Research On Decaying Mechanism Of Gas-Liquid Swirl Annular Flow

The transient and complexity of the two-phase flow make the accurate measurement of the phase fraction more difficult,and the influence of the flow pattern on measurement result is significant.In this paper,a method of regularizing the flow pattern by swirler is used,which converts other flow pattern to swirl annular flow and lays a foundation for the accurate measurement of the phase fraction for the gas-liquid two-phase flow.In order to improve the accuracy of measurement results,this paper combines CFD simulation,theory and experimental three methods to study the decaying characteristics of gas-liquid two-phase swirl annular flow,and proposes pressure drop prediction model and decaying model of swirl annular flow,providing a reference for engineering applications.In this paper,the impeller is used as the swirl flow generator.With air and water as the medium,the numerical simulation method on swirl annular flow is studied by Fluent software.Due to the density difference between gas and liquid and centrifugal force,the swirl annular flow is formed.Based on the results of numerical simulation,the characteristic parameters of swirl annular flow such as velocity distribution,pressure distribution,phase distribution,velocity distribution and pressure drop are analyzed.It gives us a certain understanding about decaying characteristics and flow mechanism of the swirl annular flow.During the swirl flow flowing along pipe,the mutual friction between the fluid and the pipe wall and the fluid phase gradually make tangential velocity decay.Finally the swirl flow pattern converts to an ordinary gas-liquid two-phase flow.This paper proposes two parameters k_l and k_tp,to characterize the influence of single-phase and two-phase swirl flow decaying on pressure drop respectively.The expression of k_lis mathematically derived.The relative error of the pressure drop prediction model of single-phase swirl flow is less than±5%.This paper analyzed the k_tp by the method of dimensional analysis.The coefficient of k_tp is modified by experimental data.Finally,the pressure drop prediction of gas-liquid two-phase swirl annular flow is obtained.The model has a relative error of±15%.In order to study the decaying mechanism of the swirl annular flow along the flow direction,a two-dimensional velocity sensor is designed.The axial velocity and tangential velocity of the liquid film were calculated by the time and length of passing through upstream and downstream electrodes.The designed sensor is installed on four different positions along flow direction to measure liquid film mean velocity.Combined pressure drop model and momentum equation,the swirl decaying model is established,which is in good agreement with the experimentally measured data by velocity sensor.The absolute error of 90%experimental data is within±0.1.According to the established decaying model of swirl annular flow,the effective length expression is obtained.The increase of liquid volume fraction and the increase of gas superficial velocity contribute to the increase of the effective length of gas-liquid two-phase swirl annular flow.It provides theoretical support for engineering applications.