Determination of thermal diffusivity of suspended porous silicon films by thermal lens technique

An alumina suspension containing 21 vol.% solids was made to flow through a needle at rates between 10^-12–10^-11 m³s^-1 and was subjected to electrostatic atomization at different applied voltages in the range 5–13 kV. The resulting modes of atomization were studied. The stable cone-jet mode was first obtained at 7 kV and 2.2×10^-12 m³s^-1 and the effect of increasing flow rate and applied voltage on the jet diameter was investigated. Using a pointed ground electrode the alumina droplets produced by the jet in the stable cone-jet mode were printed according to a pre-determined architecture. Alumina relic diameters in the print were <35 m. PACS 81.05.Je; 81.20.Ev; 81.20.Rg; 81.15.Pq; 47.27.Wg     

Thermal diffusivity of rhodamine 6G incorporated in silver nanofluid measured using mode-matched thermal lens technique

Dual beam mode-matched thermal lens method has been employed to measure the heat diffusion in nanofluid of silver with various volumes of rhodamine 6G, both dispersed in water. The important observation is an indication of temperature dependent diffusivity and that the overall heat diffusion is slower in the chemically prepared Ag sol compared to that of water. The experimental results can be explained assuming that Brownian motion is the main mechanism of heat transfer under the present experimental conditions. Light induced aggregation of the nanoparticles can also result in an anomalous diffusion behavior.     

Study of gold nanoparticles effect on thermal diffusivity of nanofluids based on various solvents by using thermal lens spectroscopy

Dual beam thermal lens technique is used to determine the thermal diffusivity of different solvents in presence of gold nanoparticles. In this technique an Ar⁺ laser (wavelength 514 nm, power 40 mW) and intensity stabilized He-Ne laser were used as the heating source and probe beam respectively. The experimental results showed that thermal diffusivity values of the studied solvents (water, ethanol and ethylene glycol (EG)) were enhanced by the presence of gold nanoparticles.     

Evaluation of the thermal diffusivity of vegetable oils during frying by Thermal Lens Spectrometry

In this work we report on the use of the Thermal Lens method to verify the evolution of the thermal diffusivity of sunflower and soybean vegetable oils utilized in preparation of twenty five snacks portions. Our results show that the thermal diffusivity for sunflower oil does not change between 1 and 25 portions of fried snacks. By another hand, the soybean thermal diffusivity exhibits a little decrease for higher portion of fried snacks, indicating that for this oil the triglyceride level is reduced as a degradation process.     

Laser-induced thermal lens study of the role of morphology and hydroxyl group in the evolution of thermal diffusivity of copper oxide

The paper explores the evolution of thermal behavior of the material by studying the variations in thermal diffusivity using the single beam thermal lens (TL) technique. For this purpose, the decomposition of Cu(OH)₂ into CuO is studied in a time range up to 120 h, by subjecting the sample to morphological, structural, and spectroscopic characterizations. The time evolution of thermal diffusivity can be divided into three regions for demonstrating the dynamics of the reaction. When the reaction is complete, the thermal diffusivity is also found to be saturated. In addition to the morphological modifications, from rods to flakes, the variations in the amount of hydroxyl group are attributed to be responsible for the enhancement of base fluid's thermal diffusivity by 165%. Thus the study unveils the role of hydroxyl groups in the thermal behavior of CuO.     

Ageing evaluation of thermal barrier coatings by thermal diffusivity

Ceramic thermal barrier coatings (TBC) are widely applied for protecting from combustion gases hot path components of gas turbines for both aero- and land-based applications. In order to prevent the detachment of TBC, it would be essential to monitor their degradation in terms of sintering kinetic. As sintering strongly affects also the thermal diffusivity of TBC, the idea is to measure the latter parameter to account for the former. The technique to measure thermal diffusivity using pulsed thermography is described, together with the model that leads to the identification of TBC diffusivity. Tests and results on specimens artificially aged are reported.     

Measurement of thermal diffusivity by magnetic resonance imaging

Nuclear magnetic resonance (NMR) may be used for monitoring temperature changes within samples based on measurements of relaxation times, the diffusion coefficient of liquids, proton resonance frequency or phase shifts. Such methods may be extended to the explicit measurement of the thermal diffusivity of materials by NMR imaging. A method based on measuring nuclear spin phase shifts or changes in the equilibrium nuclear magnetization has been developed for measuring transient thermal diffusion effects and thermal diffusivity with potential applications in NMR thermotherapy and materials science. In this method, a thermal pulse is applied to a medium, and the resultant temporal variations of the nuclear spin phase or of the magnitude of the nuclear magnetization produced by the thermal pulse are monitored at a spatial distance. The results obtained on common fluids agree well with the data from other methods.     

Thermal diffusivity of liquid gallium

The thermal diffusivity of liquid gallium was measured by the laser flash technique at temperatures from 45 to 512° C. By using values from the literature for the specific heat, density, and electrical conductivity, the present measurements were found to be in reasonable agreement with a temperature-independent Lorenz ratio equal to the Sommerfeld value.     

