Kinetic parameter determination of vegetable oil oxidation under Rancimat test conditions

In this research, five different vegetable oils were oxidized at four different temperatures (373, 383, 393, and 403 K) under Rancimat test conditions. An increasing rate of oxidation could be observed as temperature increased. The natural logarithms of the kinetic rate constant (k value) varied linearly with respect to temperature, with the temperature coefficients (T_Coeff) ranging from 6.95×10^–2 to 7.40× 10^–2 K^–1 for the vegetable oils. On the basis of the Arrhenius equation and the activated complex theory, frequency factors (A), activation energies (E_a), Q₁₀ numbers, activation enthalpies (ΔH⁺⁺), and activation entropies (ΔS⁺⁺) for oxidative stability of the vegetable oils were calculated. The A, E_a, Q₁₀, ΔH⁺⁺, and ΔS⁺⁺ values for the vegetable oils ranged from 6.38×10³ to 28.03×10³ h^–1, from 86.86 to 92.42 kJ/mol, from 2.08 to 2.18, from 83.64 to 89.20 kJ/mol, and from –116.66 to –104.35 J/mol K, respectively.     

Melting parameters of poly(glycolic acid)

Equilibrium melting temperature T_m⁰, heat of fusion ΔH_f, and entropy of fusion ΔS_f of poly(glycolic acid) (PGA) was determined by using Clapeyron-Clausius equation. Equilibrium melting temperature T_m⁰ was 504.6 K which was determined by Hoffman-Weeks plots. The pressure dependence of T_m⁰ was determined by high pressure DTA up to 150 MPa. Volume change ΔV_f at melting was determined by using dilatometer. Heat of fusion in PGA was 183.2 (J g⁻¹), which is very close to the value reported by Chujo et al. who determined it by using T_m depression in copolymer with poly(lactic acid). ΔS_f of PGA was 0.363 (J g⁻¹ K⁻¹), which is about twice that of PLA, and the reason was discussed on the basis of the elastic modulus below T_m.     

The growth of ice crystals

An experimental investigation is reported of the A-axis and C-axis growth rates in water and brine in a channel immersed in a thermostatically controlled bath. Single crystals were nucleated from a capillary nucleating head, which could be rotated for measurement of C-axis growth rates. A-axis results are presented for subcoolings from 0.1 K to 1.0 K, for growth in water at velocities between 5 cm/sec and 23 cm/sec and in brine up to 6% salt concentration at 5 cm/sec and 12.5 cm/sec. While growth rates in water agree well with those of previous workers, those in brine are lower than any previously reported. At low subcoolings the growth rate varies linearly with ΔT, but at higher subcoolings the relationship is ν = AΔTⁿ, where n increases from about 1.45 for water to about 2.25 for 5% salt concentration. A new theory, based on conduction in the ice crystal, is outlined for the growth rate at high ΔT, and this yields more reasonable values of the constant A than previous theories. The experimental results presented for C-axis growth indicate considerably lower growth rates than any previously published.     

Thermogravimetric investigations in prediction of coking behaviour and coke properties derived from inertinite rich coals

The coal quality, temperature, pressure, heating rate, various processes and reactor type affect coking behaviour of coal and resulting coke properties. Several petrographic and chemical methods were proposed earlier for prediction of coking behaviour of coals. Inertinite rich coal samples (I^mmf>30 vol%) having different petrographic compositions were selected for thermogravimetric investigations (DTA, DTG and TGA) and their coking behaviour was studied. The petrographic build up, micro-structural properties (porosity and cell wall thickness) and mechanical strength of the resulted cokes were also investigated. ΔH and ΔH_max (the main endothermic area of heat absorption and fast absorbing main endothermic area, respectively) were distinguished in DTA curves. ΔA and ΔA_max (the main decomposition area and fast disintegrating main decomposition area) under DTG curves were identified. ΔH_max/ΔA_max shows good correlation with Roga's indices (RI, caking properties) as well as with petrographic caking ratio (PCR). The coarse mosaic content of cokes seem to depend on LΔT_max/ΔT_max (ratio of weight loss during fast decomposing main reaction to temperature difference) under DTG. L^mΔT/ΔT (ratio of weight loss during main decomposing reaction to temperature difference) under DTG exhibits correlation with p₁ (mean pore size) and t₁ (mean cell wall thickness) of cokes. ΔA_max/(L^mΔT_max) also indicates good relationship with mechanical strength of cokes. (L^mΔT_A−T_B)/(L^mΔT) (i.e. ratio of weight loss during main endothermic reaction under DTA to weight loss during main decomposing reaction) appears to have relationship with DD (compactness) of cokes. The course of main endothermic reaction/main decomposition reaction under DTA, DTG and TGA seems to govern coking behaviour and the resulting coke strength, which in turn is controlled by microlithotypes.     

