ChemEngineering — Open Access Journal

Desalination of sea or brackish water sources to provide clean water supplies has now become a feasible option around the world. Escalating global populations have caused the surge of desalination applications. Desalination processes are energy intensive which results in a significant energy portfolio and associated environmental pollution for many communities. Both electrical and heat energy required for desalination processes have been reduced significantly over the recent years. However, the energy demands are still high and are expected to grow sharply with increasing population. Desalination technologies utilize various forms of energy to produce freshwater. While the process efficiency can be reported by the first law of thermodynamic analysis, this is not a true measure of the process performance as it does not account for all losses of energy. Accordingly, the second law of thermodynamics has been more useful to evaluate the performance of desalination systems. The second law of thermodynamics (exergy analysis) accounts for the available forms of energy in the process streams and energy sources with a reference environment and identifies the major losses of exergy destruction. This aids in developing efficient desalination processes by eliminating the hidden losses. This paper elaborates on exergy analysis of desalination processes to evaluate the thermodynamic efficiency of major components and process streams and identifies suitable operating conditions to minimize exergy destruction. Well-established MSF, MED, MED-TVC, RO, solar distillation, and membrane distillation technologies were discussed with case studies to illustrate the exergy performances. Full article

Environmental friendly refrigerants with zero ozone depletion potential (ODP) and zero global warming potential (GWP) are in great demand across the globe. One such popular refrigerant is isobutane (R600a) which, having zero ODP and negligible GWP, is considered in this study. This paper presents the two most popular artificial intelligence (AI) techniques, namely support vector regression (SVR) and artificial neural networks (ANN), to predict the heat transfer coefficient of refrigerant R600a. The independent input parameters of the models include mass flux, saturation temperature, heat flux, and vapor fraction. The heat transfer coefficient of R600a is the dependent output parameter. The prediction performance of these AI-based models is compared and validated against the experimental results, as well as with the existing correlations based on the statistical parameters. The SVR model based on the structural risk minimization (SRM) principle is observed to be superior compared with the other models and is more accurate, precise, and highly generalized; it has the lowest average absolute relative error (AARE) at 1.15% and the highest coefficient of determination (R²) at 0.9981. ANN gives an AARE of 5.14% and a R² value of 0.9685. Furthermore, the simulated results accurately predict the effect of input parameters on the heat transfer coefficient. Full article

The present paper deals with the mixing of a highly viscous fluid by close-clearance impellers in cylindrical vessels. The study is performed via numerical simulations. Calculations are achieved by the discretization of continuity and momentum equations with the finite volume method. The effect of blade diameter and its shape on the well-stirred region size and the power consumption is investigated. For highly viscous fluids, the obtained results suggest the use of impellers rotating at low Reynolds number, and having a blade with the same shape of the tank to ensure mixing near the vessel base. A comparison is made between the performance of a simple helical ribbon (HR), a simple small screw (SS), helical ribbon-small screw (HR-SS) and a large screw (LS) impeller. The predicted results allow the following classification of impellers studied, based on less power requirements and small size of well-agitated region: SS < HR < HR-SS < LS. Full article

Dividing Wall Columns (DWCs) allow the separation of a ternary mixture in one column shell by applying a vertical partition wall, yielding a reduction of operational and capital costs of up to 30%. Multiple DWC (mDWC), the consequent advancement of standard DWC, makes use of more than one partitioning wall, allowing the separation of quaternary or even higher mixtures in one column shell accompanied by a further reduction of energy consumption. Since no dedicated models for these columns are available in commercial process simulators, thermodynamic consistent flowsheets have to be designed and implemented. The thermally fully coupled Petlyuk arrangement is one important example. However, the initial convergence of these substituting flowsheets is demanding, since a large number of meaningful initial guesses have to be provided. A promising method for generating these first estimates are minimum vapor (V_min) diagrams. All internal flows can be extracted from these diagrams and used for robust initialization of the simulation. The goal of this work is to present the V_min method in a comprehensive way in order to initialize mDWC simulations to predict the separation of four component mixtures. Additionally, the adaptation of the diagram to configurations different than Petlyuk arrangements for mDWC is evaluated and a systematic procedure to obtain them is presented. In the end, an example of a converging simulation is given, which was obtained with the values from the V_min diagram. Full article

