Thermal effusivity

Fig. 5.8 Thermal effusion of H20 and C02 from a 196 nm thick anodic oxide film for a temperature ramp from RT to 1100°C. After [Le22],...

This equation describes the change of the difference of the mass fraction of component 1 with respect to a change in temperature at stationary states. This effect is called thermal effusion. 

J. Ristein, R.T. Stief, L. Ley, W. Beyer A comparative analysis of a-C H by infrared spectroscopy and mass selected thermal effusion. J. Appl. Phys. 84, 3836 (1998)... 

Roy Y. Mathis N, Closs S, et al. Online thermal effusivity monitoring A promising technique for determining when to conclude blending of magnesium stearate. Tablets Capsules 2005 3(2) 38-47. 

Additionally, near-infirared spectroscopy has been utilized to monitor moisture for endpoint determination (155,156), though this technique is limited to detecting only moisture at the bed surface. The FBRM is a technique for panicle size determination in a study by Dilworth et al. (157), comparing power consumption. FBRM, and acoustic signals, these measurements were found to be complimentary. Thermal effusivity is a material propeny that combines thermal conductivity, density and heat capacity. Fariss et al. (158) used at-line samples and found colinearity between power consumption and thermal effusivity. 

The data reported here were obtained using a Micromeritics ASAP 2010 equipped with optional 10- and 1-torr pressure transducer. Low-pressure data were corrected for thermal effusion. 

It is clearly difficult to employ this technique at high pressures since reactant and product ions ejected by the ejection pulse may be scattered differently on their passage out of the source. Under such conditions, it is apparently preferable to rely on thermal effusion, provided high enough pressures are employed. 

Jannot, Y. and Meukam, P. (2004) Simplified estimation method for the determination of the thermal effusivity... 

Fig. 4.11 Determination of the velocity distributions n(v ) and n(v i) by measuring the Doppler profile of absorption lines in a thermal, effusive NO2 beam [409]...

The new results expressed by Eqs. (3.50), (3.56), (3.57) and (3.58) are of interest in the study of chemical reactions. The above treatment has been utilized successfully to develop the necessary formalism for thermal effusion and thermomolecular pressure for an isomeric reaction, particularly for liquid He II. 

For surface heated inhomogeneous samples, thermal waves experience reflection or absorption when they encounter buried interfaces wherein there is a change in the thermal effusivity ratio ... 

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 ... 

The major thermal constants of solids are the thermal conductivity a (W/mK) and the heat capacity per unit volume, C (J/m K). Related thermal parameters are the thermal diffusivity D = a/C (m /s) and the thermal effusivity e = (Ws /m K). As a dynamic factor, the thermal penetration... 

The newness of these testing points has spurred a plethora of new companies and instrumentation. In addition to traditional spectroscopic ranges, laser-induced fluorescence, thermal effusivity, and acoustics (passive and active) have made appearances. Raman has also become process-hardened, along with other techniques. In the rush to be part of the pharmaceutical process revolution, some very interesting new players have entered the game. 

El has been used for other primary beam sources such as SFs" or which have been developed to enhance the ion yields for large molecular ions. For C o, a thermal effusive source in which Ceo powder is vaporized at 400 °C is combined... 

A primary beam mass filter may be used to insure the purity of the beam reaching the sample. The Cameca IMS instruments with a dual beam system of a duoplasmatron and cesium source use a primary beam magnet as the beams exit the source area to mass separate the ion beam. A mass gate or filter would be used to select ions of different masses traveling at different velocities in the column of a thermal effusive ion source (example and Cgo in a Cgo source) [16]. A mass... 

From the maximum of the shifted absorption profile the most probable velocity Vp can be deduced [10.17]. Figure 10.6b illustrates the measurement of velocity distributions of Na molecules in specified quantum states at different oven temperatures. The narrowing of the velocity distribution with increasing oven temperature and the increase of the most probable velocity Vp characterize the transition region from a thermal effusive molecular beam to a supersonic beam. The velocity distribution in the supersonic beam can be described by... 

A gas at a stable temperature and at atmospheric pressure is in a disturbed molecular state. The rates of the molecules have an isotropic distribution in the space, varying as the temperature square root varies. If a chamber under atmospheric pressure and a chamber under low pressure are connected together through a small hole, it is possible to obtain a thermal effusion or a supersonic beam. The isentropic pressure reduction enables the molecules to reach some supersonic speeds in a few micro seconds. Therefore, intermolecular recombinations are not possible and a molecular beam in only one direction is obtained. Pressure reduction releases the impact between the molecules. 

Thermal diffusion, which has just been discussed, occurs in mixtures in which molecules of solute and solvent interact with each other. Thermal effusion, the effect discussed next, occurs when the molecules of a pure gas react largely with surroundings. 

Thermal effusion is most clearly illustrated by the schematic drawings in Fig. 21.5-2. In these drawings, a pure gas is placed in a closed tube and separated into two volumes by a porous diaphragm. The gas on one side of the diaphragm is heated, so the gas pressure changes. After a while, the pressure reaches a constant value and can be measured. 

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