| The content of the thesis covers two parts. One is the theoretical modeling and numerical simulation of the air jet flow field with high temperature. The other is the foundation of the air drawing model of polymer in which the theoretical model of the air jet flow field is integrated.In foreword the background of topic selection of this thesis is described.In chapter 1 the recent progress in the world of studies on the mechanism of air drawing of polymer melts in the air jet flow field with high temperature is introduced. As the research work done by Shambaugh's group at the University of Oklahoma in the United States represents the most advanced level in the above field, their research works are, therefore, majorly mentioned.In chapter 2 a solution of the air jet flow field of dual slot die in melt blowing process by using classical analytic method is proposed. By substituting vortex pairs for the synthesis of jet flows, the distribution of air velocity along the spinneret axis is deduced, and its computed results are confirmed by the experimental data measured by Laser Doppler Velocimeter. By introducing the theoretical formula of the air velocity distribution into the air drawing model of the polymer for the prediction of fiber diameter, the results also coincide with the measured diameter. The effects of the die design parameters on the air velocity distribution are also discussed. It is found that the air velocity in the direction of the spinneret axis can be increased by decreasing the angle between the air slot and the spinneret axis, increasing the slot width and decreasing the head width, which shows that the modeling of the flow field is of benefit to improving the melt blowing process. This method can be used for quickly predicting the final fiber diameter under certain processing conditions and analyzing the effects of both different processing and die design parameters on the final fiber diameter. However, the method is limited because it can only determine the air velocity distribution along the spinneret axis.The numerical simulation method and experimental verifications are further employed in studying the air jet flow field of dual slot die in chapter 3, 4, 5 and 6 for a comprehensive understanding of it.In chapter 3 some basic knowledge are briefly introduced, including the finite difference methods, i.e. the control volume method, the regulations of the discretization of the partial differential equations, and the methods common used for solving the algebraic equations which is the sequent of the governing differential equations discretization.In chapter 4 the theoretical model of the air jet flow field of dual slot die in melt blowing is founded. It is actually the model of two plane jets flow field developed by jet collision and mixing. The model consists of the continuity equation, momentum equations, energy equation, turbulent kinetic energy equation, equation of dissipation rate of turbulent kinetic energy and boundary conditions. The k- s model is adopted as the turbulence model because there are recirculation flows in the flow field and the convective and diffused effects must be taken into account. The governing equations are discretized by the control volume method and the corresponding finite difference equations are obtained.In chapter 5 the numerical simulation procedure of the theoretical model is described in detail. The power-law scheme is chosen as the preferred difference scheme at first. The "Primitive Variables Method" is then used for solving the pressure linked equations. To avoid the tooth-like distribution of pressure and velocity, the staggered grid and SIMPLE algorithm are introduced, and also the computation procedure of SIMPLE algorithm is given. The use of TDMA method in combination with relaxation method to solve the algebraic equations is discussed. Based on the above study, the computation setup and running procedure of PHOENICS software are analyzed with the aid of modular construction. The integrated structure of the computation program is...
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