Large Temperature Ratio Research Articles

Pulsar eclipsing mechanisms: the effect of photon-beam-induced acoustic turbulence

Pulsar eclipse due to induced three-wave interactions involving low-frequency acoustic turbulence is discussed. We consider both the case of electron acoustic waves when the ion temperature Ti is higher than the electron temperature Te and that of ion acoustic waves whenTe >Ti. In each case the corresponding growth rate for low-frequency acoustic waves induced by a high-frequency photon beam is evaluated. For Ti > Te, the maximum growth rate for electron acoustic waves depends strongly on Ti/Te and may be comparable to that of a Langmuir counterpart for sufficiently large temperature ratio Ti/Te. It is shown that induced scattering off electron acoustic waves can be important and can cause pulsar eclipse. We show also that for Te > Tiand in the small-angle approximation, growth of low-frequency ion acoustic waves due to the photon beam is always slower than Langmuir waves and the corresponding induced scattering is less effective than induced Raman scattering. Thus, induced Brillouin scattering involving low-frequency ion acoustic waves cannot be the main cause for pulsar eclipses.

Rarefied gas flow through a long tube at any temperature ratio

The mass flow rate of a rarefied gas through a long capillary caused by small pressure and temperature gradients has been calculated based on the s-model for the diffuse specular gas-surface interaction in the range of the rarefaction parameter from 0.005 to 50. A simple method of calculation of the thermomolecular pressure effect and the thermal creep caused by a large temperature ratio have been elaborated. Numerical calculations of both phenomena for the temperature ratio T2/T1=3.8—usually realized in experiments—have been carried out. It has been determined that the nonlinear thermomolecular pressure effect does not depend on the temperature distribution along the capillary. The nonlinear thermal creep has been calculated for two different temperature distributions along the capillary. A dependence of the creep on the temperature distribution has been found. It has been shown that the application of the linear theory based on the average rarefaction parameter to the gas flow at a large temperature ratio gives a significant error.

Ulysses Radio and Plasma Wave Observations at High Southern Heliographic Latitudes

Ulysses spacecraft radio and plasma wave observations indicate that some variations in the intensity and occurrence rate of electric and magnetic wave events are functions of heliographic latitude, distance from the sun, and phase of the solar cycle. At high heliographic latitudes, solartype Ill radio emissions did not descend to the local plasma frequency, in contrast to the emission frequencies of some bursts observed in the ecliptic. Short-duration bursts of electrostatic and electromagnetic waves were often found in association with depressions in magnetic field amplitude, known as magnetic holes. Extensive wave activity observed in magnetic clouds may exist because of unusually large electron-ion temperature ratios. The lower number of intense in situ wave events at high latitudes was likely due to the decreased variability of the high- latitude solar wind.

Natural Convection From Isothermal Cubical Cavities With a Variety of Side-Facing Apertures

An experimental investigation of heat transfer by natural convection from a smooth, isothermal cubic cavity with a variety of side-facing apertures is described in this paper. The study was motivated by the desire to predict the convective loss from large solar thermal-electric receivers and to understand the mechanisms which control this loss. Hence, emphasis is placed on the large Rayleigh number, Ra, regime with large ratios of the cavity wall temperature Tw to the ambient temperature T∞. A cryogenic wind tunnel with test section temperatures which are varied between 80 K and 310 K is used to facilitate deduction of the influences of the relevant parameters and to obtain large temperature ratios without masking the results by radiative heat transfer. A 0.4-m cubic cavity, which is mounted in the side wall of this tunnel, is used. The area of the aperture Aa and its location are key variables in this study. The data which are presented cover the ranges: 1 < Tw/T∞ < 3, L2/18 ≤ Aa ≤ L2, and 3 × 107 < Ra < 3 × 1010.

The effects of differential ion flows on EISCAT observations in the auroral ionosphere

During geomagnetic storms different partial pressure gradients in the auroral ionosphere may result in H +, He +, O + and molecular ions drifting with different velocities along the Earth's magnetic field line. For relative drift velocities ⪡ 400 m s −1 it is shown that differential ion flows may be identified by two signatures in the autocorrelation function (ACF) measured by EISCAT. For larger relative drifts numerical simulations show that these signatures still exist and may result in an asymmetry in the incoherent scatter spectrum for O + and molecular ions. It is demonstrated that UHF data can be reliably analysed for k 2 λ D 2 ≲ 1, but at high altitudes, where O +–H + flows are expected, UHF observations will be restricted by large Debye lengths ( k 2 λ D 2 > 1). Examples of ACFs based on polar wind theory are presented and discussed for the VHF system and finally it is shown that large ion temperature ratios ( T i ( H +) > T i ( O +)) can significantly affect the velocity determination.

