scholarly journals A thermodynamic model to predict the aqueous solubility of hydrocarbon mixtures at two-phase hydrate-liquid water equilibrium

2016 ◽  
Vol 414 ◽  
pp. 75-87 ◽  
Author(s):  
Srinath C. Velaga ◽  
Jonathan S. Levine ◽  
Robert P. Warzinski ◽  
Brian J. Anderson
Keyword(s):  
Liquid Water ◽  
Thermodynamic Model ◽  
Aqueous Solubility ◽  
Two Phase ◽  
Hydrocarbon Mixtures ◽  
Water Equilibrium

scholarly journals An Accurate Model to Calculate CO2 Solubility in Pure Water and in Seawater at Hydrate–Liquid Water Two-Phase Equilibrium

Minerals ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 393
Author(s):  
Mengyao Di ◽  
Rui Sun ◽  
Lantao Geng ◽  
Wanjun Lu
Keyword(s):  
Experimental Data ◽  
Phase Equilibrium ◽  
Liquid Water ◽  
Model Comparison ◽  
Pure Water ◽  
Co2 Storage ◽  
Co2 Solubility ◽  
Two Phase ◽  
Hydrate Phase ◽  
Water Equilibrium

Understanding of CO2 hydrate–liquid water two-phase equilibrium is very important for CO2 storage in deep sea and in submarine sediments. This study proposed an accurate thermodynamic model to calculate CO2 solubility in pure water and in seawater at hydrate–liquid water equilibrium (HLWE). The van der Waals–Platteeuw model coupling with angle-dependent ab initio intermolecular potentials was used to calculate the chemical potential of hydrate phase. Two methods were used to describe the aqueous phase. One is using the Pitzer model to calculate the activity of water and using the Poynting correction to calculate the fugacity of CO2 dissolved in water. Another is using the Lennard–Jones-referenced Statistical Associating Fluid Theory (SAFT-LJ) equation of state (EOS) to calculate the activity of water and the fugacity of dissolved CO2. There are no parameters evaluated from experimental data of HLWE in this model. Comparison with experimental data indicates that this model can calculate CO2 solubility in pure water and in seawater at HLWE with high accuracy. This model predicts that CO2 solubility at HLWE increases with the increasing temperature, which agrees well with available experimental data. In regards to the pressure and salinity dependences of CO2 solubility at HLWE, there are some discrepancies among experimental data. This model predicts that CO2 solubility at HLWE decreases with the increasing pressure and salinity, which is consistent with most of experimental data sets. Compared to previous models, this model covers a wider range of pressure (up to 1000 bar) and is generally more accurate in CO2 solubility in aqueous solutions and in composition of hydrate phase. A computer program for the calculation of CO2 solubility in pure water and in seawater at hydrate–liquid water equilibrium can be obtained from the corresponding author via email.

Effect of Common Impurities on the Phase Behavior of Carbon-Dioxide-Rich Systems: Minimizing the Risk of Hydrate Formation and Two-Phase Flow

SPE Journal ◽  
2011 ◽  
Vol 16 (04) ◽  
pp. 921-930 ◽  
Author(s):  
Antonin Chapoy ◽  
Rod Burgass ◽  
Bahman Tohidi ◽  
J. Michael Austell ◽  
Charles Eickhoff
Keyword(s):  
Experimental Data ◽  
Carbon Dioxide ◽  
Phase Behavior ◽  
Water Content ◽  
Thermodynamic Model ◽  
Two Phase Flow ◽  
Hydrate Formation ◽  
Experimental Methodology ◽  
Phase Flow ◽  
Two Phase

