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Two-phase Region (two-phase + region)

Distribution by Scientific Domains

Polymers and Materials Science	60%

Selected Abstracts

An assessment of friction factor and viscosity correlations for model prediction of refrigerant flow in capillary tubes

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 3 2005
Zhang Yufeng
Abstract In this paper, a homogeneous model including the metastable liquid and metastable two-phase region is presented to assess the effects of various friction factor equations and two-phase viscosity correlations on simulating the behaviour of capillary tubes. Both straight and coiled capillary tubes are considered and R-22 is used for comparison. The predicted pressure distribution, tube lengths or mass flow rates are compared with experimental data reported in literature. It is confirmed that the predicting accuracy with homogeneous model can be improved by employing the suitable correlations of friction factor and two-phase viscosity. For straight capillaries, the Churchill and Colebrook friction factor correlations give almost the same simulating results. However, the numerical results show that the optimum combination of correlations of friction factor and two-phase viscosity may be different when compared with different experimental data. For coiled capillaries, the Mori and Nakayama friction factor correlation agrees well with Ito's formula for single liquid-phase flow. Together with Giri's friction factor equation for two-phase flow, Cicchitti viscosity model best predicts the measured mass flow rate with an average error of 4.88%. Copyright © 2004 John Wiley & Sons, Ltd. [source]

Numerical simulation of thermal,hydraulic characteristics in a proton exchange membrane fuel cell

INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2003
Y.M. Ferng
Abstract The thermal,hydraulic characteristics of a proton exchange membrane fuel cell (PEMFC) are numerically simulated by a simplified two-phase, multi-component flow model. This model consists of continuity, momentum, energy and concentration equations, and appropriate equations to consider the varying flow properties of the gas,liquid two-phase region in a PEMFC. This gas,liquid two-phase characteristic is not considered in most of the previous simulation works. The calculated thermal,hydraulic phenomena of a PEMFC are reasonably presented in this paper, which include the distributions of flow vector, temperature, oxygen concentration, liquid water saturation, and current density, etc. Coupled with the electrochemical reaction equations, current flow model can predict the cell voltage vs current density curves (i.e. performance curves), which are validated by the single-cell tests. The predicted performance curves for a PEMFC agree well with the experimental data. In addition, the positive effect of temperature on the cell performance is also precisely captured by this model. The model presented herein is essentially developed from the thermal,hydraulic point of view and can be considered as a stepping-stone towards a full complete PEMFC simulation model that can help the optima design for the PEMFC and the enhancement of cell efficiency. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Comprehensive Linkage of Defect and Phase Equilibria through Ferroelectric Transition Behavior in BaTiO3 -Based Dielectrics: Part 1.

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2008
Defect Energies Under Ambient Air Conditions
Defect and phase equilibria have been investigated via the ferroelectric phase transition behavior of pure and equilibrated nonstoichiometric BaTiO3 powder samples. Through fabricating the BaTiO3 materials under highly controlled conditions to preserve the equilibrium conditions with respect to Ba/Ti ratio, annealing temperature (T), and oxygen partial pressure (PO2), systematic variations in the phase transition temperature can be noted with respect to Ba/Ti ratio and T. From the data extracted, we can then determine solubility limits. Equilibrating the defect reactions at the solubility limits provides a direct approach to identify and calculate the defect energetics. The phase transition temperature decreased with increasing concentration of the TiO2 partial-Schottky defects (BaTi1,,O3,2,) and the BaO partial-Schottky defects (Ba1,,TiO3,,), and showed discontinuous changes in the two-phase region. The formation enthalpy and entropy for the partial-Schottky defect reactions was evaluated to be 2.32±0.1 eV and 10.15±0.7 kB for the BaO partial-Schottky defect, and 2.89±0.1 eV and 8.0±1.5 kB for the TiO2 partial-Schottky defects equilibrated under air annealing conditions. [source]

Interpenetrating Polymer Networks with Spatially Graded Morphology Controllable by UV-Radiation Curing

MACROMOLECULAR SYMPOSIA, Issue 1 2006
Hideyuki Nakanishi
Abstract Interpenetrating Polymer Networks (IPNs) composed of polystyrene (PS) and poly(methyl methacrylate) (PMMA) were synthesized from a precursor mixture by using dissimilar photo-cross-link reactions. When the reation yields exceeded a certain threshold, the mixture was quenched from one-phase region into two-phase region, leading to phase separation. Upon irradiation with strong UV-light, an intensity gradient was formed along the propagating direction of the exciting light, generating a gradient of quench depth via the spatial inhomogeneity of the cross-link reactions. As a consequence, a gradient of the characteristic length scales was continuously generated from the top to the bottom of the mixture. The resulting three-dimensional (3-D) morphology was in-situ observed at different depths of the mixture by using a laser-scanning confocal microscope (LSCM). From this 3-D observation, it was found that phase separation was accelerated at the bottom of the mixture and proceeded in an autocatalytic fashion. The mechanism for the formation of the graded morphology was discussed in conjunction with the kinetics of the autocatalytic phase separation. [source]

Solubility islands for polymer blends , a new option to homogenize incompatible polymers?

MACROMOLECULAR SYMPOSIA, Issue 1 2003
Attila R. Imre
Abstract Experimental results of liquid-liquid phase equilibrium in a polydisperse blend of two polyalkylsiloxane are presented here. The UCST has an unusual pressure dependence: pressure induced miscibility at moderate pressures and pressure induced immiscibility at higher pressures, above a double critical point. The cloud point curve has two maxima in (concentration, temperature) as well as in (concentration, pressure) space. Approaching the double critical point, the high and low pressure branches of the cloud point curve merge and in a certain stage of this merging, they form a miscibility island located inside the two-phase region. Islands of this kind can give us a new tool to mix virtually immiscible blends. [source]