• 설비공학논문집
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• 제16권4호
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• pp.340-348
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• 2004

The air and refrigerant side heat transfer performances are key parameters to improve heat transfer efficiency of the heat exchanger including the fan performance. Design of the fins, treatment of the tube inside, tube diameter and tube array effect heat transfer performance of the heat exchanger. The heat exchanger is used as a condenser at cooling mode and used as an evaporator at heating mode in the heat pump system. The heat pump system uses R410A as the refrigerant. The heat exchangers are consisted with 7 mm diameter tubes with slit-type fins. The study was conducted with variation of arrangement of the refrigerant path and air flow rate and refrigerant pressure drop and heat transfer rate were measured with a code tester. The capacity of the 3 path heat exchanger is more efficient than 2 or 4 path heat exchangers in heating or cooling modes.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
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• pp.297-302
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• 2000

Pipe cooling method is widely used for reduction of hydration heat and control of cracking in mass concrete structures. However, in order to effectively apply pipe cooling systems to concrete structure, the coefficient of flow convection relating the thermal transfer between inner stream of pipe and concrete must be estimated. In this study, a device measuring the coefficient of flow convection is developed. Since a variation of thermal distribution caused by pipe cooling has a direct effect in internal forced flows, the developed testing device is based on the internal forced flow concept. Influencing factors on the coefficient of flow convection are mainly flow velocity, pipe diameter and thickness, and pipe material. finally a prediction model of the coefficient of flow convection is proposed using experimental results from the developed device. According to the proposed prediction model, the coefficient of flow convection increases with increase in flow velocity and decreases with increase in pipe diameter and thickness. Also, the coefficient of flow convection is largely affected by the type of pipe materials.

• Journal of Advanced Marine Engineering and Technology
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• 제23권1호
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• pp.47-53
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• 1999

Small compression-ignition direct injection engines have been developed as a measure to improve a fuel efficiency and reduce harmful exhaust gases. Those small engines generally employ high injection pressure increase on the spray impacting on a wall is discussed in this paper. The gas phase is modelled by the Eulerian continuum conservation equations of mass momentum energy and fuel vapour fraction. The liquid phases is modelled following the discrete droplet model approach in Lagrangian form and the droplet wall interaction is modelled as a func-tion of the velocity normal to impaction lands. The droplet distributions vapor fractions and gas flows are analyzed in various injection pres-sure cases. The penetrations of wall spray and vapor increase and the Sauter mean diameter decreases with increasing injection pressure.

• 대한기계학회논문집
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• 제18권5호
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• pp.1338-1346
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• 1994

The objective of this study is to investigate the effect of various parameters, such as temperature, mean current density and voltage on the performance of phosphoric acid fuel cell (PAFC) by numerical analysis. Two types of flow passages, which are Z-parallel type and Z-counter type, are evaluated to obtain the best current density and temperature distribution. Parametric studies and sensitivity analysis of the PAFC system's operation in single cell are accomplished. A steady state simulation of the entire system is developed using nonlinear ordinary differential equations. The finite difference method and trial and error procedures are used to obtain a solution.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2008년도 동계학술발표대회 논문집
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• pp.3-8
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• 2008

Effect of external heating rate on the conversion efficiency for the steam reforming of methanol is investigated numerically considering both heat and mass transfer of the species in a packed bed microreactor. In a results from the numerical simulation, the conversion efficiency of methanol has been obtained for the external heating rate. The axial variation of mole fraction of methanol has been additionally presented for several cases of external heating rates. The results show that for the constant inlet temperature condition the conversion efficiency of methanol increases with external heating rate over the range of operating conditions.

• 대한조선학회지
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• 제23권4호
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• pp.1-10
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• 1986

A container ship, due to wide hatch openings, has characteristics of poor torsional rigidity, strong coupling of horizontal-torsional modes and significant discontinuity in the longitudinal variation of hull sections. In the mathematical formulation of the problem the hull is modeled as a beam and the transfer matrix method is utilized. The cross decks between cargo hatch opening are separated from the main hull and regarded as equivalent springs restraining torsion of hull. The effect of shear deformation of ship-side plating on torsion is taken into account in addition to St. Venant's and bending torsional rigidities. Compatibility requirements at cross section discontinuity are approximately considered. Developing the practical calculation procedure and the computer programs for application to an actual ship, some parametric studies on modeling methods of the cross deck, the compatibility condition, added-mass center etc. are out for the purpose of comparison.

• 한국항공운항학회지
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• 제13권3호
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• pp.34-42
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• 2005

The objectives of the study are to present simple physical and mathematical models of liquid fuel in the tank of an aerospace vehicle such launch vehicle or missile and to investigate its dynamic stability for a parameter space. In this paper, liquid in the container is modeled as multi-mass system subject to parametric excitations, and a stability diagram for determination of stable-unstable regions of the motion is obtained by using an analytical method. Also, computer simulations are conducted at various parameter points to verify the analytical results, and time histories of motion are compared to explain the effect of variation of parameters of the system.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1998년도 추계학술대회 논문집 학회본부A
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• pp.91-93
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• 1998

This paper describes the braking performance of the eddy current brake for high speed trains according to the number of poles. The eddy current brake systems have to be equipped with the maximum braking force and deceleration in the given volume or mass, high braking force rate, as small normal forces as possible and stable construction. The parameters, such as the number of poles, electric ampere turns, slot width have influence on the braking force characteristics. In this paper, the effect of braking performance from the variation of the number poles is calculated by using FEM, the number of the pole which makes the maximum braking force is proposed.

• 한국소음진동공학회논문집
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• 제18권11호
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• pp.1170-1176
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• 2008

In this study, we propose a new method to control both the beat clarity and beat period in a ring structure. An equivalent ring which satisfies the measured mode condition is determined by using the equivalent ring theory. Theoretical analysis and finite element analysis on the equivalent ring are performed to investigate the effect of the local structural modification on the beat clarity and beat period. Beat clarity and period are improved by attaching asymmetric mass or decreasing local thickness. Through the analysis on the equivalent ring, the proper position and the amount of the local variation are determined to satisfy the required clarity and period condition. All the analysis results are compared and verified by the experiment.

• 수산해양기술연구
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• 제12권2호
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• pp.37-42
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• 1976

Each term of heat badget equation in the eastern Yellow Sea was calculated and the variation in relation to meteorological condition was shown for the period from September 1973 to February 1974, At Mal-do near Gunsan the maximum heat exchange occurred at the last ten days of December (--522 1y/day), while at Sunmi-do near Incheon it occurred at the middle ten days of November (--665 1y /day), The contribution of the sensible heat to total heat exchange increased rapidly, while the effect of cloudiness decreased to be negligible in winter. The values of the heat exchange fluctuated considerably with the periodic occurrence of the cold Siberiaa air mass. The mean evaporation heat estimated indirectly from the aerological data was 32 ly/day at the northern part and 269 ly/dlY at the southern part of the Yellow Sea in December 1973.