Short communicationExperimental study of pressure fluctuation in a gas-solid cyclone separator
Graphical abstract
Introduction
Cyclone separators (hereafter “cyclones”) are widely used as inertial separating device in many industrial manufacturing processes, such as circulating fluidized bed combustion, residue fluid catalytic cracking, coal tar oil distillation, gas drilling, etc. Though a cyclone is featured with simple structure, the flow fields and separation process prevailing inside it are extremely complex and depend on many factors. To optimize the structure parameters and improve the separation performance, the characteristics of gas-solid two-phase flow have been constantly studied since the late 1920s.
In most of the past studies, time-average velocity and turbulence characteristics have been given much importance so that the time-averaged flow fields in cyclones have been revealed clearly. However, the flow inside a cyclone is unsteady and non-axisymmetrical mainly due to swirling of core of the main vortex about its geometrical axis in a quasi-periodic manner (Derksen et al. [1]). With the increase in computer processing speed and latest development in instrumentation, studies into the dynamic property of the vortex have also gradually gained researchers' attention in recent past. Some important publications concerning the studies on dynamic property of the vortex are listed in Table 1 along with a short description. These researches mainly focus on the instantaneous tangential velocity or the so-called PVC (precessing vortex core) phenomenon. The results are helpful in improving our understanding of the instability prevailing in the cyclone vortex. However, literature on experimental work on frequency and power of the fluctuation in the whole space of the cyclone is scarce. Since the quasi-periodic motion of the vortex core results in quasi-periodic fluctuations of the velocity and pressure (Cai et al. [12]), the position and dynamic property of the vortex tail in a gas cyclone can be characterized by wall pressure measurements (Gao et al. [9]). In this work, the pressure signals at various axial, radial and circumferential positions in a gas-solid cyclone were measured by multi-input dynamic pressure transducer and analyzed using probability density function, standard deviation and power spectral density methods to deepen our understanding of dynamic property of the cyclone vortex.
Section snippets
Experiment
A cylinder-on-cone cyclone with a 180° volute inlet was used in the experiments. Its geometrical dimensions are shown in Fig. 1. The diameter of the cylinder of cyclone was 300 mm. The inlet size was 176 mm in height and 84 mm in width. The origin of the coordinates was set at the geometrical center of the entrance of the vortex finder. The positive direction of z-axis was downward. The cyclone was made of Plexiglas for the convenience of observation. The apparatus was electrically grounded in
Time-average and instantaneous pressure
The time-averaged pressure profiles along with the radial directions at different axial positions are shown in Fig. 4. In the experiments, the measured pressures are negative as air circulation fan draws air into the cyclone. From Fig. 4, the inner (r/R = 0–0.4) and outer (r/R = 0.4–1) regions are easily distinguishable, which coincides with Derksen's [1] simulation results of the flow field. The time-average pressure shows good symmetry in the radial direction. With the decrease of the radius, it
Conclusions
Pressure signals at various positions in a gas-solid cyclone were measured by multi-input dynamic pressure transducer and analyzed by several methods in this paper. The main results of the experiments are concluded as follows:
- (1)
During the measurement of the pressure fluctuation in the gas phase flow field, two dominant frequencies (about 71 Hz and 179 Hz) are detected. The former (about 71 Hz) is related to the rotation of the quasi-forced vortex, while the latter (about 179 Hz) is related to the
Acknowledgements
The authors gratefully acknowledge the financial support of Science Foundation of China University of Petroleum, Beijing (No. 2462015YQ0302) and National Natural Science Foundation of China (Grant No. 21566038, Grant No. 21176250).
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2022, Chemical Engineering Research and DesignCitation Excerpt :The radial velocity at the bottom of vortex finder is greater than that at other positions of the same section, which is an important factor for the formation of short-circuit flow phenomenon. However, some scholars (Song et al., 2017; Gu et al., 2016) believe that the inlet flow of cyclone separator will collide with the rotating flow in annular spacer before it converges into the main flow. This kind of collision will inevitably produce local eddy current near the wall of the cylinder, and eventually lead to the occurrence of short-circuit flow.