• Journal of Korean Society on Water Environment
• /
• v.30 no.2
• /
• pp.166-174
• /
• 2014

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.

• Journal of environmental and Sanitary engineering
• /
• v.10 no.2
• /
• pp.30-35
• /
• 1995

In this research effect of physicochemical parameter on flocculation using PASS-100 were evaluated. pEt flocculant dosage, mixing intensity and detention time were adopted as experimental variables. The physicochemical parameter( p% mixing intensity and mixing time ) were important Parameter on flocculation performance. Effluent pH range for effective flocculation was 4.5-7. Optimum Gt$_{d}$ range was 20,000-30,000 and its range similar to alum flucculation. Rapid mixing was very important parameter to floe formation in PASS- 100 flocculation. Whereas, slow mixing did not affect to the removal efficiency at settling time for 30minute or more.

• Korea-Australia Rheology Journal
• /
• v.18 no.3
• /
• pp.153-160
• /
• 2006

We analyzed the non-Newtonian and non-isothermal flow with Carreau-Yasuda viscosity model in co-rotating and counter-rotating twin screw extruder systems. The mixing performances with respect to the screw speed, the screw pitch, and the rotating direction have been investigated. The dynamics of mixing was studied numerically by tracking the motions of particles. The extent of mixing was characterized in terms of the deformation rate, the residence time distribution, and the average strain. The results showed that the high screw speed decreases the residence time but increases the deformation rate. Small screw pitch increases the residence time. It is concluded that the high screw speed increases the dispersive mixing performance, while the small screw pitch increases the distributive mixing performance. Co-rotating screw extruder has the better conveying performance and the distributive mixing performance than counter-rotating screw extruder with the same screw speed and pitch. Co-rotating screw extruder developed faster transport velocity and it is advantageous the flow characteristics to the mixing that transfers polymer melt from one barrel to the other barrel.

• Elastomers and Composites
• /
• v.48 no.2
• /
• pp.103-113
• /
• 2013

The properties of the rubber composites containing a silane and silica were evaluated by changing the mixing time and temperature, in order to find the optimum mixing conditions. Characteristics of the compounds were evaluated after mixing at $120^{\circ}C$, $140^{\circ}C$, and $160^{\circ}C$ with various mixing time. With increasing of mixing time, mooney viscosity decreased while the bound rubber contents of the compounds increased. Viscosity rise by increased mixing time was bigger at low temperature and the higher the mixing temperature the faster in the formation of bound rubber. With lower mixing temperature of $120^{\circ}C$, cross-linking rate was almost constant. Dynamic viscoelastic properties and dispersity of the compound showed that dispersion of ingredients and reaction was not sufficient with the mixing time of less than 10min. On the contrary, with high temperature, it was obvious that good dynamic and physical properties could be obtained due to sufficient coupling reaction, however it was thought this high temperature is not optimum because of sensitive cross-linking rate and physical properties and excessive formation of bound rubber. Consequently, it was confirmed that the mixing condition of 10min at $140^{\circ}C$ was optimum for the silane coupling reaction and dispersion of functionalized S-SBR containing silica and silane.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2008.11a
• /
• pp.593-596
• /
• 2008

The bleeding of concrete is defined as a kind of separation of materials. The durability of concrete, as well as the quality caused by the bleeding. Therefore, This study is intended to find influence of cement and mixing time factor on the bleeding of concrete. We want to know two factors that determine the change, to provide it to our customers. According to the results, The bleeding ratio increase by the increase of mixing time factor. At the 90 second of mixing time, the amount of bleeding differ greatly from cement properties. This paper presents an experimental study on bleeding ratio, slump and compressive strength properties with three days. In addition, the mixing time is inversely related slump loss ratio, the initial value of the compressive strength is only affected by the mixing time. As a result, the bleeding of concrete was obtained that their characteristics depends on the cement and mixing time factor, also in the future, to derive optimum mixing time for a variety of review is necessary.

