Testing method for fabric thermal protection (radiation) performance tester

 

 

Convective heat dissipation is the transfer of heat through the movement of fluids such as liquids (such as water) or gases (such as air). The way in which heat is transferred due to fluid movement caused by uneven temperature is called natural convection. There is natural convection in the air within the boundary layer of the human body and clothing surface. The heat transfer caused by fluid movement due to external factors is called forced convection. The heat convection resistance of fabrics is closely related to their weight, density, and air properties. Increasing the weight of the fabric can increase the time required to cause second degree burns on the skin. Meanwhile, multi-layer fabrics have better heat convection resistance compared to single-layer fabrics.

 

Thermal conduction refers to the transfer of heat along an object. It transfers from objects with high temperatures to objects with low temperatures. This transmission is mainly achieved through continuous collisions between adjacent molecules in the material. In the application of thermal protective clothing, heat conduction refers to the use of sparks, molten metal sprays, and other carriers of heat that come into contact with clothing and transfer the heat to the human body through the clothing, causing harm to the human body.

Usually, the thermal conductivity of fabrics against molten metal can be measured by placing artificial skin made of standard PVC film behind the fabric and measuring the damage caused by the heat of molten metal passing through the fabric to the artificial skin. According to the area and degree of damage, the thermal protection performance of fabrics can be classified into levels one to seven. Level 1, no harm; Second and third degree burns refer to first-degree burns with an injury area of less than or greater than 0.01 square meters, respectively; Grade four and five are second degree burns with an injury area of less than or greater than 0.01 square meters, respectively; Grade 6 and Grade 7 are third degree burns with an injury area of less than or greater than 0.01 square meters, respectively.

 

Thermal radiation refers to the outward radiation of heat from an object along a straight line. The essence of thermal radiation is the heat radiation caused by the temperature of an object, and its magnitude is proportional to the fourth power of the heat source temperature. Unlike heat conduction and convection, thermal radiation is a non-contact heat transfer method that does not require any substance as a medium, but transfers heat in the form of electromagnetic waves. In the practical application of thermal protective clothing, thermal radiation is one of the main forms of heat transfer that causes harm to victims. Even with flame combustion, up to 80% of its energy includes thermal radiation.

 

In the testing of the thermal radiation resistance of thermal protective clothing, the fabric is often vertically exposed to a radiant heat source. Within a specified distance, the heat source radiates heat to the fabric sample. The thermal radiation resistance of the sample is evaluated by measuring the time and heat flux density required to cause second degree burns to the human skin behind the sample.