•A thermal conductivity model is developed based on the analogy concept and is applied to pure substances.•Data are included for 24 organic families and 56 functional groups in a temperature range of ...16.6 to 604.65 K and pressures below 4032 bar.•The final model presents one interaction parameter that is generalized using the group contribution technique.•Prediction of thermal conductivity in the saturation and single-phase conditions are done.•The model provides acceptable results when in comparison to other correlations.
The aim of this work is to apply a group contribution method to describe the thermal conductivity of pure substances. The model has five adjustable parameters that have been generalized using the acentric factor, RTc/Pc relation, and a contribution of each group in the substance through a tendency graphical analysis. The thermodynamical properties included in the model are estimated using a modified Peng-Robinson EoS. The proposed model is applied to 351 substances distributed into 160 for the correlation, 96 for testing, and 95 for predictive capabilities. The above includes 24 organic families and 56 functional groups. The average absolute deviations are below 6.51% for the liquid-vapor coexistence and below 7.93% for the one-phase condition. The overall results are compared to other literature works on saturation and single-phase conditions. These results show that the model provides acceptable values of deviations and can be used to describe different types of substances. Finally, three cases of study are done as an alternative to represent the alkanes, 1-alcohols, and water substances. The average absolute deviations for 1-alkanes and 1-alcohols are below 7.00% and for water is around 3.76%. In general, the generalized model can be used as an alternative to describe the thermal conductivities of pure substances in the saturation and single-phase conditions with acceptable results.
A group contribution method to model the thermal conductivity of pure substances. Luis F. Cardona, Luis A. Forero and Jorge A. Velásquez. Display omitted
Students? misconceptions in science can lead to a range of learning difficulties if the teacher does not choose the appropriate teaching strategies to reduce their frequency. In this paper, ...13?14-year-old students? misconceptions regarding structure and states of matter, pure substances, and mixtures are explored. The teaching strategy with E-learning material was applied to examine its effects on the frequency of misconceptions. The research was conducted in urban schools in Bosnia and Herzegovina with 7th- and 8th-grade students. Findings pointed to the misconceptions originating in transferring the macroscopic observations into the submicroscopic level and in misinterpretation of the size of particles. Students who used E-learning material at school mostly had lower percentages of misconceptions in comparison to students from the control group and students who accessed the same E-learning material from their home. This indicates that the E-learning strategy could have promising results if applied more extensively at schools. This study aims to direct teachers? attention toward applying E-learning in chemistry teaching, for students to gain scientifically accepted knowledge and to reduce the occurrence of misconceptions.
This paper presents the results of a series of studies aimed at investigating the reference material (RM) of a multicomponent solution. An algorithm for estimating the uncertainty induced by the ...chemical element content in the RM is proposed taking into account the mass of the measurand in each component of the mixture. The results calculated according to the preparation procedure using the proposed algorithm were confirmed by the Monte Carlo method, while the elemental content in the mixture was confirmed via inductively coupled plasma optical emission spectroscopy. The applicability of weighted mean estimates for characterizing an RM of a multicomponent solution is shown.
Se aplica un modelo para el cálculo de la viscosidad del tipo ecuación cúbica de estado de Peng-Robinson. El modelo ha sido empleado para correlacionar y predecir viscosidades de sustancias puras y ...mezclas en especial en la región de saturación. Los parámetros del modelo han sido generalizados en términos de la masa molar. Las expresiones generalizadas son estimadas mediante el ajuste de datos experimentales de alcanos y alcoholes. Las desviaciones absolutas promedio para la viscosidad, entre los valores correlacionados y los experimentales, son 6.26% y 7.21% para alcanos y alcoholes, respectivamente. Se realizan cálculos predictivos con desviaciones absolutas promedio de 3.99% para alcanos y 13.76% para alcoholes. Para viscosidades de mezclas se utilizaron tres enfoques de reglas de mezclado. Las desviaciones promedio calculadas son 18.66%, 10.31% y 3.85% para las reglas simples, de uno y dos parámetros respectivamente. Los resultados indican que el modelo propuesto proporciona resultados adecuados y consistentes, teniendo en cuenta la simplicidad de las expresiones generalizadas desarrolladas.
A technique for synthesis of high-pure tellurium oxide (IV) by chemical combustion of tellurium vapor in dry oxygen has been developed. The technique allows synthesizing crystalline β-TeO2 ...(paratellurite) free of OH-groups. Numerical simulation of the technique processing in a quartz-glass reactor let’s propose the mechanism of crystalline TeO2 formation as 2–5 μm particles and found out ranges of parameters of the combustion reaction of Te-vapor in oxygen atmosphere: temperature, tellurium vapor pressure, argon-carriage-gas flow, oxygen flow and total gas pressure in the reactor. The experimentally optimized parameters made it possible to synthesize crystalline β-TeO2 as pure as 99.999994 wt% (65 elements detected) using 99.997 wt% Te and 99.999 vol% oxygen with the yield of 85%.
•Numerical simulation of the combustion reaction of Te vapor in oxygen was fulfilled.•Synthesis technique of crystalline TeO2 by the chemical combustion reaction was developed.•β-TeO2 powder preparation with chemical purity 99.999994 wt% was produced.
