• Journal of the Korean Society for Heat Treatment
• /
• v.35 no.1
• /
• pp.27-32
• /
• 2022

Microbubble technology has been widely applied in various industrial fields. Recently, research on many types of microbubble application technology has been conducted experimentally, but there is a limit in deriving the optimal design and operating conditions. Therefore, if the computational fluid dynamics (CFD) analysis of multiphase flow is used to supplement these experimental studies, it is expected that the time and cost required for prototype production and evaluation tests will be minimized and optimal results will be derived. However, few studies have been conducted on multiphase flow CFD analysis to interpret fluid flow in microbubble generators using swirl flow. In this study, CFD simulation of multiphase flow was performed to analyze the air-water mixing process and fluid flow characteristics in a microbubble generator with a dual-chamber structure. Based on the simulation results, it was confirmed that a negative pressure was formed on the central axis of rotation due to the strong swirling flow. And it could be seen that the air inside the suction tube was introduced into the inner chamber of the microbubble generator. In addition, as the high-speed mixed fluid collided with external water sucked by the negative pressure near the outlet, a large amount of microbubbles was ejected due to the shear force between the two flows flowing in opposite directions.

• Computers and Concrete
• /
• v.32 no.2
• /
• pp.185-206
• /
• 2023

This article aimed to explore the optimization of mineral admixtures and retarding admixture for high-performance concrete. In essence, fresh concrete can be regarded as a mixture in which both coarse and fine aggregates are suspended in a cement-based matrix paste. Based on this view, the test procedure was divided into three progressive stages of binder paste, mortar, and concrete to explore their rheological behavior and mechanical properties respectively. At each stage, there were four experimental control factors, and each factor had three levels. In order to reduce the workload of the experiment, the Taguchi method with an L9(3⁴) orthogonal array and four controllable three-level factors was adopted. The test results show that the use of the Taguchi method effectively optimized the composition of high-performance concrete. The slump of the prepared concrete was above 18 cm, and the slump flow was above 50 cm, indicating that it had good workability. On the other hand, the 28-day compressive strength of the hardened concretes was between 31.3-59.8 MPa. Furthermore, the analysis of variance (ANOVA) results showed that the most significant factor affecting the initial setting time of the fresh concretes was the retarder dosage, and its contribution percentage was 62.66%. On the other hand, the ANOVA results show that the most significant factor affecting the 28-day compressive strength of the hardened concretes was the water to binder ratio, and its contribution percentage was 79.05%.

• Journal of Animal Science and Technology
• /
• v.47 no.6
• /
• pp.1081-1086
• /
• 2005

This study was conducted to investigate the effect of mixture types which consist of different species on the dry matter(DM) yield, botanical composition and forage quality. The experimental design includes three mixture types: Conventional mixtures(orchardgrass 50% + tall fescue 20% + perennial ryegrass 10% + Kentucky bluegrass 10% + white clover 10%), complex mixtures(orchardgrass 40% + tall fescue 20% + perennial ryegrass 10% + Kentucky bluegrass 10% + redtop 10% + alfalfa 5% + red clover 5%) and simple mixtures(orchardgrass 80% + red clover 20%). The DM yield was higher in conventional mixtures(13,070kg/ha) than in other mixtures(p<0.05). In the chemical composition and dry matter digestibility, there was significant difference among mixtures. Crude protein content and dry matter digestibility were higher in complex mixtures than in other mixtures(p<0.05). But, the content of fibrous constituents was higher in conventional mixtures than in other mixtures. The yield of crude protein dry matter(CPDM) and digestible dry matter(DDM) were higher in complex mixtures than in other mixtures. In this experiment, DM yields and quality of mixture types were observed significant difference. therefore, the complex mixtures which combined various species were more effective in enhancing the dry matter digestibility(DMD) and digestible dry matter(DDM) yield.

• Computers and Concrete
• /
• v.19 no.4
• /
• pp.395-404
• /
• 2017

In this paper, the mechanical property of CFRP, BFRP, GFRP and their hybrid FRP was experimentally studied. The elastic modulus and tensile strength of CFRP, BFRP, GFRP and their hybrid FRP were tested. The experimental results showed that the elastic modulus of hybrid FRP agreed well with the theoretical rule of mixture, which means the property of hybrid composites are linear with the volumes of the corresponding components while the tensile strength did not. The bearing capacity, peak strain, stress-strain relationship of circular concrete columns confined by CFRP, BFRP, GFRP and hybrid FRP subjected to axial compression were recorded. And the confinement effect of hybrid FRP on concrete columns was analyzed. The test results showed that the bearing capacity and ductility of concrete columns were efficiently improved through hybrid FRP confinement. A strength model and a stress-strain relationship model of hybrid FRP confined concrete columns were proposed. The proposed stress-strain model was shown to be capable of providing accurate prediction of the axial compressive strength of hybrid FRP confined concrete compared with Teng et al. (2002) model, Karbhari and Gao (1997) model and Miyachi et al. (1999) model. The modified stress-strain model was also suitable for single FRP confinement cases and it was so concise in form and didn't have piecewise fitting, which would be easy for use in structural design.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.38 no.11
• /
• pp.899-905
• /
• 2014

