• Journal of the Korean Society of Visualization
• /
• v.4 no.2
• /
• pp.76-80
• /
• 2006

The data for friction factor of the pipe correlated by Reynolds number and relative roughness have been reported well as a Moody chart. However, the results for corrugated shapes have been not investigated sufficiently. In this research, therefore, the pressure drop and friction factor are obtained. Flexible metal tubes with corrugations for the measurement are made of stainless steel plates. The kinds of tubes for the measurement are 5 annular types and helical types. The pressure drop & the velocity of the flow are obtained by micromanometer & digital pressure sensor, supplying dry air at several steps. Then the pressure drop is calculated for each tube, using the obtained data. The result shows that the pressure drop is strongly influenced by the viscous dissipation of kinetic energy due to the circulation of flows, rather than a viscous friction loss. The pressure drop increased consistently as the Reynolds number increases.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.14 no.4
• /
• pp.94-100
• /
• 2006

The purpose of this case study is to determine the possibility of Numerical Forecasting of sea fog at West Sea in spring time. For practical method of analyzing the data collected from 24th to 26th March 2003, Numerical Weather Prediction model MM5(Mesoscale Model Version 5) and synoptic field study using synoptic chart, upper level chart, and sea surface temperature were employed. The results of synoptic field analysis summarized that sea fog at West sea in spring is intensified by the inflow of the warm flow from west or southwest, low sea surface temperature to increase the temperature difference between air and sea surface, and inversion layer to disturb the disperse. It appears that the possibility of sea fog forecasting by MM5, in view of the result that the MM5 output is similar to the synoptic fields analysis.

• International Journal of Air-Conditioning and Refrigeration
• /
• v.11 no.4
• /
• pp.178-187
• /
• 2003

In this study, ventilation flow rate and pressure rise through a tunnel are simulated numerically using computational fluid dynamics (CFD) for various conditions such as roughness height of the surface of tunnel, swirl angle and hub/tip ratio of jet fan, and entrance and exit effects. By using a modified wall function, friction factor can be predicted with respect to the Moody chart within 10% of error for the circular pipe flow and 15% for the present tunnel. For more accurate design, the effect of the swirl angle and hub/tip ratio of jet fan, which is not included in the theoretical equation of pressure rise by jet fan needs to be considered.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.16 no.10
• /
• pp.895-900
• /
• 2004

With the phaseout of CFC and HCFC refrigerants, refrigeration and heat pump systems must be redesigned to match and improve system performance with alternative refrigerants. A generalized flow model for predicting mass flow rate through short tube orifices is derived from a power law form of dimensionless parameters generated by Pi-theorem. The database for developing the correlation includes extensive experimental data for R12, R22, R134a, R407C, R410A, and R502 from the open literature. The correlation yields an average deviation of $0.3\%$ and a standard deviation of $6.1\%$ based on the present database. In addition, rating charts for predicting refrigerant flow rate through short tube orifices are generated for R12, R22, R134a, R407C, R410A, and R502.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.5 no.1
• /
• pp.66-73
• /
• 2010

The curriculum of programming education including algorithm has been recognized as a very important subject to many students majoring in natural sciences and engineering including electronic engineering and computer related departments. However, many students have had difficulties with it due to its characteristics; as a consequence, they have been in trouble taking upper-level subjects. Flow chart is a diagram that expresses logical stages necessary to solve certain problems and has been widely used to have an understanding of the flow of algorithm. The practice-oriented education of algorithm and programming would be very important to assist the understanding of operation processes. Furthermore, it has been desperately required to the necessity of auxiliary programs that could enhance an understanding of the concept of algorithm and program execution process. This study was aimed to design and embody the learning system of programming languages using basic algorithms so as for students to easily learn basic algorithm among the entire programming curriculum.

• Proceedings of the SAREK Conference
• /
• 2008.11a
• /
• pp.157-164
• /
• 2008

The temperature-entropy diagram of water or vapor displays graphically the thermophysical properties, so it is very conveniently used in various thermal systems. On general T-s chart of water, there are temperature, pressure, quality, specific volume, specific enthalpy, specific entropy. However, various state and process values besides above properties can be plotted on T-s diagram. In this study, we developed the software drawing twenty six kinds of properties, that is temperature, pressure, quality, specific volume, specific internal energy, specific enthalpy, specific entropy, specific exergy, exergy ratio, density, isobaric specific heat, isochoric specific heat, ratio of specific heat, coefficient of viscosity, kinematic coefficient of viscosity, thermal conductivity, prandtl number, ion product, static dielectric constant, isentropic exponent, velocity of sound, joule-thomson coefficient, pressure coefficient, volumetric coefficient of expansion, isentropic compressibility, and isothermal compressibility. Also, this software can analyze and print the system values of mass flow rate, volume flow rate, internal energy flow rate, enthalpy flow rate, entropy flow rate, exergy flow rate, heat flow rate, power output, power efficiency, and reversible work. Additionally, this software support the functions such as MS-Power Point.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.14 no.7
• /
• pp.567-574
• /
• 2002

In the present study, ventilation flow rates and pressure rises through a road tunnel are simulated numerically using CFD with the various conditions such as roughness height, swirl angle of jet fan, entrance and exit effect and hub to tip ratio. By using a modified wall function, friction factor can be predicted under 10％ of error with respect to the Moody chart for the circular pipe flow and 15％, for the present tunnel. For more precise design, the effects of the swirl angle and hub to tip ratio of jet fan, which is not included in the theoretical equation of pressure rise by jet fan are necessary to be considered.

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

• Journal of Advanced Marine Engineering and Technology
• /
• v.40 no.8
• /
• pp.698-703
• /
• 2016

Francis hydro turbines have been most widely used throughout the world because of their wide range of head and flow rate applications. In most applications, they are used for high heads and flow rates. Currently, Korea is developing technology for Francis hydro turbine design and manufacture. In order to understand the internal details of Francis hydro turbines further, a new Francis turbine model runner is designed and model internal flow characteristics are investigated. The specific speed of the Francis hydro turbine model runner is $Ns=200m-kW-min^{-1}$. The runner blade is designed successfully according to the port area and one-dimensional loss analysis. The best efficiency point of the Francis hydro turbine model achieves 90% at the design condition. CFD analysis yields a hill chart of the Francis hydro turbine model for use in predicting performance.

• Proceedings of the KIEE Conference
• /
• 2003.11a
• /
• pp.432-434
• /
• 2003

This paper developed the web based power flow program for education. Since a lot of users can connect and implement the web based program, the only one computer can get much evaluation burden not to compute. Using the XML technology, which supports the distributed computing technology, we have developed the web-based power flow software and system that are distributed the above calculation burden to three computers: web server, database server, application server. Also, this software was developed to get the difference of number of iteration and evaluation speed as veil as the results of state variables for each node according to the each calculation method for power flow using the chart. Therefore, users can get the physical concept of power flow in addition to the difference among the evaluation methods for power flow. We have performed the case studies with IEEE 14 bus system using the developed software.