Stefan Van Vaerenbergh

A benchmark study on the thermal conductivity of nanofluids

This article reports on the International Nanofluid Property Benchmark Exercise, or INPBE, in which the thermal conductivity of identical samples of colloidally stable dispersions of nanoparticles or “nanofluids,” was measured by over 30 organizations worldwide, using a variety of experimental approaches, including the transient hot wire method, steady-state methods, and optical methods. The nanofluids tested in the exercise were comprised of aqueous and nonaqueous basefluids, metal and metal oxide particles, near-spherical and elongated particles, at low and high particle concentrations. The data analysis reveals that the data from most organizations lie within a relatively narrow band (±10% or less) about the sample average with only few outliers. The thermal conductivity of the nanofluids was found to increase with particle concentration and aspect ratio, as expected from classical theory. There are (small) systematic differences in the absolute values of the nanofluid thermal conductivity among the various experimental approaches; however, such differences tend to disappear when the data are normalized to the measured thermal conductivity of the basefluid. The effective medium theory developed for dispersed particles by Maxwell in 1881 and recently generalized by Nan et al. [J. Appl. Phys. 81, 6692 (1997)], was found to be in good agreement with the experimental data, suggesting that no anomalous enhancement of thermal conductivity was achieved in the nanofluids tested in this exercise.

Contribution to the benchmark for ternary mixtures: Measurement of diffusion and Soret coefficients of ternary system tetrahydronaphtalene-isobutylbenzene-n-dodecane with mass fractions 80-10-10 at 25 °C

This paper provides the molecular diffusion and Soret coefficients of the ternary system 1,2,3,4-tetrahydronaphtalene, isobutylbenzene, n -dodecane system at mass fractions 0.8-0.1-0.1 and temperature 25 °C for implementation into the benchmark presented in this topical issue. The Soret coefficients are determined by digital interferometry using the data of DSC-DCMIX microgravity experiment. The method used takes into account the influence of the thermal field on the Soret separations and the selection of the image processing techniques results in reproducible Soret coefficients.The diffusion coefficients are obtained by the Open Ended Capillary technique The fitting of the data collected through a set of two complementary experimental runs allows retrieving the four Fickian diffusion coefficients.Graphical abstract

Nanofluids Thermal Conductivity Measurement in a Bénard Cell

Thermal conductivity measurements of nanofluids were the subject of a considerable amount of published research works. Up to now, the experimental results reported in the current literature are still scarce and show many discrepancies. In this paper we propose measurements of this parameter using another experimental set-up. Because of very good thermal controls and big aspect ratio, the Bénard set-up is particularly well suited to determine the thermal conductivity. The aim of this paper is to detail the experimental measurement protocol. The investigated liquid is composed of single walled carbon nanotubes dispersed in water. The effect of liquid temperature on thermal conductivity was investigated. Obtained results confirm the potential of nanofluids in enhancing thermal conductivity and also show that the thermal conductivity temperature dependence is nonlinear, which is different from the results for metal/metal oxide nanofluids.

Soret measurement for multi-component hydrocarbon mixtures from space experiment conducted onboard FOTON M3 unmanned satellite

In an unprecedented experimental investigation, a binary, a ternary and a four-component hydrocarbon mixture at different pressure have been studied in a nearly convection free environment to understand the thermodiffusion process. Experimental investigations of the mixtures have been conducted in space onboard the spacecraft FOTON-M3. The experiment objective was to measure the thermodiffusion coefficient for multi-component hydrocarbon mixtures. Then the experimental results have also been used to test a thermodiffusion model that has been calibrated based on the results of previous experimental investigations. Results showed a good agreement with current theoretical results except for the four-component system where discrepancies were found and discussed.

A Survey of the Thomaes Flow Cell Method for the Soret Coefficient

The thermaldiffusion flow cell was imagined to measure small Soret coefficients but, even for normal values, perturbating phenomena were recorded and not explained. The major intriguing effect was the separation dependence in the basic Poiseuille flow, while the stability problems were partially understood. Recent studies report that natural convection generated by the inlet of the homogeneous mixture has no significant effect. More effective is the finite geometry of the outlet flow separator which provides a Poiseuille flow dependence of the vertical separation. Numerical simulations fit well existing experimental data for series of varied basic flows.