Orthotropic Materials:

Thermal Characterization and Optimization of Anisotropic Polymer Composite Pin Fins
Avram Bar-Cohen – PI
Raj Bahadur – Graduate Research assistant

Objective:
Develop governing equations that capture the parametric sensitivity of the anisotropic fin and guide the design of such heat sinks.

Background:
Polymer carbon-fiber filled high thermal conductivity composite materials provide a viable alternative for the design of less-energy intense, non-corrosive, and light weight heat sinks and heat exchangers. The low thermal conductivity of polymers can be enhanced by filling the polymer resins with high thermal conductivity carbon fibers. The magnitude of the bulk thermal conductivity increases with the volume percentage of carbon fibers, but it also increases the anisotropy of the thermal conductivity because of the directional orientation of carbon fibers in the matrix. The energy content of the polymer composites increases and mechanical properties degrade with the increase in the carbon fiber percentage in the polymer matrix. Therefore, optimization of the anisotropic thermal conductivity resulting in least volume percentage of carbon fibers is crucial for the success of thermo-mechanical least-energy designs.

The classical Garden Murray assumptions for fin heat transfer analysis include isotropic thermal conductivity as one of the basic assumptions. The high thermal conductivity polymer composite material provides a unique opportunity to revisit the classical fin analysis and relax the isotropic thermal conductivity assumption in fin heat transfer analysis.

Completed Effort:
Experimental data has been obtained for a natural convection-cooled commercial enhanced PPS heat sink.

Current Effort:
The present study is focused on thermal design and least material optimization by including anisotropic thermal conductivity effects for polymer carbon-fiber composite pin-fin arrays.

Research Plan:

• Determine the effect of anisotropic thermal conductivity in the thermal performance of single pin fin by re-deriving single pin fin equation including anisotropic thermal conductivity.
• Study the effect of filler volume percentage and orientation on the anisotropic thermal conductivity value using microscopy and 3? thermal conductivity measurements.
• Characterizing the thermal performance of the high thermal conductivity polymer composite pin fin arrays through analytical, numerical and experimental methods.
• Determine the least material anisotropic pin fin and develop a methodology for anisotropic thermal conductivity based least material pin fin array optimization.
• Experimental – verification of the developed anisotropic thermal conductivity analytical heat transfer equations.

Recent Publications:

Raj Bahadur, Bar-Cohen, "Thermal Design and Optimization of Polymer Based Pin Fin Natural Convection Heat Sinks," Inter Society Conference on Thermal Phenomena, 2004, pp. 268-275.

Bar-Cohen, A., Bahadur, R., Iyengar, M., "Least energy optimization of air cooled heat sinks for sustainability-theory, geometry and material selection", Proceedings of The ASME - ZSIS International Thermal Science Seminar II Bled, Slovenia, June 13 - 16, 2004, pp. 33-51.

Raj Bahadur, Bahgat Sammakia, Frank Andros, "Thermal management of a microdisplay engine assembly," Inter Society Conference on Thermal Phenomena, 2004, pp. 381-388.