Optimal thermodynamic synthesis of thermal energy recovery systems

A thermodynamic method is proposed to generate sequences of optimal non-ideal thermal energy recovery systems (TERS). The two-fold objective of using the thermal energy recovered from hot process streams primarily as heating power and then as shaft power is considered. Shaft power generation might be a technical goal by itself. However, it always gives a way of measuring the possibilities for the original set of streams to be efficiently integrated with additional process streams. If T_v is the absolute temperature of the steam utility and T_o is that of the cold utility, then the total power recovered is assessed as G = Q_E(T_v - T_o)/(T_v) + τ, where Q_E is the recovered heating power and τ is the shaft power that the system is able to generate. Each solution in a sequence of optimal non-ideal TERS will show: (i) the maximum value of G for the total exchange area A required and (ii) the maximum value for Q_E, provided that condition (i) has already been met. Therefore, generation of shaft power is subsidiary to thermal energy recovery as heating power. It is shown that for optimal networks the rate of internal generation of entropy, σ, attains its minimum value compatible with constraints describing: (i) the transformations to be operated on the process streams and (ii) the subsidiary character of shaft power generation to thermal energy recovery as heating power. A systematic procedure is deviced to incorporate these constraints to the functional form for σ making use of the operating line concept. Optimal non-ideal networks are derived from a family of operating lines that are extremals (minimals) for the functional σ subject to the prescribed constraints. A procedure to evolve from this type of optimal networks to new ones showing a maximum for the ratio β = Q_E/A for each given size of the exchange area, is also outlined. Applications to a test problem available in the literature and to an azeotropic distillation are also made.     

Influence of the electrohydrodynamic process on the properties of dried button mushroom slices: A differential scanning calorimetry (DSC) study

In this paper, drying of button mushroom (Agaricus bisporus) slices with an innovative drying technique of hot air combined with Electrohydrodynamic (EHD) drying process was investigated at three electrode gaps (5, 6, and 7 cm) and voltage levels (17, 19, and 21 kV). The effects of different hot air combined with EHD drying treatments on the temperature of the mushroom slices, drying time, final color and protein denaturation features including enthalpy (ΔH), onset temperature (T_o), peak transition temperature (T_p), conclusion temperature (T_c), and temperature range (T_c–T_o) of endothermic peaks were systematically evaluated. In addition, water state changes in DSC cooling thermograms of dried mushroom slices were investigated. The results obtained by differential scanning calorimetry showed that the ΔH values in the DSC traces of the EHD-dried mushroom slices were reduced with a decrease in the electrode gap and an increase in the voltage. Specifically, among voltages of 21, 17, and 19 kV, a voltage of 21 kV resulted in the lowest ΔH and T_c–T_o values and the highest T_p and T_o values. This result indicated that voltage had a significant effect on these responses. Similarly, the DSC results showed a considerable effect of high electric field intensity on ΔH, T_c–T_o and T_p responses related to protein denaturation in comparison to low electric field intensity.     

Effect of radiation dose on the thermal degradation of poly(ethylene terephthalate) fabric

