Experimental and Numerical Studies on Flow and Turbulence Characteristics of Impinging Stream Reactors with Dynamic Inlet Velocity Variation
Abstract
:1. Introduction
2. Model Description
2.1. Fluid Dynamics Modeling Framework
2.2. Inlet Velocity Variation
2.3. Boundary Conditions
2.4. Simulation Conditions and Grid Test
3. Experimental Setup
4. Results and Discussion
4.1. Experimental Verification
4.2. Flow Characteristics of the Flow Field
4.2.1. Velocity Distribution on the Axis
4.2.2. Motion Characteristics of the Impinging Surface
4.3. Turbulence Characteristic Analysis
5. Conclusions
- The outstanding features of the flow field in the impinging stream reactor with dynamic inlet flow patterns are that the impinging surface is instantaneously moving and that the position variation of the impinging surface varies linearly with w every half-period and makes a back-and-forth motion in one period under dynamic inlet velocity conditions.
- Dynamic inflow conditions play an important role in motion characteristic of the impinging surface. The range of motion of the impinging surface increases with an increase in T, A or ∆u. Increasing inlet velocity from either of the two inlets provides continuous and additional energy into the flow field, leading to a more severe impinging force and improving momentum transfer in the impinging zone.
- The turbulence characteristic of the impinging surface is closely related to inlet parameters and L/D. The maximum k(turbulence kinetic energy) of the flow field is still located at the impinging center in impinging stream reactors with dynamic inflow conditions. The mean k of the impingement region increases as A, u0aver, or ∆u increase and decreases with an increase of L/D. Besides, the mean k of the impingement region reaches a maximum value at some T or ∆φ (initial phase difference between two inlet velocities).
- Dynamic inflow conditions brings more intense turbulence into impinging zone with weak mean inlet velocities. Compared with conventional impinging stream reactors with equal mean inlet velocities, impinging stream reactors with dynamic inflow conditions under the same operating conditions can cause more intensely turbulent flows in the impinging zone with an instantaneously moving impinging surface.
- The results presented in this paper should be useful for designing future, optimized impinging stream reactors with more intense turbulence characteristics. Future research should focus on the development of impinging stream reactors with dynamic inflow conditions in practical applications, such as mixing, drying, combustion, etc.
Author Contributions
Funding
Conflicts of Interest
Nomenclature
Symbol | Comment | Unit |
k | Turbulence kinetic energy | m2/s2 |
S | Modulus of mean rate of strain tensor | - |
ε | Energy dissipation rate | m2/s3 |
xi, xj | Coordinates | m |
∆t | Time step | s |
T | Period | s |
A | Amplitude | m/s |
ρ | Density | kg/m3 |
ui, uj | Velocity component | m/s |
g | Gravitational acceleration | m2/s |
τ | Stress tensors of liquid phase | Pa |
t | Time | s |
μ | Dynamic viscosity | kg/(m∙s) |
μt | Turbulent viscosity | kg/(m∙s) |
σk | Turbulent Prandtl number for k | - |
σε | Turbulent Prandtl number for ε | - |
υ | Kinematic viscosity | m2/s |
u0 | Constant inlet velocity | m/s |
u0aver | Average inlet velocity in one period | m/s |
N | Number of periods, N ≥ 15 | - |
uL, uR | Left inlet velocity, right inlet velocity | m/s |
φL, φR | Initial phase of left and right inlet | ° |
∆φ | Phase difference | ° |
∆u | Inlet velocity difference between both opposed jets | m/s |
u* | Instantaneous mean velocity of both inlet fluids | m/s |
u0aver, L | Left mean inlet velocity during one period | m/s |
u0aver, R | Right mean inlet velocity during one period | mm |
D | Nozzle diameter | mm |
L | Impinging spacing | mm |
w | Degree of completed inflow conditions with dynamic inlet velocity variation in one period, w∈[0,1] | - |
x | Coordinate of the nozzle axis | m |
V | Liquid instantaneous velocity magnitude | m/s |
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Flow Pattern | uL | Notes |
---|---|---|
Sinusoidal inlet velocity | uR = 2um − uL ≥ 0, where a1, a2, b1, b2, c1, c2, c3, d1 and d2 are constant; uL reaches a maximum value at t = T/4 and a minimum value at t = 3T/4 for all inlet velocity flow patterns. The maximum and minimum value and T are equal for different inlet velocity flow patterns. | |
Parabolic inlet velocity | ||
Step inlet velocity | ||
Triangular inlet velocity | ||
Constant inlet velocity (conventional impinging streams) |
Parameter | CFD Model | Experiment | Inlet Velocity Flow Pattern |
---|---|---|---|
um (m/s) | 1.25, 1.4, 1.5 | 1.25, 1.4, 1.5 | Constant |
T (s) | 0.2, 0.3, 0.4, 0.5, 0.6 | 0.2, 0.3, 0.4, 0.5, 0.6 | Sinusoidal, Step |
A (m/s) | 0.15,0.2, 0.25, 0.35, 0.4 | 0.15,0.2, 0.25, 0.35, 0.4 | Sinusoidal, Step |
∆φ | T/12, T/6, T/4, T/3, 5T/12, T/2 | - | Sinusoidal |
Property/Symbol | Unit | Value |
---|---|---|
Water density/ρ | kg/m3 | 998.2 |
Water viscosity/μ | kg/m∙s | 0.001003 |
Nozzle diameter/D | mm | 20 |
Impinging distance/L | mm | 80, 100, 120, 140, 160 |
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Liu, X.; Yue, S.; Lu, L.; Gao, W.; Li, J. Experimental and Numerical Studies on Flow and Turbulence Characteristics of Impinging Stream Reactors with Dynamic Inlet Velocity Variation. Energies 2018, 11, 1717. https://doi.org/10.3390/en11071717
Liu X, Yue S, Lu L, Gao W, Li J. Experimental and Numerical Studies on Flow and Turbulence Characteristics of Impinging Stream Reactors with Dynamic Inlet Velocity Variation. Energies. 2018; 11(7):1717. https://doi.org/10.3390/en11071717
Chicago/Turabian StyleLiu, Xueqing, Song Yue, Luyi Lu, Wei Gao, and Jianlan Li. 2018. "Experimental and Numerical Studies on Flow and Turbulence Characteristics of Impinging Stream Reactors with Dynamic Inlet Velocity Variation" Energies 11, no. 7: 1717. https://doi.org/10.3390/en11071717