© 2008 ANSYS, Inc. All rights reserved. 1 ANSYS, Inc. Proprietary

Advanced Cooling Systems

© 2008 ANSYS, Inc. All rights reserved. 2 ANSYS, Inc. Proprietary

Spray Cooling of a Hot Surface

with Water Droplets

• Spray Angle

• Flow Rate

• Droplet Size

• Initial Droplet Speed

• Droplet Material and Properties

• Droplets Colored by Diameter

(splashing)

• Surface Colored by Temperature

• Planar Cut Shows Concentration

of Water Vapor

© 2008 ANSYS, Inc. All rights reserved. 3 ANSYS, Inc. Proprietary

Micro Channels

• Very Small Hydraulic Diameters ~ 100 m

• Very High Heat Transfer Coefficient

(10,000 < h < 100,000 w/m2K)

• But Very High Pressure Drop!

parallel flow

counter flow

© 2008 ANSYS, Inc. All rights reserved. 4 ANSYS, Inc. Proprietary

Heat Pipes

evaporator adiabatic condenser

vaporliquid

• Passive Device of Very High “Effective” Thermal Conductivity

• Heat is Transferred By:

– Evaporation (evaporator section)

– Convection (adiabatic section)

– Condensation (condenser)

© 2008 ANSYS, Inc. All rights reserved. 5 ANSYS, Inc. Proprietary

Heat Pipes Case Study

Temperature Pressure

liquid flow

vapor

flow

Vadakkan et al. “Transient Analysis of flat heat pipes”, SHTC, HT2003-47349

© 2008 ANSYS, Inc. All rights reserved. 6 ANSYS, Inc. Proprietary

Multiphysics

Cooling Systems

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Piezoelectric Fan

• Piezoelectric Fan

– Spot cooling for electronic components

– Low magnetic permeability

– Blade driven by piezoelectric bimorph

Blade

Bimorph

FR4 Board

Finite Element Mesh

Two piezoelectric

layers with opposing

polarity

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Piezoelectric Fan

• Results

– Fan Driven at Resonance

– 115Volts at 60 Hz

+VinFixed

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Thermoelectric Cooler

• Multistage Thermoelectric Cooler

– Thermal-electric coupling

• n-type and p-type semiconductors

20 Amps

Ground

Cold Side

(Heat Absorbed)

Hot Side (Heat Rejected)

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Thermoelectric Cooler

• Thermoelectric Results

– Thermal gradient in Peltier blocks

Hot Side (Heat Rejected)

Cold Side (Heat Absorbed)

Temperature

Electric

Potential

Current

Density

© 2008 ANSYS, Inc. All rights reserved. 11 ANSYS, Inc. Proprietary

Thermoelectric Cooler

• Optimization

– Response surface and sensitivity