Analysis of Thermal Resistance and Humidity Resistance Test
Analysis of Thermal Resistance and Humidity Resistance Test
Why it matters?
Clothing thermal and wet comfort refers to the performance of clothing in which the human body exchanges heat and moisture with the environment under different environmental conditions and human activity levels until it reaches a balanced state.
Clothing thermal and wet comfort performance has a wide range of applications in all walks of life, summer clothing is required to be refreshing and breathable, winter clothing is required to be warm. In extremely hot environments, clothing must be insulated and cooled, such as fire-fighting clothing, mineral clothing, and liquid-cooled clothing; in extremely cold environments, clothing must be cold-resistant and warm, such as cold-proof clothing and aerospace clothing.
Thermal resistance and humidity resistance are two important indicators for measuring the thermal and wet comfort of clothing. Factors such as clothing, environment, and sports will affect its measurement results. This is of great significance for evaluating the thermal and wet comfort performance of clothing, the design of functional clothing, the establishment of thermophysiological models, and the improvement of sweating and warming dummy.
Definition of thermal resistance and humidity resistance:
Human body heat loss is mainly divided into sensible heat and latent heat. Sensible heat refers to the heat released by the human body to the outside when there is a temperature difference between the human body and the environment. The main forms are conduction, radiation, and thermal convection; latent heat refers to the heat that is removed in the form of sweat evaporation.
Clothing thermal resistance (° C · m2 / W) represents the resistance to heat flow due to the temperature difference between the layers of the clothing. The thermal resistance value can be expressed by the ratio of the temperature difference between the clothing layer and the layer and the heat flux passing through the unit area of the clothing vertically. At present, the internationally common indicator is the clo value, which is defined as: indoors where the temperature is 21 ℃, humidity is 50% ± 0.2%, and the wind speed is less than 0.1 m / s. Adult men who sit quietly or engage in light mental work feel comfortable (The metabolic heat generation is about 58.15 W / m2), and the thermal insulation ability of the clothing worn when the average skin temperature is maintained at about 33 ° C is 1 clo (1 clo = 0.155 ° C · m2 / W).
Clothing wet resistance (Pa · m2 / W) means the moisture permeability resistance caused by the water vapor pressure difference between the inside and outside of the clothing. The wet resistance value can be expressed by the ratio of the water vapor pressure difference between the inside and outside of the garment and the evaporative heat flux in the vertical passage unit area. When the human body feels hot flashes, sweat will be secreted from the skin to take away the body’s heat. Among them, the amount of attached sweat (amount of sweat adhered to the skin surface) and the amount of sweat flowing (amount of sweat flowing down) are both ineffective sweat amounts. The amount of evaporated sweat can take away the body’s heat, which is called effective sweat.
Thermal resistance test:
Note: To conduct the test, you will need a instrument called Sweating Guarded Hotplate. or you can know more by watching this video https://youtu.be/GlXE8_1F2nU
(1) The test process is: cold machine preheating-thermal resistance parameter setting-thermal resistance empty plate test-thermal resistance test
(2) Cold machine preheating: After the power is turned on, the whole machine needs to be warmed up for 45min. A medium-thick fabric is added to the test board, and the test board is brought to 35 degrees Celsius, and the fabric is removed. Then observe the temperature of the heating plate and the temperature of the bottom plate to about 35.2, complete the preheating of the cold machine, and then put the test sample (or standard sample) into the test bench.
(3) Thermal resistance parameter setting: Set according to standard requirements.
(4) Thermal resistance plate test: The thermal resistance under the temperature gradient is measured without putting the test sample. The empty board test does not have to be done every time, because the repeat error of the empty board test is quite small, it is recommended to test it from March to June.
(5) Thermal resistance test: Put the test sample on the surface of the test plate, adjust the lift button on the front of the test bench inside the test chamber, cover the four sides of the metal blank, and when the metal blank is exactly horizontal, then lower the plexiglass cover , Close the instrument door, and press the start button, the instrument will run automatically. When it is stable, press the stop button, the instrument will keep the displayed thermal resistance value as the test result.
(6) Replace the sample and repeat the previous steps for testing. Finally, take the mean value for evaluation. The result retains 3 significant digits.
Humidity wet resistance test:
(1) The test sequence is: preheating of the cold machine-setting of the wet resistance parameters-humidification and replenishment and placement of the test film-wet block test-wet resistance test
(2) Preheating of the cold machine: After the power is turned on, the whole machine needs to be warmed up for about 60min. A piece of fabric of medium thickness is added to the test board, and the test board is brought to 35 degrees Celsius, and the fabric is taken out. Then observe the temperature of the heating plate and the temperature of the bottom plate to about 35.2, complete the preheating of the cold machine, and then put the test sample (or standard sample) into the test bench.
(3) Except for humidification and replenishment and film placement, the wet resistance test is similar to the thermal resistance, and is not repeated here. Humidification and replenishment: Press the wet resistance key on the control panel, loosen the waterproof joint of the adjustment rod a little, and the water in the replenishment tank will automatically flow into the test box. When water comes out, you can stop the water level adjustment lever to pull up and tighten the waterproof joint.
- Take two sheets of film, the elastic side is used for testing, flatten the surface of the perforated plate, and the two layers of film can be appropriately wetted with distilled water. Take the cotton pad in the attachment to smooth the film
Conduct a specific test is the only way to get the full story of the clothing performance, for comfort wearing, thermal and humidity resistance test is a must.