Mixing Of Chemicals Research Articles

AN AGAROSE GEL-BASED APPROACH FOR THE REMOVAL OF METALLIC-BASE INK STAIN FROM THE PAPER SURFACES OF A 17TH CENTURY BOOK

Removing ink stains from the pages of ancient and valuable books is a very challenging and sometimes impossible task. Only in some circumstances, restorers are able to improve the appearance of an ink-stained page by lightening the spots using an ink eradicator. This paper reports on an approach for the removal of ink stains from a 17th century book using a combination of two commercial houseware products, the rust remover for textile and bleach. The products were chosen on the basis of their active ingredients such as hydrofluoric acid (HF), which facilitates the removal of metal ions contained in the inks (such as iron and chromium) and sodium hypochlorite (NaClO), known for its whitening abilities. The products were first tested by direct application to one of the several stained pages as a control experiment. The ink stain was successfully removed from the book, but by SEM analysis the page results in a clear detachment of the cellulose fibers from the paper pulp, which reflect a significant change in the paper fine structure. Moreover, the mixing of chemicals occurring during this procedure generated toxic vapors and the entire protocol could only be performed under a chemical fume hood. A new procedure was developed to mitigate these negative effects. Each of the two commercial products was dispersed in a 2% agarose solution shortly before its gelification and the two gels thus obtained were applied consecutively on the surface of the paper to be cleaned. The results showed an effective removal of the ink stain from treated page, avoiding irreparable damage to the paper structure and improving the working conditions of the restorers. Hence, the proposed gel cleaning procedure offers three main advantages: i) a simple and practical tool for effective removal of metallic ink stains from the paper surface; ii) reduction of damage caused by aggressive reagents (HF and NaClO) contained in cleaning products for a better conservation of paper fibers; iii) a great decrease of the risk of accidentally exposing the operators to harmful toxic vapor (produced by accidental mixing of aforementioned chemical reagents).

On Various Soil Moisture Measurement Techniques Available in the Literature

The sustainability and health of soil associated with its productivity and health are closely related to soil moisture. The amount of water or moisture in the soil is an important parameter in the mobility of nutrients in the soil, in soil reclamation studies, and in the washing-transportation and mixing of fertilizers and other chemicals applied to the soil into the ground water. On the other hand, it has become important today not only to minimize water consumption but also to accurately measure the amount of moisture in the soil so that proper amount of water that the plant needs can be circulated to the root zone of the plant. In this context, information was given about various measurement methods for determining soil moisture (direct and indirect - thanks to correlations) existing in the literature, and among these studies, especially the studies on microwave methods were examined. Comparison results of the dielectric constant values obtained for three different soil samples with different gravimetric volumetric moisture rates by one of the calibration-independent non-resonant microwave measurement methods, which has a high application potential and is different from the existing calibration-requiring microwave measurement methods, and the dielectric constant values predicted by the Mironov model in the literature are presented. The comparison result showed that this new type of microwave measurement method has a high potential for measuring the moisture value of soil samples

