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• Mathematical modelling of electrodialysis for liquid desiccant was proposed. • Effect of solution concentration on membrane characteristics was considered. • Methods to identify the membrane characteristics by experiments are provided. • Influence of design and operating parameters on ED performance of ED was analysed. • Simulation analyses were carried out by varying two parameters simultaneously. The regeneration process is crucial to guarantee continuous dehumidification in liquid desiccant air conditioning systems. Electrodialysis (ED) is recently considered as an alternative solution to assist in regenerating liquid desiccants. This paper presents the mathematical modelling of mass transfer and electrical energy consumed by the ED stack for regenerating liquid desiccant by taking into account the effect of solution concentration and current density on the characteristics of membrane pairs. The model was validated using the data collected from the experiments. Based on which, simulations were conducted to examine how the design and operating parameters affect the regeneration performance of ED using the proposed mathematical model. It was found that the concentration increase per unit power consumption was lower with a larger effective area of one membrane pair and a larger number of membrane pairs. When the inlet concentration of the regenerated solution was below 28% (wt ⋅ wt−1), the concentration increase of the regenerated solution decreased with an elevation in the solution concentration at the inlet of the regenerated channel. When the inlet concentration of the regenerated solution was above 28% (wt ⋅ wt−1), the concentration increase of the regenerated solution elevated with an increase in the solution concentration at the inlet of the regenerated channel. [ABSTRACT FROM AUTHOR]

This paper introduces a new mathematical model built under the PC-PWM methodology to describe the aeration process in a full-scale WWTP. This methodology enables a systematic and rigorous incorporation of chemical and physico-chemical transformations into biochemical process models, particularly for the description of liquid-gas transfer to describe the aeration process. The mathematical model constructed is able to reproduce biological COD and nitrogen removal, liquid-gas transfer and chemical reactions. The capability of the model to describe the liquid-gas mass transfer has been tested by comparing simulated and experimental results in a full-scale WWTP. Finally, an exploration by simulation has been undertaken to show the potential of the mathematical model. [ABSTRACT FROM AUTHOR]

Abstract: The paper deals with modelling of hygro-thermal performance and thermo-chemical degradation of concrete exposed to high temperature. Several possible simplifications in modelling of heat and mass transport phenomena in heated concrete are considered and their effect on the results of numerical simulations is analyzed. A mathematical model of concrete at high temperature, already extensively validated with respect to experiments, is used as the reference model. It is based on mechanics of multiphase porous media and considers all important couplings and material nonlinearities, as well as different properties of water above the critical point of water, i.e. 647.3K (374.15°C). In this part of the paper, first physical phenomena, as well as heat and mass flux and sources in a concrete element are studied, both during slow and fast heating process, to examine the relative importance of different flux components. Then, the mathematical model of concrete at high temperature, developed by Authors in the last 10years, is briefly presented and for the first time all the constitutive relationships of the model are summarized and discussed in detail. Finally, the method of numerical solution of the model equations is thoroughly presented. In the companion paper (part II) a brief literature review of the existing mathematical models of concrete at high temperature and a summary of their main features and physical assumptions will be presented. Then, extensive numerical studies will be performed with several simplified models, neglecting chosen physical phenomenon or flux components, to evaluate the difference between the results obtained with the simplified models and with the reference model. The study will concern hygric, thermal and degradation performance of 1-D and 2-D axisymmetric concrete elements during fast and slow heating. The analysis will allow us to indicate which simplifications in modeling of concrete at high temperature are practically and physically possible, without generating excessive errors with respect to the full reference model. [Copyright &y& Elsevier]

Abstract: In this paper, a three-dimensional hydrogen absorption model is developed to precisely study the hydrogen absorption reaction and resultant heat and mass transport phenomena in metal hydride hydrogen storage vessels. The 3D model is first experimentally validated against the temperature evolution data available in the literature. In addition to model validation, the detailed 3D simulation results show that at the initial absorption stage, the vessel temperature and H/M ratio distributions are uniform throughout the entire vessel, indicating that hydrogen absorption is very efficient early during the hydriding process; thus, the local cooling effect is not influential. On the other hand, non-uniform distributions are predicted at the subsequent absorption stage, which is mainly due to differential degrees of cooling between the vessel wall and core regions. In addition, a parametric study is carried out for various designs and hydrogen feed pressures. This numerical study provides a fundamental understanding of the detailed heat and mass transfer phenomena during the hydrogen absorption process and further indicates that efficient design of the storage vessel and cooling system is critical to achieve rapid hydrogen charging performance. [Copyright &y& Elsevier]

