performance of pyramidal fin arrays
TRANSCRIPT
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Performance of
Pyramidal Fin ArraysYannickCormier
April 12th,2013
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Outline
Background
Objectives
Experimental Procedure and Testing
Calculation Method
Heat Transfer and Pressure Drop Results
Conclusion
2
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Background Heat Exchanger
Important parameters of an heat exchanger
Heat transfer Pressure drop across the fin array Dimensions
Background 3
Global Heat Transfer, Cooler Design, http://www.ghtthx.com/Design.aspx , Consulted March2013
http://www.ghtthx.com/Design.aspxhttp://www.ghtthx.com/Design.aspxhttp://www.ghtthx.com/Design.aspxhttp://www.ghtthx.com/Design.aspx -
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Background Straight Cut
Braytons Wire Mesh Heat Exchanger (WMHE) with
straight cut fins
Background 4
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Background Pyramidal Fins
Manufactured using cold spray
Pure aluminium Good thermal conductivity
Melting point at 933 K
Stainless steel 304L Melting point at 1673 K
Background 5
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Background - Nomenclature
The nomenclature used to characterize the fin array tested
12x12x0.035x1.3 AlFin per inch (x axis)
Z
X
Fin per inch (z axis)
Wire diameter in inches Fin height in millimeters
Fin material
Background 6
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Background - Nomenclature
Background 7
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Objectives
Characterize the heat transfer and pressure dropperformances of the pyramidal fins
Compare these performances with traditional fins (straight
cut currently used at Brayton Energy Canada)
Help the design process by providing accurate empirical
correlations
Objectives 8
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Experimental Procedure
Fin Sample
2" x 2" Sample 2" x 4" Sample
PureAluminium Stainless Steel304L PureAluminium Stainless Steel304L
Thermal
Conductance &Total Pressure
Drop
Fin Pressure
Drop
Friction Factor
Experimental Procedure and Testing 9
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Experimental Procedure Pressure Drop
Total Pressure Drop for a 2" x 2" Sample
Fin Pressure Drop on 2" x 4" Sample
10Experimental Procedure and Testing
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Testing Apparatus
Experimental Procedure and Testing 11
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Testing Apparatus Accuracy
Comparison with Kays and London experiment for an
unfinned surface (flat plate) Maximum of 20% of error on the Colburn factor
0 1 2 3 4 5 6 7 8 9 100.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
0.018
ExperimentalResults
Kays andLondonExperimentalResults
ReD
StPr2/3
Experimental Procedure and Testing 12
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Calculations Method Heat Transfer
Reynolds
Number
Hydraulic Diameter
Heat Transfer
Coefficient
Log Mean Temperature
Difference
Calculation Method 13
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Calculations Method Heat Transfer
Thermal
Conductance
Heat Flux
Colburn FactorNusselt Number
Calculation Method 14
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Heat Transfer (HT) Results
Traditional straight cut fins are presently used at Brayton
Energy Canada
The theory of bank of tubes is similar to the pyramidal fintested in the point of view of their discontinuity
Pyramidal FinsStraight Cut Fins Bank of Tubes
Heat Transfer and Pressure Drop Results 15
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0 1 2 3 4 5 6 7 8 9 100
2
4
6
8
10
12
14
1618
20
12x12x0.035x1.35Al
ReD
Nu
HT Results- Bank of Tubes
ukauskas separated data in three regimes: Laminar (0 < < 1000) Sub-critical ( 500 < < 200 000) Critical ( > 200 000)
Sub-critical
Heat Transfer and Pressure Drop Results 16
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HT Results Comparison with traditional fin
0 1 2 3 4 5 6 7 8 9 100
50
100
150
200
250
300
350
400
24x24x0.014x1.4 Al
Straight Cut Al
ReD
h(W/m2K)
Sub-critical regime
Heat Transfer and Pressure Drop Results 17
Laminar regime
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HT Results Comparison with traditional fin
Higher convective heat transfer coefficient due to theincrease in turbulence
Pyramidal Fins Straight Cut Fins
Heat Transfer and Pressure Drop Results 18
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19
0 1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
2.5
Unfinned Surface
12x12x0.035x1.8 Al
16x16x0.028x2.2 Al
24x24x0.014x1.4 Al
ReD
UA(W/K)
0 1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
2.5
ReD
UA(W/K)
Fin density effect on the aluminium samples
Higher fin density results in better thermalconductance
HT Results Aluminium Fins
Heat Transfer and Pressure Drop Results
