• 제목/요약/키워드: Mixing Factor

검색결과 469건 처리시간 0.027초

실험계획법을 적용한 무연 (Na1/2K1/2)NbO3세라믹스의 CuO 및 MnO2 첨가에 따른 압전 및 유전 특성 (Piezoelectric and Dielectric Characteristics of Lead Free (Na1/2K1/2)NbO3 Ceramics Doped with CuO and MnO2 using Design of Experiments)

  • 윤중락;이창배;이경민;이헌용;이동희
    • 한국전기전자재료학회논문지
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    • 제22권8호
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    • pp.665-670
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    • 2009
  • Lead-free piezoelectric ($Na_{1/2}K_{1/2}$)$NbO_3$ ceramics doped with CuO and $MnO_2$ were fabricated using the conventional oxide-mixing technique. With increasing content of CuO and $MnO_2$, the dielectric constant(${\varepsilon}_{33}$) and mechanical quality factor($Q_m$) value increased, while electromechanical coupling factor($K_p$) and piezoelectric constant($d_{33}$) decreased. The piezoelectric and dielectric properties ($Na_{1/2}K_{1/2}$)$NbO_3$ ceramics doped with CuO 2.461 wt% and $MnO_2$ 0.538 wt% at sintered temperature $1050\;^{\circ}C$ were attained ${\varepsilon}_{33}$ = 403, $K_p$ = 15, $Q_m$ = 122 and $d_{33}$ = 36 pC/N. Based on response surface methodology results using design of experiment, it was concluded that ($Na_{1/2}K_{1/2}$)$NbO_3$ doped with CuO 0.477 wt% and $MnO_2$ 0.269 wt% has possibility composition of being used for piezoelectric transformer.

무주지역 수질특성자료의 통계학적 분석에 의한 소유역 구분 (Watershed Classification Using Statistical Analysis of water Quality Data from Muju area)

  • 한원식;우남칠;이기철;이광식
    • 한국지하수토양환경학회지:지하수토양환경
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    • 제7권3호
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    • pp.19-32
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    • 2002
  • 본 연구는 무주군 적상산 부근에 위치하는 소유역에서 지표수의 수질과 인접한 천층지하수 수질사이의 관계 및 지질매체와 오염원의 유입에 의한 계절적인 변동을 규명하기 위하여 수행되었다. 8월과 10월 두 차례의 조사결과 이곳 지표수와 지하수 수질은 Ca-$HCO_3$유형이 주를 이루고 있었으며 인근 광산부근에서는 중금속에 의한 오염이 나타나고 있었다. 10월 조사시에 인가가 밀집한 지역에서는 질산성 질소의 의한 오염 또한 높게 나타나는 특징을 보이고 있다. 이러한 자료를 토대로 군집분석(Cluster Analysis)과 주성분 분석(Principal Component Analysis)을 실시하였으며, 군집분석결과 지표수는 5개의 그룹으로 구분되었고 지하수는 3개의 그룹으로 구분되었다. 주성분분석 결과는 군집분석 시에 나타난 결과를 효과적으로 지지하고 있으며 (1)지질매체의 수리지화학적 반응, (2)오염물질의 유입 (3) 인근광산에 의한 중금속 오염이 복합적으로 반응하여 나타난 결과로 해석된다.

식물배양세포(植物培養細胞)-Rhizobium에 의(依)한 질소고정(窒素固定)에 관한 연구 (Nitrogen fixation by Rhizobium-Plant cell cultures)

  • 박우철;곡전택도언
    • 한국토양비료학회지
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    • 제12권1호
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    • pp.43-46
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    • 1979
  • 수년간(數年間) 계속배양(繼續培養)한 식물배양세포(植物培養細胞)와 근류균(根瘤菌)과의 질소고정(窒素固定)에서 그 mechanism을 알기 위(爲)하여 근류형성(根瘤形成) 및 감염과정(感染過程)을 알기 위(爲)해 연구하던 중 배양세포(培養細胞)에 단일균주(單一菌株) 및 혼합균주(混合菌株)의 접종(接種)에 의(依)한 Nitrogenase의 활성(活性)이 높은 것을 발견(發見)하였기에 그 차이(差異)를 조사(調査)한 결과(結果)는 다음과 같았다. 1. 단일접종(單一接種)에 있어서는 대두(大豆)에서의 Nitrogenase의 활성(活性)이 비(非)콩과 식물보다 대체적(大體的)으로 높았고, 혼합접종(混合接種)에 있어서는 비(非)콩과 식물에서 활성(活性)이 높았다. 2. 근류형성(根瘤形成) 및 Nitrogenase활성(活性)에 있어서의 특성(特性)인 host factor를 Callus에서는 대두중(大豆中) 북낭(北娘) 및 동양령(東洋鈴), 비(非)콩과 식물중에서는 Datura를 제외(除外)하고는 찾아볼 수가 없었다. 3. 균주별(菌株別)의 Nitrogenase활성(活性)은 비(非)콩과 식물에서는 012균주(菌株)가 콩과 식물인 대두(大豆)에서는 010, 023, 024균주(菌株)가 대체(大體)로 높았다.

