Effect of pressure on the solid-liquid phase equilibria of binary organic systems

Solid-liquid phase equilibria of the binary mixtures of the organic liquids have been investigated at temperatures from 278 to 343 K and pressures up to 500 MPa using a high-pressure optical vessel. The systems investigated are as follows: (1) simple eutectic systems-benzene + cyclohexane system and benzene + 2-methyl-2-propanol system; (2) eutectic systems with formation of intermolecular compounds — carbon tetrachloride + p-xylene system and carbon tetrachloride + benzene system; (3) partial solid solution system--methylnaphthalene + -methylnaphthalene system; and (4) complete solid solution system-chlorobenzene + bromobenzene system. The uncertainties of the measurements of temperature, pressure and composition are within ±0.1 K, ± 0.5 MPa, and ±0.001 mole fraction, respectively. The freezing and melting temperatures at a constant composition increase monotonously with pressure. The eutectic mixture becomes richer in the component whose temperature coefficient of the freezing pressure is larger and the eutectic temperature rises monotonously with increasing pressure in the eutectic systems. The pressure-temperature-composition relation of the solid-liquid phase equilibria can be expressed satisfactorily by an equation newly proposed.Paper presented at the Tenth Symposium on Thermophysical Properties, June 20–23, 1988, Gaithersburg, Maryland, U.S.A.     

Application of RCM to a medium scale industry

The factors which are assuming considerable importance in cost effective decision making of operation of any industrial enterprise are in the order of significance liability, safety and environmental conditions. Hence, preventive maintenance (PM) optimisation is providing wide opportunities and challenges to everyone involved in all aspects of operation of industrial enterprise. Reliability centred maintenance (RCM) methodology offers the best available strategy for PM optimisation. It incorporates a new understanding of the ways in which equipment fails.In this paper, the concept of RCM has been applied to steel melting shop of a medium scale steel industry. By systematically applying the RCM methodology, failures, failure causes and effects on the system are analysed. To preserve the system function, PM categories are suggested for various failure modes in the components such as (1) time directed (2) condition directed (3) failure finding (4) run to failure. Features of predictive maintenance of a medium scale steel industry are deduced through this paper in a rather generalised form.     

A matrix interpretation of the estimate of the extension of uncertainties when constructing a temperature scale

A matrix method of extending the uncertainties when constructing a temperature scale in the 0–660°C range using the calibration of a platinum resistance thermometer at fixed points and interpolating the temperature scale, using it in accordance with the ITS-90, is considered. __________ Translated from Izmeritel’naya Tekhnika, No. 7, pp. 41–45, July, 2006.     

A pilot scale bioreactor using EMMC for carbon and nitrogen removal

A pilot scale (100 l reactor) of an entrapped mixed microbial cell (EMMC) process was fabricated and tested for simultaneous removal of carbon and nitrogen. Process performance, operational stability, and maintenance requirements were all determined. Two sources of actual agricultural processing wastewater containing a high concentration of chemical oxygen demand (COD) (about 800–1,000 mg/l) and domestic sewage containing a low concentration of COD (about 150–200 mg/l) were investigated in this study. Various HRT (hydraulic retention time) and aeration schedules were operated. It was found that soluble COD (SCOD) and soluble total nitrogen (STN) could be removed in the range of 40–70% and 20–90%, respectively, for domestic sewage depending on the operational conditions provided. For agricultural processing wastewater, removal efficiencies of SCOD and STN are 89–91% and 60–75%, respectively, depending on the HRTs and aeration schedules applied. Economic evaluation for the application of domestic sewage was conducted. It was found that at an HRT of 6 h with 24 h of aeration it costs U.S.$1.75 for the treatment of 1,000 gal/day (3.8 m³/day). It is apparent that the EMMC process is technically feasible for simultaneous removal of carbon and nitrogen under the operation of an alternated schedule of the aeration in one single bioreactor. Ultimately, it can replace or upgrade the existing conventional wastewater treatment plant by combining the secondary and tertiary wastewater treatment plant in one bioreactor and provides simple maintenance and operation. This will also assist in providing the high quality of treated effluent meeting current and future environmental regulation for reuse. Electronic Publication     