• Korean Journal of Agricultural Science
• /
• v.48 no.3
• /
• pp.535-544
• /
• 2021

When baking, the proper blending or mixing of materials will affect the quality of the product. The mixing strength is important when establishing the optimal conditions for batter, and control of the mixing condition is accordingly an important factor. This study investigated the effects of the mixing speed and time on the quality characteristics of a gluten-free type of rice batter. The batter samples manufactured for this purpose are as follows: control (+) (wheat flour), control (-) (rice flour), T1 (1,800 rpm, 1 min), T2 (1,800 rpm, 2 min), T3 (1,800 rpm, 3 min), T4 (3,600 rpm, 1 min), T5 (3,600 rpm, 2 min), T6 (3,600 rpm, 3 min). In this study, rice flour was used in the T1 to T6 samples. The pH of the batter tended to be higher when the mixing speed was slower and the time was shorter depending on the ultra-high mixing conditions. The moisture content of T3 was highest, and there was no difference according to the ultra-high speed conditions. The specific volumes of the ultra-high mixing treatments were higher than those of the control samples. The relationship between the specific volume, hardness and springiness of rice bread according to the mixing speed and time was weak. Therefore, it is considered that the application of ultra-high speeds when manufacturing gluten-free batter can have a positive effect on improving the production efficiency by reducing the processing time.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.1 s.244
• /
• pp.48-56
• /
• 2006

We investigated gas residence time and mixing characteristics due to various swirl numbers generated by normal injection of secondary air to a lab-scale cylinderical combustor. The residence time was estimated by measuring the temporal pressure difference which was caused by deposition of test particles on a filter media after the injection by a syringe. The mixing characteristics were evaluated by standard deviation value of test gas concentration at different measuring points. The test gas concentration was detected by a gas analyzer. The swirl number of $20{\sim}30$ for ${\theta}=5^{\circ}$ caused long residence time enough to improve mixing characteristics. Numerical calculations were also carried out to understand physical meanings of the experimental results.

• Journal of Mechanical Science and Technology
• /
• v.20 no.12
• /
• pp.2284-2291
• /
• 2006

The present study investigates gas residence time and mixing characteristics for various swirl numbers generated by injection of secondary air into a lab-scale cylindrical combustor. Fine dust particles and butane gas were injected into the test chamber to study the gas residence time and mixing characteristics, respectively. The mixing characteristics were evaluated by standard deviation value of trace gas concentration at different measurement points. The measurement points were located 25 mm above the secondary air injection position. The trace gas concentration was detected by a gas analyzer. The gas residence time was estimated by measuring the temporal pressure difference across a filter media where the particles were captured. The swirl number of 20 for secondary air injection angle of 5$^{\circ}$ gave the best condition: long gas residence time and good mixing performance. Numerical calculations were also carried out to study the physical meanings of the experimental results, which showed good agreement with numerical results.

• Journal of the Korean Vacuum Society
• /
• v.3 no.3
• /
• pp.316-321
• /
• 1994

Rate of mixing of Cu particles to polyimide substrate at interfaces under different thermal treatments was analyzed by Rutherford Backscattering spectroscopy using 2.0 MeV He+ ions. T he mixing rate was a function of annealing temperature and time and was constant at afioxed temperature. The amount of mixing increased linearly with time and the mixing rate increased with temperature. The activation energy for interface mixing between Cu and polyimide was 2.6 kcal/mol. The X-ray studies showed the Cu(111) plane peak changed with annealing time at fixed temperature. The mixing of Cu to polyimide was explained with segmental motion of PI chain and with interaction between functional group of the chain and metal electron donor. The comparisons were made bewteen the mixing induced by ion irradiation and by thermal treatment. The various factors affecting the interface mixing are discussed.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.30 no.1 s.244
• /
• pp.32-41
• /
• 2006

We analyzed the non-Newtonian and non-isothermal flow in the melt conveying zone in co-rotating and counter-rotating screw extruder system with the commercial code, STAR-CD, and compared the mixing performance with respect to screw speed and rotating direction. The viscosity of fluid was described by power-law model. The dynamics of mixing was studied numerically by tracking the motion of particles in a twin screw extruder system. The extent of mixing was characterized in terms of the residence time distribution and average strain. The results showed that high screw speed decreases the residence time but increases the shear rate. Therefore higher screw speed increases the strain and has better mixing performance. Counter-rotating screw extruder system and co-rotating screw extruder has the similar shear rate with the same screw speed in spite of different rotating direction. However, the counter-rotating screw has good mixing performance, which is resulted from longer residence time than that of co-rotating screw extruder.