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ABSTRACT
An electro-swirling coupling device coupled with electric field and centrifugation can achieve demulsification and dewatering of emulsion efficiently and economically. But, the vortex structure and its implication on separation performance under the coupling condition are unclear. Accordingly, a vortex analysis for the coupling separator was conducted numerically, and the effect of eccentricity on the efficiency was investigated. The results show that the iso-vortex surface is twisted and fluctuates. And there is a vibrational radial deviation between the vortex core and central axis, and increasing inlet velocity and voltage amplitude can increase the radial deviation of the vortex at the z-coordinate range from 250 to 550 mm. Furthermore, the underlying reason for the increase in vortex eccentricity is different where the electric coalescence is for the increase in voltage amplitude and the fluid kinetic energy is for the increase in inlet velocity. Moreover, the separation efficiency increases with the increase in vortex eccentricity at the case that the coalescence is dominant, but the separation efficiency gradually decreases with the increase in breakage rate and the droplet breakup is dominant.
Nomenclature
| D | = | Nominal diameter, (mm) |
| Di | = | Inlet diameter, (mm) |
| DL,ij | = | Molecular diffusion |
| Do | = | Overflow orifice diameter, (mm) |
| Ds | = | Swirl chamber diameter, (mm) |
| DT,ij | = | Turbulent diffusion |
| Du | = | Underflow orifice diameter, (mm) |
| E | = | Electric field intensity, (kV·m−1) |
| Fe | = | Electric field force, (N) |
| I | = | Identity tensor |
| Lu | = | Length of underflow pipe, (mm) |
| Lo | = | Length of overflow pipe, (mm) |
| n | = | Coalescence times, (n = 0, 1, 2 …) |
| Pij | = | Stress production |
| P | = | Pressure, (Pa) |
| Qin | = | Inlet flow rate, (m3·h−1) |
| Q | = | Value of Qcriterion |
| R | = | Radius of the horizontal cross section, (mm) |
| Rd | = | Radial deviation, (%) |
| Rp | = | Initial average size of droplets, (mm) |
| r | = | Radial distance, (mm) |
| rp | = | Average size of droplets after coalescence, (mm) |
| S | = | Strain rate tensor |
| U | = | Voltage amplitude, (kV) |
| u | = | Velocity of emulsion, (m·s−1) |
| udr,k | = | Drift velocity, (m·s−1) |
| uk | = | Velocity of phase k, (m·s−1) |
| ui,uj,uk | = | Velocity component in direction of i, j, k, (m·s−1) |
| = | The velocity gradient tensor | |
| uwo | = | Slip velocity, (m·s−1) |
| α | = | Large cone angle, (°) |
| αk | = | Volume fraction of phase k, (%) |
| β | = | Small cone angle, (°) |
| σf | = | Viscous stress tensor |
| ε | = | Relative permittivity of emulsion, (F·m−1) |
| εij | = | Dissipation |
| ε0 | = | Permittivity of vacuum, (F·m−1) |
| εk | = | Relative permittivity of phase k, (F·m−1) |
| η | = | Separation efficiency |
| μ | = | Viscosity of emulsion, (mPa·s) |
| μk | = | Viscosity of phase k, (mPa·s) |
| ρ | = | Density of emulsion, (kg·m−3) |
| ρk | = | Density of phase k, (kg·m−3) |
| ϕij | = | Pressure strain |
| ϕw | = | Volume fraction of water, (%) |
| = | Vorticity tensor |
Acknowledgements
This work was partially supported by grants from the National Natural Science Foundation of China (Grant No. 21878334, 22008016 and 22178036), CSTC projects (Grant No. cstc2019jscx-gksbX0032, cstc2019jcyj-msxmX0296 and cstc2020jcyj-msxmX0157), and projects of science and technology research program of Chongqing Education Commission of China (Grant No. KJZD-k201800801, KJZD-M201900802, KJQN202100817, KJQN201900825, KJZD-K202000803 and CXQT21023,).
Disclosure statement
No potential conflict of interest was reported by the author(s).
Statement of Novelty
This work systematically investigates the vortex structure and its implication on separation performance of an electro-swirling coupling device coupled with electric field and centrifugation. It also studies the effects of inlet velocity and voltage amplitude on vortex structure. The axial distribution of radial deviation of the vortex based on minimum pressure center was obtained. Finally, the impact of vortex eccentricity on separation efficiency was investigated.
Supplementary material
Supplemental data for this article can be accessed online at https://doi.org/10.1080/01496395.2022.2151472.