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기계적 혼합과 고상법에 의한 LiNiO2의 합성과 전기화학적 특성 (Study on the Synthesis by Milling and Solid-State Reaction Method and Electrochemical Properties of LiNiO2)

  • 김훈욱;윤순도;이재천;박혜령;송명엽
    • 한국세라믹학회지
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    • 제42권5호
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    • pp.319-325
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    • 2005
  • [ $LiNiO_2$ ] was synthesized by the solid-state method after mixing $LiOH{\cdot}H_2O$ and $Ni(OH)_2$ with SPEX mill. The optimum condition for the synthesis of $LiNiO_2$ was the calcination at $750^{\circ}C$ for 30h in $O_2$ stream after milling for 1 h. The $LiNiO_2$ synthesized under this condition showed relatively large value of $I_{003}/I_{104}$ and relatively small value of R-factor. When $LiNiO_2$ was cycled in 2.7$\~$4.15 V at 0.1C-rate, the first discharge capacity was not very large (145.8 mAh/g) but it showed good cycling performance. When $LiNiO_2$ was cycled in 2.7$\~$4.2 V at 0.1C-rate, the first discharge capacity was large but ,it showed poor cycling performance probably because of the transition of H2 hexagonal structure to H3 hexagonal structure. In addition, when $LiNiO_2$ was cycled in 1.0$\~$4.8 V at 1/24C- rate, the first discharge capacity was very large (257.7 mAh/g) and the discharge capacity increased with the number of cycles.

환기부족 구획화재에서 수직 개구부의 형상 및 위치가 화재특성에 미치는 영향 (Effects of the Geometry and Location of an Vertical Opening on the Fire Characteristics in the Under-Ventilated Compartment Fire)

  • 문선여;박충화;황철홍;박설현
    • 한국화재소방학회논문지
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    • 제27권3호
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    • pp.20-29
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    • 2013
  • 실규모 환기부족 구획화재에서 수직 개구부의 형상 및 위치변화에 따른 열 및 화학적 화재특성 변화를 수치적으로 검토하기 위하여, 이론적 최대 공기 유입량을 결정하는 환기인자($A\sqrt{h}$)와 heptane pool 화재의 질량 감소율이 모든 조건에 대하여 동일하게 설정되었다. 주요 결과로서, 출입문 형상의 변화는 구획 내부의 열 및 화학적특성 변화에 큰 영향을 미친다. 창문 위치의 변화는 화재지속시간 및 재순환 유동구조를 포함한 추가적인 화재특성의 복잡한 변화를 초래하였다. 이들 결과는 개구부 유동 및 연료/공기의 혼합현상을 포함한 다차원 유동 및 화재특성을 통해 상세히 분석되었다.

사인 웨이브 핀과 타원관으로 구성된 핀-관 열교환기의 공기측 성능 (Air-Side Performance of Fin-and-Tube Heat Exchangers Having Sine Wave Fins and Oval Tubes)

  • 최병남;풍익;심현민;김내현
    • 설비공학논문집
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    • 제25권5호
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    • pp.279-288
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    • 2013
  • Heat transfer and pressure drop characteristics of fin-and-tube heat exchangers having sine wave fins and oval tubes were investigated. Oval tubes having an aspect ratio of 0.6 were made, by deforming 12.7 mm round tubes. Twelve samples, having different fin pitch and tube row, were tested. The effect of fin pitch on the j and f factors was negligible. The effect of the tube row on the j factor, however, was different from that of common fin-and-tube heat exchangers having plain fins and round tubes. The highest j factor was obtained for a two-row configuration, while the lowest one was obtained for a one-row configuration. A possible reason was attributed to the flow mixing characteristics of the sine wave channel of the present geometry. Comparison with a plain fin-and-tube heat exchanger having 15.88 mm O. D. round tube reveals that the present oval fin-and-tube heat exchanger shows generally superior thermal performance, except for the one-row configuration.

A computational estimation model for the subgrade reaction modulus of soil improved with DCM columns

