The heat transfer process within ceramic fiber linings is highly complex. Due to the material's inherently high porosity, ceramic fiber modules exhibit low thermal conductivity and minimal heat storage. Since air and most gases have very low thermal conductivity, this characteristic fundamentally defines the properties of porous refractory fibers. However, in specialized furnace applications where the atmosphere-such as reducing conditions-varies significantly, the thermal conductivity of refractory ceramic fibers can also change.
On the inner surface of a ceramic fiber module wall, perpendicular to the high-temperature face, heat transfer occurs mainly through convection and radiation. As the distance from the inner surface increases and the temperature gradient diminishes, convection and radiation are hindered, and their energy attenuates. At this stage, heat transfer within the furnace wall becomes dominated by conduction.
For conduction-dominated furnace walls, higher porosity results in better insulation. Therefore, the selection of wall thickness, composite layers, and the material properties of each layer should primarily be based on the operating temperature of the furnace. Effective thermal insulation is crucial for optimal furnace performance.
Thermal insulation aims to maximize resistance to heat flow, requiring insulating materials to possess low thermal conductivity, heat transfer coefficient, and radiant heat transfer coefficient-meaning the material must have high thermal resistance. This depends on the following factors:
1. Material structure
2. Apparent density
3. Pore size and characteristics
4. Humidity
5. Direction of heat flow
6. Temperature
