Research On The Performance And Reverse Design Method Of Jet-Assisted Exhaust Hood

The airflow characteristics of the traditional exhaust hood lead to its weak momentum control ability,relatively low pollutant capture efficiency,and relatively high energy consumption.The demand for high-performance and low-energy ventilating terminals in the industrial environment makes the efficient ventilating terminals one of the important directions for the development of the industrial ventilation.This paper proposes a new type of high-efficiency ventilation terminal-a jet enhanced rectangular exhaust hood,which aims to determine the performance of the jet-assisted rectangular exhaust hood and the key parameters that affect the performance,and then form the reverse optimization design method of the exhaust hood by studying the mechanism of the effect of jet flow on the performance enhancement of the exhaust hood.This paper systematically studies the flow field characteristics,key parameters affecting performance and design methods of jet-assisted exhaust hoods,and solves the problems of how to use jet theory to increase the momentum control ability,improve the capture efficiency of the local exhaust hood and reduce energy consumption,and construct the control speed method,limit flow ratio method,the reverse optimization design method of jet-assisted exhaust hood and then develop the calculation software for optimization of exhaust hood parameters.The results of the article provide theoretical guidance and reference for the design and application of the jet-assisted rectangular exhaust hoods.The main works and results of the thesis are as follows:(1)The critical jet velocity required to enhance the exhaust hood and confluence velocity distribution are studied.The flow field characteristics of the exhaust hood under free opening conditions are studied.The effective range of the jet outflow angle is determined,and the conditions for enhancing the momentum control ability of the exhaust hood are determined.The critical jet velocity of the exhaust hood and its influencing factors are studied,and the critical jet velocity calculation model is given.The boundary layer separation phenomenon at the suction inlet of the jet-assisted rectangular exhaust hood is studied,and the main factors affecting the separation phenomenon of the airflow boundary layer are obtained.The distribution characteristics of the suction speed in front of the exhaust hood are studied and proposed,and the relationship between the suction speed and its influencing factors is obtained.(2)The pollutant control performance of the exhaust hood under the coupling effect of jet and heat buoyancy jet pollutant air flow is studied.The effect of jet flow and heat source strength(velocity and temperature of the heat source)on the performance of the exhaust hood is studied.According to the influence of external parameters on the performance of the exhaust hood,the operation strategy of the exhaust hood with high capture efficiency is studied,and the method to determine the optimal jet velocity and the optimal exhaust rate of the exhaust hood was obtained.Through the analysis of the capture efficiency of the exhaust hood at different distances between the exhaust hood and the pollution source,the temperature and the speed of the pollution source,the operation strategy of high capture efficiency is verified and the operating parameters obtained by using the efficient operating strategy can make the exhaust hood operate efficiently at a capture efficiency greater than 90%.(3)The forward design-calculation method of the exhaust rate of the exhaust hood based on the control speed method and the flow ratio method is studied.Based on the study of the jet enhancement effect,viscosity effect and geometric effect,the distribution law of the axial velocity of the exhaust hood is studied,and the calculation model of the axial velocity of the exhaust hood is obtained.The research has established a speed control method suitable for the calculation of the exhaust rate for the exhaust hood.On the basis of the research on the capture efficiency and influencing factors of limit flow ratio of the exhaust hood,the flow ratio method for calculating the exhaust air rate of the exhaust hood is studied.The model of the flow ratio method and the temperature difference correction model are established.(4)The method of establishing the mapping relationship between the design parameters and the design target of the exhaust hood is researched.Through the data set obtained from the above research,with the critical jet velocity and the capture efficiency of the exhaust hood as the design goals,the neural network method that tablished the mapping relationship between the design parameters and the design goal of the exhaust hood was studied and the accuracy of prediction result of the method is also compared and analyzed.The recommended values of the minimum number of variables,the minimum data set and the required number of hidden layer nodes of the prediction method are determined.(5)The reverse optimization design method of design parameters of the exhaust hood is researched.The neural network was introduced into the reverse design of the exhaust hood,and the reverse optimization method of the exhaust hood parameters was studied.The study shows that the multi-objective optimization method that takes the capture efficiency and total air volume as the objective function is more suitable for the reverse optimization design of the parameters of the exhaust hood.Compared with the flow ratio method,it can save 31.19%～43.12% of the total air volume,and can increase3.17%～9.18% of the capture efficiency.And based on the reverse optimization method,the exhaust hood parameter optimization design software that can output the optimized parameters and corresponding results is developed.