What affects the thermal conductivity of insulating refractory bricks?
There are three ways of heat transfer in mullite insulating refractory bricks:
Heat conduction Q1, convective heat transfer Q2 and radiation heat transfer Q3. Heat conduction refers to the heat transfer between objects in contact with each other through the thermal movement of free electrons, molecules, atoms and other microscopic particles. Convection heat transfer refers to the relative displacement between fluids, causing the mutual penetration of hot and cold fluids to achieve heat transfer. Radiation heat transfer is It refers to the temperature of the object itself that emits electromagnetic waves or photons to transfer heat.
Generally, thermal insulation materials are multi-phase materials, and each phase has its own unique structure. Therefore, the thermal conductivity of thermal insulating refractory bricks is affected by many factors such as the composition, content, and internal structure of the phases. Therefore, there are many thermal insulation mechanisms and factors that affect its thermal insulation effect. The thermal conductivity of the thermal insulation material interacts with the bulk density, porosity, phase composition, etc. of the material.
(1)Stomata size:
The number of pores and the size of the pores generally appear at the same time. On the premise of keeping the total number of pores unchanged, reducing the pore diameter can increase the number of pores, thereby reducing the thermal conductivity of the material; when the number of pores increases, the thermal insulation material The specific surface area will increase and the radiation conductivity will decrease.
(2)Bulk density:
The thermal conductivity of solids is higher than that of gases. The decrease in volume density means that the gas phase in the material increases, so the thermal conductivity decreases. However, when the bulk density is too low, the effect of gas phase heat transfer in the material will be enhanced and the thermal conductivity will increase. Therefore, in order for thermal insulation insulating refractory bricks to have excellent thermal insulation properties, it is not that the lower the volume density, the better. At a specific temperature, each material will have an appropriate thermal conductivity.
(3) Material components:
The emissivity of thermal insulation materials is related to the material, temperature and particle size. Therefore, the ratio of thermal insulation materials can be appropriately increased or components with low emissivity such as Al2O3, MgO, CaO, and ZnO can be added, while Fe, Ni, and Cr should be avoided. Incorporation of transition element oxides.
