Procédé de stockage de chaleur solaire intersaisonnier par absorption LiBr-H2O

Un procédé de stockage de chaleur est développé, basé sur le principe de l'absorption. L'objectif visé est de stocker de l'énergie solaire en excès lors de journées chaudes et ensoleillées pour pouvoir la valoriser lors de journées plus froides, lorsque l'ensoleillement reçu par un système de chauffage solaire est insuffisant. Le principe de l'absorption présente l'intérêt d'une densité de stockage importante (de l'ordre de 2 à 4 fois celle du stockage par chaleur latente) et de pouvoir adapter la durée de stockage, du cycle jour/nuit au stockage intersaisonnier

Les adaptations à la volvation du squelette externe de la tête chez \u3cem\u3eCaecosphaeroma burgundum\u3c/em\u3e Dollfus, Crustacé Isopode des eaux souterraines

The study of the cephalic capsule of Caecosphaeroma burgundum, a subterranean waters Isopod, demonstrates improved adaptations to volvation; these concern in a similar manner the other regions of the body, particularly the pleotelson. From a primitive aquatic Isopod structure, the head of this blind Spheromid has been completely fashioned by many mechanical factors: posterior margin of pleotelson providing support on the head, relation of anterior angles of the second pereionit and, above all, the mandibular palps and antennae which retract into two deep grooves of the face. The comparative study of the head of other volvational Isopods shows the importance of that “antennary factor”, e.g. in Oniscoids, epigean Spheromids and some other subterranean waters Isopods (two Spheromids and one Cirolanid). This comparison shows that Caecosphaeroma burgundum is certainly the most specialized of all; it approaches perfection in volvation for it is the only one which rolls up into a hermetic sphere without outwards projections. Volvation seems to play a two-fold role. It is a mean of defence against predators used by single specimens and by copulating pairs, males and females being then associated in two concentric spheres. Furthermore, it is a very important way for passive dissemination allowing settlement of these Crustacea in distant subterranean waters

Mise en evidence de substances fluorescentes dans les organes jaunes de Caccosphaeroma burgundum Dollfus, Crustacé Isopode des eaux souterraines

Chromatographic analysis of the yellow organs of the fresh-water Isopod Crustacean Caecosphaeroma burgundum Dollfus revealed, through observation of the chromatograms in ultraviolet light, the occurrence of both absorbing and fluorescent substances. Among the latter, only isoxanthopterin has been identified. The yellow pigment, which probably has a pteridine nucleus, could not be identified as a known compound and will be the object of later investigations

Measurement Of Two-phase Mass Flow Rate And Quality Using Venturi And Void Fraction Meters

