Study On Contact Heat Transfer Characteristics In Granular Systems

Granular matter is one of the most widely existing forms of matter in nature,From big stars to small grains of sand dust are granular matter.Generally,a large aggregate composed of a large number of discrete macro particles with a diameter of more than1?m is called a granular system.The system is widely used in industrial manufacturing,civil engineering,geological engineering and other fields.It is closely connected with people's production and life.The research on the behavior of granular system have great scientific significance for human daily life and economic development.It has been found that when the granular system is under external loading.The force will be transferred from one loaded granular to another in contact and not directly loaded granular.When the force balance is reached,a complex force chain will be formed in the granular system.Because of the complexity of granular system,it is relatively difficult to study the heat transfer characteristics of granular system,especially under the action of external forces.In this thesis,temperature sensitive coatingEu?TTA?₃ is used to measure the whole field temperature of granular system in real time.A representative experimental model of non photoelastic particles is used.In the calculation method,the granular element method?GEM?and the digital image correlation method?DIC?are used to give the contact force distribution characteristics of the granular system,and the characteristics of heat transfer in various granular systems under the action of external forces are obtained.The main results are as follows:?1?Choosing theEu?TTA?₃ as the temperature sensitive material.The correlation between luminance and temperature of the material was calibrated in the vacuum cavity environment.The function relationship between luminance and temperature is fitted,which provides the basis for the subsequent experimental measurement.?2?Through the method of surface spray,the loading speckle pattern of granular system before and after is obtained.Using digital image correlation?DIC?to calculate the deformation characteristics of granular system.Then,the coordinates of the contact points between particles are calculated by the Hough transform,which is input into the GEM algorithm as a parameter,and the contact force distribution characteristics of the granular system under the action of external forces are obtained.The size and direction of the contact force chain are analyzed.The contact force chain measured by this method is compared with the traditional photoelastic experiment and the accuracy of the method is verified.?3?The heat transfer characteristics of the granular system with regular arrangement and the granular system with irregular random arrangement under the action of external force are compared and analyzed.The results show that for granular system:No matter in regular or irregular random arrangement,the direction of heat transfer is always the same as that of the main force chain,and the heat flow will preferentially propagate along the main force chain,regardless of granular size,loading mode,heat source location,etc.?4?A similar heat transfer experiment is carried out for a typical granular system which uses"soft"granular to replace some"hard"granular to realize force chain direction control.The results show that the different spatial configuration of the force chain of the granular system results in the final heat transfer which is consistent with the force chain,and thus realizes a kind of artificial control of the heat transfer of the granular system.