Reaserch On Numerical Simulation Of Dense Phase Gas-solid Flow And Sensor Modeling Based On Multi-physics Field

Dense phase pneumatic conveying is most widely used in transporting solid phase particles. Since the dense phase pneumatic conveying is defined as dense phase gas-solid flow, whose flow pattern, solid phase concentration, and velocity distribution are remarkably mutable, its solid phase's flow parameters are difficult to be measured.In the two-phase flow detection field, due to lack of the effective combination with flow mechanism analysis in dense phase pneumatic conveying, the interaction between the flow field and the detection field created by the capacitance sensors is ignored so that the sensor characteristics are usually researched in a single detection field. As a result, most of the existing theoretical models and the finite element analytical models are inadequately simple. Therefore, to increase the measurement accuracy of the solid phase flow parameters in dense phase pneumatic conveying, two main factors should be taken into consideration:one is to research the change laws of the multiphase flows'flow patterns; the other is to research the modeling methods of sensors in multi-physics field. Numerical simulation method is used in this dissertation to analyze the change of the flow patterns of the gas-solid two-phase flow.Aiming at these problem, this dissertation researches the solid material flows' change laws in the dense phase pneumatic conveying process and the sensor signals in multi-physics field by analyzing the array capacitance sensor' output. Fluid analysis software FLUENT and finite element analysis software ANSYS are used to do some simulating work. A series of experiments are proceeded to validate the simulations. The main works as follow:(1) The characteristics of multiphase flow models are analyzed by using CFD pre-processing modeling software, the pipe model and applicable grid volume element model are built; The normal stress model and the friction shear viscosity model are revised based on the characteristics of dense phase pneumatic conveying process; Three-dimensional turbulent flow multiphase model is built based on Euler coordinate system by introducing the particle dynamic theory;(2) The interaction of fluid and particles is took into consideration, and the drag force function between gas phase and solid phase is programmed; The boundary conditions'User Define Functions of the gas and solid phase at the entrance of the pipe are programmed; SIMPLE algorithm is used to solve the calculation.(3) The particle phases' physical property parameters and operating conditions'influence on the dense-phase flow patterns' formation and variation are analyzed; The boundary conditions which can change the flow patterns are summarized; The slug flow and stack layers'formation and flow process are reproduced; The stable movement of the slug flow is analyzed and the factors which have influence on the stable movement of the slug flow are ascertained;(4) Considering the slug flow and dune flow as primary flow patterns in the dense phase conveying, an array capacitance sensor structure is proposed, and which can simultaneously measure the flow pattern of gas-solid phase and the solids concentration distribution The basic structure, measurement principle, and sensor signal characteristics of the array capacitance sensor are researched and the finite element method of electrostatic field is analyzed; Three-dimensional finite element sensor model under the influence of the coupling of flow field and electric field is built based on the partitioned indirect coupled method;(5) The characteristics of the sensors' output signal of the solid phase particles' flow parameters in different dense phase flow patterns are analyzed based on simulation;(6) In the lab condition, two-phase flow detection system is built based on arrays capacitance sensor and stable slug flow is produced; The characteristics of the sensor signals created by stable slug flows are validated in multi-physics field.