| Summary: | 碩士 === 國立成功大學 === 航空太空工程學系 === 103 === It is popular to perform the Eulerian-Lagrangian approach to simulate the two-phase flow using a hard-sphere model. The cohesive force between small particles is significant; however, the standard hard-sphere model does not consider the cohesive force between the colliding particles. Because of this, it is necessary to develop an extended hard-sphere model considering the influence of cohesive force to simulate some problems such as industrial processes that involve agglomeration phenomena. A reasonable extended hard-sphere model should quantify the cohesive force between two particles and define the duration of the cohesive force influences. The quantification of cohesive force is based on the Bradley model as well as a modification of the ideal van der Waals force model. The duration of the cohesive force acting on two colliding particles refers to the Lennard-Jones model. In addition, in this paper, in order to save computer resources, a link-list method rather than a full-search domain method is used as the particle collision inspection method.
The developed extended hard-sphere model is used to simulate the motion of micro-size particles and to observe the agglomeration phenomenon in different test cases.
According to the results of the simulations, we conclude four points as follows. First, as the reduced radius of colliding particles becomes smaller, agglomeration appears more easily. Next, the extended hard-sphere model not only could quantify the agglomeration conditions but also the effect of the post-collisional relative velocity. Third, in a simulation with periodic gravity, the agglomeration rate is based on particle size and the magnitude of the gravity constant. Over a long period of time, the micro-size particles agglomerate into a bigger particles. Lastly, the results of all of the different tests discussed in this thesis show that when the size of two colliding particles increases, the cohesive force and the reduced mass between the two colliding particles would increases as well. However, in the case of the impulse, the influence of particle size is greater than the effect of cohesive forces unless the pre-collisional relative velocity is very small.
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