Study On The 3-D Powerful Rotational Turbulent Flow Field Inside The Separating Column Of The Circumfluent Circulation Cyclone System

The cyclone is a piece of gas/solid separating equipment applying the philosophy of centrifugal force caused by the rotation of the dust-containing gas to separate the dust from the air flow. The cyclone is widely applied in such industries as chemical, mining, metallurgical, mechanical, light, environmental protection, energy conservation, etc. due to its advantages of simple structure, convenient operation, stable performance, less investment and area requirement, etc. Ordinary cyclones have high efficiency in capturing dusts bigger than 10μm, while low efficiency in capturing dusts less than 5μm, and that limits their application scope.The circumfluent circulation cyclone system is a new type of cyclones which has the common advantages enjoyed by ordinary cyclones, furthermore, it can effectively remove submicron dusts contained in the dusty gas. Therefore, it has a wide application in various industries and engineering fields.The separating column is one of the key separating elements in the circumfluent circulation cyclone system, and the separating efficiency of the separating column plays a decisive role in the separating efficiency and the entirety of the circumfluent circulation cyclone system, whereas the efficiency of the separating column depends on the features of the internal flow field inside the separating column. Consequently, a detailed and systematic study of the internal flow field of the separating column has great significance in the understanding of the separating mechanism of the circumfluent circulation cyclone system and also in the further increase of its efficiency. The present paper gives a summary of a series of studies about the internal flow field of the separating column in terms of experiment, academic study and numerical simulation, and the achievements made so far can be boiled down to the following:1. Experimental devices to simulate the actual flow conditions havebeen adopted for detailed tests of the velocity field and pressure field of the gas inside of the separating column of the circumfluent circulation cyclone system, and that provides tangential and axial gas velocity and the rules of pressure distribution at different locations in the separating column at a certain inlet gas flow velocity and the reflux quantity. The test results show that the tangential velocity inside the separating column basically reveals a centrosymmetric distribution, typical of the combination of sub-forced vortex and sup-free vortex. The axial velocity inside the separating column is basically distributed in the form of axial symmetry, only with the exception of the area near the outlet, and the value near the axle center of every section reaches maximum, while it decreases gradually when moving outward along the radial direction. When it reaches the wall surface the value tends to be zero. The static pressure near the axle center is the lowest, and there exists a low pressure column from the bottom to the top. The intensity of the pressure increases with the increase of the radius. It was discovered also that it fishtails when the gas in the separating column rotates at a high speed, the axial line of the vortex core fishtails along the geometrical axle center, and that results in unstable flow field which brings down the separating efficiency.2. Based on the Navier-Stokes equation and continuity equation underthe column coordinate, the inviscid fluid was assumed and an approximate analysis was carried out on the velocity and pressure distribution of the flow field inside the separating column, and a basic expression about the 3-dimenssional velocity, pressure gradient and the distribution of static pressure were given. On the one hand, it serves as a necessary academic basis for more detailed follow-up studies on the flow field analysis, on the other hand, the impact of the change in the reflux ratio and the dimension of the exhaust pipe against the various parameters of the flow field has also been investigated. Besides, its comparison with the experiment result has been made. Theoretic studies show that the inviscid fluid model can approximately forecast the basic rule of change of the velocity field and the pressure field of the flow field inside the separating column in the areas other than that which is near the axle center. The change in the dimension of the exhaust pipe has only little impact on the tangential velocity, the radial pressure gradient and static pressure, but much impact on the axial velocity and radial velocity. Furthermore, the reflux ratio has also impact on the velocity and pressure.3.The turbulent flow viscidity theory and the average velocity field have been adopted. The basic equation of the powerful turbulent flow field inside the separating column of the circumfluent circulation cyclone system has been deducted on the bases of the Reynolds equation and the continuity equation under the column coordinate system. And it shows the rule of distribution of the velocity field and static pressure field of the internal flow field of the separating column under the turbulent flow model conditions. After comparing with the actual measured value of the flow field, the studies show that the turbulent viscidity simulation can very well predict the velocity field and pressure field of the internal flow of the separating column. In the area outside the boundary layer of the wall surface, the calculated value and the experimental value of the tangential velocity and the static pressure coincide with each other either in the value or in the rules of change. The error of the calculated value and the experimental value of the axial velocity is evidently less than that of the non viscidity model. Furthermore, the rule of change is also quite the same as that of the experiment. It was discovered also that the viscidity of the turbulent flow has quite big impact on the tangential velocity and the static pressure, while little impact on the axial velocity.4. The tangential velocity expression is used to directly deduce thecalculation formula of the implicit form of the interface radius of the internal and external rotational flow inside the flow field of the separating column. Thus, the minimum overall pressure drop principle which was usually used to indirectly obtain the radius of the interface of the internal and external rotational flow is no longer necessary.5. Numerical simulation and analysis of the 3-d powerful turbulentfield inside the separating column of the circumfluent circulation cyclone system has been done by adopting the large common hydromechanics calculation software (FLUENT 6.2) and the Reynolds stress model (RSM) to obtain the total velocity vector diagram, the contour chart, and also the detailed distribution of the velocity field and pressure field as well as the cloud pictures of the turbulent flow intensity and its energy of the 3-dimentional flow field inside the separating column. Through analysis and comparison with the actual measured parameters of the flow field, it has been found that the general trend of the simulative flow field and the actual flow field is basically the same, i.e. the distribution of the tangential velocity is basically in the form of axial symmetry. Approximately, it is a combination of internal sub-forced vortex and external sub-free vortex, which coincides with the academic analysis. All the axial velocity within the separating column directs upwards, and the velocity distribution becomes more homogeneous and regular. This is helpful for fine dusts to be collected onto the edge wall of the separating column to be separated. There exists turbulent motion of the flow inside the separating column, and this coincides with the "fishtail" phenomenon which is discovered in the experiment. The distribution of the static pressure and the total pressure is quite similar, and the distribution symmetry along the radius direction is good. The distribution configuration shows that the pressure at the center vortex core is the lowest, and with the increase of the radius, the pressure also increases, therefore, the pressure near the edge wall is the highest. The turbulence energy in the area near the center of the separating column is the lowest while the turbulence energy at the lower part of the annular space and the exhaust end is quite high. The dissipation rate of the turbulence energy at the wall surface is extremely high.