Heat transfer in a jacketed agitated vessel equipped with multistage impellers

In this work, heat transfer via the cylindrical part of the jacket in an agitated vessel has been investigated. Heat transfer coefficients were determined using the transient method based on measuring the temperature dependency of the liquid batch on time. A multistage impeller made of two impellers was used in a cylindrical vessel with dished bottom. The lower impeller was a curved blade turbine with the diameter of d = 100 mm and the upper impeller was either a pitched three-blade or pitched four-blade impeller with the diameter of d₁ = 67 mm. Three different impeller clearances in a multistage configuration, H₃/d₁ = 1, 1.5, and 2, were used in our measurements. The vessel was equipped with two baffles. Experimental results were evaluated using the Euler’s method and nonlinear regression procedure in the Matlab® software and they are summarized in form of Nusselt number correlations describing their dependency on the Reynolds number.     

Power consumption for an agitated vessel equipped with pitched blade turbine and short baffles

Power characteristics for an agitated vessel equipped with planar short baffles of length L and pitched blade turbine of pitch β are presented in the paper. The studies were carried out in the vessel of inner diameter D = 0.6 m, where the baffles were located in the distance p from the vessel bottom (p + L = H). Torque was measured using strain gauge method within the turbulent regime of the flow of Newtonian liquid in the agitated vessel. The effects of the pitch β and geometrical parameter p/H on the power number Ne were determined mathematically. The results showed that, for the assumed value of the angle β, the function Ne = f (L/H) decreases with the decrease in the baffle length L (i.e. with the increase in the parameter p). Moreover, for the assumed value of the baffle length L, the function Ne = f (β) increases with the increase in the angle β of the inclination of the impeller blade.     

Experimental and CFD-PBM Study of Oxygen Mass Transfer Coefficient in Different Impeller Configurations and Operational Conditions of a Two-Phase Partitioning Bioreactor

In this work, gas dispersion in a two-phase partitioning bioreactor is analyzed by calculating volumetric oxygen mass transfer coefficient which is modeled using a commercial computational fluid dynamics (CFD), code FLUENT 6.2. Dispersed oxygen bubbles dynamics is based on standard “k-ε” Reynolds-averaged Navier-Stokes (RANS) model. This paper describes a three-dimensional CFD model coupled with population balance equations (PBE) in order to get more confirming results of experimental measurements. Values of k _L a are obtained using dynamic gassing-out method. Using the CFD simulation, the volumetric mass transfer coefficient is calculated based on Higbie’s penetration theory. Characteristics of mass transfer coefficient are investigated for five configurations of impeller and three different aeration flow rates. The pitched six blade type, due to the creation of downward flow direction, leads to higher dissolved oxygen (DO) concentrations, thereby, higher values of k _L a compared with other impeller compositions. The magnitude of dissolved oxygen percentage in the aqueous phase has direct correlation with impeller speed and any increase of the aeration magnitude leads to faster saturation in shorter periods of time. Agitation speeds of 300 to 800 rpm are found to be the most effective rotational speeds for the mass transfer of oxygen in two-phase partitioning bioreactors (TPPB).     

Transition from two-to three-dimensional behavior in anisotropic polymer layers

Two types of anisotropic polymer systems were studied in the spherical approximation used in the classical theory of ferromagnetism. These were a three-dimensional system composed of weakly interacting layers with isotropic interactions between chain segments in the layer planes and thin quasi-two-dimensional polymer films possessing intra-and interchain interaction anisotropy, whose behavior is close to that of two-dimensional systems. Laws that govern a change in the temperature T _cr of phase transition from the long-range order state to a disordered state depending on the magnitude of anisotropy and the size of the layers were established. For systems of the former type in which interlayer interactions is weakened, T _cr tends to zero, being inversely proportional to lng, where g is the ratio of the interaction constant between the layers to that of inplane interaction in a layer. For systems of the latter type, the transition temperature T _cr → 0 according to the T _cr ～ √? law, where ? is the parameter that characterizes the anisotropy of intra-and interchain interactions. The number of layers required for the systems to be considered three-dimensional was estimated. Regardless of the type of boundary conditions for finite systems, the number of layers increases with enhancement of interaction anisotropy (a decrease in g and ?) and an increase in the number of chains in the layers, especially for systems of the former type. Transverse orientational correlations of chain segments with respect to the arrangement of the layers decrease according to a power law, as in the case of infinite two-dimensional systems. There are fluctuations of three-dimensional long-range orientation order in the plane of the layers, the fluctuations are enhanced with an increase in the anisotropy of interactions in the system.     

