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Heat conduction mechanism

Time:2017-12-14Browse:1909Second

The heat conduction process takes the form of diffusion, but the heat conduction mechanism of all kinds of materials is different. The thermal conduction mechanism of the materials is discussed in detail. The heat conduction carriers in the solid are 3 kinds of electrons, phonons (lattice waves) and photons (electromagnetic radiation). For the polymer, it is usually a saturated system, without free electrons, and the carrier is a phonon, and the heat conduction depends mainly on the lattice vibration. The polymer has large molecular weight and polydispersity. The molecular chains exist in the way of irregular entanglement. It is difficult to completely crystallize, and the vibration of the molecular chain has the effect of scattering on phonons, so that the thermal conductivity of polymer materials is very small.

    To make the polymer has better thermal conductivity rate can be modified by the following 2 ways: (1) synthetic polymers have high thermal conductivity; (2) rate of material with high thermal conductivity of filled polymer, preparation of thermally conductive polymer composites. In the production practice, the thermal conductivity of polymer materials is improved by adding high thermal conductivity fillers, and the thermal conductive polymer composites are obtained. The heat transfer network chain 1.1 thermal network chain packing and distribution form of thermal conductivity in the polymer matrix determines the thermal conductivity of the composite rate. When the amount of filler is less, the packing in the matrix is distributed approximately in the form of islands. The dispersed phase is polymerized to form a "Sea Island" structure similar to that in polymer blends. When the filling amount of the filler reaches a certain critical value, the filler contacts each other to form a heat conduction network chain. With the increase of the filling amount, the heat conduction network chain runs through each other, and the thermal conductivity of the composite material is greatly improved. This is like a simple circuit, the matrix and the filler are regarded as 2 thermal resistance respectively. When the filling ratio is small, can not form a thermal network chain, from the direction of heat flow, thermal resistance matrix and filler equivalent series resistance, higher thermal conductivity is poor; when the filling amount is large, the contact between the packing, formation of thermal conduction chains. Thermal conductivity network has small heat resistance, this matrix and filler in heat the direction of the equivalent parallel, plays a dominant role in the heat transfer process of heat conduction chain network, Agari model is based on thermal network chain based mechanism. This is like a simple circuit, the matrix and the filler are regarded as 2 thermal resistance respectively. When the filling ratio is small, can not form a thermal network chain, from the direction of heat flow, thermal resistance matrix and filler equivalent series resistance, higher thermal conductivity is poor; when the filling amount is large, the contact between the packing, formation of thermal conduction chains. Thermal conductivity network has small heat resistance, this matrix and filler in heat the direction of the equivalent thermal conductivity network in parallel, the heat transfer process plays a leading role,. The Agari model is based on the mechanism of heat conduction network chain. Thermoelastic composite reinforced type

     1.2 thermo elastic combination enhanced Li Bin and so on were used to prepare polymer matrix thermal conductive composite materials by melt blending. The changing laws and intrinsic reasons of composites thermal conductivity and conductivity with filler particle size and other factors were studied. The research results show that the composite system of thermal conductivity with increasing filler content always showed a gradual upward trend, showed no dramatic changes in conductivity that; under the same loading, the thermal conductivity of the composites with the particle size decreases, and the opposite conductivity with the particle size variation. This difference is mainly due to the different conduction mechanism of the two. In this paper, the rule of the change is explained by the thermoelastic composite enhancement mechanism. According to the theory of solid physics, solid phononic lattice vibration wave for quantification of the differences and the electronic solid material particle movement and transfer are substantial. The conducting process is the directional movement and conduction of free electrons, so it is very important to form the conduction path. By analyzing the change rule of thermal properties of various minerals, it is found that the thermal conductivity of materials is very similar to the elastic moduli in classical vibration and elastic mechanics. Therefore, the thermal conductivity of materials can be regarded as the elastic modulus of phonon (i.e. thermal vibration) transfer process. Similarly, the thermal conductivity of polymer matrix composites filled with thermal conductive filler can be considered as a composite of high thermal conductivity filler for low thermal conductivity matrix.

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