Numerical Simulation And Parameter Study Of Steam Ejector In Steam Heating System

Cogeneration has a problem of large cold end loss.Based on the requirements of energy saving and emission reduction,it is proposed to recover the waste heat from the exhausted steam.The steam ejector can utilize the high temperature and high pressure fluid to suck the low temperature and low pressure exhaust steam;the medium-temperature and mediumpressure steam after mixing is used for heating the hot water,which can effectively reduce the heat energy loss.Although the structure of the steam ejector is simple,its structural design is often difficult to meet the actual working conditions;it is also difficult to determine the mixing process and mixing mechanism between the steam inside the steam ejector.In traditional designs,charts and empirical calculations are often used to determine the structural dimensions of a steam ejector.,and the design method has a large error.In this paper,the optimization research of small steam injectors mainly includes the structural design of steam injectors,numerical simulation and intelligent algorithm optimization of structural parameters.Firstly,the basic theory and common design methods of steam ejector are introduced and analyzed.Under certain operating conditions,the structural parameters of the steam ejector are designed according to the gas dynamics calculation method.Secondly,a two-dimensional numerical model of the steam ejector is established based on the calculated structural parameters,and the flow field characteristics inside the ejector are analyzed.Using the repeatability of the numerical model,the influence of the mixed outlet vapor pressure on the ejector coefficient is analyzed,and the reliability of the numerical model is verified.The effects of changes in steam pressure,ejector steam pressure,nozzle distance,and length of the mixing chamber of the cross section on the performance of the injector were investigated.The numerical simulation results show that the ejector coefficient of the working steam pressure is too high or too low,which corresponds to a small ejector coefficient;if the pressure of the ejector steam is large,the ejector coefficient is larger;there are optimal structural parameters,so that Steam ejectors have superior performance.Finally,the GA-BP neural network algorithm is programmed,and the sample data obtained by the numerical model is applied to establish a nonlinear mapping relationship between the structural parameters and the ejector coefficients.In the established GA-BP neural network,the method of controlling the step size is used to search for the maximum ejector coefficient,and the corresponding structural parameter is the optimal structural parameter.The optimization results are verified by CFD numerical results.The verification results show that the ejector coefficient obtained by algorithm optimization is 6.12% higher than before.