Viscosities and Surface Tensions of Phenetole with <Emphasis Type="Italic">N</Emphasis>-Methyl-2-pyrrolidone, <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dimethylformamide and Tetrahydrofuran Binary Systems at Three Temperatures

Viscosities, η, and surface tensions, σ, of binary systems of phenetole (ethoxy benzene or ethyl phenyl ether) with N-methyl-2-pyrrolidone, N,N-dimethylformamide or with tetrahydrofuran were measured over the entire mole fraction range and at (298, 303 and 308) K. The experimental data was used to compute the deviations in viscosity, Δη, and surface tension, Δσ. Values of the excess Gibbs energy of activation G*^E, surface entropy S _σ and surface enthalpy H _σ were calculated. Viscosity data of the binary systems were calculated using the Grunberg and Nissan and the three-body and four-body McAllister correlations. The Redlich–Kister method was used for evaluation of coefficients and standard deviations for Δη, Δσ and G*^E. The results were interpreted in terms of the probable effect of molecular interactions between components as well as polarity.     

Room Temperature Ionic Liquids: Their Cohesive Energies,Solubility Parameters and Solubilities in Them

The cohesive energies of room temperature ionic liquids, RTILs, at the reference temperature T _ref = 298.15 K have been obtained from their molar enthalpies of vaporization. They are ce(298) = ?_v H°(298) ? 298.15R, on regarding the vapors as single ion-paired molecules. The cohesive energy densities, ced = ce/V = δ _H ² are the squares of the (Hildebrand) solubility parameters of the RTIL, which are presented for many RTILs. The solubilities of a variety of solutes in RTILs are discussed in relation to the solubility parameters. It turned out that the δ _H values of RTILs, obtained from the enthalpies of vaporization, may be used for empirical correlations, but are not able to predict the solubilities of solutes in RTILs.     

Method validation parameters for drugs and explosives in ambient pressure ion mobility spectrometry

An approach using method validation (MV) parameters, otherwise known as analytical figures of merit was combined with electrospray ionization high performance ion mobility spectrometry (ESI-HPIMS) to describe an approach for evaluating drugs and explosives analysis in the field. MV parameters such as reduced mobility (K _o ), conditional reduced mobility (K _c ), resolving power (R _p ), theoretical plates (N), linearity, accuracy, precision, limit of detection (LOD), limit of quantitation (LOQ), repeatability, range, and reporting limit were investigated and developed for eleven drugs and six explosives. Our investigation estimated resolving power at 66 ± 0.64 for the ESI-HPIMS used. The LOD’s calculated ranged from 0.45–2.97 ng of material electrosprayed into the ESI-HPIMS. The LOQ’s calculated falls in the range 4.11–8.63 ng of material electrosprayed into the ESI-HPIMS. The key findings from this investigation were the following: K _c proves to be a measure of the identity of an explosive or drug ion; a parameter that may be applied to help aid IMS devices when detecting drugs and explosives. MV parameters, especially, K _c , introduced in this study is an effective parameter for establishing a unique identity of a drug or explosive. A control chart is an effective way to monitor the performance of an instrument and may be a useful tool for establishing reliability of confirmatory data in forensic investigations. MV parameters may be a reliable, accurate and unique identification marker for target drugs and explosives capable of differentiating these substances from false positive responses.     

