• 한국해양공학회지
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• 제15권2호
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• pp.39-45
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• 2001

With uniform heat generation from the inner surface of the cylindrical heater placed in a cross flow boundary condition, heat flow that is conducted along the wall of the heater creates a non-isothermal surface temperature and non-uniform heat flux distribution. In the present investigation, the effects of circumferential wall heat conduction on convection heat transfer is investigated for the case of forced convection around horizontal circular tube in cross flow of air. The wall conduction number which can be deduced from the governing energy equation should be used to express the effect of circumferential wall heat conduction. It is demonstrated that the circumferential wall heat conduction influences local Nusselt numbers of one-dimensional and two-dimensional solutions.

• 한국전산유체공학회지
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• 제18권2호
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• pp.35-40
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• 2013

Natural convection of air with Pr=0.7 between two horizontal plates with small magnitude non-uniform temperature distribution[${\in}{\Delta}Tsin({\kappa}X/H)$, H : gap width, X : horizontal coordinate] in the lower plate is numerically(${\in}=0.01$) investigated. In the conduction-dominated regime with $Ra{\leq}1700$, two upright cells are formed over one wave length($2{\pi}/{\kappa}$). For small wave number, the flow becomes unstable with increase of Rayleigh number, and multicellular convection occurs above a critical Rayleigh number. The flow patterns are classified by the number of eddies over one wave length. When ${\kappa}=1$, a transition of $2{\rightarrow}4{\rightarrow}6$ eddy flow occurs with increase of Rayleigh number, and no hysteresis phenomenon is observed. Dual and triple solutions are found for ${\kappa}=1$, and transitions of $10{\rightarrow}8$, $8{\rightarrow}6$, $6{\rightarrow}4{\rightarrow}2$ eddy flow occur with decrease of Rayleigh number.

• 대한기계학회논문집B
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• 제20권2호
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• pp.641-648
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• 1996

Thermophoretic particle deposition on a circular cylinder in a uniform laminar air flow was numerically investigated using a control volume method based on the generalized non-orthogonal coordinate system. Variation of air properties due to the change of temperature was taken into account. Effects of variable property on the distribution of heat transfer and deposition rates of particle were discussed. A new correlation of thermophoretic particle deposition on a circular cylinder was proposed in the present study.

• 대한기계학회논문집B
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• 제21권5호
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• pp.615-627
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• 1997

An experiment was performed to local heat transfer coefficient and Nusselt number in the circular duct of 180.deg. bend for Re=6*10$^{4}$, 8*10$^{4}$ and 1*10$^{5}$ at swirling flow and non-swirling flow conditions. The test tube with circular section was made by stainless which has curvature ratio 9.4. The wall of test tube was heated directly by electrical power to 3.51 kw and swirling motion of air was produced by a tangential inlet to the pipe axis at the 180 degree. Measurements of local wall temperatures and bulk mean temperature of air are made at four circumferential positions in the 16 stations. The wall temperatures show particularly reduced distribution curve at bend for non-swirling flow but this effect does not appear for swirling flow. Nusselt number distributions for swirling flow which was calculated from the measured wall and bulk temperatures were higher than that of non-swirling flow. Average Nusselt number of swirling flow increased about 90 ~ 100% than that of non-swirling flow whole through the test tube. The Nu/N $u_{DB}$ values at the station of 90.deg. for non-swirling flow and swirling flow are respectively about 2.5 and 4.8 at Re=6*10$^{4}$. Also that is good agreement with Said's result for non-swirling flow. flow.

• 설비공학논문집
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• 제18권4호
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• pp.328-334
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• 2006

Industrial electrostatic precipitators require a highly uniform velocity distribution in the collecting chamber. Increasing divergence angle of a diffuser makes a non-uniformity flow distribution characteristics on the diffuser exit. This paper provides CFD results of optimum positions and opening rates of perforated plates which were installed in the electrostatic precipitator. The considered divergence angels were 60 degree and 90 degree. In 90 degree diffuser, a blanking method was used.

