Volume 44, Issue 1

If the von Neumann equation is modified by time dependent statistical weights, the time rate of entropy, the entropy exchange and the production of a Schottky system are derived whose Hamiltonian does not contain the interaction with the system’s environment. This interaction is semi-classically described by the quantum theoretical expressions of power and entropy exchange.

In this study, the phase equilibria of semi-clathrate hydrates of methane (CH 4 ), carbon dioxide (CO 2 ), nitrogen (N 2 ), and hydrogen sulfide (H 2 S) in an aqueous solution of tetra-n-butyl ammonium bromide (TBAB) were modeled using a correlation based on a two-stage formation mechanism: a quasi-chemical reaction that forms basic semi-clathrate hydrates and adsorption of guest molecules in the linked cavities of the basic semi-clathrate hydrate. The adsorption of guest molecules was described by the Langmuir adsorption theory and the fugacity of the gas phase was calculated by Peng–Robinson (PR) equation of state (EOS). The water activity in the presence of TBAB was calculated using a correlation, dependent on temperature, the TBAB mass fraction, and the nature of the guest molecule. These equations were coupled together and form a correlation which was linked to a genetic algorithm for optimization of tuning parameters. The results showed an excellent agreement between model results and experimental data. In addition, an outlier diagnostic was performed for finding any possible doubtful data and assessing the applicability of the model. The results showed that more than 97 % of the data were reliable and they were in the applicability domain of the model.

The Euler–Euler method and soft computing methods are recently utilized for the purpose of bubbly flow simulation and evolution of the dispersed and continuous phase in a two-phase reactor. Joining computational fluid dynamics (CFD) to the adaptive neuro-fuzzy inference system (ANFIS) method can enable the researchers to avoid several runs for heavy numerical methods (multidimensional Euler–Euler) to optimize fluid conditions. This overview can also help the researchers to carefully analyze fluid conditions and categorize their huge number of data in their artificial neural network nodes and avoid a complex non-structure CFD mesh. In addition, it can provide a neural geometry without limitation of an increasing mesh number in the fluid domain. In this study, gas and liquid circulation were considered as one of the main CFD factors in the scale-up of reactors used as an output parameter for prediction tool (ANFIS method) in different dimensions. This study shows that a combination of ANFIS and CFD methods provides the non-discrete domain in various dimensions and makes a smart tool to locally predict multiphase flow. The integration of numerical calculation and smart methods also shows that there is a great agreement between CFD results and ANFIS output depending on different dimensions.

The shock structures of a 13 moment generalized hydrodynamics system of rarefied gases are simulated. These are first order hyperbolic equations derived from the Boltzmann equation. The investigated moment system stands out due to having an entropy evolution. In addition, a particular interest arises from the fact that the equations not only contain nonconservative products, but also provide the key to solving this mathematical and numerical issue by means of a simple substitution utilizing the physical entropy evolution. The apparent success of this method warrants investigation and provides a new perspective and starting point for finding general approaches to nonconservative products and irreversible processes. Furthermore, the system shows physically accurate results for low Mach numbers and is able to reveal the nonequilibrium entropy profile across a shock wave.

In this work, the velocities of individual components during the immersion process using mathematical modeling of a nonsolvent-induced phase separation process are investigated. For this purpose, a mass average velocity correction factor was defined as the ratio of mass average velocity in the absence of a zero polymer velocity assumption to the mass average velocity with zero polymer velocity assumption. The velocities were computed and the result was coherent with observations of a considered case study. It was concluded that the polymer moves towards the interface, as the sign of the polymer velocity at early moments of immersion was positive, which is in accord with accumulation and vitrification of the polymer at the interface. The positive sign of the solvent and the negative sign of nonsolvent are in accord with the observations as solvent leaves the cast film and nonsolvent penetrates into the film. The reduction of velocity values to the order of magnitude of diffusivities is in accord with the limiting role of the rigid skin layer for mass exchanges. Relatively large velocity values of the solvent rather than the nonsolvent imply that much more solvent is probably left in the cast film rather than the nonsolvent enters into it as observed by densification of the cast film.

In this theoretical study, fully developed forced convective laminar water flow is considered in circular micro-tubes, for the constant wall heat flux boundary condition. The change in entropy generation rate (ΔS˙gen\Delta {\dot{S}_{\mathrm{gen}}}) for N micro-tubes (each of diameter DN{D_{\mathrm{N}}}) relative to a reference tube (of 1 mm diameter) was investigated towards the micro-scale, for different tube length ( l ). A given total heat flow rate is to be removed using a fixed total mass flow rate through N tubes. Hence, the wall heat flux for one of the N tubes decreases towards the micro-scale, which is “thermal under-loading”. For given l , ΔS˙gen\Delta {\dot{S}_{\mathrm{gen}}} due to fluid conduction decreases and ΔS˙gen\Delta {\dot{S}_{\mathrm{gen}}} due to fluid friction increases towards the micro-scale. There exists an optimum DN{D_{\mathrm{N}}} (=DN,opt={D_{\mathrm{N},\mathrm{opt}}}) at which the change in sum-total S˙gen{\dot{S}_{\mathrm{gen}}} (ΔS˙gen,tot\Delta {\dot{S}_{\mathrm{gen},\mathrm{tot}}}) is minimum; where DN,opt{D_{\mathrm{N},\mathrm{opt}}} decreases with decreasing l . For given l , cooling capacity of the heat sink increases towards the micro-scale. A general criterion for minimization of ΔS˙gen,tot\Delta {\dot{S}_{\mathrm{gen},\mathrm{tot}}} is obtained in terms of Reynolds number, Brinkman number, and dimensionless l .

The presented work describes issue of magnetic mixing and segregation of metals during the formation of micro-joints using the capacitor welding method. The key aspect is the very short weld time, which is below 2 ms. The Pt/Inconel 625 micro-joints have been tested in the work. The 100-μm platinum wire was welded to Inconel 625 with the same thickness. During the welding process, the capacitor discharge characteristics were recorded with the oscilloscope. This allowed for a mathematical description of phenomena occurring during the creation of the micro-joint. Observations of the micro-structures from the scanning electron microscope in BSE mode confirmed the strong micro-segregation of the joint components. In addition, the effect of magnetic mixing of the joint components was observed. Weld geometry results obtained from the calculations showed good compliance with the real joint micro-structure observation data.