The internal rotation potential functions of the methacryloyl chloride molecule in the ground and excited electronic states

The systems of torsional vibration levels of the trans and cis methacryloyl chloride isomers in the ground (S ₀) and excited (S ₁) electronic states obtained by analyzing the vibrational structure of the gas-phase UV spectrum were used to reproduce the internal rotation potential functions of the molecule in both electronic states. The kinematic F factor in the S ₀ and S ₁ electronic states was calculated taking into account the relaxation of geometric parameters depending on the internal rotation angle. The internal rotation potential function parameters in the S ₀ state are substantially different from the parameters obtained using the torsional levels of the IR Fourier transform spectrum; at the same time, they are substantiated by quantum-mechanical calculations.     

Structural state of solvent in electrolyte solutions

Isoentropic compressibilities were determined for aqueous solutions of five electrolytes ranging from dilute to almost saturated solutions at 278.15–308.15 K based on precision measurements of ultrasound velocity. Using correct relations we have found hydration numbers (h) and molar parameters of volume and compressibility of hydrated complexes (V _h , β_h V _h ), water in the hydration shell (V _1h , β 1_h V _1h ), and void containing a stoichiometric mixture of ions (V _2h , β _2h V _2h ). In the temperature range under study, the hydration numbers h and the parameters β_h V _h are independent of temperature; molar compressibilities of hydration sphere (β _1h V1_h) are independent of concentration. Since β_h V _h is independent of temperature at a constant concentration of electrolyte, Y _K,S ^e also becomes independent of temperature. It is shown that the chemical potentials of bound and unbound water are equal and that γ_R = F(h) is an example of a discontinuous function that defines the abrupt change in the solvent at the complete solvation limit in solution.     

The mutual influence between <Emphasis Type="Italic">π</Emphasis>-hole pnicogen bonds and <Emphasis Type="Italic">σ</Emphasis>-hole halogen bonds in complexes of PO<Subscript>2</Subscript>Cl and XCN/C<Subscript>6</Subscript>H<Subscript>6</Subscript> (X = F,Cl, Br)

The bimolecular and termolecular complexes involving PO₂Cl and XCN/C₆H₆ (X = F, Cl, Br) were designed to form the π-hole pnicogen bonds and σ-hole halogen bonds, to compare the two types of interactions and investigate the mutual influences between them. PO₂Cl was used as simultaneous π-hole and σ-hole donor; it can interact with electron donor to form π-hole pnicogen bond and σ-hole halogen bond. The π-hole interactions are stronger than the σ-hole interactions, in both the bimolecular and the termolecular complexes. Comparing the mutual effects of the π-hole interactions and σ-hole interactions, the π-hole interaction has a greater influence on the σ-hole interaction than vice versa. With the addition of σ-hole halogen bond, the V _S,max value outside the π-hole region of PO₂Cl becomes decreasingly positive, resulting in a weaker π-hole interaction. With the addition of π-hole pnicogen bond, the V _S,max value outside the σ-hole region of PO₂Cl becomes small, also resulting in a weaker σ-hole interaction. The π-hole pnicogen bond and σ-hole halogen bond weaken each other, i.e., there is a negative cooperative effect in the termolecular complexes.     

Evaluation of Acid Dissociation Constants in DMSO and DMF by Quantum-Chemical Methods

We have calculated total electronic energies (E) and Gibbs energies (G) of a large number of acids and their anions in water, dimethylsulfoxide, and dimethylformamide using the hybrid B3LYP functional DFT method in the 6-31++G(d,p) basis set, taking into account the solvent effect by the conductor-like polarizable continuum model method. A linear correlation has been found between the experimental values of acid dissociation constants (pK_a) of different nature and the difference between anion and acid E values, and between pK_a and the difference between anion and acid G values. The obtained correlations allowed us to evaluate the pK_a values of both inorganic and organic acids. Such an evaluation is of special importance for nonaqueous solvents as it is quite problematic to determine these dissociation constants.     

