Enhanced thermal conductivity of nano-SiC dispersed water based nanofluid

Silicon carbide (SiC) nanoparticle dispersed water based nanofluids were prepared using up to 0·1?vol% of nanoparticles. Use of suitable stirring routine ensured uniformity and stability of dispersion. Thermal conductivity ratio of nanofluid measured using transient hot wire device shows a significant increase of up to 12% with only 0·1?vol% nanoparticles and inverse dependence of conductivity on particle size. Use of ceramic nanoparticles appears more appropriate to ensure stability of dispersion in nanofluid in closed loop single-phase heat transfer applications.     

Prediction of size effect on thermal conductivity of nanoscale metallic films

Incorporating both the scattering mechanisms of the rough film surfaces and the microscopic grain boundaries, we report on a realistic simulation of the in-plane thermal conductivity of nanoscale gold, copper and aluminum films on the basis of non-interacting electron and kinetic theory. The results are consistent with previous theoretical analyses and molecular dynamic simulations, as well as available experimental data. The thermal conductivity of metallic films is found to drop much below the bulk value, even showing dielectric effects. As with the size effect on the electrical conductivity of metallic films, the fine-grain structure has a greater effect on the thermal conductivity than the film surface properties. The influence of temperature on the thermal conductivity is also investigated.     

Enhanced electrical and thermal conductivity of modified poly(acrylonitrile-co-butadiene)-based nanofluid containing functional carbon black-graphene oxide

Solution refluxing and high-pressure homogenization technique were reported for synthesizing nanofluids based on modified poly(acrylonitrile-co-butadiene) (M-PANB) as base fluid and carbon black (CB)/carbon black-graphene oxide (CB-GO) as filler. The physiochemical properties were studied to analyze the structure, morphology, thermal and electrical conductivity. FTIR analysis corroborated the structure of CB-GO nanobifiller and nanocomposite. Microstructure analysis of M-PANB/CB-GO revealed good dispersion of CB-GO nanosheets, while CB series showed granular distribution. XRD studies confirmed amorphous structure of M-PANB/CB-GO nanocomposite. Thermal conductivity of nanofluid was found to increase upto 1.41 W/mK for 10 wt.% CB-GO loading and electrical conductivity was increased to 2.5 × 10^?3 Scm^?1.     

Dissolution kinetics of Si into Ge (111) substrate on the nanoscale

In this paper we present experiments and simulations on the dissolution of Si into single crystalline Ge(111) substrates. The interface shift during the dissolution was tracked by X-ray Photoelectron Spectroscopy. It was obtained that the interface remained sharp and shifted according to anomalous kinetics similarly to our previous measurement in the Si/amorphous-Ge system. The interface shift, x, can be described by a power function of time x ∝ t^k_c with a kinetic exponent, k_c, of 0.85 ± 0.1, larger than the one measured for the amorphous system (0.7 ± 0.1). Both exponents, however, are different from the k_c = 0.5 Fickian (parabolic) value and it is interpreted as a nanoscale diffusional anomaly caused by the strong composition dependence of the diffusion coefficients.     

Stability and thermal conductivity enhancement of carbon nanotube nanofluid using gum arabic

This experimental study reports on the stability and thermal conductivity enhancement of carbon nanotubes (CNTs) nanofluids with and without gum arabic (GA). The stability of CNT in the presence of GA dispersant in water is systematically investigated by taking into account the combined effect of various parameters, such as sonication time, temperature, dispersant and particle concentration. The concentrations of CNT and GA have been varied from 0.01 to 0.1?wt% and from 0.25 to 5?wt%, respectively, and the sonication time has been varied in between 1 and 24?h. The stability of nanofluid is measured in terms of CNT concentration as a function of sediment time using UV-Vis spectrophotometer. Thermal conductivity of CNT nanofluids is measured using KD-2 prothermal conductivity meter from 25 to 60°C. Optimum GA concentration is obtained for the entire range of CNT concentration and 1–2.5?wt% of GA is found to be sufficient to stabilise all CNT range in water. Rapid sedimentation of CNTs is observed at higher GA concentration and sonication time. CNT in aqueous suspensions show strong tendency to aggregation and networking into clusters. Stability and thermal conductivity enhancement of CNT nanofluids have been presented to provide a heat transport medium capable of achieving high heat conductivity. Increase in CNT concentrations resulted in the non-linear thermal conductivity enhancement. More than 100–250% enhancement in thermal conductivity is observed for the range of CNT concentration and temperature.     