• 한국반도체및디스플레이장비학회:학술대회논문집
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• 한국반도체및디스플레이장비학회 2007년도 춘계학술대회
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• pp.149-156
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• 2007

Non-contact transportation of the large-sized glass plate using air-cushion is considered for sputtering system of LCD panel. The Argon gas from second gas injection holes is injected to levitate and transport the glass plate. Low maximum pressure and uniform pressure distribution on the bottom surface of the glass plate must be maintained for stable levitation and transportation of the glass plate. Therefore, the analysis of fluid flow between the glass plate and the air-pad is numerically performed for varying space between the injection holes in this study. The pressure uniformity on the bottom surface of the glass plate is evaluated for overall glass plate. The distance between the injection holes must be designed below 90 mm for obtaining the low maximum pressure and uniform pressure distribution.

• 설비공학논문집
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• 제20권7호
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• pp.478-485
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• 2008

The extreme steam temperature deviation experienced in the superheater of a tangentially fired boiler can seriously affect its economic and safe operation. This temperature deviation is one of the main causes of boiler tube failures. The steam temperature deviation is mainly due to the thermal load deviation in the lateral direction of the superheater. The thermal load deviation consists of several causes. One of the causes is the non-uniform heat flow distribution of burnt gas on the superheater tube system. This distribution is very difficult to measure in situ using direct experimental techniques. So, we need thermal load model to estimate the tube temperature. In this paper, we propose a thermal load distribution model by using CFD analysis and plant data. We successfully predict the tube temperature and the steam flow rate in a final superheater system from the thermal load model and one dimensional heat-flow system analysis. The proposed model and analysis method would be valuable in preventing the frequent tube failure of the final superheater tubes.

• 설비공학논문집
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• 제19권12호
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• pp.811-820
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• 2007

A Study on the optimal design of the AIG(Ammonia Injection Grid) to improve the performance of DeNOx facilities in the HRSG(Heat Recovery Steam Generator) was performed using the CFD analysis. On the basis of the flow analysis results in the case that the AIG in the HRSG was not installed, the numerical analyses according to the positions of AIG, injection angles of nozzle and the control of ammonia injection quantity were carried out. The standard deviation according to factors was calculated for quantitative comparison. As the results, the AIG in the HRSG should be installed in the position that the uniform flow field shows through the exact flow analysis in the previous of the AIG design and installation. In the case the AIG has already been installed and non uniform flow distribution shows, it is recommended that flow correction device or KoNOx catalyst should be used. Otherwise, the control of ammonia injection angle or the ammonia injection quantity using the velocity profile analysis is demanded to accomplish the optimal performance.

• 설비공학논문집
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• 제17권3호
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• pp.216-222
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• 2005

An experimental investigation was executed to determine the capacity degradation due to fin conduction and non-uniform refrigerant distribution in a multi-path evaporator with cross-counter flow. The finned-tube evaporator, which had a three-path and three-depth-row, was tested by controlling inlet quality, exit pressure, and exit superheat for each refrigerant path. The capacity reduction due to superheat unbalance between each path was as much as $25\%$ for non-cutting evaporator, even when the overall evaporator superheat was kept at a target value of $5.6^{\circ}C$. It indicates that the internal heat transfer within the evaporator assembly causes the partial capacity drop. The capacity of cutting-evaporator with respect to non-cutting evaporator was enhanced according to the increment of air flow rate when superheat or superheat unbalance increased.

• 오토저널
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• 제15권2호
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• pp.92-104
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• 1993

In the present study, the velocity profiles and entrance length of developing transitional pulsating flows are investigated both analytically and experimentally in the entrance region of a square duct. The systems of conservation equations for transitional pulsating flows in a square duct are solved analytically by linearizing the non-linear convective terms. Analytical solutions are obtained in the form of infinite series for velocity pofiles. The experimental study for the air flow in a square duct(40mm*40mm*4000mm) is carried out to measure velocity profiles and other parameters by using a hot-wire anemometer with a data acquisition and processing system. The distribution of velocity profiles( $u_{ps}$ / $u_{m,ta}$) in the decelerating period is higher than in the accelerating period. The distribution of the axial component of the axial component of velocity in the transitional flow is nearly uniform in the central region of the duct, and decrease rapidly near the wall. The entrance length correlation of the transitional pulsating flows in a square duct is obtained to be $L_{e}$/ $D_{h}$=0.83 $A_{1}$R $e_{ta}$ /(.omega. sup+1)$^{2}$TEX>