  • Dehghanbanadaki, Ali;Rashid, Ahmad Safuan A.;Ahmad, Kamarudin;Yunus, Nor Zurairahetty Mohd;Said, Khairun Nissa Mat
    • Geomechanics and Engineering
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    • 제28권4호
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    • pp.385-396
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    • 2022
  • The accurate determination of the subgrade reaction modulus (Ks) of soil is an important factor for geotechnical engineers. This study estimated the Ks of soft soil improved with floating deep cement mixing (DCM) columns. A novel prediction model was developed that emphasizes the accuracy of identifying the most significant parameters of Ks. Several multi-layer perceptron (MLP) models that were trained using the Levenberg Marquardt (LM) backpropagation method were developed to estimate Ks. The models were trained using a reliable database containing the results of 36 physical modelling tests. The input parameters were the undrained shear strength of the DCM columns, undrained shear strength of soft soil, area improvement ratio and length-to-diameter ratio of the DCM columns. Grey wolf optimization (GWO) was coupled with the MLPs to improve the performance indices of the MLPs. Sensitivity tests were carried out to determine the importance of the input parameters for prediction of Ks. The results showed that both the MLP-LM and MLP-GWO methods showed high ability to predict Ks. However, it was shown that MLP-GWO (R = 0.9917, MSE = 0.28 (MN/m2/m)) performed better than MLP-LM (R =0.9126, MSE =6.1916 (MN/m2/m)). This proves the greater reliability of the proposed hybrid model of MLP-GWO in approximating the subgrade reaction modulus of soft soil improved with floating DCM columns. The results revealed that the undrained shear strength of the soil was the most effective factor for estimation of Ks.

Numerical Life Prediction Method for Fatigue Failure of Rubber-Like Material Under Repeated Loading Condition

  • Kim Ho;Kim Heon-Young
    • Journal of Mechanical Science and Technology
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    • 제20권4호
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    • pp.473-481
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    • 2006
  • Predicting fatigue life by numerical methods was almost impossible in the field of rubber materials. One of the reasons is that there is not obvious fracture criteria caused by nonstandardization of material and excessively various way of mixing process. But, tearing energy as fracture factor can be applied to a rubber-like material regardless of different types of fillers, relative to other fracture factors and the crack growth process of rubber could be considered as the whole fatigue failure process by the existence of potential defects in industrial rubber components. This characteristic of fatigue failure could make it possible to predict the fatigue life of rubber components in theoretical way. FESEM photographs of the surface of industrial rubber components were analyzed for verifying the existence and distribution of potential defects. For the prediction of fatigue life, theoretical way of evaluating tearing energy for the general shape of test-piece was proposed. Also, algebraic expression for the prediction of fatigue life was derived from the rough cut growth rate equation and verified by comparing with experimental fatigue lives of dumbbell fatigue specimen in various loading condition.

Prediction of Forced Convective Boiling Heat Transfer Coefficient of Pure Refrigerants and Binary Refrigerant Mixtures Inside a Horizontal Tube

  • Kim, Min-Soo;Hong, Eul-Cheong;Shin, Jee-Young;Kyungdoug Min;Ro, Sung-Tack
    • Journal of Mechanical Science and Technology
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    • 제17권6호
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    • pp.935-944
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    • 2003
  • Forced convective boiling heat transfer coefficients were predicted for an annular flow inside a horizontal tube for pure refrigerants and nonazeotropic binary refrigerant mixtures. The heat transfer coefficients were calculated based on the turbulent temperature profile in liquid film and vapor core considering the composition difference in vapor and liquid phases, and the nonlinearity in mixing rules for the calculation of mixture properties. The heat transfer coefficients of pure refrigerants were estimated within a standard deviation of 14% compared with available experimental data. For nonazeotropic binary refrigerant mixtures, prediction of the heat transfer coefficients was made with a standard deviation of 18%. The heat transfer coefficients of refrigerant mixtures were lower than linearly interpolated values calculated from the heat transfer coefficients of pure refrigerants. This degradation was represented by several factors such as the difference between the liquid and the overall compositions, the conductivity ratio and the viscosity ratio of both components in refrigerant mixtures. The temperature change due to the concentration gradient was a major factor for the heat transfer degradation and the mass flux itself at the interface had a minor effect.

Airside Performance of Convex Louver Fin-and-Tube Heat Exchangers

  • Kim, Nae-Hyun;Oh, Wang-Kyu
    • International Journal of Air-Conditioning and Refrigeration
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    • 제16권3호
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    • pp.100-107
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    • 2008
  • The heat transfer and friction characteristics of heat exchangers having convex louver fins are experimentally investigated, and the results are compared with those of wave fin counterparts. Eighteen samples (nine convex louver fin samples and nine wave fin samples) which had different fm pitches (1.81 mm to 2.54 mm) and tube rows (one to four) were tested. The convex angle was $11.7^{\circ}$. The j factors are insensitive to fin pitch, while f factors increase as fin pitch increases. The effect of fin pitch on f factor is more significant for the wave fin compared with the convex louver fin. It appears that the complex fin pattern of the convex louver fin induces intense mixing of the flow, and thus reduces the effect of fin pitch. Both the j and f factors decrease as the number of tube row increases. However, as the Reynolds number increases, the effect of tube row diminishes. Comparison of the convex louver fin j factors with those of wave fin reveals that convex louver fin j factors are 18% to 29% higher than those of wave fin. The f factors are 16% to 34% higher for the convex louver fin. The difference increases as fin pitch decreases. Existing correlation fails to adequately predict the present data. More data is needed for a general correlation of the convex louver fin geometry.