• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.7
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• pp.649-658
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• 2005

Flow condensation heat transfer coefficients (HTCs) of R22, R410, Propane (R290) were measured inside a horizontal 9 hole aluminum multi-channel flat tube. The main test section in the refrigerant loop was made of a 0.53m long multi-channel flat tube of hydraulic diameter of 1.4 mm. Refrigerant was cooled by passing cold water through an annulus surrounding the test section. Data were obtained in qualities of $0.1\~0.9$ at mass flux of $200\~400kg/m^2s$ and heat flux of $7.3\~7.7kW/m^2$ at the saturation temperature of $40^{\circ}C$. All popular heat transfer correlations in single-phase subcooled liquid flow and flow condensation originally developed for large single tubes predicted the present data of the multi channel flat tube within $25\%$ deviation when effective heat transfer area was used in determining experimental data. This suggests that there is little change in flow characteristics and patterns when the tube diameter is reduced down to 1.4 mm diameter range. Hence, a modified correlation based on the present data was proposed which could be applied to small diameter tubes with effective heat transfer area. The correlation showed a mean deviation of less than $20\%$ for all data.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.249-255
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• 2005

Flow condensation heat transfer coefficients(HTCs) of R22, R4IO, Propane(R290) were measured inside a horizontal 9 hole aluminum multi-channel flat tube. The main test section in the refrigerant loop was made of a 0.53 m long multi-channel flat tube of hydraulic diameter of 1.4 mm. Refrigerant was cooled by passing cold water through an annulus surrounding the test section. Data were obtained in qualities of 0.1 ${\sim}$ 0.9 at mass flux of $200{\sim}400$ $kg/m^2s$ and heat flux of $7.3{\sim}7.7$ $kW/m^2$ at the saturation temperature of $4^{\circ}C$. All popular heat transfer correlations in single-phase subcooled liquid flow and flow condensation originally developed for large single tubes predicted the present data of the multi channel flat tube within 25% deviation when effective heat transfer area was used in determining experimental data. This suggests that there is little change in flow characteristics and patterns when the tube diameter is reduced down to 1.4 mm diameter range. Hence, a modified correlation based on the present data was proposed which could be applied to small diameter tubes with effective heat transfer area. The correlation showed a mean deviation of less than 20% for all data.

• Proceedings of the KIEE Conference
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• 1999.11b
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• pp.226-228
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• 1999

This paper presents a dynamic simulation algorithm for studying the effect of Unified Power Flow Controller(UPFC) on the low frequency power system oscillations and transient stability studies. The algorithm is a Newton-type one and gives a fast convergence characteristics. The algorithm is applied to inter-area power oscillation damping regulator design of a sample two-area power system. The results show that UPFC is very effective for damping inter-area oscillations.

• Proceedings of the KSME Conference
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• 2003.11a
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• pp.828-833
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• 2003

This work analyzes the effects of the independent variation of different geometric dimensions of compressor valves on the effective flow and force areas using a circular valve plate, such as different geometry of the valve seat, and the valve reed is opened and closed by pressure pulsation, the flow characteristic of the refrigerant passing the valve is very important. In the present study, a circular disk with inclination is assumed to be the valve reed of a reciprocating compressor and numerical analysis of three dimensional velocity fields are performed for theradial flow through the valve model. The effective flow and force area which are required to predict the efficiency of the valve are required to predict the efficiency of the valve are measured and compared with the numerical analysis in this research.

• Journal of Advanced Marine Engineering and Technology
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• v.25 no.1
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• pp.115-123
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• 2001

This study describes the combustion characteristics under various condition of air excess ratio and ignition timing in a 2-valve gasoline optically accessible engine with swirl control valve(SCV). It adapted three different types of SCA(open ration 72.5%, 78%, 89%) to strengthen a swirl flow. Pressure data were acquired using pressure sensor to investigate the effect of swirl flow on combustion, and from these pressure data, IMEP(indicated mean effective pressure) and MFB(mass fraction burnt)were calculated to explain burn rate and flame speed. From acquired flame images, inspected the flame propagation direction, flame area, and flame centroid, Flame propagation direction was shown different tendency between with/without SCV, and flame area with SCV was faster and larger than that of conventional engine. Finally, the representative flame image at each crank angle were acquired by PDF method to verify flame growth process. It is found that strengthened swirl flow is more beneficial for faster and stable combustion.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.1
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• pp.46-52
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• 2000

