Thermal Diffusivity Of Nanofluids Research Articles

Laser flash technique as an efficacious assessment approach for thermal conductivity of tungsten disulphide nanofluids

Two-dimensional tungsten disulphide (WS2) dispersed oil-based nanofluids are prepared by a two-step process and their stability and thermal properties are assessed. UV–visible spectrophotometry reveals marginal loss in relative absorbance over 15 days ensuring dispersion stability of the nano-additives. Thermal diffusivity of nanofluids is measured using the laser flash analyzer while specific heat capacity is studied by differential scanning calorimetry. The thermal diffusivity coupled with the specific heat capacity of the nanofluids provides an estimate of the thermal conductivity of the prepared nanofluids. Specific heat of the nanofluids is observed to increase with temperature and reduce with an increase in the concentration of the nano-additives. A statistical model is developed to predict the influence of density and temperature on the specific heat of the nanofluids. Higher thermal conductivity in comparison to the base fluid is observed which further enhances with an increment in concentration of the nano-additive. The parameters such as concentration of dispersoid and temperature reveal the effect on the thermal conductivity at elevated temperatures. Enhancement in thermal conductivity is observed between 3–12 % which is validated with an analytical model for thermal conductivity of composite nanofluids.

Experimental investigation on thermal properties of Al2O3 nanoparticles dispersed paraffin for thermal energy storage applications

ABSTRACT Addition of Al2O3 nanoparticles into paraffin wax is beneficial to improve the thermal conductivity of paraffin wax. Moreover, it has effect on the other thermophysical properties of paraffin wax such as the thermal diffusivity and volumetric heat capacity. In the present paper, the two-step method was used to prepare the nanofluids of Al2O3 nanoparticles and paraffin wax and then the influence of temperature and volume fraction of Al2O3 nanoparticles on the thermal conductivity, thermal diffusivity, and volumetric heat capacity of the nanofluids was investigated. The experimental results show that the changing trend of the above-mentioned properties of Al2O3/paraffin shows a slight regularity with increasing temperature. The thermal conductivity of nanofluids is enhanced at 20°C, and the largest thermal conductivity attained is 0.38 W/m·K at the volume fraction of 0.01%, which led to 40% augmentation, compared with paraffin. The thermal diffusivity of nanofluids with the volume fraction 0.01%, 0.1%, and 1% varies by −31%, 13.5%, and −21% in solid state, respectively. Moreover, the volumetric heat capacity fluctuates with the increase in temperature, and the volumetric heat capacity of nanofluids with the volume fraction 0.01% and 0.1% is higher than that of 1% in liquid state.

Photothermal spectroscopy: A promising tool for nanofluids

In recent years, the demand for more efficient cooling circuits has resulted in active studies of nanofluids, two-component liquids consisting of a base fluid, and dispersed nanoparticles with high thermal conductivity. From the viewpoint of both physics and chemistry, nanofluids are systems that require the characterization of many interconnected thermal and chemical properties. This perspective article sums up the state of the art and recent trends in the development and applications of nanofluids and especially carbon nanofluids. A focus of the paper is the possibilities of photothermal and photoacoustic methods—as techniques combining molecular spectroscopy and thermal characterization—for the assessment of thermal conductivity and thermal diffusivity of nanofluids. The possibilities of photothermal spectroscopy for wider characterization of nanofluids and related materials are discussed and compared with other techniques. As nanofluids are one of the examples of complex objects dedicated to photothermal spectroscopy, more general outlooks of phototermics are also discussed.

Thermal diffusivity control in titanium dioxide nanofluid through phase tuning

The potential of TiO2 is greatly understood in diversified fields of science and technology. With the advent of nanotechnology, the study of nanofluids has gained significant attention. The physical properties of a fluid can considerably be varied with nanoparticle incorporation. The present work describes methods for controlling the thermal diffusivity of TiO2 nanofluid. The thermal diffusivity of the nanofluid is measured by single beam thermal lens technique. TiO2 nanoparticles synthesized by sol–gel method with different amount of oxalic acid and the sample calcined at different temperatures are analyzed by x-ray diffraction (XRD) technique. The field emission scanning electron microscopic (FESEM) image and XRD analysis confirmed the particle formed to be nano in size. The transformation of phase from anatase to rutile with temperature and the amount of oxalic acid is studied from the XRD pattern. The thermal lens study of the samples reveals that the thermal diffusivity increases with temperature and amount of oxalic acid. The study also suggests the possibility of controlling the thermal diffusivity of TiO2 nanofluid through phase tuning.