Expected evolution of the binary system PTF J2238+743015.1

Binary systems harboring a low-mass CO WD and a He-rich donor are considered to be the possible progenitors of explosive events via He detonation, producing low-luminosity thermonuclear supernovae with a peculiar nucleosynthetic pattern. Recently, the binary system PTF J223857.11+743015.1 was proposed as a candidate for this kind of stars. We investigate the evolution of the PTF J223857.11+743015.1 system, which is composed of a 0.75\ CO WD and a 0.390\ subdwarf. We consider the rotation of the WD component. Using the FuNS code, we computed the evolution of the two stars simultaneously, taking into account the possible evolution of the orbital parameters, as determined by mass transfer between the components and by mass ejection from the system during episodes of Roche lobe overflow. We consider that the WD gains angular momentum due to accretion and we followed the evolution of the angular velocity profile as determined by angular momentum transport via convection and rotation-induced instabilities. As the donor H-rich envelope is transferred, the WD experiences recurrent very strong H-flashes triggering Roche lobe overflow episodes during which the entirety of the accreted matter is lost from the system. Due to mixing of chemicals by rotation-induced instabilities during the accretion phase, H-flashes occur inside the original WD. Hence, pulse by pulse, the mass of the accretor is reduced down to 0.7453\ Afterwards, when He-rich matter is transferred, He detonation does not occur in the rotating WD, which undergoes six very strong He-flashes and subsequent mass-loss episodes. Also in this case, due to rotation-induced mixing of the accreted layers with the underlying core, the WD is eroded. Later, as the mass-transfer rate from the donor decreases, a massive He buffer is piled up onto the accretor, which ends its life as a cooling WD. The binary system PTF J2238+743015.1 and all other binary systems with components of similar masses and similar orbital parameters are not good candidates as thermonuclear explosion progenitors.

Apportioning sources of chemicals of emerging concern along an urban river with inverse modelling

Concentrations of chemicals in river water provide crucial information for assessing environmental exposure and risks from fertilisers, pesticides, heavy metals, illicit drugs, pathogens, pharmaceuticals, plastics and perfluorinated substances, among others. However, using concentrations measured along waterways (e.g., from grab samples) to identify sources of contaminants and understand their fate is complicated by mixing of chemicals downstream from diverse diffuse and point sources (e.g., agricultural runoff, wastewater treatment plants). To address this challenge, a novel inverse modelling approach is presented. Using waterway network topology, it quantifies locations and concentrations of contaminant sources upstream by inverting concentrations measured in water samples. It is computationally efficient and quantifies uncertainty. The approach is demonstrated for 13 contaminants of emerging concern (CECs) in an urban stream, the R. Wandle (London, UK). Mixing (the forward problem) was assumed to be conservative, and the location of sources and their concentrations were treated as unknowns to be identified. Calculated CEC source concentrations, which ranged from below detection limit (a few ng/L) up to 1μg/L, were used to predict concentrations of chemicals downstream. Using this approach, >90% of data were predicted within observational uncertainty. Principal component analysis of calculated source concentrations revealed signatures of two distinct chemical sources. First, pharmaceuticals and insecticides were associated with a subcatchment containing a known point source of treated effluent from a wastewater treatment plant. Second, illicit drugs and salicylic acid were associated with multiple sources, interpreted as input from untreated sewage including Combined Sewer Overflows (CSOs), misconnections, runoff and direct disposal throughout the catchment. Finally, a simple algorithmic approach that incorporates network topology was developed to design sampling campaigns to improve resolution of source apportionment. Inverse modelling of contaminant measurements can provide objective means to apportion sources in waterways from spot samples in catchments on a large scale.

Design Optimization Method for Large-Size Sidewall-Driven Micromixer to Generate Powerful Swirling Flow.

Microfluidic devices, which miniaturize cell culture and chemical experiments from lab-scale to microchip dimensions, have gained significant attention in recent years. Extensive research has been conducted on microfluidic mixers, which facilitate the mixing and agitation of chemicals. The "Sidewall-Driven Micromixer" that we are currently developing employs a unique mechanism; it induces a swirling flow within the main chamber by vibrating the silicone wall situated between the main and driving chambers using pressure fluctuations. In an earlier study, we found that Sidewall-Driven Micromixers of a size suitable for small cells could indeed produce this swirling flow. Furthermore, we successfully established concentration gradients within each mixer. However, when attempting to upscale the mixer while maintaining conventional proportions to accommodate larger cell aggregates such as spheroids, the desired swirling flow was not achieved. To address this challenge, we made adjustments to the wall dimensions, aiming to amplify wall deformation and thereby enhance the mixer's driving force. Concurrently, we modified the mixer's shape to ensure that the increased wall deformation would not hinder the fluid flow. These alterations not only improved the mixer's performance but also provided valuable insights for positioning the mixer's neck channel, considering the extent of wall deformation.

