• 대한기계학회논문집B
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• 제36권3호
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• pp.325-333
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• 2012

원형 및 타원노즐의 내부유동과 외부유동의 상관관계를 알아보기 위해 실험적 연구가 수행되었다. 분사압력에 따라 유량, 분무각, 액적크기 등의 외부유동에 관해 관찰하였고, 노즐 내부유동의 유속 및 압력분포 등을 수치해석을 통해 정량적인 결과를 도출하였다. 외부유동의 경우, 동일한 압력조건하에서 타원형 노즐의 경우, 원형 노즐에서 나타나지 않는 표면분열의 분무특성을 관찰할 수 있었고, 수치해석을 통해 노즐 내부의 유동을 분석한 결과, 원형의 경우와는 달리 타원형 노즐의 단축에서 내부유동의 재부착이 노즐 벽면에서 발생되었다. 타원노즐 외부유동의 표면분열이 내부유동에 따른 결과라고 판단된다.

• Journal of Biosystems Engineering
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• 제13권3호
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• pp.11-19
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• 1988

분무량(噴霧量) 및 유량계수(流量係數)에 관(關)한 많은 연구(硏究)가 실험결과자료(實驗結果資料)에 기초하여 수행(遂行)되어졌다. 그러나 공시체(供試體)의 노즐의 특성(特性)에 따라서 유선(流線)의 특성(特性)이 다르므로 많은 실험결과(實驗結果) 및 해석(解析)이 서로 상치되는 점이 많다. 본(本) 연구(硏究)에서는 이론분석결과(理論分析結果)가 실험결과(實驗結果)와 다소 다르더라도 노즐 설계(設計)의 실제응용면(實際應用面)에서 필요(必要)한 노즐구조(構造)의 기본기능(基本機能)을 이론적(理論的)으로 분석(分析), 이해(理解)시키고저 한다. 이론분석(理論分析)의 결과(結果)는 다음과 같다. 공동면적(空洞面積)은 분구경(噴口徑), 와실경(渦室徑), 중자도구경(中子導溝徑) 및 중자도구각(中子導溝角)에 관계되고 있으며, 특히 중자도구각(中子導溝角)이 공동현상(空洞現象)에 큰 영향을 미친다. $$r_r{^6}-3r_o{^2}r_r{^4}+[3r_o{^4}+\frac{r_c{^4}r_o{^2}}{(r_c-r_g)^2\;tan^2{\theta}}]r_r{^2}-r_o{^6}=0$$ 반경방향(半徑方向) 힘의 요소(要素)로 인(因)한 유량계수(流量係數)($C_t$)는 산출식(算出式)은 아래와 같다. $$C_t=[1-(\frac{r_r}{r_o})^2]^{3/2}$$ 분무각(噴霧角)(${\alpha}$)은 공동반경(空洞半徑) 및 분구반경(噴口半徑)에 의(依)하여 변화(變化)된다. $${\alpha}=2\;tan^{-1}\(\frac{r^r}{\sqrt{r_o{^2}-r_r{^2}}}\)$$분무각(噴霧角)은 특히 와실유선각(渦室流線角)의 영향을 많이 받음을 시사하고 있다.

• 한국재료학회지
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• 제30권10호
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• pp.550-557
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• 2020

Used in the ceramic tile market as a representative building material, relief ceramic tile is showing increased demand recently. Since ceramic tiles are manufactured through a sintering process at over 1,000 ℃ after uniaxial compression molding by loading granule powders into a mold, it is very important to secure the flowability of granular powders in a mold having a relief pattern. In this study, kaolin, silica, and feldspar are used as starting materials to prepare granule powders by a spray dryer process; the surface of the granule powders is subject to hydrophobic treatment with various concentrations of stearic acid. The effect on the flowability of the granular powder according to the change of stearic acid concentration is confirmed by measuring the angle of repose, tap density, and compressibility, and the occurrence of cracks in the green body produced in the mold with the relief pattern is observed. Then, the green body is sintered by a fast firing process, and the water absorption, flexural strength, and durability are evaluated. The surface treatment of the granule powders with stearic acid improves the flowability of the granule powders, leading to a dense microstructure of the sintered body. Finally, the hydrophobic treatment of the granule powders makes it possible to manufacture relief ceramic tiles having a flexural strength of 292 N/cm, a water absorption of 0.91 %, and excellent mechanical durability.