The effect of radiation dose (10–30 kGy) on the thermal decomposition of poly(ethylene terephthalate) was studied using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X‐ray diffraction (XRD) analysis. The TGA and DSC were carried out in a flowing nitrogen atmosphere at heating rates of 5 and 30°C/min for TGA and 10°C/min for DSC. The degradation process was composed of three overlapping stages. The second stage, at which a rapid degradation occurs, was studied in detail. The process was found to follow a second‐order kinetics and was independent of radiation dose or heating rate. The reaction rate constant (k) was found to depend on the heating rate and iradiation dose. The apparent activation energy (Q) and the logarithm of the preexponential rate constant (log A) were found to decrease linearly with the increase in dose at rates of 3.32 kJ mol^?1 kGy^?1 and 0.177 s^?1 kGy^?1 with intercepts of 249 kJ/mol and 12.26 s^?1 for Q and log A of unirradiated fabric, respectively. A direct relationship was found between the percentage decrease in Q and log A and the percentage decrease in the temperature corresponding to 50% conversion (T_50%) for samples irradiated at different doses. It was found that a decrease in T_50% by 1% resulted in a decrease in Q and log A by 1.855 and 2.1%, respectively. Changes in Q and log A resulting from radiation, mechanical and thermal treatments, or their combinations can be predicted from the shift in T_50%. The history of the fibers substantially affected the thermal properties. DSC and XRD studies revealed changes in the fabric crystallinity. DSC measurements indicated a linear increase in heat of fusion with dose increase at a rate of 0.855 kJ kg^?1 kGy^?1. XRD analysis confirmed structural changes, rearrangement by plane rotations, and formation of compact crystalline lattice with patterns characterizing irradiated samples. An attempt to explain the dependency of the apparent activation energy on dose was given. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3710–3720, 2004     

Temperature fluctuations and heat transfer in a fluidized-bed combustor of waste oil

Temperature fluctuations and heat transfer characteristics were investigated in a fluidized-bed combustor of 0.102 m ID and 2.5 m in height, which was designed for waste oil combustion. Effects of excess air (A_E), injection height (H_I) and feeding rate of waste oil (Q_F) on the mean bed temperature (T_B), Kolmogorov entropy (K₂) of phase space portraits and heat transfer coefficient (U₀) in the fluidized-bed combustor were determined. T_B increased, but K₂ and U₀ decreased with increasingA _E . K₂ had a local minimum, but T_B and U₀ had a maximum at H_I of 0.4 m. T_B increased, but K₂ had a minimum and U₀ had a maximum with increasing Q_F in the combustor. T_B, K₂ and U₀ obtained at the optimum operating condition (A_E=40%, H_I=0.4 m, Q_F=30 g/min) were about 855 ‡C, 22 bits/s and 382 W/m²K, respectively.     

Separation of some light monocarboxylic acids from water inbinary solutions in a reverse osmosis pilot plant

The separation of formic (C₁), acetic (C₂), propionic (C₃), and n-valeric (C₅) acids in binary water solutions has been studied using a reverse osmosis (RO) membrane pilot plant operating at different temperatures and pressures (usually 21 °C and 1.72 MPa). The RO membrane, which is composite, polyamide and spiral-wound, having a surface area of 2.6 m², was fed by a solution of 0.5 M of C₁, C₂ and C₃ acids and 0.146 M of C₅. The pilot plant was used to simulate a cascade series of RO modules by recycling the permeate flux at the end of each semi-batch run. The influence on the retention coefficient, R, of molecular weight and molar volume, pK_a of the different acids was determined. For acetic acid the influence of temperature (T) and transmembrane pressure (ΔP) was also studied, obtaining an inverse and direct good linear correlation for R vs. T and R vs. ΔP, respectively. The results are particularly interesting for acetic acid-water separation, which is an open question in industrial applications.     

Time–temperature superposition in the enthalpy relaxation study of polystyrene

Enthalpy recovery measurement was used to study the physical aging behavior of a polystyrene. The aging experiments at temperatures (T_A) near T_g were conducted with aging times (t_A) ranging from several minutes to several days. The recovered enthalpy, ΔH(t_A, T_A), increased with t_A, and then a plateau value of ΔH_plate appeared in the long time aging experiment. The master curve was successfully constructed concerning the normalized relaxation isotherm of ? for the temperature range of T_g?16 < T_A < T_g?8 if ΔH_plate was used to calculate the normalized term. This implies that the enthalpy relaxation evolves with the same molecular dynamics in respective T_A. The shift factor in the master curve was interpreted in terms of the WLF (Williams–Landel–Ferry) equation to determine the coefficients for the superposition of ?–t_A curves. A smaller value was found in c₁ in comparison with those reported in the literature on polystyrene viscoelastic data, which was discussed in terms of temperature dependence of the relaxation rate in the enthalpy decay. POLYM. ENG. SCI., 56:561–565, 2016. © 2016 Society of Plastics Engineers     

