Limits on Aspect Ratio in TwoFluid MicroScale Heat Exchangers

1
Limits on Aspect Ratio in Two-Fluid Micro-Scale
Heat Exchangers

• Brian K. Paul
• Hadi Hasan
• Joseph Thomas
• Ind/Mfg Engineering
• Oregon State University

Rick D. Wilson David Alman Department of
Energy Albany Research Center Albany, Oregon
2
Introduction

• Microtechnology-based Energy and Chemical Systems
  (MECS) are microfluidic devices that rely on high
  aspect ratio microchannels for their function
• High aspect ratios provide large surface area to
  volume ratios which is critical for improved heat
  and mass transfer
• Miniaturization of centralized energy and
  chemical systems will result in decentralization
  and portability

3
Counter-flow Heat Exchanger
TOP VIEW
End Plate
Header and Channel A
Header and Fin
Header and Channel B
1. Laser Machined 2. Diffusion Bonded
OUT 1
IN 1
IN 2
OUT 2
4
Problem
end plate
channel A
A
A
fin
channel B
fin
Pressing Direction
channel A
fin
channel B
fin
channel A
end plate
CROSS-SECTION AA
5
Problem
Fluid A
Asterisks represent regions not receiving
adequate bonding pressure


Fluid B
Fluid B
pressing direction
Fin
Fluid A
6
Cross-flow Heat Exchanger
end plate
channel B
fin
channel A
fin
Pressing Direction
channel B
fin
channel A
fin
channel B
end plate
Fluid A
Fluid B
7
Problem


pressing direction
8
Theoretical
P
Fluid 1
CHANNEL

FIN

Fluid 2
CHANNEL
FIN
Fluid 1
CHANNEL
P
9
Theoretical
10
Test Articles
11
Results
Diffusion Bonding (750 psi, 800 C, 2 hrs.)
7
6
5
LEAKAGE
4
3
1/4
A100(h)

1/4
3
3
A43.406(h)

2
BONDING
1
0
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
Lamina Thickness, h (mm)
12
Results
13
Conclusions

• There is a limit on fin aspect ratio in
  two-fluid, microchannel heat exchangers based on
  bonding conditions
• Key bonding characteristic in our model is the
  max. in-process deflection, ycomp
• ycomp found to be on the order of 1.95 µm for
  diffusion bonding of 304 SS
• Higher fin aspect ratios can be achieved at
  smaller scales

14
Acknowledgements

• Office of Naval Research
• Young Investigator Program
• Zess Technologies, Inc.
• OSU Micromanufacuring Laboratory
• Stephen Etringer