Biodegradable polymer possesses significant potential for applications in different fields, since flexibility gives rise to materials with great physical and mechanical property diversity. The poly-caprolactone (PCL) and chitosan derivatives (CS) have the ability to form scaffolds, which adhere to the surface of mesoporous silica nanoparticles (MSNs) and its porous networks. The novel characteristics of the developed PCL/MSNs and CS/MSNs, such as very low in vivo degradation rate, ordered pore network, uniform and tunable size and shape of the particles, high pore volume and surface area, non-toxicity, and biocompatibility, among others, are responsible for its favorable gene delivery device and makes this conjugation a very good biomaterial for this application. In the present study, we investigated the synthesis of silica nanoparticles MCM-41 covalently grafted with PCL and CS and their use as a potential small interfering RNA (siRNA) carrier. The physical–chemical and morphological characterizations, as well as the applicability of functionalized MSNs as platforms for gene delivery, were assessed. Our results confirmed that MSNs that were successfully functionalized with PCL and CS kept their typical morphology and pore arrangement. Furthermore, their surface modification was successfully held. In vitro biocompatibility and cytotoxicity assays suggest the ability of MSNs to support passive uptake and indicated the potential of this material as a gene delivery system for cervical cancer cells (HeLa). Full article

Amongst the strategies applicable for CO₂ capture and sequestration, the adsorption process has a high potential to be applied as an alternative CO₂ separation strategy as it offers large adsorption capacity, requires low energy for regeneration with economical equipment cost, prevents corrosion problems, and provides ease of applicability. Inspired by the most applicable amine-based chemical absorption for CO₂ capture, the modification of adsorbent by amine was first considered and then investigated. This study introduces kenaf (Hibiscus Cannabinus L.) as a potential low-cost material in evaluating the effect of amine functional group concentrations on CO₂ adsorption capacity. Monoethanolamine (MEA) and tetraethylenepentamine (TEPA) were impregnated on kenaf via a wetness impregnation method to achieve the aim. The ratios of amine to kenaf were varied at 1:2, 7:10, 1:1, 2:1, 5:1, 7:1, and 10:1. Then, the prepared amine-modified kenaf core sorbent was characterized using different morphology and structural characterization techniques such as a field emission scanning electron microscope (FESEM) analyzer and Fourier transform infrared (FTIR) spectroscopy. Results obtained through the analyses showed that amine (MEA and TEPA) were successfully impregnated on the kenaf core surfaces, and that amine concentrations have a significant effect on the morphological structures of the kenaf core support. The study on CO₂ adsorption capacity was conducted in a pressure swing adsorption system (PSA). Results revealed that the highest CO₂ adsorption capacity for MEA-modified kenaf adsorbent was achieved at an amine to kenaf ratio of 1:1 (2.070 mmol/g), while for TEPA-modified kenaf adsorbent at a ratio of 2:1 (2.086 mmol/g). The study on the effect of amine concentration on kenaf adsorbent is beneficial in introducing kenaf as a sorbent in capturing CO₂. Full article

Montmorillonite–TiO₂ nanocomposites were prepared using two different methods (ultrasonic or stirring) and using titanium(IV) isopropoxide as precursor. The solids were characterized by element chemical analysis, X-ray diffraction, FTIR spectroscopy, thermal analyses, and nitrogen adsorption. The evolution of the properties as a function of the preparation method was discussed. These nanocomposites were used as catalysts for the photodegradation of 1,2,4-trichlorobenzene. The degradation pathway and the nature of the by–products were investigated by mass spectrometry. Full article

We describe a hydrodynamic simulation method (HSM) that is based on hydrodynamic considerations in Batch and Semi Batch stirred reactor systems. The method combines hydrodynamic studies of the mixing procedure obtained from experiments in small and large scale stirred reactors together with process simulation by VisiMix software. We describe how this hydrodynamic simulation method can aid in process optimization and scale up. The use of the simulation method described in this article, will offer the user the possibility to achieve the best results during production stage, saving time and currency, and at the same time increasing the knowledge of the performed process. Several examples in the article demonstrate the benefits of the proposed method. Full article

Photocatalytic fuel cells (PFCs) are a sustainable technology with application in waste water treatment, in which energy is obtained from the photocatalytic degradation of organic pollutants. However, the application of PFCs is limited by the photoanode, in particular its low efficiency for treating recalcitrant pollutants. In this study, a double chamber PFC reactor was constructed. Visible-light-driven Ag-TiO₂ photocatalyst supported carbon foam was used as the anode and platinum was used as the cathode. 4-Chlorophenol (4-CP) was used as a model pollutant in the cation chamber to investigate the efficiency of pollutant degradation and power generation. The effects of the electrolyte type and solution pH on the 4-CP degradation and power production were investigated. The results showed that 32.6% of 4-CP was degraded by the PFC in 6 h. Na₂SO₄ was the optimum electrolyte and had the least side effects on the degradation of 4-CP when compared with NaCl, NaHCO₃ and NaH₂PO₄. The optimum pH range was 6.4–8.4 when sodium sulfate was used as the electrolyte. The power density was approximately 36.0 mW/m² under the above experimental conditions. Full article