A phase field model for the freezing saturated porous medium

In terms of the mixture theory and phase field theory, a phase field model is developed for the saturated porous medium undergoing phase transition. In the proposed model, it is postulated that during the phase transition of the porous medium, both the solid skeleton and pore fluid will undergo phase transition. The phase states of the solid skeleton and pore fluid are characterized by respective order parameters. To simplify the proposed phase field model, the temperatures and order parameters of the solid skeleton and pore fluid are assumed to be equal. The balance laws of the porous medium are given by the conventional mixture theory. The order parameter and the porosity of the porous medium are considered as internal variables and their evolution equations are determined by the entropy inequality of the porous medium. The constitutive representations for the stresses, entropies, heat fluxes, drag force and the evolution equations for the order parameter and porosity are derived by exploitation of the entropy inequality. To illustrate the proposed model, a concrete phase field model for the freezing porous medium is established in the paper. In the model, the memory effect associated with phase transition of the porous medium is taken into account by assuming Stieltjes integral for the strain energy of the porous medium. The constitutive representations for the above variables are then derived according to the proposed free energy expression for the porous medium. Finally, the boundary condition associated with the proposed model and the determination of some parameters involved in our model are discussed in the paper briefly.     

Modeling phase equilibria in polymer-solvent systems for process design

An excess Gibbs energy model is presented for calculating phase equilibria in multicomponent systems containing polymers and solvents. The model represents a combination of a physical contribution obtained from a lattice model and a chemical contribution that accounts for association and solvation effects. The lattice model is based on a revised version of Freed's latticc-field theory developed by Hu, Prausnitz, and co-workers. The model accurately represents solvent activities and liquid-liquid equilibria in binary and ternary polymer solutions over wide ranges of temperature and polymer molecular weight. It is capable of reproducing liquid-liquid equilibria with upper and lower critical solution temperatures as well as closed-loop and hourglass-shaped phase diagrams. Because of its numerical simplicity, a reasonably small number of binary parameters, and its applicability to multicomponent systems, the model cm be useful for modeling industrial processes involving polymers.Paper presented at the Twelfth Symposium on Thermophysical Properties, June 19–24, 1994, Boulder, Colorado, U.S.A.     

Adsorption equilibria of benzodiazepines on a hybrid polymeric chiral stationary phase

The chromatographic behavior of a series of racemic benzodiazepines was evaluated under linear and nonlinear conditions on a new hybrid polymeric (DACH-ACR) chiral stationary phase (CSP). Differently substituted benzodiazepines were employed as probes to make hypotheses concerning possible molecular interaction mechanisms originating between target compounds and active sites on the CSP. Hydrogen bonds were found to be pivotal for chromatographic retention and chiral selectivity. The competitive effect from a mobile-phase (MP) modifier able to interact with the CSP through H-bonds was investigated. The performance of the polymeric DACH-ACR CSP for preparative purposes was also evaluated. The competitive adsorption isotherms of two benzodiazepines, lorazepam and temazepam, were measured at different MP compositions through the so-called inverse method. The adsorption data were fitted with a competitive bi-Langmuir adsorption isotherm. Enantiomeric separations under nonlinear conditions were modeled by using the equilibrium dispersive (ED) model of chromatography. Theoretical overloaded band profiles (obtained by solving the system of partial differential equations described by the ED model) matched, in a significantly accurate way, the profiles experimentally measured.     

Methods for constructing analytic phase function for small spherical particle polydispersions

Two ways of constructing analytic phase function for a polydispersion of small spherical non-absorbing particles have been investigated. First one is a straightforward procedure emanating from the implementation of single particle scattering input into the defined polydisperse phase function. This results in an analytic phase function in terms of moments of the distribution. The second approach is a new strategy, based on the Lagrange mean value theorem. A clear understanding of the relationship between these two approaches has been developed. The efficacy and accuracy of the scattering phase functions is illustrated by applying it to a power-law size distributed sphere ensemble.     

