Study Of Gas-liquid Two-phase Drag-Reducing Flow Induced By Polymers In A Horizontal Pipe

The application of drag reduction agents(DRA) can lower the friction resistance of conduits,increase the transport quantity,and economize the energy and equipment investment.The effects of drag-reducing polymers on gas-liquid two-phase flow in a horizontal pipe have been investigated in this thesis based on the former study of DRA,turbulence theory,single phase flow drag-reducing effect and multiphase flow characteristics.Through checking and validating the pressure gradient and drag-reducing models,the effects of polymers on gas-liquid two-phase flows have been further studied and explored.From the pressure gradient model,it can be known that the pressure gradient of gas-liquid two-phase flow in a horizontal pipe is composed by the interfacial fiction,drop entrainment and gas pressure.The application bound is also given by this model.From the drag-reducing model validating,less than 5%deviations have been obtained between the prediction and available experimental data.It is found that the interracial friction and drop entrainment dominate alternatively in the horizontal annular gas-liquid two-phase flow at different gas and liquid superficial velocity.The pipe diameter and pipeline absolute pressure affect relative importance of the interfacial friction and drop entrainment in the drag-reducing mechanism.Then the flow regimes of gas-liquid two-phase flow in a horizontal pipe have been simulated by applying CFD.The simulations are performed for the cases of constant liquid flux with gradually increasing gas flux,and constant gas flux with gradually decreasing liquid flux.The VOF model is applied and the unsteady,implicit, segregated solvers are used to carry out the numerical calculation to get flow fields and patterns in pipe.After obtaining the flow regimes which are consistent with Mandhane flow pattern,the effects of polymer water solution with different concentrations on the flow regimes of gas-liquid two-phase flow in a horizontal pipe have been further studied.By contrast it can be seen clearly that the drop entrainment in the pipe core decreases,liquid holdup in pipe bottom increases,however it is still of limitation to explain the multiphase drag-reducing mechanism in the aspect of interface friction.The drag-reducing model prediction and two-phase flow regimes simulation explain the polymer drag-reducing mechanism in some certain extent,and further more studies are needed.