Abstract: In this paper, the authors present an efficient three-dimensional algorithm, based on the fully explicit matrix inversion free finite element version of the Characteristic Based Split (CBS) scheme, and apply it for the first time to the simulation of complex thermo-fluid-dynamic problems in domains containing simultaneously a fluid and a porous layer. The stability analysis recently developed for the two-dimensional version of the algorithm is here extended to the three-dimensional version. Unstructured grids have been successfully employed to solve complex interface problems. The present code produces an effective solution for complex 3D problems, and does not require large computing resources. The advantages deriving from the algorithm’s stability, the use of unstructured meshes and the low computing requirements make the present three-dimensional procedure a powerful and flexible tool for efficient modeling of real life problems. The present 3D code is used to solve both forced and natural convection in partially porous domains. [Copyright &y& Elsevier]

Abstract: A new, fast and flexible, time-dependent, one-dimensional numerical model was developed in order to study in detail the operation of an active magnetic regenerator (AMR). The model is based on a coupled system of equations (for the magnetocaloric material and the heat-transfer fluid) that have been solved simultaneously with the software package MATLAB. The model can be employed to analyze a wide range of different operating conditions (mass-flow rate, operating frequency, magnetic field change), different AMR geometries, different magnetocaloric materials and heat-transfer fluids, layered and single-bed AMRs, etc. This paper also presents an optimization of the AMR’s geometry, where the AMR consists of a packed-bed of grains (spheres) of gadolinium (Gd). The optimization of the mass-flow rate and the operating frequency of the AMR were performed by studying five different diameters of Gd spheres. [Copyright &y& Elsevier]

Abstract: Methanol is a well known toxic congener that contaminates many spirits. Chilean legislation indicates that methanol content in wine distillates should not exceed 1.5 g/L absolute alcohol (a. a.). To achieve this stringent limit, distillers need new tools to improve their operational policies since trial and error experiments are too slow. In this paper, a fast pseudo-stationary simulator for batch distillations in packed bed columns was developed. Packed bed columns are preferable for batch productions of fruit wine distillations since they have a wider range of stable hydraulic operations. The model was solved using orthogonal collocations and considers a liquid vapour equilibrium model of the ternary water-ethanol-methanol mixture, which accounts for most of the volatiles in wine. Simulations compared favourably with our own laboratory batch distillations of water-ethanol-methanol mixtures. In addition, our model simulations were able to qualitatively reproduce the results reported in the literature for methanol recovery in experimental batch distillations. Ethanol recovery errors were within measurement errors, while methanol simulations showed a 3% bias by the end of the distillation. Hence, the developed model is accurate and could be used to explore optimal operational policies in order to minimize methanol content in the heart cut used in the final product. [Copyright &y& Elsevier]

Abstract: This paper presents a numerical modeling study of CO2 injection in a chalk core based on experimental data, as reported by Karimaie (2007). The experiment consisted of a vertically-oriented 19.6cm long chalk outcrop core initially saturated with reservoir synthetic oil consisting of C1 and n-C7 at a temperature of 85°C and pressure of 220bar. After saturating the core with the oil mixture by displacement, a small “fracture” volume surrounding the core was created by heating the solid Wood''s metal that originally filled the volume between the core and core holder. Gas injection was conducted initially using an equilibrium C1–n-C7 gas at 220bar. This gas should have had no recovery by thermodynamic mass transfer, only from immiscible Darcy-controlled displacement driven by pressure gradients and gravity-capillary forces. Once oil production ceased in this first displacement, a second period with pure CO2 gas injection followed. Our numerical modeling was conducted with a compositional reservoir simulator. The 2-dimensional r-z model used fine grids for the core matrix and the surrounding fracture. Automated history matching was used to match the experimental data (surface volumetric oil production profile). The match to reported production data gave a high degree of confidence in the model. Oil recovery improved significantly with CO2 injection. Our numerical model study indicates that the recovery mechanism in the Karimaie experiment was dominated by Darcy displacement because of a low conductivity in the surrounding fracture, with little impact of capillary–gravity displacement. Another observation made in our study was the strong influence of surface separator temperature on surface oil volumetric production. Finally, gas-injection rate changes had a significant impact on recovery performance for CO2 injection. Gravity–capillary recovery mechanism was of minor importance in the Karimaie experiments. [Copyright &y& Elsevier]