Effects of nanoscale size dependent parameters on lattice thermal conductivity in Si nanowire

The effects of nanoscale size dependent parameters on lattice thermal conductivity are calculated using the Debye-Callaway model including transverse and longitudinal modes explicitly for Si nanowire with diameters of 115, 56, 37 and 22 nm. A direct method is used to calculate the group velocity for different size nanowire from their related calculated melting point. For all diameters considered, the effects of surface roughness, defects and transverse and longitudinal Gruneisen parameters are successfully used to correlate the calculated values of lattice thermal conductivity to that of the reported experimental curve. The obtained fitting value for mean Gruneisen parameter has a systematic dependence on all Si nanowire diameters changing from 0·791 for 115 nm diameter to 1·515 for the 22 nm nanowire diameter. The dependence also gave a suggested surface thickness of about 5–6 nm. The other two parameters were found to have partially systematic dependence for diameters 115, 56, and 37 nm for defects and 56, 37 and 22 nm for the roughness. When the diameters go down from 115 to 22 nm, the concentration of dislocation increased from 1·16 × 10¹⁹cm⁻³ to 5·20 × 10¹⁹cm⁻³ while the surface roughness P found to increase from 0·475 to 0·130 and the rms height deviation from the surface changes by about 1·66 in this range of diameter. The diameter dependence also indicates a strong control of surface effect in surface to bulk ratio for the 22 nm wire diameter.     

A study on the effects of temperature and volume fraction on thermal conductivity of copper oxide nanofluid

By using copper oxide nanofluid fabricated by the self-made Submerged Arc Nanofluid Synthesis System (SANSS), this paper measures the thermal conductivity under different volume fractions and different temperatures by thermal properties analyzer, and analyzes the correlation among the thermal conductivity, volume fraction, and temperature of nanofluid. The CuO nanoparticles used in the experiment are needle-like, with a mean particle size of about 30 nm. They can be stably suspended in deionized water for a long time. The experimental results show that under the condition that the temperature is 40 degrees C, when the volume fraction of nanofluid increases from 0.2% to 0.8%, the thermal conductivity increment of the prepared nanofluid towards deionized water can be increased from 14.7% to 38.2%. Under the condition that the volume fraction is 0.8%, as the temperature of nanofluid rises from 5 degrees C to 40 degrees C, the thermal conductivity increment of the prepared nanofluid towards deionized water increases from 5.9% to 38.2%. Besides, the effects of temperature change are greater than the effects of volume fraction on the thermal conductivity of nanofluid. Therefore, when the self-made copper oxide nanofluid is applied to the heat exchange device under medium and high temperature, an optimal radiation effect can be acquired.     

Alternative analytical solutions of the diffusion (thermal conductivity) equation for an arbitrary initial concentration (temperature) distribution

Alternative analytical solutions of the diffusion (or thermal conductivity) equation are presented, which ensure rapid convergence even for small values of Dt/l ² (αt/l ²), where D is the diffusion coefficient, α is the thermal diffusivity, t is the time, and l is the characteristic size. The solutions possess a general character and are valid for an arbitrary initial distribution of the concentration (temperature).     

Effect of thermal coarsening on the thermal conductivity of nanoporous gold

The thermal conductivities of nanoporous gold (NPG) microwires annealed at different temperatures have been measured in the temperature range from 100 to 320 K. Considering the electron-surface scattering, the thermal conductivity is expected to increase with the increase of ligament diameter. However, the thermal conductivity of NPG microwire is found to decrease after thermal coarsening, and has a maximum value at around 250 K for the as-dealloyed sample. We suggest that the defects accumulating at a relatively high temperature and the reduction in defect spacing may cause these temperature behaviors of thermal conductivity. Taking into account the electron scattering on ligament surfaces and defects, a modified theoretical model for the thermal conductivity of nanoporous metal is proposed to agree with our experimental results.     

Effect of additives on the thermal conductivity of cyclohexane

The thermal conductivity of pure cyclohexane with an addition of benzene has been measured over the 77–300K temperature range.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 23, No. 1, pp. 139–140, July, 1972.     

Interface kinetics and morphology on the nanoscale

Diffusion on the nanoscale in multilayer, thin films has many challenging features even if the role of structural defects can be neglected and ‘only’ the effects related to the nanoscale arise. Recently, we have discovered different examples for diffusional nanoscale effects, which are summarized in this contribution. Interface shift kinetics may be different from the ones predicted by continuum approximations (anomalous kinetics). Moreover we show that in solid state reactions, reaction layers form and start to grow highly non-stoichiometrically and an initially existing stoichiometric compound layer may dissolve then re-form non-stoichiometrically. Our findings are of primary importance for nanotechnologies where early stages of solid state reaction (SSR) are utilized. We also show that an initially diffused interface may sharpen even in completely miscible systems. This phenomenon could provide a useful tool for the improvement of interfaces and offer a way to fabricate, for example, better X-ray or neutron mirrors, microelectronic devices, or, multilayers with giant magnetic resistance.A variety of different UHV-based techniques (AES/XPS and synchrotron facilities) have been used to prove the above theoretical findings in different systems (e.g. Ni/Cu, Ni/Au, Si/Ge, Co/Si).     

Effect of wetting on the thermal conductivity of granular materials

It is shown that the measured values of the thermal conductivity of a granular system are substantially affected by the wetting of the grains, the nature of the distribution of the liquid, the conditions of wetting of the grains, and the drying of a layer of grains at a heated wall.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 31, No. 6, pp. 973–980, December, 1976.     

