CFD Modelling of an evaporative Cooling System
Andres Pinilla, Jorge López, Hugo Pineda, Miguel Asuaje, Nicolás Ratkovich
Chemical Engineering Department
Universidad de los Andes. Colombia
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Content
• Introduction• Cooling by fogging system
• Objectives
• Methodology • Cases of Study
• Results
• Conclusions
• Future Work
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Introduction
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Turbines that work in hot weathers
Lower performance at higher temperatures
Cooling system
IntroductionCooling by fogging system
• Water is used to cool down the air.
• Rapid energy transfer given thesmall drop size diameter (3 - 5 𝜇𝑚)• Necessary a complete evaporation
before the turbine inlet.
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Objectives
CFD modeling of an evaporative cooling system.
• To validate the results found in the simulation with reportedexperimental results.
• To study the heat and mass transfer in the duct.
• To investigate the water droplets behavior in terms ofagglomeration and fractionation.
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Methodology
• Physical models for dispersed phase (water)• NTC collision model• SSD breakup & SSD distortion• LISA• Two-Way Coupling
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MethodologyCases of StudyAir
• Ideal gas
Water• Fixed Variables
• Temperature: 30°C• Velocity: 4 m/s • Pressure: 2000 psi (~140 bar)
• Droplet Size• 20 𝜇𝑚
• 50 𝜇𝑚
• Relative humidity• 20%
• 60%
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MethodologyGeometry
8Figure 1: Duct geometry where the cooling occurs (in mm).
ResultsHeat Transfer
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Figure 2: Results for temperature for each case
ResultsHeat Transfer (cont…)
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Case Experiment
temperature (°C)
Simulation
temperature (°C)
Difference (%)
A 15.50 16.09 3.82
B 15.34 16.33 6.44
C 23.76 24.73 4.06
D 23.53 24.97 6.12
Figure 3: a) Lateral contour plot of temperature. b) Up contour plot of temperature
ResultsHeat Transfer (cont…)
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ResultsMass Transfer
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Figure 4: Results of relative humidity for case: a) A. b) B, c) C, d) D
ResultsMass Transfer (cont…)
The exact position on the sensors was not clearly specified, this can be a possible cause of error.
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Case Experiment (%) Simulation (%) Difference %
A 96.00 91.87 4.30
B 95.90 88.74 7.46
C 96.51 92.07 4.59
D 95.66 95.66 7.07
Figure 5: Distribution of the sensors across the duct
ResultsVolume Fraction of Water
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Figure 6: a) Liquid volume fraction of water a) Lateral view y b) Upside view
ResultsParticle Diameter
After the reduction zone, the droplet size reduces faster, as expected
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Figure 7: Water droplets diameter
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Time (s)20HR 50μm 60HR 50μm
Conclusions
• The discrepancy of the experimental and numericalresults are due the not knowledge of the exact location ofthe sensors in the duct. Despite that the final result wasvery close.
• The CFD simulation helps to complement theexperimental study because it is possible to obtainprofiles and contour graphs along the duct and to studyother variables of interest as the density and the behaviorof the water droplets.
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Conclusions & Future Work
• It is recommended to use nozzles that atomize water with a particlediameter of 20 𝜇𝑚, and with the lowest relative humidity.
• Using CFD tool it is possible to identify where can exist corrosionproblems and also it is possible to modify the geometry in order toimprove the mass and heat transfer.
17Figure 8: Corrosion problem in the duct
CFD Modelling of an evaporative Cooling System
Andres Pinilla, Jorge López, Hugo Pineda, Miguel Asuaje, Nicolás Ratkovich
Chemical Engineering Department
Universidad de los Andes. Colombia
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