Apéndice – Papers Gases

Autores: Muhittin Bilgili, Recep Fatih Yumşakdemir

Abstract

Hydrogen-fueled, fuel-cell-powered cars offer environmentally friendly alternative for near future. One of the critical part of this technology is to store hydrogen efficiently and securely. Many different methods have been developed to store hydrogen. The most popular storage method for hydrogen storage in vehicles is compressible hydrogen storage tanks due to their lightweight and efficiency. One of the most important factors during filling is the filling time. During rapid filling, the tank temperature rises significantly, which can cause damage to the tank and create a dangerous situation. In this research, CFD simulation has been made for fast filling condition for compressible hydrogen storage tanks. It was decided to use the k-[Math Processing Error]� turbulence model and different real gas equations for numerical simulation. The effects of four different real gas equations and also ideal gas equation on the temperature, the pressure, and filling times are investigated numerically. As a result of the simulation, it was concluded that the use of different real gas equations does not have a significant effect on the temperature and the pressure of the storage tank. However, the filling duration of storage tank is slightly affected by usage of different real gas equations. Filling durations of hydrogen according to Redlich-Kwong equation of state increased for Soave-Redlich-Kwong equation 1.3 %, for Aungier Redlich-Kwong equation 1.5 %, for Peng-Robinson’s equation of state 5.85 %, for ideal gas equation of state 24.2 %.

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Autores: Saripudin ^ac, Tutuka Ariadji ^a, Sanggono Adisasmito ^b, Leksono Mucharam ^a, Doddy Abdassah ^a

Abstract

The rapid expansion of supercritical gas technology for high-content CO₂ separation from natural gas is a promising avenue of research. However, CO₂-rich natural gas cools immediately after being separated and expands when the CO₂ dew point is reached in the absence of a refrigerant system. In our previous study, supercritical expansion experiments using various CO₂ compositions revealed that the Joule–Thomson equation gives a significant absolute average error value of 16.28%. This paper describes corrections to the Joule–Thomson expansion equation under supercritical conditions with various CO₂ concentrations. The results show that the trend of the expansion coefficient is highly dependent on the CO₂ composition. Using an improved Joule–Thomson equation of state over a CO₂ range of 25%–45% mol, the expansion coefficient tends to fall immediately when a rapid expansion occurs. For a supercritical fluid, the specific heat Cp depends on temperature, pressure, and density changes. The Van der Waals expansion coefficient profile is simulated using MATLAB, resulting in a correction factor of 1.17–1.32 being applied to the Cp value for CO₂ concentrations of 25%–40% mol, whereby the absolute average error tends to zero. For CO₂ concentrations of more than 40%, the Joule–Thomson equation cannot be applied because the expansion coefficient exhibits significant errors compared with the experimental data. The expansion coefficient does not directly determine the performance of supercritical expansion, but does affect the vapor fraction. Integrated production systems based on supercritical expansion are expected to produce an annual profit of around US$18 million from turbine expansion and US$489 million from the production of sweet gas with a purity of 96.6% and less than 2% mol CO₂.

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Autores: Xu Tang, Hongguang Zhang, Zhenjiang Guo, Xianren Zhang, Jing Li, Dapeng Cao

Abstract

The gas-containing nanobubbles have attracted extensive attention due to their remarkable properties and extensive application potential. However, a number of fundamental aspects of nanobubbles, including thermodynamic states for the confined gas, remain still unclear. Here we theoretically demonstrate that the van der Waals (vdW) gases confined in nanobubbles exhibit a unique thermodynamic state of remarkably deviating from the bulk gas phase, and the state transition behavior due to the size-dependent Laplace pressure. In general, the vdW gas inside nanobubbles present multiple stable or transient states, where 0–2 states are for supercritical gas and 0–4 for subcritical gas. Our further analysis based on Rayleigh–Plesset equation and free energy determination indicates that the gas states in nanobubbles exhibits different levels of stability, from which the coexistence of multiple bubble states and microphase equilibrium between droplets and bubbles are predicted. This work provides insight to understand the thermodynamic states appeared for gas in nanobubbles.

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Autores: S.B. Øyen, H.A. Jakobsen, T. Haug-Warberg, J. Solsvik

Abstract

This work unifies the concepts of chemical reaction equilibrium and transport phenomena applied to fluid flow of reactive gas mixtures over solid catalysts. Different from accurate modeling of reactions, which in the outset relies on reaction kinetics, the current approach is rather based on calculation of thermodynamic equilibrium thus requiring far fewer model parameters. Here, minimization of Gibbs or Helmholtz energy is solved in an inner loop inside the transport equations for heat, mass, and momentum. In addition to ideal gas, the non-ideal virial expansion and Soave-Redlich-Kwong equations of state have been used to model the gas mixture. The use of thermodynamic energy potentials ensures that all the derived properties like e.g. heat capacity, density, reaction enthalpy and equilibrium composition are derived from one fundamental relation only. The complete model framework is exemplified using the steam methane reforming and methanol synthesis processes. Herein, different combinations of energy potential (Gibbs versus Helmholtz) and numerical solution method for solving the transport equations (finite volume versus orthogonal collocation) have been studied with focus on model complexity, and efficiency and robustness of the solver. Orthogonal collocation is shown to be more efficient than finite volume, and Gibbs energy is shown to be more efficient than Helmholtz energy. The last statement depends on both flow conditions and implementation details and is therefore not a general result. The proposed model framework is a novel tool for calculating industrial reactors which operate quite close to equilibrium and might as such be useful for process design studies, albeit not for accurate simulation.

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Autores: Iris de Krom ^a, Wijnand Bavius ^a, Ruben Ziel ^a, Evtim Efremov ^a, Davina van Meer ^a, Peter van Otterloo ^a, Inge van Andel ^a, Deborah van Osselen ^a, Maurice Heemskerk ^a, Adriaan M.H. van der Veen ^a, Matthew A. Dexter ^b, Warren T. Corns ^b, Hugo Ent 

Abstract

Mercury poses one of the greatest current direct threats to human, animal and environmental health across the globe. Robust, defensible and traceable measurements of mercury concentrations are essential to underpin global efforts to reduce the concentration of mercury in the environment, meet the obligations of legislation and to protect human health. Currently, instruments for gaseous mercury concentration measurements are calibrated based on mercury vapour pressure equations (e.g., the Dumarey or the Huber equation). Currently these equations differ from each other by more than 7% at 20 °C. In this paper, the performed characterisation and implementation of mercury diffusion cells and the development of the first primary mercury gas standard show that metrological traceability to the International System of Units (SI) is possible for mercury concentrations. The primary mercury gas standard will provide a lower measurement uncertainty (between 1.8% and 3%) than can be obtained using the most commonly adopted mercury vapour pressure equations (5% up to 21%). Measurement methods have been developed for the SI traceable calibration of mercury analysers and mercury gas generators which have been used for the comparison between the primary mercury gas standard and the Dumarey equation. The developed primary mercury gas standard will contribute to more reliable mercury measurement results at emission and ambient air levels.

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