Optimizing the hydrothermal performance of helically corrugated coiled tube heat exchangers using Taguchi’s empirical method: energy and exergy analysis

Journal of Thermal Analysis and Calorimetry - In this work, a three-dimensional study of shell and helically corrugated coiled tube heat exchanger with considering exergy loss is investigated....     

The features of ignition of hydrogen–methane and hydrogen–isobutene mixtures with oxygen over Rh and Pd at low pressures

The flammability limits of stoichiometric mixtures (20–80% H₂ + 80–20% CH₄) + O₂ over Rh and Pd were determined in the pressure range 0–200 Torr and the temperature range 200–500 °C. It has been shown that the dark reaction in the mixture (80% H₂ + 20% C₄H₈)_stoich + O₂ leads to the formation of carbon nanotubes with a mean diameter of 10–100 nm.     

Suppression of laminar flames of natural gas–oxygen mixtures with complex obstacles

It has been experimentally shown that a complex obstacle consisting of two confusers oriented in opposite directions of a cylindrical vessel completely prevents the propagation of diluted methane – oxygen flames, i.e., the obstacle is the most effective flame arrester; the theoretical predictions are consistent with the experiments.     

Soft-SAFT modeling of vapor–liquid equilibria of nitriles and their mixtures

Nitriles are strong polar compounds showing a highly non-ideal behavior, which makes them challenging systems from a modeling point of view; in spite of this, accurate predictions for the vapor–liquid equilibria of these systems are needed, as some of them, like acetonitrile (CH₃CN) and propionitrile (C₂H₅CN), play an important role as organic solvents in several industrial processes. This work deals with the calculation of the vapor–liquid equilibria (VLE) of nitriles and their mixtures by using the crossover soft-SAFT Equation of State (EoS). Both polar and associating interactions are taken into account in a single association term in the crossover soft-SAFT equation, while the crossover term allows for accurate calculations both far from and close to the critical point. Molecular parameters for acetonitrile, propionitrile and n-butyronitrile (C₃H₇CN) are regressed from experimental data. Their transferability is tested by the calculation of the VLE of heavier linear nitriles, namely, valeronitrile (C₄H₉CN) and hexanonitrile (C₅H₁₁CN), not included in the fitting procedure. Crossover soft-SAFT results are in excellent agreement with experimental data for the whole range of thermodynamic conditions investigated, proving the robustness of the approach. Parameters transferability has also been used to describe the isomers n-butyronitrile and i-butyronitrile. Finally, the nitriles soft-SAFT model is further tested in VLE calculation of mixtures with benzene, carbon tetrachloride and carbon dioxide, which proved to be satisfactory as well.     

Solvatochromic effect and kinetics of methyl violet reduction with potassium iodide in water–isopropanol mixtures

The solvent influence on the reduction kinetics of methyl violet with iodide in binary mixture of aqueous isopropanol was investigated spectrophotometrically. The absorption spectra of methyl violet were recorded in water, aqueous isopropanol and absolute isopropanol. In these solvents λ_max was in the range from 580.5 to 582.5 nm. The CNIBS/R-K model was used to calculate the solvatochromic parameters in a binary mixture; polynomial equation was also applied to describe the experimental data. The transition energies (E_T) were calculated. They show bathochromic shift with the decrease in the polarity of the solvent. The temperature was varied from 298–318 K, while the pH of the reaction was maintained at 4.99 and 6.00. The reduction reaction was found to be first order by potassium iodide and zero order by methyl violet. The thermodynamic parameters were also evaluated to support the kinetic data.     