Flow injection thermal lens spectrometric detection of hexavalent chromium

A new highly sensitive flow-injection analysis (FIA) method with thermal lens spectrometric detection (TLS) was developed for determination of hexavalent chromium (Cr(VI)) in water. TLS measurements of Cr(VI) with diphenylcarbazide (DPC) method in a batch mode are subject to lower sensitivity and are less reproducible due to photodegradation of Cr-DPC complex during the measurement. In a FIA mode the decomposition of Cr-DPC induced by an intensive excitation laser source (140 mW at 514.5 nm) can be avoided or significantly reduced. For this purpose a FIA-TLS system was assembled and Cr(VI) determined by on-line generation of Cr(VI)-DPC. Under optimal conditions, a linear calibration graph was obtained for the range of Cr(VI) concentrations 1–20 μg/L. A LOD (limits of detection) value of 0.07 μg/L was achieved for Cr(VI) in water.     

Thermal diffusivity measurements in porous ceramics by photothermal methods

Received: 16 September 1996/Accepted: 6 January 1997     

GaP材料热导率的测量

针对目前用于半导体材料掺杂浓度纵向深度分布测量用的方法，如Ｃ－Ｖ法、电化学法等方法对样品造成的损伤或污染，本文提出一种非接触式的光热法测量技术。并结合室温下光热法测得的实验数据计算了ＧａＰ∶Ｎ多层材料中不同杂质浓度下的热导率，获得热导率随半导体内掺入的杂质浓度增加而减小的关系。这一结果与现有用光热法测量单层结构的半导体材料得到的规律相符合，从而表明了用光热法对层状半导体材料进行掺杂浓度纵向分布测量的可行性；同时还讨论半导体内临近层间结晶程度的差异对光热信号幅度造成的影响。     

PTR技术测量材料的热扩散系数的线性化方法

报道了一种用光热辐射 (PTR)技术测量不透明材料热扩散系数的优化方法。从光热辐射理论出发 ,在一定条件下 ,推导出位相信号和调制频率的关系表现为线性关系 ,分析实验数据得出材料的热扩散系数。     

Thermal conductivity and thermal diffusivity of the R134a refrigerant in the liquid state

Thermal conductivity and thermal diffusivity of “ozone-safe” refrigerant R134a in liquid state within the range of temperatures 295.9–354.9 K and pressures from the liquid — vapor equilibrium line up to 4.08 MPa have been studied by high-frequency thermal-wave method. The experimental uncertainties of the temperature, pressure, thermal conductivity and thermal diffusivity measurement errors were estimated to be 0.1 K, 3 kPa, 1.5 and 2.5 %, respectively. Values of thermal conductivity and thermal diffusivity of liquid R134a on saturated line have been calculated. Approximation dependences for thermal conductivity and thermal diffusivity within the whole studied range of temperatures and pressures as well as on the saturated line have been obtained. The work was financially supported by the Russian Foundation for Basic Research (grant No. 07-08-00295-a).     

Processing of thermal lens fringes by S-transform

Thermal lens fringes are obtained by using Mach-Zehnder interferometer on the nile-blue/ethanol solution. S-Transform algorithm is used firstly to obtain local phase and refractive index change distributions by analyzing the thermal lens fringes. In the result, it was seen that this method showed a better result than that obtained by continuous wavelet transform in the previous work mentioned in the literature, since the frequency resolution and filtration effect of the S-transform method are better than other algorithms.     

Thermal conductivity and thermal diffusivity of SiO<Subscript>2</Subscript> nanopowder

A 3ω approach for the simultaneous determination of the effective thermal conductivity and thermal diffusivity of nanopowder materials was developed. A 3ω experimental system was established, and the thermal properties of water and alcohol were measured to validate and estimate the accuracy of the current experimental system. The effective thermal conductivity and thermal diffusivity of the SiO₂ nanopowder with 375, 475, and 575 nm diameters were measured at 290–490 K and at different densities. At room temperature, the effective thermal conductivity and thermal diffusivity of the SiO₂ nanopowder increased with temperature; however, both values decreased as the particle diameter was reduced. An optimum SiO₂ powder density that decreased with decreasing diameter was also observed within the measurement range. The minimum effective thermal conductivity and maximum effective thermal diffusivity were obtained at 85 × 10⁻³ kg/L, when the particle diameter was 575 nm. The optimum densities of the particles with 375 and 475 nm diameters were less than 50.23 × 10⁻³ and 64.82 × 10⁻³ kg/L, respectively.     

Thermal conductivity and thermal diffusivity of tantalum in the temperature range from 293 to 1800 K

Thermal diffusivity of polycrystalline tantalum at the temperature range from 293 to 1800 K has been measured by the laser flash method with the error of 2–4 %. Thermal conductivity has been calculated with the use of reference data on density and heat capacity. Approximating equations and tables of reference data for the temperature dependence of heat transfer coefficients have been obtained; comparison with the published data has been carried out. The work was financially supported by the Russian Foundation for Basic Research (Grant No. 07-08-00071).