Summary Carbon dioxide (CO2) produced by carbon-capture processes is generally not pure and can contain impurities such as N2, H2, CO, H2 S, and water. The presence of these impurities could lead to challenging flow-assurance issues. The presence of water may result in ice or gas-hydrate formation and cause blockage. Reducing the water content is commonly required to reduce the potential for corrosion, but, for an offshore pipeline system, it is also used as a means of preventing gas-hydrate problems; however, there is little information on the dehydration requirements. Furthermore, the gaseous CO2-rich stream is generally compressed to be transported as liquid or dense-phase in order to avoid two-phase flow and increase in the density of the system. The presence of impurities will also change the system's bubblepoint pressure, hence affecting the compression requirement. The aim of this study is to evaluate the risk of hydrate formation in a CO2-rich stream and to study the phase behavior of CO2 in the presence of common impurities. An experimental methodology was developed for measuring water content in a CO2-rich phase in equilibrium with hydrates. The water content in equilibrium with hydrates at simulated pipeline conditions (e.g., 4°C and up to 190 bar) as well as after simulated choke conditions (e.g., at -2°C and approximately 50 bar) was measured for pure CO2 and a mixture of 2 mol% H2 and 98 mol% CO2. Bubblepoint measurements were also taken for this binary mixture for temperatures ranging from -20 to 25°C. A thermodynamic approach was employed to model the phase equilibria. The experimental data available in the literature on gas solubility in water in binary systems were used in tuning the binary interaction parameters (BIPs). The thermodynamic model was used to predict the phase behavior and the hydrate-dissociation conditions of various CO2-rich streams in the presence of free water and various levels of dehydration (250 and 500 ppm). The results are in good agreement with the available experimental data. The developed experimental methodology and thermodynamic model could provide the necessary data in determining the required dehydration level for CO2-rich systems, as well as minimum pipeline pressure required to avoid two-phase flow, hydrates, and water condensation.

Two-Phase Transport in Proton Exchange Membrane Fuel Cells

1999 ◽  
Author(s):  
C. Y. Wang ◽  
Z. H. Wang ◽  
Y. Pan
Keyword(s):  
Fuel Cell ◽  
Current Density ◽  
Liquid Water ◽  
Proton Exchange Membrane ◽  
Threshold Current ◽  
Threshold Current Density ◽  
Proton Exchange ◽  
Air Cathode ◽  
Two Phase ◽  
Exchange Membrane

Abstract Proton exchange membrane (PEM) fuel cells have emerged, in the last decade, as a viable technology for power generation and energy conversion. Fuel cell (FC) engines for vehicular applications possess many attributes such as high fuel efficiency, low emission, quiet and low temperature operation, and modularity. An important phenomenon limiting fuel cell performance is the two-phase flow and transport of fuel and oxidant from flow channels to reaction sites. In this paper a mathematical model is presented to study the two-phase flow dynamics, multi-component transport and electrochemical kinetics in the air cathode, the most important component of the hydrogen PEM fuel cell. A major feature of the present model is that it unifies single- and two-phase analyses for low and high current densities, respectively, and it is capable of predicting the threshold current density corresponding to the onset of liquid water formation in the air cathode. A numerical study based on the finite volume method is then undertaken to calculate the detailed distributions of local current density, oxygen concentration, water vapor concentration and liquid water saturation as well as their effects on the cell polarization curve. The simulated polarization curve and predicted threshold current density corresponding to the onset of liquid water formation for a single-channel, 5cm2 fuel cell compare favorably with experimental results. Quantitative comparisons with experiments presently being conducted at our laboratory will be reported in a forthcoming paper.

Simulation of Liquid Water Evaporation in GDL for PEMFC Under Gas Purge Condition

2011 ◽  
Author(s):  
Gen Inoue ◽  
Naoyuki Ishibe ◽  
Yosuke Matsukuma ◽  
Masaki Minemoto
Keyword(s):  
Porous Structure ◽  
Network Model ◽  
Liquid Water ◽  
Gas Diffusion ◽  
Water Evaporation ◽  
Uniform Structure ◽  
Interface Area ◽  
Two Phase ◽  
Actual Structure ◽  
Gas Purge

In automotive Polymer Electrolyte Fuel Cell (PEFC) system, dry gas purge operation is needed at shutdown condition in order to remove the liquid water in gas diffusion layer (GDL) and to reduce the oxygen diffusion inhibition by liquid water in GDL. However, exceed drying operation leads to degradation of electrolyte membrane because of little water content. Therefore, drying process has to be optimized. In this study, various GDL structure with unique fiber orientation were simulated by numerical analysis, and the real GDL structure was reconstructed by X-ray CT image of carbon paper GDL. Next, our past two-phase network model was improved to include phase change effect. The multi-block two-phase network model based on an actual structure was developed by a direct 3D networking porous structure. As results, the evaporation interface area depended on the porous structure of GDL, and the overall evaporation rate of homogeneous GDL which has uniform structure was 1.5 time higher than that of heterogeneous GDL because of the difference of this interface area. In addition, in the case of rib and channel, liquid water under channel evaporated faster than that under Rib. It is very important to control the drying operation in order to prevent the excess membrane drying.

