- Title
- Advanced applications of tunable magnetite nanofluids in energy systems and energy harvesters
- Creator
- Alam, Mohammad Khairul
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2018
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The properties of nanofluids have the potential to provide a wide range of resources to overcome energy associated difficulties, in addition to offering new ways to gain, store and exchange of energy. A significant improvement in energy saving is possible by improving the performance of a heat exchanger circuit and may in part alleviate current challenging issues such as global warming, climate change and the fuel crisis. Ferrofluids or Magnetic nanofluids are the suspensions of magnetic nanoparticles and non-magnetic base fluid. Ferrofluids have drawn considerable attention due to the possibility of tuning their heat transfer and flow properties through the application of an external magnetic field. They can also be utilised to improve the performance of an energy harvester, which can supply power and enhance the capability, assertion and lifespan of those devices where batteries or direct electricity are currently used as the primary source of power. Electromagnetic ferrofluid based energy harvesters convert the ferrofluids’ sloshing movement into electromotive force (EMF), hence it is necessary to estimate the feasibility, stability and efficacy of ferrofluids through several physico-chemical studies. This study is divided into five different sections. Initially, we look at the preparation of various conventional metal oxide nanofluids, their stability and thermophysical properties. Secondly, the heat transfer performance of these conventional nanofluids under various flow conditions as well as the different amount of surfactant in the nanosuspensions is considered. Then the focus is shifted to the specific case of magnetite nanofluids, which includes the preparation and characterisation of magnetite nanofluid. This is followed by the heat transfer performance measurement of this colloid compared to the conventional nanofluids by varying the external magnets configurations. Finally, different types of magnetite nanofluids are implemented in vibration-based energy harvester. Stability of nanofluids is a major concern in heat transfer applications. The objective of this work is to prepare a stable Al2O3/DI-water, CuO/DI-water and Fe3O4/DI-water nanofluids with the aim of applying them in the novel heat transfer applications as well as energy harvester devices. This study is investigated the overall stability of Al2O3 and CuO nanofluids with respect to pH, zeta potential, particle size distribution and its effect on viscosity and thermal conductivity at various weight concentrations of anionic surfactants (sodium dodecylbenzene sulfonate). The results clearly showed that nanofluid’s stability has a strong effect on viscosity and thermal conductivity of these colloids. The stability of the nanofluids is enhanced with a decrease in viscosity and an increase in thermal conductivity. Furthermore, water based polymer coated Fe3O4 nanofluids are prepared by using a chemical precipitation method. The thermogravimetric analysis (TGA) and differential thermal gravimetry (DTG) have been carried out to determine the chemical and physical changes of ferrofluids due to the thermal effect. Besides, X-ray diffraction (XRD) was employed to identify the crystal structure of Fe3O4 nanoparticle. The stability and physico-chemical properties of Fe3O4 particles were also investigated. The results showed that the synthesised nanoparticles are magnetite and shows a very good stability (more than two months). A linear relationship is also found among the dosing rate of ammonium hydroxide, nanoparticle size distribution, viscosity and thermal conductivity. Higher dosing rates of ammonium hydroxide reagent during the preparation of nanoparticles resulted in an increase in the average particle size. A circulating rig is built to conduct the convective heat transfer experiments under constant heat flux boundary condition. The convective heat transfer performance and exergy loss of Al2O3/DI-water, CuO/DI-water and Fe3O4/DI-water nanofluids flowing through a straight vertical tube are experimentally investigated under laminar, transitional and turbulent flow regimes. The effect of external magnetic field on heat transfer performance and pumping power of Fe3O4 nanofluids under the laminar and turbulent flow regimes are studied. The experiments are also conducted at various mass flow rates with different nanofluids’ weight fractions and input powers. The results confirm an improvement in the convective heat transfer coefficient for both Al2O3 and CuO nanofluids compared to DI-water at all flow conditions. The maximum enhancement of 25% in heat transfer coefficient was observed for the 0.50 wt% CuO/DI-water nanofluid. The pumping power of alumina and copper oxide nanofluids was similar to that of DI-water under laminar flow condition, however, the difference in pumping power is more pronounced under the transitional and turbulent flow regimes. On the other hand, the enhancement in local heat transfer coefficient of magnetite nanofluids is more pronounced by introducing more magnets on the tube of the test section, especially in the turbulent flow regime. In addition, the effect of the magnetic field was not significant on the increment of pressure loss. Moreover, when comparing the results of aluminium oxide and copper oxide nanofluids, the highest energy efficiency is found to be 84% with 12.8% and 3.45% average reduction in exergy loss for 0.50 wt% of CuO/DI-water nanofluid in laminar and turbulent flow conditions, respectively. However, the highest performance index and lowest exergy loss were found for external magnets configurations in case of ferrofluids at 0.25 wt% of magnetite nanoparticles. New correlations are proposed based on the experimental results for conventional nanofluids, which can predict the Nusselt number for Al2O3 and CuO nanofluids under the fully laminar and turbulent flow regimes with high accuracy. The rise in heat transfer of ferrofluids is assumed to be the result of Fe3O4 nanoparticle accumulation near the ring magnets due to the magnetic fields, which may lead to a local thermal conductivity improvement. This aggregation formation enhancing the momentum and energy transfer in the fluid flow. This study also examined the concept and implementation of an energy harvesting device which utilises ferrofluids sloshing movement to convert mechanical vibration directly into electromotive force (EMF). Unlike traditional electromagnetic generators that implement a solid magnet, ferrofluids can easily change shape and respond to very small vibrations. The results demonstrated that variations in the container volume and volume concentrations of nanoparticles influence the output power of the electromagnet energy harvester. The output power by using the container 2 (cylindrical shape, large height and small diameter) demonstrated about 85.50% and 24.60% greater than the container 1 (cylindrical shape, small height and large diameter) for 3vol% and 4vol% of ferrofluids, accordingly. Besides, a significant enhancement in output power is obtained for 4vol% of Fe3O4/DI-water nanofluid in container 2. Therefore, the magnetite nanofluids might be a good candidate for heat transfer as well as vibration energy harvesting applications because of their superior features in comparison to other classes of conventional nanofluids.
- Subject
- tunable magnetite nanofluids; energy systems; energy harvesters
- Identifier
- http://hdl.handle.net/1959.13/1385053
- Identifier
- uon:32161
- Rights
- Copyright 2018 Mohammad Khairul Alam
- Language
- eng
- Full Text
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