Thermal insulation properties

2019-06-11

1, thermal conductivity. Thermal conductivity is a physical indicator of the thermal conductivity of a material and represents the amount of conduction energy of the material itself. Physically speaking, under stable heat transfer conditions, when the temperature difference within the unit thickness of the material layer is 1 ° C, the heat of 1 m 2 of surface area is passed within 1 s. It can be seen that the larger the thermal conductivity, the worse the thermal insulation performance of the material, and the better the thermal insulation performance of the material. The factors affecting the thermal conductivity of materials are as follows: composition of matter, porosity, void characteristics, temperature, humidity, heat flow direction, compressive strength, etc.

2. The material composition of the material. The material composition of the material is very different, and the thermal conductivity of the metal is usually the largest, generally between 2.31 and 419 W/(m?K). Followed by non-metal, the liquid is smaller and the gas is smaller. In the range of non-metallic materials, organic materials generally have lower thermal conductivity than inorganic materials. Even materials with the same composition but different structure have different thermal conductivity. Generally, the material of the crystal structure has the highest thermal conductivity, the microcrystal is the second, and the glass structure is the smallest. It can be seen that the material structure of the material can be changed, and the thermal conductivity thereof can be reduced, thereby achieving better thermal insulation.

3. Porosity and void characteristics of the material. Since the apparent density of the material is directly related to the porosity of the material, the material with a small apparent density has a large porosity, and the material with a large apparent density has a small porosity. Since the thermal conductivity of the solid matter is much larger than the thermal conductivity of the air, when the porosity is the same, the void size is small and the closed material is weaker due to the air convection, and the material has a larger thermal conductivity than the relative empty metal. .

4. The temperature and humidity of the environment in which the material is located. When the temperature rises, the thermal motion of the material increases, and at the same time, the heat conduction of the air in the pores of the material and the radiation between the pore walls are enhanced, and the thermal conductivity of the material is increased. However, when the temperature is within 0-50 °C, the effect is not obvious. Only in the case of high temperature or low temperature, the influence of temperature on the thermal conductivity of the material is considered.