USE OF A TWO-DIMENSIONAL PSEUDO-HOMOGENEOUS MODEL FOR THE STUDY OF TEMPERATURE AND CONVERSION PROFILES DURING A POLYMERIZATION REACTION IN A TUBULAR CHEMICAL REACTOR UPORABA DVODIMENZIONALNEGA PSEVDOHOMOGENEGA MODELA ZA [TUDIJ TEMPERATURE IN PROFILA PRETV

A two-dimensional pseudo-homogeneous model is used to study temperature and conversion profiles during the polymerization reaction of low-density polyethylene (LDPE) in a tubular chemical reactor. This model is integrated with the Runge-Kutta 4 th -order semi-implicit method, using orthogonal collocation to transform a system of complex equations into the ordinary differential ones, with respect to the heat and mass transfers involved. Ethylene polymerization has been simulated over a range of temperatures and pressures and according to the mechanisms of radical polymerization. The results of several tests, carried out under the conditions similar to those of an industrial-scale polymerization, are presented. The influences of the initial temperature T 0 , the total pressure P t and the ratio L/D (the main dimensions of the reactor) on the profiles of the temperature and conversion rates are tested and analyzed to predict the behavior and performance of the tubular chemical reactor considered. The focus was on the effect of an increase in the initial temperature T 0 since such a rise results in a decrease in T c (hot spot) appearing at the entrance of the reactor on the one hand, and in an improved conversion on the other hand. An opposite effect is observed for P t since a pressure increase will result in a rapid rise in T c and a decrease in the conversion. The ranges of pressures and temperatures are thus limited by the system performance: excessive pressures must be avoided and working temperatures must be chosen in the range where the polymerization reaction is very fast; such conditions allow not only a good conversion, but also a resulting polymer with a low crystallinity and, thus, a low density. In the present work the effect of the L/D ratio was also studied in order to find the most suitable ratio that permits the best evacuation of the heat released during the polymerization. Keywords: modeling, tubular reactor, simulation, low-density polyethylene, pseudo-homogeneous two-dimensional model Dvodimenzijski psevdohomogeni model je bil uporabljen za {tudij temperature in profila pretvorbe med reakcijo polimerizacije polietilena z nizko gostoto (LDPE) v cevastem kemijskem reaktorju. V model je bila vklju~ena Runge-Kuttova semiimplicitna metoda 4. reda z uporabo ortogonalne kolokacije za pretvorbo sistema kompleksnih ena~b v navadne diferencialne ena~be glede na vklju~en prenos toplote in mase. Simulirana je bila polimerizacija etilena v {ir{em podro~ju temperature in tlaka skladno z mehanizmom radikalne polimerizacije. Predstavljenih je ve~preizkusov polimerizacije, izvedenih v razmerah, podobnih industrijskim. Preizku{en in analiziran je bil vpliv za~etne temperature T 0 , celotnega tlaka P t in razmerja L/D (glavne dimenzije reaktorja) na profil temperature in hitrost pretvorbe, da bi bilo mogo~e napovedati pona{anje in zmogljivost uporabljenega cevastega reaktorja. Pozornost je bila usmerjena na u~inek povi{anja za~etne temperature T 0 , ker to po eni strani vpliva na zni`anje T c (vro~a to~ka) na vstopu v reaktor, po drugi pa na izbolj{anje pretvorbe. Nasproten u~inek je bil opa`en za P t , ker se narastek tlaka izra`a v hitrem povi{anju T c in zmanj{anju konverzije. Obmo~je tlaka in temperature je torej omejeno z zmogljivostmi sistema: treba se je izogibati prekomernemu tlaku, delovne temperature pa je treba izbrati v obmo~ju, kjer je reakcija polimerizacije zelo hitra; take razmere omogo~ajo dobro konverzijo, in nastali polimer ima majhno kristalini~nost in s tem nizko gostoto. V tem delu je bilo preu~evano tudi razmerje L/D, da bi dobili najbolj primerno razmerje, ki omogo~a najbolj{i odvod toplote, ki se spro{~a med polimerizacijo

Solar limb darkening function and solar diameter with eclipses observations

We introduce a new method to perform high resolution astrometry of the solar diameter from the ground, through the observations of eclipses. A discussion of the solar diameter and its variations is linked to the Limb Darkening Function (LDF) using the luminosity evolution of a Baily's Bead and the profile of the lunar limb available from satellite data. The inflexion point of the LDF is defined as the solar limb. The method proposed is applied for the videos of the eclipse in January, 15, 2010 recorded by Richard Nugent in Uganda and Andreas Tegtmeier in India. An upper limit for the inflexion point position has been set for that eclipse.Comment: 3 pages, 2 figures. Proceedings of the Fourth French-Chinese meeting on Solar Physics Understanding Solar Activity: Advances and Challenges, 15 - 18 November, 2011 Nice, Franc

