Effects of nozzle inlet size and curvature on the flow development in a bidirectional vortex chamber

Abstract

A finite-volume solver is used to describe the cyclonic motion in a cylindrical vortex chamber comprising eight tangential injectors and a variable nozzle size. The simulations are performed under steady, incompressible, and inviscid flow conditions with air as the working fluid. First, we apply a fine tetrahedral mesh to minimize cell skewness, particularly near injectors. Second, this mesh is converted into a polyhedral grid to improve convergence characteristics and precision. After achieving convergence, the velocity components are evaluated and compared to existing analytical solutions. We find that well-resolved numerical simulations can accurately predict the expected forced vortex behavior in the core region as well as the free vortex tail in the outer region. We also confirm that the swirl velocity remains axially invariant irrespective of the outlet radius. Similarly, we are able to ascertain that the axial and radial velocities embody the bidirectional nature of the motion. As for the computed pressure distribution, it is found to agree quite well with both theoretical formulations and experimental measurements of cyclone separators. Then using a parametric trade study, the effect of nozzle variations on the internal flow character, mantle structure, and recirculation zones is systematically investigated. Apart from the exit diameter, we find that the nozzle length and inlet curvature can substantially affect the internal flow development including the formation of backflow regions, recirculation zones, and mantle excursions. Finally, an empirical relation is constructed for the nozzle radius of curvature and shown to effectively suppress the emergence of recirculation and backflow regions.

Bidirectional vortex stabilization of a supersonic inductively coupled plasma torch

“…The nozzle design (i.e. inlet diameter, inlet curvature, and throat diameter) relative to the mantle diameter is expected to have an important effect on the gas flow [43], and consequently the overall plasma torch performance. Also, trying to force a large quantity of very hot gas through a small nozzle is expected to result in increased relative heat losses to the nozzle walls and a decreased thermal efficiency compared with a larger diameter nozzle.…”

“…While the reverse vortex has been used in several subsonic ICP torches, there have been very few fundamental investigations with supersonic ICP torches. Compared with subsonic nozzles, compressible flow effects become particularly important in supersonic nozzles, and the dimensions and geometry of the nozzle itself (such as the inlet and throat diameters compared with the size of the vortex mantle) may strongly influence the resulting vortex flows [42,43]. Supersonic ICPs have a number of practical industrial applications however, such as plasma assisted supersonic jet deposition, where improved thermal efficiency when using reverse vortex injection offers a number of benefits in terms of reduced gas or input power consumption, or even the possibility of different torch construction materials [44,45].…”

Parametric study of a vortex-enhanced supersonic inductive plasma torch

“…where the subscripts refer to the pressure upstream or downstream of the nozzle respectively. For argon, equation (40) gives pup p down > 2.05. Figure 6 shows the measured upstream-todownstream pressure ratio as a function of mass flow rate at an RF power of 800 W for all nozzles.…”

“…Figure 6 shows the measured upstream-todownstream pressure ratio as a function of mass flow rate at an RF power of 800 W for all nozzles. The horizontal black dashed line shows the minimum required pressure ratio from equation (40). Due to resolution limits, pressure sensor measurements are less reliable for pressures below about 150 Pa.…”

“…parallel to the torch centerline) gas velocity of zero [37]. Computational fluid dynamics (CFD) simulations [40,41] have shown that the nozzle dimensions, including the inlet and throat diameter, and the nozzle curvature, affect the gas dynamics of the bidirectional vortex. These parameters are therefore expected to influence plasma torch performance.…”