• Journal of Power Electronics
• /
• v.7 no.4
• /
• pp.286-293
• /
• 2007

This paper proposes a distribution voltage control method when a voltage increase condition occurs due to reverse power flow from the clustered photovoltaic (PV) system. This proposed distribution voltage control is performed a by distribution-unified power flow controller (D-UPFC). D-UPFC consists of a hi-directional ac-ac converter and transformer. It does not use any energy storage component or rectifier circuit, but it directly converts ac to ac. The distribution model and D-UPFC voltage control using the ATP-EMTP program were simulated and the results show the voltage increase control in the distribution system.

• Journal of Korea Water Resources Association
• /
• v.32 no.3
• /
• pp.265-279
• /
• 1999

In this study, one of the techniques on the extension of low flow series has been developed, in which the daily streamflows were simulated by the Tank model with the input of extended daily rainfall series which were stochastically generated by the Markov chain model. The annual lowest flow serried for each of the given durations were formulated form the simulated daily streamflow sequences. The frequency of the estimated annual lowest flow series was analyzed. The distribution types to be used for the frequency analysis were two-parameter and three-parameter log-normal distribution, two-parameter and three-parameter Gamma distribution, three-parameter log-Gamma distribution, Gumbel distribution, and Weibull distribution, of which parameters were estimated by the moment method and the maximum likelihood method. The goodness-of-fit test for probability distribution is evaluated by the Kolmogorov-Sminrov test. The fitted distribution function for each duration series is applied to frequency analysis for developing duration-low flow-frequency curves at Yongdam Dam station. It was shown that the purposed technique in this study is available to generate the daily streamflow series with fair accuracy and useful to determine the probabilistic low flow in the watersheds having the poor historic records of low flow series.

• 한국신재생에너지학회:학술대회논문집
• /
• 2007.06a
• /
• pp.172-175
• /
• 2007

The Performance of a PEMFC stack is strongly dependent on the uniform reactants distribution on MEA. The uniform distribution can be achieved by flow-field pattern and manifold design optimized to satisfy operating conditions. This paper investigates uniform reactants distribution in channels by changing manifold shape and inlet mass flow rate. Typical U and Z shape and modified U and Z shape manifolds with buffer zone were designed. To check the uniform reactants distribution, standard deviation of mass flow rate was compared. The numerical results show that the inlet mass flow rate, inlet shape, and manifolds shape are critical factor for uniform distribution.

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

A header is the device that makes uniform flow distribution in all branches from header of heat exchangers, pipe burner or chemical equipments. In this study, experimental tests have been performed in order to investigate the flow distribution characteristics in a straight header and tapered header which have 6 and 11 glass pipe branches. The experimental equipment consists of a water circulation system where the fluid velocity in each glass pipe is measured by Ar-ion LDV system. From the experiments and the theoretical equation, it could be recommended that tapered header should be determined so that its internal velocities inside the header become uniform according to taper of the header and number of attached branches for uniform flow distribution in energy systems.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.21 no.3
• /
• pp.176-185
• /
• 2009

A general flow distribution model and a simple process of numerical analysis, which can be applied to multi-pass systems with manifolds, are presented. A numerical procedure, namely a modified equal pressure method based on the discrete model, was developed to predict flow rates at branch tubes. The predicted pressure distribution agreed well with the previous research with the average error less than 11%. A parametric study was performed to demonstrate the effect on the flow distribution.

• Journal of Korean Society of Water and Wastewater
• /
• v.26 no.3
• /
• pp.423-430
• /
• 2012

This study was conducted to qualify the equality of the flow distribution from open channel between rapid mixing basin and flocculation basins in a domestic S_ water treatment plant, and to suggest a remedy for improving the equality. In order to evaluate the feasibility of the suggested remedy, computational fluid dynamics (CFD) technique are used, and for verifying the CFD simulation results tracer tests were carried out. From the results of CFD simulation and tracer tests, it was investigated that the modification of hydraulic structure in the distribution channel, which is to install the longitudinal orifice baffle in flow direction, could improve the equality of the flow distribution over 75%.

• Geomechanics and Engineering
• /
• v.14 no.2
• /
• pp.187-193
• /
• 2018

Water inrush through the destruction of water resisting rock mass structure was divided into direct water inrush, key block water inrush and splitting water inrush. In the direct water inrush, the Reynolds numbers has a significant effect on the distribution of the water flow and vortex occurred in the large Reynolds numbers. The permeability coefficient of the fracture is much larger than the rock, and the difference is between 104 and 107 times. The traditional theory and methods are not considering the effect of inertia force. In the position of the cross fracture, the distribution of water flow can only be linearly distributed according to the fracture opening degree. With the increase of Reynolds number, the relationship between water flow distribution and fracture opening is studied by Semtex.

• Journal of the Korean Society of Visualization
• /
• v.19 no.2
• /
• pp.32-40
• /
• 2021

Vapor-driven solutal Marangoni flow is governed by the concentration distribution of solutes on a liquid-gas interface. Typically, the flow structure is investigated by particle image velocimetry (PIV). However, to develop a theoretical model or to explain the working mechanism, the concentration distribution of solutes at the interface should be known. However, it is difficult to achieve the concentration profile theoretically and experimentally. In this paper, to find the concentration distribution of solutes around 2D droplet, the reverse tracking method with an artificial neural network based on PIV data was performed. Using the method, the concentration distribution of solutes around a 2D droplet was estimated for actual flow data from PIV experiment.

• Journal of the Korean Society of Industry Convergence
• /
• v.24 no.5
• /
• pp.617-623
• /
• 2021

The objective of this study is to simulate valve flow coefficient and flow characteristics such as velocity and pressure distribution for butterfly valve. The size of the valve used in this study is 125A. The range of the valve opening angle was α=15°~70°, and it was changed by 5°. At the range of α=15°~30°, the valve flow coefficient K_𝜐 gradually increased, and after α=30°, it increased rapidly. In the range of α=20°~70°, the pressure change in the -2.9cm~+2.9cm region in the pipe greatly depended on the opening angle and the position within the pipe. However, after +2.9cm, the pressure at the rear end of the valve was shown to depend only on the opening angle. At α=20°, Vortex shedding occurred for the first time at time t=0.25sec and continuously occurred in rear end of the valve over time. After α=45°, in the flow pattern at the rear end of the valve, the upward flow at the lower end of the valve and the flow at the upper end met each other to form a mixed flow. This flow phenomenon was shown to form a more intense mixed flow in the rear end region as the opening angle increased. Vortex flow occurred for the first time at α=15°, and the opening angle increased, the occurrence and disappearance of this flow phenomenon occurred periodically according to the certain flow region. The pattern of the pressure distribution in the region at the rear end of the valve showed a tendency to agree well with the results of the vorticity distribution.

• Journal of Mechanical Science and Technology
• /
• v.20 no.5
• /
• pp.717-727
• /
• 2006

The present study experimentally investigated the effect of flow direction and other flow parameters on two-phase flow distribution of refrigerants at a T-junction, and also suggested a prediction model for refrigerant in a T-junction by modifying previous model for air-water flow. R-22, R-134a, and R-410A were used as test refrigerants. As geometric parameters, the direction of the inlet or branch tube and the tube diameter ratio of branch to inlet tube were chosen. The measured data were compared with the values predicted by the models developed for air-water or steam-water mixture in the literature. We propose a modified model for application to the reduced T-junction and vertical tube orientation. Among the geometric parameters, the branch tube direction showed the biggest sensitivity to the mass flow rate ratio for the gas phase, while the inlet quality showed the biggest sensitivity to the mass flow rate ratio among the inlet flow parameters.