Search

The volumetric flow meter for gases with magnetic fluid is built using a sensing unit (without moving solid mechanical components but exploiting the properties of magnetic fluids) and an electronic measuring system. The sensing unit consists of two sensors, one for differential pressure in gases (equipped with a laminar flow-measuring tube) and another for acceleration or inclination angle. Starting from some technical characteristics (of these sensing units) obtained by a numerical simulation method (or by an analytical one), the paper presents the possibility of using this kind of transducers in a N +1 flow meters network for gases. Every N flow meters of closed range are supervised by another flow meter of higher range. This structure can warn (by software) about any problem (e.g. gases leakage) in the network.

This paper presents a dielectric and magneto-dielectric study of magnetic fluids made of three different, partially substituted, manganese ferrite particles dispersed in kerosene. Measurements were performed using a wholly automated spectrometer in the frequency range 1 mHz–10 MHz and a temperature range from −200°C up to 100°C. We can distinguish the two phases (solid and liquid) in pure kerosene and three phases for all the magnetic fluid samples. We observed the effect of anisotropy constant and domain magnetization of the particles on magneto-dielectric measurements. We also observed the temperature sensitivity of these fluids.

The aim of this paper is to present the NH 2 dielectric behaviour in the primary amines for the importance it bears in the interaction of aminoacids and proteins and their influence in the electric conduction processes. For that, the dielectric properties of 1-propylamine, 1-butylamine and 1-pentylamine have been studied. Measurements were performed between room temperature and −180 °C in the low frequency range and micro-waves measurements were done between −40 °C and 25 °C. The isofrequency recordings of dispersion e ′ and absorption e ′′, for these three primary amines, show clearly the relaxations and the effect of the aliphatic chain length.

Dans ce travail nous presentons un systeme haute impedance totalement automatique fonctionnant dans la gamme de frequence 1 mHz-10 kHz et concu pour la mesure des impedances complexes (Rp // Cp) jusqu'a 10 12 Ω. Pour cela nous avons construit, autour d'un analyseur vectoriel, un electrometre haute impedance programmable fonctionnant en mode shunt. Ce dispositif utilisant des resistances de hautes valeurs et des condensateurs a faibles fuites, fait appel a l'electronique haute impedance; les composants sont selectionnes au moyen de relais Reed de tres haute isolation commandes par un bus VXI.

We have measured the susceptibility of two ferrofluids in the frequency range 0.1–20 GHz. We confine the liquid under test in a coaxial line cell and we use the reflection/transmission method to obtain χ ∗ . If we add a constant axial magnetic field to the microwave field we evidence an increase of the gyromagnetic resonance phenomenon appearing as a consequence of the artificial increase of anisotropy.

We studied the shear viscosity and the main dielectric relaxation time of dibutyl phthalate from 97°C down to −96°C (near its glass transition temperature Tg). A visco penetrometer and a dielectric spectrometer built in our laboratories allowed us to obtain experimental data in the ranges 10-109 Pa.s for viscosity and 1 mHz–2 MHz for dielectric relaxation time. All these data and those of different authors give viscosity and dielectric relaxation time versus temperature on twelve decades; they are well fitted by the Cohen and Grest relation. These fits obtained on a large temperature range show that there is a strong correlation between viscosity and dielectric relaxation time. Furthermore it appears that the dielectric relaxation time distribution is broadening in the vicinity of Tg.

We propose an appropriate calculation method, giving both the complex permittivity epsilon * and permeability mu * of a liquid sample, from transmission/reflection measurements obtained from a network analyser working on a coaxial line between 0.1 and 20 GHz. A 20 mm long specific coaxial cell has been constructed using two polytetrafluoroethylene joints to ensure air tightness. Its small length allows rejection towards the upper frequencies of the measurement anomalies given by the Nicolson-Ross equations. Positions and thickness of the joints are taken into account by the calculus. The whole system has been tested with the empty cell and then on several alcohols and ferrofluids. The results on alcohols are in excellent agreement with all previous results; measurement on one of the magnetic fluids (Fe2MnO4 in CCl4) has shown a Neel relaxation and also a gyromagnetic resonance.

