• 한국정밀공학회지
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• 제26권12호
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• pp.123-130
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• 2009

This study presents the application of a polymer behavior model that considers fluid mechanics and heat transfer effects in a deposition system. The analysis of the polymer fluid properties is very important in the fabrication of precise microstructures. This fluid behavior model involves the calculation of velocity distribution and mass flow rates that include the effect of heat loss in the needle. The effectiveness of the proposed method was demonstrated by comparing estimated mass fluid rates with experimental values. The mass fluid rates under various process conditions, such as pressure, temperature, and needle size, reflected the actual deposition state relatively well, and the assumption that molten polycaprolactone(PCL) is a non-Newtonian fluid was reasonable. The successful fabrication of three-dimensional microstructures demonstrated that the model is valid for predicting the polymer behavior characteristics in the microstructure fabrication process. The results of this study can be used to investigate the effect of various parameters on fabricated structures before turning to experimental approaches.

• 한국가스학회지
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• 제2권4호
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• pp.53-59
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• 1998

기-액 2상유동장에서 유동양식은 압력강하, 보이드율분포, 유동장의 기하학적 형상과 밀접한 관계가 있다. 한편 원유수송, 비등이 발생하는 유동, 펌프에서 발생하는 케비테션 현상, 그리고 화학 반응로와 같은 상변화 장치 등의 2상유동에서 고분자물질에 의한 저항감소 현상의 적용이 가능할 것으로 예상된다. 그러나 2상유동장에서 고분자물질에 의한 저항감소에 관한 연구는 매우 미비하다. 그래서 본 연구는 2상유동장에 합성고분자물질(A611p)에 의한 저항감 소율을 실험을 통하여 계측 및 분석하였다. 본 연구에서는 고분자물질의 농도를 증가시킬수록 국부보이드율의 최고치가 관의 중심에서 관의 벽쪽으로 이동하며 2상유동의 유동양식이 변화됨을 규명하였다. 그래서 저항감소율과 유동양식과 밀접한 관계가 있음을 예측할 수 있었다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 추계학술대회논문집B
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• pp.324-329
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• 2001

This experimental study concerns the characteristics of a transitional flow in a concentric annulus with a diameter ratio of 0.52, whose outer cylinder is stationary and inner one rotating. The pressure losses and skin-friction coefficients have been measured for the fully developed flow of $0.1\sim0.4%$ aqueous solution of sodium carbomethyl cellulose (CMC), respectively at inner cylinder rotational speed of $0\sim600rpm$. The transitional flow has been examined by the measurement of pressure losses to reveal the relation of the Reynolds and Rossby numbers with the skin-friction coefficients. The present results show that the skin-friction coefficients have the significant relation with the Rossby numbers, only for laminar regime. The occurrence of transition has been checked by the gradient changes of pressure losses and skin-friction coefficients with respect to the Reynolds numbers. The increasing rate of skin-friction coefficients due to the rotation in uniform for laminar flow regime, whereas it is suddenly reduced for transitional flow regime and, then, is gradually declined for turbulent flow regime. Consequently, the critical(axial-flow) Reynolds number decrease as the rotational speed increases. Thus, the rotation of inner cylinder promotes the early occurrence of transition due to the onset of taylor vortices.

• 에너지공학
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• 제18권2호
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• pp.87-92
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• 2009

본 논문은 안쪽축이 회전하는 동심환형관 물과 비뉴튼유체의 고-액 2상 유동연구를 수행하였다. 점탄성유체의 유변학은 굴착구멍의 청결, 입자의 밖으로 수송하는 등 여러 가지 응용에 중요하다. 연구에서 투명한 아크릴관은 고체입자의 이동을 관찰하기 위하여 사용하였다. 환형관 속도는 0.3m/s에서 2.0m/s로 변한다. 머드시스템은 물과 CMC 수용액을 혼합하여 사용하였다. 연구에서 고려된 주요 변수들은 축회전속도, 유체 유동영역과 입자 주입율이다. 입자이송속도와 압력강하는 유체유량(Q, LPM)이 5~30의 범위에서 측정하였다. 물과 0.2% CMC 수용액에서 고체입자의 농도가 높을수록 압력손실이 커짐을 알 수 있었다.

