| In the production process of proprietary Chinese medicine,the native powder of Chinese medicine needs to be sterilized in a suitable way.Using a new type of powder sterilization device which using light wave sterilization,in the sterilization process,some of the particles will stick to the wall of the tank,so that the light transmission rate of the tank is reduced,affecting the sterilization efficiency,the need to install the upper and lower sides of the air vents to remove the particles on the wall.Numerical simulations were used to study the removal of particles from the wall by air vents with different arrangements and to explore the effect of air disturbance on the particle flow field in a limited space.Using ANSYS CFX software,the flow field of free-falling particles in a limited space was simulated,and the influence of particle size and density on the flow field of free-falling particles in a limited space was investigated.The flow field of particles under perturbation of four kinds of single-sided vents and five kinds of double-sided vents was simulated,and the law of the change of particle flow field with wind speed under different vents was investigated.Within the scope of the study of this paper,the following conclusions were drawn:(1)When the particles fall freely in a limited space,the particle flow continuously entrains the surrounding air,forming a vortex between the wall surface and the falling particle flow.The particles on the lower side flow upward along the wall surface along with the vortex.The smaller the particle density is,the more likely it is to spread to the upper part of the space along with the vortex.The diffusion radius of the particle stream gradually increases with the increase of the falling distance,the velocity of the central region of the particles is the largest,and with the increase of the radial distance,the velocity of the particle gradually decreases.The size of the particle is 104?m and the density is 727kg/m~3,the particle falling distance increases from 0.3m to 1.2m,the particle flow axis velocity increases from 1.69m/s to 2.08m/s and then decreases to 1.82m/s.The particle size of the particles remains unchanged,the particle density increases from 727kg/m~3 to 2165kg/m~3,and the peak velocity of the particles increases from 1.68m/s to 2.01m/s at the same falling height.Particle size from 70?m increasing to 150?m,the peak velocity of the particles at the same falling height increased from 1.67m/s to 2.08m/s.(2)Under the single-sided vent conditions,the vent airflow in space to the direction of rotation away from the wall to form a vortex,the direction of the vent and the direction of the particle down the same vortex area,larger than the direction of the vent and the direction of the particle down the opposite of the vortex area;as the vent velocity increases,the vortex area increases,the formation of the air flow field strength enhancement.Located in the upper part of the tank downward blowing vent and located in the middle of the tank downward blowing vent can make the particle flow to around after dispersal,and located in the tank down side upward blowing vent and located in the middle of the tank upward blowing vent is not effective to make the particle dispersed.The particulate removal rate increases with vent wind speed,while the vent blowing upward on the lower side of the tank and upward in the middle of the tank do little to remove particulates.The rate of removal of particles from the wall by a vent in the same direction as the particle drop is greater than the rate of removal of particles from the wall by a vent in the opposite direction of the particle drop.The vent located in the upper part of the tank blowing downwards has the best particle removal rate at different wind speeds,28.9%at a vent wind speed of 8m/s,and 16.8%at a vent located in the middle of the tank blowing downwards.(3)Under the single upper vent,the particle density and wind speed at the vent remain unchanged.With the increase of particle size,the peak velocity that can be reached in the flow field formed by the upward convergence of eddy currents on both sides decreases.When particle size increases from 70 meters to 250 meters,the peak particle velocity decreases from 1.76m/s to 1.24m/s.Particle size and vent wind speed is constant,the particle density of 471 kg/m~3,when particles falling distance is less than 0.743 m,particles to the model inlet direction movement,when falling distance is greater than 0.743 m,particles to the model export direction movement,particle density of 727 kg/m~3,when particles falling distance is less than 0.619 m,particles to the model inlet direction movement,when falling distance is greater than 0.619 m,particles to the model export direction movement,particle density of 1200kg/m~3 and 1980kg/m~3,particles always to the model export direction movement,particle speed was first increased then reduced then increased trend.(4)The relationship between vent wind speed and vortex and field velocity in the double-sided vents is similar to that in the single-sided vents.The particulate removal rate is best at different vent wind speed in the case of downward blowing vent located on the upper and middle sides of the tank,which is about twice as high as that of a single upper side vent,when the vent wind speed was 8m/s,the removal rate was 57.7%.The removal rate of particles in other working conditions was all within 20%.When the upper and middle vent blow down,the tank length is 0.75m and the vent wind speed is greater than7m/s,the particle can be avoided hanging on the wall(5)The wind speed of the air outlet is maintained at 7m/s.The upper vent adds a bottom relative vent,and the removal rate is reduced by 45.4%.The upper vent adds a middle relative air outlet,and the removal rate is reduced by 58.2%.At the bottom vent,the top relative vent is added,and the removal rate is increased by 638.9%.At the bottom vent,the middle co-direction vent is added,and the removal rate is increased by 611.1%.The vent in the middle of the downward air supply is added with the top co-directional vent,and the removal rate is increased by 226.1%,and the vent in the central downward air supply is added with the bottom relative vent,and the removal rate is reduced by 27.4%.Since the removal rate of the vent that sends air upward in the middle is zero,adding any vent at any position and direction can increase the removal rate.Comparing the particle removal rate of a single-sided vent and a double-sided vent,when the direction of the vent on one side is the same as the direction of the particle flow,the addition of an vent opposite to it will reduce the removal efficiency,and the addition of a vent in the same direction will increase the removal efficiency.When the direction of the vent on one side is the opposite of the direction of the particle flow,the addition of a vent in different directions can increase the removal efficiency. |
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