基于相位解调的光纤MEMS压力传感器

提出了一种新的压力传感器,该传感器基于Fabry-Perot腔干涉和相位解调理论测量压力。设计用MEMS技术以及普通的光通讯接插件制作出工艺简单,分辨率高的光纤MEMS压力传感器。阐述了传感器的工作原理,分析了硅膜的厚度对传感器性能的影响以及FP腔的长度对反射光信号的影响。研究了基于相位解调法的傅里叶变换方法,傅里叶解调法受光源强度波动的影响较小,解调精度高。实验结果表明改传感器在[0-3]MPa测量范围内,线性好,灵敏度可达到3.50 m/MPa（腔长改变/压力）。     

A comparison of phase equilibria in some II-IV-VI compounds based on PbTe

The solubilities of the group II elements Cd, Zn, Hg, Ca and Mg in PbTe are compared over the temperature range 250 to 800° C. Cd, Zn and Mg have retrograde solubilities whilst Hg and Ca are virtually insoluble in “as-grown” material. A consequence of these solubilities is a change in the properties of the alloys compared with PbTe. Thus the phase widths of the Cd/PbTe, Mg/PbTe and Zn/PbTe systems differ from that of PbTe. With the exception of the Zn/PbTe system, (where there is reasonable evidence to support the solubility of Zn in PbTe) there is a significant change in all measured electrical properties compared with PbTe.     

A method for the prediction of vapour-liquid equilibria of refrigerant mixtures at low and moderate pressure

This paper is a contribution to the development of a method for the prediction of the thermodynamic behaviour of refrigerant mixtures at low and moderate pressure, for which experimental data are not always available. The proposed model is based on a modified Redlich-Kwong-Soave equation of state, with mixing rules as proposed by Huron and Vidal. The calculation of the attractive parameter is based on infinite-pressure activity coefficients according to Soave et al. Activity coefficients are expressed by a group-contribution model derived from UNIFAC. A list of groups and subgroups is proposed for CFCs, HCFCs, HFCs and FCs. Two interaction parameters are regressed from experimental infinite-dilution activity coefficients of binary mixtures. As a result, only the structure, critical constants and vapour pressure of pure components are needed to calculate thermodynamic properties of refrigerant mixtures. The proposed approach is able to predict experimental data with satisfactory accuracy over the full composition range.     

Thermodynamic modelling of phase equilibria in Al-Ga-P-As system

A generalized thermodynamic expression of the liquid Al-Ga-P-As alloys is used in conjunction with the solid solution model in determining the solid-liquid equilibria at 1173 K and 1273 K. The liquid solution model contains thirtyseven parameters. Twentyfour of them pertain to those of the six constituent binaries, twelve refer to the specific ternary interactions. Additionally the liquid solution model also contains a specific quaternary interaction parameter. The latter has been evaluated here based on the experimental data available in the literature. The present research shows an excellent agreement between the derived and experimental values at 1173 K and 1273 K for the system. The article also presents a comparison between the evaluated values with those based on the regular solution model for the liquid alloys.     

A confirmatory study of Rasch-based optimal categorization of a rating scale

The purpose of this study was to determine if the characteristics of the optimal categorization identified by the Rasch analysis in a previous study can be maintained when the revised scale is applied to the same population. Based on the results of the previous Rasch analysis, a 23-item exercise barrier scale was modified from its original five-category structure ("Very often" = 1, "Often" = 2, "Sometimes" = 3, "Rarely" = 4, and "Never" = 5) to a three-category structure ("Very Often" = 1, "Sometimes" = 2, and "Never" = 3). The modified scale was then mailed to the original sample (N = 381), of which 206 returned the survey; a return rate 57.5%. The data was again analyzed using the Rasch Rating Scale model. Overall, the Rasch model fit data well and similar change patterns were observed in two category statistics provided by the Rasch analysis. The order of item severity was also well kept and the correlation of item severities generated from two studies was very high, with r = .98. In addition, similar results were also found in respondents' ability estimations, and the correlation between the two studies was moderately high, with r = .68. These results verified that the characteristics of the optimal categorization identified by the Rasch post-hoc analysis can be maintained after the original scale was modified based on such an analysis.