The effect of stationary and sweeping frequency AC electric fields on frost crystal removal on a cold plate

The effect of stationary and sweeping frequency AC electric fields on frost crystals growth and frost control/removal on a cold plate was studied for the first time in this paper. The main results of this study showed that the presence of AC electric fields can greatly affect both the frost crystals growth pattern and mass accumulation on cold surfaces. The ice surface electrical properties and basic electrostatics were used to explain the main findings in this paper. Up to 46% frost reduction was obtained when the electric field frequency spanned 370 Hz to 7.5 kHz while the applied voltage was 14.5 kV. Two different sets of environmental conditions were tested, which showed that the plate temperature placed an important effect on frost crystals growth under electric fields. An optimum application time of the AC electric fields was found based on least frost mass accumulation on the cold plate.     

Energetic Macroscopic Representation of a linear reciprocating compressor model

This article introduces the energetic macroscopic representation (EMR) as approach for the dynamic nonlinear modeling of a reciprocating air compressor. EMR has been introduced recently for research development in complex electromechanical systems and is based on action reaction principle. The compressor is divided into simple subsystems including: driver mechanism, cylinder head, valves and reservoir. Models are developed for different subsystems, which are assembled into a final overall system EMR. Since the final application of this model will be an isothermal Compressed Air Energy Storage system (CAES), special attention has been paid to transient heat transfer considering the thermal resistor and capacitor effect of the walls adopting a thermoelectric analogy. The results were verified both using Finite Element method and experiment. The EMR modeling presented here allows the modeling of multi-physics components and highlights the interactions of the electromechanical, heat transfer and fluid mechanics phenomena that occur simultaneously in an air compressor.     

Development of microwave assisted zeolite–water adsorption heat pump

A microwave assisted zeolite–water adsorption heat pump system was designed, manufactured and investigated experimentally. The influence of operation time of microwave oven on performance of the adsorption heat pump was studied. The performance criteria: coefficient of performance, specific cooling power and volumetric cooing power, were calculated for the designed and tested adsorption heat pump system. The regeneration of adsorbent bed was achieved very rapidly (35 min) by using microwave heating system. The poor thermal conductivity of adsorbent did not affect the periods of isosteric heating and isobaric desorption processes.     

Study on prevention of ice adhesion to cooling wall due to voltage impression in ice storage—discussion on possibility of attraction of oil to wall

For ice storage, one of authors has studied new ice slurry formed by cooling a water–oil mixture with stirring. When the mixture is stirred in a vessel, oil is charged by static electricity due to friction. If the vessel wall can attract charged oil, prevention of ice adhesion to the wall may be realized. Therefore, in this paper, in order to observe behavior of charged water–oil droplet or mixture in electric field by a high speed camera or video camera, two types of experiments were carried out. One was that the water–oil droplet charged by static electricity was made to fall plumb down between two electrodes with electric field or without electric field, varying the water content of droplet. The other was that a constant voltage was applied on the vessel filled with the water–oil mixture stirred. From experiments, it was confirmed that attracting force between the charged wall (electrode) and charged oil acted.     

Effects of electrode materials on freezing of supercooled water in electric freeze control

In order to clarify effects of electric charge on freezing of supercooled water, experiments were carried out with various kinds of electrodes in supercooled water. Water sample was kept in a test tube and cooled down at a constant cooling rate. When the water sample was maintained under a supercooling state, an electric charge was applied to the water sample with a small electric current. The degree of supercooling was measured continuously. Then the degree of supercooling at freezing was determined. Six kinds of materials were used for electrodes. Those materials were Aluminum, Copper, Argentum, Aurum, Platinum and Carbon. It was found that the effects of electric charge were distinct according to the material used for electrodes. The degree of supercooling at freezing was the lowest in the case of Aluminum. On the other hand, the highest value of the degree of supercooling at freezing was obtained in the case of carbon. The reason for the difference in the degree of supercooling at freezing by six materials was discussed.     

