| When the traditional ring-sieve hammer mill works,the gas-solid flow field in the crushing chamber will form a circulation layer,which will cause the problems of low productivity and high energy consumption of the hammer mill.Therefore,on the basis of previous research,three different types of special-shaped screens(sectional are screen,wing screen and wing triangle combination screen)were optimized and designed to destroy material circulation layer and improve the performance of mill.This paper combines theoretical analysis,numerical simulation,flow field measurement and experimental research to explore the influence of the shape change of the grinder screen on the flow field characteristics,and then to explore the relationship between the flow field characteristics and the performance of the mill.The main research results are as follows:1.Three kinds of special-shaped screens are designed and their design principles are elaborated.Taking the wing screen installed in the mill as an example,the flow field motion characteristics of the wing screen installed in the mill are analyzed.The analysis shows that installing wing screen in the mill will change the clearance between hammer and screen,change the law of airflow movement,and help to destroy the material circulation layer and improve the performance of mill.2.Based on CFD software FLUENT,the numerical simulation of internal flow field of mill with different shapes of screens is carried out.The simulation results show that there is a distinct negative pressure zone near the rotor when the mill is installed with annular flat screen,the outlet pressure is small,and the air velocity near the hammer is too high,which is not conducive to the grinding and sieving of materials.After installing the special-shaped screen,the flow field characteristics are obviously improved,the pressure in the negative pressure zone decreases,the outlet pressure increases,and the air velocity near the hammer decreases.The negative pressure near the rotor is annular flat screen>circular arc screen>wing screen>wine triangle combination screen from large to small,and the outlet pressure is annular flat screen<circular arc screen<wing screen<wing triangle combination screen from small to large.The velocity of air flow in the area swept by hammer blade is annular flat screen>sectional circular are screen>wing screen>wing triangle combined screen from large to small,and the flow field characteristics of wing triangle combination screen installed by mill are the best.3.In order to verify the accuracy of the numerical simulation results,a flow field characteristic test system based on Arduino Pro micro is designed and developed.The error between the flow field test results and the numerical simulation results is 10.30%,which shows that the numerical simulation results are true and credible.4.Pulverizing performance tests were carried out under different screens installation conditions.Productivity,power consumption per ton of feed,temperature rise and uniformity of finished feed particles were taken as evaluation indexes.The results show that the comprehensive performance of the mill when installing special-shaped screen is better than that when installing circular flat screen.The mill has the best comprehensive performance when using wing triangle combination screen,the productivity is increased by 19.89%,the power consumption per ton of material is reduced by 17.88%,the temperature rise is reduced by 0.95?,and the uniformity of finished feed particles is the best.The experimental results verify the correctness of the numerical simulation and theoretical analysis results.The research results of this paper can provide theoretical basis for the optimal design of hammer mill. |
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