• 대한기계학회논문집
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• 제15권5호
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• pp.1683-1696
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• 1991

본 연구에서는 정4각단면덕트 입구영역에서 층류맥동유동(laminar pulsating flows)의 유동특성을 이론 및 실험적으로 규명하기 위하여, 이론적 방법으로 덕트 입 구영역에서의 층류맥동유동에 대한 운동량방정식을 유도한 후 비선형인 대류항을 선형 화 시켜서 라플라스변환으로 속도분포식의 해를 구하였고, 실험적인 방법으로는 시험 덕트 크기는 횡단면의 가로*세로가 40mm*40mm이고, 길이가 4000mm인 정4각단면덕트 입구영역에서 송풍기에 의한 공기흡입유동으로 층류진동유동을 발생하며 이들 두유동 을 합성시켜 발생한 층류맥동유동에 대하여 열선유속계의 열선신호로부터 얻어진 속도 파형을 고찰하여 덕트내의 맥동유동에 대한 임계레이놀즈수를 결정하고 속도분포를 측 정하였다. 그리고 이론적으로 얻어진 속도분포식과 열선유속계로 측정한 속도분포를 비교검토하여 정확성을 검증하고, 이들 해석결과로 부터 층류맥동유동의 입구길이(en- trance lenght)식을 결정하여 제안하였다.

• 대한조선학회논문집
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• 제32권3호
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• pp.51-61
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• 1995

비정상 층류 유동을 위한 수치 계산법이 개발되었다. 정규 격자계와 유한 차분법이 이용되었고, 압력-Poisson 방법을 이용하여 매시간 지배 방정식을 만족하는 속도장이 구해졌다. 우선 계산 방법의 검증을 위해 원통 주위의 유동이 계산되었고, 그리고 날개 단면 주위에서 자연적으로 발생하는 비정상 박리 형상을 계산하였다. 계산 결과는 유선형 물체 주위의 층류 박리의 비정상성을 잘 보여주고 있다.

• Journal of Mechanical Science and Technology
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• 제15권9호
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• pp.1339-1345
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• 2001

Laminar film condensation of a saturated pure vapor in forced flow over a flat plate is analyzed as boundary layer solutions. Similarity solutions for some real fluids are presented as a function of modified Jakob number (C$\_$pι/ ΔΤ/Prh$\_$fg/) with property ratio (No Abstract.see full/text) and Pγ as parameters and compared with approximate solutions which were obtained from energy and momentum equations without convection and inertia terms in liquid flow. Approximate solutions agree well with the similarity solutions when the values of modified Jakob number are less then 0.1 near 1 atmospheric pressure.

• 대한기계학회논문집B
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• 제20권3호
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• pp.979-987
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• 1996

A theoretical study for the laminar round jet diffusion flame impinging on the wall was carried out to predict the characteristics and structure of impinging jet flame and heat transfer to the wall. Finite chemistry via Arrhenius equation was adopted as the combustion model. All the transport properties were considered as the variable depending on the temperature and composition. For the parametric study, the distance from nozzle to perpendicular wall and Reynolds number at nozzle exit were chosen as the major parameters. As the results of the present study, the characteristics of flow field and the distributions of temperature, density and each chemical species were obtained. The heat transfer rate from flame to the wall and the effective heating area were calculated to investigate the influence of the major parameters on the heat transfer characteristics.

• 설비공학논문집
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• 제3권4호
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• pp.215-221
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• 1991

Laminar film condensation of a saturated vapor in forced flow over a flat plate is analyzed by using integral method. Laminar condensate film is so thin that the inertia and thermal convection terms in liquid flow can be neglected. Approximate solutions for water are presented and well agreed with the similarity solutions over the wide range of physical parameter, Cp1(Ts-Tw)/Pr.hfg. For the strong condensation case, it is found that magnitude of the interfacial shear stress at the liquid-vapor interphase boundary is approximately equal to the momentum transferred by condensation, i.e., ${\tau}_i{\simeq}\dot{m}(U_O-U_i)$.

• Journal of Mechanical Science and Technology
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• 제18권7호
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• pp.1258-1266
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• 2004

It is important to completely understand heat/mass transfer from a flat plate because it is a basic element of heat/mass transfer. In the present study, local heat/mass transfer coefficient is obtained for two flow conditions to investigate the effect of boundary layer using the naphthalene sublimation technique. Obtained local heat/mass transfer coefficient is converted to dimensionless parameters such as Sherwood number, Stanton number and Colburn j-factor. These also are compared with correlations of laminar and turbulent heat/mass transfer from a flat plate. According to experimental results, local Sherwood number and local Stanton number are in much better agreement with the correlation of turbulent region rather than laminar region, which means analogy between heat/mass transfer and momentum transfer is more suitable for turbulent boundary layer. But average Sherwood number and average Colburn j-factor representing analogy between heat/mass transfer and momentum transfer are consistent with the correlation of laminar boundary layer as well as turbulent boundary layer.

• International Journal of Air-Conditioning and Refrigeration
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• 제15권2호
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• pp.47-53
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• 2007

Laminar heat transfer experiments were conducted in flat extruded aluminum tubes. Three different flat tubes-two with smooth inner channel, one with micro-finned inner channel-were tested. Smooth tube data were in reasonable agreement with the predictions by simplified theoretical models. The heat transfer coefficients of the micro-fin tube were significantly smaller than those of the smooth tube. The reason was attributed to the decelerating flow in the inter-fin region. Heat transfer correlations were developed from the data.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2014년도 제49회 KOSCO SYMPOSIUM 초록집
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• pp.191-194
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• 2014

The characteristics of laminar free jet flow with having applied AC electric fields have been investigated experimentally. A single electrode configuration was adopted such that electric fields were applied directly to nozzle and thus the surrounding could be an infinite ground. The experimental results showed that the jet flow with AC was modified significantly. At a certain axial distance, the laminar fuel stem was broken down and subsequently it was separated into three parts when AC electric fields were applied over a certain voltage in a range of frequencies less than 120 Hz. The breakdown point was measured by varying applied AC voltage and frequency. The effect of applying electric fields to jet flow was discussed in detail.

• 한국항공운항학회지
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• 제12권3호
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• pp.25-39
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• 2004

An experimental study was quantitatively carried out in order to investigate the influence of flow conditions on a boundary layer in the near-wake of a flat plate. Tripping wires attached at various positions were selected to change flow conditions of a boundary layer in the vicinity of trailing edge. The flows such as laminar, transitional, and turbulent boundary layer at 0.98C from the leading edge are imposed to investigate the evolution of symmetric and asymmetric wake. Measurements were made at freestream velocity of 6.0m/s, and the corresponding Reynolds number is $2.8{\times}10^5$. An x-type hot-wire probe(55P61) was employed to measure at 8 stations in the near-wake region. Test results show that the near-wake of the flat plate for the case of a laminar and transitional boundary layer is sensitive to mean flow shear generated after separation but for the case of turbulent boundary layer is insensitive.

• 대한기계학회논문집
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• 제17권2호
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• pp.452-457
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• 1993

For the calculation of transonic laminar relative flow fields on the axisymmetric H-S and B-B stream surfaces in turbomachinery, a finite volume method developed in Part (I) is extended. Energy equation is replaced for simplicity by the condition of constant rothalpy throughout the flow fields. For axisymmetric H-S flow the circumferential componets of absolute velocity are given in advance so that this component of momentum equations can be neglected. Some numerical results show good agreement with experimental data.