Photopyroelectric Calorimetry of $$\hbox {Fe}_{3}\hbox {O}_{4}$$ Fe 3 O 4 Magnetic Nanofluids: Effect of Type of Surfactant and Magnetic Field

Five types of magnetic nanofluids, based on \(\hbox {Fe}_{3}\hbox {O}_{4}\) nanoparticles with water as the carrier liquid, were investigated by using the two photopyroelectric (PPE) detection configurations (back (BPPE) and front (FPPE)), together with the thermal-wave resonator cavity (TWRC) technique as the scanning procedure. The difference between the nanofluids was the type of surfactant: double layers of lauric (LA–LA), oleic (OA–OA), and miristic (MA–MA) acids and also double layers of lauric–miristic (LA–MA) and palmitic-oleic (PA–OA) fatty acids were used. In both detection configurations, the information was contained in the phase of the PPE signal. The thermal diffusivity of nanofluids was obtained in the BPPE configuration, from the scan of the phase of the signal as a function of the liquid’s thickness. Using the same scanning procedure in the FPPE configuration, the thermal effusivity was directly measured. The influence of a 0.12 kG magnetic field on the thermal effusivity and thermal diffusivity was also investigated. Because of different surfactants, the thermal effusivity of the investigated nanofluids ranges from \(1530\,\hbox {W}\cdot \hbox {s}^{1/2} \cdot \hbox { m}^{-2}\cdot \hbox { K}^{-1}\) to \(1790\,\hbox { W}\cdot \hbox {s}^{1/2}\cdot \hbox { m}^{-2}\cdot \hbox { K}^{-1}\), and the thermal diffusivity, from \(14.54~\times ~10^{-8}\,\hbox { m}^{2}\cdot \hbox { s}^{-1}\) to \(14.79~\times ~10^{-8}\,\hbox { m}^{2}\cdot \hbox { s}^{-1}\). The magnetic field has practically no influence on the thermal effusivity, and produces a maximum increase of the thermal diffusivity (LA–LA surfactant) of about 4 %.

Thermal diffusivity of nanofluids composed of rod-shaped silver nanoparticles

The thermal diffusivity of nanofluids containing silver nanorods in cetyltrimethyl ammonium bromide micelle has been investigated by measuring the time constant of transient thermal lens. The important observation is that the nanofluids exhibits improved thermal diffusivity in comparison to the base fluid. Also, it is found that, the effective thermal diffusivity of nanofluids with rod-shaped nanoparticles is greater than that of nanofluid with spherical nanoparticles. This is explained on the basis of the empirical shape factor by Hamilton Crosser model. Several factors such as chemical environment, formation of nanolayer around the particle surface, nanolayer thickness and interfacial resistance are also considered to explain the results. These results are discussed in connection with the possibility of using rod-shaped silver nanoparticles to enhance the thermal diffusivity of heat transfer fluids.

Thermal diffusivity measurement of silver nanofluid by thermal lens technique

The thermal lens technique was utilized in silver nanofluid containing silver nanoparticles in polyvinylpyrrolidone solution to study the effect of nanoparticle size on thermal diffusivity. The different sizes of silver nanoparticles were prepared by irradiating the solution of silver nitrate in polyvinylpyrrolidone with respective dose of γ-radiation. The average sizes of particle in the prepared samples were measured using nanophox machine. The thermal lens measurement was carried out by using a diode laser of wavelength 514 nm and a He–Ne laser for the excitation source and the probe beam, respectively. The obtained result showed a decrease in the thermal diffusivity of nanofluid with the decrease in particle size.

