The development of advanced heat transfer fluids with enhanced thermal conductivity is essential to improve the effective heat transfer behavior of conventional coolants. Thermal conductivity enhancement has been reported for colloidal suspensions formulated with different nanoparticles. Reliable thermal conductivity measurement requires that the suspension is stable against sedimentation during the measurement since particle sedimentation may effect the experimental results. The present study proposes a criterion to ensure that thermal conductivity data is independent of the particle sedimentation. A measuring device based on the transient hot-wire method is designed to allow vertical and horizontal thermal conductivity data collection. Our investigation shows that the thermal conductivity measurements in the horizontal and vertical configurations are almost identical when the colloidal suspension is stable while they differ for unstable systems.
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