| In recent years,fiber suspension has been widely used in papermaking industry,sewage treatment,seawater desalination and other fields.As the basic industry of our country,the scale of the paper industry is generally small and there is still a big gap compared with the developed countries.In order to increase the production capacity and respond to the call for energy saving and emission reduction,research on pumping fiber suspension and high performance pulp pump is particularly important.To this end,an open-type test bench was built with a twisted impeller open centrifugal pulp pump as the carrier.The external characteristic test,high-speed photography test and PIV test were carried out to explore the fiber suspension under different working conditions and different concentrations.The process of fiber suspension transported by pulp pump was simulated by CFD-DEM coupling calculation.Then the flow field and the motion of fiber particles under different working conditions and concentrations were analyzed.The research results of fiber suspension are as follows:(1)The head and efficiency of pulp pump conveying 0.5%,1.0% and 1.5% fiber suspension were measured and analyzed.The results show that with the increase of fiber suspension concentration,the head and efficiency of pulp pump are totally improved.In terms of head,when transporting 1.5% concentration of fiber suspension under larger working conditions,the head is 0.46 m higher than that of clear water.In terms of efficiency,the optimal operating point is maintained at 0.7Q.With the increase of fiber suspension concentration,the pulp pump efficiency of transporting fiber suspension is higher than that of clear water.Near the optimal operating point,the efficiency does not always increase with the increase of fiber suspension concentration.In the range of 0.4Q to 1.0Q,the efficiency of transporting 1.0% fiber suspension is higher than that of the other three concentrations and increased by up to 3.65%.With the increase of working conditions,the efficiency of the pulp pump when conveying 1.5% concentration is higher than that of other concentrations,with a maximum increase of 6.97%.(2)The impeller and volute flow channel of pulp pump conveying 0.5%,1.0% and 1.5%fiber suspension concentration were photographed by high-speed photography equipment.Under different concentrations and working conditions,the fiber particles in the impeller channel generally maintain the movement trend from the inlet to the outlet,and tend to be distributed on the working face of blade.With the increase of the working conditions,the distribution of fiber particles is more uniform.When the concentration of fiber suspension and working conditions increase,the wake phenomenon at the trailing edge of the blade is more obvious and the generation speed is faster.With the increase of working conditions,the fiber particles at the entrance of the impeller is difficult to accumulate.(3)The impeller flow channel of pulp pump conveying clear water,0.4% and 0.7% fiber suspension was photographed by PIV.Then the change of relative velocity in the flow field was analyzed.With the improvement of working conditions,the relative velocity in the flow channel gradually increases,the velocity change trend is more stable and the velocity gap is gradually narrowed.Under lager fiber suspension concentrations,the relative velocity at the outlet of the impeller when transporting 0.7% fiber suspension is higher than that of the other two concentrations,and the velocity change of fiber suspension is more stable than that of clear water.The low-speed zone is easy to appear in the middle part of the impeller,and the strength of the low-speed zone decreases with the increase of concentration.The relative velocity changes in different flow channels are different.Compared with L2 channel,L1 channel near the tongue is more likely to appear the low-speed zone,and the relative velocity in the L1 channel near the blade is lower than that in the L2 channel.(4)Through CFD-DEM coupling calculation,the efficiency of transporting fiber suspension is higher than that of clear water,which is consistent with the external characteristics test.With the increase of the fiber suspension concentration,the vortex in the impeller channel is obviously improved and the streamline is more uniform.In terms of fiber particles,with the increase of the fiber suspension concentration,the velocity of fiber particles in the impeller channel is more concentrated,the velocity value is larger,and the distribution of fiber particles in the impeller channel is more uniform.Generally speaking,the existence of fiber particles improves the flow in the pump,reduces the low-speed zone and increases the flow rate. |