This paper presents an experimental dielectric study of a ferrofluid, magnetic particles of CoFe/sub 2/O/sub 4/ dispersed in dibutylphthalate at different volume concentrations over a large temperature range (40 to -100/spl deg/C), between 1 mHz and 10 MHz, with and without a continuous axial or radial magnetic field. The analysis of static permittivity indicates that the magnetodielectric anisotropy which exists at room temperature, persists at lower temperature, near the glass transition temperature of the carrier liquid. Moreover these results show a possible existence and growth of aggregates at the upper concentrations of ferrites. The position of the relaxation peaks of different solutions is modified by the presence of an axial continuous magnetic field. >

We studied the complex permittivity of alkylhydrazines/water mixtures from room temperature down to − 120°C between 50 mHz and 2 MHz, in the mole fraction range 0.1 ≤ x ≤ 1. The addition of a second suitable component decreases and even eliminates, at sufficient concentration, the anomalies of pure water and allows, according to Oguni and Angell, to separate the “normal” and the “anomalous” parts of water physical properties. The static permittivity of alkylhydrazines - water mixtures (with monomethylhydrazine and 1,1-dimethylhydrazine) leads to estimate, by extrapolation at x = 0, the static permittivity of normal supercooled water below its homogeneous nucleation temperature, in spite of chemical associations present in the solutions. The values calculated by this method are in good agreement with our previous results obtained on alcohol/water mixtures and the data predicted by the random network model of Sceats and Rice.

Using numerical simulation methods, the paper presents the influence of some geometrical dimensions (radius of the coil, radius and thickness of magnetic shell) on the performances of the inductive transducers with magnetic fluids. The conclusions of the paper allow the calculation of some geometrical tolerances of the transducer so that the assembly will be placed in a desired precision class.

We present a dielectric study on ferrofluid solutions of Fe 2 CoO 4 in diethylene glycol or dibutyl phthalate, from 50 mHz to 10 MHz, in the temperature range -160–+40°C. When a transversal magnetic field is applied, a magnetodielectric anisotropy is in evidence. Above a concentration limit the colloidal suspensions do not remain well dispersed at low temperature. Moreover it seems that the melting point of a solution could be affected.

This paper presents a dielectric study of a ferrofluid Fe2CoO4 in dibutyl phthalate at different concentrations from room temperature down to low temperature less than -100°C. With results from our spectrometer we discuss, for a large interval of temperature, the homogeneity of the ferrofluid solutions when a continuous magnetic field is applied perpendicularly to the electric field.

The paper describes the possibility to capture the energy of the vertical movement of the ocean waves, using a gravitational electrical generator on magnetic fluid cushion. This is constructed from a permanent magnet in a magnetic fluid shell, which, under the ocean waves action, is moving by translation inside a hermetically sealed tube.

The paper presents the influence of relative magnetic permeability of the magnetic fluid ( μ r L ) on the sensitivity of the inductive transducers and the influence of relative magnetic permeability of the magnetic shell ( μ r E ) on its performances.

The paper investigates the calculus possibilities of coils inductances for the construction of inductive transducers with magnetic fluid (MF) for aerodynamic measurements, acceleration and inclination angle. These transducers have as essential electrical components one or two pairs of identical coils of circular cross section, uniformly wound. The carcasses of every pair of coils have the role of vertical cylindrical reservoir and communicate at the bottom creating a vertical U-shaped tube half filled with MF. The MF has the role of magnetic liquid core for the electrical coils. The paper presents a comparative study between four different calculus methods of the inductance versus the level of MF (one numerical simulation method, and, three different analytical methods based on the images method for a non-homogeneous medium).

