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VISCOSITY AND DENSITY OF CUO NANOLUBRICANT Mark A. Kedzierski
NIST, 100 Bureau Drive, Stop 861, Gaithersburg, MD 20899-8631 USA Mark.Kedzierski@nist.gov; fax:1-301-975-8973
This paper presents liquid kinematic viscosity and density measurements of a synthetic polyolester based copper (II) oxide (CuO) nanoparticle dispersion (nanolubricant) at atmospheric pressure for a temperature range from approximately 288 K to 318 K. The polyolester was a commercially available chiller lubricant. The CuO particles were approximately 30 nm-diameter, spherical, and well dispersed in the lubricant. Viscosity and density measurements were made for the pure base lubricant along with three nanolubricants with differing nanoparticle mass fractions (2.9 %, 5.6 % and 39.2 %). The viscosity and the density were shown to increase with respect to increasing nanoparticle mass fraction. Correlations of the viscosity and the density are presented as a function of temperature and nanoparticle concentration. The measurements are important for the design of nanolubricants for heat transfer and flow applications.
The U.S. National Nanotechnology Initiative (NNI) has supported an explosion of research in recent years including the investigation of the heat transfer properties of liquids with dispersed nano-size particles called nanofluids. Prior to the initiative, nanofluids research was mainly confined to thermal conductivity investigations. Eastman et al. (2001) found that the thermal conductivity of some nanofluids, with nanoparticles at a volume fraction of less than 0.4 % resulted in the nanofluid having an effective thermal conductivity that was more than 40 % greater than that of the pure base fluid. For this reason, lubricant based nanofluids, i.e., nanolubricants, are believed to have a great potential for the enhancement of heat transfer.
Recent studies by Kedzierski (2008) and Bi et al. (2007) have recommended the use of nanolubricants as a means for improving efficiencies of chiller and refrigerators, respectively. Viscosity measurements of potential nanolubricants for these applications will benefit both fundamental research and design considerations. For example, Kedzierski (2001) has shown that lubricant viscosity significantly influences the performance of boiling refrigerant/lubricant mixtures. The efficiency of the boiling process in a chiller is a key determinant in the overall efficiency of a chiller. In addition, compressors in refrigerators and chillers have specific requirements for lubricant viscosity. Redesign of either the compressor or the nanolubricant requires nanolubricant viscosity and density measurements to ensure proper lubrication.
2. TEST LIQUIDS
A commercial polyolester lubricant (RL68H)1, commonly used with R134a chillers, with a nominal liquid kinematic viscosity of 72.3 mm2·s-1 at 313.15 K was the base lubricant that was mixed with nominally 30 nm diameter copper (II) oxide (CuO) nanoparticles. Copper (II) oxide
1 Certain commercial equipment, instruments, or materials are identified in this paper in order to specify the experimental procedure adequately. Such identification is not intended to imply recommendation or endorsement by the National Institute of Standards and Technology, nor is it intended to imply that the materials or equipment identified are necessarily the best available for the purpose.
Paper No. IIR-177
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