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Technical Brief

The Importance of the Heat Capacity of Lubricants With Nanoparticles in the Static Behavior of Journal Bearings

[+] Author and Article Information
Rodrigo Nicoletti

Department of Mechanical Engineering,
São Carlos School of Engineering,
University of São Paulo,
Trabalhador São-Carlense 400,
São Carlos 13566-590, Brazil
e-mail: rnicolet@sc.usp.br

Contributed by the Tribology Division of ASME for publication in the JOURNAL OF TRIBOLOGY. Manuscript received March 14, 2014; final manuscript received May 26, 2014; published online July 15, 2014. Assoc. Editor: George K. Nikas.

J. Tribol 136(4), 044502 (Jul 15, 2014) (5 pages) Paper No: TRIB-14-1058; doi: 10.1115/1.4027861 History: Received March 14, 2014; Revised May 26, 2014

Nanoparticle additives increase the viscosity of lubricants, thus being an interesting solution for improving the load carrying capacity of hydrodynamic bearings. But, nanoparticles also change the thermal properties of the lubricant. Would these thermal properties be important to the static characteristics of lubricated bearings? The answer is yes, being the volumetric heat capacity an important parameter. In this work, the static behavior of journal bearings is studied when nanoparticles are added to the lubricant. A thermohydrodynamic analysis is performed with oil ISO VG68 (base fluid) and six different nanoparticles are considered as additives: Si, SiO2, Al, Al2O3, Cu, and CuO. The numerical results show that the bearing load capacity can be increased up to 10%, not only because of the higher viscosity, but also because of the higher volumetric heat capacity of the lubricant with nanoparticles. Higher volumetric heat capacity of the lubricant decreases temperature development in the bearing gap, thus resulting in higher viscosity distribution for the same operating conditions. In fact, the best results were obtained with ISO VG68 + copper oxide (CuO), whose volumetric heat capacity is the highest among the tested nanofluids. Such results were not equaled when only the viscosity of the lubricant had been changed.

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Figures

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Fig. 1

Journal bearing in study

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Fig. 2

Percentage variation of the bearing load capacity using nanofluids in comparison to the base fluid (φ=4%)

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Fig. 3

Percentage variation of the bearing load capacity in comparison to the base fluid

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Fig. 4

Percentage variation of the physical properties of the nanofluids in comparison to the base fluid (φ=4%)

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Fig. 6

Percentage variation of the temperature in the bearing gap in comparison to the base fluid

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Fig. 5

Percentage variation of the thermal capacity (ρC) of the nanofluids in comparison to the base fluid (φ=4%)

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