It is shown that a “nanofluid” consisting of copper nanometer-sized particles dispersed in ethylene glycol has a much higher effective thermal conductivity than either pure ethylene glycol or ethylene glycol containing the same volume fraction of dispersed oxide nanoparticles. The effective thermal conductivity of ethylene glycol is shown to be increased by up to 40% for a nanofluid consisting of ethylene glycol containing approximately 0.3 vol % Cu nanoparticles of mean diameter <10 nm. The results are anomalous based on previous theoretical calculations that had predicted a strong effect of particle shape on effective nanofluid thermal conductivity, but no effect of either particle size or particle thermal conductivity.

Anomalously increased effective thermal conductivities of ethylene glycol-based nanofluids containing copper nanoparticles

Oxide nanofluids were produced and their thermal conductivities were measured by a transient hot-wire method. The experimental results show that these nanofluids, containing a small amount of nanoparticles, have substantially higher thermal conductivities than the same liquids without nanoparticles. Comparisons between experiments and the Hamilton and Crosser model show that the model can predict the thermal conductivity of nanofluids containing large agglomerated Al{sub 2}O{sub 3} particles. However, the model appears to be inadequate for nanofluids containing CuO particles. This suggests that not only particle shape but size is considered to be dominant in enhancing the thermal conductivity of nanofluids.

Measuring Thermal Conductivity of Fluids Containing Oxide Nanoparticles

We have produced nanotube-in-oil suspensions and measured their effective thermal conductivity. The measured thermal conductivity is anomalously greater than theoretical predictions and is nonlinear with nanotube loadings. The anomalous phenomena show the fundamental limits of conventional heat conduction models for solid/liquid suspensions. We have suggested physical concepts for understanding the anomalous thermal behavior of nanotube suspensions. In comparison with other nanostructured materials dispersed in fluids, the nanotubes provide the highest thermal conductivity enhancement, opening the door to a wide range of nanotube applications.

Anomalous thermal conductivity enhancement in nanotube suspensions

Heat transfer characteristics of nanofluids: a review

Pore fluids strongly influence the seismic properties of rocks. The densities, bulk moduli, velocities, and viscosities of common pore fluids are usually oversimplified in geophysics. We use a combination of thermodynamic relationships, empirical trends, and new and published data to examine the effects of pressure, temperature, and composition on these important seismic properties of hydrocarbon gases and oils and of brines. Estimates of in-situ conditions and pore fluid composition yield more accurate values of these fluid properties than are typically assumed. Simplified expressions are developed to facilitate the use of realistic fluid properties in rock models. Pore fluids have properties that vary substantially, but systematically, with composition, pressure, and temperature. Gas and oil density and modulus, as well as oil viscosity, increase with molecular weight and pressure, and decrease with temperature. Gas viscosity has a similar behavior, except at higher temperatures and lower pressures, where the viscosity will increase slightly with increasing temperature. Large amounts of gas can go into solution in lighter oils and substantially lower the modulus and viscosity. Brine modulus, density, and viscosities increase with increasing salt content and pressure. Brine is peculiar because the modulus reaches a maximum at a temperature from 40 to 80°C. Far less gas can be absorbed by brines than by light oils. As a result, gas in solution in oils can drive their modulus so far below that of brines that seismic reflection bright spots may develop from the interface between oil saturated and brine saturated rocks.

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Seismic properties of pore fluids

In this paper we describe a new, high-precision oscillating-disk viscometer which has been designed specifically to measure the viscosity of concentrated ionic solutions at temperatures extending to 300°C and to pressures of 35 MPa, simultaneously. The viscometer is intended to provide reliable values of the viscosity of a wide spectrum of aqueous salt solutions under conditions similar to those prevailing in hydrothermal geothermal reservoirs. Results of preliminary calibration runs are included. They indicate that the behavior of the viscometer is reliable and satisfactory. This is further confirmed by new measurements of the viscosity of liquid water up to 200°C and 30 MPa.



In dieser Arbeit wird ein neues Schwingungviskosimeter hoher Prazision beschrieben, das speziell fur die Messung der Viskositat ionischer Losungen hoher Konzentration bei Temperaturen uber 300°C und gleichzeitigen Drucken von 35 MPa entwickelt wurde. Von diesem Viskosimeter wird erwartet, das es zuverlassige Messungen in verschiedenartigen wasrigen Salzlosungen ermoglicht, und zwar unter Bedingungen, die mit denen in geothermischen Quellen vergleichbar sind. Ergebnisse fur eine erste Kalibrierung des Mesinstruments werden angegeben. Sie zeigen, das das Viskosimeter sicher und ohne Beanstandungen arbeitet. Dies wird auch durch neue Messungen der Viskositat von Wasser im Bereich bis zu 200°C und 30 MPa bestatigt.

Joseph Kestin

Papers

A high-temperature, high-pressure oscillating-disk viscometer for concentrated ionic solutions