Research On Numerical Simulation And Mixing Chamber Structural Optimization Of Steam Ejector In Waste Steam Heating System

In the production process,the thermal energy utilization efficiency of thermal power plants has been criticized.How to utilize the wasted low-grade thermal energy and maximize the power supply capacity under the condition of ensuring the heat,which has become the biggest challenge for the development of power plants.Steam ejector is a fluid machinery with simple structure and no mechanical energy consumption.It converts the pressure energy to the mechanical energy through the pressure difference between high pressure steam and low pressure steam,and obtains the outlet steam of medium pressure whicn heats the circulating water of the heat network.In this paper,the main structure of the medium-sized steam ejector is designed through the given operating parameters.The single factor analysis method is used to explore the relationship between the operating parameters,the structural parameters of the mixing chamber and the ejection coefficient,and the two sets of parameters are optimized to achieve the purpose of improving the ejector performance.Firstly,the working principle of steam ejector is introduced.Through the method of gas dynamics function,the size of the main part of the steam ejector under the corresponding operating parameters is obtained.The structure is designed and the ejector coefficient is calculated.Secondly,the computational fluid dynamics software ICEM and Fluent are used to carry out geometric modeling and numerical simulation of the previously obtained steam ejector,and the post-processing results of numerical simulation are integrated to make a detailed analysis under the single factor analysis method.The influence of operating parameters of working fluid,ejector fluid,mixed fluid and three structural parameters of decreasing section length,equal section length and throat diameter of the mixing chamber on the jet performance of the steam ejector is obtained.The operating parameters and structural parameters of better jet performance are obtained.The simulation results show that,among the operating parameters,there is an optimal solution to maximize the ejection coefficient under the working fluid pressure.The ejection fluid pressure is positively correlated with the ejection coefficient.The mixed fluid pressure keeps the ejection coefficient constant until it exceeds the critical value,and there will have a sharp negative correlation between mixed fluid pressure and ejection coefficient.In the structural parameters of the mixing chamber,there is an optimal solution to maximize the ejection coefficient about the length of the tapered segment and the diameter of the throat.The effect of constant section length on ejection coefficient is not obvious.Finally,Quadratic Orthogonal Regression was used to analysis and process the data of simulation,and the objective function of the operating parameters,the structural parameters of the mixing chamber and the ejection coefficient were respectively fitted by MATLAB.Because the Particle Swarm Optimization algorithm is easy to fall into the local optimal problem,the inertia weight and learning factor are changed in the improved process of Particle Swarm Optimization algorithm and Gaussian perturbation is added in the programming in MATLAB.Then the improved Particle Swarm Optimization algorithm is used to solve two objective functions,and the optimal operating parameter set and the structural parameter set of the mixing chamber are obtained respectively.On this basis,through the numerical simulation of the two sets of optimal parameters,the results show that the optimized operating parameters and the structural parameters of the mixing chamber can increase the ejection coefficient by 18.2% and 2.3% respectively.