Convective heat transfer characteristics of nanofluids

• Main Author: Ho, Jin Yao.
• Other Authors: Leong Kai Choong
• Format: Final Year Project
• Language: English
• Published: 2010
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics
• Online Access: http://hdl.handle.net/10356/40356
• Institution: Nanyang Technological University

In this report, the potential use of nanofluids as coolants has been experimentally investigated. A miniature heat exchanger system was fabricated to examine the convective heat transfer performances of the nanofluids under constant wall temperature and laminar flow conditions. The whole experimental setup is an open loop system whereby the flow rates of the nanofluids, corresponding to 54 < Re < 505, are controlled by two syringe pumps. A total of four different types of nanofluids were tested namely Au nanofluid with deionized water as base fluid, Al2O3 with deionized water as base fluid, Al2O3 with ethylene glycol as base fluid and Al2O3 with glycerol as base fluid.Before commencing on the convective heat transfer investigation, the viscosities of a few specimens of the nanofluids are measured and their results show that the classical models by Einstein and Batchelor are incapable of predicting the nanofluid viscosity. By using the latest viscosity model proposed by Wang et al., which takes into account the effect of nanoparticle clustering, a relatively closer prediction is observed but the model still falls short of the measured values by a big margin. Hence, this suggests the presence of even larger particle clusters within the specimens. After the viscosity measurements have been accomplished, experiments are conducted on all the nanofluids, under constant wall temperature of approximately 61.5ºC, to examine their convective heat transfer characteristics. The results show that the nanofluids’ convective heat transfer performance of the nanofluids tested increases with increasing nanoparticle loading and higher flow rates. By using different base fluids of different viscosities, the results have also justified that, apart from the higher thermal conductivity, Brownian diffusion and particle ii migration due to temperature gradient are also the heat transport mechanisms responsible for the significant heat transfer enhancement. Finally, in an effort to select the most favourable base fluid which could maximise the nanofluid’s heat transfer capacity, a trade-off between better heat transfer enhancement through greater particle loading and better heat transfer enhancement through Brownian diffusion effect is observed.