Thermal conductivity experimental techniques

An overview of some basic mathematical techniques for data correlation is to be found herein together with background on several types of physical property correlating techniques and a road map for the use of selected methods. Methods are presented for the correlation of observed experimental data to physical properties such as critical properties, normal boiling point, molar volume, vapor pressure, heats of vaporization and fusion, heat capacity, surface tension, viscosity, thermal conductivity, acentric factor, flammability limits, enthalpy of formation, Gibbs energy, entropy, activity coefficients, Henry s constant, octanol—water partition coefficients, diffusion coefficients, virial coefficients, chemical reactivity, and toxicological parameters. 

The number of experimental factors which influence the results increases considerably when thermogravimetry is combined with other techniques such as DTA, gas chromatography46, mass spectrometry, X-ray etc. A systematic discussion of all these additional factors would lead too far, therefore only a representative example will be discussed here. One of the often-applied multiple techniques is the combination TG-DTA. Besides the actual thermal reactions of the sample, the important factors in DTA are the heat capacity and the thermal conductivity of the sample. Optimum heat transfer is required for such thermoanalytical measurements therefore the shape of the sample and its contact with the crucible is of special importance. 

Contrary to the experimental techniques discussed above, spatial transport is important in flames. However, the laminar flame presents fewer difficulties than most other spatially varying combustion problems, because the relevant transport parameters are fairly well defined [427], Heat transport takes place primarily by thermal conduction, while transport of chemical species is dominated by molecular diffusion. 

In the second edition of this volume, special attention has been paid lo improving the accuracy of the estimation techniques used for liquid heat capacity, vapor and liquid viscosity. and vapor thermal conductivity. Improved methods of extending data on liquid density and thermal conductivity have been used m this edition New experimental data has also been included. Particular attention has been paid to include new data on aqueous solution and pressure effects on physical properties... 

The calorimeter method is an older technique which is a direct measurement of Fourier s law. It is one of the ASTM [2] standard tests for thermal conductivity, designation C201. The experimental configuration is shown in Figure 9.3. A SiC slab... 

Using the experimental values for the width of the traveling wave front (portion be, Fig. 8), let us estimate the propagation velocity for the case of a thermal mechanism based on the Arrhenius law of heat evolution from the known relationship U = a/d, where a 10"2 cm2/s is the thermal conductivity determined by the conventional technique. We obtain 5 x 10"2 and 3 x 10-2cm/s for 77 and 4.2 K, respectively, which are below the experimental values by about 1.5-2 orders of magnitude. This result is further definite evidence for the nonthermal nature of the propagation mechanism of a low-temperature reaction initiated by brittle fracture of the irradiated reactant sample. 

The extent of gas dispersion can usually be computed from experimentally measured gas residence time distribution. The dual probe detection method followed by least square regression of data in the time domain is effective in eliminating error introduced from the usual pulse technique which could not produce an ideal Delta function input (Wu, 1988). By this method, tracer is injected at a point in the fast bed, and tracer concentration is monitored downstream of the injection point by two sampling probes spaced a given distance apart, which are connected to two individual thermal conductivity cells. The response signal produced by the first probe is taken as the input to the second probe. The difference between the concentration-versus-time curves is used to describe gas mixing. 

In this work, microscale evaporation heat transfer and capillary phenomena for ultra thin liquid film area are presented. The interface shapes of curved liquid film in rectangular minichannel and in vicinity of liquid-vapor-solid contact line are determined by a numerical solution of simplified models as derived from Navier-Stokes equations. The local heat transfer is analyzed in term of conduction through liquid layer. The data of numerical calculation of local heat transfer in rectangular channel and for rivulet evaporation are presented. The experimental techniques are described which were used to measure the local heat transfer coefficients in rectangular minichannel and thermal contact angle for rivulet evaporation. A satisfactory agreement between the theory and experiments is obtained. 

Abstract. In this study we report a literature review on the research and development work concerning thermal conductivity of nanofluids as well as their viscosity. Different techniques used for the measurement of thermal conductivity of nanofluids are explained, especially the 3co method which was used in our measurements. The models used to predict the thermal conductivity of nanofluids are presented. Our experimental results on the effective thermal conductivity by using 3co method and effective viscosity by vibro-viscometer for Si02-water, Ti02-water and A Os-water nanofluids at different particle concentrations and temperatures are presented. Measured results showed that the effective thermal conductivity of nanofluids increase as the concentration of the particles increase but not anomalously as indicated in the some publications and this enhancement is very close to Hamilton-Crosser model, also this increase is independent of the temperature. The effective viscosities of these nanofluids increased by the increasing particle concentration and decrease by the increase in temperature, and cannot be predicted by Einstein model. 

The different techniques for measuring the thermal conductivity of liquids can be classified into two main categories steady-state and transient methods. Both of these methods have some merits and disadvantages. The equipment for steady state method is simple and the governing equations for heat transfer are well known and simple. The main disadvantage is the very long experimental times required for the measurement and the necessity to keep... 

The most important experimental techniques in this field are structural analyses by both X-ray and neutron diffraction methods, and infrared and Raman spectroscopic measurements. Less frequently used techniques are nuclear magnetic resonance, both broad band NMR spectroscopy and magic angle spinning methods (MAS), nuclear quadrupole resonance (NQR), inelastic and quasielastic neutron scattering, conductivity and permittivity measurements as well as thermal analyses such as difference thermal analysis (DTA), differential scanning calorimetry (DSC), and thermogravimetry (TG and DTG) for phase transition studies. 

Simple a,/3-unsaturated aldehydes, ketones, and esters participate preferentially in inverse electron demand (LUMOdlcne controlled) Diels-Alder reactions with electron-rich, strained, or simple olefinic and acetylenic dienophiles.3 5 The thermal reaction conditions for promoting the [4 + 2] cycloadditions of simple 1-oxabutadienes (R = H > alkyl, aryl > OR), cf. Eq. (1), are relatively harsh (150-250°C), and the reactions are characterized by competitive a,/3-unsaturated carbonyl compound dimerization or polymerization. Usual experimental techniques employed to compensate for poor conversions include the addition of radical inhibitors to the reaction mixture and the use of excess 1-oxabutadiene for promoting the [4 + 2] cycloaddition. Recent efforts have demonstrated that Lewis acid catalysis and pressure-promoted reaction conditions28-30 may be used successfully to conduct the [4 + 2] cycloaddition under mild thermal conditions (25-100°C). 

Some points of experimental technique should be mentioned. The contact pressures under which the apparatus can be operated are increased by the use of diamond, which is mechanically stronger than glass, as the plate material. Furthermore, diamond has good thermal conductivity, so that heating of the contact zone as the experiment proceeds is easier to control. The average refractive index of the oil in the pressurized gap is computed from the Lorenz equation. 2-1... 

TPS (Transient Plane Source) technique has been shown to be effective method to measure the thermal conductivity, diffusivity of rare earth oxide powder such as gadolinium oxide, samarium oxide, and yttrium oxide. The details of the measutrement are described in Ref 66. The experimental results of effective thermal conductivity as well as thermal diffusivity of the above described three rare earth oxides are tabulated in Table 5-7. 

Th is chapter deals with the measurement of thermal conductivity, thermal diffusivity. and specific heat. Other properties that are sometimes included under the umbrella term "thermal properties" are dealt with in other parts of this volume. In most cases it does not matter whether the sample is a rubber or a plastic, the experimental techniques arc the... 

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