Determinants of knowledge associated with occupational hazards and perceived health problems among dye workers in Abeokuta, Nigeria.

Identification of potential hazards, their adverse health effects, and predisposing factors in the workplace are critical to improving safety. The objective of the study was to assess the knowledge of occupational hazards, the prevalence of perceived health problems and their predictors among textile dye workers in Abeokuta Nigeria who work in unsupervised settings. In this cross-sectional study, data were collected from 199 participants using a validated semi-structured interviewer-administered questionnaire. Multiple linear regression analysis was used to determine the predictors of knowledge while Pearson Chi-square was employed to test the association between perceived health problems, sociodemographics and work environment characteristics. The mean age of the respondents was 40 (SD=12) years with an average work experience of 19 years. The majority of respondents 139 (69.8%) had lower than average scores on knowledge of 25 questions on chemical hazards. There was no correlation between knowledge score and work experience (P=0.492) or age (P=0.462) but the knowledge was significantly associated with exposure score (P=0.004), gender (P=0.002) and adherence to instructions on chemicals usage (P=0.041) after adjusting for safe practice. The most frequent health problems among the dye workers were respiratory disorders (53.8%), allergies (51.8%), and skin disorders (24.1%). Airborne gaseous pollutants from the mixing of chemicals were associated with allergies (P=0.045), circulatory (P=0.02) and skin disorders (P=0.049) while air-borne textile fiber/dye particles could predict allergies (P=0.028). Findings revealed that exposure, gender and adherence to instruction labels on dye/chemical containers could determine knowledge of chemical hazards while physical work environment characteristics could determine health problems.

SUSTAINABILITY IN DENTISTRY

The ever-increasing world population, uncontrolled developing industrialization, and urbanization mixing of harmful chemicals to the environment, water, and soil cause environmental pollution and increase environmental problems. Sustainability is ensuring the continuity of the diversity and productivity of the systems. Sustainability aims to transfer natural resources for the future generations. Because of rising financial costs, growing demand, and a high environmental burden, there is a risk that the current existing healthcare facilities will not be sustainable in the future. Dentists must understand the General Dental Council guidelines as well as the relationship between planetary and human health in their practice. The issues associated with global warming are becoming more widely recognized, but there is a lack of understanding about how to become more environmentally friendly. This study aims to eliminate this lack of understanding, raise awareness on this issue, open up a new horizon in every dentist and prevent environmental problems that we will encounter today and in the future. This study will inform dentists and dental students about examining the practices of our profession, both personally and professionally, in a way that contributes to the solution of environmental problems. It will also inform us about integrating sustainable development aims into everyday activities in the pursuit of a healthy life and prosperity for all at all levels of life.

Hydrodynamics and dilution of an oil jet in crossflow: The role of small-scale motions from laboratory experiment and large eddy simulations

Experimental results were presented for the release of diesel oil from a one-inch (2.5 cm) vertical pipe in a crossflow at 0.27 m/s. The ratio of jet velocity to crossflow speed was 5.0 and the Reynolds number based on jet velocity and pipe diameter was 7.1×103. In the experiments, the plume shape was photographed, and the oil droplets were measured at two vertical locations on the center axis of the plume. Acoustic Doppler velocimetry (ADV) data was also obtained and compared to numerical predictions. The plume was simulated using large eddy simulation (LES), and the mixture multiphase model. The impact of the oil buoyancy was captured by adding a transport term to the volume fraction equation. Using the rise velocity based on d50 (volume-median) droplet size in the lower part of the plume allowed us to capture the lower boundary of the plume, but the estimated upper boundary of the plume penetrated less into the crossflow as compared to the experimental findings. However, using the rise velocity of the d50 at the upper part of the plume allowed one to estimate the upper boundary of the plume. As the droplets are too small to be resolved by the LES, we could not use a systematic approach to allow the multiphase plume to spread to mimic the observations. Based on the simulation results, the interaction between the jet and crossflow yielded small-sized flow structures near the upper boundary of the plume. The wake vortices initiated from the leeward side of the plume showed an alternating vorticity pattern in the wake. The shear layer vortices were induced by Kevin-Helmholtz instabilities mostly on the windward side of the plume. The formation of counter rotating vortex pair (CVP) altered greatly the hydrodynamics of the jet from that of a vertical jet to manifest flow reversals in all directions. The formation of CVP is likely to enhance the mixing of chemicals and droplets within the plume.