Suppression of ice adhesion force to cooling wall due to voltage application

For ice storage, one of the authors has previously reported on the ice slurry formed by cooling water–silicone oil mixture with stirring. When the mixture is stirred in a vessel, the oil is charged due to static electricity. If the vessel can attract the charged oil, suppression of ice adhesion force to a cooling wall may be possible. In this study, therefore, a certain voltage was applied to the vessel filled with the mixture with cooling and stirring simultaneously, and water was frozen in the vessel. Then, the ice adhesion force to the cooling vessel wall was measured under a constant apparent adhesion area between the ice and cooling vessel wall. From the measurement results, optimal conditions of the oil viscosity, rotation speed and applied voltage to suppress the ice adhesion force effectively were clarified. Moreover, the factors governing suppression of the ice adhesion force were clarified.     

Etude des caractéristiques hydrodynamiques des sols par la méthode TDR (time domain reflectometry)

The object of this laboratory study was to determine any relationship between the soil volumetric water content θ, the dielectric constant (permissivity –ε), and the impedance of the same soil (R₁). Time domain reflectometry (TDR) allows the measurement of material dielectric constant and impedance by determining electromagnetic pulse transit time and pulse attenuation. Using the established relations of the TDR method, it is possible to trace the volumetric water content and electric conductivity (or the impedance) of the soil simultaneously in a continuous manner. It was hoped that, thereafter, it may be possible to calculate the soil suction using soil permissivity and impedance. TDR measurements were carried out for different leachates and soils. Relationships found in previous work by the authors were used to compare water contents given by the TDR method with water contents obtained by drying the soil samples. The test results showed a relationship between water content and soil type and the electrical conductivity of the liquid when the TDR parameter was soil impedance. It was concluded that permissivity could be used to characterise the soil's water content. This relationship is used to study the changes in bentonite water content during air drying. Volumetric water content and impedance vs time curves allows the determination of shrinkage limit.     

Emerging pulsed electric field (PEF) and static magnetic field (SMF) combination technology for food freezing

The potential of an innovative freezing technique by applying combined pulsed electric field (PEF) and static magnetic field (SMF) was successfully tested and validated. 0.9% sodium chloride (NaCl) solution was frozen under the PEF (1.78 V cm⁻¹, duty ratio: 0.5) at the frequencies of 0–20 kHz and different SMF conditions (attractive and repulsive). At −20 °C, an increase in the working frequencies reduced the phase transition time and the shortest phase transition time (1443 ± 2 s) was obtained at 20 kHz. The patterns of ice crystals became uniformly round (roundness: 0.88–0.90) under the PEF. The effects of attractive and repulsive SMFs showed different patterns in ice crystal formation with the shortest phase transition time under the repulsive SMF. The combined PEF (1.78 V cm⁻¹ at 20 kHz) and repulsive SMF resulted in an effective and synergistic freezing process, forming uniformly round and the smallest mean size of ice crystals in the shortest phase transition (1004 ± 3 s).     

Radiocommunications et mobilité radiocommunications and mobility

Des études sont actuellement en cours pour définir la prochaine génération de systèmes, destinés à fournir les services de radiocommunication avec les mobiles du futur. Ces systèmes, identifiés par des sigles tels que UMTS, FPLMTS, IMT 2000, seront universels, multiservices, multienvironnements, et à très grande capacité. Ils font ľobjet de programmes internationaux de recherche et de normalisation. Le cnet participe à ces actions à travers le projet Rameau. Quatre chapitres portant chacun sur un domaine ďétude du projet (caractérisation du canal de propagation à large bande pour les mobiles, analyse de la technique ďaccès multiple par répartition en code (amrc ou cdma), étude portant sur la disponibilité et la capacité des futurs systèmes mobiles par satellites, développement de nouvelles classes ďalgorithmes pour la mise à jour de la localisation des mobiles dans le réseau) servent à illustrer la diversité des techniques qu’il est nécessaire ďétudier en préalable à la définition et la mise en œuvre des services futurs de radiocommunications avec les mobiles. Research is currently under way to define the next generation of systems to provide radiocommunication services with the mobiles of the future. These systems, with acronyms such as umts, fplmts and imt 2000, will be universal, multiservice, multienvironment and of very high capacity. They are the object of international research and standardization programs. The French national telecommunications research centre, cnet, is involved in these developments through the Rameau project. Four research areas of the project are examined (characterization of the wideband propagation channel for mobiles, analysis of the code distribution multiple access (cdma) technique, the availability and capacity of future satellite mobile systems and the development of new classes of algorithms for updating the locations of mobiles in the network) to illustrate the diversity of techniques that must be researched before the mobile radio services of the future can be defined and deployed.