An experimental investigation was carried out to study the effect of heater surface preparation on pool boiling of nanofluids. The boiling surface was prepared using different methods: (1) using a diamond turning machine, (2) a conventional lathe machine, and (3) polished using emery sandpaper. The average surface roughness of the diamond turning machined surface was 6 nm and 470 nm for the surfaces prepared using the lathe and sandpaper. The boiling surfaces considered in this study are flat copper surfaces with a diameter of 25.4 mm. Al2O3-Water nanofluids prepared using nanoparticles with an initial size of 10 nm and concentration of 0.05%wt were used throughout the present study. In order to improve the nanofluids stability Sodium dodecylbenzenesulfonate (SDBS) was added to the base fluid (water) with a concentration of 0.1%wt. In order to understand the effect of the nanofluids and the surfactant separately and together, pool boiling experiments using distilled water only, nanofluids, distilled water plus the SDBS surfactant, and nanofluids mixed with SDBS (nanosuspensions) were carried out on clean surfaces. The nanofluids and nanosuspensions boiling experiments were followed by distilled water boiling experiments in order to assess the change of the surface characteristics due to any nanoparticles deposition. The same set of boiling experiments was carried out on each of the three prepared surfaces.
The experimental results indicated that for the smooth and rough machined surfaces, the heat transfer coefficient was increased for the nanofluids and the nanosuspensions with respect to distilled water. Distilled water boiling experiments on the unclean (used) surfaces showed that the heat transfer behavior is almost similar to the distilled water on the clean surface, which indicates that the deposition on the smooth and rough machined surfaces was minimal and hence the enhancement in the heat transfer was due to the change in the thermo-physical properties of the nanofluids and not due to the change in the heater surface condition.
A similar trend was observed in the case of the polished surface in which case nanofluids and nanosuspensions resulted in an enhancement in the rate of heat transfer. However, distilled water boiled on unclean surfaces showed that the boiling curve has shifted to the left compared with the curve of the distilled water on the clean surface. Boiling of distilled water on unclean surfaces showed that the boiling curve was enhanced, which can be attributed to the change in the surface condition and the change in the thermo-physical properties of nanofluids. Photographs of the boiling surfaces and surface measurements taken before and after the nanofluids and nanosuspensions experiments showed that the machined surfaces had less nanoparticles deposition than the sandpaper polished surface. These results indicate that the method of surface preparation has a significant effect on nanoparticles deposition and consequently on the pool boiling heat transfer in which the polished surface tends to have higher number of the active nucleation sites. / Thesis / Master of Applied Science (MASc)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/18201 |
| Date | 11 1900 |
| Creators | Almalki, Naief |
| Contributors | Hamed, M. S., Mechanical Engineering |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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