Thermal conductivity experimental methods

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... 

Ffe. 6.2 Thermal conductivity experimental setup using Lee s Disc method... 

If the contact resistance is assumed to be independent of sample thickness, an assumption supported by experimental results (20), equation 10 implies a plot of AT/Q vs Ax should 3ueld a straight line with slope 1/kA and intercept equal to contact resistance. In Figure 3 precautions have been taken in curve A to reduce contact resistance, whereas in curve B no precautions have been taken. Contact resistance was, as expected, smaller in curve A. However, both cases jdelded straight lines and an identical, and uniequivocal, value of thermal conductivity. This method should probably be preferred for the most accurate work, but it requires three or more specimens of varying thickness, adding enormously to the cost or time of measurement. 

Control of sonochemical reactions is subject to the same limitation that any thermal process has the Boltzmann energy distribution means that the energy per individual molecule wiU vary widely. One does have easy control, however, over the energetics of cavitation through the parameters of acoustic intensity, temperature, ambient gas, and solvent choice. The thermal conductivity of the ambient gas (eg, a variable He/Ar atmosphere) and the overaU solvent vapor pressure provide easy methods for the experimental control of the peak temperatures generated during the cavitational coUapse. 

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. 

In the laser flash method, the heat is put in by laser flash instead of electric current in the stepwise heating method mentioned above. Thus this method may be classified as a stepwise heating method. A two-layered laser flash method was developed by Tada et al. " The experimental method and the data analysis, including a case involving radiative heat flow, are described in detail in the review article by Waseda and Ohta. A thin metal plate is placed at the surface of a melt. A laser pulse is irradiated onto a metal plate of thickness / having high thermal conductivity. The sample liquid under the metal plate and the inert gas above the plate are designated as the third and first layers, respectively. The temperature of the second layer becomes uniform in a short time" and the response thereafter is expressed by... 

The spatial temperature distribution established under steady-state conditions is the result both of thermal conduction in the fluid and in the matrix material and of convective flow. Figure 2. 9.10, top row, shows temperature maps representing this combined effect in a random-site percolation cluster. The convection rolls distorted by the flow obstacles in the model object are represented by the velocity maps in Figure 2.9.10. All experimental data (left column) were recorded with the NMR methods described above, and compare well with the simulated data obtained with the aid of the FLUENT 5.5.1 [40] software package (right-hand column). Details both of the experimental set-up and the numerical simulations can be found in Ref. [8], The spatial resolution is limited by the same restrictions associated with spin... 

The experimental methods used for the determination of thermal conductivity are described by Tsederberg (1965), who also lists values for many substances. The four-volume handbook by Yaws (1995-1999) is a useful source of thermal conductivity data for hydrocarbons and inorganic compounds. 

The complete data series is used to calculate the temperature response, but only certain parts of the experimental data are used to calculate the error. An example of a calibration run is given in Figure 53, the final calibrated TRNSYS model run is shown in Figure 54. Using the first part of the data (with constant heat flux) an estimate of ground thermal conductivity of 2.15 was obtained. Yavatzturk s method yielded an estimate of 2.18, while the estimate obtained with the TRNSYS parameter estimation method was 2.10. 

The main experimental difficulties in both methods are due to the presence of shunt thermal conductances (i.e. electrical wires) and series thermal conductances (thermal contacts). The latter problem can be overcome by the potentiometric method (see Fig. 11.2). 

Thermodynamic data (enthalpy of reaction, specific heat, thermal conductivity) for simple systems can frequently be found in date bases. Such data can also be determined by physical property estimation procedures and experimental methods. The latter is the only choice for complex multicomponent systems. 

Fig. 4. Energy below the conduction band of levels reported in the literature for GaP. States are arranged from top to bottom chronologically, then by author. At the left is an indication of the method of sample growth or preparation liquid phase epitaxy (LPE), liquid encapsulated Czochralski (LEC), irradiated with 1-MeV electrons (1-MeV e), and vapor phase epitaxy (VPE). Next to this the experimental method is listed photoluminescence (PL), photoluminescence decay time (PLD), junction photocurrent (PCUR), photocapacitance (PCAP), transient capacitance (TCAP), thermally stimulated current (TSC), transient junction dark current (TC), deep level transient spectroscopy (DLTS), photoconductivity (PC), and optical absorption (OA).

The increased understanding of turbulence and the extension of the analysis of potential flow have made possible the consideration of many thermal and material transfer problems which formerly were not susceptible to analysis. However, at present the application of such methods is hampered by the absence of adequate information concerning the thermal conductivities and diffusion coefficients of the components of petroleum. The diffusion coefficient in particular is markedly influenced by the state of the phase. For this reason much experimental effort will be required to obtain the requisite experimental background to permit the quantitative application of the recent advances in fluid mechanics and potential theory to dynamic transfer problems of practical interest. 

Thermal conductivity is a fundamental property of substances that basically is obtained experimentally although some estimation methods also are available. It varies somewhat with temperature. In many heat transfer situations an average value over the prevailing temperature range often is adequate. When the variation is linear with... 

The methods of measurement of thermal conductivity can be divided into steady state methods and transient methods. Traditionally, steady state methods were most widely used as they are mathematically more simple, but because, particularly for materials of low conductivity, they can be very time consuming and involve expensive apparatus, non-steady state or transient methods have been developed. These can have experimental advantages once the much more difficult mathematical treatment has been worked out. 

Further advancements in the theory of fixed bed reactor design have been made(56,57) but it is unusual for experimental data to be of sufficient precision and extent to justify the application of sophisticated methods of calculation. Uncertainties in the knowledge of effective thermal conductivities and heat transfer between gas and solid make the calculation of temperature distribution in the bed susceptible to inaccuracies, particularly in view of the pronounced effect of temperature on the reaction rate. 

No experimental data on the effective thermal conductivity of an assemblage of micron size zeolite crystals under the conditions of sorption tests used in the examples above could be found in the literature. However, several methods are available for the calculation of k for an assemblage of particles with void fraction f. The thermal conductivities of the solid phase (k ) and the gas phase (k ) in the voids are needed [29]. We Bsed the method develop d by Maxwell. 

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... 

DC1, HF, and DF, rotational collision numbers appear to decrease with increasing temperature over the intervals for which data are available (see Table 3.2). His comparison of acoustic-absorption and thermal-conductivity data for both HC1 and H20 indicates consistent results for these two experimental methods and their respective interpretations. However, the apparent decrease of Zr with increasing temperature is in contradiction to Zeleznik s... 

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. 

Equation (13) can also be used for the calculation of molecular diameters from experimental viscosity data. These can be compared with molecular diameters as determined by other experimental methods (molecular beams, diffusion, thermal conductivity, x-ray crystallographic determination of molecular packing in the solid state, etc.). 

Thermal Conductivity. In [82], experimental data and calculation methods for ammonia liquid and vapor for the ranges 0.1-49 MPa (1-490 bar) and 20-177 °C... 

A careful test of Nernst s theory was reported by Isnardi243 in 1915. His work consisted of the measurement of the thermal conductivity of iodine (whose dissociation as a function of temperature and pressure was well known), comparison of the experimental results with those of Nernst s theory, and the use of the method to determine JD(H2) which was not then known. Isnardi measured thermal conductivities by the hot wire method, in which the rate of heat removal by conduction from the wire arranged concentrically in a cylinder containing the gas is given by... 

---