| The subject of the paper is study the mechanism and consequences of unsteady flow which occur in the process of pipe filling.Research Methods inlude experimental,theoretical and numerical simulations.Due to the non-negligible error caused by the rotation speed in measuring the rheology of gangue fly ash filling slurry,the relationship between the slurry concentration and the minimum rotation speed was analyzed by theory and experiment.After determining the minimum rotation speed associated to the different concentration,elaborate the optimal group distribution ratio of gangue and fly ash paste-like slurry is determined by the experimental.Theoretical analysis and numerical simulation were used as means to study the unstable flow phenomenon of the filled slurry during the pipe transfer process.The unsteady flow characteristics of gangue fly ash filling slurry were simulated by ANSYS ICEM CFD and FLUENT.(1)By simulating the volume fraction distribution of the gangue particles near the outlet of the pipeline at different flow rates,the non-silting velocity of the slurry transport is determined.Unstable flow of slurry in the pipeline will block the pipeline when the flow rate is lower than the non-silting velocity.It is clearied by the newly developed equipment that the pipeline will be blocked when the velocity is under non-silting velocity.(2)The unstable flow of slurry caused by slurry water hammer phenomenon was studied.The relationship between valve closing time and tube burst accident was explained by comparing the pressure pulsation curve caused by water hammer phenomenon under different valve closing time.(3)Theoretical analysis of the mechanism of dissatisfaction of pipe flow in vertical pipe sections,simulating the impact of "cavitation" and "jet erosion" on pipe damage.The main research contents of this paper are as follows:(1)Based on the Cauchy stress equation and the Renault-Rie Runlin formula,analysis the rotation state of the slurry in the container,and then,the relationship between slurry concentration and required minimum rotation speed was explained.Based on the experimental data,the relationship between the slurry concentration and the required minimum rotational speed was obtained.Under the premise of the minimum required rotation speed at different concentrations,the slurry rheology experiment was carried out to determine the optimal ratio of the gangue fly ash filling slurry.(2)The rheological properties of gangue fly ash filling slurry was determined using the Vane torque rheometer.The best composition ratio of slurry is 76%.the optimal ratio of gangue:fly ash:cement is 8:3:1.Combined with the experimental results and the rheological theory,it is determined that the gangue fly ash filling slurry belongs to the Bingham fluid and the rheological model is established.(3)When the transporting velocity is higher than the non-silting flow velocity,most of the gangue particle moving in a suspended state,and some large and heavy gangue particle settled at the bottom of the pipeline and moving in the state of shifting in the horizontal pipeline.After analyzing the loss of resistance along the path caused by the gangue particle of the two motion states,the resistance loss of the slurry in the horizontal pipe is obtained.(4)CFD FLUENT was used to simulate the flow characteristics of the slurry during the pipe transfer process.The cross section near the outlet of the pipe was selected as the research object.According to the difference of the volume fraction of the gangue particle at different velocities,the non-silting velocity was determined.When the flow rate is lower than the non-silting velocity.the deposition of the gangue particle causes the slurry transition from a steady flow to an unsteady flow.(5)Analyzes the mechanism of the pipeline damaged in slurry water hammer using the conservation of momentum;using the method of characteristics calculated the fluctuations pressure of the pipeline sufrerred in the slurry water hammer.(6)The dynamic mesh technique is used to simulate the peak pressure curve formed when the globe valve is closing in different time.The results show that the slower the valve closing,the smaller the pressure peak caused by the slurry water hammer.By comparing the peak pressures caused by the different closing time,the results shows that the slower the valve closing,the smaller the peak pressure caused.Therefore,in order to avoid the pipeline damage caused by the slurry water hammer,the valve closing time should be delayed as much as possible.(7)The mechanism of the unsteady flow in the vertical pipe is analyzed by theoretical analysis.And then,the velocity count and pressure count of the dissatisfied flow in the vertical pipe are simulated by FLUENT software.By simulating the pressure count formed by "cavitation","jet erosion" and falling impact of slurry column,it is found that "cavitation" and "jet erosion" are the main causes of pipeline damage. |
PDF Full Text Request