Effect of photoanode active area on photovoltaic parameters of dye sensitized solar cells through its effect on series resistance investigated by electrochemical impedance spectroscopy

In the present work, the dependence of photovoltaic parameters of laboratory-scale dye sensitized solar cells (DSSCs) on photoanode active area (A) and also the effect of using current collector on this dependency were investigated. Current collectors were applied, in the form of silver strips, on the edges of electrodes. Electrochemical impedance spectroscopy (EIS) and current-voltage (I-V) curve measurement were employed as characterizing methods. The role of current collector was to decrease the resistance against current collection from the surface of electrodes and thus to decrease series resistance of DSSCs. It was observed that all photovoltaic parameters, i.e., short circuit current density (J _sc), open circuit voltage (V _oc), fill factor (FF), and power conversion efficiency (η), decrease with increasing A. Applying current collector had no influence on photovoltaic parameters of smallest DSSC, but it improved the performance of larger DSSCs. Also, applying current collector caused the photovoltaic parameters of DSSCs to be less dependent on A. It was shown that A dependence of photovoltaic parameters was due to the effect of A on area-specific series resistance (r _s) of DSSC. Also, the effect of current collector on A dependency of photovoltaic parameters was due to its effect on A dependency of r _s.     

A comparison of energy changes accompanying growth processes by <Emphasis Type="Italic">Saccharomyces cerevisiae</Emphasis>

Calculations are made using the equations Δ_r G = Δ_r H ? TΔ_r S and Δ_r X = Δ_r H ? Δ_r Q where Δ_r X represents the free energy change when the exchange of absorbed thermal energy with the environment is represented by Δ_r Q. The symbol Q has traditionally represented absorbed heat. However, here it is used specifically to represent the enthalpy listed in tabulations of thermodynamic properties as (H _T  ? H ₀) at T = 298.15 K, the reason being that for a given substance TS equals 2.0 Q for solid substances, with the difference being greater for liquids, and especially gases. Since Δ_r H can be measured, and is tangibly the same no matter what thermodynamics are used to describe a reaction equation, a change in the absorbed heat of a biochemical growth process system as represented by either Δ_r Q or TΔ_r S would be expected to result in a different calculated value for the free energy change. Calculations of changes in thermodynamic properties are made which accompany anabolism; the formation of anabolic, organic by-products; catabolism; metabolism; and their respective non-conservative reactions; for the growth of Saccharomyces cerevisiae using four growth process systems. The result is that there is only about a 1% difference in the average quantity of free energy conserved during growth using either Eq. 1 or 2. This is because although values of TΔ_r S and Δ_r Q can be markedly different when compared to one another, these differences are small when compared to the value for Δ_r G or Δ_r X.     

The electronic structure of nanoparticle: theoretical study of small Cobalt clusters (Co<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>, <Emphasis Type="Italic">n</Emphasis> = 2–5) (part A)

Electronic and geometrical structures of small Cobalt cluster (Co _n , n = 2–5), which were used as building block in Cobalt cluster compounds, were fully investigated in this article. Since small Cobalt clusters as a nanoparticle have many applications in scientific works and technology, it is essential for understanding their relatively accurate electronic structure. The most stable symmetrically and electronically structure confirmed by frequency test for studied clusters is as follows: 5-et (quintet) Co₂ is of course linear, and its HOMOs described by degenerate d _xy orbitals in β-spin part located on both atoms; 8-et (octet) Co₃ is almost scalene triangle and its HOMO in s-orbital of α-spin part located on Co₍₁₎; 11-et Co₄ is rhombus, d _xz orbital of β-spin part located on Co₍₂₎ is its HOMO part. 12-et Co₅ is pyramidal with HOMO in p _x orbital located on Co₍₅₎ in β-spin part, which show very low (0.06) occupation number. This large depletion of electron in HOMO occupation of Co₅ explains high chemical reactivity of this species. Density functional theory, DFT, was used through software Gaussian 09. Xc-correlation functional was chosen among the many recommended xc-functionals for transition metal in the literature by calibration procedure in such a way that the results can match with experimental values. So suitable xc-functional B3P86 and 6-311++G* basis set were found. Natural bond orbital, NBO, has also been used for analysis.     