Study of the Effect of Volume Fraction Concentration and Particle Materials on Thermal Conductivity and Thermal Diffusivity of Nanofluids

Nanofluids, a mixture of nanoparticles and fluids, have exceptional potential to improve their effective thermal conductivity and thermal diffusivity, aluminum and aluminum oxide nanofluids with five different volume fractions of nanoparticle suspensions in different base fluids, i.e., distilled water, ethylene glycol (EG), and ethanol were prepared by mixing nanopowder and base fluids. Sonication with high-powered pulses was used to ensure the dispersion of nanoparticles in good uniformity in the base fluids. The hot wire-laser beam displacement technique was used to measure thermal conductivity and thermal diffusivity of the prepared nanofluids. The effects of the volume fraction concentration and particle materials on the thermal conductivity and thermal diffusivity of nanofluids were determined. The results showed that the thermal conductivity and thermal diffusivity increased linearly with increasing volume fraction concentration of nanoparticles in the respective base fluids. In addition, the thermal conductivity and thermal diffusivity increased faster in the Al2O3 nanofluids than in all the three base fluids.

Study of the Effect of Volume Fraction Concentration and Particle Materials on Thermal Conductivity and Thermal Diffusivity of Nanofluids

Study of the Effect of Volume Fraction Concentration and Particle Materials on Thermal Conductivity and Thermal Diffusivity of Nanofluids

나노유체의 열확산율 측정을 위한 비정상열선법 센서모듈 실험

Key Words: Nanofluids(나노유체), Thermal Diffusivity(열확산율), Thermal Conductivity(열전도율), TransientHot-wire Method(비정상열선법)초록: 본논문은나노유체의열확산율을측정하는센서와주변회로그리고데이터의처리방법을제시한것이다. 기존비정상열선법을이용하면이론상유체의열전도율과열확산율을동시에측정할수있으나열전도율과비교하여열확산율은많은오차가발생한다. 본연구에서제시한방법은측정변수가단순하고복잡한센서의교정과정을생략할수있는실용적측면의장점이있다. 먼저열확산율이잘알려진유체들에대한검증실험을실시하였고나노유체의열확산율을측정하여기본유체와비교하는과정을예시적으로설명하였다. 본연구는기존열전도율측정에한정되어왔던나노유체연구의범위를열확산율또는비열의개념으로확장하였다는관점에서중요성을갖는다.Abstract:: A technique for measuring the thermal diffusivity of nanofluids is proposed in this study. In theory, it hasbeen well known that the transient hot-wire method can be used to measure the thermal conductivity and diffusivity offluids simultaneously. However, when traditional methods were employed, the accuracy of the calculated thermalconductivity was considerably higher than that of diffusivity. The proposed method has two advantages for practical use:it only needs a simple data-conversion process for calculating the diffusivity, and it can skip the tedious calibrationprocess involved in the case of a wire sensor. A validation experiment for the new system has been performed with thebasic fluids, and the comparison experiment to compare the change in diffusivity of the base oil and the change indiffusivity of the nano oil has been carried out. It is expected that the present system will provide numerous methods forinvestigating the variation in the thermal properties other than thermal conductivity.

The effect of volume fraction concentration on the thermal conductivity and thermal diffusivity of nanofluids: Numerical and experimental

This article reports on the effect of aluminum (Al) volume fraction concentration on the thermal conductivity and thermal diffusivity of Al nanoparticles suspended in water, ethylene glycol, and ethanol based fluids prepared by the one step method. The Al nanoparticles were independently produced and then mixed with a base fluid to produce the nanoparticles suspension. The thermal conductivity and thermal diffusivity of the nanofluids were measured using the hot wire-laser beam displacement technique. The thermal conductivity and thermal diffusivity were obtained by fitting the experimental data to the numerical data simulated for Al in distilled water, ethylene glycol, and ethanol. The thermal conductivity and thermal diffusivity of the nanofluids increase with an increase in the volume fraction concentration.

Thermal-Conductivity and Thermal-Diffusivity Measurements of Nanofluids by 3ω Method and Mechanism Analysis of Heat Transport

A 3ω technique is developed for simultaneous determination of the thermal conductivity and thermal diffusivity of nanofluids. The 3ω measuring system is established, in which a conductive wire is used as both heater and sensor. At first, the system is calibrated using water with known thermophysical properties. Then, the thermal conductivity and thermal diffusivity of TiO2/distilled water nanofluids at different temperatures and volume fractions and the thermal conductivity of SiO2 nanofluids with different carrier fluids (water, ethanol, and EG) are determined. The results show that the working temperature and the carrier fluid play important roles in the enhancement of thermal transport in nanofluids. These results agree with the predictions for the temperature dependence effect by the Brownian motion model and the micro-convection model. For SiO2 nanofluids, the thermal-conductance enhancement becomes strong with a decrease in the heat capacity of the carrier fluids. Finally, according to our results and mechanism analysis, a corrected term is introduced to the Brownian motion model for providing better prediction of heat transport performance in nanofluids.

