Flow Characteristic Curve Research Articles

Gas–liquid two-phase flow patterns in parallel channels for fuel cells

Two-phase flow in horizontal parallel channels has been experimentally investigated under fuel cell related operating conditions. Pronounced hysteresis is observed in the pressure drop versus flow characteristic curve when starting from either flooded or dry conditions. When gas is introduced into channels initially filled with water (flooded initial condition), both gas and liquid tend to flow predominantly in one channel at low gas or liquid flow velocities. As the gas flow velocity increases, even distribution of gas and liquid flow in both channels is observed, accompanied with a sudden decrease in the pressure drop. On the other hand, even gas and liquid flow distribution between both channels is found at comparatively lower gas flow velocities when starting with dry-gas flow conditions with liquid introduced into channels filled with gas (stratified flow regime). The flow regimes of this system are visualized in plots of the pressure drop against gas and liquid flow velocities. However, this phenomenon tends to vanish at high gas and liquid flow velocities, suggesting that high gas and liquid flow velocities are required to ensure even flow distribution in parallel channels. The hysteresis points appear at the same level of the pressure drop, reflecting intrinsic characteristics of the parallel channels used in this study. These results have important implications for PEM fuel cell operational strategies. In order to avoid reactant mal-distribution in parallel flow channels in the flow field in the two-phase flow regime, fuel cells should be operated at sufficiently high gas flow velocities.

Experimental and numerical study of spouted bed fluif dynamics

Spouted beds, originally invented in Canada by Mathur and Gishler (1955) as an alternative to fluidized beds for handling coarse particles, are now widely studied in a variety of physical operations, such as drying, coating and granulation. In this work the particle velocity, minimum spouting flow rate and characteristic fluid-dynamic curves of the spouted bed were obtained using a Eulerian granular multiphase model. The computational work was significantly reduced for axisymmetric gas-solid flows. The experimental data obtained in two spouted bed configurations, conical-cylindrical and two-dimensional, were compared with the simulated results, showing good agreement

DYNAMIC SIMULATION AND EXPERIMENTAL RESEARCH ON CHARGE OF GAS BOOSTER

Based on the analysis of principle and structure of the gas booster, this paper studied on its charging process from low-pressure gas bottle to high-pressure one, considered the effect of some facts, including the changing of inlet and outlet pressure, clearance space, friction, according to the principle of kinematics, gas dynamics and thermodynamics ,established the mathematical and dynamics model of a gas booster system, which includes pressure differential equation of each chamber, flow rate equation, as well as the temperature equation and piston acceleration equation. The system is simulated with M-File of MATLAB software, and we got the pressure change curves, flow characteristic curve and time of charging gas, and the experimental data proved the correctness of simulation result, and provide theoretical basis for model selection and overall design. �

不均等負重合案内弁を用いた空気圧案内弁・シリンダの周波数特性

Measurements of the underlap for four-way valves gave results that the underlap was not only uneven but also geometrically asymmetric for some four-way valves. Both the unevenness and the asymmetricity have considerable influence on the characteristics of the valve-controlled cylinder. In addition to the unevennesses i=(Δ1/Δ)- 1, i= (Δ'1/Δ')-1, the asymmetricity η=Δ'1/Δ is introduced for a valve, where Δ, Δ' are the mean underlaps of the left side and the right side three-way valves and Δ1, Δ'1 are the underlaps on the supply sides. represents the right side. Considering i, η and Δ of a valve, the frequency response of a valve-controlled cylinder with viscous friction, Coulomb friction and mass load was theoretically analyzed where the flow versus pressure characteristic curves were approximated partially as polynomials of degree 3 of the pressure. The tendency shown by the theoretical results agreed fairly well with that of the experimental results. The frequency characteristics of (piston velocity)/(spool displacement) = V(jω)/ Y(jω)show the same tendency for an asymmetric valve as that for a symmetric valve. But, for the case where an asymmetric valve is used, there is null shift of the valve ( δο) for avoiding the piston drift. δο changes in proportion to i, and |δο| becomes larger according to the increase in η (for η>1) or 1/η (for η <1).δο changes little for the changes in Δ and frequency ω.