• Journal of Advanced Marine Engineering and Technology
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• 제29권1호
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• pp.68-77
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• 2005

A transient liquid crystal technique has become one of the most effective ways in measuring the local heat transfer coefficients on the entire surface. The key Point of this technique is to convert the inlet flow temperature into an exponential temperature profile using a mesh heater. In order to verify the validity of this technique. the heat transfer characteristics on the wall surface by a pair of longitudinal vortices is investigated experimently and numerically. A standard ${\kappa}-{\varepsilon}$ is used for the numerical analysis of turbulent flow field. It is found from experiment and numerical analysis that two peak values exist over the whole domain. as the longitudinal vortices move to the farther downstream. these peak values decrease and the dimensionless averaged Nusselt number with the lapse of time is maintained nearly at constant values. The experiment results obtained from the present experiment in terms of the transient liquid crystal technique are in good agreement with the numerical results. Therefore, the transient liquid crystal technique developed for the measurement of heat transfer coefficient is proved to be a valid method.

• 대한기계학회논문집B
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• 제27권11호
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• pp.1618-1629
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• 2003

The effects of the interaction between flow field and heat transfer caused by the longitudinal vortices are experimentally investigated using a five hole probe and a transient liquid crystal technique. The test facility consists of a wind tunnel with vortex generators protruding from a bottom surface and a mesh heater. In order to control the strength of the longitudinal vortices, the angle of attack of vortex generators used in the present experiment is 20$^{\circ}$, and the spacing between the vortex generators is 25mm. The height and cord length of the vortex generator is 20mm and 50mm, respectively. Three-component mean velocity measurements are made using a f-hole probe system, and the surface temperature distribution is measured by the hue capturing method using a transient liquid crystal technique. The transient liquid crystal technique in measuring heat transfer has become one of the most effective ways in determining the full surface distributions of heat transfer coefficients. The key point of this technique is to convert the inlet flow temperature into an exponential temperature profile using the mesh heater set up in the wind tunnel. The conclusions obtained in the present experiment are as follows: The two maximum heat transfer values exist over the whole domain, and as the longitudinal vortices move to the farther downstream region, these peak values show the decreasing trends. These trends are also observed in the experimental results of other researchers to have used the uniform heat flux method.

• 대한기계학회논문집B
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• 제30권7호
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• pp.656-662
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• 2006

The effects of concave hemispherical surface with inclined angle on the local heat transfer from a turbulent round jet impinging were experimentally investigated using transient liquid crystal method. This method suddenly exposes a preheated wall to an impinging jet and then the video system records the response of liquid crystals for the measurement of the surface temperature. The Reynolds numbers were used 11000, 23000 and 50000, nozzle-to-surface distance ratio from 2 to 10 and the surface angles $\alpha=0^{\circ},\;15^{\circ},\;30^{\circ}\;and\;40^{\circ}$. Correlations of the stagnation point Nusselt number according to Reynolds number, jet-to-surface distance ratio and dimensionless surface angle are investigated. In the stagnation point, in term of $Re^n$, n ranges from 0.43 in case of $2{\leq}L/d\leq6$ to 0.45 in case of $6. The maximum Nusselt number occurs in the direction of upstream. The displacement of the maximum Nusselt number from the stagnation point increases with increasing surface angle or decreasing nozzle-to-surface distance. The maximum displacement is about 0.7 times of the jet nozzle diameter.

• Journal of Advanced Marine Engineering and Technology
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• 제27권5호
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• pp.581-588
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• 2003

Heat transfer characteristics of a pair of longitudinal vortices using a transient liquid crystal technique are studied experimentally. In order to control the strength of longitudinal vortices, angle of attack of the vortex generators is $20^{\circ}$and the length of space from the centerline the vortex generations is 25mm apart. The heat transfer measurements using a transfer coefficients. The following conclusions are obtained from the present experiment. When any vortex generators are not set up in wind tunnel test, heat transfer rate is low respectively. However, with the vortex generators of rectangular winglet, the heat transfer on the local surface can be enhanced.

• 대한기계학회논문집B
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• 제22권3호
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• pp.373-385
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• 1998

The local Nusselt numbers have been measured for a round turbulent jet impinging on the convex surface with and without rib. Liquid crystal/transient method was used to determine the Nusselt number distributions along the surface. The temperature on the surface was measured to within .+-.0.25 deg. C accuracy using liquid crystal and a digital color image processing system. The experiments were made for the jet Reynolds number (Re) 23,000, the dimensionless nozzle-to-surface distance (L/d) from 6 to 10, the dimensionless surface curvature (d/D) 0.056, and the various rib types (height(d$_{1}$) from 1 to 2 mm, pitch (p) from 6 to 32 mm). It was found that the average Nusselt numbers on the convex surface with rib are higher than those without rib, mainly due to an increase in the turbulent intensity caused by flow separation, recirculation and reattachment on the wall surface. In addition, we compared the results by the steady-state method using the gold-film Intrex with those by the transient method.

