Study On Pulp Distribution Technology And Distributor Of Modern Paper-making Machine Based On CFD

With rapid development of economy in our country, the paper industry met a largechange of development. Meanwhile a new and higher request aimed to the equipment of pulpand paper was put forward. Modern paper-making machine was a device with technology,high technical content and rapid development where the rectangularly tapered pulp distributorwas a key unit that decided pulp distribution performance. This paper studied hydrodynamiccharacteristic of pulp from the view of flow hydromechanics and researched flowcharacteristic of pulp in rectangularly tapered pulp distributor and the questions of structureoptimal design of pulp distributor adopting the methods of computational fluiddynamic(CFD） and experiment. The results offered important theory reference for developand application of pulp distribution technology and distributor of modern paper-makingmachine.Pulp suspension was a complicated three-phrase(solid-liquid-gas） disperse system. Tothe low consistency pulp, its flow characteristic depended on fibre and water and was closedto water. Because pulp consistency in hydrodynamic headbox was higher than criticalconsistency, the fibre would complect into network which intensity depended on pulpconsistency. The fibre flocculation occurred when pulp consistency was low, velocity slow,turbulence weak. Dispersion of the fibre flocculation depended on shear stress on flocculation.Turbulence of pulp could effectively disperse fibre flocculation network, meanwhile providechange to form flocculation.When pulp flowed in the pulp distributor, friction head loss, bifurcation head loss andcontraction head loss existed at the same time. Design methods of rectangularly taperedheader were different in consideration of the three flow losses. The simplified design methoddid not consider any flow loss. Baines method merely considered friction head loss. Thedesign method which considered friction head loss and bifurcation head loss was also applied.Those methods made some hypothesis condition in order to deduce final results. So therewere errors and vices in the results so that they influenced uniformity of pulp distribution.In design methods of header, Baines method was most commonly used. Backwall curveof header was usually replaced by beeline because of limit of manufacture, but flowcharacteristic of pulp was obviously influenced by length of header, length of transition tubeand flow direction to the inlet of the header. Influence on flow characteristic in the simplifiedrectangular tapered header under above three design parameters was studied by means of CFD method. The simplified design method by Baines formula of rectangular tapered header wassuit for the shorter header. With increase of the length of the header, the pressure and the massflow rate out of the branch tubes were more nonuniform. Flow to the inlet of the header ismore stable and the pressure in the header and the mass flow rate out of the manifold tubeswas more uniform with increase of the length of the transition tube. Pressure in the header andthe mass flow rate out of the branch tubes was more uniform when the flow entered the inletof the header along the back wall than along the front wall. Furthermore the flowcharacteristic of rectangular tapered header designed by Baines method and methods derivedfrom Baines method was investigated detailedly. Height of the approximation type header andthe modified type header were distinctly greater than simplified type header so that thenonuniformity of pressure and mass flow rate in the the approximation header and themodified header is more obvious than simplified header. In three headers, backwall shape ofthe simplified header was more closed to expected shape of header.In order to research reasonable backwall shape of rectangularly tapered header, optimalstructure design of the simplified header was executed, which adopted CAD/CFD integrationmethod that included Process integration and data integration and optimal design object wasto control deviation between the mass flow rate out of branch pipes and expected value. In theheader optimally designed, the velocity contour and pressure contour were more uniform andpressure curve at the location corresponding to branch pipes was nearly a horizontal line. Themass flow rate distribution out of the branch pipes was more uniform else and was closer tothe expected value curve and the deviation of the mass flow rate in every branch pipe wereless than1%. To compare optimally designed header and simplified header, it could be knownthat though their backwall shape were similar, difference were obvious at inlet and outlet ofthe header. According to the optimal designed results, the backwall curve fitting of headerwas done and a more complicated curve was obtained.To make the best of nonuniformity of pulp distribution, a new pulp distribution mode，namely complementary pulp distribution, was put forward which inversely superimposed twomass flow rate curves of the branch pipes of two same rectangular tapered header. Mechanismof complementary pulp distribution was detailedly studied and mathematical model of pulpdistribution was established. Furthermore another merit of the pulp distribution mode was thattwo same header could be designed by the simplified design method. The new distributor wascomposed of same two rectangular tapered headers which were symmetrically put togetherone on top of another, not to communicate with each other, at inlet of headers where pulpflowed face to face and at outlet where pulp flowed back to back. So the pulp out of branch pipes was mixed complementarily in the mixing chamber and pulp distribution out of themixing chamber was closer to the expected value than the old one.The method of numerical simulation was adopted to research the flow characteristic ofpulp in the new distributor. When pulp from two headers ejected into mixing chamber by wayof branch pipes, the parallel jet group or jets in corresponding branch pipes of two headersformed sufficiently mutual interference and mixture, especially to the jets in correspondingbranch pipes of two headers. So the distribution of mass flow rate from outlet of mixingchamber was more uniform than simplified header and deviation of mass flow rate toexpected value were less. Further results of experiment showed that the consequences ofmechanism of complementary pulp distribution, of numerical analysis and of experiment werevery coincident.