Steam Jet Ejector
- This Steam Jet Ejector unit model:
Simulates the performance of a steam jet ejector for thermal vapor compression.
Uses semi-empirical correlations for entrainment ratio, pressure correction factor (PCF), and temperature correction factor (TCF), based on El-Dessouky (1997).
Operates in steady-state only.
Assumes the discharge mixture pressure equals its saturation pressure.
Degrees of Freedom
In addition to the inlet state variables (i.e., temperature, pressure, and component flowrates for motive steam and entrained vapor), the Steam Ejector model has at least 1 degree of freedom that must be fixed for the unit to be fully specified. Typically, the following variables are fixed:
Entrainment ratio
Compression ratio
Model Structure
This Steam Ejector model consists of state blocks for the properties of the motive steam inlet, entrained vapor inlet, and discharge mixture. It incorporates semi-empirical equations to model key performance parameters.
Sets
Description |
Symbol |
Indices |
---|---|---|
Time |
\(t\) |
[0] |
Inlet/Outlet |
\(x\) |
[‘in’, ‘out’] |
Phases |
\(p\) |
[‘Liq’, ‘Vap’] |
Components |
\(j\) |
[‘H2O’] |
Performance Metrics
Metric |
Equation |
---|---|
Entrainment Ratio |
\(Ra = \frac{\dot{m}_{motive}}{\dot{m}_{entrained}}\) |
Compression Ratio |
\(CR = \frac{P_s}{P_{ev}}\) |
Variables
Description |
Symbol |
Variable Name |
Units |
Bounds |
---|---|---|---|---|
Entrainment Ratio |
\(Ra\) |
entrainment_ratio |
Dimensionless |
<4 |
Compression Ratio |
\(CR\) |
compression_ratio |
Dimensionless |
>1.89 |
Pressure Correction Factor |
\(PCF\) |
PCF |
Dimensionless |
N/A |
Temperature Correction Factor |
\(TCF\) |
TCF |
Dimensionless |
N/A |
Motive Steam Pressure |
\(P_m\) |
properties_motive_steam[0].pressure |
kPa |
[100, 3500] |
Entrained Vapor Pressure |
\(P_{ev}\) |
properties_entrained_vapor[0].pressure |
kPa |
N/A |
Discharge Mixture Pressure |
\(P_s\) |
properties_discharge_mix[0].pressure |
kPa |
N/A |
Equations
Description |
Equation |
---|---|
Pressure Correction Factor |
\(PCF = 3 \times 10^{-7} P_m^2 - 0.0009 P_m + 1.6101\) |
Temperature Correction Factor |
\(TCF = 2 \times 10^{-8} T_{ev}^2 - 0.0006 T_{ev} + 1.0047\) |
Entrainment Ratio Model |
\(Ra \times TCF = 0.296 \frac{P_s^{1.19}}{P_{ev}^{1.04}} \left(\frac{P_m}{P_{ev}}\right)^{0.015} PCF\) |
Entrainment Ratio Definition |
\(Ra = \frac{\dot{m}_{motive}}{\dot{m}_{entrained}}\) |
Compression Ratio |
\(CR = \frac{P_s}{P_{ev}}\) |
Class Documentation
References
El-Dessouky, H., Modeling and simulation of thermal vapor compression desalination plant. Symposium on Desalination of Seawater with Nuclear Energy, Taejon, Republic of Korea, 26-30 May, 1997.