Research On The Application Of Dynamic Grid Technology In The Numerical Calculation Of Microwave Heating

As an efficient and clean energy source,microwave energy has attracted wide attention and has been applied in industrial heating in metallurgical,chemical and biological fields.Internal heating and integral heating of microwaves is more efficient compared with conventional electric heating and steam heating.However,this is also a unique heating method.The local overheating caused by microwave heating results in poor temperature uniformity,“hot spot” phenomenon,and even “thermal runaway”.The phenomenon of microwave heating hot spots can be analyzed from two aspects:(1)on the one hand,due to the uneven distribution of the electromagnetic field intensity in the microwave resonant cavity where the heated object is located,the temperature on the heated material is unevenly heated;(2)on the other hand,the physical property parameters of the material,such as the dielectric constant,thermal conductivity,and electrical conductivity,will be change with increasing temperature,leading to some special macroscopic thermal phenomena in the microwave heating process.In this paper,the microwave heating applicator is regarded as a kind of medium-transmitting coupled microwave resonator by combined with the theory of generalized transmission line and the principle of dielectric resonator.The microwave is totally reflected back and forth in the direction of propagation to form a standing wave in the microwave heating applicator,and interacts with the medium to generate heat due to directional degradation and loss.By changing the distances of the dielectric terminations in microwave heating applicator,the distribution of voltage and current standing wave nodes and anti-node points on the dielectric-like transmission lines can be changed.In order to carry out research on the uniformity of temperature during microwave heating,this paper proposes an analytical calculation model for the microwave heating motion state medium base on this principle and idea,that the microwave energy in the applicator is evenly distributed by changing the position of the anti-node and the node of the standing wave,therefore,it is effectively avoided that the local microwave directing degradation loss produces excessively high or low heat,and the goal of improving the temperature uniformity is achieved.The key issue is to determine the application space solution domain including the medium in accomplish the analysis and calculation of the microwave heating motion medium model.When determining voltage and current standing wave nodes and anti-node points on the dielectric transmission line are use the finite element meshing of the solution domain when using the current mainstream numerical calculations,the finite element mesh will produce cross-winding because of the deformation of the air field caused by the movement of the medium.The paper introduced the moving mesh technology,established a numerical analysis and calculation model for the microwave heating motion state medium,studied the temperature uniformity of the microwave heating process,and used the following analytical calculation method:(1)Different solution domains use different control and optimization measures.The air domain grid adopts a fixed strategy,and irregularly heated object meshes are included in the regular grid,which can reduce the deformation complexity of the grid;(2)Tracking the variation of the domain boundaries,the control functions are proposed for the movement of the grid within the solution domain and its boundaries,that ensure the continuous movement of the grid at the boundary.The numerical calculation and experimental results show that combine with the moving mesh technology is effective and feasible for the numerical analysis and calculation of the temperature uniformity of the microwave heated moving media.