Exergy conservation in parallel thermal insulation systems

This paper is a Second-Law study of thermal insulation systems consisting of two 1-dim. insulations in parallel. It is shown that the parallel-insulation model applies to power and refrigeration systems exposed to large absolute temperature ratios. The insulation design which conserves maximum exergy (available work) is determined for two classes of parallel-insulation systems: in one class, the two parallel insulations are cooled continuously by two streams, in the other class they are cooled partly (intermittently) by one stream of single-phase fluid. The study shows that, in contradiction to previously published results, the continuous-cooling method is thermodynamically superior to the partial-cooling method.

Wave formation and heat transfer at an ice-water interface in the presence of a turbulent flow

Under some conditions of temperature and flow an ice-water interface in the presence of a turbulent stream has been observed to be unstable. In this paper the source and the conditions for the instability were investigated for a well-defined turbulent boundary-layer flow. It was found that the instability resulted from the interaction that occurs between a wavy surface and a turbulent flow over it. Such an interaction results in a heat transfer variation which is 90 to 180 degrees out of phase with the surface wave shape – a result which is consistent with the calculations of Thorsness & Hanratty (1979a,b).The main factor controlling damping of the instability at an ice-water interface was found to be the rate at which heat is conducted away from the interface into the ice.In the past it has been found that when an ice layer is melting, that is when the heat conduction in the ice is small, the ice surface is highly unstable. In the present study it was found that for a sufficiently large temperature ratio (Tf−Tw)/(T∞−Tf), a steady-state ice layer is also unstable. Furthermore it is predicted, from the present observations, that a growing ice layer with a ratio of ice-side to water-side heat fluxes of up to 2.3 could be unstable.Under sufficiently unstable conditions waves on the ice surface grow to an amplitude at which flow separations occur near the wave crests. This results in a ‘rippled’ ice surface pattern very similar to the patterns observed on mobile bed surfaces (Kennedy 1969) or surfaces which are being dissolved into a flowing stream (Allen 1971). The development of a ‘rippled’ ice surface results in a very substantial increase in the mean heat-transfer rate which would have an important influence on predictions of ice formation in the presence of a turbulent stream.

A procedure for nonlinear least squares refinement in adverse practical conditions

During geomagnetic storms different partial pressure gradients in the auroral ionosphere may result in H+, He+, O+ and molecular ions drifting with different velocities along the Earth's magnetic field line. For relative drift velocities ⪡ 400 m s−1 it is shown that differential ion flows may be identified by two signatures in the autocorrelation function (ACF) measured by EISCAT. For larger relative drifts numerical simulations show that these signatures still exist and may result in an asymmetry in the incoherent scatter spectrum for O+ and molecular ions. It is demonstrated that UHF data can be reliably analysed for k2λD2 ≲ 1, but at high altitudes, where O+–H+ flows are expected, UHF observations will be restricted by large Debye lengths (k2λD2 > 1). Examples of ACFs based on polar wind theory are presented and discussed for the VHF system and finally it is shown that large ion temperature ratios (Ti(H+) >Ti(O+)) can significantly affect the velocity determination.

Electrostatic heating of solar wind ions beyond 0.1 AU

It is argued that the large electron-proton temperature ratio predicted by the Hartle-Sturrock two-fluid solar wind model may be unstable to generation of ion acoustic waves beyond 0.1 AU, and that this instability is capable of providing a turbulent mechanism for the preferential heating of protons to produce ratios Te/Tp ≲ 5–10 near 1 AU in accord with experimental observations.

Effective absorption coefficients for radiant energy transport in nongrey, nonscattering gases

An approximation for integrated intensity in nongrey, nonscattering gases is presented that uses a new mean absorption coefficient in the grey gas transport equation. This absorption coefficient is called an effective absorption coefficient. To test the approximation, the integrated intensities were calculated by exact and approximate methods for 40 cases. The integrated intensities calculated by the effective absorption coefficient approximation had errors of only - 25 to + 28 per cent, which demonstrated the superiority of this approximation over a similar approximation using the Planck mean absorption coefficient. Despite certain restrictions on the form of the spectral absorption coefficient, the effective absorption coefficient approximation is expected to be useful for most problems in LTE nonscattering plasmas, even where large temperature ratios and inhomogeneities are present.

On the power scattered from density fluctuations in a plasma

Abstract : The power spectral density for scattering from density fluctuations in a plasma was numerically integrated to check an approximate analytical ex pression for the total scattered power. For all wavelength - Debye-length ratios, the analytical expression decreases monotonically with increas ing electron-ion temperature ratio. The numeri cal results differ significantly from this be havior only for temperature ratios greater than to a maximum for large temperature ratios. The discrepancy is more important for less massive ions and for larger-wavelength - Debye-length ratios. (Author)