Determination of thermal diffusivity from experimental data

An algorithm is discussed for determining the temperature dependence of the thermal diffusivity from thermocouple measurements at one or more points within a body.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 29, No. 1, pp. 87–90, July, 1975.     

Measurement of the thermal diffusivity of liquids with a laser-induced thermal-grating technique: An experimental investigation of systemtic errors

The laser-induced thermal-grating; technique has been developed to determine the thermal diffusivity of liquids and liquid mixtures. Here we report an experimental investigation of the systematic errors. which are caused by departures from one-dimensional heat conduction. In particular. the effects of cell wall and intersection angle of the heating beams have been thoroughly studied through measurements on toluene and methanol. A comparison has been made between experimental results and numerical predictions. The excellent agreement between experiments and theoretical predictions shows that the theoretical error analysis can be used for the estimation and accurate correction of systematic errors in measurements by this technique.     

直接接触式蓄冷传热特性的试验研究

设计了直接接触式蓄冷试验台,观察了蓄冷罐内的蓄冷现象,对直接接触式蓄冷系统蓄冷罐内的传热特性进行了研究。通过试验对蓄冷罐水位、制冷节流阀的开度、罐内水的初温及系统充灌量对蓄冷罐内容积换热系数及温度分布迸行了研究,研究表明,蓄冷罐内的容积换热系数随罐内水位升高而降低,随初始水温的升高而增加,制冷节流阀的开度的增大将会增大蓄冷罐内的容积换热系数,而制冷剂的充罐量对容积换热系数影响不大。     

冷轧变形纳米晶钴的X射线衍射研究

对冷轧变形前后纳米金属钴的微观应变。晶格常数以及晶粒尺寸的变化进行了研究，对X射线衍射图谱进行了分析计算，结果表明，变形过后晶体内部存有残余内应力并导致了微观应变，应变大小为ε=1．412×10q；对变形前后的晶格常数进行计算，得到变形后的晶格常数为a=0．25241nm；c=0．40782nm；透射电镜的观察和衍射谱线的计算表明变形后纳米金属钴的晶粒大小与形状基本未发生变化，平均晶粒尺寸为18．8nm。有可能是空位的活动降低了变形过程中的晶界迁移几率，使得变形后的晶粒尺寸基本没有发生变化。     

Isothermal thermal diffusivity of iron oxide

Using the flash technique, the thermal diffusivity of iron oxide has been measured as a function of time at temperatures ranging from 623 to 753 K to study the isothermal decomposition of wustite to magnetite and iron. The results are briefly discussed in terms of transformation kinetics and it is shown that the data are consistent with the growth of a fixed number of nuclei, all of which are present at the start of transformation.     

An apparatus for measuring the thermal conductivity and diffusivity of solid materials

An apparatus is described for measuring the thermal conductivity and diffusivity on small specimens of solid materials; also the results are shown which have been obtained for refractive high-alumina concrete by such measurements.Notation thermal conductivity at the mean temperature of specimens, W/m· °C - Q power of the central heater, W - F cross section area of a specimen, m² - t_1,2 temperature drop across the specimens, °C - ₁, ₂ difference in heights between the thermocouple beads, center-to-center, in the first and in the second specimen respectively, m - t temperature, °C - time coordinate, min - d₁= (d_1u+d_1l )/2 mean distance between specimen contact plane and nearest thermocouple beads, for the upper and lower specimen, m - d₂= (d_2u+d_2l )/2 mean distance between specimen contact plane and farthest thermocouple beads, for the upper and lower specimen, m - dt(d₁,)/d rate of temperature rise at section d₁ of the specimen at time, °C/h - t=t₁+t₂ sum of temperature drops in the specimens at time, °C - m heating rate, h^–1 - a thermal diffusivity of specimens, referred to their mean temperature, m²/h - =m/a, m^–1 b=¦(t_u–t_l)/t_u¦ heating nonuniformity factor Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1049–1054, June, 1972.     

Effect of radiation heat transfer on thermal diffusivity measurements

Experimental data on thermal conductivity and thermal diffusivity of a semitransparent material generally include an error due to the radiation heat transfer. This error varies in accordance with the experimental conditions such as the temperature level of the sample and the measuring method. In this paper, research on the influence of radiation heat transfer on thermal diffusivity are reviewed, and as an example, the method to correct the radiation component in the apparent thermal diffusivity measured by the stepwise heating technique is presented. The transient heat transfer by simultaneous thermal conduction and radiation in a semitransparent material is analyzed when the front surface is subjected to stepwise heating. The apparent thermal diffusivity, which includes the radiation component, is calculated for various parameters.Paper presented at the Second U.S.-Japan Joint Seminar on Thermophysical Properties, June 23, 1988, Gaithersburg, Maryland, U.S.A.     

陶瓷热障涂层的热导率和热扩散率测量

提出了应用3ω法进行等离子喷涂热障涂层材料的热导率和热扩散率测量的方法。测试了室温下2种典型的热障涂层材料Y2SiO5和La2Zr2O7的热导率和热扩散率,测试结果与文献中的结果吻合良好。实验中对不同孔隙率的样品的热导率在室温附近的温度区间内进行测试,结果表明,孔隙率的变化对热导率有明显的影响。另外,孔隙率对热扩散率有双向的影响,即存在某一孔隙率值使得涂层样品的热扩散率最大。     

A high-temperature laser-pulse thermal diffusivity apparatus

A high-temperature laser-pulse apparatus for the measurement of thermal diffusivity in the temperature range from 1500 to 2500 K has been designed. constructed, and tested at the National Institute of Standards and Technology. A curve-fitting method is introduced by which the entire experimental temperature history curve is fitted with the theoretical curve under the boundary condition of radiative heat losses. The new apparatus and the curve-fitting method permit thermal diffusivity measurements with an uncertainty of not more than 3%.     

