• Title/Summary/Keyword: Mixing effects

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Supersonic Jet Noise Control via Trailing Edge Modifications

  • Kim, Jin-Hwa;Lee, Seungbae
    • Journal of Mechanical Science and Technology
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    • v.15 no.8
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    • pp.1174-1180
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    • 2001
  • Various experimental data, including mixing areas, cross correlation factors, surface flow patterns on nozzle walls, and far field noise spectra, was used to draw a noise control mechanism in a supersonic jet. In the underexpanded case, mixing of the jet air with ambient air was significantly enhanced as presented before, and mixing noise was also dramatically reduced. Screech tones, in the overexpanded case, were effectively suppressed by trailing edge modifications, although mixing enhancement was not noticeable. From mixing and noise performance of nozzles with modified trailing edges, enhancing mixing through streamwise vortices seems an effective way to reduce mixing noise in the underexpanded flow regime. However, screech tones in the overespanded flow regime is well controlled or suppressed by making shock cells and/or spanwise large scale structures irregular and/or less organized by a proper selection of trailing edges. The noise field in the overexpanded flow regime was greatly affected by the symmetricity of the nozzle exit geometry. In the underexpanded flow regime, the effects of the symmetricity of the nozzle exit on mixing were negligible.

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The Study on the Effects of Mixer Configurations on Fluid Mixing Characteristics in SCR Systems (SCR 시스템의 믹서 구조 특성에 따른 유동 혼합 특성에 관한 연구)

  • Seo, Jin-Won;Lee, Kyu-Ik;Oh, Jeong-Taek;Choi, Yun-Ho;Lee, Jong-Hwa;Park, Jin-Il
    • Transactions of the Korean Society of Automotive Engineers
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    • v.16 no.6
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    • pp.192-199
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    • 2008
  • The key issues for the reduction technologies of the exhaust gas from diesel engine being developed are to reduce particulate matters and NOx. The SCR system is known to be one of the most efficient and stable technologies to remove NOx through the mixing of NOx and urea solution. In the present research, the effects of mixer configurations of SCR system have been investigated to enhance the SCR performance. First, a Schlieren technique is employed to visualize the mixing characteristics of urea solution and exhaust gas. The results show that a mixer is essential to obtain proper fluid mixing. In addition, numerical studies have been made to understand the mixing characteristics through the comparison of the mal-distribution index of concentration at the several locations of the diffuser. In particular, the effects of number of blade and mixer angles on mixing characteristics were studied. The results show that the blade angle has a larger effect on the mixing characteristics than the number of blades.

Effects of Design Parameters of Mixer Blades on Particle Mixing Performance (혼합기 블레이드 설계변수에 따른 입자의 혼합성능 연구)

  • Hwang, Seon-Pil;Park, Sanghyun;Sohn, Dongwoo
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.30 no.4
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    • pp.363-370
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    • 2017
  • This paper is concerned with the evaluation of mixing performance of a particle mixer, which consists of a vertical cylindrical vessel and a rotating impeller with several blades. We consider four design variables for the mixer blades, such as the angle, length, and number of blades, and the gap between the blades and the vessel bottom. The particle mixing process due to the impeller rotation is simulated using the discrete element method, and the mixing performance is quantitatively evaluated by introducing a mixing index. Analyzing the main effects and interactions of the four design variables through the design-of-experiments approach, it is concluded that the blade angle has the most dominant influence on the mixing performance whereas the gap has no significant influence. In addition, we determine the best combination of design parameters to maximize the mixing performance.

Effect of burnt gas mixing on the extinction of interacting flames premixed (기연가스의 혼합이 상호작용을 하는 예혼합화염의 소화특성에 미치는 영향에 관한 연구)

  • 임홍근;정석호
    • Journal of the korean Society of Automotive Engineers
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    • v.11 no.3
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    • pp.37-48
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    • 1989
  • The effects of burnt gas mixing, which can be caused by turbulent eddy mixing, on the interaction and extinction characteristics of premixed flames are analyzed using large activation energy asymptotics adopting counterflow as a model problem. The results show that the burnt gas mixing, preferential diffusion and heat loss affect the fuel consumption rate, flame temperature and the oxidizer concentration at the flame which influence the flame behavior and the extinction characteristics.

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Effect of Melt-mixing Conditions on Fracture Properties of Bioabsorbable HA/PLLA Composite Materials (생체흡수성 HA/PLLA 복합재료의 용융혼련조건이 파괴특성에 미치는 영향)

  • Park, Sang-Dae;Lee, Deok-Bo
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.31 no.7 s.262
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    • pp.732-738
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    • 2007
  • Effects of melt-mixing conditions on fracture properties of hydroxyapatite filled bioabsorbable poly(L-lactic acid)(HA/PLLA) composites was investigated by measuring the firacture toughness value of HA/PLLA composites prepared under different mixing time and rotor speed. The fracture surface morphology was also examined by profile measurement and scanning electron microscopies. It was found that the fracture toughness of HA/PLLA composites decreases due to decrease of ductile deformation of PLLA matrix and debonding of interfaces with increase of the rotor speed and mixing time. Effect of mixing process on neat PLLA was also assessed, and it was found that the fracture toughness of PLLA decreases due to disappearance of multiple craze formation and increase of defects. Such thermal and shear-stress degradation were found to be the primary mechanisms of the degradation of HA/PLLA composites during melt-mixing process.

