H.F.P. Knaap

Some simplified expressions for the thermal conductivity in an external field

For a polyatomic gas simple expressions have been derived for the thermal conductivity as well as for the variation of the thermal conductivity as a function of an external field. This has been achieved by using the total heat transport as a trial function in the kinetic theory instead of the usual approach in which translational and rotational heat transport are treated separately. For a number of gases a numerical comparison is made between both methods.

The thermal conductivity of polar gases in a magnetic field

Measurements are reported of the change in the thermal conductivity coefficients ▵λ∥ and ▵λ⊥ of polar gases under the influence of a magnetic field at room temperature. Investigated are the linear molecules HCl, DCl, HCN, OCS and CO2 and the symmetric top molecules CH3F, CD3F, CH3CN, CHF3, NH3 and ND3. The results on the nonequilibrium polarizations WJ and W⊔JJ obtained from these experiment are expressed in terms of effective cross sections. With the present results the amount of data now available on certain effective cross sections has grown to an extent that justifies a systematic overview. Correlations are presented between the effective cross sections and various molecular properties such as the electric dipole moment and the moments of inertia.

The viscomagnetic effect in polar gases

The magnetic field effect on the viscosity has been measured for several polyatomic gases with the emphasis on symmetric top molecules with strong electric dipoles. Theoretical expressions are given for the field dependent viscosity coefficients for various types of angular momentum polarizations, both for linear and symmetric top molecules. For CO2, OCS, N2O, SF6, CH3F, CHF3, PF3 and NF3 a decrease of the viscosity in a magnetic field was observed, which can be well described on the basis of a single angular momentum tensor polarization of the type . For NH3 and ND3, however, an increase in the viscosity was observed. In this case, a single polarization of the type J is involved. For HCl, DCl, AsH3 and PH3, no effects could be observed (|Δη/η|⩽2×10−5). No simple correlation is found between the magnitude of the effect and the strength of the molecular electric dipole moment. The experimental results are expressed in terms of effevtive cross sections.

A classical dynamics study of rotational relaxation in nitrogen gas

Rotational relaxation, related to the experimentally accessible volume viscosity, is described to the first order in the Sonine polynomial expansion of nonequilibrium distribution functions by the well known Wang Chang, Uhlenbeck, and De Boer expression. By a classical trajectory evaluation of a classical limit of this expression, using a recently proposed anisotropic inter-molecular potential for N2-N2, results are obtained for the rotational relaxation cross section. A corresponding expression including second order Sonine terms is also investigated. The second order results are found to differ significantly from the first order treatment (by about 18% at room temperature) and to agree very well with ultrasonic measurements over a temperature range from 77 K to 293 K.

The influence of a magnetic field on the thermal diffusion of polyatomic gas-noble gas mixtures

Experiments on the influence of a magnetic field on the thermal diffusion (DT) have been performed. Both the transverse coefficient, DtrT, as well as the difference between the longitudinal coefficients, D⊥T − D T, were measured for binary mixtures of N2, nD2, HD and nH2 with the nob le gases Ar, Ne and He and for the system pH2 Ar. For most of thesesystems, the results can be adequately described with the dominant angular momentum polarization of the form WJJ. For some mixtures, however, a significant contribution from a second polarization (viz. WJ) was found to be present. The results are expressed in terms of effective molecular cross sections. Using these results and those earlier obtained for the magnetic field effect on the thermal conductivity, an estimate is made about the magnitude of the Senftleben-Beenakker effect on the diffusion.

The temperature dependence of the viscomagnetic effect in the hydrogen isotopes

Experiments have been performed on the viscosity change of para and normal H2, and ortho and normal D2, under the influence of a magnetic field. This viscomagnetic effect is investigated as a function of the temperature between 140 K and room temperature. The data of this work are expressed in terms of effective cross sections for several elastic and inelastic collision processes. A comparison is made with results for HD, as obtained by Burgmans.

On the Senftleben-Beenakker effect on the thermal conductivity

Experimental results on the influence of a magnetic field on linear, spherical top and symmetric top molecules have been analyzed in terms of the kinetic theory based on the Waldmann-Snider equation. The traditional analysis on the basis of the two angular momentum polarizations W· and W ∧ J is compared with an alternative analysis on the basis of the three irreducible tensors of .

The transverse dufour effect

Experiments have been performed to study the influence of a magnetic field on the Dufour effect (or diffusion-thermo effect) in an equimolar N2 Ar mixture at room temperature. By comparing these experimental results with those obtained previously for the field effect on the thermal diffusion, an Onsager relation between these field effects is confirmed.

The Senftleben-Beenakker effect in ammonia and its mixtures with noble gases

Experimental results are presented for the influence of a magnetic field on the viscosity of NH3-He and NH3-Ar and on the thermal conductivity of NH3-Ar gas mixtures. Data are reported for various mixture compositions at room temperature. The data are analyzed in detail in an attempt to clarify the unique behavior of ammonia.

The Viscomagnetic Effect in Mixtures

A study is presented of the viscomagnetic effect in binar mixtures consisting of diatomics and noble gas atoms. The following systems have been investigated: HD -He, HD -Ne, HD-Ar and N2 -He, N2-Ne, N2-Ar. The purpose of this research is to obtain effective cross sections for the relatively simple interaction between monatomic and diatomic molecules. Various effective cross sections are presented.