• Journal of Biosystems Engineering
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• 제31권3호
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• pp.153-160
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• 2006

This study was performed to evaluate some geometrical characteristics of disc type swirl nozzles and to develop nozzles having improved spraying performance for knapsack sprayers. Considered geometrical characteristics of the nozzles were disc thickness, orifice diameter, swirl chamber diameter and shape of the swirl chamber (nozzle chamber). 3 types of nozzle cores were compared. Main results of this study were as follows. 1. Spraying angle (A) was increased with decreasing disc thickness (x), and with increasing orifice diameter (y) or spraying pressure (z). The equation was as a follow. $$A=3.95\frac{1}{x}+73.50\sqrt{y}+18.97\sqrt{z}-60.16$$ 2. Spraying flow rate (F) was increased with decreasing disc thickness (x), and with increasing orifice diameter (y) or spraying pressure (z). The equation was as a follow. $$F=-89.95x+611.09y+620.49\sqrt{z}-868.20$$ 3. Mean spraying droplet size (V) was decreased with decreasing disc thickness (x), with increasing orifice diameter (y) in low spraying pressure, with decreasing orifice diameter (y) in high spraying pressure, and with increasing spraying pressure (z). $$V=148.77x^4-746.85x^3+1311.76x^2-917.31x$$ 4. The spray pattern was compared using CV values. The CV value of the nozzle core type 1 was 26.7% in spraying pressure $3\;kgf/cm^2$, the CV value of the core type 2 was 23.6% in spraying pressure $2\;kgf/cm^2$, the CV value of the core type 3 was 20.6% in spraying pressure $1\;kgf/cm^2$. 5. Minimum spraying pressure was improved from $1.5\;kgf/cm^2\;to\;1.0\;kgf/cm^2$ by changes of nozzle core shape.

• 한국자동차공학회논문집
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• 제15권4호
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• pp.10-16
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• 2007

A rubber seal for wheel bearing which has been mainly applied to car wheel supporting device is required to have both high sealing performance and drag torque. Because of severe operational conditions like infiltration of mud or splashed water, the importance of rubber seal which is aimed for leakage prevention of grease and effective blocking of foreign substances has been increasing continuously. The sealing performance of this seal depends on several factors such as materials of seal, friction conditions of contact regions and geometry of seals and so on. We have focused on the effects of geometric characteristics such as the angle of main lip, interference between lip edge and inner metallic ring. In this study, the optimization of geometric variables was performed using the finite element analysis. For the sake of finite element analysis, uniaxial tensile tests were conducted and several constants for Mooney-Rivlin's equation were obtained. According to the results of this study, mock-up bearing was made. To verify this study, drag torque and mud spray test were preformed.

• Journal of Biosystems Engineering
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• 제37권6호
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• pp.335-341
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• 2012

Purpose: While an unmanned helicopter has been extensively used for spraying chemicals on agricultural crops, its low utilization (two months per year from July to August) has recently become an issue. This study aimed to increase the utilization of the unmanned helicopter. The centrifugal rice seeder, a mounting device for rice seeding for unmanned helicopter was developed and assessed its performance. Methods: The concept of the centrifugal spraying device was to obtain design criteria for centrifugal distribution. Four types of blade shapes namely straight, curved, straight wing and curved wing were developed and used. The rotational speed of the blades was tested at 1,000, 1,200 and 1,400 rpm. Results: The blade shapes, rotational blade speed and angle of trajectory were theoretically analyzed and results were validated with a series of laboratory experiments. Conclusions: The curved wing blades provided the distribution uniformity (DU) at 1,200rpm of rotational speed and 60 degree of seed drop point. The spray uniformity of 4.2% was also achieved.

