Introduction to the application areas of XPS extruded plastic panels

I. Type of material

Different types of insulation materials (thermal insulation materials) have different thermal conductivity. The physical thermal properties of insulation materials differ according to their material composition, and their thermal conductivity or thermal conductivity varies according to their insulation mechanism.

Even for insulation materials made of the same substance, the difference in thermal conductivity can sometimes be significant due to differences in internal structure or in the control process of production. For solid insulation materials with low porosity, the thermal conductivity is greatest for crystalline structures, followed by microcrystalline structures and least for vitreous structures. However, for insulation materials with high porosity, the solid part has little influence on the thermal conductivity due to the main effect of the gas (air) on the thermal conductivity, whether it is the crystalline structure or the glassy structure.

Second, the working temperature

Temperature has a direct effect on the thermal conductivity of all types of insulation materials, temperature increases, the thermal conductivity of the material rises. Because the temperature increases, the material solid molecular thermal movement enhanced, while the material pores in the air thermal conductivity and radiation between the pore walls also increased. This effect, however, is not significant in the temperature range of 0-50°C. Only for materials at high or negative temperatures should the effect of temperature be considered.

Third, the moisture content ratio

The vast majority of thermal insulation materials have a porous structure, easy to absorb moisture. After the material absorbs moisture, its thermal conductivity increases. When the moisture content is greater than 5%-10%, the increase in thermal conductivity in the porous material is most obvious.

This is because when the pores of the material have moisture (including water vapour), the pores of the diffusion of steam and the movement of water molecules will play a major role in heat transfer, and the thermal conductivity of water is about 20 times greater than the thermal conductivity of air, which causes a significant increase in its effective thermal conductivity. If the water in the pore space becomes ice, the thermal conductivity of the ice is even greater, which results in an even greater thermal conductivity of the material. Therefore, non-hydrophobic insulation materials must be applied in a waterproof manner to avoid moisture.

Fourth, pore characteristics

Under the same condition of porosity, the larger the size of pore, the larger the thermal conductivity; the thermal conductivity of interconnected pores is higher than that of closed pores, and the higher the closed porosity, the lower the thermal conductivity.

Five, the capacity is large and small

As the thermal conductivity of gas phase is usually smaller than the thermal conductivity of solid phase, thermal insulation materials tend to have high porosity, i.e., they have a small capacity. In general, increasing the porosity or decreasing the weight will result in a decrease in thermal conductivity.

However, for materials with a very low apparent density, especially fibrous materials, the thermal conductivity increases when the apparent density is below a certain limit, due to the fact that when the porosity increases the number of interconnected pores increases considerably, thus enhancing the convection effect. There is therefore an optimum apparent density for these materials, i.e. the density at which thermal conductivity is minimised.