Research On The Distribution Law Of Flow Field In The Dry Papermaking Forming Distributor

Traditional wet papermaking technology caused water and air pollution,which is not conducive to the national green sustainable development strategy.Dry papermaking technology has the advantages of low energy consumption,no water pollution,high utilization rate of base paper fiber,low investment cost,etc.It is gradually becoming the mainstream technology of papermaking industry.The dry papermaking technology adopts the air-laid method to form the paper web,and the uniformity of the airflow flow field determines the uniformity of the paper web.At present,there is a lack of relevant research on the distribution characteristics of the airflow field of the dry papermaking machine forming device.In this thesis,the distribution of air flow field of forming distributor in different working conditions is studied by combining experiment with numerical calculation,which has important guiding significance for the practical application of engineering.The thesis analyzes the characteristics of the flow field of the negative pressure box,and uses the uneven coefficient of velocity as the evaluation index of the uniformity of the flow field,and designs the structure of the negative pressure box with a uniform flow field.By simplifying the negative pressure box model and using CFD fluid simulation software,the influence of different duct structures and different exhaust air volume on the flow field distribution of the negative pressure box was obtained.Using the velocity unevenness coefficient as the evaluation index for the uniform distribution of the flow field,the flow field of the unclosed five-air duct structure is obtained to be the most uniform,so it is most conducive to the uniform formation of the paper web.Based on the theory of porous media and the idea of hole matrix equivalent modeling,the equivalent analysis model of molding net was established.Through the simulation experiment,the pressure-drop and velocity of the molding net were obtained,the quadratic function relationship between the pressure drop and flow rate was established,and the characteristic parameters of the porous medium were obtained.The experiment verifies the effectiveness of the equivalent model.Using the method of simulation and experiment,the flow field characteristics of the molding distributor under the initial working condition were analyzed by using Fluent software.By changing the way of exhaust air volume and wind pressure,three matching coefficients were introduced to measure the matching degree of the exhaust air volume and wind pressure,and the flow field distribution rule of the forming distributor under the three matching coefficients is obtained.The research shows that:(1)Along the+Y and+Z directions,the pressure field and the velocity field are more evenly distributed,the pressure is increasing,and the speed is decreasing,which also shows that the molding net can be quickly and evenly laid.(2)The numerical calculation results under the initial working conditions are consistent with the change trend of the experimental test results,but there is a certain error between the two results,and the causes of the errors are analyzed.(3)As the matching coefficient decreases,the negative pressure increases significantly,and the velocity is basically unchanged;When the matching coefficient is less than 0.0156,the pressure field of the forming distributor completely changes to the negative pressure field;When the matching coefficient is fixed,the larger the exhaust volume,the greater the pressure and the greater the flow velocity.In general,the matching coefficient directly affects the pressure change of the forming distributor,but has little effect on the velocity change.The main factor affecting the velocity change is the amount of exhaust air.