Pervaporation dehydration of ethanol–water mixtures with chitosan/hydroxyethylcellulose (CS/HEC) composite membranes: I. Effect of operating conditions

Composite hydrophilic pervaporation membranes were prepared from chitosan blended with hydroxyethylcellulose using cellulose acetate as a porous support. The membranes were tested for dehydration performance of ethanol–water mixtures of ethanol concentrations 70–95 wt.% in the laminar flow region, at temperatures 50–70°C and at permeate pressures of 3–30 mmHg. The composite membrane showed an improved dehydration performance compared with dense CS/HEC membrane developed earlier. The effects of operating conditions also revealed that pervaporation of low water content feed carried out at high feed flow rate and at low temperature and permeate pressure was an advantage.     

Modification of high-density polyethylene with binary mixtures of ɛ-caprolactone and ɛ-caprolactam

Modification of high-density polyethylene with binary mixtures of ?-caprolactone and ?-caprolactam was performed. The composition-property diagrams reflecting the dependences of the physicomechanical, rheological, and optical properties of the resulting polymeric compounds on the content of modifying mixture components were constructed, and the thermal oxidative degradation of the blend samples was studied. Based on the results obtained, the optimal modifier concentrations were suggested.     

Refractivity and polarizability of mixtures of L-histidine–metformin hydrochloride–water at 30°C

The molar refractivity and polarizability of mixtures of L-histidine (0.01–0.11 mol L^–1)–metformin hydrochloride (0.03, 0.05, 0.07 mol L^–1)–water were calculated from density and refractive index data at 30°C. Enhancement in the polarizability has been observed with increase in L-histidine concentration as well as metformin hydrochloride content in the solution. The molar refractivity and polarizability of solutions increased appreciably after 0.09 mol L^–1 L-histidine in each aqueous solution.     

Performance studies of electrolyte-supported solid oxide fuel cell with Ni–YSZ and Ni–TiO2–YSZ as anodes

Redox cycling of Ni-based anode induces cell degradation which limits the cell's lifetime during solid oxide fuel cell operation. In the present study, the redox testing of electrolyte-supported cells has been investigated with TiO₂-added NiO–YSZ anode matrix. Button cells were fabricated by die-pressing YSZ powder as electrolyte, and onto which NiO–YSZ or NiO–TiO₂–YSZ anode and LSM–YSZ composite cathode were painted. The electrochemical performance and stability have been evaluated by measuring current–voltage characteristics followed by impedance spectroscopy after each redox cycling. Anode matrices before and after cell operation have been characterized by X-ray diffraction (XRD), elemental dispersive X-ray (EDX), and scanning electron microscopy (SEM). During cell operation the peak power density decreases from 111 mW cm^?2 (239 mA cm^?2) to 84 mW cm^?2 (188 mA cm^?2) between 23 and 128 h with five redox cycles for cell having NiO–YSZ (40:60) anode. But for cell with NiO–TiO₂–YSZ (30:10:60), the anode peak power density was constant and stable around 85 mW cm^?2 (194 mA cm^?2) throughout the cell run of 130 h and five redox cycles. No loss in the open circuit voltage was observed. SEM and XRD studies of NiO–TiO₂–YSZ (30:10:60) anodes revealed formation of ZrTiO₄, which may be responsible for inhibition of Ni coarsening leading to stable cell performance.     

The shapes of critical loci of binary fluid mixtures on the p–T plane

The relations between the shapes of the critical loci of binary fluid mixtures and the positions of the critical points of their component fluids on the p–T plane were considered theoretically. The consideration was carried out for vapor–liquid phase equilibria in the model systems without liquid–liquid equilibria. We focused only the relations between the shapes and the tangent of the straight lines connecting the critical points of the component fluids on the p–T plane, and so the effects of the distance between the critical points were out of the scope of this work. The changes in the shapes of the critical loci were classified logically into three patterns. Literature survey has shown that the two patterns exist in the experimental results for several types of mixtures. The shapes of the critical loci of the binary fluid mixtures on the p–T plane are closely related to the relative positions between the critical points of their component fluids.     