Effective thermal conductivity and thermal diffusivity of nanofluids containing spherical and cylindrical nanoparticles

This paper reports on measurements of the effective thermal conductivity and thermal diffusivity of various nanofluids using the transient short-hot-wire technique. To remove the influences of the static charge and electrical conductance of the nanoparticles on measurement accuracy, the short-hot-wire probes are carefully coated with a pure Al2O3 thin film and only those probes that are coated well are used for measurements. In the present study, the effective thermal conductivities and thermal diffusivities of Au/toluene, Al2O3/water, and carbon nanofiber (CNF)/water nanofluids are measured and the effects of the volume fraction and thermal conductivity of the nanoparticles and temperature are clarified. The average diameters of Au and Al2O3 spherical particles are 1.65 and 20nm, respectively. The average length and diameter of CNFs are 10μm and 150nm, respectively. The uncertainty of the present measurements is estimated to be within 1% for the thermal conductivity and 5% for the thermal diffusivity. The measured results demonstrate that the effective thermal conductivities of the nanofluids show no anomalous enhancements and can be predicted accurately by the model equation of Hamilton and Crosser [Ind. Eng. Chem. Fundam. 1, 187 (1962)] for the spherical nanoparticles and by the unit-cell model equation of Yamada and Ota [Waerme-Stoffuebertrag. 13, 27 (1980)] for carbon nanofibers.

Effective thermal conductivity and thermal diffusivity of nanofluids containing spherical and cylindrical nanoparticles

The effective thermal conductivity and thermal diffusivity of Au/toluene, Al 2O 3/water, TiO 2/water, CuO/water and CNT/water nanofluids have been measured by using the transient short-hot-wire technique. The average diameters of Au, Al 2O 3, TiO 2 and CuO spherical particles are 1.65, 20, 40 and 33 nm, respectively. The average length and diameter of CNFs are 10 μm and 150 nm, respectively. The uncertainty of the present measurements is estimated to be within 1% for the thermal conductivity and 5% for the thermal diffusivity. The measured results demonstrate that the effective thermal conductivities of the nanofluids show no anomalous enhancements and can be predicted accurately by the model equation of Hamilton and Crosser for the spherical nanoparticles, and by the unit-cell model equation of Yamada and Ota for carbon nanofibers.

Measurements of the Effective Thermal Conductivity and Thermal Diffusivity of Nanofluids

This paper reports on the measurements of the effective thermal conductivity and thermal diffusivity of various nanofluids by using the transient short-hot-wire technique. To remove the influences of the static charge and electrical conductance of the nanoparticles on measurement accuracy, the short-hot-wire probes are carefully coated with a pure Al2O3 thin film. Using distilled water and toluene as the standard liquids, the length and radius of the hot wire and the thickness of Al2O3 film are calibrated before and after the coating. The electrical leakage of the short-hot-wire probes is frequently checked, and only those probes coated well are used for measurements. In the present study, the effective thermal conductivities and thermal diffusivities of Al2O3/water, ZrO2/water, TiO2/water and CuO/water nanofluids are measured and the effects of the volume fractions and thermal conductivities of nanoparticles and temperatures are clarified. The average diameters of Al2O3, ZrO2, TiO2 and CuO particles are 20, 20, 40 and 33 nm, respectively. The uncertainty of the present measurements is estimated to be within 1 % for the thermal conductivity and 5 % for the thermal diffusivity. The measured results show that the effective thermal conductivities of the nanofluids with the spherical nanoparticles have no anomalous enhancements and can be predicted by the model equation of Hamilton and Crosser in a lower volume fraction range. Furthermore, the measured values are lower than those predicted in a higher volume fraction range because the settling of some particles occurred in this range.