Numerical study of the hydrodynamics and mass transfer in the external loop airlift reactor

The objective of this study was to investigate the hydrodynamics and the gas-liquid mass transfer coefficient of an external-loop airlift reactor (ELAR). The ELAR was operated in three cases: different inlet velocities of fluids, different alcohols solutions (water, 0.5% methanol, 0.5% ethanol, 0.5% propanol and 0.5% butanol) and different concentration of methanol in solutions (0%, 0.5%, 1%, 2% and 5%). The influence of superficial gas velocity and various diluted alcohol solutions on hydrodynamics and the gas-liquid mass transfer coefficient of the ELAR was studied. Experimentally, the gas hold-up, liquid velocities and volumetric mass transfer coefficient values in the riser and the downcomer were obtained from the literature source. A computational fluid dynamics (CFD) model was developed, based on two-phase flow, investigating different liquids regarding surface tension, assuming the ideal gas flow, applying the finite volume method and Eulerian-Eulerian model. The volumetric mass transfer coefficient was determined using the CFD and artificial neural network model. The effects of liquid parameters and gas velocity on the characteristics of the gas-liquid mass transfer were simulated. These models were compared with the appropriate experimental results. The CFD model successfully simulates the influence of different alcohols regarding the number of C-atoms on hydrodynamics and mass transfer

Hydrodynamics of a self-agitated draft tube airlift reactor

The main hydrodynamic characteristics of a novel-constructed, self-agitated draft tube airlift reactor (DT-ALR) were investigated. Ten impellers, driven only by the means of gas throughput and induced liquid circulation, were inserted in the draft tube. The insertion of impellers caused bubble breakup and reduction of both mean bubble size and coalescence, even under the conditions of high gas throughputs. Although the impellers induced energy losses, the resistance to the flow was relatively lower due to their rotation, unlike the internals used in other research reported in the literature. In comparison to the conventional configuration of a DT-ALR, it was found that the presence of impellers led to significant changes in hydrodynamics: riser gas holdup and mixing time increased, while overall gas holdup and liquid velocity in the downcomer decreased. [Projekat Ministarstva nauke Republike Srbije, br. 172025

Results of IMS participation in international intercomparisons for whole body dosemeters – 10 years of study

The regular participation of an accredited individual monitoring service (IMS) in the international and/or interlaboratory intercomparisons (IC) is required according to ISO/IEC 17025:2017 standard, General requirements for the competence of testing and calibration laboratories. By taking the part in an IC, IMS shows competence, reliability, and has an opportunity to learn further and improve its measurement method. The European Dosimetry Group (EURADOS) Working Group 2 (WG2) has acknowledged the value of the regular IC and also found that data and results from it are fundamental for the harmonization of the measurement process [1]. Thus, EURADOS started a self-sustained program of IC for IMS for external radiation on a biannual basis. The results of an accredited IMS at the Department of Radiation and Environmental Protection, “VINČA” Institute of Nuclear Sciences, Belgrade, Serbia (IMS VINS) in the EURADOS IC for the period 2010-2020 (excluding 2014) are presented. IMS VINS use thermoluminescent whole body dosemeters based on two TLD-100TM (Thermo Scientific™ Harshaw™, USA) detectors. The readouts are done on the Harshaw TLD™ Model 6600 Plus Automated Reader (Thermo Fisher Scientific, USA). The whole glow curve is used for dose estimation (all of 200 channels). The calibration of the dosimetric system is done twice a year in S-Cs (previously in S-Co) field at the secondary standard dosimetry laboratory (SSDL VINS), according to ISO 4037-3:2019. The IC had 40 different reference values of personal dose equivalent, Hp(10) in noted period ranging from 0.431 mSv to 501 mSv. There were 20, 16, 22, 22, 20 dosemeters irradiated in year 2010, 2012, 2016, 2018, 2020, respectively. The radiations were done in 12 different fields: N-60, S-Co, S-Cs, N-40, N-150, S-Cs+Sr90, S-Cs+N-40, W-110, S-Cs+W-250, W-60, S-Cs+W-80, and S-Cs+N-150. The relative response (R) range is from 0.23 to 2.26. Quantile values for R are: 0.23, 0.79, 0.90, 1.1, and 2.26, respectively for (0%, 25 %, 50 %, 75 % and 100 % of points). Mean and standard deviation of R are 0.97 and 0.30, respectively. The performance limits are established according to ISO 14146 trumpet-curve [1]. Due to trumpet-curve there were 6 outliers (2 in 2010, 4 in 2016). All of the outliers were for reference dose around 1 mSv and lower. One outlier from 2010 was irradiated in N-40 field and 30° of incident angle. The other outlier was irradiated in the S-Cs field, without any rotation, and thus should have had a satisfying response. The possible explanation is an insensitive TL detector. The outliers in 2016 were all for N-40 quality and ±60° angle. Thus, considering the low number of outliers (only one true outlier) and expected dosemeters faulty response for given irradiation parameters, we conclude that the IMS VINS dosimetry system had satisfactory behavior during IC from 2010-2020.X JUBILEE International Conference on Radiation in Various Fields of Research : RAD 2022 (Spring Edition) : book of abstracts; June 13-17, 2022; Herceg Novi, Montenegr

