Flow Study And Numerical Simulation Of CMC Solution On The Vertical Perforated Plate

Polymer devolatilization plays an important role in the process of polymer production.And the devolatilization element is the key to control the devolatilization efficiency.The devolatilization element can influence the mass transfer efficiency by changing the surface renewal.To improve the devolatilization efficiency,a new type of falling film element is proposed.Its flow pattern is also studied which will be the theoretical basis and instruction basis for the further research.Carboxy methyl cellulose sodium(CMC)solution was selected as the experimental fluid,because most polymer solutions are non-Newtonian fluids.The vertical perforated plate is based on the structure which has the slit element with supporting wires.The falling film flow on the vertical perforated plate was studied by means of experiment and simulation.And the influence was also studied which was caused by experimental operating conditions and holes’ size.Firstly,Laser Doppler velocimetry(LDA)was used to measure the velocity distribution curve on the special positions.On the basis,the computational fluid dynamics software(CFD)was used to simulate the falling film flow.Compared with the simulation and experiment values,it was found that VOF model was suitable for the simulation of gas-liquid falling film flow.The simulation results showed the information of the falling film flow and its thickness under different operating conditions and hole’s size.Both the experiment and simulation results showed that the central region of the falling film in the holes had the maximum velocity and the minimum thickness.From the central region,the velocity decreased and the film thickness increased gradually.With the increase of the solution concentration,the film velocity decreased and the film thickness increased inner the holes.With the increase of the flow rate,both the film velocity and the film thickness increased inner the holes.The entrance slit width directly influenced the falling film velocity and thickness.As the holes’ size changed,the falling film flow and its thickness would also change.With the increase of the holes’ width,the film velocity increased,and the film thickness of the central region decreased.With the increase of the holes’ length,the film velocity of the central region increased a little.When the holes’ length increased to a certain value,the falling film thickness would significantly decrease.Then it can be obtained that to ensure the liquid film not be broken there is a maximum value both for the holes’ width and length.When the holes’ size do not exceed the maximum value,and at the same time,the liquid film is spread completely,the influence caused by the holes’ width is more obvious than the length to the falling film velocity and thickness.Furthermore,the increase of the holes’ width got the liquid film thickness thinner which caused the increase of the surface update frequency.But the change of the holes’ length did not have influence on surface update frequency.