Abstract: Dew point evaporative cooling system is an alternative to vapor compression air conditioning system for sensible cooling of ventilation air. This paper presents the theoretical performance of a novel dew point evaporative cooling system operating under various inlet air conditions (covering dry, moderate and humid climate) and influence of major operating parameters (namely, velocity, system dimension and the ratio of working air to intake air). A model of the dew point evaporative cooling system has been developed to simulate the heat and mass transfer processes. The outlet air conditions and system effectiveness predicted by the model using numerical method for known inlet parameters have been validated with experimental findings and with recent literature. The model was used to optimize the system parameters and to investigate the system effectiveness operating under various inlet air conditions. [ABSTRACT FROM AUTHOR]

Abstract: In this work, the experimental properties of a carbon molecular sieve membrane made out of cellophane were used to model and simulate a membrane module for the production of nitrogen from air. The mass transport across the membrane has been related to its porous structure. The mathematical model developed accounts for counter- and co-current operation modes, pressure-dependent permeabilities and pressure drop along the membranes. A product stream of high pure nitrogen (>99.9%) was obtained from the retentate side, with recoveries up to 65%. It was considered different feed to permeate pressure ratios and different feed pressures. It was concluded that higher ratios and higher feed pressures favor the separation. Furthermore, the pressure drop along the membranes has a negative impact on the performance of the unit. [Copyright &y& Elsevier]

Abstract: Understanding the heat and mass transfer phenomena in a coal gasifier is very useful for the assessment of gasifier performance and optimization of the design and operating parameters. In this paper, performance of an entrained flow air blown laboratory scale gasifier is numerically simulated with Fluent software. In the model, the continuous phase conservation equations are solved in an Eulerian frame, while those of particle phase are solved in a Lagrangian frame, with coupling between the two phases carried out through interactive source terms. The dispersion of the particles due to turbulence is predicted using a stochastic tracking model, in conjunction with the k–ε equations for the gas phase. The coal gasification model adopted includes devolatilization, combustion of volatiles, char combustion and gasification. The gasification performance inside the gasifier has been predicted for different air ratios as well as for different air and steam inlet temperatures. The overall temperature inside the gasifier is found to increase when the degree of air/steam pre-heating is increased, resulting in acceleration of the different reaction steps in the gasifier. The overall gasification performance indices such as carbon conversion, heating value of the exit gas and cold gas efficiency have been predicted. The predicted results show good agreement with available experimental data in literature. [Copyright &y& Elsevier]

Abstract: The paper presents the geometry of infinite regular polyhedrons that can be used to construct the heat exchange units. The basic structural component of the infinite solid consists of six hexagons, which meet in the common vertex. The mathematical model of heat and mass transfer inside the labyrinth heat exchanger is shown. The first and the second Kirchhoff’s laws are used to simulate fluid flow distribution at hydraulic network created with connected basic solids. Heat balance equations are adopted to describe forced convection heat transfer inside developed heat exchanger. Good accordance among the experimental data and calculation results over whole simulation range is obtained. The efficiency and thermal characteristic of the labyrinth heat exchanger is presented in the form of graphs. [Copyright &y& Elsevier]

Abstract: This paper presents the advantages of a Branch Eigenmodes Reduced Model used in a control process of a heating system. The experimental setup is a 3D heat conductive system in which a heat source is set. First, the reduced model is used to solve the non-linear Inverse Heat Conduction Problem: identification of the heat source strength variations from time-varying temperatures. Then, the reduced model is used to control hot points in the system. The objective of the method is to allow sequential temperature control by decreasing the computation time necessary for the simulation. [Copyright &y& Elsevier]