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HT Results Stainless Steel Fins
Fin density effect on the stainless steel samples Same trend as aluminium samples
Heat Transfer and Pressure Drop Results 20
0 1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
2.5
Unfinned Surface12x12x0.035x2.0SS16x16x0.028x1.5SS24x24x0.014x1.1SS
ReD
UA(W/K)
0 1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
2.5
ReD
UA(W/K)
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HT Results Aluminium Fins
Height effect on the aluminium samples
Heat Transfer and Pressure Drop Results 21
0 1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
2.5
Unfinned Surface12x12x0.035x1.8 Al
12x12x0.035x2.4 Al
12x12x0.035x1.3 Al
ReD
UA(W/K)
0 1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
2.5
ReD
UA(W/K)
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HT Results Aluminium Fins
Compromise between the heat transfer convective
coefficient (h) and the total area (Atot)
Heat Transfer and Pressure Drop Results 22
0 1 2 3 4 5 6 7 8 9 100
100
200
300
400
500
600
700
Unfinned Surface
12x12x0.035x1.8Al
12x12x0.035x2.4Al
12x12x0.035x1.3Al
ReD
h(W/m2K)
0 1 2 3 4 5 6 7 8 9 100
100
200
300
400
500
600
700
ReD
h(W/m2K)
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HT Results Aluminium Fins
Compromise between the heat transfer convective
coefficient (h) and the total area (Atot)
Heat Transfer and Pressure Drop Results 23
ReD = 500
ReD = 1500
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HT Results Stainless Steel Fins
Height effect on the stainless steel samples
Heat Transfer and Pressure Drop Results 24
0 1 2 3 4 5 6 7 8 9 100.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
Unfinned Surface
12x12x0.035x1.0 SS
12x12x0.035x1.4 SS
12x12x0.035x1.9 SS
12x12x0.035x2.0 SS
ReD
UA(W/K)
0 500 1000 1500 2000 2500 30000.0
0.5
1.0
1.5
2.0
ReD
UA(W/K)
0 1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
ReD
UA(W/K)
0 1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
ReD
UA(W/K)
0 1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
ReD
UA(W/K)
0 1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
ReD
UA(W/K)
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HT Results Aluminium vs. Stainless Steel
Aluminium is more efficient in terms of heat transfer for
the same fin geometry
0 1 2 3 4 5 6 7 8 9 100.0
0.5
1.0
1.5
2.0
2.5
Unfinned Surface
12x12x0.035x1.3 Al
12x12x0.035x1.4 SS
ReD
UA(W/K)
Heat Transfer and Pressure Drop Results 25
Pressure Drop (PD) Results
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Pressure Drop (PD) Results Comparison with traditional fin
Similar total pressure drop even if the thermal conductance
for the pyramidal fin is higher
Heat Transfer and Pressure Drop Results 26
0 2 4 6 8 10 12 14 160
1000
2000
3000
4000
5000
6000
7000
24X24X0.014X1.4 Al
Straight Cut Al
ReD
DifferentialPressure(Pa)
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PD Results Total Aluminium
Better thermal conductance results in higher pressure
drop
Heat Transfer and Pressure Drop Results 27
0 500 1000 1500 2000 2500 30000
1000
2000
3000
4000
5000
6000
Unfinned Surface
12x12x0.035x1.8 Al
16x16x0.028x2.2 Al
24X24X0.014X1.4 Al
ReD
DifferentialPressure(P
a)
0 500 1000 1500 2000 2500 30000
1000
2000
3000
4000
5000
6000
ReD
DifferentialPressure(Pa)
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0 500 1000 1500 2000 2500 30000
1000
2000
3000
4000
5000
6000
7000
Unfinned Surface
12x12x0.035x1.8 Al
12x12x0.035x2.4 Al
12x12x0.035x1.3 Al
ReD
DifferentialPressure(Pa)
PD Results Total Aluminium
Heat Transfer and Pressure Drop Results 28
Height effect on the aluminium samples
0 500 1000 1500 2000 2500 30000
1000
2000
3000
4000
5000
6000
7000
ReD
DifferentialPressure(Pa)
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PD Results Friction Factor
Useful design tool Similar to the Moody chart
Laminar drop at low Reynolds number Close to constant friction factor in the turbulence
region
Heat Transfer and Pressure Drop Results 29
0 2 4 6 8 10 12 14 160.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
12x12x0.035x1.3 Al
16x16x0.028x1.4 Al
24x24x0.014x1.8 Al
ReD
DarcyFrictionFactor(f)
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Conclusion
The pyramidal fins outperform traditional straight cut
fins at the same fin density while having the samepressure drop
For the pyramidal fins, higher thermal conductanceresults in higher pressure drop, which is expected
Fin density increases the thermal conductance andthe pressure drop
Fin height influence depends on the compromisebetween the total area and the convective heat
transfer coefficient
Conclusion 30
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Future Work
Need an efficiency index that includes the thermal
performance and the pressure drop effects
Obtain samples at same height with different fin
densities
Conclusion 31