Acid dissociation constants of anilinium and mono-nitro anilinium ions in formamide

The acid dissociation constant of anilinium ion and those of o-, m- and p-nitro anilinium ions have been determined accurately in formamide over the temperature range 10–50°C (283.15–323.15 K) from the measurement of the emf of the cells, Pt, H₂/B(m₁), BHCl(m₂)/AgClAg.The dissociation constants at 25°C (298.15 K) have been checked by determining the same with the help of the cells, Pt, Q-QH₂/B(m₁), BHCl(m₂/AgClAg.Thermodynamical changes ΔG⁰, ΔH⁰ and ΔS⁰ for the dissociation processes have been evaluated. The results show that the dissociation constants of these conjugate acids are in general lower (pK_a's higher) in formamide than their corresponding values in water.     

High mechanical quality factor and piezoelectricity in potassium sodium niobate ceramics

Plenty of works have done to enhance the piezoelectricity of potassium-sodium niobate (KNN), aiming to replace lead-zirconate titanate (PZT) in the consideration of eco-friendly requirement. However so far, KNN ceramics with high piezoelectric performances tend to have a low mechanical quality factor (Q_m), which could result in excessive dielectric loss, especially when working in high frequencies. Thus, increasing Q_m is a crucial task in KNN-based ceramics. By constructing phase boundaries together with inducing oxygen vacancies, a new KNN ceramic system is built by using conventional solid-state method with high Q_m (>250), high piezoelectric performance as well as outstanding temperature stability. Optimum overall properties of KNN-based ceramics can be as large as d₃₃ = 231 pC/N, Q_m = 355, T_C = 366 °C. This work provides a deeper insight to KNN-based ceramics with high mechanical quality factor and makes a progress on the high frequency application of lead-free ceramics.     

Isothermal crystallization study on aqueous solution of poly(vinyl methyl ether) by DSC method

A study on the isothermal crystallization of water in aqueous solutions of poly(vinyl methyl ether) (PVME) was carried out by the differential scanning calorimetry (DSC). The influence of PVME concentration (49.5, 44.5 and 39.5 v%) and the crystallization temperature (T_c) on crystallization rate G, crystallization enthalpy (ΔH_c) and melting enthalpy (ΔH_m) was investigated. Avrami equation cannot be used to describe the crystallization process of water in aqueous PVME solution. Within the measured temperature range, the crystallization rate G increases with the crystallization temperature T_c and with the decreasing PVME content. The crystallization enthalpy ΔH_c linearly increases with the degree of supercooling. The influence of T_c on the ΔH_c becomes more marked with increasing PVME concentration. For 49.5 and 44.5 v% PVME solutions, the amount of water arrested in solution during the isothermal crystallization and the final concentration of PVME-rich phase increase linearly with the T_c, whereas for 39.5 v% PVME solution, these two values almost do not change with T_c. The amount of frozen water in the subsequent cold crystallization is approximately proportional to the initial T_c. The approximately constant ΔH_m for a given concentration at the different initial isothermal crystallization temperatures suggests that the total amount of ice from the first isothermal crystallization and the second cold crystallization is same. The quantitative relation of the amount of frozen water in the cold crystallization and the initial T_c demonstrates that PVME/water complexes are thermodynamically unstable.     

