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 evaporation resistance are two essential indicators for measuring the thermal and wet comfort of clothing. Factors like clothing, vicinity, and sports will affect its measurement results. This is of great importance for assessing the thermal and wet comfort performance of clothing, the planning 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 especially divided into sensible heat and heat of transformation . Sensible heat refers to the warmth released by the physical body to the surface when there's a temperature difference between the physical body and therefore the environment. the most forms are conduction, radiation, and thermal convection; heat of transformation refers to the warmth that's removed within the sort of sweat evaporation.

Clothing thermal resistance (° C · m2 / W) represents the resistance to heat flow thanks to the temperature difference between the layers of the clothing. The thermal resistance value are often expressed by the ratio of the temperature difference between the clothing layer and therefore the refore the layer and the heat flux passing through the unit area of the clothing vertically. at the present , the internationally common indicator is that the clo value, which is defined as: indoors where the temperature is 21 ℃, humidity is 50% ± 0.2%, and therefore the wind speed is a smaller amount 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 therefore the thermal insulation ability of the clothing worn when the typical 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 vapour pressure difference between the within and out of doors of the clothing. The wet resistance value are often expressed by the ratio of the water vapour pressure difference between the within and out of doors of the garment and therefore the evaporative heat flux within the vertical passage unit area. When the physical body feels hot flashes, sweat are going to be secreted from the skin to require away the body's heat. Among them, the quantity of attached sweat (amount of sweat adhered to the skin surface) and therefore the amount of sweat flowing (amount of sweat flowing down) are both ineffective sweat amounts. the quantity of evaporated sweat can deduct the body's heat, which is named 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 method 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 textile is added to the test board, and the board is brought to 35 degrees Celsius, and the textile is removed. After that 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 it 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) Change 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 facility is turned on, the entire machine must be warmed up for about 60min. a bit of cloth of medium thickness is added to the test board, and therefore the test board is delivered to 35 degrees Celsius, and therefore the fabric is taken out. Then observe the temperature of the heating plate and therefore the temperature of rock bottom plate to about 35.2, complete the preheating of the cold machine, then put the test sample (or standard sample) into the test bench.

(3) apart from humidification and replenishment and film placement, the wet resistance test is analogous to the thermal resistance, and isn't repeated here. Humidification and replenishment: Press the wet resistance key on the instrument panel , loosen the waterproof joint of the adjustment rod a touch , and therefore the water within the replenishment tank will automatically flow into the test box. When water comes out, you'll stop the water level adjustment lever to tug up and tighten the waterproof joint.

Take two sheets of film, the elastic side is employed for testing, flatten the surface of the perforated plate, and therefore the two layers of film are often appropriately wetted with water . Take the cotton pad within the attachment to smooth the film, and take away the air bubbles between the film and therefore the perforated plate.

Conclusion:

Conduct a selected test is that the only thanks to get the complete story of the clothing performance, for comfort wearing, thermal and humidity resistance test may be a must.