Miniaturized high-throughput synthesis and screening of responsive hydrogels using nanoliter compartments.

The traditional pipeline of hydrogel development includes individual one-by-one synthesis and characterization of hydrogels. This approach is associated with the disadvantages of low-throughput and high cost. As an alternative approach to classical one-by-one synthesis, high-throughput development of hydrogels is still tremendously under-represented in the field of responsive material development, despite the urgent requirement for such techniques. Here, we report a platform that combines highly miniaturized hydrogel synthesis with screening for responsive properties in a high-throughput manner. The platform comprises a standard glass slide patterned with 1 ​× ​1 ​mm hydrophilic regions separated by superhydrophobic liquid-impermeable barriers, thus allowing deposition of various precursor solutions onto the hydrophilic spots without cross-contamination. The confinement of these solutions provided by the hydrophilic/superhydrophobic pattern allows encapsulation of cells within the hydrogel, and enables variation in hydrogel height and width. We have also proved the proper mixing of chemicals within the nanoliter-sized droplets. We have successfully implemented this platform for the synthesis of hydrogels, constructing 53 unique hydrogels, to demonstrate the versatility and utility of the platform. Photodegradation studies were performed on 20 hydrogels, revealing structure/function relationships between the hydrogel composition and photodegradability, and covering the range of degradability from non-degradable to rapidly degradable materials.

Augmenting Cleansing Process for Reducing Occupational Hazards Experienced by Labours Handling Pyrotechnical Chemicals in Firecracker Units

The value of Human resource is considered to be very important in fire work industries. Nearly 90% of fire crackers are manufactured in Sivakasi, which is considered to be the hub of fireworks production in India. The manufacturing process, type of storage and handling of chemicals are some of the important factor which bears the responsibility of affecting the worker’s health. Firecrackers manufacturing involves mixing of various chemicals. Moreover, it leads to lot of health issue to the workers like respiratory disorders, skin problems, damage to kidney, mental impairment and eye irritation, also it can cause cancer. Out of these major problems, skin and respiratory issues are mainly caused due to the direct handling of chemicals without safety precautions. Chemicals such as Sulphur-di-oxide, copper nitrate and magnesium are highly used in manufacturing the crackers. In order to overcome these hazardous problems, we have planned to make a soap for the affected people through precipitation method, using organic solvent (ETHANOL) and with the mixture of alum and sodium lauryl sulphate salts. The main aim of doing this project is to give a product of low cost with longevity and with good quality, which provides ample protection through cleanliness to the people who work in fire cracker units

Analytical solutions of incompressible laminar channel and pipe flows driven by in-plane wall oscillations

Emerging flow control strategies have been proposed to tackle long-lasting problems, for instance, precise mixing of chemicals and turbulent drag reduction. Employing actuators imposing in-plane wall oscillations are particularly popular. This paper investigates incompressible laminar rectangular channel and circular pipe flows driven by uniform and traveling wave in-plane wall oscillations. A comprehensive set of exact analytical solutions are presented describing parallel and concentric flows. Dimensionless groups are identified, and it is described how they characterize the one- and two-dimensional time-dependent velocity and pressure fields. The solutions enable to compute the oscillating boundary layer thickness. It is demonstrated that the dimensionless groups and the boundary layer thickness narrows the region of interest within the parameter space. In particular, the oscillating boundary layer thickness obtained from these laminar flows estimates a “radius of action” within which flow features can be altered to boost mixing or reduce turbulent friction drag. The results are suitable for software validation and verification, may open the way to promising complex wall oscillations, and ease the optimization task that delays the industrial application of flow controls.

