What is the way of conducting heat in Ceramic Thermal Insulation Materials

Ceramic Thermal Insulation Materials are two phase media composed of gas phase and solid phase. Heat transfer forms are mainly conduction, convection and radiation. Good insulation materials can meet both thermal insulation performance and environmental conditions.

Heat conduction

Heat conduction of heat insulation materials includes solid phase heat conduction and gas phase heat conduction. Solid particles produce solid phase heat conduction; The thermal motion of molecules in the stomata produces gas phase heat conduction. Under atmospheric pressure, the influence of gas phase heat conduction on heat insulation performance is greater than that of solid phase heat conduction, and the difference is more obvious under vacuum condition.

Thermal convection

Heat is transferred with the flow of the medium. It can be divided into forced convection and free convection. Convection caused by external causes is called forced convection; The convection caused by density difference due to temperature change of medium is called free convection.

Thermal radiation

Radiation from an object is partially absorbed by another object, and the rest may be reflected or penetrated. Radiative heat transfer is enhanced with increasing temperature. At the same time, the increase of pores and voids will also increase the radiation heat transfer.

The thermal conductivity of materials is affected by many factors. There are four kinds of heat conduction carriers: molecules, phonons, photons and electrons. Because the heat insulation material is inorganic non-metallic material, electronic heat conduction can be ignored. The micro heat conduction mainly includes molecular heat conduction, phonon heat conduction and photon heat conduction.

Molecular heat conduction

Gas heat conduction is realized through molecules and atoms. Heat conduction is the result of collisions between gas molecules caused by irregular thermal movements. The higher the temperature, the higher the kinetic energy of the polymer, and the molecules collide with each other to transfer heat from high to low temperature.

Phonon heat conduction

Atoms in solids have limited degrees of freedom and can only vibrate in fixed positions. The amplitude depends on the energy of each atom. When there is a temperature difference, the vibration intensity is different, and thus the interaction occurs to achieve energy transfer. This mechanism calls for the conduction of heat. The main factor affecting the heat conduction of phonons is the mean free path of phonons.

Photon heat conduction

Particle vibration and rotation in solid radiate high frequency electromagnetic wave. When there is a temperature difference, part of the heat energy is transferred from the high temperature to the low temperature through the action of this electromagnetic wave, and this mechanism is called photon heat conduction. The influence of photon heat conduction depends mainly on the mean free path of photon.