Thermodynamic Simulation on the Performance of Twin Screw Expander Applied in Geothermal Power Generation
Abstract
:1. Introduction
2. Geothermal Power Projects in China
3. Geometry Model
3.1. 3D Model and Basic Parameters
3.2. Leakage Paths
4. Thermodynamic Model
4.1. Assumptions
- 1.
- State parameters of the steam in a working chamber are uniform.
- 2.
- Heat transfer between working chamber and the surroundings is negligible and working fluid leak through clearance is isentropic.
- 3.
- Discharge process is isobaric.
4.2. Governing Equations
4.3. State Equation of Steam
4.4. Suction Steam Mass and Leakage Mass
5. Results and Discussion
5.1. Model Verification
5.2. Simulation Results
5.2.1. Comparison of the Ideal and Actual Working Process
5.2.2. Comparison of Leakage through Different Paths
5.2.3. The Effect of Inlet Pressure and Rotational Speed on the Performance of Expander
6. Conclusions
- (1)
- Throttling losses, pressure drop losses, and leakage losses during the working process are the main influence for the internal efficiency of twin screw expander.
- (2)
- The mass in the chamber decreases with the increase of rotation angle at the beginning of expansion and then increases until the discharge process starts. Because of the large leakage area, leakage through rotor tip-housing clearance is predominant.
- (3)
- Leakage in the suction process and the early stage of expansion process are most serious, while the contact line and the rotor tip are two main leakage paths. Large pressure difference is the cause of the serious leakage of the former, and the long sealing line of the rotor tip-housing clearance contribute to the serious leakage of the latter. The increase of inlet pressure and the decrease of the rotational speed will increase the mass of leakage.
- (4)
- The throttling losses and pressure drop losses increase with the increasing rotate speed and inlet pressure, and with higher inlet pressure, the pre-expansion begins earlier. Power increases with the inlet pressure and rotate speed but has a slow ascending trend at high pressure.
Author Contributions
Conflicts of Interest
Abbreviations
V | specific volume, m3/kg |
Vi | volume of working space at the end of inlet, m3 |
Vmax | the maximal volume, m3 |
P | pressure, Pa |
Pind | power, KW |
T | temperature, K |
W | output work, J/kg |
m | mass of steam, kg |
cp | specific heat of steam at constant pressure, J/(kg·K) |
cv | specific heat of gas at constant volume, J/(kg·K) |
h | specific enthalpy, J/kg |
θ | male rotor rotation angle, ° |
Al | effective area of leakage paths, m2 |
Ai | cross sectional area of inlet port, m2 |
V | volume, m3 |
Rg | gas constant, J/(mol·K) |
C | flow coefficient, |
L | rotor length, m |
K | ratio of specific heats, |
ω | male rotor rotation speed, rpm |
ρ | density of steam, kg/m3 |
β | wrap angle of male rotor, ° |
ƞi | internal efficiency, |
Subscript | |
I | steam into the control volume |
O | steam into the control volume |
1 | high pressure zone |
2 | low pressure zone |
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Number of Lobes | Wrap Angle | External Diameter (mm) | Length (mm) | Volume Ratio | Inter lobe Clearance (mm) | Rotor Tip-Housing Clearance (mm) | Clearance of Inlet End Face (mm) | |
---|---|---|---|---|---|---|---|---|
Male rotor | 4 | 300° | 510 | 840 | 4.05 | 1 | 0.7 | 0.5 |
Female rotor | 6 | 200° |
Inlet Pressure (MPa) | Inlet Temperature (°C) | Inlet Mass Flow Rate (t/h) | Outlet Pressure (MPa) | Rotation Speed (rpm) | |
---|---|---|---|---|---|
Case 1 | 0.68 | 164 | 32 | 0.25 | 3000 |
Case 2 | 0.80 | 170 | 28 | 0.25 | 2400 |
Case 3 | 0.41 | 145 | 9 | 0.10 | 2250 |
Case 4 | 0.45 | 148 | 15 | 0.16 | 2400 |
Case 5 | 1.3 | 192 | 20 | 0.19 | 2400 |
Case 1 | Case 2 | Case 3 | Case 4 | Case 5 | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
Pind | mt | η | Pind | mt | η | Pind | mt | η | Pind | mt | η | Pind | mt | η | |
Measured | 980 | 32 | 68% | 995 | 28 | 68% | 432 | 9 | 80% | 463 | 15 | 68% | 1181 | 20 | 79% |
Calculated | 1032 | 30.95 | 71.64% | 1053 | 26.91 | 71.97% | 452 | 9.5 | 83.73% | 477 | 14.8 | 71.01% | 1233 | 19.2 | 82.54% |
Error | 5.5% | 3.28% | 5.36% | 5.83% | 3.91% | 5.84% | 4.63% | 5.56% | 4.67% | 3.02% | 1.33% | 2.95% | 4.4% | 4% | 4.49% |
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Qi, Y.; Yu, Y. Thermodynamic Simulation on the Performance of Twin Screw Expander Applied in Geothermal Power Generation. Energies 2016, 9, 694. https://doi.org/10.3390/en9090694
Qi Y, Yu Y. Thermodynamic Simulation on the Performance of Twin Screw Expander Applied in Geothermal Power Generation. Energies. 2016; 9(9):694. https://doi.org/10.3390/en9090694
Chicago/Turabian StyleQi, Yuanqu, and Yuefeng Yu. 2016. "Thermodynamic Simulation on the Performance of Twin Screw Expander Applied in Geothermal Power Generation" Energies 9, no. 9: 694. https://doi.org/10.3390/en9090694