• International Journal of Air-Conditioning and Refrigeration
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• v.7
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• pp.11-21
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• 1999

The capillary tube and short tube orifice have been widely used as an expansion device in the refrigeration and air-conditioning system. To improve the system performance, expansion devices need to be optimized with the components of a refrigeration system. In the present study, a numerical model for a capillary, which could predict the flow rate and properties along a tube, was developed by assuming homogeneous two-phase flow. A semi-empirical flow model for evaluation of the flow rate through a short tube orifice was also developed by using the experimental data. Finally, the results of the numerical model for a capillary was compared with those of the semi-empirical model for a short tube orifice to identify the dominant flow factors for the expansion devices.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.1
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• pp.118-128
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• 1998

Capillary and short tube orifice have been widely used as an expansion device in refrigeration and air-conditioning system. To improve the system performance, expansion devices need to be optimized with the components of a refrigeration system. In the present study, a numerical model for a capillary, which can predict properties along a tube and flow rate through a tube, was developed by assuming homogeneous two-phase flow, A semi-empirical flow model that can be used to evaluate the flow rate through a short tube orifice was also developed by summarizing the experimental data. Finally, the results of the numerical model for capillaries were compared with those of the semi-empirical model for short tube orifices to verify dominant flow factors for the expansion devices.

• Journal of Power System Engineering
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• v.7 no.3
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• pp.69-73
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• 2003

In this paper, the relation between displacement of piezoelectric disk and electric field was proposed. From Navier-Stokes equation and Reynold's equation, the relation between flow and gap of plate was determined. This models were further verified by experiments. Based on theoretical study and experimental verification, the proposed model between flow rate and voltage can be used in the design of mass flow controller in gas supplying system.

• Proceedings of the KIEE Conference
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• 2000.11a
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• pp.13-16
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• 2000

Continuation power flow has been developed to remove the ill-condition problem caused by singularity of power flow Jacobian at and near steady-state voltage instability point in conventional power flow. When solving large-scale power transmission systems, continuation power flow require large computational costs. Therefore, technique to improve the speed of continuation power flow system was required. In this paper Decoupled Power Flow Method (DPFM), Enhanced Decoupled Power Flow Method (EDPFM), Robust Fast Decoupled Power Flow Method (RFDPFM) are applied to continuation power flow algorithm to improve the speed of continuation power flow system.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.4
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• pp.89-94
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• 2008

Differential pressure flow meters which have a shape of triangular separate bar(TSB) were tested for investigating the flow rate characteristics of the flow meters with varying the temperature of the gas flow. Three kinds of the triangular separate bar flow meters whose aerodynamic angles are different one another are used. The mass flow rate of the flow meters are evaluated using a non-dimensional parameter which includes the gas temperature, exhaust gas pressure and differential pressure at the flow meters, and atmospheric pressure. A burner system which is similar to gas turbine was used for raising the gas flow temperature. The burner system was operated with varying the air/fuel ratio by controlling both the fuel injection rate from the fuel nozzle and air flow rate from a blower. An empirical correlation between the mass flow rate at the TSB flow meter and the non-dimensional parameter was obtained. The empirical correlation showed linear relationship between the mass flow rate and the non-dimensional parameter H. Also, the mass flow rate characteristics at the TSB flow meter was affected by the gas temperature.

• The Journal of the Society of Korean Medicine Diagnostics
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• v.16 no.1
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• pp.19-26
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• 2012

Objectives The aim of this study is to develop a cardiovascular simulator that can reproduce blood pressure pulse and blood flow similar to those of the human body. Methods In order to design a system similar to the human cardiovascular system, the required performances were determined by investigating the hemodynamic characteristics of the heart and the arterial system. Main organ to be imitated is heart in simulator. The rest of the system was minimally designed. Also, a blood pressure and blood flow measurement system was developed for measuring the results. Results The developed system showed blood pressure pulse at similar range of the human aorta. The result waveform include primary wave caused by ventricular systole except reflected wave. Conclusions The blood pressure and blow flow patterns were replicated by the simulator. These patterns were similar to those of the human body. The system will play an important role in studying pulse diagnostics.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.6
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• pp.1861-1871
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• 1991

In this study, the piping system conveying unsteady flow is considered. The effects of coupling between the pipe motion and the velocity and pressure of fluid are included for the dynamic stability and response analysis of the piping system. The dynamic equations for a piping system are derived by Newtonian dynamics. For the momentum and continuity equations, the concept of moving control volume is applied. Thus, the governing equations derived herein are valid for the applications to the vibration problems occurred when a piping system starts up or shuts down and also when the valves and pumps operate. For a simply supported straight pipe, the stability analysis is conducted for various nondimensional parameters. The dynamic responses, in both stable and unstable region of stability chart, are numerically tested by the use of central difference method.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.10a
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• pp.458-462
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• 2004

The hydraulic system for discharging compressed gas is composed of compressor tank, proportional flow control servo valve, expulsion spool valve and discharging tube. Purpose of this study is to control of expulsion spool valve. First, we analyzed the hydraulic system. The flow control servo valve is modeled as a 2nd order transfer function and friction force of the expulsion spool valve is modeled as nonlinear model with stribeck effect. However, it is difficult to include the flow reaction force in modeling. So, we exchanged from the simplified flow reaction force of the compressed gas affection into the flow analysis code written in FORTRAN code. Our simulation of the oil pressure system for discharging gas used MATLAB/Simulink. So, we realized ＆apos;Level -2 S-Function Fortran＆apos; to cooperate for MATLAB/Simulink and FORTRAN code. PD controller is selected to control in this system. Simulation results show that with given conditions the controllers give a good tracking performance.

• Journal of Power System Engineering
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• v.16 no.5
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• pp.26-31
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• 2012

A numerical study has been carried out to investigate the heat and mass transfer of an oil pumping system with a variable shape of the housing using the CFD method. Especially, the electric motor and the pump combined together, accomplishes a research about the oil supplying system. In this study, the temperature and velocity distribution of the oil pumping system by varying the flow rate of supplying oil have been investigated. The temperature changes with each five conditions(flow rate of supply oil : 2, 4, 8, 12, and 16 liter/min) have also been studied. The numerical results show that the exhaust temperature decreases as the flow rate of the supplying oil increases. It also reveals that the temperatures change differently with the housing shape.

• Journal of the Korean Solar Energy Society
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• v.31 no.5
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• pp.140-145
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• 2011

In this study, the performance and behavior of solar heating system according to the system control scheme, variable flow control (proportional control) and constant flow control (on-off control) was carried out by experiment. The on-off control is used generally for solar thermal system by now. But the proportional control is used for the solar district heating system which is supplied the higher temperature of water than that of desired. The proportional control logic that pump speed is varied in an attempt to maintain a specified outlet temperature of solar heating system was developed and tested for the use widely for the small and medium solar thermal system. The results are as following. First, the proportional controller which is made here could be adopted the characteristics for setting temperature control. Second, the proportional control is better than the on-off control in the side of the performance of thermal stratification in storage tank. Third, the operating energy(electricity consumption by pump) of solar thermal system can be saved more than 60% using the proportional control comparing to the on-off control.