Determination of variable coefficient of thermal diffusivity

The coefficient of thermal diffusivity as a function of time is determined for a given temperature and its gradient on the boundary of a semiinfinite region.     

Thermal diffusivity of inhomogeneous systems. II. Experimental determination of thermal diffusivity

We investigated the methodical error in the measurement of the effective thermal diffusivity of inhomogeneous systems. We give the recommendation for the choice of the dimensions of the inhomogeneous specimen.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 5, pp. 859–861, November, 1980.     

Determining the thermal diffusivity of pyroelectric materials

Formulas are derived for the thermal diffusivity of pyroelectric materials made in the shape of plane-parallel plates. The thermal diffusivity of grade TsTS-19 pyroactive piezoceramic was measured. The test results are shown here.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 26, No. 4, pp. 738–741, April, 1974.     

A study of thermal stability in electrodeposited nanocrystalline Fe-Ni invar alloy

The grain growth of an electrodeposited nanocrystalline Fe-Ni invar alloy was studied with differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The results showed very limited grain growth below the temperature of 0.36T_m, and the activation energy was 40 ± 3 kJ/mol in the low temperature range, which implied the possible mechanism of grain growth as re-ordering of grain boundaries; an abrupt grain growth happened above 0.36T_m with a DSC exothermic peak detected, of which the heat release was about 14 ± 2 J/g; at temperatures above 0.36T_m, the grain growth activation energy was obtained through Kissinger analysis and isothermal kinetics analysis, both of the results suggested the grain growth mechanism as grain boundary diffusion.     

Simultaneous measurement of the thermal conductivity and thermal diffusivity of liquids

In theory, the hot-wire technique for measuring the thermal conductivity of liquids can be used simultaneously to determine the thermal diffusivity. In practice, however, the latter property has so far been determined only with moderate accuracy because of (a) inaccurate bridge balancing due to drift problems, (b) parasitic capacities that delay the heating, and (c) poor precision in the determination of the time. A new measurement procedure has been developed which features (a) a short measuring time, (b) a reduced significance of the balancing technique, (c) a good reproducibility, and (d) a low sensitivity to most error sources. Thermal conductivity and thermal diffusivity results using this procedure, for toluene and n-heptane, which are the generally accepted standards for thermal conductivity, are presented and compared with results from other sources.     

Spatially resolved thermal diffusivity measurements on functionally graded materials

Photothermal generation of thermal waves was used in combination with the probe beam deflection technique to study the thermal diffusivity of functionally graded materials (FGMs) quantitatively. An amplitude modulated Ar ion laser was used as a heat source and the HeNe probe laser was reflected from the specimen surface at almost normal incidence. It is demonstrated that this measuring technique can be used for a precise determination of the thermal diffusivity for a wide variety of materials if appropriate measuring conditions are chosen. The precision of the thermal diffusivity measurement was better than 5% for all materials studied. The achieved spatial resolution of the thermal diffusivity measurement was about 100 m, but higher spatial resolutions can be achieved if necessary. In a graded Al₂O₃/Al composite local fluctuations of the thermal diffusivity were observed due to the coarseness of the microstructure, but the overall behaviour of the thermal conductivity could be described well by the Maxwell-Eucken relationship. In a functionally graded AlCu alloy, a smooth thermal diffusivity profile was observed in the region where the alloy consisted of a solid solution of Cu in Al.     

An experimental study concerning the electrical and the thermal characteristics of stabilized arcs

Results are shown of an experimental study concerning the electric field intensity and the useful power of a plasma jet as well as the electron and the atom-ion gas temperature in an argon arc under atmospheric pressure.Notation l _a length of arc - E electric field intensity in the arc column - d diameter of arc channel - d₀ unit diameter - H enthalpy - I _a arc current - Re Reynolds number - T_e electron temperature - T atom-ion gas temperature Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 22, No. 6, pp. 1089–1095, June, 1972.     

Optical measurements of thermal diffusivity of a material

The measurement of thermal diffusivity of a material (in particular, a thin film) is important for various reasons, e.g., to predict the heat transfer in the solid subjected to a thermal process, to monitor surface composition or morphology, or to detect invisible subsurface defects like delaminations. This measurement can be done in a noncontact manner using various photothermal methods. Such methods typically involve pulsed heating of the surface by small amounts using a laser source; the decay of the surface temperature after this pulsed photothermal heating is then probed to provide the thermal diffusivity. Various probing methods have been developed in the literature, including the probing of reflection, refraction, and diffraction from the pulsed heated area, infrared thermal radiometry, and surface deformation. This paper provides an overview of such techniques and some examples of their applications.     

Measurement of the thermal diffusivity coefficient of materials

A theoretical substantiation of the measuring procedure for the thermal diffusivity coefficient of substances is given. In doing this, the two-dimensional problem of heat conduction for a cylindrical semi-infinite specimen and the circular modulated heat flux is considered. The coefficient sought is estimated from the phase shift between temperature fluctuations on the flat surface of the speciment exposed to the heat flux and the fluctuations of this flux.Translated from Inzhenerno-fizicheskii Zhurnal, Vol. 64, No. 1, pp. 73–76, January, 1993.