• 한국자동차공학회논문집
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• 제16권6호
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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.

• The Journal of Advanced Prosthodontics
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• 제7권2호
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• pp.85-92
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• 2015

PURPOSE. This study aimed to investigate the efficacy of cleaning solutions on saliva-contaminated zirconia in comparison to air-abrasion in terms of resin bonding. MATERIALS AND METHODS. For saliva-contaminated air-abraded zirconia, seven cleaning methods)-no contamination (NC), water-spray rinsing (WS), additional air-abrasion (AA), and cleaning with four solutions (Ivoclean [IC]; 1.0 wt% sodium dodecyl sulfate [SDS], 1.0 wt% hydrogen peroxide [HP], and 1.0 wt% sodium hypochlorite [SHC])-were tested. The zirconia surfaces for each group were characterized using various analytical techniques. Three bonded resin (Panavia F 2.0) cylinders (bonding area: $4.5mm^2$) were made on one zirconia disk specimen using the Ultradent jig method [four disks (12 cylinders)/group; a total of 28 disks]. After 5,000 thermocycling, all specimens were subjected to a shear bond strength test with a crosshead speed of 1.0 mm/minute. The fractured surfaces were observed using an optical and scanning electron microscope (SEM). RESULTS. Contact angle measurements showed that groups NC, AA, IC, and SHC had hydrophilic surfaces. The X-ray photoelectron spectroscopy (XPS) analysis showed similar elemental distributions between group AA and groups IC and SHC. Groups IC and SHC showed statistically similar bond strengths to groups NC and AA (P>.05), but not groups SDS and HP (P<.05). For groups WS, SDS, and HP, blister-like bubble formations were observed on the surfaces under SEM. CONCLUSION. Within the limitations of this in vitro study, some of the cleaning solutions (IC or SHC) were effective in removing saliva contamination and enhancing the resin bond strength.

• 폴리머
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• 제36권2호
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• pp.163-168
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• 2012

최근에 내시경 관련기술의 진보에 따라서 시술 편리성, 회복시간 단축, 환자 고통 경감 등의 장점으로 인해 스텐트 삽입술이 빠르게 진보하였다. 본 연구에서 양성담관 협착 치료를 목적으로 파클리탁셀을 이용한 약물방출 스텐트를 전기분사 방법에 의해 제조하였으며, 이 때 사용된 고분자는 polyether-based polyurethane(상표명 : PELLETHANE 2363-80AE$^{(R)}$)과 첨가제로서 Pluronic F127, 약물로서 파클리탁셀을 사용하여 금속스텐트 표면에 코팅하였다. 그 결과로서, 약물이 코팅된 고분자 필름의 물리적 특성은 SEM, FTIR, 접촉각 측정기, XRD에 의해 확인하였으며, 약물방출속도는 약물함량이 높을수록 감소하였음을 알 수 있었다.

• 한국항공우주학회지
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• 제37권2호
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• pp.175-180
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• 2009

이 논문은 폴리머 기반의 전기 분무 장치를 만들기 위하여 이온빔 장치를 통하여 초소수성으로 가공 된 polytetrafluoroethylene(PTFE) 노즐을 사용하였다. 초소수성 표면을 만들기 위하여, PTFE 표면은 Ar과 $O_2$를 이용한 이온빔 공정 장치를 사용하였다. 최적의 표면 공정 조건은 Ar과 $O_2$ 유량 및 에너지 단위를 변화 시켜 얻을 수 있었다. 공정된 노즐의 표면 특성을 분석하기 위하여 접촉각 측정을 수행하였고, 표면의 형태적 분석을 위해 scanning electron microscope(SEM) 그리고 atomic force microscope(AFM) 측정을 하였다. 초소수성으로 공정된 노즐을 사용함으로써 보다 안정적이고 반복적인 전기 분무가 가능함을 확인 하였으며, 공정 된 노즐의 성능을 평가하기 위하여 외팔보와 이온빔으로 표면 처리 된 노즐 그리고 레이져 변위센서를 이용하여 마이크로 스케일의 추력을 측정하였다.