This project will investigate the use of encapsulated high-pressure water dispersed as Phase Change Material (PCM) in a heat transfer liquid with the intent to simultaneously increase the effective heat capacity and thermal conductivity of the suspending parent fluid. This enhancement is pursued by dispersion of a new class of closed tubular nanovessels, which consist of multi-wall carbon nanotubes filled with water, mostly in its liquid state. Nanotubes as small as a few nanometers in diameter will be used with the ultimate goal to produce a super nanofluid, which features extremely high cooling capacity uniquely suited for microelectronic devices.
Suspensions will be synthesized using large numbers of fluid-filled carbon nanotubes at variable concentrations in several traditional heat transfer fluids, i.e., water, oils and ethylene glycol. The impregnated liquids will be tested for viscosity, quantifying how this property changes with nanotube concentration. The effective heat capacity of the suspensions and its dependence on nanotube concentration will be measured via AC calorimetry. The effective thermal conductivity of the suspensions will be measured as a function of nanotube concentration and encapsulated water content via the transient hot-wire method. Finally, suspension stability will be monitored to create viable PCM fluids. Preliminary theoretical estimates have been made of the relative enhancement of a parent (bulk) fluid heat capacity as a function of the contained water/bulk fluid mass ratio. These estimates suggest that encapsulated-water mass loadings of only a few percent may enhance the heat capacity of the host liquid by up to 50% or even higher. The proposed work will be conducted in collaboration with Argonne National Laboratory where significant expertise on nanofluids exists.
Intellectual merit: The proposed work combines the recently documented advantages of nanofluids (which contain solid nanoparticles) and PCM-fluids (which contain microcapsules encasing other fluids) to synthesize an environmentally friendly nanofluid with superior cooling properties. The problem is rich in terms of fluid transport, heat transfer and phase change phenomena in a closed nanoscale system (filled nanotube) and investigates how a large population of these nanovessels could affect the macroscopic heat transfer properties of conventional heat transfer liquids. The proposed work can be viewed as an attempt to create a composite fluid material with thermal-fluid properties tunable to heat transfer applications where exceedingly high heat fluxes render traditional fluids ineffective.
Broader impacts: The research, if successful, is expected to have a significant impact in creating a new generation of nanofluids, which feature not only superior thermal conductivity but also extremely high specific heat, thus featuring cooling capacity meeting or exceeding the severe requirements of electronic microsystems with ultra-high heat fluxes. To this end, the work will generate a valuable science base and intellectual property of immediate use to industry. UIC personnel will interact with ANL researchers, while aspects of the research will be made accessible to undergraduate students and K-12 teachers through existing NSF-supported sites; the PI currently participates in a REU-NSF Site with 12 undergraduate students, as well as in a RET-NSF program with 9 K-12 teachers. These outreach/training activities will be conducted to highlight the relevance of the studied carbon nanotube systems in addressing real-life heat transfer technological challenges.
