Characteristics of thermal insulation materials and factors affecting thermal conductivity of thermal insulation materials
Characteristics of insulation materials
The thermal insulation functional index of the thermal insulation material is determined by the thermal conductivity of the material. The smaller the thermal conductivity, the better the thermal insulation performance. In general, materials with a thermal conductivity less than 0.23 W/(m·K) are called thermal insulation materials, and materials with a thermal conductivity less than 0.14 W/(m·K) are called thermal insulation materials; usually the thermal conductivity is not more than 0.05 W/(m). The material of K) is called high-efficiency insulation material. The materials used for building insulation generally require low density, low thermal conductivity, low water absorption, good dimensional stability, reliable thermal insulation performance, convenient construction, environmental friendliness and reasonable cost.
Factors affecting the thermal conductivity of thermal insulation materials
1. The nature of the material. The thermal conductivity is the largest in the metal, the second is the non-metal, the liquid is smaller, and the gas is smaller.
2. Apparent density and pore characteristics. A material with a small apparent density has a small thermal conductivity. When the porosity is the same, the larger the pore size, the larger the thermal conductivity.
3. Humidity. After the material absorbs moisture and moisture, the thermal conductivity increases. The thermal conductivity of water is 0.5 W/(m·K), which is 20 times larger than the thermal conductivity of air of 0.029 W/(m·K). The thermal conductivity of ice is 2.33 W/(m·K), which results in a higher thermal conductivity of the material.
4. Temperature. The thermal conductivity of the material increases with increasing temperature, but the temperature is not significant at 0 to 50 ° C. Only for materials at high temperature and negative temperature, the effect of temperature should be considered.
5. Heat flow direction. When the heat flow is parallel to the fiber direction, the heat preservation performance is weakened; and when the heat flow is perpendicular to the fiber direction, the heat resistance of the heat insulating material is best.