Effects of Back Pressure on Flow Regime and Suction Performance of Gas–Liquid Swirl Ejector
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Abstract
The back pressure of a gas–liquid swirl ejector is a critical parameter that affects the flow regime and entrainment performance of the system. In the case of a weak swirl injection, the motive jet carries relatively higher axial momentum thus remains in a single phase and the liquids appear glassy. With increasing in the back pressure of the bubble flow, the suction rate drops rapidly. For a strong swirl injection, the liquid jet is disintegrated due to higher angular momentum and the spray is atomized. Augmentation in the back pressure also causes the reduction in the suction rate but it tends to grow more gradual than the weak swirl injection. As a result, the suction rate of the strong swirl is greater than that of the weak swirl in the majority of the back-pressure range. However, owing to the high transition pressure, only the weak swirl entrains the air in the bubble flow regime at low back pressure. The relationship between the suction and the swirl intensity is not fixed and is influenced by the back pressure.
Funding statement: This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.
Nomenclature
- d
geometrical parameter of a swirl body (dimensionless)
- D
diameter (mm)
- e
geometrical parameter of a swirl body (dimensionless)
- g
gravitational acceleration(m·s–2)
- Gax
preserved value in axial direction from axial momentum equation (N)
- Gθ
preserved value in axial direction from angular momentum equation (mN)
- h
lead of swirl helix (mm)
- H
height of swirl body (mm)
- KLa
volumetric mass transfer coefficient (s–1)
- L
length (mm)
- Mr
Ratio of mass flow rate of the entrained fluid to the motive fluid (dimensionless)
- P
pressure (Pa)
- △P
pressure difference between the bubble column exit
- Pb
back pressure (abs. bar)
- r
radius (m)
- Q
volumetric flow rate (LPM)
- R
radius of swirl body (mm)
- Sn
general swirl number (dimensionless)
- Snb
body swirl number (dimensionless)
- U
averaged axial velocity (m·s–1)
- UG0
averaged velocity at suction chamber inlet (m·s–1)
- W
averaged angular velocity (m·s–1)
- Greek letters
- α
helix angle (°)
- β
angle (°)
- εG
holdup (dimensionless)
- μ
dynamic viscosity (kg·m−1s−1)
- ρ
density (kg·m−3)
- σ
surface tension (N·m−1)
- Subscripts
- b
bubble column
- bc
bubble to coaxial
- c
converging section
- cb
coaxial to bubble
- d
diffuser
- G
gas
- L
liquid
- m
mixing tube
- n
nozzle
- o
orifice of nozzle
- s
suction chamber
- t
throat
- trans
flow regime transition
Declarations of interest: None
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- Effects of Chemical Reactions on the Local Hydrodynamics in Slurry Bubble Column Reactors Operating under Typical Fischer-Tropsch Process Conditions – Ii
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