Overflow Dyeing Machine Nozzle Flow Field Analysis And Structure Design Based On CFD

When the overflow dyeing machine dyes cylindrical fabrics, fabric tangle phenomenon and"tambour"phenomenon often appear on the nozzle, the quality of dyeing fabrics and the efficiency of dyeing machines are seriously affected. In order to solve those phenomenon, the overflow dyeing machine nozzle flow field is taken as the research object, using Solidworks software, geometric model of overflow dyeing machine nozzle is established, according to the flow field state and the actual working conditions, mathematical model of nozzle flow field is established, using computational fluid dynamics simulation software accomplish simulation analysis, based on the simulation results, the impact of flow field transport properties for round nozzle on fabrics dyeing is studied, and the structure of the circular nozzle is improved.When establishing mathematical model of nozzle flow field, according to the local instantaneous characteristics of the gas-liquid two-phase flow, without regard to the impact of the fabric movement on the temperature field and flow field, continuity equations and momentum equations for gas-liquid two-phase flow is established. The macroscopic governing equations for gas-liquid two-phase flow have been developed by applying the volume averaging method to the"loeal instantaneous equations"of two-phase flow. According to the actual working parameters, the flow field state is analyzed. Based on flow field state, the RNG k-εnumerical model is selected as the mathematical modeling of the closure model, which make the equation group of continuity equations and momentum equations for gas-liquid two-phase flow enclosed. In order to makes them easy to calculate with the computer, applying the discretization method, partial differential equations is transformed into ordinary differential equations. In order to solve the pressure-velocity coupling problems, SIMPLEST algorithm is used to establish the pressure correction equation, combined with the boundary conditions of nozzle flow field, the correction pressure is obtained, which is used to correct velocity distribution of nozzle flow field.Based on the results of CFD numerical simulation, dynamic and static pressure changes in the nozzle cap and the velocity and pressure field distribution in the nozzle are analysed. The impact of flow field transport properties for round nozzle on fabrics dyeing is studied from several aspects of the vortex suction role, the effect of secondary flow on spiral flow and turbulent energy transfer. Based on simulation results, physics knowledge and Gibbs adsorption equation, the producing reasons and forming process of "tambour" phenomenon are discussed.The results show that: the intensity of vortex in the jet orifice is one of main factors that cause the gas pressure change in the nozzle, the stronger the vortex is, the greater the gas pressure change; secondary flow in the bent pipe of the nozzle is main factor that generate spiral flow, spiral flow make the fabrics wound together, which seriously affected the quality of fabric dyeing; regulating the energy transfer between the large-scale vortex and the small-scale vortice can weaken the energy of small-scale vortex in the bent pipe, lower the secondary flow production rate, thereby weaken the effect of spiral flow on the fabric tangle phenomenon. The main source of the cylinderical fabrics internal gas are that the gas bubbles escaped with the decrease of gas solubility in water, the inflow gas coming from the outer of the nozzle and plenty of steam coming from dyeing solutionAccording to the experiment argumentation and theoretical analysis, the structure of the circular nozzle is improved, four uniform distribution adjusting-flow board are added on the core seat of the nozzle, which better solve the fabric tangle phenomenon and the"tambour"phenomenon.