Flow across bank of tubes

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Flow across bank of tubes

• Mathilda Lindén
• Emma Wingstedt

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Introduction

• Relevant in many industrial applications
• Steam generation in a boiler
• Heat exchanges
• Air cooling in an air conditioner
• Dominated by boundary layer separation and wake
  interactions

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Introduction

• Different grids
• Different tube arrangements
• Different fluids
• Different Reynolds number

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Grid

• Coars grid, 1021 nodes
• Fine grid, 6924 nodes
• Superfine grid, 8522 nodes

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Tube arrangement

• Staggered

• Aligned

ST 0.2 m, SL 0.15 m and D 0.1 m
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Boundary conditions

• Walls with constant temperature (400K)
• Symmetry
• Periodic with given inlet massflow and
  temperature (300K)

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Grid dependence

• No wall-functions used
• y lt 5 required

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Convergence
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Grid convergence
Coarse grid
Fine grid
Velocity profiles
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Turbulence model

• k-? SST
• k-? standard
• k-e realizable

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Result
Velocity profile
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Nusselt number

• Stagnation point at ?0
• Minimum at ?115

Experimental result for Lienhard
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Staggered vs. Aligned
Velocity profiles
Temperature profiles
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Air vs. Water
Velocity profile
Temperature profile
Air on top and water below
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Long case

• 5 tubes in staggered arrangement
• ST 0.032m, SL 0.036m, D 0.016m
• Velocity inlet 6m/s
• Pressure outlet

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Pressure drop
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Velocity profile
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Validation
Nusselt number based on average heat transfer
coefficient over any particular isothermal tube

Correlation for tube-bundle heat transfer
(Lienhard)

where
The simulated Nusselt number were calculated as
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Nu for different Re
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Conclusions

• A fine grid close to the wall is required due to
  boundary layer separation
• Nusselt number along a tube wall shows
  approximately the same result as other experiment
• Validation shows an overprediction of Nusselt
  number compared to correlation