• 한국추진공학회지
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• 제6권3호
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• pp.37-43
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• 2002

지금까지 많은 열전달 계수의 측정에 관한 연구가 수행되고 있다. 본 논문에서는 액정을 이용하여 국소 열전달 계수를 측정하는 방법을 다루고 있다. 과도방법과 정상방법을 사용하여 실린더 표면의 지역적인 열전달 계수를 측정하였다. 정상상태일 때는 금박막 필름으로 실린더를 코팅하여 실험하였고, 과도방법일 때는 삽입기법과 바이패스 기법으로 각각 실험하였으며, 두 경우 모두 열풍동을 이용하여 실린더를 가열시키는 방법과 냉각시키는 방법으로 각각 실험하였다. 이와 같은 실험으로 과도방법과 정상방법을 이용하여 실린더표면에서의 대류열전달계수의 측정실험을 수행하고, 각 방법들에 대한 비교분석을 통해 액정을 이용한 열전달 측정방법의 특징들을 살펴보았다.

• 설비공학논문집
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• 제11권5호
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• pp.647-657
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• 1999

An experimental study has been peformed to investigate the heat transfer characteristics of impinging jets with multiple orifice nozzles. Four different shapes of multiple orifice nozzle were tested to improve the heat transfer characteristics of impinging jet. Heat transfer coefficients were obtained by using transient and steady method based on the liquid crystal thermography, and both methods showed very similar results. The effects of multiple orifice nozzles on the heat transfer characteristics of impinging jets were discussed in detail. The results showed that multiple orifice nozzles improved the heat transfer characteristics of impinging jet. Especially, heat transfer coefficients around stagnation region of impinging jets were highly increased.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.87-92
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• 2000

This study is to investigate the heat transfer characteristics the for a round turbulent jet impinging on the flat plate with and without rib. Liquid crystal/transient method was used to determine the Nusselt number distributions along the surface. The temperature on the surface was measured using liquid crystal and a digital color image processing system. The experiments were made fur the jet Reynolds number (Re) 23,000, the dimensionless nozzle-to-surface distance (L/d) from 2 to 10, and the rib type [height ($d_1$) 2mm, pitch (p) from 12 to 36mm]. It was found that for $L/d{\ge}6$ the average Nusselt numbers on the flat plate with rib type C ($p/d_1=16$) are higher than those without rib, mainly due to an increase in the turbulent intensity caused by flow separation, recirculation and reattachment on the wall surface.

• 대한전자공학회논문지SD
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• 제39권4호
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• pp.10-18
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• 2002

본 논문에서는 IPS모드의 액정 셀에서 전압에 따른 액정 거동을 수치 해석적으로 계산하는 방법을 보고한다. 액정 거동을 해석하기 위해 복잡한 구조에 적용이 용이한 3차원 유한 요소법을 사용하여 액정 셀 내부의 전압 분포와 전계 분포를 계산하였다. 전기 에너지와 액정 분자의 탄성 에너지로 이루어지는 액정 셀 내부의 자유에너지 밀도를 고려하였으며, 에릭슨-레슬리(Ericksen-Leslie) 방정식과 라플라스(Laplace) 방정식을 해석함으로서 액정 셀의 스위칭 특성을 계산하였다. 24㎛×12㎛×4.5㎛ 사이즈의 IPS 모드 액정 셀에 대하여 1,859개의 노드와 8,640개의 사면체 요소를 생성하여 16ms까지 과도 해석하였다. 그 결과, 전극 위 부분을 제외한 영역에서 횡방향의 전계가 형성되었고, 전극 위 영역에서 전경선(disclination)이 발생하는 것을 확인하였다.

• 대한기계학회논문집B
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• 제23권6호
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• pp.734-743
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• 1999

The local Nusselt numbers have been measured for a round turbulent jet impinging on the concave surface with and without rib. Liquid crystal/transient method was used to determine the Nusselt number distributions along the surface. The temperature on the surface was measured using liquid crystal and a digital color image processing system. The experiments were made for the jet Reynolds number (Re) 23,000, the dimensionless nozzle-to-surface distance (L/d) from 4 to 10, the dimensionless surface curvature (d/D) 0.056, and the rib type (height ($d_1$) 0.2 cm, pitch (p) from 1.2 to 3.2 cm). It was founded that only when $L/d{\geq}6$, the average Nusselt numbers on the concave surface with rib are higher than those without rib, mainly due to an increase in the turbulent intensity caused by the effect of rib attached to the wall surface. It was realized that the rib attached to the concave surface may no longer enhance the heat transfer rate or even lowers it depending on the rib type and flow conditions. In addition, the results by the steady-state method using the gold-film Intrex were in good agreement with those by the transient shroud method.