| With the environmental problem becoming more and more serious.Chemical industry is facing enormous challenges.To develop new resource-saving and environment-friendly chemical reactor becomes the inevitable trend of modern chemical industry.Gas-liquid impinging stream reactor(G-LISR)as a new type of chemical reactor,its advantages lie in the better heat and mass transfer characteristics and these features are showed through the distribution and strength of flow field.At the same time,the structure modes and operating conditions change may affect the mixing efficiency of the entire reactor.So it’s needed to study the flow field characteristics under different structure modes and operating conditions to explore the mixing mechanism and provide theoretical basis and support to the optimization of the structure.Currently,the experimental research on the flow field of a gas-liquid impinging stream reactor is rarely.As restricted by experimental method,the flow field information is limited and time consuming.In order to avoid these disadvantages,numerical simulation study on the characteristics of G-LISR mixing process was discussed in this paper which is based on computational fluid dynamics software FLUENT platform.The Euler-Lagrange concept is used to establish the mathematical model of the behavior of gas—liquid two-phase flow in G-LISR.The physical models are established by software ANSYS-Workbench and simulated by software FLUENT to discuss the distribution characteristics of flow field under different structure modes and operating conditions.Main conclusions are as follows: structure modes and operating conditions change does not affect the trends of gas-phrase for the fluctuation of pressure and velocity over time.Within 0 to 6s the fluctuations is more drastic,pressure of impact center will rise sharply.Pressure and velocity on the axial and radial exists spurt and steep fall.After the collision the direction of velocity changes from the radial to the axial.After 6s,the flowfield tends to be stable.Structure modes and operating conditions change does not affect the trends of gas-phrase for the fluctuation of pressure and velocity over space.The fluctuation will be serve when near the impact area and placid when away from the area.The distribution of pressure in reactor seems to be a “Hat-shaped” which is symmetrical.The maximum pressure locates at the impact center.In planar z=0 and y=0 four whirlpools form close to the wall and move towards the exit.The velocity In planar y=0 is in the“butterfly-shaped” distribution.The distribution of velocity on the x axis is axial symmetry and on the z axis is always present as "twin-peaks",the peak position is symmetrical about the origin.Structure modes and operating conditions change does not affect the distribution trends of liquid-phrase for the concentration.The distribution of concentration is always converge on the impact area.In plane z =0 the concentration is in the “vase-shaped”distribution along the y direction.Ensure that the rest of the structure modes and operating conditions are the same,with the rising of the distance between accelerating tubes,the perturbed range of gas-phase increases.The pressure at impact center decrease from 190 pa to 140 pa when distance increase from 100 mm to 400 mm.The pressure is inversely proportional to the distance.In terms of the velocity of gas-phase,the radial velocity up and axial velocity down after the impact and the stable velocity is inversely proportional to the distance.The speed of the origin is relatively small.In terms of liquid-phrase’s flow field,with the rising of the distance the flow path of the liquid particles increase and its oscillation area expand which leads to the increase of concentration distribution and residence time of liquid particle phase rising from 0.54 s to 0.67 s with the distance increased to 400 mm.The decrease of the distance contribute to the turbulent intensity of gas-phrase but hindered the liquid dispersion and mixing at the same time.Ensure that the rest of the structure modes and operating conditions are the same,with the rising of velocity of gas-phrase,turbulence intensity in the reactor increasedwhile the pressure of impact surface also increased sharply.When the initial gas-phrase velocity is 10 m/s,the amplitude of pressure fluctuation reach 62.5pa,as the velocity increased to 15 m/s and 20 m/s,the amplitude of pressure fluctuation respectively reached 2.2 times and 4 times of the former which makes energy consumption.In terms of liquid-phrase flow field,when the gas-phase initial velocity increased from 10 m/s to15 m/s the concentration of liquid particle in the G-LISR decreases to 0.3 times,as the initial velocity rising from 15 m/s to 20 m/s concentration of liquid-phrase comes to 0.66 times which reduces the particle concentration distribution in the reactor.The average residence time of the liquid-phrase decrease from 0.81 s to 0.42 s as the initial velocity increased to 20m/s.Ensure that the rest of the structure modes and operating conditions are the same,the integral variation of gas-phase flow field in the reactor is not affected by the change of the initial velocity of liquid-phrase but it has obvious effect on liquid flow field.The concentration of liquid particle in the reactor will decrease with the increase of initial liquid velocity.When the initial velocity of liquid is 5m/s,the concentration of liquid particle is 1.08 times of the situation when velocity of liquid is 8m/s or 10m/s.The average residence time of the liquid-phrase decrease as the rising of liquid velocity,When the velocity of liquid is 5 m/s,the residence time of liquid particles in the reactor is0.81 s,as the speed increased to 8 m/s,the residence time reduced to 0.71 times of the former one which is only 0.58 s,as the speed increased to 10 m/s,the average residence time reduce to 0.56 s.Judging from the energy loss and the characteristic of flow field,when distance is400 mm and initial velocity of gas-phase is 10 m/s and initial velocity of liquid is 5 m/s,G-LISR shows high mixing efficiency. |
PDF Full Text Request