**1. Introduction**

372 Computational Simulations and Applications

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0316

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Computational Fluid Dynamics is now a new ramification of the numerical discretization method based on high-performance electronic computers, which focuses on fluid mechanics simulation. Fluid mechanics has two main braches that one is theoretical analysis and another is experimental research. Therefore, theoretical and experimental fluid mechanics were created as most important constituents in early days. Although the theoretical method could give the quantum results of the solving problem, it was still little used for its complicated solution procedure.

Computational fluid mechanics has developed rapidly to cover the shortage of theoretical method. It has been involved each fluid field though its development history is short. Many numerical solution methods were formed according to different simulation purpose. Finite difference calculus and finite element method were mainly involved. In the application, Finite difference calculus was usually used in resolving fluid problem, while finite element method was exploited to research solid mechanics themes.

Gas-solids two phase flow means solid particles are conveyed by compressed gas phase. The particles' traces are irregular, which caused by the dispersion action and coupling force between gas and solids phase. The interaction process leads to the irregular motion of gas solid two phase flow and the flow characteristic parameter altering greatly. Nowadays, the recognization and analysis of gas solid two phase flow was not enough with limitation of test technique, which restricted the application development and system optimization of gas solid flow. So some fresh technique must be appeared to suit the application situation.

Until now, the research technique in gas solid two phase flow focus on experiment cases because of the complexity of gas solid flow. Te gas solid two phase flow theory became more and more sophisticated with the development of particle dynamics and aerodynamics. Both had some deficiency. For example, in experimental research, calculation of some conveying parameters mostly depends on empirical equations based on experiments which leads to the limitation, and which are the same with its experimental condition commonly and generalized hardly. Theoretical studies are mostly short of accuracy because of lots of hypothesis in the process of deduction. Therefore, in this thesis, simulation study on the process of dense-phase gas-solid two phase flow was carried on based on experimental and theoretical investigations in order to cover the shortage of experimental and theoretical investigations.

Numerical Simulation of Dense Phase Pneumatic Conveying in Long-Distance Pipe 375

GP/DP transmitters were used to measure pressure of the feeder, setting points along

Fly ash was transported from the feeder vessel into the receiver in dense phase. The material

GP DP GP DP GP

8 8 8

4 3 12

Fig. 1. Schematic diagram of experimental system. 1. air compressor 2. gas storage pot 3.oilwater segregator and air drier 4. gas adapter 5. gas inlet valve 6. gas flow meter 7. feeder 8. static pressure gauge 9. differential pressure gauge 10 dust catcher 11. collecting bin 12. weighing-appliance 13 data acquisition equipment 14. micro-computer 15. bleeder valve.

After being put into the feeder, fly ash was fluidized by compressed air. Then at a preset transporting pressure in the feeder, fly ash passed through the conveying pipeline and reached the collecting bin finally. Five test segments along horizontal pipeline were employed averagely to analyze the tendency of pressure drop along the pipeline. A differential pressure transmitter and a gauge pressure transmitter were assembled in the segments of 52.2 -53.4 m, 90.5 -91.7 m, 126.5 -127.7 m, 176-177.2 m. Gauge pressure transmitters were also installed at the terminal of pipeline (6) as well as the vent of feeder. In this experiment, operating condition was mainly controlled by changing the pressure of feeder The experiments under different operating conditions and each with several

Fly ash 60 770 0.96

The gas velocity along the pipe is an important parameter, and it can be expressed by the

*g g*

*A Ap* 

*M M RT*

 

*g*

A/ D

13 14

Bulk density

(kg·m-3) Sphericity

(1)

GP DP

9

8

GP DP

9

8

9 9

6 5

7

8

GP

15

11

pipeline and pressure drop of test segments.

10

12

repetitions were carried out in total.

Table 1. Experimental material properties.

**3. Experimental results** 

following equation.

**3.1 Gas velocity along the pipe** 

Material Equivalent spherical

diameter (μm)

*g*

*u*

properties were shown in Table 1.

Numerical simulation technique improves rapidly with the advance of computer hardware. And it plays more and more important role in the research of dense-phase gas solid flow. This article gave the numerical simulation conclusions based on the experimental and theoretical research. By associating with experimental condition and the applicability of experimental equations, transport equation of Reynolds was deduced by using time averaged method based on instantaneous equation of gas and solid. The control equations of turbulent energy and turbulent dissipative ratio were formed, which considered reciprocity between gas and solid, collision of particles and interaction between particle and wall. The model included continuity equation, momentum equation, turbulent kinetic energy equation and turbulent kinetic energy ratio equation. Physical meaning of primary item of control equation was discussed too.

Two-fluid model of gas-solid turbulence in process of dense-phase gas solid two phase flow was founded, so did the corresponding numerical solution and calculating flow. The model could mention reciprocity between gas and solid, collision of particles and interaction between particle and wall.

The process of dense phase gas solid two phase flow in pipeline under experimental conditions was simulated with FLUENT software by founded model and corresponding arithmetic. Pressure distribution diagram, density distribution diagram and velocity vectogram etc. were given which displayed the flow alternation of dense-phase pneumatic conveying. And comparison between simulated result and experimental case showed good suitable which illuminated the model had good accuracy and forecasting capacity.

In all, in this study, fluid mechanics characteristics of dense-phase gas solid two phase flow in pipeline were discussed by computational fluid dynamics method based on flow theory of gas-solid, and a series of significative results were obtained. The research showed that the numerical simulation of dense-phase pneumatic conveying can complement experimental and theoretical studies which had promoted effect on the application and development of dense-phase gas solid flow in pipeline technique.
