Study On The Behavior Of Fluid In Catalyst Bed Under High Gravity Field

In order to study the flow behavior of fluid in catalyst bed under high gravity field,the rotating packed bed(RPB)consisting of transparent rotor and shell is designed.The transparent spherical beads with diameters of 2.5-5 mm are used to simulate the catalyst particles of the same size in the RPB,and the black colored water is used to simulate the flow of the liquid in the catalyst bed.A high-speed camera is used to capture the flow behavior of fluid in the RPB.On the basis of the experiment,the mathematical model of the channel flow in the catalyst bed and the mathematical model of the spherical flow around the surface of the catalyst particles are established respectively.The results and conclusions are as follows:(1)The experimental results show that the experimental scheme can clearly show the flow behavior of the fluid on the surface of the catalyst,and can also capture the fluid flow covered in the catalyst bed to a certain extent.The liquid in the bed can be clearly divided into the end effect area and the development area according to its distribution.The wetting catalyst area can also be divided into the Actual wetting and False wetting area.In the False wetting area,the liquid adheres to the surface of the catalyst particles under the action of molecular force and cannot be thrown out.Therefore,the liquid is hardly moves out in the False wetting area.False wetting area's contribution to the chemical mass transfer,heat transfer and reaction is quite different from the liquid in the Actual wetting area.(2)The movement rule of liquid in the catalyst bed can be divided into two kinds:the channel flow in the catalyst bed and the liquid film flow around the catalyst surface.The two kinds of flow patterns change with the environment.There are two typical forms of liquid in the cavity outside the rotor.The droplet is formed by breakage of liquid filament,and the diameter of droplet is generally between 0.4-2.2 mm.(3)The movement speed of liquid in catalyst particle bed increases with time.The velocity of liquid increases with the increase of rotational speed and catalyst size.The phenomenon of"stagnation"will occur in the process of liquid flow,which will decrease as the speed increases or the size of packing decreases.Liquid flow rate and liquid flow pattern almost have no effect on liquid velocity.Under experimental conditions,the velocity of liquid motion is between 0.01-0.8 m/s.The residence time is less than 1 s,and the minimum can reach 40 ms.(4)The mathematical model of liquid flow in the catalyst bed and the mathematical model for the flow around the spherical surface of the catalyst particles are established respectively.The simulation results are compared with the experimental results.The results show that the flow resistance model of unit length can describe the channel flow of liquid in the catalyst bed better.The superficial velocity of the simulated value is 0.03-0.23 m/s,which is consistent with the experimental results.The inertial term of the flow model around the surface of the catalyst particles in the supergravity field is related to the inertial term of the frictionless fluid at infinity.The mathematical model can clearly describe the spherical surface flow around the surface of the catalyst particles in the centrifugal field.The thickness of the liquid film is about 10-5-10-4 nm,which is very consistent with the reported results.It shows that the model can nicely describe the real flow state of liquid in the catalyst bed.