This paper describes preliminary research conducted for developing a high-efficiency clean large cauldron using the liquid-vapor phase change heat transfer. To improve the isothermal environment of the cauldron, naphthalene and FC-40 were selected as the working fluids to operate well in the temperature range of $100-200^{\circ}C$ and used in experimental investigations of the heat transfer characteristics. A two-phase closed thermosyphon was designed and built to demonstrate the functionality of the working fluids. Startup, boiling, and condensation tests were performed, and the test results were used to examine the possibility of complementary effects of the startup and heat transfer characteristics of the two-phase closed thermosyphon using a mixture of naphthalene and FC-40.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.03a
• /
• pp.790-798
• /
• 2008

Counter-rotating axial flow fan(CRF) consists of two counter-rotating rotors without stator blades. CRF shows the complex flow characteristics of the three-dimensional, viscous, and unsteady flow fields. For the understanding of the entire core flow in CRF, it is necessary to investigate the three-dimensional unsteady flow field between the rotors. This information is also essential to improve the aerodynamic characteristics and to reduce the aerodynamic noise level and vibration characteristics of the CRF. In this paper, experimental study on the three-dimensional unsteady flow of the CRF is performed at the design point(operating point). Flow fields in the CRF are measured at the cross-sectional planes of the upstream and downstream of each rotor using the $45^{\circ}$ inclined hot-wire. The phase-locked averaged hot-wire technique utilizes the inclined hot-wire, which rotates successively with 120 degree increments about its own axis. Three-dimensional unsteady flow characteristics such as tip vortex, secondary flow and tip leakage flow in the CRF are shown in the form of the axial, radial and tangential velocity vector plot and velocity contour. The phase-locked averaged velocity profiles of the CRF are analyzed by means of the stationary unsteady measurement technique. At the mean radius of the front rotor inlet and the outlet, the phase-locked averaged velocity profiles show more the periodical flow characteristics than those of the hub region. At the tip region of the CRF, the axial velocity is decreased due to the boundary layer effect of the fan casing and the tip vortex flow. The radial and the tangential velocity profiles show the most unstable and unsteady flow characteristics compared with other position of rotors. But, the phase-locked averaged velocity profiles of the downstream of the rear rotor show the aperiodic flow pattern due to the mixture of the front rotor wake period and the rear rotor rotational period.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.36 no.6
• /
• pp.415-421
• /
• 2023

In this study, the piezoresistive properties of cementitious composites enhanced with carbon nanotubes for improved electrical conductivity were analyzed using a deep learning-based transformer algorithm. Experimental execution was performed in parallel for acquisition of training data. Previous studies on mixture design, specimen fabrication, chemical composition analysis, and piezoresistive performance testing are also reviewed in this paper. Notably, specimens in which fly ash substituted 50% of the binder material were fabricated and evaluated in this study, in addition to carbon nanotube-infused specimens, thereby exploring the potential enhancement of piezoresistive characteristics in conductive cementitious materials. The experimental results showed more stable piezoresistive responses in specimens with fly-ash substituted binder. The transformer model was trained using 80% of the gathered data, with the remaining 20% employed for validation. The analytical outcomes were generally consistent with empirical measurements, yielding an average absolute error and root mean square error between 0.069 to 0.074 and 0.124 to 0.132, respectively.

