Gester Instruments | Professional Textile, Footwear and PPE Testing Equipments Manufacturers Since 1997
Analysis of GB/T 11048 moisture absorption and perspiration test method
1. Test principle GB/T11048 introduces two methods for testing the thermal resistance of fabrics——Evaporative hot plate method and static plate method. The principle of the two test methods is the same. The static flat plate method requires that the air velocity in the climate chamber is not greater than 0.1m/s, while the former requires 1m/s. Among them, the evaporation hot plate method can also test the moisture resistance of the fabric, and the test components are slightly different from the thermal resistance method. Thermal resistance: The sample is covered on an electrothermal test board, and the test board and its surrounding and bottom thermal guard rings can maintain the same constant temperature. The whole test device is placed in a climate chamber with constant temperature, constant humidity and constant wind speed, and the temperature on the electric heating test plate forms a temperature gradient with the temperature in the climate chamber. The electric heating test board dissipates heat to the surroundings through the sample, and the thermal resistance value can be obtained by bringing the power consumed in this heat dissipation process into the corresponding formula. Moisture resistance: For the measurement of moisture resistance, the porous electric heating test plate should be covered with a breathable but water-impermeable film. After the water entering the electric heating plate evaporates, it passes through the film in the form of water vapor (no liquid water contacts the sample). After the sample is placed on the film, the heat flow required to maintain the constant temperature of the test class under a certain moisture evaporation rate is measured, and the moisture resistance of the sample is calculated by substituting it into the formula together with the water vapor pressure passing through the sample. According to the principle of the test, the test of moisture resistance requires the test plate to be a through-hole structure, and it also needs to be equipped with a water supply system. 2. Evaluation of thermal resistance and moisture resistance Thermal resistance: The calculation formula is, where Tm and Ta are the surface temperature of the test board and the surface temperature of the climate chamber, respectively. A is the area of the sample, these are certain. H is the power value dissipated through the fabric to dissipate heat under the temperature gradient. ΔHc is the power correction value. Rct0 is the thermal resistance value calculated when no sample is added, that is, when the plate is empty, which is called the empty plate value. , Hct0 is the power value of direct heat dissipation under temperature gradient. Wet resistance, the calculation formula is, the surface temperature of the test plate and the surrounding air temperature are controlled at 35 ℃, and the air flow rate is 1m/s. The humidity of the air should be kept at 40%, and its water vapor pressure Pa is 2250Pa. The saturated steam pressure Pm was 5620Pa. Ret0 is the moisture resistance value calculated when no sample is added, which is called the empty plate value. , Het0 is the power consumption of the instrument under the water vapor concentration gradient. 3. Analysis of test equipment parts This part mainly introduces the parts in the evaporation hot plate method. 1. Temperature and water vapor control and measurement device (with the test board as the main body) The test board is placed in a thermal guard ring (to prevent heat dissipation). The test board is mainly composed of the following components: 1. Metal plate; 2. Temperature sensor; 3. Temperature controller; 4. Calorimetry device; 5. Quantitative water supply device; As can be seen from the figure, the heat generated by 6 is transferred to the metal plate 1, and the two constitute the test plate. The function of 5 is for water supply (source of water vapor) when measuring moisture resistance. It should be noted here that the test wet resistance is that the metal plate is in a porous form, and the surface of the electric heating wire metal component in contact with the porous plate is a groove, so that the water provided by the water supply device 5 can enter the electric heating plate. 2. Thermal Guard Ring with Temperature Control There are two forms of thermal guard ring. Each number in the figure indicates: 7. Temperature and water vapor control and measuring device; 8. Thermal guard ring; 9. Temperature controller; 10. Temperature measuring device; 11. Sample stand; 12. Test plate; 14. Bottom plate; 15. Wooden frame; 16. Cork strip; 17, 18. Temperature measuring device. The dimensions of specific devices are described in detail in the standard. 4. Test process and conditions The empty board value is measured before the test. The measured value shall be recorded once no more than 3 minutes, and the test time shall be at least 30 minutes to achieve stability (excluding warm-up time). Thermal resistance: adjust the surface temperature Tm of the test board to 35°C, the temperature of the climate chamber to be 20°C, the relative humidity to be 65%, and the air flow rate to be 1m/s (static flat plate method is not more than 0.1m/s). After placing the sample on the test plate, after the Tm, Ta, relative humidity, and H are stable, the recorded value is substituted into the formula for calculation. Moisture resistance: A film that is permeable to water vapor but not water is placed on a test panel. Adjust the surface temperature Tm of the test panel and the air temperature Ta to 35°C, the relative humidity to be 40%, and the air flow rate to be 1 m/s. After placing the sample on the test plate, after the Tm, Ta, relative humidity, and H are stable, the recorded value is substituted into the formula for calculation. More about Moisture Wicking Tester: http://www.gnxcs.com
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