Soil lacquer peel do-it-yourself: simply capturing beauty

Abstract. Visualization can greatly benefit understanding of concepts and processes, which in soil science and geology can be done using real-life snapshots of soils and sediments in lacquer peels and glue peels. While it may seem complicated, anyone can make such a soil peel for use in classrooms, public places, homes, and offices for teaching, outreach, decoration, and awareness. Technological development has considerably simplified the making of soil peels, but this methodological innovation has not been described in the literature. Here, we report on a thoroughly tested and simple method for taking peels of sandy soils using readily available tools and materials. Our method follows the main previously published steps of preparing a soil face, impregnating the soil face with a fixation agent in the field, extracting the resulting peel, and mounting it on a wooden panel. Yet instead of using lacquers and thinning agents, we use strong though flexible contact adhesive (glue), which has the major advantage that it no longer requires use and mixing of toxic chemicals in the field or reinforcement of the peel to prevent breaking. Moreover, the preservation potential is much higher than with the old method. This new twist to old methods makes creation of soil peels safer, simpler, and more successful, and thereby a true DIY (do-it-yourself) activity. The resulting increased accessibility of making soil and sediment peels can benefit research, teaching, and science communication and can thereby bring the value and beauty of the ground below our feet to students, schools, policy makers, and the general public.

The Effect of Ingredients Mixing Sequence in Rubber Compounding upon Vulcanization Kinetics of Natural Rubber: An Autocatalytic Model Study

This study examined the effect of ingredients mixing sequence to the vulcanization kinetics of natural rubber. The effects of mixing temperature, vulcanization temperature, and the carbon black type upon the kinetics were also studied by using rheography and an autocatalysis reaction model approach. The results showed that this model is good in providing information on vulcanization reaction kinetics of natural rubber. High vulcanization temperature resulted in high reaction rate constant. The more black carbon mixed at the beginning of the rubber mixing process, the higher reaction rate constant would be. The mixing of carbon black and rubber chemicals mixed into the rubber subsequently resulted in the higher reaction rate constant compared with that of simultaneously.

A Review of Planar PIV Systems and Image Processing Tools for Lab-On-Chip Microfluidics.

Image-based sensor systems are quite popular in micro-scale flow investigations due to their flexibility and scalability. The aim of this manuscript is to provide an overview of current technical possibilities for Particle Image Velocimetry (PIV) systems and related image processing tools used in microfluidics applications. In general, the PIV systems and related image processing tools can be used in a myriad of applications, including (but not limited to): Mixing of chemicals, droplet formation, drug delivery, cell counting, cell sorting, cell locomotion, object detection, and object tracking. The intention is to provide some application examples to demonstrate the use of image processing solutions to overcome certain challenges encountered in microfluidics. These solutions are often in the form of image pre- and post-processing techniques, and how to use these will be described briefly in order to extract the relevant information from the raw images. In particular, three main application areas are covered: Micro mixing, droplet formation, and flow around microscopic objects. For each application, a flow field investigation is performed using Micro-Particle Image Velocimetry (µPIV). Both two-component (2C) and three-component (3C) µPIV systems are used to generate the reported results, and a brief description of these systems are included. The results include detailed velocity, concentration and interface measurements for micromixers, phase-separated velocity measurements for the micro-droplet generator, and time-resolved (TR) position, velocity and flow fields around swimming objects. Recommendations on, which technique is more suitable in a given situation are also provided.