TLD-100 post-irradiation fading characteristics according to IEC 62387:2020 standard

The results of the post-irradiation fading of whole body dosemeters based on two TLD-100TM (Thermo Scientific™ Harshaw™, USA) detectors are presented. The dosemeters are regularly used by accredited individual monitoring service (IMS) at Vinca Institute of Nuclear Science (VINS), Belgrade, Serbia. The testing of post-irradiation fading was carried out according to International Electrotechnical Commission (IEC) 62387:2020 standard. The irradiations are done in S-Cs137 field at secondary standard dosimetry laboratory (SSDL) at VINS, according to International Organization for Standardization document ISO 4037-3:2019. The chosen reference personal dose equivalent value was 3 mSv. The research was carried out in the period from October 2020 to February 2021, and it lasted 128 days. The frequency of irradiations was approximately 7 days, while 3 periods between irradiations were longer than 10 days, due to COVID-19 pandemic. The irradiations were performed at different dates; thus, all dose readouts were done on the same day to prevent influence of reader’s instabilities. The irradiated dosemeters were stored at the same room where the average temperature was nearly 20°C. There were 14 groups with 6 dosemeters for irradiation and 2 dosemeters for natural background radiation level correction. The reader was Harshaw TLD™ Model 6600 Plus Automated Reader (Thermo Fisher Scientific, USA). The whole glow curve was used for dose estimation (all of 200 channels). The time as influence quantity was considered to be of type F, thus the range of relative response was limiting factor in the analysis. The results showed that the maximum measurement time tmax is 72 days for deep dose (Hp(10)) detector, and 85 days for shallow dose (Hp(0.07)) detector. Thus, the standard’s requirement is satisfied, as it is required minimum of 30 days. The relative response range for all of the 14 groups was from 0.82 to 1.14 and from 0.83 to 1.17, for deep and shallow dose, respectively. The research has limitation as the irradiations were organized aligned to COVID-19 working schedule. One of the consequences of this timetable is lack of 7 days’ time point, thus the values from 16 days’ time point was used as referential.IX International Conference on Radiation in Various Fields of Research : RAD 2021 : book of abstracts; June 14-18, 2021; Herceg Novi, Montenegr

Simple correlations for bubble columns and draft tube airlift reactors with dilute alcohol solutions

Simple empirical correlations were developed to predict gas holdup, liquid circulation time, downcomer liquid velocity and volumetric mass transfer coefficient in dilute alcohol solutions in bubble columns and draft tube airlift reactors with single orifice sparger. Also, new experiments were conducted with diluted alcohol solutions to n-octanol, expanding the experimental data from C1 up to C8. The proposed empirical correlations include, beside the superficial gas velocity, the alcohol chain length as the only factor to characterize the liquid phase. The suggested correlations have shown good agreement between the calculated and the experimental data

Optimization of Radiation Output Mathematical Model Parameters for X-Ray Devices Used in Diagnostic Radiology

Primena jonizujućeg zračenja u medicini je neizbežan deo moderne medicinske dijagnostike. S obzirom na globalni porast izlaganja zračenju u medicinske svrhe raste i potreba za optimizacijom doza koje se isporučuju pacijentu. U dijagnostičkoj radiologiji doza koja se isporučuje pacijentu može se proceniti ulaznom dozom na površini kože (Entrance Surface Air Kerma) i jedan od metoda za dobijanje ESAK jeste proračun na osnovu vrednosti radijacionog izlaza. Radijacioni izlaz može se izmeriti ili dobiti proračunom pomoću matematičkih formula ili Monte Karlo simulacijama. U ovom radu izmeren je radijacioni izlaz za 15 različitih rendgen-aparata i izračunati su parametri u matematičkoj formuli kako bi se dobio precizniji model za radijacioni izlaz. Rezultati su upoređeni sa rezultatima Monte Karlo simulacija, kao i sa rezultatima dobijenim u sličnim studijama.Application of ionizing radiation in medicine is an inseparable part of modern medical diagnostics. With increasing number of medical exposures in the world the need for optimization of doses delivered to patients arises. Doses delivered to the patient in diagnostic radiology can be estimated with Entrance Surface Air Kerma, where one of the methods for obtaining ESAK is the calculation based on radiation output. Furthermore, radiation output can be measured or calculated using mathematical formulas or Monte Carlo simulations. In this paper we measured radiation output for 15 different x-ray devices and calculated parameters for mathematical formula to obtain a more accurate model for radiation output. These results were compared with the results of Monte Carlo simulations and the results obtained in similar studies.XXXI Симпозијум Друштва за заштиту од зрачења Србије и Црне Горе, 06-08. октобар 2021.Proceedings: [https://vinar.vin.bg.ac.rs/handle/123456789/9668

