The Woodruff School

SUMMARY

Pool boiling is a very effective energy transfer mechanism, which is used in a variety of industrial applications such as heat exchangers, power generation, and cooling of high-power electronics. While large heat transfer coefficients can be realized through pool boiling, the enhancement of the heat transfer coefficient and critical heat flux are of interest to improve the efficiency of the heat transfer mode. The enhancements of pool boiling can obtained by controlling the surface wettability and by patterning surface features, controlling micro/nano porosity, as well as patterning the surface energy through chemical functionalization. In this study pool boiling experiments will be conducted on copper surfaces with patterned hierarchical features (porous and nonporous) to determine how the morphologies impact the pool boiling properties and to introduce flow path control in order to maximize the heat transfer coefficient and critical heat flux (CHF). This will be accomplished by investigating the boiling curve for DI water on flat, micromachined, and micro-porous copper surfaces (spherical particles, 125-150 μm). The surfaces were tested as-fabricated by coating them with hydrophilic nanoparticles (25 nm SiO2) to increase surface wetting, and by machining channels into the coated surfaces to control vapor and liquid flow paths. Additional functionalization using hydrophobic surface treatments will also be studied. Preliminary data regarding the number of micromachined channels in porous copper show that the CHF can be increased over 100% and boiling heat transfer coefficient over 200% when compared to a porous coating without channel features. This result also corresponds to more than 400% increase in CHF and 300% increase in boiling heat transfer coefficient over those of flat surfaces. This large enhancement is believed to be attributed to the effective removal of the partial dry-out within the patterned porous copper as well as the separation of liquid and vapor flow over the surface. While the use of the hydrophyllic nanoparticles shows very little impact on the microporous surfaces, it shows a noticeable enhancement on the solid microchannel surface from the preliminary study. Additonal work will be conducted to understand the fundamental nature of the two phase heat transfer in terms of surface texturing including the impact of chemical functionalization.

SUBJECT:	Ph.D. Proposal Presentation

BY:	Min Seok Ha

TIME:	Wednesday, December 14, 2015, 12:00 p.m.

PLACE:	MRDC Building, 4404

TITLE:	Mechanical and Chemical Texturing of Surfaces to Enhance Two Phase Heat Transfer

COMMITTEE:	Dr. Samuel Graham, Chair (ME) Dr. Yogendra Joshi (ME) Dr. Mostafa Ghiaasiaan (ME) Dr. Dennis Hess (ChBE) Dr. Jacopo Buongiorno (MIT)

SUMMARY Pool boiling is a very effective energy transfer mechanism, which is used in a variety of industrial applications such as heat exchangers, power generation, and cooling of high-power electronics. While large heat transfer coefficients can be realized through pool boiling, the enhancement of the heat transfer coefficient and critical heat flux are of interest to improve the efficiency of the heat transfer mode. The enhancements of pool boiling can obtained by controlling the surface wettability and by patterning surface features, controlling micro/nano porosity, as well as patterning the surface energy through chemical functionalization. In this study pool boiling experiments will be conducted on copper surfaces with patterned hierarchical features (porous and nonporous) to determine how the morphologies impact the pool boiling properties and to introduce flow path control in order to maximize the heat transfer coefficient and critical heat flux (CHF). This will be accomplished by investigating the boiling curve for DI water on flat, micromachined, and micro-porous copper surfaces (spherical particles, 125-150 μm). The surfaces were tested as-fabricated by coating them with hydrophilic nanoparticles (25 nm SiO2) to increase surface wetting, and by machining channels into the coated surfaces to control vapor and liquid flow paths. Additional functionalization using hydrophobic surface treatments will also be studied. Preliminary data regarding the number of micromachined channels in porous copper show that the CHF can be increased over 100% and boiling heat transfer coefficient over 200% when compared to a porous coating without channel features. This result also corresponds to more than 400% increase in CHF and 300% increase in boiling heat transfer coefficient over those of flat surfaces. This large enhancement is believed to be attributed to the effective removal of the partial dry-out within the patterned porous copper as well as the separation of liquid and vapor flow over the surface. While the use of the hydrophyllic nanoparticles shows very little impact on the microporous surfaces, it shows a noticeable enhancement on the solid microchannel surface from the preliminary study. Additonal work will be conducted to understand the fundamental nature of the two phase heat transfer in terms of surface texturing including the impact of chemical functionalization.