The thermodynamic properties of 5-vinyltetrazole and poly-5-vinyltetrazole over the temperature range from <Emphasis Type="Italic">T</Emphasis> → 0 to 350 K

The temperature dependences of the heat capacities of 5-vinyltetrazole and poly-5-vinyltetrazole were measured by adiabatic vacuum calorimetry over the temperature range 6-(350–370) K with errors of ～0.2%. The results were used to calculate the thermodynamic functions of the compounds, C _p ^° , H ^°(T) - H ^°(0), S ^°(T), and G ^°(T) - H ^°(0), over the temperature range from T → 0 to 350–370 K. The energy of combustion of 5-vinyltetrazole and poly-5-vinyltetrazole was measured in an isothermic-shell static bomb calorimeter. The standard enthalpies of combustion Δ _c H ^° and thermodynamic characteristics of formation Δ_f H ^°, Δ_f S ^°, and Δ_f G ^° at 298.15 K and p = 0.1 MPa were calculated. The results were used to determine the thermodynamic characteristics of polymerization of 5-vinyltetrazole over the temperature range from T → 0 to 350 K.     

Peroxy radicals as motional probes at the end of isolated polystyrene chains and on the cellulose surfaces in vacuum

The isolated polystyrene chains spin-labeled with peroxide radical at the free end (IPSOO) in which the chain roots were covalently bonded to the surface of microcrystalline cellulose (MCC) powder were produced by mechanochemical polymerization of styrene initiated by MCC mechanoradicals. The IPSOO was used as motional probes at the ends of isolated polystyrene chains tethered on the surface of MCC powder. Two modes for the molecular motion of IPSOO were observed. One was a tumbling motion of IPSOO on the MCC surface, defined as a train state, and another was a free rotational motion of IPSOO protruding out from the MCC surface, defined as a tail state. The temperature of tumbling motion (T _tum ) of IPSOO at the train state was at 90 K with anisotropic correlation times. T _tum (90 K) is extremely low compared to the glass transition temperature (T _g ^b ; 373 K) of polystyrene in the bulk. At temperatures above 219 K, the IPSOO was protruded out from the MCC surface, and freely rotated at the tail state. The train–tail transition temperature (T _train–tail ) was estimated to be 222 K. T _tum (90 K) and T _train–tail (222 K) are due to the extremely low chain segmental density of IPSOO on the MCC surface under vacuum. The interaction between IPSOO and the MCC surface is a minor contributing factor in the mobility of IPSOO on the surface under vacuum. It was found that peroxy radicals are useful probes to characterize the chain mobility reflecting their environmental conditions.     

The thermodynamic properties of the [(Me<Subscript>3</Subscript>Si)<Subscript>7</Subscript>C<Subscript>60</Subscript>]<Subscript>2</Subscript> fullerene complex

The temperature dependence of the heat capacity C _p ^o of the [(Me₃Si)₇C₆₀]₂ fullerene complex was measured for the first time using precision adiabatic vacuum calorimetry over the temperature range 6.7–340 K and high-accuracy differential scanning calorimetry at 320–635 K. For the most part, the error in the C _p ^o values was about ±0.5%. An irreversible endothermic effect caused by the splitting of the dimeric bond between fullerene fragments and the thermal decomposition of the complex was observed at 448–570 K. The thermodynamic characteristics of this transformation were calculated and analyzed. Multifractal analysis of the low-temperature (T < 50 K) heat capacity was performed, and conclusions were drawn concerning the character of the heterodynamicity of the structure. The experimental data obtained were used to calculate the standard thermodynamic functions C _p ^o (T), H ^o (T) ? H ^o (0), S ^o (T) ? S ^o (0), and G ^o (T) ? H ^o (0) over the temperature range from T → 0 to 445 K and estimate the standard entropy of formation of the compound from simple substances at 298.15 K. The standard thermodynamic properties of [(Me₃Si)₇C₆₀]₂ are compared with those of the (C₆₀)₂ dimer, the [(η⁶-Ph₂)₂Cr]⁺[C₆₀]^?? fulleride, and the initial C₆₀ fullerene.     