Effect of porosity on the effective thermal conductivity of graphite

An equation of the hyperbolic kind is proposed for describing the effective thermal conductivity of porous graphite over the 0.6 to 0.01 range of porosity.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 2, pp. 325–329, August, 1973.     

Stability,viscosity, thermal conductivity,and electrical conductivity enhancement of multi-walled carbon nanotube nanofluid using gum arabic

This experimental investigation discussed on the stability and rheological behavior of multi-wall carbon nanotubes (MWCNTs) nanofluids with and without gum arabic (GA). The stability of MWCNT in the presence of GA dispersant in solar glycol is systematically investigated by taking into account the combined effect of different parameters, such as sonication time, temperature, dispersant and particle concentration. The concentrations of MWCNT and GA have been varied from 0.2 to 0.6% volume concentration and from 0.25 to 1.25 wt%, respectively, and the sonication time has been varied in between 30 and 120 min. The effect of sonication time on viscosity was discussed. It was perceived that the shear thinning behavior is exhibited by all the nanofluid samples. The stability of nanofluid is measured in terms of MWCNT concentration as a function of sediment time using UV-Vis spectrophotometer. Rheological behavior of MWCNT nanofluids is measured using Bohlin CVO Rheometer in the temperature range of 30–50°C, with step sizes of 5°C. Optimal GA concentration is obtained for the entire range of MWCNT concentration and 0.25–1.25 wt% of GA is found to be sufficient to steady all MWCNT range in solar glycol. Rapid sedimentation of MWCNTs is observed at higher GA concentration and sonication time. The presence of MWCNT and GA enhanced the thermal conductivity of the nanofluids by 30.59% at 0.6 vol.% particle concentration and 1.25 GA wt% at 50°C. The electrical conductivity is enhanced in a linear manner with respect to the loading of MWCNT and GA. Nevertheless, the electrical conductivity is increased linearly with increasing the temperature of the nanofluid. At particle concentration of 0.6 vol.% of MWCNT and 1.25 wt% of GA, the electrical conductivity of the nanofluid is improved by 190.57% at a temperature of 50°C.     

纳米氧化锌对液体硅橡胶导热性能的改进研究

以直接沉淀法合成了纳米氧化锌(ZnO),使用硅烷偶联剂对其进行表面改性,并制备了纳米ZnO与液体硅橡胶的复合材料,对改性前后纳米ZnO的结构进行了表征,并对复合材料的相关性能进行了研究。结果表明:通过接枝反应,硅烷偶联剂可以接枝到纳米ZnO表面,改性前后ZnO的晶型不发生变化;在较低添加量的情况下,纳米ZnO可以在一定程度上提高液体硅橡胶的力学性能,当添加量为2%时,改性前后纳米ZnO制备的液体硅橡胶复合材料的导热系数可以从0.189W/m.K分别提高到0.506W/m.K和0.61W/m.K。     

Effect of porosity and temperature on the thermal conductivity of cermets

The thermal conductivities of sintered specimens of iron powder, as functions of porosity, temperature, and powder particle size, were experimentally determined.     

Effect of the pore shape on the thermal conductivity of porous media

The effect of the pore shape on the thermal conductivity of porous media is studied in this work, considering random and aligned distributions of spheroidal pores within the matrix. This is done by using the Bruggeman differential effective medium theory which is suitable for pores with different sizes, as is usually the case of practical interest. The obtained results can be applied for porous media with low as well as high porosities, and they show that: (1) the effect of the pore shape becomes stronger as the porosity increases. (2) The thermal conductivity for randomly oriented pores takes its maximum value for spherical pores and this value is the geometric average of the thermal conductivities along the three principal axes of the pores, when they are aligned. (3) In the case of aligned pores, the thermal conductivity along a principal axis increases with its length, in such a way that it is larger along the principal axis with longer dimensions. The predictions of the proposed approach are in good agreement with reported data and are expected to be useful to provide insights on the thermal behavior of porous media.     

Effect of thermometer thermal conductivity and dimensions on accuracy of thermal flux measurements

Expressions are presented for evaluating errors in steady-state thermal flux measurements within massive objects with consideration of the effect of thermal conductivity and size of the active thermometer zone.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 5, pp. 847–853, November, 1988.     

Effect of electron-electron interaction on thermal conductivity of disordered systems

We present a calculation of a correction to the thermal conductivity due to the inclusion of electron-electron interaction in a disordered metallic system. We find that, to the first order in electron-electron interaction, the Wiedemann-Franz law is not satisfied.     

高填充ZnO对EVA胶膜导热性能的影响

制备了高含量ZnO/EVA胶膜。研究了ZnO粒径、用量等对复合胶膜导热性能、力学性能以及粘接性的影响。比较了晶须ZnO与粉状ZnO对复合胶膜导热系数的影响。采用热重分析仪测定了胶膜热失重曲线,并采用扫描电镜(SEM)观察了复合胶膜中ZnO的分散和界面结合状态。复合材料导热系数的实验结果与Maxwell-Eucken模型较吻合,但Maxwell-Eucken模型只适用于低填充情况。