heating DC. Adopting 7071 digital voltmeter for measuring thermocouple thermoelectric potential.

1. Insulating container; 2. Test chamber; 3. Sample unit; 4. Regulated power supply; 5. Digital voltmeter; 6. Vacuum unit

Figure 1 try to install instructions

1. heating wire; 2. thermocouple; 3. sample;

Figure 2 sample unit shown intention 4, try

Using this test, the hemispherical emissivity of the cerium glass secondary nominal mirror (OSR) and a phase change data under opposite heat were tested. Before the test, the nominal product of the sample is measured and the thermocouple is vivid in the name of the sample. Then, the sample unit is charged into the vacuum chamber, and the vacuum unit is opened. When the vacuum degree reaches 1 × 10-3 Pa, liquid nitrogen is injected into the insulated container. When the cavity heat is solid, the measurement and recording data are finished. The hemispheric emissivity is calculated by the formula (2), and the calculated data is compared with the literature value. 5, the consequences and explore

The ratio of the ambient temperature hemispheric emissivity of the measured OSR measured by the test installation to the value provided in the Vacuum Skill Online is shown in Table 1. It can be seen that the error between the installed room temperature test value and the literature value is less than 2.00%, and the installation can measure the hemispheric emissivity of the data more accurately.

Table 1OSR room temperature test value comparison

Table 2 is the use of the installation of the reverse heat under the OSR and a phase change data hemispheric emissivity test value. It can be seen from Table 2 that the emissivity of OSR decreases gradually with the increase of heat, and decreases from 190 to 350K, which is 0.08. The emissivity of phase change data increases with the increase of heat, Obviously, especially in the 230 ~ 270K, the increase reached 0.17, in the entire test area, the hemisphere emission rate increased by 60%. This is important because the material is at high temperatures in the non-metallic phase, reflecting the non-metallic thermal radiation characteristics, there is a lower emissivity value, can reduce the heat radiation, heat destruction; high heat, the material reflects the non-conductor Of the thermal radiation characteristics, there is a high emissivity value, can enhance the radiation heat, dissipate excess heat.

Table 2 Hemispherical emissivity of OSR and phase change data under opposite heat.