Vapor–liquid equilibria predictions of hydrogen–hydrocarbon mixtures with the Huron–Vidal mixing rule

An excess Gibbs-equation of state (G^E-EoS) framework based on the Huron–Vidal mixing rule, has been applied to study vapor–liquid equilibria (VLE) of hydrogen–hydrocarbon mixtures. The mixing rule couples the Peng–Robinson–Stryjek–Vera (PRSV) EoS with a local composition solution model. The solution model is based on one-fluid theory treatment and assigns a single energy parameter to each binary pair. This energy parameter relates to the preference of the molecules for like to unlike interactions. The allocation of a system's number of interactions to the individual species in a binary mixture, incorporates the use of size parameters which gain significance only in the liquid phase. In a two parameter form, the framework has been used for the simultaneous data reduction of a large number of binary and several ternary hydrogen–hydrocarbon mixtures. These systems were taken over an extended range of pressures and temperatures. Results from the data reduction are reported in both tabular and graphical forms. Correlations for the model parameters have been identified with the acentric factor of the hydrocarbon in hydrogen–hydrocarbon binary mixtures. In a fully predictive mode, the model has shown to describe well VLE of binary hydrogen–linear alkane systems. Comparisons of these results with calculations from the Peng–Robinson (PR) EoS and the classical mixing rule (vdW) are included.     

Low-temperature liquid–liquid extraction of phenols from aqueous solutions with hydrophilic mixtures of extractants

The volume ratios in acetonitrile–ethyl acetate (90 : 10, 95 : 5), acetonitrile–isopropanol–ethyl acetate (70 : 15 : 15, 80 : 5 : 15), and isopropanol–1-butanol (50 : 50) mixtures were determined. Their mixing with water (1 : 1) and storage at–10°C led to partitioning into two immiscible liquid phases without formation of the ice phase. The mixtures were shown to be useful as hydrophilic extractants in low-temperature liquidliquid extraction of phenol from aqueous solutions.     

Interfacial rheology of protein–surfactant mixtures

The distribution of proteins and surfactants at fluid interfaces (air–water and oil–water) is determined by the competitive adsorption between the two types of emulsifiers and by the nature of the protein–surfactant interactions, both at the interface and in the bulk phase, with a pronounced impact on the interfacial rheological properties of these systems. Therefore, the interfacial rheology is of practical importance for food dispersion (emulsion or foam) formulation, texture, and stability. In this review, the existence of protein–surfactant interactions, the mechanical behaviour and/or the composition of emulsifiers at the interface are indirectly determined by interfacial rheology of the mixed films. The effect on the interfacial rheology of protein–surfactant mixed films of the protein, the surfactant, the interface and bulk compositions, the method of formation of the interfacial film, the interactions between film forming components, and the displacement of protein by surfactant have been analysed. The last section tries to understand the role of interfacial rheology of protein–surfactant mixed films on food dispersion formation and stability. The emphasis of the present review is on the interfacial dilatational rheology.     

Characterization and reactivity with NO/O2 of the soot formed in the pyrolysis of acetylene–ethanol mixtures

Characterization analyses and soot–O₂ and soot–NO interaction experiments have been performed for soot samples obtained in the pyrolysis of acetylene–ethanol mixtures at different temperatures from 1275 to 1475 K. The objective of these analyses is to address the influence of soot formation conditions on soot properties and structure, as well as on its capability to interact with gaseous compounds.The characterization techniques used are: elemental analysis, transmission electron microscopy (TEM), Brunnauer–Emmett–Teller (BET) surface area analysis, Raman spectroscopy and X ray diffraction (XRD). The characterization of soot samples is useful to increase the database on soot composition and structure and may help to find a dependence of those characteristics with soot formation conditions and the fuel from which soot is formed. From these data it can be observed a certain degree of graphitization for the soot samples formed at higher temperatures and/or from fuel mixtures with a higher content in ethanol.The interaction of soot with NO and O₂ is investigated in order to analyze the capability of soot to interact with gas reactants. Soot samples formed at the highest temperatures are less reactive towards O₂ and NO than those formed at lower temperatures. Soot samples appear to be more reactive when the fuel mixture presents a lower initial volume of ethanol. These observations can be related to the higher C/H ratio, associated to slightly higher degree of ordering, for the soot samples formed in such conditions. Experimental results have also demonstrated that soot samples are more reactive towards O₂ than NO, although the initial concentration of O₂ is lower.     