• Journal of Animal Science and Technology
• /
• v.48 no.3
• /
• pp.375-382
• /
• 2006

This study was conducted to investigate the effects of dietary herbal plant mixture on growth performance, blood immunological parameters, fecal VFA and NH3-N concentrations in growing pigs. The dietary treatments were 1) NC (negative control; antibiotics-free diet), 2) PC (positive control; NC diet added 0.16% antibiotic), 3) NCK0.2 (NC diet added 0.2% herbal plant mixture (koppuul??)) and 4) PCK0.1 (PC diet added 0.1% herbal plant mixture (koppuul??)). Eighty crossbred (Landrace×Yorkshire×Duroc) pigs (16.35±0.05kg average initial body weight) were used for 42 days. The pigs were assigned to the treatments according to body weight and each treatment had 5 replicates of 4 pigs per pen in a randomized complete block design. During the whole experimental period, PCK0.1 and PC treatments had significantly higher ADG than NC treatment (P<0.05). Gain/feed of pigs fed PC diet was higher than that of pigs fed NC diet (P<0.05). For blood immunological parameters investigations, white blood cells (WBC) counts and IgG level increased in the pigs fed PC, NCK0.2 and PCK0.1 diets compared to pigs fed NC diet. In addition, higher (P<0.05) serum lymphocyte concentration was found in PCK0.1 treatment compared to NC treatment. NH3-N concentration in pigs fed NCK0.2% diet was lower than that in pigs fed PC and NC diets. There were no significant differences in DM and N digestibilities among the treatments. In conclusion, the results suggested that the dietary additions of herbal plant mixture or antibiotics increase ADG, the concentrations of WBC counts and IgG, lymphocyte, while decrease NH3-N concentration in feces.

• Food Science and Preservation
• /
• v.16 no.4
• /
• pp.472-481
• /
• 2009

Response surface methodology (RSM) is frequently used for optimization studies. In the present work, RSM was used to determine the antimicrobial activitiesof grapefruit seed extract (GFSE) and a lactic acid mixture (LA) against Staphylococcus aureus, Bacillus cereus, Escherichia coli, Salmonella typhimurium, Pseudomonas fluorescens, and Vibrio parahaemolyticus. A central composite design was used to investigate the effects of independent variables on dependent parameters. One set of antimicrobial preparations included mixtures of 1% (w/w) GFSE and 10% (w/w) LA, in which the relative proportions of component antimicrobials varied between 0 and 100%. In further experiments, the relative proportions were between 20% and 100%. Antimicrobial effects against various microorganisms were mathematically encoded for analysis. The codes are given in parentheses after the bacterial names, and were S. aureus ($Y_1$), B. cereus ($Y_2$), E. coli ($Y_3$), S. typhimurium ($Y_4$), P. fluorescens ($Y_5$), and V. parahaemolyticus ($Y_6$). The optimum antimicrobial activity of the 1% (w/w) GFSE:10% (w/w) LA mixture against each microorganism was obtained by superimposing contour plots ofantimicrobial activities on measures of response obtained under various conditions. The optimum rangesfor maximum antimicrobial activity of a mixture with a ratio of 1:10 (by weight) GFSE and LA were 35.73:64.27 and 56.58:43.42 (v/v), and the optimum mixture ratio was 51.70-100%. Under the tested conditions (a ratio of 1% [w/w] GFSE to 10% [w/w] LA of 40:60, and a concentration of 1% [w/w] GFSE and 10% [w/w] LA, 70% of the highest value tested), and within optimum antimicrobial activity ranges, the antimicrobial activities of the 1% (w/w) GFSE:10% (w/w) LA mixture against S. aureus ($Y_1$), B. cereus ($Y_2$), E. coli ($Y_3$), S. typhimurium ($Y_4$), P. fluorescens ($Y_5$), and V. parahaemolyticus ($Y_6$) were 24.55, 25.22, 20.20, 22.49, 23.89, and 28.04 mm, respectively. The predicted values at optimum conditions were similar to experimental values.

• Journal of The Korean Society of Grassland and Forage Science
• /
• v.26 no.3
• /
• pp.127-132
• /
• 2006

This experiment was conducted to evaluate the effect of manure and chemical fertilizer on the forage yield and quality of oat at no-tillage. The experimental design was a randomized complete block design. The three treatments were: chemical fertilizer, manure fertilizer, and chemical and manure mixture. Seedling vigor was higher at chemical fertilizer than manure, but more greener at manure application than chemical fertilizer. Dry matter (DM) content of oat at manure was higher than chemical and mixture fertilizer (p<0.05). There was no difference in DM yield, TDN (total digestible nutrients) yield, and CP (crude protein) yield of oat at no-tillage system, but the fresh yield was significantly higher in chemical fertilizer compared to manure. The CP content for oat was significantly higher in manure than chemical fertilizer. However, no significant effects were observed for NDF (neutral detergent fiber), ADF (acid detergent fiber), TDN and RFV (relative feed value) in different fertilizer application. Based on the results of this study, manure don't affected forage production and quality of no-till oat except CP content because forage oat is used off-season crop.