Understanding dense active nematics from microscopic models

We study dry, dense active nematics at both particle and continuous levels. Specifically, extending the Boltzmann-Ginzburg-Landau approach, we derive well-behaved hydrodynamic equations from a Vicsek-style model with nematic alignment and pairwise repulsion. An extensive study of the phase diagram shows qualitative agreement between the two levels of description. We find in particular that the dynamics of topological defects strongly depends on parameters and can lead to ``arch'' solutions forming a globally polar, smectic arrangement of N\'eel walls. We show how these configurations are at the origin of the defect ordered states reported previously. This work offers a detailed understanding of the theoretical description of dense active nematics directly rooted in their microscopic dynamics

Učinkovitost biološkog uklanjanja šesterovalentnog kroma suspendiranom i imobiliziranom mikrobnom biomasom na pucolanu: proučavanje mehanizma samočišnjenja

Hexavalent chromium is one of the hazardous metals that can be found in industrial effluents such as wood treatment units, mining, leather tanning, pigment, steel and electroplating industry. The present work aimed to evaluate the self-purification capacity of the microbial flora taken from the domestic wastewater effluent of Chlef City, with the perspective of designing a microbial bed in the secondary sewage treatment to prevent an industrial Cr(VI) contamination. Under various operating conditions, the bioremoval performance of Cr(VI) was evaluated by using suspended biomass and immobilised biomass (fixed onto pozzolana grains). The results showed that the immobilised biomass was more efficient and more resistant to Cr(VI) toxicity than the suspended biomass. Indeed, the Cr(VI) was totally eliminated within 96 h for an initial concentration of 50 mg l–1 by the immobilised biomass, while this rate was obtained after 120 h for the suspended biomass. The kinetic data fit well to the pseudo-first order kinetic model. The intraparticle diffusion kinetic model suggested that the diffusion process of Cr(VI) was greatly influenced by the initial concentration. The microbial flora present in domestic wastewater is a promising biosorbent that is able to treat effluent containing Cr(VI). This work is licensed under a Creative Commons Attribution 4.0 International License.Šesterovalentni krom je jedan od opasnih tvari koja se može naći u otpadnim tokovima drvne industrije, rudarstva, štavljenja kože, industrije pigmenta, čelika i galvanizacije. Cilj ovog rada bio je procijeniti kapacitet samopročišćavanja mikrobne flore uzete iz komunalnih otpadnih voda grada Chlefa, s perspektivom projektiranja mikrobnog sloja primjenjivog za sekundarnu obradu industrijskih voda s ciljem sprječavanja kontaminacije kromom(VI). Učinak biološkog uklanjanja šesterovalentnog kroma procijenjen je pri različitim radnim uvjetima primjenom suspendirane te imobilizirane biomase (fiksirane na zrna pucolana). Rezultati su pokazali da je imobilizirana biomasa učinkovitija i otpornija na toksičnost kroma(VI) od suspendirane biomase. Primjenom imobilizirane biomase, 50 mg l–1 kroma(VI) je potpuno uklonjeno tijekom 96 h dok je uz primjenu suspendirane biomase bilo potrebno 120 h. Kinetika odgovara modelima pseudo prvog reda. Kinetički model unutarčestične difuzije ukazao je na veliki utjecaj početne koncentracije kroma(VI) na proces njegove difuzije. Mikrobna flora prisutna u komunalnim otpadnim vodama obećavajući je sorbens koji se može primijeniti za pročišćavanje voda koje sadrže krom(VI). Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna

Real time Data Acquisition of Solar Panel

We created a real-time acquisition system to track the voltage, current and temperature changes of the solar panel as we installed it in a charging regulator with a battery. The system consists of an Arduino Uno board, the controllership, which is programmed by the Arduino IDE application, based on the C language, and sensors to capture the variables, we put the SD card to save the data and the LCD to see it currently and can be monitoring the data by connecting the Arduino Uno board to the computer and processing it with the Excel application

Gain Enhancement of Monopole Antenna using AMC Surface

A CPW rectangular-ring antenna over an Artificial Magnetic Conductor (AMC) is presented in this work. The AMC is a designed as a dual-band structure having an array of unit cells and operates at 2.45GHz and 5.20 GHz. A CPW antenna uses this dual-band AMC structures as a back-plane. Performance comparison is carried out with and without incorporation of AMC. The simulated and measured results show that the combination of the AMC reflector and the antenna provide directional properties at both frequency bands. It has been found that the antenna gain increases by about 5 dB