| Pneumatic conveying is a convenient way to transport powder or bulk materials to the destination by pressure difference,which is widely used in all walks of life.In this thesis,lithium cobaltate,a new energy material in port,is used as the transport object to simulate the positive compaction phase pneumatic conveying system by FLUENT.Due to the small particle size and high density of lithium cobaltate,the Euler-Lagrange method would require a long computation time and a large memory for simulation.Therefore,the model chosen in this thesis is a two-fluid model,which equates the particle phase and gas into a continuous medium that co-exists and permeates with each other.The specific research content of this thesis is as follows:First of all,the working principle of the positive compaction phase pneumatic conveying system,the functions of each equipment in the system,the possible faults during operation and the solutions are introduced.Some basic parameters of pneumatic conveying and the calculation method of pressure drop are introduced in detail,which provides a theoretical basis for simulation.Secondly,through the simulation of multiple working conditions in FLUENT,the velocity,pressure and concentration values of different sections at different times were made into curves to analyze the variation rules of various parameters in the pipeline during the transportation process.In addition,we also analyzed the velocity,pressure and concentration nephogram of different sections at different times to obtain the material flow conditions in the pipeline during the conveying process.Among them,the check valve at the pulse port is realized by changing the wall conditions at the pulse port.Simulation data show that:1)The positive pressure dense phase pneumatic conveying system has the following characteristics: the pressure in the pipeline decreases from the highest point to the lowest point,and the main reason for the pressure drop is hindered by the material and the offset cancelling situation when it meets another air source,his situation mostly occurs in the pulse action.2)Under the same working condition,when the material in the launching tank is sufficient,after the material arrives at the receiving bin,the conveying condition of the material in the conveying tube will be in a stable state.It can also be considered that the material starts to carry out periodic changes with one pulse action time and one pulse non-action time as a cycle.Before reaching a stable state,the velocity in the tube decreases gradually with time and the rate of decline decreases gradually over the same period of time.3)At the same moment,under adjacent concentrations,the lower the concentration,the greater the rise of its velocity.For example,in a certain working condition,at 2.2s,the rise of 0.8concentration is 8.4% compared with 0.9 concentration,and the rise of 0.7 concentration is 10%compared with 0.8 concentration.Finally,through simulation experiment and analysis,the following working conditions are obtained which are more in line with the technical requirements of lithium cobalt acid pneumatic conveying: Firstly,the launch tank with compressed air inlet pipe diameter of 0.064 m is selected,and then the material concentration is fluidified from 1 to about 0.9 before material conveying.Finally,the inlet pressure,pulse cutter pressure,pulse duration and pulse action interval time are set as 0.2MPa,0.3MPa,0.2s and 1.0s respectively.This thesis can provide some guidance for the optimal design and parameter setting of positive compaction phase pneumatic conveying system. |
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