The authors present a dielectric study of ferrofluid, magnetic particles of Fe/sub 2/CoO/sub 4/ dispersed in dibutyl phthalata, at different volume concentrations in a large temperature range (from 40/spl deg/C down to -100/spl deg/C) between 1 MHz and 10 MHz, with and without a continuous axial or radial magnetic field. The analysis of static permittivity shows a small magnetodielectric anisotropy, even at low temperature, and the possible existence and growth of aggregates at higher concentrations. It is shown that, in the given experimental conditions, and under a continuous longitudinal or transverse magnetic field, this ionic colloidal suspension does not remain well-dispersed above a limit volume concentration (x /spl ap/ 0.05) when temperature is decreasing.

We report on the dielectric and magnetodielectric effects in the different phases of an ionic ferrofluid made of nanometric particles of manganese ferrite (Fe/sub 2/MnO/sub 4/) diluted at different volume concentration in carbon tetrachloride (CCl/sub 4/) used as carrier liquid. To obtain a fast recording of experimental data we have used an automated spectrometer working in the frequency range 1 mHz-10 MHz and from -200/spl deg/C up to 50/spl deg/C. This study shows the presence of three phases (liquid, plastic and solid) for pure CCl/sub 4/, these phases remain for the ferrofluid. Our experimental results allow an investigation of homogeneity and stability of these ionic dispersions at different concentrations and phases. Finally, a magnetodielectric anisotropy is observed when a continuous magnetic field (parallel or perpendicular to the electric field) is applied. This anisotropy observed at room temperature remains at very low temperature, in particular in the plastic phases.

We propose an appropriate method giving the complex permittivity of a liquid sample from transmission/ reflection measurements obtained from a network analyzer working on a coaxial line between 0.1 and 20 GHz. A specific coaxial cell was made with two etancheity joints in teflon encased at its extremities, Positions and thickness of this joints are taken into account by the calculus. This technique has been tested with the empty cell and then on several dielectric liquids. The results are in excellent agreement with all previous measurements, This method allows also to obtain complex permittivity and permeability of the liquid sample (ferrofluids), but then we have the "length resonance" problem which may be solved with an appropriate algorithm.

The author present results from an experimental study on binary polar-nonpolar mixtures (propylene carbonate-toluene) from ambient down to their glass transition temperatures. The values of static permittivity and dielectric relaxation time obtained made it possible to estimate the temperature dependence of dipole moment and the Kirkwood correlation factor of propylene carbonate as well as the molecular relation time of toluene (or methylbenzene). >

Results are presented which lead to the characterization of (alcohol)/sub x/(water)/sub 1-x/ mixtures between ambient and glass temperature over the whole molar fraction range. Suitable extrapolations to zero alcohol concentration allow one to calculate the dielectric relaxation time and the static permittivity of supercooled water below its homogeneous nucleation temperature. Use is made of a dielectric relaxation spectrometer operating from 1 MHz to 10 MHz in the temperature range -200, +100 degrees C and a total influence cell. The results obtained confirm that supercooled water dielectric parameters down to T/sub g/, are independent of alcohol. >

We present a magneto-optical method using Brown's relaxation in ferrofluids. This method permits one to make some viscosimetric measurements by putting a drop of miscible ferrofluid into a test liquid, glycerol or diethylene glycol (DEG). To test this method we have compared our results obtained for glycerol with those obtained from a more conventional method and we observed good agreement. After this validation, we were able to study the viscosity of DEG between -20 and +90 °C by using our magneto-optical method. The comparison of these results with those obtained in standard ways (in the temperature range from -10 to +20 °C) revealed very slight deviations.

Dielectric properties of 1-cyanoadamantane C10H15CN are analysed with very low frequencies between 80 K and 320 K. The critical frequency in the (stable and supercooled) plastic phases does not follow an Arrhenius law. This behaviour corresponds to the glassy state of cyanoadamantane. However, β relaxation in the glassy phase certainly does not exist in this compound.