Enhancement of thermal conductivity of fluids upon addition of nanoparticles has been previously observed. In this study, Fe3O4 magnetite particles were used and thermal conductivity enhancements both in water and in heptane with increasing volume fraction have been shown. Upon measuring thermal conductivity under externally applied magnetic field, it has been shown experimentally that thermal conductivity can be further increased even at low concentrations and low magnetic field strengths in both fluids. Theoretical calculations are presented to support the effect of magnetic field on the thermal conductivity enhancement. This enhancement is attributed to the thermomagnetic convection which due to a temperature gradient, results in a non-uniform magnetic body force resulting in more efficient thermal conductance.

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A new primary standard for generation of vacuum pressures between 9 × 10 −4 Pa and 10 3 Pa has been completed at the Ulusal Metroloji Enstitüsü (UME). It is based on the static expansion method, whereby the range is extended to lower pressures by multiple expansions. The apparatus consists of six vessels that provide a pressure reduction by a factor of about 10 −6 in the main calibration vessel after a three-step expansion. Seventeen platinum resistance thermometers are mounted on the vessels to determine the correction due to temperature effects. The whole apparatus is built using the UHV technique and can be baked up to 400 ˚C. The expanded (k = 2) relative uncertainties of pressures, generated by this new standard, range from 2.1 × 10 −3 at 9 × 10 −4 Pa to 9.5 × 10 −4 at 10 3 Pa.

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