| The labyrinth control valve is a throttling valve with multi-stage multi-channel continous resistance trim,which solves a series of high flow velocity problems such as cavitation,erosion,vibration and noise that are all caused by high pressure difference.It is mainly used in steam pipleline systems with high temperature,high pressure and high pressure difference in high-parameter thermal power,coal-chemical air separation and other devices.In this thesis,the pressure reducing mechanism and flow characteristic of labyrinth control valve for compressible steam conditioning were studied based on the theoretical formula derivation and numerical simulation,combined with the field flow test data.The main research contents and conclusions are as follows:(1)The study of calculation method of the depressurization stage number of labyrinth control valve.Based on the knowledge of fluid mechanics and engineering thermodynamics,combined with the structural characteristics of the labyrinth flow channel,the throttling processes when liquid,ideal gas and superheated steam flow through the labyrinth control valve were analyzed.Then,the theoretical formulas for calculating the depressurization stage number for different medium eonditions were derived Out.(2)The study of the pressure-reducing and velocity control mechanisms of the labyrinth channel.With the help of CFX software,the thermodynamics and flow processes while steam flow through the labyrinth channel were numerically analysed.The results show that the mechanism of pressure-reducing stage by stage of the labyrinth channel is that its continuous right-angled turn structure forces the flow direction to change,creating a flow separation and an unrecoverable pressure gradient after the "the turning facing the incoming steam ".Meanwhile,the expansion stage by stage of the flow channel is adapted to the volume expansion of compressible fluid,leading to the increase of the main flow zone area,thus the flow velocity of the medium was controlled effectively.(3)The study of the influences of structural parameters of labyrinth channel on the pressure-reducing and flow characteristics.Different geometric models of labyrinth channels were established.The influences of structural parameters such as excessive segment parameters,depressurization stage number and expansion coefficient,as well as the series-parallel structure on flow were analyzed.The results show that the prolonged length stage by stage of the excessive segment benefits the decrease of flow velocity.The more the depressurization stage number,the better the pressure-reducing performance;when the depressurization stage number can meet the need,the series-parallel structure with its shunting action should be used to decrease flow velocity.With the increase of the expansion coefficient,the sharp change of structure of labyrinth channel is more obvious thus its pressure-reducing performance is stronger.However,if the expansion coefficient is oversized,the eddy area in the labyrinth channel also increases,as a consequence,it has a little contribution to decrease the flow velocity.When the expansion coefficient is selected,the smaller value should be taken from the range of 1.12?r?1.23.(4)The study of internal flow field and flow characteristics of labyrinth steam control valve.The internal flow field of actual labyrinth steam control valve was numerically analyzed.The results show that the labyrinth disc-stack bears most of the pressure drop of the control valve,the flow differences between the cavity and outlet zones of control valve are inevitable.The flow coefficient and flow characteristic curve calculated by numerical method agree with the experimental results basically,and the error between numerical analysis and field flow test result is within the allowable range of the engineering.Therefore,at the beginning of the design of the labyrinth control valve,the numerical simulation method can be used to measure the flow coefficient of the labyrinth control valve. |
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