Cocktail effect of Profenophos and Abamectin on tadpoles of Asian Common Toad (<i>Duttaphrynus</i> <i>melanostictus</i>)

Farmers mix two or more pesticides as mixing saves the spraying time and the labour cost and also with the idea that it increases the efficiency. The cocktail effect of two agrochemicals, profenophos and abamectin, was tested on the tadpoles of the Asian common toad, Duttaphrynus melanostictus under laboratory conditions. First, the 48 hr lethal concentrations (LC50) was determined. Then, a chronic exposure to a series of ecologically relevant concentrations (profenophos: 0.125, 0.25, 0.5, 1.0, 2.0 ppm and abamectin: 0.01, 0.02, 0.03, 0.04, 0.05 ppm) and a mixture of these were carried out. A control was set up using de-chlorinated tap water. Survival, growth, behaviour and development of malformations were observed until metamorphosis. The LC50 value of profenophos and abamectin were 3.78 ppm and 0.12 ppm, respectively. Both pesticides caused lethal and sub lethal effects at low concentrations while abamectin was more toxic. In the chronic exposure to field level had greatly reduced the survival of tadpoles in profenophos (Chi square test, χ2= 133.8, p = 0.001), abamectin (χ2 = 105.5, p = 0.001) and the cocktail (χ2 = 137.5, p> 0.001) when compared with the control. All the exposures caused a reduction in the growth parameters with a significant reduction in snout-vent length and body mass in 15 days post-hatch tadpoles (one way ANOVA, p = 0.001). Moreover, exposed tadpoles took a longer time to metamorphose (40-42 days), developed malformations and showed behavioural abnormalities like altered feeding and swimming behaviours. Profenophos induced scoliosis and kyphosis, abamectin caused oedema while the cocktail exposed tadpoles developed both scoliosis and oedema. The effects of the cocktail exposure on survival, growth and development of malformations were higher than the lone effects. Although pesticide cocktail may have potential benefits in pest resistance management, what chemicals to be mixed have to be studied before recommending the mixing of chemicals to farmers to minimize the harmful effects on the environment.

Rubber mixing process and its relationship with bound rubber and crosslink density

This research studied the relationship between bound rubber and crosslink density based on rubber mixing process. Bound rubber was obtained after natural rubber was masticated and mixed with rubber chemicals and filler while crosslink density was collected after rubber compound was vulcanized. Four methods are used and each method refers to four ways of incorporating carbon black during mixing. The first method, after rubber was masticated for 5 minutes, the addition of rubber chemicals and filler was done simultaneously. Rubber was masticated for 1 minute and continued mixing of rubber chemicals and filler where mixing was different from first method. This was the second method. The third method was the same as the second method but the filler used N 660 while in the second method N 330. The last method is not the same as the first and second, the rubber is only masticated for 3 minutes and then mixed with filler and followed by rubber chemicals sequentially. The results showed that bound rubber and crosslink density were influenced by mixing and mastication process. Bound rubber dropped and crosslink density was relatively stable in the first three mixing methods for increasing carbon black at the beginning of the mixing process. Bound rubber and crosslink density stated opposite results in the fourth mixing method. The higher the bound rubber the lower the crosslink density. Without regard to mixing methods, there is a non-linear relationship between bound rubber formation and crosslink density determination

Structure Characterization of Low Cost Fabricated Soft Material Built Microchannel

To perform the entire laboratory activities on a centimeter limit scale electronic chip, the most important aspect is to fabricate a device which persist sensitive and selective for the delivery of fluids flow and have the ability to execute a fast mixing of distinctive chemicals and bio samples. To resolve this issues the current paper is one of the good struggle, therefore the objective was arranged in according to the scope of research such as; to design and fabricate a polydimethylsiloxane (PDMS) material made, micro channel and its structure characterization for the investigation of internal subterranean area. By using an AutoCAD software the channel was first designed, however for the fabrication process the design was transferred to mask. Starting from SU-8 resist the pattern was transferred, and then by using the polydimethylsiloxane (PDMS) the mold was fabricated by adopting a low cost photolithography technique. Finally by employing Hawk 3 D surface nanoprofiler the structure was characterized. In our forthcoming research the device will be tested for real biological samples using a simple hand-operated inoculation technique.

