INDEX thermal diffusivity

Tables 2,3, and 4 outline many of the physical and thermodynamic properties ofpara- and normal hydrogen in the sohd, hquid, and gaseous states, respectively. Extensive tabulations of all the thermodynamic and transport properties hsted in these tables from the triple point to 3000 K and at 0.01—100 MPa (1—14,500 psi) are available (5,39). Additional properties, including accommodation coefficients, thermal diffusivity, virial coefficients, index of refraction, Joule-Thorns on coefficients, Prandti numbers, vapor pressures, infrared absorption, and heat transfer and thermal transpiration parameters are also available (5,40). Thermodynamic properties for hydrogen at 300—20,000 K and 10 Pa to 10.4 MPa (lO " -103 atm) (41) and transport properties at 1,000—30,000 K and 0.1—3.0 MPa (1—30 atm) (42) have been compiled. Enthalpy—entropy tabulations for hydrogen over the range 3—100,000 K and 0.001—101.3 MPa (0.01—1000 atm) have been made (43). Many physical properties for the other isotopes of hydrogen (deuterium and tritium) have also been compiled (44).

The flow process in an injection mould is complicated by the fact that the mould cavity walls are below the freezing point of the polymer melt. In these circumstances the technologist is generally more concerned with the ability to fill the cavity rather than with the magnitude of the melt viscosity. In one analysis made of the injection moulding situation, Barrie showed that it was possible to calculate a mouldability index (p.) for a melt which was a function of the flow parameters K and the thermal diffusivity and the relevant processing temperatures (melt temperature and mould temperature) but which was independent of the geometry of the cavity and the flow pattern within the cavity. 

The spatially periodic temperature distribution produces the corresponding relxactive index distribution, which acts as an optical phase grating for the low-power probing laser beam of the nonabsorbed wavelength in the sample. The thermal diffusivity is determined by detecting the temporal decay of the first-order diffracted probing beam [°o exp(-2t/x)] expressed by... 

Since the interferometer used for (dn / dT)c>p measurement is heated completely, and not just the cuvette, it has been made out of Zerodur (Schott, Mainz), which has a negligible thermal expansion coefficient. Precise values of the refractive index increments are crucial for the determination of the thermal diffusion coefficient and the Soret coefficient. The accuracy achieved for (dn / dc)ftP is usually better than 1 %, and the accuracy of (dn / dT)rp better than 0.1 %. 

The ratio of 6.8 for the two peak areas from stochastic TDFRS is close to the value of 5.9 as expected from the concentration ratio and the refractive index increments of the two PS, which depends on molar mass due to end-group effects. The thermal diffusion coefficient DT= 1.12 x 10 7 cm2 (sK) l is in excellent agreement with the value found previously in our laboratory [36]. 

FTIR reflectance and transmission spectroscopy is used for analysis of thin films. Nevertheless, due to the high absorptivities of mid-IR bands, the film thickness must be limited (up to 100 pm, depending on the specific bands chosen) in order to perform an accurate qualitative analysis. Other IR methods, such as attenuated total reflectance (ATR) and photoacoustic methods provide IR spectra of thick material, because they penetrate a very thin layer at the surface of a sample. However, is important to point out that the effective pathlength for the ATR and the photo-acoustic methods depends on the refractive index and thermal diffusivity, respectively. Therefore, the use of these techniques for the quantitative analysis of non-homo-geneous materials can be difficult. 

Viscosity index of fractions from thermally diffused ng oil. (a) Isoparaffins. (b) Condensed cycloalkanes. (c) nsed cycloakanes. (d) Aromatics. From data by Melpolder c ... 

Viscosity Index Distributions in Base Stocks Use of Thermal Diffusion... 

Other properties of these critical mixtures have also been investigated. In particular, the refractive index [153], the thermal conductivity Ath, and the thermal diffusivity Ah [124135] have been measured. Near the critical endpoint P , all these properties exhibit anomalous behavior as the temperature approaches the critical temperature. 

In another approach, which is a little more complicated [8], a glass capillary is placed on a cooled metal plate to stabilize the temperamre of the fluid, and then an infrared laser pulse heats up a mass of liquid. Because the refractive index is a function of temperature, instruments that are sensitive to the change of refractive index are installed downstream to detect the heated liquid. However, thermal diffusion makes it complicated to accurately determine the arrival time of the heated mass of liquid. 

Indices i and j refer to adjacent layers, kj and kj (W m s ) are thermal conductivities, and D, and Dj are the thermal diffusivities. Thermal effusivity is analogous to a refractive index for thermal waves. Reflection and absorption may be evaluated by the thermal reflection coefficient ... 

These volumes contain extensive tabulations of physical data relevant to concentrated solutions of binary systems, both organic and inorganic. The properties that are tabulated include dielectric constant, viscosity,. equivalent conductivity, surface tension, diffusion and thermal diffusion coefficients, vapor pressure, specific heat, electrochemical data, enthalpy of combustion, enthalpy of dilution and solution, transition enthalpies, and other properties. These books contain extensive tabulations of data pertinent to water and electrolyte solutions. The data are well organized and there is a general compound index as well as references to the original data sources. 

Increase in temperature causes a change in the index of refraction. Hence, a transient thermal lens is formed in the volume element absorbing the radiation. The temperature rise is typically of the order of lO C within a volume element of less than 10" cm. Several physical and chemical properties of materials such as thermal diffusivity, optical absorption coefficient, multiphoton crossections quantum yield of photoprocesses etc... may be determined by monitoring the time dependence of the amplitude of the thermal lens. This technique is fast, precise and contactless. 

Thermophysical Properties of Matter (14 volumes), by Touloukian, Y.S., Kirby, R.K., Taylor, R.E. Lee, T.Y.R. (eds.)(1970-1977). New York, IFI/Plenum Press. Thermal conductivity (vol. 1-3), Specific heat capacity (4-6), Thermal radiative properties, and thermal diffusivity (10), Absolute and Dynamic Viscosity (11), Coefficients of Thermal Expansion (12-13) and index (14). 

The index of refraction of the material in the layer can be estimated to be 1.333. The total intensity of the quasi elastically scattered light is proportional to the isothermal compressibility. From intensity measurements we estimate it to be about a factor 500 higher than the compressibility of water at O C. A diffusion constant, which describes the dynamics of the entropy fluctuations, has been determined to be about 3 10" cm /s. This value has to be compared with the thermal diffusivity in water a 10 cm /s or the constant for self diffusion in water Djj20 lO" cm /s. 

In 1971, Eichler, et al of the I. Physikalisches Institut der Technischen Universitat Berlin, reported the first detection of a transient grating. They used a ruby laser to produce a thermal refractive index grating in dye-containing methanol. In 1972, they reported additional measurements, including the time decay of the grating due to thermal diffusion, on a time scale of 1 ms. 

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