Continuous adsorption of methylene blue dye on the maize stem ground tissue

Continuous adsorption of methylene blue from aqueous solutions onto maize stem ground tissue in column mode was investigated. The study encompassed the effects of important parameters such as flow rate, initial concentration of methylene blue, and bed depth on methylene blue removal from model solutions. The maximum adsorption capacity of the maize stem was 45.9 mg/g at the initial methylene blue concentration of 20 mg/L, bed height of 6.5 cm and flow rate of 8 mL/min. It was found that the breakthrough time for reaching saturation increased with a decrease in the flow rate, and also occurred earlier for a higher influent concentration. The breakthrough times increased with the bed depth, thus allowing a larger volume to be treated. The Adams-Bohart, Yoon-Nelson, Clark and artificial neural network models were used to predict the breakthrough curves. These models gave excellent approximations of the experimental behavior.[Project of the Serbian Ministry of Education, Science and Technological Development, Grant no. 172025

Burkholderia cepacia complex in Serbian patients with cystic fibrosis: prevalence and molecular epidemiology

The Burkholderia cepacia complex (Bcc) organisms remain significant pathogens in patients with cystic fibrosis (CF). This study was performed to evaluate the prevalence, epidemiological characteristics, and presence of molecular markers associated with virulence and transmissibility of the Bcc strains in the National CF Centre in Belgrade, Serbia. The Bcc isolates collected during the four-year study period (2010-2013) were further examined by 16 s rRNA gene, pulsed-field gel electrophoresis of genomic DNA, multilocus sequence typing analysis, and phylogenetic analysis based on concatenated sequence of seven alleles. Fifty out of 184 patients (27.2 %) were colonized with two Bcc species, B. cenocepacia (n = 49) and B. stabilis (n = 1). Thirty-four patients (18.5 %) had chronic colonization. Typing methods revealed a high level of similarity among Bcc isolates, indicating a person-to-person transmission or acquisition from a common source. New sequence types (STs) were identified, and none of the STs with an international distribution were found. One centre-specific ST, B. cenocepacia ST856, was highly dominant and shared by 48/50 (96 %) patients colonized by Bcc. This clone was characterized by PCR positivity for both the B. cepacia epidemic strain marker and cable pilin, and showed close genetic relatedness to the epidemic strain CZ1 (ST32). These results indicate that the impact of Bcc on airway colonization in the Serbian CF population is high and virtually exclusively limited to a single clone of B. cenocepacia. The presence of a highly transmissible clone and probable patient-to-patient spread was observed

Volumetric gas-liquid mass transfer coefficient in an external-loop airlift reactor with inserted membrane

The effects of the inserted membrane in the downcomer of an external-loop airlift reactor, the gas sparger type (single orifice and sinter plate) and added alcohol (ethanol, n-butanol, or n-hexanol) on the volumetric gas-liquid mass transfer coefficient (kLa) were studied. Due to the presence of the membrane in the downcomer, kLa did not change significantly; the differences were smaller than 10%. The highest values of the kLa were obtained using the sinter plate. It was found that the addition of small amounts of alcohol increased the mass transfer. Using our experimental results and the data of other authors, the feed-forward back propagation neural network for prediction of kLa in external-loop airlift reactors with alcohol solutions was proposed. [Projekat Ministarstva nauke Republike Srbije, br. 172025

Characterization of Thermoluminescent Dosimetry Systems According to the IEC 62387:2020 Standard

A need for detailed testing of individual monitoring systems used in accredited service at the Vinca Institute of Nuclear Sciences was recognized following changes in individual, workplace, and environmental monitoring passive dosimetry systems acceptability criteria stated in IEC 62387:2020 and changes related to reference fields used in radiation protection defined in ISO 4037:2019. Reliability and accuracy of dosimetry data acquired by passive dosimetry systems used for individual monitoring is assured by carrying out type tests. In this manner, the effects of different radiation influence quantities are examined. Passive dosimetry systems comprised of an LiF:Mg,Ti (TLD-100) detector card placed in two different holder models (8814 and 8850) and the Harshaw TLD Model 6600 Plus Automated Reader were tested. Type tests were done in an extended range of photon energies from 40 keV up to 1.25 MeV, angle of incidence values of ±45° and ± 60° for both vertical and horizontal dosimeter orientation, and in the dose range from 0.05 mSv to 1 Sv. Both dosimetry system configurations perform in line with IEC 62387:2020 within mandatory range for tested influence quantities. Dosimeters that use the 8850 holder type showed less pronounced energy and angular dependence of the response in the low-energy range