The paper presents a brief overview of experiments on volumetric mass transfer coefficient in bubble columns. The available experimental data published are often incomparable due to the different type of gas distributor and different operating conditions used by various authors. Moreover, the value of the coefficient obtained experimentally is very sensitive to the particular method and to the physical models used in its evaluation. It follows that the Dynamic Pressure Method (DPM) is able to provide physically correct values not only in lab-scale contactors but also in pilot-scale reactors. However, the method was not correctly proven in bubble columns. In present experiments, DPM was employed in a laboratory-scale bubble column with a coalescent phase and tested in the pure heterogeneous flow regime. The method was successfully validated by the measurements under two different conditions relevant to the mass transfer. First, the ideal pressure step was compared with the non-ideal pressure step. Second, the pure oxygen absorption was compared with the simultaneous oxygen-and-nitrogen absorption. The obtained results proved that DPM is suitable for measuring the mass transport in bubble columns and to provide reliable data of volumetric mass transfer coefficient. Full article

The bubble shape influences the transfer of momentum and heat/mass between the bubble and the surrounding fluid as well as the flow field around the bubble. The shape is determined by the interaction of the fluid field in the bubble, the physics on the surface, and the surrounding flow field. It is well known that contaminations can disturb the surface physics so that the bubble shape can be influenced. Indeed, an influence of sodium chloride (NaCl) on the hydrodynamics of bubbly flows was shown for air/water systems in previous studies. The aim of the present work is to investigate if, and to what extent, the NaCl concentration affects the bubble shape in bubble columns. For this purpose, several experiments at the Helmholtz-Zentrum Dresden-Rossendorf and at the pilot-scale bubble column at the Politecnico di Milano are evaluated. The experiments were executed independently from each other and were evaluated with different methods. All experiments show that the bubble shape is not distinctly affected in the examined concentration range from 0 to 1 M NaCl, which is in contrast to a previous study on single bubbles. Therefore, the effect of NaCl on the hydrodynamics of bubbly flows is not induced by the bubble shape. Full article

Chemical reactions of amino acids induced by discharge plasma are important for understanding the mechanism of biological effects of discharge plasma in biomedical applications. In this study, we generated a nano-second pulsed discharge plasma under atmospheric pressure over an aqueous solution containing glycine. The reaction products after the pulsed discharge plasma treatments were analyzed by high-performance liquid chromatography and matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy. The oligomerization reaction of glycine was induced in aqueous solution and produced glycine oligomers at the beginning of the discharge plasma. However, the glycine oligomers were decomposed into products with low molecular weight by excessive pulsed discharge plasma. According to comparative experiments, physical force of the plasma is believed to induce the glycine reaction. Moreover, the reactions depended on the pH, but not the conductivity, of the glycine solution. Glycine in aqueous solution was reacted by the discharge plasma only at neutral pH because the reaction proceeded only when glycine ions were in the zwitterionic state. Anions and cations of glycine reacted very little under the discharge plasma. Full article

Vertical vibration is known to cause bubble breakup, clustering and retardation in gas-liquid systems. In a bubble column, vibration increases the mass transfer ratio by increasing the residence time and phase interfacial area through introducing kinetic buoyancy force (Bjerknes effect) and bubble breakup. Previous studies have explored the effect of vibration frequency (f), but minimal effort has focused on the effect of amplitude (A) on mass transfer intensification. Thus, the current work experimentally examines bubble size, void fraction, and mass transfer in a bubble column under relatively high amplitude vibration (1.5 mm < A <9.5 mm) over a frequency range of 7.5–22.5 Hz. Results of the present work were compared with past studies. The maximum stable bubble size under vibration was scaled using Hinze theory for breakage. Results of this work indicate that vibration frequency exhibits local maxima in both mass transfer and void fraction. Moreover, an optimum amplitude that is independent of vibration frequency was found for mass transfer enhancements. Finally, this work suggests physics-based models to predict void fraction and mass transfer in a vibrating bubble column. Full article

Hydrogen interactions with Nd₂Fe₁₇ and Nd₂Fe₁₄B was investigated by means of the calorimetric method with application of differential heat-conducting calorimeters that were of the Tean-Calvet type. The reaction of hydrogen absorption and desorption was carried out at 250 and 300 °C for Nd₂Fe₁₇, while the pressure-composition-isotherms (P-C-T) and enthalpy change with hydrogen concentration in the intermetallic compound (IMC) were obtained. The Nd₂Fe₁₄B-H₂ system was studied at 50 °C and the dependence of the enthalpy change with hydrogen concentration in the intermetallic compound was also obtained. Based on the measured data, the assumption about the order of filling the interstitial sites by hydrogen atoms was made. Full article

