Investigations On Regional Turbulence Characteristics Of Single-Phase Water Driven By Steam Jet

Due to the high heat and mass transfer rate of steam jet direct contact condensation phenomenon,it has been widely used in engineering.When the steam jet enters the pool to condense,it will also cause a series of hydrodynamic phenomena.Among them,the phenomenon of turbulence is closely related to the heat and mass transfer process in the condensation process and the movement of water in the pool.At present,the research on direct contact condensation of steam mainly focuses on the study of steam flow pattern,pressure oscillation and other characteristics.These studies have studied the characteristics of direct contact condensation at the macro level,while ignoring the characteristics of turbulence in this phenomenon.Among the important effects,turbulent flow will directly affect the steam condensation process.During the condensation process,the energy is gradually transferred downstream from the steam plume to the single-phase water region,and gradually dissipated in this region.The turbulence characteristics in this region are closely related to the flow characteristics during the condensation process to a certain extent.Direct contact with condensation is an important aid.In order to study the turbulence characteristics of the single-phase water region driven by the steam jet,an experimental bench suitable for the steam jet PIV(Particle Image Velocimetry)experiment was designed.Using the test bench,the area between 150mm and 230mm downstream of the nozzle outlet was studied under the conditions of water temperature of 20°C,40°C,and 50°C,and steam pressure of 0.25MPa,0.4MPa,and 0.5MPa.The experimental results show that the steam-driven turbulent jet has similar characteristics to the turbulent characteristics of the single-phase jet in the study area.The peak value of turbulent kinetic energy and turbulent kinetic energy dissipation rate is located at r/b_g=0.5,and the valley value is located at the center line.The values of turbulent kinetic energy and turbulent kinetic energy dissipation rate both increase with the increase of steam pressure and water temperature,and their values do not change significantly with water temperature,but the change of steam pressure will significantly affect their values.Numerical simulations were carried out for the experimental conditions,and the results of the numerical simulations were compared with the experimental values.The simulation results show that the prediction value of the turbulence characteristics by the numerical simulation is generally smaller than the experimental value,indicating that the simulation results are weak in predicting the mixing in the pool.Among them,the relative error between the predicted value of the jet radius growth rate and the experimental value under typical working conditions is15.48%;the relative error between the predicted value and the experimental value of the turbulent kinetic energy and the turbulent kinetic energy dissipation rate at the center line has reached 50%.According to the experimental data,the calculation coefficient of the realizable k-?turbulence model was corrected,and the value of the coefficient C2 suitable for different working conditions was obtained,and the value was between 1.621 and 1.695.Numerical simulation calculations were carried out using the modified coefficients,and the accuracy of the simulation results has been significantly improved.Among them,the relative error between the predicted value of jet radius growth rate and the experimental value under typical working conditions is reduced to 5.6%;the relative error of turbulent kinetic energy and turbulent kinetic energy dissipation rate at the center line is reduced to 3.9%and 8.3%,respectively.In addition,the penetration length of the steam jet was selected as the upstream parameter for verification.The verification results show that the accuracy of the simulated value of the penetration length is also improved,that is,the method of correcting the model with the downstream parameters can be compared with the upstream simulation.The parameters are also optimized.