Performance Evaluation of a Steam Ejector Considering Non-Equilibrium Condensation in Supersonic Flows
Abstract
:1. Introduction
- (1)
- We established an experimental system for the steam ejector refrigeration cycle to provide an experimental reference for numerical calculation and analysis;
- (2)
- We developed a numerical model of the ejector under wet steam conditions and verified the veracity and validity of the numerical model by comparing it with experimental data;
- (3)
- We studied the flow of the effective area, expansion nuclei, and excitation waves inside the ejector under the flow of choking flow and the effect on the induced coefficient of the ejector and then discussed the law of the influence of the choked flow on the priming coefficient at different operating and pumped gas pressures;
- (4)
- We investigated the importance of choked flow in preventing backflow at the outlet, improved and optimized the operating conditions of the ejector, and analyzed the performance improvement of the ejector under different choking flows.
2. Experimental Systems
2.1. Experimental Setup
- (1)
- The expansion process of working steam ejected from the nozzle;
- (2)
- The mixing process between the working steam and the induced steam in the ejector;
- (3)
- The process of mixed steam being compressed at the throat of the diffuser.
2.2. Physical Model and Operating Conditions of Ejectors
3. Mathematical Models
3.1. Governing Equations
3.2. Wet Steam Flow Transport Equations
3.3. Wet Steam State Equations
3.4. Numerical Methods and Validation
4. Results and Discussion
4.1. Effect of Primary Fluid Pressure on Entrainment Ratios
4.2. Effect of Secondary Fluid Pressure on Entrainment Ratios
4.3. Effect of Back Pressure on Entrainment Ratios
5. Conclusions
- (1)
- The experimental system of ejector cooling was established, and the relevant experimental data were obtained. The comparison between the experimental and simulated values showed that the relevant data of the ejector were closer to the experimental values under the non-equilibrium spontaneous condensation conditions and were more effective and realistic.
- (2)
- The results indicated that the excessive primary fluid pressure enlarged its expansion core, thereby reducing the effective flow area of the secondary fluid and the entrainment ratio.
- (3)
- As the mass flow rate and pressure of the primary fluid remained unchanged, the increased secondary fluid pressure elevated the entrainment ratio due to the reduction in the expansion angle after passing the Laval nozzle.
- (4)
- When the back pressure was lower than the critical back pressure of 4500 Pa, the entrainment ratio remained unchanged; however, when the back pressure exceeded its critical value, the entrainment ratio gradually reduced. The entrainment ratio approached 0 when back pressure consistently increased.
- (5)
- The location of the choking is a major flow characteristic that affects ejector performance and ejector failure. Mastering the flow of the choke helps us improve ejector efficiency, reduce and minimize the risk of ejector failure, and provides an important reference for optimizing the geometry and improving the efficiency of the ejector.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
Nomenclature
ρ, ρl, ρv | Density, liquid density, and vapor density (kg/m3). |
u | Velocity (m/s). |
u’ | Fluctuation velocity (m/s). |
P | Pressure (Pa). |
τij | Stress tensor. |
E | Total energy. |
αeff | Effective thermal conductivity. |
β | Mass fraction. |
Γ | Mass generation rate (kg/s). |
Droplet average radius (m). | |
r* | Critical droplet radius (m). |
I | Nucleation rate (1/s). |
η | Droplet number density (1/m3). |
qc | Evaporation coefficient. |
θ | Non-isothermal correction factor. |
σ | Droplet surface tension (kg/m). |
T | Thermal temperature (K). |
K | Boltzmann constant. |
M | Molecular mass (kg). |
γ | Specific heat capacities ratio. |
hv | Vapor-specific enthalpy (J/kg). |
R | Gas law constant. |
S | Super saturation ratio. |
Cp | Isobaric heat capacity (J/(kgK)). |
T0 | Droplet temperature (K). |
Vd | Average droplet volume (m3). |
B, C | Virial coefficients (m3/kg, m6/kg2). |
αv | Volume fraction. |
h | Specific enthalpy (J/kg). |
s | Specific entropy (J/(kg.mol.K)). |
k | Turbulent kinetic energy. |
μt | Eddy viscosity. |
ε | Turbulence kinetic energy dissipation. |
Sij | Strain rate. |
C2, C1ε, C3ε, σk, σε | Model coefficients. |
V | Kinematic viscosity. |
Sk, Sε | Source terms. |
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Component | Aspect | Size (mm) |
---|---|---|
Nozzle Throat | Diameter | 2.5 |
Nozzle Outlet | Diameter | 11 |
Nozzle Throat to Outlet | Length | 48 |
Diffuser Throat | Diameter | 24 |
Diffuser Throat | Length | 192 |
Diffuser Inlet | Diameter | 70 |
Diffuser Outlet | Diameter | 70 |
Diffuser Inlet Reducer | Length | 188 |
Diffuser Outlet | Length | 322 |
Ejector Suction Port | Diameter | 54 |
Discrete Format | The control equations are discretized into algebraic equation systems that can be numerically solved using the finite volume method. The coupled implicit solver is employed to solve these equations. The diffusion was discretized using the central difference scheme in the Coupled Implicit Model. The second-order upwind scheme was used to discretely solve the convective terms. |
Meshing | The mesh element in certain areas of the nozzle wall was refined to cope with the Enhanced Wall Treatment near-wall modeling method. The initial generated mesh number was 53,463. After the mesh fining with the aid of an adaptive technique, the final mesh number was 62,796. |
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Xie, Y.; Han, Y.; Wang, X.; Wen, C.; Yang, Y. Performance Evaluation of a Steam Ejector Considering Non-Equilibrium Condensation in Supersonic Flows. Energies 2023, 16, 7755. https://doi.org/10.3390/en16237755
Xie Y, Han Y, Wang X, Wen C, Yang Y. Performance Evaluation of a Steam Ejector Considering Non-Equilibrium Condensation in Supersonic Flows. Energies. 2023; 16(23):7755. https://doi.org/10.3390/en16237755
Chicago/Turabian StyleXie, Youhao, Yu Han, Xiaodong Wang, Chuang Wen, and Yan Yang. 2023. "Performance Evaluation of a Steam Ejector Considering Non-Equilibrium Condensation in Supersonic Flows" Energies 16, no. 23: 7755. https://doi.org/10.3390/en16237755
APA StyleXie, Y., Han, Y., Wang, X., Wen, C., & Yang, Y. (2023). Performance Evaluation of a Steam Ejector Considering Non-Equilibrium Condensation in Supersonic Flows. Energies, 16(23), 7755. https://doi.org/10.3390/en16237755