Pressure drops of water and critical steam flowing in the fixed bed of mono-sized spheres are studied using SolidWorks 2017 Flow Simulation CFD code. The effects of the type of bed formation, flow velocity, density, and pebble size are evaluated. A new equation is concluded from the data, which is able to estimate pressure drop of a packed bed for high particle Reynolds number, from 15,000 to 1,000,000. Full article

We present a comprehensive literature review on the two-phase bubble column; in this review we deeply analyze the flow regimes, the flow regime transitions, the local and global fluid dynamics parameters, and the mass transfer phenomena. First, we discuss the flow regimes, the flow regime transitions, the local and global fluid dynamics parameters, and the mass transfer. We also discuss how the operating parameters (i.e., pressure, temperature, and gas and liquid flow rates), the operating modes (i.e., the co-current, the counter-current and the batch modes), the liquid and gas phase properties, and the design parameters (i.e., gas sparger design, column diameter and aspect ratio) influence the flow regime transitions and the fluid dynamics parameters. Secondly, we present the experimental techniques for studying the global and local fluid dynamic properties. Finally, we present the modeling approaches to study the global and local bubble column fluid dynamics, and we outline the major issues to be solved in future studies. Full article

This paper presents an in-depth numerical analysis on the hydrodynamics of a bubble column. As in previous works on the subject, the focus here is on three important parameters characterizing the flow: interfacial forces, turbulence and inlet superficial Gas Velocity (UG). The bubble size distribution is taken into account by the use of the Quadrature Method of Moments (QMOM) model in a two-phase Euler-Euler approach using the open-source Computational Fluid Dynamics (CFD) code OpenFOAM (Open Field Operation and Manipulation). The interfacial forces accounted for in all the simulations presented here are drag, lift and virtual mass. For the turbulence analysis in the water phase, three versions of the Reynolds Averaged Navier-Stokes (RANS) k-ε turbulence model are examined: namely, the standard, modified and mixture variants. The lift force proves to be of major importance for a trustworthy prediction of the gas volume fraction profiles for all the (superficial) gas velocities tested. Concerning the turbulence, the mixture k-ε model is seen to provide higher values of the turbulent kinetic energy dissipation rate in comparison to the other models, and this clearly affects the prediction of the gas volume fraction in the bulk region, and the bubble-size distribution. In general, the modified k-ε model proves to be a good compromise between modeling simplicity and accuracy in the study of bubble columns of the kind undertaken here. Full article

This work concerns the performance of bubble columns equipped with porous sparger and investigates the effect of gas phase properties by conducting experiments with various gases (i.e., air, CO₂, He) that cover a wide range of physical property values. The purpose is to investigate the validity of the design equations, which were proposed in our previous work and can predict with reasonable accuracy the transition point from homogeneous to heterogeneous regime as well as the gas holdup and the mean Sauter diameter at the homogeneous regime. Although, the correlations were checked with data obtained using different geometrical configurations and several Newtonian and non-Newtonian liquids, as well as the addition of surfactants, the gas phase was always atmospheric air. The new experiments revealed that only the use of low-density gas (He) has a measurable effect on bubble column performance. More precisely, when the low-density gas (He) is employed, the transition point shifts to higher gas flow rates and the gas holdup decreases, a fact attributed to the lower momentum force exerted by the gas. In view of the new data, the proposed correlations have been slightly modified to include the effect of gas phase properties and it is found that they can predict the aforementioned quantities with an accuracy of ±15%. It has been also proved that computational fluid dynamics (CFD) simulations are an accurate means for assessing the flow characteristics inside a bubble column. Full article

Laboratory scale experiments on the behaviour of two phase change materials, a salt and a paraffin, during fusion and solidification cycling processes, were accomplished. To do this, a system using thermal oil as the heat transfer carrier was used and the phase change material being tested operated in a fusion and solidification cycle. The heat transfer oil transferred heat to the phase change material during the fusion step and carried heat away from the change phase material during the solidification step. The influence of the mass flow rate of the heat transfer fluid, as well as of its temperature, in the response of the phase change material, was studied. Axial and radial temperature profiles inside the phase change materials were obtained during the experiments and subsequently analysed. From these temperature profiles and through an adequate mathematical treatment, global heat transfer coefficients between the heat transfer oil and the phase change material were determined, as well as average heat transfer coefficients for the phase change materials. Full article