Comments on: “Toward improved heat transfer performance of annular heat exchangers with water/ethylene glycol based nanofluids containing graphene nanoplatelets,Journal of Thermal Analysis and Calorimetry 126.3 (2016): 1427–1436”

The present study has investigated the complex mechanisms in the aluminum–titanium system with different percentages of titanium through a combination of thermal and X-ray analyses. Thermogravimetry, derivative thermogravimetric, X-ray diffraction, scanning electron microscope and transition electron microscope were used for characterization of the samples. Initially, different Al–Ti powder mixtures were produced by high-energy ball milling and after 30 h of milling the phases generated at different percentages of Ti were analyzed. The XRD results revealed that the intermetallic Al₃Ti powder is obtained after a certain duration of milling. In addition, L1₂ to D0₂₃ phase transformation is possible with increase of the Ti percent. Analyses of the powder annealed at different temperatures yielded interesting results, including the effect of stearic acid as the surface control agent on phase transformations of the aluminum–titanium system and also the formation of unexpected phases such as Al₄C₃ and TiC. Moreover, ductile to brittle transition during phase transformations of the intermetallic Al₃Ti powder was quite conspicuous, which could result in more homogeneity of the powders and the occurrence of more reactions in the system. For example, formation of D0₂₃-Al₃Ti powder which is more brittle compared to L1₂ resulted in the exit of Al from among its layers, leading to the increase of the chances for Al reaction with the system impurities.     

Complexes of β-cyclodextrin with chloronitrobenzenes and with solvents in water + organic solvent mixtures

Inclusion complexes of chloronitrobenzenes with -cyclodextrin in aqueous 0.1 M phosphate buffer solutions containing various concentrations of ethanol, dimethylsulfoxide, dimethylformamide, acetone and acetonitrile have been studied by a polarographic method. The diffusion coefficients and the stability constants of the corresponding complexes have been determined. Using an equation derived by us which takes account of the change in the cyclodextrin concentration due to the simultaneous complexation of the solvent, both stability constants have been calculated. The influence of solvent on the stability constant of chloronitrobenzenes is discussed     

Performance and Attributes of Liquid Chromatography–Mass Spectrometry with Targeted Charge Separation in Quantitative Analysis of Therapeutic Peptides

Herein we describe a new method, targeted enhanced multiply charged scans (tEMC), for the quantification of therapeutic peptides in tandem mass spectrometry on the linear ion trap mass spectrometer. Therapeutic peptides with chain lengths between eight and 39 amino acid residues and charge states from 2+ to 6+ were used to evaluate and illustrate the method which relies on the ability to separate ions trapped in a linear ion trap according to their charges. In particular, interference from singly charged ions on multiply charged ions can be effectively minimized. The method requires optimization of relatively few parameters, the most important of which being the exit lens barrier (EXB) voltage, thereby offering substantial time saving in a high-throughput quantification environment that currently relies on selected reaction monitoring.     

Thermal and volumetric properties of methanol–hexamethylphosphortriamide mixtures under standard conditions

Enthalpic and volumetric characteristics of mixing in a methanol (MeOH)–hexamethylphosphortriamide (HMPT, 2) mixture are studied. Based on an analysis of concentration changes in the obtained data and the calculated partial molar characteristics, it is shown that at 0.2 molar fractions > х ₂ > 0.7 molar fractions, the variation in the composition of the mixture slightly alters the character of intermolecular interactions characteristic of pure components. It is found that MeOH–HMPT mixtures experience most changes in intermolecular interaction and structure within the range of 0.2–0.7 molar fractions of HMPT.