The difference in the thermal conductivity of nanofluids measured by different methods and its rationalization

Abstract

A suspension of particles below 100 nm in size, usually termed as nanofluid, often shows a notable enhancement in thermal conductivity, when measured by the transient hot-wire method. In contrast, when the conductivity of the same nanofluid is measured by the laser flash method, the enhancement reported is about one order of magnitude lower. This difference has been quantitatively resolved for the first time on the basis of the collision-mediated heat transfer model for nanofluids proposed earlier by our research group. Based on the continuum simulation coupled with stochastic analysis, the present theoretical prediction agrees well with the experimental observations from different measuring methods reported in the literature, and fully accounts for the different results from the two measuring methods mentioned above. This analysis also gives an indication that the nanofluids are unlikely to be effective for heat transfer in microchannels.

Recent advances on the fundamental physical phenomena behind stability, dynamic motion, thermophysical properties, heat transport, applications, and challenges of nanofluids

“…[401] found a 16.5% increase in knf of Al2O3/water nanofluids against the water data, and Zagabathuni et al [387] also used the same technique. Kleinstreuer et al [402] investigated the thermal conductivity of polyalphaolefin (PAO)-based nanofluids based on the laser flash method.…”

“…Apart from the theoretical models, the experimental techniques is considered to determine the knf. Various techniques are considered to evaluate the knf [387][388][389].…”

On the Morphology of Nanostructured TiO2 for Energy Applications: The Shape of the Ubiquitous Nanomaterial

“…Reasons for these discordant values can be traced both to the different experimental techniques used for the thermal characterization and, more interestingly, to the different NFs’ physical and chemical characteristics [ 222 , 223 ]. As for the experimental techniques, for example, the most common methods used to measure the effective thermal conductivity of nanoparticle suspensions, such as the transient hot-wire method [ 224 ], the steady-state parallel method [ 217 , 225 ], the temperature oscillation method [ 226 ] and the hot strip method [ 227 ], can influence the natural thermal convection of the base fluid by adding additional heating that can affect the measurement results. Diversely, the forced Rayleigh light scattering method [ 220 , 228 , 229 ] is a contact-free method with a very short measuring time that limits the temperature rise during the measurement, leaving the system conditions unaltered.…”

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“…Using the same experimental methods adopted by [ 113 ] to measure the thermal conductivity of NFs, Zagabathuni et al [ 114 ] showed that when the conductivity of the same nanofluid is measured by the laser method, the enhancement reported is about one order of magnitude lower than when measured by the transient hot-wire method. The authors explained that a small volume (about 50 μL), normally used in the laser flash method, severely restricts the Brownian motion of particles compared to the much larger volume (more than 50 mL) available in the transient hot-wire method.…”

“…The differences in the results obtained by [ 114 ] had been explained by Ghosh et al [ 115 ] through a collision model that was later improved by Karthik et al [ 116 ]. According to them, during the collisions of NPs with the heat source, rapid heat exchange occurs increasing the temperature of the particles.…”