• 한국추진공학회지
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• 제17권3호
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• pp.47-55
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• 2013

본 연구에서는 곡관 채널에서의 비뉴튼 젤 추진제의 유동 특성에 대해 연구하였다. 물을 기본유체로 하는 모사젤을 Carbopol 941 젤화 작용제와 NaOH 농축액을 혼합하여 제작하였으며 입자 유무에 따른 유동 특성을 파악하기 위해 $Al_2O_3$ 나노 입자가 첨가된 젤을 제작하여 두 젤 추진제간의 유변학적 특성을 비교하였다. 두 모사젤에 대해 U-자형의 곡관부 위치별 유동특성과 Dean 와류(vortices)의 경향은 상이하였으나 나노 입자가 첨가된 모사젤 추진제의 경우 높은 컨시스턴시 지수에도 불구하고 두 모사젤 모두 비슷한 범위의 임계 Dean 수를 도출하였다. 나노 입자 첨가 유무와 무관하게 power-law 지수값이 임계 Dean 수를 결정하는데 주요 변수임을 판단할 수 있었으나 나노입자가 첨가된 젤의 경우 Dean 와류 강도의 변동폭이 상대적으로 크다는 결론을 내릴 수 있었다.

• 대한기계학회논문집B
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• 제22권9호
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• pp.1208-1216
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• 1998

The present numerical study investigates the effect of a secondary flow on the heat transfer in order to delineate the mechanism of laminar heat transfer enhancement of a viscoelastic fluid in rectangular ducts. The second normal stress generating a secondary flow is modeled by adopting the Reiner-Rivlin constitutive equation and the calculated secondary flow showed good agreement with experiments. The primary velocity U as well as the pressure drop were not affected by the secondary flow in rectangular ducts, whose order of magnitude is less than 0.1% of the primary velocity. The small magnitude of the secondary flow, however, affect moderately the temperature fields. The calculated Nusselt numbers with secondary flow show 50% heat transfer enhancement over those of a purely viscous non-Newtonian fluid, which are considerably lower than the experimental values. Therefore, we conclude that there should be an additional heat transfer enhancement mechanism involved in the viscoelastic fluid such as temperature-dependence.

• Nuclear Engineering and Technology
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• 제49권7호
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• pp.1396-1404
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• 2017

The mathematical aspects of Dufour and Soret phenomena on the peristalsis of magnetohydrodynamic (MHD) Jeffrey liquid in a symmetric channel are presented. Fluid viscosity is taken variably. Lubrication approach has been followed. Results for the velocity, temperature, and concentration are constructed and explored for the emerging parameters entering into the present problem. The plotted quantities lead to comparative study between the constant and variable viscosities fluids. Graphical results indicate that for non-Newtonian materials, pressure gradient is maximum, whereas pressure gradient is slowed down for variable viscosity. Also both velocity and temperature in the case of variable viscosity are at maximum when compared with results for constant viscosity.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2002년도 춘계학술발표대회 논문집
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• pp.184-187
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• 2002

Compression molding was specifically developed for replacement of metal components with composites. As the mechanical properties of the products are dependent on the separation and orientation, it is important to research the fiber mat structure and molding conditions. In this study, the effects of the fiber mat structure(NP: 5, 10, 25punches/$\textrm{cm}^2$) and the mold closure speed($\dot{\textrm{h}}$=0.1, 1, 10mm/min) on the viscosity of composites were discussed. The composites is treated as a Non-Newtonian power-law fluid. The parallel-plate plastometer is used and the viscosity is obtained from the relationship between the compression load and the thickness of the specimen.

• 항공우주시스템공학회지
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• 제7권3호
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• pp.51-57
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• 2013

This study describes the Federal Aviation Administration(FAA) certification policy for approving the use of Type II, III, and IV deicing/anti-icing fluids on small category airplanes. These fluids can be characterized as non-Newtonian, pseudo-plastic fluids, also known as "thickened" fluids. Deicing fluids are used before takeoff to remove frost or ice contamination, while anti-icing fluids are used before takeoff to prevent frost or ice contamination from occurring for a period of time(referred to as "holdover time") after application. Thickened deicing/anti-icing fluids can affect airplane performance and handling characteristics and their residue may cause stiff or frozen flight controls. This study also describes an approval process that may be used by type certificate holders and applicants for a type certificate under parts 23 to support operational use of these fluids on their airplanes.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 춘계학술대회논문집B
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• pp.825-828
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• 2000

The objective of the present study is to develop a new device that the viscous characteristics of fluids are determined by applying the unsteady flow concept to the traditional capillary tube viscometer. The capillary tube viscometer consists of a small cylindrical reservoir, capillary tube, a load celt system oat measures the mass flow rate, interfacers, and computer. Due to the small size of the reservoir the height of liquid in the reservoir decreases as soon as the liquid in the reservoir drains out through the capillary and the mass flow rate in the capillary decreases as the hydrostatic pressure in the reservoir decreases resulting in a decrease of the shear rate in the capillary tube. The instantaneous shear rate and. driving force in the capillary tube are determined by measuring the mass flow rate through the capillary, and the fluid viscosity is determined from the measured flow rate and the driving force.