Electrolytic process optimization by simultaneous-modular flowsheeting

A procedure is described for computer-assisted optimization of an electrolytic process flowsheet. Material, energy, and economic balances for all process units were incorporated in a nonlinear optimization routine for predicting the minimum selling price based on a discounted cash flow rate of return on investment. The optimization utilized a simultaneous-modular approach which was incorporated into the public version of the Aspen flowsheeting package, and used an infeasible path convergence method based on successive quadratic programming procedures. Electrolyte vapour-liquid equilibrium data were estimated by the non-random two-liquid model. The Lagrangian multipliers of the constraint equations were used to determine the sensitivity of the optimum to key process variables. The method was illustrated by evaluation of two process flowsheets for electrosynthesis of methyl ethyl ketone (MEK) from 1-butene based on pilot-plant performance reported in the patent literature.List of symbols A _c cell cost factor ($ cell^–1) - A _H heat exchanger cost factor ($ m^–2) - A _p pump cost factor ($ sl^–1) - A _R rectifier cost factor ($ kVA^–1) - A _T tank cost factor ($l ^–0.5) - A _cm cell maintenance factor ($ A^–1 y^–1) - A _cl cell labour ($ cell^–1 y^–1) - A _cw cooling water cost ($ m^–3) - A _e electricity cost ($ kWh^–) - A _m membrane cost ($ cell^–1 y^–1) - A _om other maintenance factor, fraction of plant capital less cell cost - C _p cooling water heat capacity (kJ kg^–1 °C^–1) - H operating hours per year - I _C current to each cell (A) - I _TOT total current to all cells (A) - L _A Lang factor for auxiliaries - L _C Lang factor for cells - L _R Lang factor for rectifiers - N number of cells in plant - Q heat removal load (kJ h^–1) - R production rate (kgh^–1) - T _cw cooling water temperature rise (°C) - T _LM cooler log mean temperature difference (°C) - U heat transfer coefficient for cooler (kW m^–2 °C^–1) - v _c electrolyte flow to each cell (l ^-1) - v _C cell voltage (V) - _R rectifier efficiency - cooling water density (kg m^–3) - _T surge tank residence time (s)     

Development of support vector regression (SVR)-based model for prediction of circulation rate in a vertical tube thermosiphon reboiler

The hydrodynamics and heat transfer in a thermosiphon reboiler interact with each other making the process very complex. Prediction of the rates of heat transfer and thermally induced flow are the primary requirements for the design of thermosiphon reboilers. The objective of this study was to develop, for the first time, a unified data-driven model, for the prediction of circulation rate in a thermosiphon reboiler for different pure components with wide variation in thermo-physical properties and operating parameters, using support vector regression (SVR)-based modeling technique. In the present work, 148 experimental data points from accessible sources, including the author's own study were used. First, a multiple regression (MR) model for circulation rate (in the form of Reynolds number) was developed as a function of dimensionless parameters namely, Peclet number for boiling (Pe_b), Subcooling number (K_sub), and the Lockhart–Martinelli parameter (X_tt), followed by the formulation of an SVR-based model. Statistical analysis revealed that the proposed generalized SVR-based model had high prediction accuracy with an average absolute relative error (AARE) of 3.82%, root mean square error (RMSE) of 0.0717, leave-one-out cross validation (Q²_LOO) of 0.9975 and mean relative error (MRE) of 0.0288 on the training data. Corresponding values of 6.11% AARE, 0.0816 RMSE, 0.9991 leave-one-out cross validation on test data (Q²_ext) and 0.0541 MRE were obtained for the test data. A comparison of the SVR-based correlation was made with the MR model and with some selected empirical correlations in the literature. It was observed that the proposed SVR-based model significantly exhibited an enhanced prediction and generalization performance.     

Na-feldspar (F) and kaolinite (K) system at high temperature: Resulting phase composition,micro-structural features and mullite-glass Gibbs energy of formation,as a function of F/K ratio and kaolinite crystallinity

The system Na-feldspar (F) and kaolinite (K) was investigated at temperatures of interest in ceramic applications (1200–1280 °C) to study the effects of F/K ratios by weight and crystallinity degree of kaolinite on the final product, micro-structural features and mullite-glass Gibbs energy of formation (ΔG^eff). Mullite and glass are the dominant phases; in general, the higher the temperature, the larger the former. An F/K increase promotes the formation of glass and secondary mullite, appearing along with the primary one. ΔG^eff was modelled by α(T) × (F/K)² + β(T) × F/K + γ(T), α, β and γ being linear functions of temperature whose coefficients were determined by fitting the ΔG^eff-theoretical to the ΔG^eff-obtained from the measured phase compositions. ΔG^eff is less affected by temperature than by F/K, whose increase shifts equilibrium towards glass phases. The ΔG^eff-curves for ordered and disordered kaolinite intersect one another at F/K ～0.5, a ratio close to that used in industrial practice.     