Analysis of Pressure Drop and Water Flooding of Two-Phase Flow Along Channels for a PEM Fuel Cell System

2009 ◽  
Author(s):  
Jinglin He ◽  
Song-Yul Choe ◽  
Chang-Ouk Hong
Keyword(s):  
Fuel Cell ◽  
Pressure Drop ◽  
Relative Humidity ◽  
Liquid Water ◽  
Water Distribution ◽  
Gas Flow ◽  
Pem Fuel Cell ◽  
Cell System ◽  
Water Flooding ◽  
Two Phase

The flow in gas flow channels of an operating polymer electrolyte membrane (PEM) fuel cell has a two-phase characteristic that includes air, water vapor and liquid water and significantly affects the water flooding, pressure distribution along the channels, and subsequently the performance of the cell and system. Presence of liquid water in channels prevents transport of the reactants to the catalysts and increases the pressure difference between the inlet and outlet of channels, which leads to high parasitic power of pumps used in air and fuel supply systems. We propose a model that enables prediction of pressure drop and liquid water distribution along channels and analysis of water flooding in an operating fuel cell. The model was developed based on a gas-liquid two-phase separated flow that considers the variations of gas pressure, mass flow rate, relative humidity, viscosity, void fraction, and density along the channels on both sides. Effects of operating parameters that include stoichoimetric ratio, relative humidity, and inlet pressure on the pressure drop and water flooding along the channels were analyzed.

Two-Phase Flow Considerations in PEMFC Design and Operation

2008 ◽  
Author(s):  
Jon P. Owejan ◽  
Jeffrey J. Gagliardo ◽  
Jacqueline M. Sergi ◽  
Thomas A. Trabold
Keyword(s):  
Liquid Water ◽  
Proton Exchange Membrane ◽  
Two Phase Flow ◽  
Bipolar Plate ◽  
Gas Diffusion ◽  
Proton Exchange ◽  
Phase Flow ◽  
Two Phase ◽  
Flowing Hydrogen ◽  
Flow Effects

A proton exchange membrane fuel cell (PEMFC) must maintain a balance between the hydration level required for efficient proton transfer and excess liquid water that can impede the flow of gases to the electrodes where the reactions take place. Therefore, it is critically important to understand the two-phase flow of liquid water combined with either the co-flowing hydrogen (anode) or air (cathode) streams. In this paper, we describe the design of an in-situ test apparatus that enables investigation of two-phase channel flow within PEMFCs, including the flow of water from the porous gas diffusion layer (GDL) into the channel gas flows; the flow of water within the bipolar plate channels themselves; and the dynamics of flow through multiple channels connected to common manifolds which maintain a uniform pressure differential across all possible flow paths. These two-phase flow effects have been studied at relatively low operating temperatures under steady-state conditions and during transient air purging sequences.

Extracting Model Parameters and Paradigms From Neutron Imaging of Dead-Ended Anode Operation

2009 ◽  
Author(s):  
Jason B. Siegel ◽  
Anna G. Stefanopoulou ◽  
Serhat Yesilyurt
Keyword(s):  
Liquid Water ◽  
Front Propagation ◽  
Neutron Imaging ◽  
Model Parameters ◽  
Two Phase ◽  
Pde Model ◽  
Saturation Limit ◽  
Gravity Driven ◽  
Water Accumulation

In a PEMFC, feeding dry hydrogen into a dead-ended anode (DEA), reduces the overall system cost, weight and volume due to reduced need for a hydrogen-grade humidification and recirculation subsystems, but requires purging to remove the accumulated water and inert gas. Although the DEA method of operation might be undesirable due to its associated high spatial variability it provides a unique perspective on the evolution of the water accumulation in the anode. Sections of the channel nearest the inlets are significantly drier than those nearest the outlet as shown in the neutron imaging of a 53 cm2 PEMFC. This method allows in-situ visualization of distinct patterns, including water front propagation along the channels. In this paper we utilize neutron imaging of the liquid water distributions and a previously developed PDE model of liquid water flow in the GDL to (a) identify a range of numerical values for the immobile saturation limit, (b) propose a gravity-driven liquid flow in the channels, and (c) derive the two-phase GDL boundary conditions associated with the presence of liquid water in the channel.

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