Nanoengineered Membrane-based Absorption Cooling for Buildings using Unconcentrated Solar and Waste Heat   

Critical Need: Development of an inexpensive and high performance heat-powered cooling system greatly expands utilization of solar-thermal energy and low-grade waste heat for cooling buildings and process fluids and improves the economics of energy efficient combined cooling, heat, and power (CCHP) systems. Two-thirds of the fuel used in the world is wasted in the form of heat. Solar energy is harnessed with only close to 20% efficiency and the rest becomes waste heat. Thus, efficient utilization of low quality heat has a revolutionary impact on our future energy economy and carbon emission.





Project Innovations + Advantages: Absorption refrigeration systems (ARS) are fundamentally attractive for our future energy economy because they can convert low quality heat energy to cooling at the highest efficiency compare to other technologies.
 
A typical ARS consists of large heat exchangers that constitute most of the system size and cost. The transport processes within the heat exchangers are responsible for their bulkiness. In this work, nanoengineered membranes are implemented to greatly enhance the transport processes. The membrane-based heat exchangers are integrated together into new configurations with significantly higher surface area per volume compare to the existing technology. The new system configuration along with the advance material and manufacturing technologies that the new generation ARS benefits from promise an inexpensive, reliable, and low maintenance ARS.

The latest experimental data on laboratory-scale system elements suggest that the heat exchangers of a high performance ARS can be made at an order of magnitude smaller size and cost compare to the existing systems. Also, the volume of the Li-Br solution in the new generation system is an order of magnitude less than that of the existing systems. 



Atomic-scale Design and Manufacturing of a New Generation Direct Methanol Fuel Cell (DMFC) Membrane Electrode Assembly (MEA)

Critical Need:
Direct methanol fuel cell (DMFC) is the most promising type of fuel cell for portable applications and, to the best of our knowledge, the only fuel cell that has been successfully commercialized. High energy density of methanol, facility of its storage, and its direct oxidation on the anode catalyst are the main reasons for the great potential of DMFCs as an alternative energy source for portable applications. The existing DMFC membrane electrode assemblies (MEAs) deliver a low power density (an order of magnitude less than the hydrogen fuel cells). At the heart of the problem are deficiencies of the existing MEAs that suffer from
a) slow kinetics of methanol electro-oxidation on anode,
b) limited operating temperature,
c) significant methanol permeation through the membrane (i.e. fuel crossover), particularly at high fuel concentrations, and
d) high water permeation through the membrane and cathode water congestion.

Project Innovations + Advantages:
In a recent study Moghaddam et al. (“An Inorganic-Organic Proton Exchange Membrane for Fuel Cells with a Controlled Nanoscale Pore Structure,” Nature Nanotechnology, vol. 5, pp. 230-236, 2010) demonstrated that through tailoring the material construct in atomic level the common deficiencies of the fuel cell MEAs could be alleviated. The membrane developed by Moghaddam et al. was engineered to achieve high power density with dry H2 supply at very low humidity ambient. The membrane delivered one order of magnitude higher performance than in the previous studies. The focus of this effort is to dramatically enhance kinetics rate through surface/interface nano-structuring and tailoring the proton selective layer construct to minimize fuel and water transport. 



Probing Interfacial Phase-Change Transport Events in Flow Boiling on Micro- and Nano-textured Surfaces

Critical Need:
Heat removal from confined spaces in modern applications has generated significant interest in implementing flow boiling in channels that are an order of magnitude smaller than the large tubes used in traditional boiling applications (i.e. microchannels). A main focus of the scientific community for nearly two decades has been to enhance the boiling heat transfer coefficient in microchannels. However, a major obstacle is the relatively limited understanding of transport characteristics, which is caused by the difficulties of diagnosing interfacial behavior in small channels. Advancing both scientific understanding and engineering practice in this field requires experimental capabilities with high-resolution characterization of the underlying interfacial processes. Transformative improvements in the understanding, prediction, and control of phase change heat transfer may come from the development of new mechanistic models, with inspiration and validation from experimental techniques that can probe temperature and heat flux with sufficient sensitivity over all relevant length and time scales.

Project Objective:
Project Objective: The major focus of this project is to use a new measurement approach to understand the physics of different microscale heat transfer mechanisms involved in flow boiling in microchannels and to measure their relative contributions to the overall surface heat transfer. The proposed approach involves a high-resolution measurement of the thermal field (temperature and heat flux) at the fluid-solid interface in microchannels. The unique aspect of the proposed measurement approach is the implementation of a composite wall with embedded micro-sensors that allow the surface heat flux to be determined. The thermal field measurements are synchronized with the high-speed imaging of bubbles as well as the thickness of the liquid film formed between the vapor and solid phases. The laser interferometry method is utilized in measuring the liquid film thickness. Experimental studies will be conducted to explain the mechanisms of heat transfer in flow boiling in microchannels, evaluate the accuracy of prominent mechanistic two-phase microchannel models, and understand the role of surface micro- and nanostructures on the interfacial transport events and flow boiling characteristics.  

Electrokinetic Dewatering of Phosphatic Clay Suspensions

Will be updated shortly