Correlations between the crystal structure and microwave dielectric properties in Ce2[Zr1-xMx]3(MoO4)9 (M = Mn1/3Nb2/3, Mn1/3Ta2/3) solid-solution ceramics

Ce₂[Zr_1-xM_x]₃(MoO₄)₉ (M = Mn_1/3Nb_2/3, Mn_1/3Ta_2/3; x = 0.02, 0.04, 0.06, 0.08 and 0.10) (abbreviated as CZ_1-xN_x and CZ_1-xT_x) ceramics were prepared through the solid-state reaction method. Effects of (Mn_1/3Nb_2/3)⁴⁺ and (Mn_1/3Ta_2/3)⁴⁺ ions on the sintering characteristics, crystal structures, microwave dielectric properties and infrared vibrational modes were studied in detail. X-ray diffraction (XRD) results reveal the formation of solid solutions for all components. Based on the chemical bond theory and Rietveld refinement, intrinsic structure parameters including the polarizability (P), the packing fraction (P.F.) and the octahedral distortion (Δ_octa.), and bond parameters including the lattice energy (U), bond energy (E) and thermal expansion coefficient (α) were calculated. Interestingly, the Ce–O bond plays a major role in the bond ionicity (f_i), while Mo–O bond dominates the contributions in the lattice energy (U), bond energy (E) and thermal expansion coefficient (α). In addition, these parameters are used to explain the variations of the microwave dielectric properties of ceramics either changing the doping contents or replacing different ions at x = 0.06. Furthermore, far infrared (FIR) spectra uncover that the phonon modes provide the major polarization contribution of 68.59% in the CZ_0.9T_0.1 ceramic, implying that the main contribution to ε_r stems from the ionic polarization instead of the electronic polarization. Typically, the optimum microwave dielectric properties are achieved for the CZ_0.9N_0.1 and CZ_0.9T_0.1 ceramics with ε_r = 10.76, Q × f = 85,893 GHz (at 9.52 GHz), τ_f = −14.83 ppm °C⁻¹ and ε_r = 10.72, Q × f = 87,355 GHz (at 9.81 GHz) and τ_f = −8.68 ppm °C⁻¹, respectively. Notably, the CZ_0.9T_0.1 ceramic has a markedly increased Q × f while maintaining a good τ_f = −8.68 ppm °C⁻¹ and a low sintering temperature of 700 °C.     

Differences between constant and intermittent drying in surf clam: Dynamics of water mobility and distribution study

Low-field nuclear magnetic resonance (LF-NMR) has been increasingly popular as analytical tools for evaluating the dynamics of water mobility and distribution. In this study, dynamics of moisture mobility and constitution of surf clam during constant drying process and intermittent drying process were evaluated by LF-NMR, while the differences of physical and chemical indexes were measured. Intermittent drying improved the product quality of clam, such as moisture content, shear force, color indices, sugar content, peroxide value, thiobarbituric acid value, and the bulk water ratio, which were closely related with moisture distribution and microstructure. The moisture constitution of constant drying process and intermittent drying process were distinctly different. Tempering process reduced drying time and resulted in lower moisture content in dried surf clam. In the meanwhile, the boundary between A₂₁ and A₂₂ was acquired by LF-NMR, revealed that bound water and immobilized water transformed from each other. During tempering process, the myofibril stretched out, verifying that moisture approached a relatively homogeneous. In addition, R² value reached 0.9897 and 0.9926 for calibration and validation, respectively, displaying good linear correlations between the T₂₁ parameters and moisture content. This study interpreted the dynamics of water mobility and distribution on the proton level to explain the reason that tempering processes to improve physicochemical indexes of surf clam.     

Another confirmation that counter-current logarithmic mean is upper bound and a note on approximations

The paper presents modifications on published demonstration that the counter-current logarithmic-mean-temperature-difference (ΔT_LM) is upper bound compared with the co-current ΔT_LM. In the published demonstration, an approach was proposed but it suffered from wrong assumption. In this paper, corrections to the wrong assumption and a property of a curve derived from the ΔT_LM curve have been used to propose another demonstration that counter-current ΔT_LM is upper bound. Optimization problems have been formulated to verify the proposed developments and demonstrate the results obtained.A class of ΔT_LM approximations including two accurate approximations proposed by the author are discussed. The selected approximations are designated as Underwood's class. This class generates accurate results over the problem temperature-difference-ratio range and has the advantage of direct use of the heat exchanger (HEX) terminal temperature differences.