Investigation on the Handling Ability of Centrifugal Pumps under Air–Water Two-Phase Inflow: Model and Experimental Validation
Abstract
:1. Introduction
2. Pump Geometry and Experimental Test Rig
3. Numerical Model and Setups
3.1. Model and Mesh
3.2. The Eulerian–Eulerian Inhomogeneous Two-Phase Flow Model
3.3. The Modified Turbulence Model
3.4. Boundary Conditions
4. Overall Pump Performances
5. Influence of Rotational Speed
6. Numerical Results
6.1. Pump Head Deterioration Ratio ψ*: Comparisons between Experiments and One-Dimensional Two-Phase Flow Model
6.2. 3D-URANS Overall Performance Results
6.2.1. Comparison between the Initial and Modified Turbulence Model (See Section 3.3)
6.2.2. 3D-URANS Results Comparison for Different Inlet Void Fraction and Flow Coefficients
6.3. Local Impeller Passage Flow Structures
6.3.1. Flow at Inlet Impeller Section
6.3.2. Flow inside the Impeller Section
7. Conclusions
- Pump performance degradation is more pronounced for low flow rates compared to high flow rates when the inlet void fraction increases. The starting point of a severe pump degradation rate is related to a specific flow coefficient, whose value corresponds to the change of the slope of the theoretical head curve. When increasing the inlet void fraction, the degradation slope curves increase (with a negative sign) with the decreasing flow coefficient. The more the rotational speed decreases, the more the experimental pump performance is affected at a given inlet void fraction value.
- Existing one-dimensional models can be considered quite good tools for the first step of a two-phase flow analysis. They give good global indications based on the mean values along one streamline, but attention should be taken when using non-dimensional flow coefficients. The chosen particle fluid model with interface transfer terms looks quite suitable for evaluating pump performance degradation up to an a value of 7%.
- For a higher a value, CFD can’t always correctly predict the sudden breakdown of the pump performance as obtained by measurements. This is probably due to the flow regime inside the impeller, which does not correspond to a bubbly one anymore. However, for the lowest flow rate, the performance breakdown is well predicted with the modified turbulence model.
- The difference between experimental and numerical results exist not because of rotational speed, but because of its consequence on the local velocity values that decrease according to the flow coefficient, and more specifically at the pump inlet tube and at the pump inlet section. Numerical simulations must take churn flow characteristics into account in order to get better results. Both bubbly and churn flow conditions may be present for inlet flow conditions depending on the experimental setup, rotational speed, and the pump flow coefficient, even at nominal conditions.
- The numerical simulation gives interesting local flow information that would be taken into consideration for new design approaches at the pump inlet section for an improved two-phase flow suction capability of centrifugal pumps.
Author Contributions
Funding
Acknowledgments
Conflicts of Interest
Nomenclature
a | inlet void fraction |
b | impeller blade width |
C | constant pressure value when modified liquid density |
D | diameter |
H | pump head |
n | exponent |
N | rotational speed |
p | local pressure |
P | shaft power |
Q | volume water flow rate |
R | radius |
Re,imp | Impeller Reynolds number |
t | time |
th | theoretical |
tp | related to two-phase condition |
u | circular velocity |
v | water cinematic viscosity |
z | impeller blade |
Greek symbols | |
η | global efficiency of the pump η = ρgQH/P |
ρ | density |
ρm | density of fluid mixture ρm = ρl (1 − α) + αρg |
φ | flow coefficient φ = Q/(2π·R2·b2·u2) |
ψ | head coefficient ψ = gH/(u2)2 |
Ωs | specific speed |
ω | angular velocity |
Subscripts | |
α | local void fraction |
B | bubble |
d | design condition |
g | gas |
l | liquid |
m | mixture fluid |
ref | reference |
0 | related to a = 0 |
1 | Impeller pump inlet |
2 | Impeller pump outlet |
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Si, Q.; Bois, G.; Jiang, Q.; He, W.; Ali, A.; Yuan, S. Investigation on the Handling Ability of Centrifugal Pumps under Air–Water Two-Phase Inflow: Model and Experimental Validation. Energies 2018, 11, 3048. https://doi.org/10.3390/en11113048
Si Q, Bois G, Jiang Q, He W, Ali A, Yuan S. Investigation on the Handling Ability of Centrifugal Pumps under Air–Water Two-Phase Inflow: Model and Experimental Validation. Energies. 2018; 11(11):3048. https://doi.org/10.3390/en11113048
Chicago/Turabian StyleSi, Qiaorui, Gérard Bois, Qifeng Jiang, Wenting He, Asad Ali, and Shouqi Yuan. 2018. "Investigation on the Handling Ability of Centrifugal Pumps under Air–Water Two-Phase Inflow: Model and Experimental Validation" Energies 11, no. 11: 3048. https://doi.org/10.3390/en11113048