Optical Band Gap Energies in Quasi-Metal Carbon Nanotubes

The structure of carbon nanotubes is described by two positive integers (n₁, n₂). The π-electron model of the nanotube band structure predicts that when the difference n₁–n₂ is multiple of three, the energy gap between the valence and conduction bands vanishes so that such tubes should exhibit quasi-metal properties. The band structure of 50 chiral and achiral (n₁, n₂) nanotubes with 4 ≤ n₁ ≤ 18 and n₂ = n₁–3q has been calculated by the linearized augmented cylindrical wave method. Nanotubes have been identified for which the optical band gaps are in the terahertz range (1–40 meV) and which can be used for design of emitters, detectors, multipliers, antennas, transistors, and other nanoelements operating in the high-frequency range.     

New linear driving force correlation spanning long and short cycle time pressure swing adsorption processes

A simple, semi-empirical, generalized expression was developed for the LDF mass transfer coefficient k as a function of the half cycle time θ _c that encompasses and transitions between the well-known regions governed by the long cycle time constant Glueckauf k and the short cycle time dependent k. This new expression can be used to estimate k = f(θ _c ) for any system, irrespective of the loading and irrespective of θ _c , no matter if k is in the cycle time dependent region or not. A three times wider transition region between the Glueckauf k and the cycle time dependent k was also established, with the Glueckauf LDF limit now valid for θ _c  > 0.3 and the short cycle time limit now valid for θ _c  < 0.01. When evaluating this region for several adsorbate-adsorbent systems, the minimum Glueckauf θ _c spanned three orders of magnitude from thousands of seconds to just a few seconds, indicating a cycle time dependent k is not necessarily limited to what is normally considered a short cycle time. For virtually any θ _c less than this minimum Glueckauf θ _c , this new first-of-its-kind expression can be used to readily provide an accurate value of k = f(θ _c ). Since the widely accepted half cycle time concept does not apply to the actual simulation of a multi-step, unequal step time, pressure swing adsorption process, the value of k = f(θ _c ) from this new expression can be based on either the shortest cycle step in the cycle or a different value of k = f(θ _c ) for each cycle step time in the cycle, with validity confirmed either by experiment or by process simulation using the exact solution to the pore diffusion equation.     

Solution Thermodynamics of <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis><Superscript>/</Superscript>-Ethylenebis-(salicylideneiminato)-diaquochromium(III) Chloride in Aqueous Dimethylsulphoxide

The densities, viscosities and refractive indices of N,N ^/-ethylene-bis(salicylideneiminato)-diaquochromium(III) chloride, [Cr(salen)(H₂O)₂]Cl, in aqueous dimethylsulfoxide (DMSO) with different mass fractions (w ₂ = 0.20, 0.40, 0.60, 0.80 and 1.00) of DMSO were determined at 298.15, 308.15 and 318.15 K under atmospheric pressure. From measured densities, viscosities and refractive indices the apparent molar volumes (V _φ ), standard partial molar volume (V _φ ⁰ ), the slope (S _V ^* ), standard isobaric partial molar expansibility (φ _E ⁰ ) and its temperature dependence (?φ _E ⁰ /?T) _p , the viscosity B-coefficient, its temperature dependence (?B/?T), solvation number (S _n ) and apparent molar refractivity (R _D ^φ ), etc., were calculated and discussed on the basis of ion–ion and ion–solvent interactions. These results revealed that the solutions are characterized by ion–solvent interactions rather than by ion–ion interactions and the complex behaves as a long range structure maker. Thermodynamics of viscous flow was discussed in terms of transition state theory.