The Woodruff School

SUMMARY

With continued growth in performance and miniaturization, electronic systems of the future are predicted to generate heat fluxes of over 1 kW/cm2, resulting in strong interest in direct liquid immersion cooling. An ideal heat transfer fluid for direct immersion should be chemically and thermally stable, and compatible with the electronic components. These constraints have led to the use of Novec fluids and fluroinerts as coolants. Although these fluids are chemically stable and have low dielectric constants, they are plagued by low thermal conductivity, about twice that of air, and low specific heat, about the same as that of air. These factors motivate the development of new fluids with improved heat transfer properties for electronics cooling.

Computer-aided molecular design (CAMD) and knowledge-based approaches were combined with figure of merit analysis to systematically design new heat transfer fluids and mixture formulations that exhibit significantly better properties than those of current high performance electronic coolants. Some of the fluids/additives that have been identified using these approaches include C4H5F3O, C4H4F6O, C6H11F3, C4H12O2Si, Methanol, and Ethoxybutane. The heat transfer performance of these new fluids/fluid mixtures is analyzed through pool boiling and flow boiling studies relevant to chip cooling. In general, a high critical heat flux (CHF) is desirable to dissipate high heat fluxes from the chip surface. In addition to using improved heat transfer fluids/fluid mixtures, CHF can be further improved using enhanced surfaces. Pool boiling experiments were performed using mixtures of above new fluids with an existing coolant (HFE 7200) on nanowire coated, and hybrid micro-nanostructured surfaces. All the fluid mixtures tested showed an improvement in the CHF when compared to the base fluid (HFE 7200).

The heat transfer performance of these new fluids is planned to be analyzed further through forced convection boiling studies in microgaps. The bubble dynamics of the fluid mixtures are planned to be studied through computational modeling using the phase field method to acquire a deeper understanding of the physics of boiling of mixtures from enhanced surfaces.

SUBJECT:	Ph.D. Proposal Presentation

BY:	Aravind Sathyanarayana

TIME:	Wednesday, December 12, 2012, 1:00 p.m.

PLACE:	Love Building, 210

TITLE:	Pool and Flow Boiling of Novel Heat Transfer Fluids from Nanostructured Surfaces

COMMITTEE:	Dr. Yogendra Joshi, Chair (ME) Dr. Amyn S. Teja (ChBE) Dr. Mostafa Ghiaasiaan (ME) Dr. Sushil Bhavnani (ME, Auburn University) Dr. Samuel Graham (ME)

SUMMARY With continued growth in performance and miniaturization, electronic systems of the future are predicted to generate heat fluxes of over 1 kW/cm2, resulting in strong interest in direct liquid immersion cooling. An ideal heat transfer fluid for direct immersion should be chemically and thermally stable, and compatible with the electronic components. These constraints have led to the use of Novec fluids and fluroinerts as coolants. Although these fluids are chemically stable and have low dielectric constants, they are plagued by low thermal conductivity, about twice that of air, and low specific heat, about the same as that of air. These factors motivate the development of new fluids with improved heat transfer properties for electronics cooling. Computer-aided molecular design (CAMD) and knowledge-based approaches were combined with figure of merit analysis to systematically design new heat transfer fluids and mixture formulations that exhibit significantly better properties than those of current high performance electronic coolants. Some of the fluids/additives that have been identified using these approaches include C4H5F3O, C4H4F6O, C6H11F3, C4H12O2Si, Methanol, and Ethoxybutane. The heat transfer performance of these new fluids/fluid mixtures is analyzed through pool boiling and flow boiling studies relevant to chip cooling. In general, a high critical heat flux (CHF) is desirable to dissipate high heat fluxes from the chip surface. In addition to using improved heat transfer fluids/fluid mixtures, CHF can be further improved using enhanced surfaces. Pool boiling experiments were performed using mixtures of above new fluids with an existing coolant (HFE 7200) on nanowire coated, and hybrid micro-nanostructured surfaces. All the fluid mixtures tested showed an improvement in the CHF when compared to the base fluid (HFE 7200). The heat transfer performance of these new fluids is planned to be analyzed further through forced convection boiling studies in microgaps. The bubble dynamics of the fluid mixtures are planned to be studied through computational modeling using the phase field method to acquire a deeper understanding of the physics of boiling of mixtures from enhanced surfaces.