The measurement of the mass flow rate and quality of a two-phase gas-liquid flow is of interest in many fields of engineering such as refrigeration, power cycles, chemical processes, nuclear plants and petroleum production. This paper presents the use of a venturi and a void fraction meter for the measurement of refrigerant R-134a liquid-vapor mass flow rate and quality in vertical pipes. Measuring a single-phase mass flow is comparatively easy. The medium is a continuum with either a laminar or a turbulent flow. Measurements of the pressure drop produced by a venturi meter allow the instantaneous mass flow rate to be determined unequivocally and with great accuracy. In two-phase flow, the phases occurring in the flow channel are discontinuous. There may be such flow regimes as bubbly, slug, churn, annular and dispersed flows, which are difficult and expensive to identify. Even pressure drop measurements do not allow the mass flow to be derived unequivocally and precisely because there is a strong dependency on the flow regime and the vapor quality (vapor mass fraction). Since these quantities are not known in practical measurements, the measuring errors of such techniques frequently range between 5 and 20%. Fundamental improvements in the accuracy of measuring two-phase flows can only be attained with the measurement of at least two independent parameters. These are typically a measure of velocity or volumetric flow rate and a measure of the mixture density or void fraction. Differential pressure instruments, such as orifice, venturi, and nozzle meter, were the earliest and simplest forms of metering devices used in two-phase mass flow rate and quality measurements. The venturi meter induces the lowest pressure loss relative to the other differential pressure instruments. In this work, the measurement of the pressure drop in a venturi meter is complemented with the measurement of the void fraction by a electrical impedance sensor. Then, the two-phase mass flow rate and quality were determined from a theoretical model. It was found that proposed theoretical model provides a good accuracy for all experimental conditions.244363368Abdul-Razzak, A., Measurement of two-phase refrigerant liquid-vapor mass flow rate - Part 1: Venturi and void fraction meters (1995) ASHRAE Transactions, 101 (2), pp. 511-522Bernier, R.N., Brennen, C.E., Use of electromagnetic flowmeter in two-phase flow (1983) Int. J. Multiphase Flow, 9 (3), pp. 251-257Class, G., Hain, K., True mass flowmeter - A mass flowmeter for nonsteady-state two-phase flow (1983) Nuclear Technology, 60, pp. 314-319Collins, D.B., Gacesa, M., Measurement of steam quality in two-phase upflow with venturi meters and orifice plates (1971) J. of Basic Engineering, 93 (11)Curtelin, R., (1991) Decompression d'un Reservoir de Propane Liquidifie, , Ph.D. Thesis, Ecole Centrale de Paris, FranceFouda, A.E., Rhodes, E., Total mass flow and quality measurement in gas-liquid flow (1978) Two-Phase Transport and Reactor Safety, 4. , T. N. Veziroglv and S. Kakac, eds., Hemisphere Publishing Corp., New YorkFoussat, A.J.M., Hulin, J.P., Vertical liquid-liquid and liquid-gas two-phase flow measurements with a vortex flowmeter (1983) Measuring Techniques in Gas-Liquid Two-Phase FlowsFrank, R., Mazars, J., Ricque, R., Determination of mass flow rate and quality using a turbine meter and a venturi (1977) Heat and Fluid Flow in Water Reactor Safety, , I Mech E Conference, Manchester, EnglandHarris, D.M., Shires, G.L., Two-phase pressure drop in a venturi (1972) Nat. Engng. Lab. UK, Report No. 549, 549, pp. 18-35Reimann, J., Measurements of two-phase mass flow rate: A comparison of different techniques (1982) Int. J. Multiphase Flow, 8 (1), pp. 33-46Vallascas, R., Application of the linear-resistance flowmeter for low Reynolds numbers two-phase flowrate measurements (1983) Rev. Sci. Instrum., 54 (11), pp. 1525-1528Wan, P.T., (1990) Two-phase Flow Measurement with Flow Nozzles, pp. 167-172. , ASME, HTD-155Wyatt, D.G., Electromagnetic flowmeter sensitivity with two-phase flow (1986) Int. J. Multiphase Flow, 12 (6), pp. 1009-1017Zivi, S.M., Estimation of steady-state steam void fraction by means of the principle of minimum entropy production (1963) 6th National Heat Transfer Conference, , ASME preprint 63-HT-16, AIChE-ASME, Bosto

Forced convective heat transfer of refrigerant 22 evaporating in upward and downward flow in U-bends

Peer reviewed: YesNRC publication: Ye

Étude des séries excitoniques jaune et verte dans des cristaux de Cu2o, dopés à l'argent

The absorption spectra of thin samples of silver-doped Cu2O have been studied at 4,2 °K and 77 °K. The concentration range was (0-2) mole %. A shift of both the yellow and green series towards the lower energies is observed. This shift increases with the concentration of silver. Furthermore, the linewidths increase and the continuum overlaps the line spectra with increasing concentration of impurities. The analogy of these phenomena with those found by thermal variation is remarkable, and may suggest an expansion of the crystal lattice, due to the impurities. The spin-orbit coupling separation of the valence band remains practically constant.Nous avons étudié, à 4,2 °K et à 77 °K, les spectres d'absorption de lames minces de Cu2 O, de différentes teneurs en Ag. On observe essentiellement un déplacement de l'ensemble des séries jaune et verte vers les faibles énergies. Ce déplacement est d'autant plus grand que la teneur en argent des échantillons est plus élevée. De plus, les raies s'élargissent et le fond continu avance sur le spectre de raies quand la concentration augmente. L'analogie de ces phénomènes avec ceux trouvés pour la variation thermique est frappante et suggère une dilatation du réseau en présence des impuretés. L'augmentation de la séparation spin-orbite de la bande de valence reste très faible

Analysis of different fouling predictive models in a Heat Exchanger from experimental data

International audienceWe present a methodology that incorporates the implementation and validation of experimental data analysis for the creation of a predictive tool of heat exchanger fouling effects. The goal is to determine a realistic fouling kinetics in order to develop an adapted maintenance practice for minimizing energetic and intervention costs. The test bench implemented is equipped with plate and gaskets heat exchanger provided with industrial plates sizes. Particles are injected into the cold fluid to simulate a fouling. A metrology device is used on heat exchanger in order to control thermal and hydraulic performance through usual parameters. Several realistic conditions are tested during a learning phase to establish predictive models based on these experimental data. Results are analyzed using: (i) the asymptotic fouling models of Kern and Seaton (ii) several predictive models from a statistical approach by different methods (multiple linear regression, artificial neural network). For each of them, conclusions are made about the accuracy of the modes and their application limits