A computational analysis has been made on fluid flow in a regenerative cooling Passage for a reduced size liquid rocket engine to predict pressure drop and heat transfer rate in it. The contraction/expansion of the cross sectional area of the passage turn out to increases both the pressure loss and the heat transfer rate of the duct. The changes of the cross sectional area near the nozzle throat are effective to protect the throat which suffers from severe thermal load. Also given is the qualitative characteristics of the performance of the regenerative cooling system due to the variation of coolant flow rate.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.1331-1334
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• 2004

Wet/Dry phenomena typically incorporate a number of complex flow mechanism. These include a momentum transfer and turbulent mixing caused by the delivery of water. However currently available one dimensional schemes applicable to wet/dry process cannot effectively simulate such process. Two dimensional finite element model, SU/PG, is used to simulate complex flow in this study. The Wetted Area Method in SU/PG allows elements to transition gradually between wet and dry states. The model is applicable to a straight river reach with irregular bathymetry. Wet/dry calculation using the wetted area method can simulate simple numerical test. The computed results of velocity vectors and water depth agree with those of observed. The methodology Presented in this study will contributed to two-dimensional wet/dry analysis in a river in this country.

• Proceedings of the Korea Water Resources Association Conference
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• 2009.05a
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• pp.827-831
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• 2009

Recently, frequency occurring flood and drought has increased the necessity of an effective water resources control and management of river flows. Therefore, the simulation of the flow distribution in natural rivers is great importance to the solution of a wide variety of practical flow problems in water resources engineering. However The serious problem facing two-dimensional hydraulic model is the treatment of wet and dry areas. The objective of this study is to investigate the wet and dry parameters that have direct relevance to model performance in situations where inundation of initially dry areas occurs. Several numerical simulations were carried out, which examined the performance of the marsh porosity method for the purpose of sensitivity analysis. Experimental channel and a variety of channel were performed for model tests. The results were compared with those of the observation data and simulation data of existing model. The RMA-2 model displayed reasonable flow distribution compare to the observation data and simulation data of existing model in dry area for application of natural river flow. As a result of this study, effectively applied marsh porosity method provide a reliable results for flow distribution of wet and dry area, it could be further developed to basis for extending to water quality and sediment transport analysis.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.38 no.1
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• pp.45-52
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• 2001

The proximal isovelocity surface area (PISA) method is an effective way of measuring the regurgitant blood flow rate in the mitral valve. This method defines the modelling required to describe the geometry of the isotach of the PISA. In the normal PISA flow model, the flow rate is calculated assuming that the surface of the isotach is either hemispherical or non-hemispherical numerically. However, this paper evaluated the estimate flow rate using a direct surface subdivision flow model based on the height field after isotach extraction using a region-based scheme. To validate the proposed method, the various PISA flow models were compared using pusatile color Doppler images with flow rates ranging from $30\;cm^3/sec\;to\;60\;cm^3/sec$ flow rate. Whereas the hemispherical flow model had a mean value of $29\;cm^3/sec$ and underestimated the measured flow rate by 35%, the proposed model and non-hemispherical model produced a c;ame mean value of $45\;cm^3/sec$, moreover, both flow models produced a similar pulsatile flow rate.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.04a
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• pp.599-602
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• 2008

This paper deals with the optimization of Gas-Gas-Heater elements for desulfurization equipment through flow analysis. The flow analysis model used in the paper is ${\kappa}-{\varepsilon}$ turbulent flow model. Temperature and flow velocity distributions for three types of panel elements are calculated. Through the analysis the following conclusions are obtained. Firstly, pressure differences of between inlet and outlet for three types of panel elements do not exceed in the standard pressure difference. Secondly, it is expected that NU-type panel element having wide area of heat transfer will be more effective in the aspect of the heat transfer.