Optimization Of Measuring Device For Measuring Steam Humidity By Spiral Heating

As the necessary equipment of thermal power plants and nuclear power plants,the safe and efficient operation of steam turbines will directly affect the safety and economy of power plants.The steam humidity has an important influence on the safety and economic operation of the steam turbine.The design and optimization of the on-line monitoring device for steam humidity can better realize the accurate measurement of the steam humidity online,thus providing the basis for the safety and economic operation of the steam turbine.The on-line monitoring device of steam humidity for steam turbine is designed on the principle of double-zone boundary heating method.The built-in spiral structure probe is used for the industrial on-line monitoring of humidity test.The data obtained are screened and analyzed in this paper.The analysis datas show that The exhaust humidity of the steam turbine is the same as the changing trend of the actual operating load.The vaporization length of the steam is inversely proportional to the heating power when the steam is completely evaporated,which is positively related to the load of the steam turbine.Meanwhile,when the design voltage is 220V,the heating of the unit length is 1250W/m,which can fullly satisfies the design requirements.In this paper,the FLUENT software is used to simulate the spiral probe of industrial tests.The continuous phase and discrete phase are analyzed respectively to optimize the spiral probe and improve the accuracy of steam humidity.The continuous phase(gas phase)simulation results show that the blockage of the pipeline is related to the flow rate and pressure drop and heating heat flux.The pressure difference is positively correlated with the flow rate.The pressure drop of the pipeline is positively related to the heating power.When the inlet blockage is not considered,the change of power is positively related to the flow rate.The coupling simulation of discrete phase(droplet)and continuous phase mainly analyzes the relationship between the complete vaporization of wet steam and the parameters of water droplet(steam velocity,steam humidity,droplet diameter,heating power,etc.),and is verified by the many experimental datas.The length of completely vaporized water droplets under the same heating power is compared with the experimental data.The error between the test value and the simulated value is less than5.8%,which indicates that the numerical simulation results are credible.Because the length of vaporization has a great influence on the measurement accuracy of humidity,this paper determines the distribution of the mass fraction of water droplets along the flow direction of the flow field and the track of water droplet particles in the numerical simulation calculation of the vaporization length,which makes the simulation result more reliable,thus providing a basis for optimizing the design of the humidity measuring device.According to the numerical simulation results,this paper gives optimization suggestions for the original humidity measuring device.The temperature sensor should be densely distributed in the interval 34~870mm.The temperature of 415~553K can be used as the standard for selecting materials.The influence of the pitch on the pressure drop can be ignored.It is possible to increase the length of the steam flow channel by appropriately reducing the pitch.A wide angle shape with a cone angle of 60 degrees can be designed at the entrance of the pipeline.The heat flow should not exceed 9000W/m~2.The results of this paper further optimization design of exhaust steam moisture on-line monitoring device for steam turbine,provides an important basis to improve the accuracy and reliability of measurement.