The Woodruff School

SUMMARY

Zeotropic mixtures exhibit a temperature glide between the dew and bubble points during condensation. This glide has the potential to increase system efficiency when matched to the thermal sink in power generation, chemical processing, heating and cooling systems. Further improvements in energy efficiency can be realized by designing heat transfer components with mini- and microchannels. However, it has been shown that the concentration gradients arising from the changing composition of the vapor and liquid phases during condensation introduce additional mass transfer resistances, degrading the overall heat transfer. Furthermore, the coupled heat and mass transfer of mixtures at the mini- and microscale is not well understood.

Thus, experiments will be conducted with ammonia/water (NH3/H2O) mixtures at varying ammonia concentration (80-100%), which typically exhibit very high temperature glides of 50 to 95 K, mass flux (50 ≤ G ≤ 200 kg m-2 s-1) and tube diameter (0.98 ≤ D ≤ 2.16 mm). A technique for calculating condensation heat duty for discrete increments of quality within the two-phase region will be developed. In addition, the proposed work will quantify the local liquid film heat transfer coefficient by accounting for mass transfer through a film model approach. This will allow the relative dominance of the vapor and liquid heat and mass transfer resistances to be quantified. The proposed approach represents a departure from the work in literature, where the combined heat and mass transfer resistances from experiments are generally aggregated into an �apparent� heat transfer coefficient. By isolating the heat transfer resistance of the liquid phase, the results can be compared with those for single-constituent fluids and corresponding models for condensation in small channels. This will enable the development of a more general predictive method that is valid for both single and multi-constituent fluids with varying properties. The results of the study will guide the design of highly efficient, compact heat transfer equipment.

SUBJECT:	Ph.D. Proposal Presentation

BY:	Brian Fronk

TIME:	Tuesday, August 27, 2013, 1:00 p.m.

PLACE:	Love Building, 210

TITLE:	Coupled Heat and Mass Transfer During Condensation of High Temperature Glide Zeotropic Mixtures in Small Channels

COMMITTEE:	Dr. Srinivas Garimella, Chair (ME) Dr. S. Mostafa Ghiaasiaan (ME) Dr. Yogendra Joshi (ME) Dr. Tom Fuller (ChBE) Dr. Krista Walton (ChBE)

SUMMARY Zeotropic mixtures exhibit a temperature glide between the dew and bubble points during condensation. This glide has the potential to increase system efficiency when matched to the thermal sink in power generation, chemical processing, heating and cooling systems. Further improvements in energy efficiency can be realized by designing heat transfer components with mini- and microchannels. However, it has been shown that the concentration gradients arising from the changing composition of the vapor and liquid phases during condensation introduce additional mass transfer resistances, degrading the overall heat transfer. Furthermore, the coupled heat and mass transfer of mixtures at the mini- and microscale is not well understood. Thus, experiments will be conducted with ammonia/water (NH3/H2O) mixtures at varying ammonia concentration (80-100%), which typically exhibit very high temperature glides of 50 to 95 K, mass flux (50 ≤ G ≤ 200 kg m-2 s-1) and tube diameter (0.98 ≤ D ≤ 2.16 mm). A technique for calculating condensation heat duty for discrete increments of quality within the two-phase region will be developed. In addition, the proposed work will quantify the local liquid film heat transfer coefficient by accounting for mass transfer through a film model approach. This will allow the relative dominance of the vapor and liquid heat and mass transfer resistances to be quantified. The proposed approach represents a departure from the work in literature, where the combined heat and mass transfer resistances from experiments are generally aggregated into an �apparent� heat transfer coefficient. By isolating the heat transfer resistance of the liquid phase, the results can be compared with those for single-constituent fluids and corresponding models for condensation in small channels. This will enable the development of a more general predictive method that is valid for both single and multi-constituent fluids with varying properties. The results of the study will guide the design of highly efficient, compact heat transfer equipment.