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[email protected] Axial flow cooling fans in ACCs
Axial flow cooling fans in ACCs
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Today
1. Background2. Power plant cooling3. Simplified representation of an axial flow fan 4. Fan-system matching5. Modelling of an ACC using CFD
• Some of this presentation comes from:• Engelbrecht (2018)• Louw (2019)
Air-cooled condenserMatimba power plant 3690 MW
BackgroundMatimba power plant 3690 MW
Background
Matimba power plant air-cooled condenser (ACC).
– 288, 9.1 m diameter, axial flow fans
– installed 45 m above ground level– Eskom currently building two new
4800 MW direct dry-cooled plants, Medupi and Kusile.
Air-cooled condensers
Medupi4800 MW coal-fired plant, located near Lephalahle, South Africa
Medupi vs Matimba ACC.
Size comparison
Power plant cycle
Power plant cooling cycles
Sea, river or lake
Turbine
Condenser
Generator
Direct cooling
Boiler flue stack
Drift eliminatorSprays
FillRain zone
Pond
Shell
Tower supports
Steamturbine
Generator
Condenser
Cooling water pump
Condensate pump
Natural draught wet cooling tower
Power plant cooling cycles
Direct dry-cooling. *
* Le Roux, F.N, The CFD simulation of an axial flow fan, M.Sc. thesis, Department of Mechanical and Mechatronic Engineering, University of Stellenbosch, South Africa, 2010.
Power plant cooling cycles
Some solar…• Solar thermal energy – SUNSPOT• Stellenbosch University Solar Power
Thermodynamic Cycle
Solar air-cooled condensers
Kaxu Solar One100 MW parabolic trough plant, located near Pofadder, South Africa
Axial flow cooling fan• Consider the use of the term fan “static pressure”
There are two terms used for fans, namely fan total pressure and fan static pressure:
Fan static pressure is actually fan total-to-static pressure. It is typically used in installations where the outlet kinetic energy of the fan is dissipated. Typical for ACCs where outlet air is dissipated.
Fan total pressure is actually fan total-to-total pressure and is used where the outlet kinetic energy of the fan plays a significant role in the system design. Typical for ducted fans where outlet energy can be recovered.
Note that efficiency is defined in the same manner
Axial flow fan testing
• Testing are performed using standardised airways. According to ISO 5801 part a, there are four standard test configurations.
• Type A: free inlet-outlet• Type B: Free inlet, ducted outlet• Type C: Ducted inlet, free outlet• Type D: Ducted inlet, ducted outlet
• The test configuration selected based on the eventual system configuration.
Axial flow fan testing
• For large diameter cooling fans, we use a Type A test facility:
Axial flow fan testing
• Fan is tested to scale at the same tip speed to maintain kinematic similarity.
• The flowrate is calculated as:
• The fan static pressure is calculated as:
• Fan shaft power
• and static efficiency is calculated as:
Axial flow fan testing
• Test results are scaled to standard speeds and density.
• Scaling is generally accurate if in fully turbulent region
Axial flow fan testing
• Scaled fan installed.• Attention is paid to repeatable accurate setting of the
blade angle.
Axial flow fan testing
• Fan test results: pressure curve• When matching a system to an experimental fan, make sure that the
matching is done correctly.
Axial flow fan testing
• Fan test results: efficiency• The correct efficiency can only be obtained if matching is done correctly.
Axial flow fan simulation:Simplified fan modelling
• Three simplified fan modelling methods are used:
– Actuator disc method– Pressure jump method– Extended actuator disc method
Axial flow fan simulationActuator disc method (ADM)
• The ADM simulates the effect of the fan blades on the flowfield by using lift and drag coefficients.
• The fan blade is subdivided into radial elements.• Lift and drag coefficients are defined as in literature for 2-D
airfoil data as dependent on angle of attack α.• Angle of attack is relative to vector mean flow angle.
Fan axial flow
directionFan rotation plane
αW∞
δL
δD rcCW LL δρδ ××= ∞2
21
rcCW DD δρδ ××= ∞2
21
Axial flow fan simulationActuator disc method (ADM)
• Typical CL and CD data used for ADM – applied over 180°.
Axial flow fan simulationPressure jump method (PJM)
• The PJM utilises a static-to-static pressure increase that isapplied as axial source terms in cells downstream of the“Fan” boundary conditions.
• The value for the pressure increase can be derived directlyfrom the standard “fan static pressure curve”, as oftenquoted by a fan supplier.
• Fan static pressure refers to total-to-static pressure values.• The data therefore needs to be transformed from the
pressure values obtained at the measurement locations tostatic pressure values in the plane where the pressureincrease is applied.
Axial flow fan simulationPressure jump method (PJM)
• Fitting a 3rd order polynomial equation to the “fan staticpressure” curve obtained from a single fan test and adding thedynamic pressure in front of the fan, as well as the inlet losses,the following equation is obtained for the pressure jump:
Static pressure behind fan
Total pressure upstream of fan
Static pressure in front of fan
2232
21
21
inletlossavessfan vKvdVcVbVap ρρ +++++=∆
Axial flow fan simulationExtended actuator disc method (EADM)
• There are three effects that occur in an axial flow fan rotor whenradial flow takes place, namely Coriolis, the cross flow effect(diagonal flow over the blade section) and stall delay.
• This leads to increased blade lift coefficients.
Axial flow fan simulationExtended actuator disc method (EADM)
• The EADM uses the same format as the ADM.• The lift coefficient used in the EADM is increased by extending
the linear section of the lift coefficient vs. angle of attack curve.• The drag coefficient is increased proportionally:
( )DLDDDLDD CCCC 2233 ×=
-1.0
0.0
1.0
2.0
3.0
4.0
-15.0 -10.0 -5.0 0.0 5.0 10.0 15.0 20.0 25.0 30.0
Angle of attack, α [°]
Lift
Coe
ffici
ent [
CL]
- - B-fan coefficients (as per Appendix C)--- Extended lift coefficient
Axial flow fan modelling
Lay-out of an A-frame air-cooled condenser (ACC).
Axial flow cooling fan
Fan-system matching:• Draft equation
Tower supports
Downstream obstacles
Upstream obstaclesHeat exchanger losses
Fan-system matching:
Outlet losses
Bundles losses
Jetting losses
Inlet contraction losses
Fan-system matching:• Heat transfer modelled using e-NTU
From experiment
Single fan ACC model
Single-fan ACC model
30-fan ACC model
30-fan ACC model
30-fan ACC model
30-fan ACC model
30-fan ACC model
30-fan ACC model
Conclusion
1. Background2. Power plant cooling3. Simplified representation of an axial flow fan 4. Fan-system matching5. Modelling of an ACC using CFD
Axial flow cooling fans in ACCsTodaySlide Number 3Slide Number 4BackgroundAir-cooled condensersMedupi vs Matimba ACC. �Power plant cyclePower plant cooling cyclesPower plant cooling cyclesDirect dry-cooling. *Some solar…Solar air-cooled condensersAxial flow cooling fanAxial flow fan testingAxial flow fan testingAxial flow fan testingAxial flow fan testingAxial flow fan testingAxial flow fan testingAxial flow fan testingSlide Number 22Slide Number 23Slide Number 24Slide Number 25Slide Number 26Slide Number 27Slide Number 28Slide Number 29Lay-out of an A-frame air-cooled condenser (ACC).Slide Number 31Slide Number 32Fan-system matching:Single fan ACC modelSingle-fan ACC model30-fan ACC model30-fan ACC model30-fan ACC model30-fan ACC model30-fan ACC model30-fan ACC modelConclusion
