Three-dimentional Measurement Of Turbulent Hydrocyclone Flow Field With Optical Methods

The research of the three-dimensional turbulent hydrocyclone flow field has vital significance on the understanding of its separation mechanism and improvement of separation efficiency. Tangential, axial and radial velocity is the three basic components to clarify the mechanism of hydrocyclone separation, in addition, some flow features also plays important roles on the hydrocyclone separation, such as the locus of zero vertical velocity, short circuit flow and secondary vortexes.The turbulent hydrocyclone flow field is highly instantaneous and three dimensional, instantaneity, requiring high accuracy and flexibility of measurement methods.This paper put forward the comprehensive utilization of Volumetric three-component velocimetry?V3V?, particle image velocimetry ?PIV? and phase doppler particle analyzer ?PDPA?, explore a way to fully detected the main parameters of three-dimensional turbulent hydrocyclone flow field of 35 mm hydrocyclone with cone Angle of 6°. The main focus is on the tangential, axial and radial velocity component, and short circuit flow, secondary vortex flow, tangential velocity index n and the locus of zero vertical velocity. The innovative research results are shown as follows:?1? By analyzing the optical path for V3V measurement, designing the refractive index matching method using sodium iodide and preparing tracer particle using microfluidic technology, for the first time three dimensional three-component velocity distributions of the hydrocyclone flow field was determined. The three-dimensional locus of zero vertical velocity was also obtained. A method adopting three dimensional axial velocity distribution to calculate short-circuit flow was put forward, and short circuit flow rate was determined to be 13%. The secondary vortex was found to go down along a spiral line and the method to calculate circulation along the spiral line was put forward. It was estimated the circulation flow rate in the lower cone is about:10.39 x 10^-6m³/s.?2? The PIV layer measurement method was put forward for the first time to solve the problem that the planar two-dimensional PIV is unable to measure the tangential velocity.When measuring tangential velocity distribution with different split ratio, it was found that the split ratio changed the upward flow of axial velocity distribution and space occupation. When the split ratio is zero, the forced vortex zone was enhanced and the tangential velocity is obviously higher, and that at the side wall was weakened. It was also measured on the r-z plane using PIV under different inlet flow rates and different split ratio. It could be found that the shape of LZVV does not change with inlet flow. With the decrease of split ratio, LZVV becomes discontinuous graduallyToo little split ratio led to excessive upward axial velocity, makes collision of the fluid on the hydrocyclone wall, and the stability of the flow field distribution are destroyed. By analyzing the the streamline distribution in r-z cross section, it was found the secondary vortex is not axisymmetric, on the whole length of the hydrocyclone it was in staggered arrangement. By measuring the axial and radial turbulent velocity, the location of highest turbulence intensity was found to be mainly in the region of the forced vortex, wihich is different from the results of light dispersed phase hydrocyclone using PDPA measurement, in which the highest axial turbulence was on the side wall.?3? It was through adhering the long narrow windows along hydrocyclone cone, flexible PDPA measurement location and more test points were realized. The total maximum error of tangential and axial velocity caused by this method was about 0.04% and 0.69%, respectively. PDPA was used to analyze tangential and axial velocity components, locus of zero vertical velocity and secondary vortexes. The distribution of tangential velocity index n, was paid special attention. It was found that the tangential velocity will increase with the decrease of inlet size.The increase of inlet size also caused the increase of tangential velocity index n. Tangential velocity distribution was more close to the free vortex with higher inlet size. The tangential velocity decrease fast from center to the side wall, adverse to the particle separation at side wall. In addition, the tangential velocity index n increase from top to bottom. Under smaller inlet size, due to the input of more energy, in the cylindrical section of the hydrocyclone, the tangential velocity near the side wall resemble the law of forced vortex. The influence of inlet size on axial velocity is also analyzed. It was found that with the increase of inlet size, the position of LZVV relatively becomed far away from the cyclone wall, at the same time moved to axis and bottom. In addition, the tangential and axial turbulent velocity was measured using PDPA. It is found that with the decrease of inlet size, tangential and axial turbulent velocity inside the hydrocyclone increase, and the energy dissipation increases, and the pressure drop will also increase.