Study On The Mechanism Of Hydraulic Headbox Key Technology And Application Of CFD

The industry of papermaking is an important industry of closely interrelated to development of the national economy. In the future, the development of economy offers great opportunities to the industry of papermaking in our country and makes greater requests on the equipment of paper and pulp making simultaneously. Headbox is a key device with high content of technology of paper machine which is developing with high speed. In the aspect of actuating medium, headbox belong to fluid machinery. This paper intensive studied the mechanisms of critical components hydraulic headbox based on hydrodynamics. The technology of CFD and experiment is adopted to study the performance of critical components of hydraulic headbox and provided reference for the hydraulic headbox structure design.Pulp suspension is different from water or solid-liquid two-phase flow. It is a complicated disperse system with three phases concomitantly. In general the consistency of pulp suspension is higher than critical consistency. The hydrodynamic force and interaction forces between fibers can lead to the forming of fiber network. The tensile strength of fiber network lies on the consistency of fiber and affected by the property of fiber at the same time. Fiber network can be dispersed by shearing force. Turbulence provides the force of hydrodynamic force which promote the forming of fiber network, in the other hand turbulence can provide the shearing force for fiber network’s dispersing.There are many ways to simulate turbulent flow. According to the purpose, request and equipments, there major kinds of simulation: direct numerical simulation (DNS), large eddy simulation (LES) and Reynolds-Averaged Navier-Stokes (RANS). According to purpose of this paper and request on level of detail of turbulent, the RANS was introduced to simulate the field of hydraulic headbox.The paper gives a systematic description of three head losses of flow in tapered header, friction, branch and contraction. The tool of numerical simulation was taken to analyze the performance of different types of tapered header to evenly distribute stock. Laser speedometer was used to measure the speed of stock at slice. The results of numerical simulation and experiment showed that overlarge quantity of reflux will cause lower mass flow rate of branches near the recycle end, on the contrary small quantity of reflux will cause large mass flow rate of branches near the recycle end.Based on the theory of turbulent jet deduced the length of beginning phase of turbulent jet and the velocity distribution of parallel jets. Presented the evaluation criterion of uniformity of velocity on cross section based on general theory of statistics. The results of numerical simulation showed the uniformity of velocity of parallel jets increased with the increasing of length of stilling chamber and the intensity of turbulence was decrease conversely. The uniformity of velocity and turbulence intensity should be taken into account to decide the length of stilling chamber. The Realizable k ?εtwo equations turbulence model was used to simulate the field in stilling chamber and then get the relation between diameter of branch pipe, velocity of inlet and the length of stilling chamber. The equation of design length of stilling chamber was provided.By applying particle image velocimetry ( PIV) technique, velocity field in stilling chamber was measured. The results of experiment are consistent with the results of numerical simulation. It proved that Realizable k ?εtwo equations turbulence model can be used to simulate the field of stilling chamber.Analyzed the mechanism of adjusting basis weight in cross direction. Compared the advantage and disadvantage of adjusting local opening of top lip and adjusting of local consistency of stock. According to the principle of T mixer, the mixing effect of stock and dilution water was simulated and got the tendency of mixing effect.Realizable k-εtwo equations turbulence model was adopted to simulated the spreading of jet in stilling chamber. The results showed jet spread along the way of velocity. In the core area of jet, the capacity of adjusting of basis weight is larger than other area can reached 8%. The capacity of adjusting basis weight by dilution water rely on retention of course.