A Study on the Homogeneity of Powder Mixture (분말약품 혼합의 균일성에 관한 연구)

  • 김길수;이민화
    • YAKHAK HOEJI
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    • v.21 no.2
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    • pp.95-100
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    • 1977
  • The effects of the particle size on the homogeneity of mixing and segregation of caffeine-lactose (1:99) mixture were studied. Using the two kinds of caffein, milled and unmilled caffein, V-type blender, the degree of mixing according to the particle size was predicted and the experiment on the change of mixedness by mixing time was carried out by the method derived from mixing index theory by Poole et al. and Hersey. the results could be summarized as follows; (1) The homogeneity of mixing was greatly affected by the particle size and the particle size should be reduced to the adepuate level to attain the desirable mixedness. (2) The homogeneity was not proportional to the mixing time and optimum mixing time for caffein-lactose was about 10 minutes. (3) Segregation tendency was increased by the particle size increase and greatly affected by the flow time in the segregation cell.

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Effect of Mixing Method on Mechanical Properties of Fiber Reinforced Concrete

  • Kim, Hyun Wook;Lee, Chang Joon
    • Journal of the Korea Institute of Building Construction
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    • v.15 no.3
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    • pp.351-357
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    • 2015
  • Fiber reinforced concrete (FRC) has been successfully used to enhance the flexural toughness of concrete. As fibers are randomly oriented in FRC, they sometimes produce clumps that reduce the mechanical performance, and a properly chosen mixing protocol can be a way to minimize this problem. In this research, the effects of mixing method on the mechanical properties of FRC were investigated. The compressive strength, flexural strength, and flexural toughness were measured using three different mixing methods. It was shown from the results that the compressive strength and peak flexural load were not affected by changes in mixing method. However, in terms of flexural toughness, the changes in mixing method clearly affected the flexural toughness of FRC. The truck-mixed FRC outperformed two pan-mixed FRCs.

Mixing effect on Properties of NTC Thermistor in Mn-Co-0 System (Mn-Co-0계 NTC 써 미스터의 물성에 미치는 혼합의 영향)

  • 윤상식;김경식;윤상옥
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2001.11a
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    • pp.459-462
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    • 2001
  • Interface effects on properties of NTC thermistors having Mn-Co-O spinel crystal structure system are analyzed by a mixing rule in case of mixed types and layered types between CuO and Al$_2$O$_3$ added compounds. With adding CuO and Al$_2$O$_3$, The compounds form completely solid solution and their resistance and B constant are changed due to the variation of conduction electrons by their ionic substitutions. The properties of mixed NTC thermistors are depended on the logarithmic mixing rule by a dispersed phase and they show slightly lower values due to the lattice mixing affect in compared with calculated values. The resistance of layered NTC thermistors is depended upon the series mixing rule containing the value of an interface layer and effected by the variation of its thickness, and it is changed rapidly to the logarithmic mixing rule by the connection between two layers with increasing the interface layer

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Effects of Quality of Alfalfa Silage by Different Wheat Bran Mixing Levels (밀기울 첨가수준이 알팔파 Silage 품질에 미치는 영향)

  • 신재순;차영호;이혁호;김정갑;진현주;정기영
    • Journal of The Korean Society of Grassland and Forage Science
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    • v.16 no.3
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    • pp.225-229
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    • 1996
  • To find out the optimum mixing level of wheat bran to improve the quality of 1st cut Alfalfa silage, this trial was canied out at two-year's Alfalfa monoculture field of the National Livestock Research Institute, Suwon, Korea, from May 1955 to Oct. 1995. The results are as follows. I. According to the increase of wheat bran mixing level, DM content was high from 23.19%(nil) to 35.70%(40% mixing), pH of silage were low from 5.51(nil) to 4.45(40% mixing). but there were not significant at 20% mixing or more(P>0.05). 2. Also it was appeared to the same trend at Lactic acid content and in the Flieg's score of silage it was highest as 59 in the 20% mixing level. 3. In chemical component of silages there were not significant at 20% mixing or more in crude protein, crude fiber and ashes content, 30% mixing or more in ether extract and 10% or less in NFE content(P>0.05). 4. TDN, NEL and StE contents were low as adding level was increased. respectively, but there were not significant(P>O.OS). As mentioned above the results, desirable mixing level of wheat bran to lstcut Alfalfa to improve the quality of silage was 20% of fresh weight.

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A Statistical Assessment of Increasing Tidal Mixing Effects on Water Quality in the Shiwha Coastal Reservoir (시화호 해수유통량 증대에 따른 통계학적 수질 영향 분석)

  • Lee, Bum-Yeon;Lee, Chang-Hee
    • Journal of Korean Society on Water Environment
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    • v.37 no.6
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    • pp.425-432
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    • 2021
  • A tidal power plant (TPP) has been in operation since the end of 2011 to improve the water quality of Shihwa Coastal Reservoir (SCR). Tidal mixing rate increased 5.6 times after the TPP operation so that in this study, its effects on water quality was assessed through statistical analysis of long-term water quality monitoring data. It was found that the increased tidal mixing contributed to solving the hypoxia problem in the bottom water by preventing the summer stratification. The analysis also showed that the increased tidal mixing had different effects depending on the relative concentration difference for each water quality substances between the SCR and the outside of SCR. The average concentrations of some substances (chemical oxygen demand, total phosphorus, chlorophyll-a) with higher concentrations than the outside of SCR decreased due to the dilution effect, but the other substances (total nitrogen, dissolved inorganic nitrogen, dissolved inorganic phosphorus) with lower concentrations compared to the outside ones increased on the contrary. Factor analysis also showed a consistent result that the first factor accounting for the water quality was changed from the organic-related substances to the nutrient-related substances after the increased tidal mixing. These results imply that the focus of future water quality management needs shifting from the organic substances to the nutrients, particularly dissolved inorganic nutrients. Considering the effect of inflow seawater on the nutrients, the management area should be extended to cover not only SCR but also a certain area outside of SCR.