Travelling Surface Acoustic Waves Microfluidics

In this paper, we demonstrate the working principle of travelling surface acoustic waves (TSAWs) in a microfluidic system. The TSAWs were incorporated to separate polystyrene (PS) particles of variable diameters and perform controlled mixing of different chemicals for concentration gradient generation, both inside a polydimethylsiloxane (PDMS) microfluidic channel. The TSAWs generated an acoustic streaming flow (ASF) upon coupling with a liquid and exerted an acoustic radiation force (ARF) on the suspended particles. The ARF was theoretically estimated for PS microspheres suspended in water, and conditions for ARF dominance over ASF or vice versa were identified. Recently reported TSAW-based PS particles separation and gradient generation results by our group are summarized here.

Defensive mixology: combining acquired chemicals towards defence

Summary The myriad chemicals produced by plants may act in combination to enhance chemical defence against herbivores. Many animals have evolved the ability to harness plant secondary metabolites (PSMs) and other chemical resources for their own defence, but few studies have addressed the compelling notion that non‐human animals combine exogenous chemicals from different sources to defend themselves against predators, parasites and pathogens. We consider the use of ‘defensive cocktails’ from an evolutionary ecology perspective, introducing the term, ‘acquired combinatorial chemical defence’ (ACCD). We define ACCD as the adaptive use of multiple chemicals of discrete origin resulting in defence against natural enemies. First, we discuss the defining characteristics of ACCD: the ability to harness interspecific chemical variation, to independently regulate it, and to obtain defensive benefits via synergy that exceed those associated with single sources. Then, we describe three non‐mutually exclusive modes by which acquired chemicals may operate against natural enemies: different chemical resources may provide defence during different stages of development, may be effective against different enemies or may work additively or synergistically against a given enemy at a given developmental stage. Next, we describe possible avenues by which chemical combinations may be acquired by herbivores and other taxa, including the mixing of exogenous chemicals from different items in the diet and mixing chemicals of dietary origin with those from non‐food resources. We discuss possible costs of ACCD, including detoxification costs and interactions with the immune system, and discuss methods of testing for ACCD and its costs. Finally, we discuss the evolutionary prediction that herbivores may converge on the use of complementary combinations of chemical resources from the environment or chemical defence syndromes. Opportunities to combine chemical resources abound, suggesting that animal and human medication may be more closely aligned than previously recognized.

CFD를 이용한 패들교반속도에 따른 속도경사 및 총물질전달시간 산정

Velocity gradient, G, a measure of the average velocity gradient in the fluid has been applied for complete mixing of chemicals in mechanical mixing devices. G values were calculated by the power input transferred to fluid in turbulent and transient range. Chemical reactions occur so fast that total mass transfer time required for even distribution of the chemicals determine the overall reaction time. The total mass transfer time is composed of the time for complete mixing through the reactor and for diffusion of the chemicals into the eddy. Complete mixing time was calculated by CFD (computer fluid dynamics) and evaluated by tracer tests in 2 liter jars at different rotating speeds. Turbulent range, Reynolds number above 10,000 in regular 2 liter jars occurred at revolution speed above 100 rpm (revolution per minute), while laminar range occurred at revolution speed below 10 rpm. A typical range of rotating speed used in jar tests for water and wastewater treatment was between 10 and 300 rpm, which covered both transient and turbulent range. G values supplied from a commercial jar test apparatus showed big difference from those calculated with power number specially in turbulent range. Diffusion time through eddy decreased 1.5 power-law of rotating speed. Complete mixing time determined by pumping number decreased increases in rotating speed. Total mass transfer time, finally, decreases as rotating speed increases, and it becomes 1 sec at rotating speed of 1,000 rpm. Complete mixing times evaluated from tracer tests showed higher than those calculated by power number at higher rotating speed. Complete mixing times, however, calculated by CFD showed similar to those of experimentally evaluated ones.