2018’de Fen Bilimleri Dersi Öğretim Programının revize edilmesiyle birlikte müfredattaki konulardan bazıları sınıf seviyesi ve kapsam bakımından değişikliğe uğramıştır. Bu durum kazanımları ölçen, ...öğretim programına uygun yeni ölçme ve değerlendirme araçlarına ihtiyaç duyulmasına neden olmuştur. Bu çalışmanın amacı; ortaokul 7. Sınıf “Saf Madde ve Karışımlar” ünitesi konu ve kavramlarına yönelik, öğretim programındaki kazanımlara uygun, geçerli ve güvenilir bir ölçme aracı geliştirmektir. Buna yönelik olarak öncelikle Fen Bilimleri Dersi Öğretim Programındaki kazanımlar listelenmiş ve kazanımlara uygun, öğrencilerin üst düzey zihinsel becerilerini ölçmeye yönelik, araştırmacı ve öğretmenlerin kullanabileceği 40 maddeden oluşan bir test hazırlanmıştır. İlgili ünite konu ve kazanımları doğrultusunda belirtke tablosu oluşturulmuştur. Ayrıca Fen Bilgisi eğitimi alanından iki öğretim üyesi ve iki Fen Bilimleri öğretmeninin görüşlerine başvurularak testin kapsam geçerliğine sahip olması sağlanmıştır. Geliştirilen Saf Madde ve Karışımlar Ünitesi Başarı Testi (SMVKÜBT) 2018-2019 eğitim-öğretim yılında Amasya ilinde 6 ortaokulda toplam 358 sekizinci sınıf öğrencisine uygulanmıştır. Örneklem belirlenirken maksimum çeşitlilik örnekleme yönteminden faydalanılmıştır. Güvenirlik katsayısı KR-200.85 olarak bulunmuştur. Testin ortalama madde güçlüğü (Pjx) 0.45 ve ortalama ayırıcılığı (rjx) 0.43 olarak hesaplanmıştır. Madde analizleri sonucunda ayırt ediciliği düşük olduğu saptanan 4 madde testten çıkarılmıştır. Testin son hali 36 maddeden oluşmaktadır. Sonuç olarak ilgili konuya yönelik hem araştırmacıların hem de öğretmenlerin faydalanabileceği geçerli ve güvenilir bir başarı testi geliştirilmiştir.
En este trabajo se modela la viscosidad dinámica de fluidos newtonianos a partir de la teoría de Eyring junto con la energía libre de Helmholtz residual. Para la estimación de esta energía se utiliza ...una versión modificada de la ecuación cúbica de estado de Peng-Robinson. Los parámetros ajustables del modelo se han determinado a partir de datos experimentales en la zona coexistencia líquido-vapor para n-alcanos y n-alcoholes. Posteriormente estos parámetros se han generalizado utilizando expresiones matemáticas simples que dependen del peso molecular de cada sustancia. Se evalúan las capacidades predictivas del modelo en condiciones de una sola fase. Las desviaciones absolutas durante el proceso de correlación son menores de 3,27%, mientras que en el proceso de predicción son menores de 5,60%. El modelo generalizado es extendido a mezclas binarias utilizando una regla de mezcla simple sin y con coeficientes de interacción, con desviaciones absolutas de 8,19% y 3,45%, respectivamente. Finalmente, el modelo es comparado con otros en la literatura y los resultados estadísticos muestran que proporciona resultados aceptables.
This paper presents a systematic analysis of the problem of providing industrial enterprises with water resources. An integrated water management system was developed for ECOS-1. It covers all ...technological and auxiliary processes where water resources are used and includes 6 hardware and technological modules, namely, water recycling, obtaining demineralized water, obtaining high-purity water, steam generation, condensate collection, and processing, collection and treatment of polluted waters, and hot water supply. The development was performed using the computer support system, Continuous Acquisition and Life cycle Support (CALS)-technology.
The article studies the development of transfer measurement standards in the form of high-purity metals (Ag, Cd, Co, Cr, Cu, Fe, Ge, Mn, Mo, Ni, Pb, V, Zn). The evaluation of the mass fraction of the ...main component (MDOK) is performed by an indirect method (100 %o minus the sum of impurities). The impurity composition of the reference measurement standard materials was determined by mass spectrometry with inductively coupled plasma, reductive and oxidative melting using the State primary measurement standard of mass (molar) fraction and mass (molar) concentration of the component in liquid and solid substances and materials, based on coulometry, GET 176. The relative expanded uncertainty of MDOK (k = 2, P = 0,95) in the reference measurement standards was less, than 0,01 %o, in gravimetrically prepared solutions of the reference measurement standard it was less than 0,05 %o in most cases. The solutions of the reference measurement standards were used in the determination of certified values of metal mass fraction and mass concentration in reference materials for composition of mono-element solutions of approved types. The relative expanded uncertainty of certified values (k = 2, P = 0,95) of reference materials variedfrom 0,22 %o to 0,54 %o. Thus, it was demonstrated that metals can be used as reference measurement standards for storing a unit of the mass fraction of the main component and transferring it during characterization of reference materials for composition of solutions of the corresponding chemical elements. This work was performed within the research project «Research in the field of measurements of physicochemical composition and properties of substances, aimed at the development of State transfer measurement standards in the form of high-purity substances for reproduction and transfer of the units, characterizing chemical composition of solid substances» under the code «Purity» (2015-2017) and research and development project «Research in the field of measurements ofphysicochemical composition and properties of substances, aimed at the development of State transfer measurement standards in the form of high-purity substances for reproduction and transfer of the units, characterizing the chemical composition of solid substances and the development of reference measurement procedures» under the code «Purity-2» in the field of physicochemical measurements of composition and properties of inorganic components in solid substances (metals and salts) and food safety indicators under the code «Purity-2b» (2017-2019).
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