Investigation of the performance of aluminium oxide (Al2O3) Nano transformer oil in a transformer heat exchanger.
Khoza, Macduff
Khoza, Macduff
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Abstract
The use of plate heat exchangers, heat extruders and blowing fans is identified as a best technology to perform the cooling duties in transformers. The use of this technology is found to have limitations because it does not directly improve the thermal properties of the cooling fluids. Moreover, the use of base fluid that has limited thermal properties cannot add value to the installed cooling equipment. The investigation of enhancing the fluid's thermal characteristics by including nanoparticles was presented as a solution to this problem. This investigation will employ Al2O3 nanoparticles since they have demonstrated a noteworthy effect on enhancing the fluid's thermal characteristics. The Al2O3/nano-transformer oil is regarded as one of the most compatible nanofluids that can function well in transformers. Reason being Al2O3/nanofluids are rich in insulation properties, heat resistance and possess high thermal characteristics. The information gathered for this study outlines the contribution made by Al2O3/nanoparticles in improving the thermophysical properties of the pure transformer oil (mineral). To understand the effect of nanoparticle volume concentration in Reynolds and Prandtl numbers, a comparison study was conducted using nanofluids from low to a higher volume concentration. The investigation is conducted at the spectrum of increasing in nanoparticles volume concentration as discussed below. The measured scale of increment is set to be 0.004, 0.006, 0.008, 0.01 and 0.015% by volume. The Al2O3/nanoparticle used is 50nm in size. The amount of pure transformer oil used to produce nanofluids is 15 litres as restricted by capacity of the oil reservoir. The experimental setup was validated with the percentage error of 3.6% that pumps the nanofluid at the increasing volume flow rate of 0.2, 0.3, 0.4, 0.5 and 0.6L/min. The safe operating temperature range starting from 35, 40, 45, 50, 55, 60, 65 to 70oC is used in the experiment. The addition of Al2O3/nanoparticles has improved the viscosity of the transformer oil by 0.017kgm-s at 0.015vol. % at a consistent notation. The maximum percentage increase in density and thermal conductivity is calculated to be 0.5% and 0.44% respectively. When compared to transformer oil, the specific heat capacity of nanofluids requires 3.3% less energy to heat up. The nanofluid heat transfer coefficient improved to a maximum of 6901.7W/m2 K at 35oC, 0.6L/min and 0.01vol. %. The overall heat transfer coefficient increased with the increase in volume concentration and volume flow rate in all temperatures. The highest increase recorded is 91.855W/m2 K at 0.6L/min and 0.01vol. %. The percentage increase in average heat transfer rate for a temperature of 35 and 60oC is 9% and 8% at 0.6L/min and 0.015vol. % respectively. The volume concentration of 0.006vol. % is found to be the most employable particle load in high temperatures of 60 to 70oC. This volume maintained the constant increase in Nusselt number resulting with the maximum percentage increase of 33%. The increase in Nusselt number is triggered by the increase in Reynolds number and nanofluid volume flow rate. The Reynolds number of 33.67 increased the Nusselt number to a value of 326.2 when the operating temperature is 35oC and 0.01vol %. The study outlines that low particle volume concentration can significantly enhance the Reynolds number whereases high concentration is the best in improving the Prandtl number. In this study the volume concentration of the nanoparticles is kept low to avoid slurry fluid or increase in viscosity. In this regard the Prandtl number of the transformer oil decreased with the increase in volume concentration. However, some base fluid like water displayed an increase in Prandtl when the volume concentration is increased. From the results it can be concluded that the most influential nanoparticle volume concentration in thermophysical properties of the transformer oil is 0.01vol. % with the varied volume flow rate of 0.2 to 0.6L/min. However, the volume concentration of 0.01vol. % is seen to lose its performance when the temperature is increased from 60 to 70oC. The volume concentration of 0.006vol. % resulted with nanofluids that are more stable in high temperatures. In this regard Al2O3/nanoparticles can be counted amongst those nanoparticles that have an effect in thermal applications where transformer oil is treated as a base fluid.
Description
Submitted in partial fulfilment of the requirements for the degree, Master of Engineering: Mechanical Engineering in the Department of Mechanical and Mechatronics Engineering in the
Faculty of Engineering and the Built Environment at the Tshwane of University of Technology.
Date
2023-09-10
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Tshwane University of Technology
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Keywords
Aluminium oxide, Nanofluids, Nanoparticles