Thermal Diffusivity of Aqueous Dispersions of Silicon Oxide Nanoparticles by Dual-Beam Thermal Lens Spectrometry

Abstract

The growing interest in heat-conducting nanofluids requires highly sensitive methods for analyzing the thermal properties. Thermal lens spectrometry (TLS), despite its advantages over classical methods, does not have a general approach for measuring and interpreting results for dispersed systems. In this paper, for nanofluids of silicon oxide in water in a wide range of concentrations and sizes, the selection of measurement parameters for transient and steady-state thermal lensing is justified, and the interpretation of the results of thermal diffusivity measurements is substantiated. The features of the measurements of thermal diffusivity by TLS under stationary states for dispersed systems are considered. Using this approach, it is possible to detect and distinguish thermal effects with high accuracy. For dispersions of silicon oxide, with increasing concentrations, the thermal diffusivity passes through a minimum threshold. Silicon oxide dispersions can be used both as coolants or as heat-removing liquids by selecting the particle size and concentration.

The Thermophysical and Physicochemical Properties of the Aqueous Dispersion of Graphene Oxide Dual-Beam Thermal Lens Spectrometry

“…A dual-beam thermal lens spectrometer was used. Optimization of the spectrometer and measurement parameters is presented in [ 57 , 68 ]. The scheme and description of the spectrometer are explained in detail in the Supplementary Materials (Figure S1 and Procedures section, thermal-lens spectrometer) .…”

“…However, it is necessary to make a small digression and note that an increase in the size of a nanophase in a dispersion, as a rule, leads to an increase in the thermal conductivity of a nanofluid. This behavior is typical for metal nanoparticles [15,18,19,57,[94][95][96], where the largest particles make the greatest contribution to the thermal diffusivity of the system. This can be caused by clustering effects at high concentrations, which contribute to an increase in thermal conductivity [56].…”

“…As proposed in [57], Equation ( 1) is presented as a function of the effective characteristic time ∼ t c (t) at each moment of the transient development curve:…”

“…At the same time, for heat-conducting NFs, it is necessary to measure not only thermal conductivity ( k ), heat capacity ( C p ), viscosity ( η ), and density ( ρ ) but also thermal diffusivity ( D ). Classical methods for measuring thermal parameters show low sensitivity to the nanophase, which makes these methods unsuitable for thermal parameters and thermal diffusivity in particular [ 57 ].…”

“…This significantly limits the applicability of TLS. Earlier papers devoted to the influence of systematic errors on the determination of thermophysical parameters for homogeneous systems [ 68 ] pose questions regarding the correctness of measurements for heterogeneous systems [ 57 ]. In [ 57 ], general recommendations for thermal-lens measurements were proposed for low-absorbing silicon oxide nanoparticles.…”