Complex or smart fluids, made of evenly and stably suspended nanoparticles, have been an object of considerable research in the last decade due to their promising applications in a number of applications such as micro-electronic cooling, high power demands in nuclear plants, smaller and more efficient heat exchangers, oil recovery, and transportation. Nanofluids consist of typically less than 100nm sized particles dispersed in base fluids. The heat transfer characteristics of several nano-oxide suspensions in pool boiling with a suspended heating NiChrome wire have been analyzed. The pH value of the nanosuspensions is important from the point of view that it determines the stability of the particles and their mutual interactions towards the suspended heated wire. Heat transfer in silica nanofluids at different acidity and base is measured for various ionic concentrations in a pool boiling experiment. Nanosilica suspension increases the critical heat flux by up to 300% compared to conventional fluids. The l0 nm particles possess a thicker double diffuse layer compared to 20 M particles. The catalytic properties of nanofluids decrease in the presence of salts, allowing the particles to cluster and minimize the potential increase in heat transfer. Nanofluids in a strong electrolyte, i.e., in high ionic concentration, allow a higher critical heat flux than in buffer solutions because of the difference in surface area. The formation and surface structure of the deposition affect the thermal properties of the liquid. When there is no particle deposition on the wire, the nanofluid increases CHF by about 50% within the uncertainty limits, regardless of pH of the base fluid or particle size. The extent of oxidation on the wire impacts CHF, and is influenced by the chemical composition of nanofluids in buffer solutions. The boiling regime is further extended to higher heat flux when there is agglomeration on the wire. This agglomeration allows high heat transfer through inter-agglomerate pores, resulting in a nearly 3-fold increase in burnout heat flux. The pool boiling heat transfer has been even higher (- up to 4 times that of the base fluid) for Double Walled Carbon Nanotubes (DWNTs). A comparison study between Single and Double Walled Carbon Nanotube suspensions has been performed. A closed flow loop has been designed and fabricated to study the thermal transport characteristics of nanosilica suspensions in heated flow. The heat transfer coefficient and pressure drop data are provided for laminar and turbulent regimes (2000
| Identifer | oai:union.ndltd.org:ucf.edu/oai:stars.library.ucf.edu:honorstheses1990-2015-1743 |
| Date | 01 January 2008 |
| Creators | Milanova, Denitsa |
| Publisher | STARS |
| Source Sets | University of Central Florida |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | HIM 1990-2015 |
Page generated in 0.0019 seconds