• KIEAE Journal
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• v.13 no.6
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• pp.93-98
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• 2013

The purpose of this study is to analyze the rate of opening windows that makes residents of a flat-type apartment feel pleasant in summer time. A few conditions were simulated on the wind flow that pass through internal and external spaces of the flat-type apartment, utilizing CFX program. The simulation was made with the criteria for the rates of opening window at 20%, 50%, 70% and 100%. When the rate of window opening was more 50%, the wind speed(more than 1m/s) that makes the residents feel pleasant was observed in more 60% of the internal space. When the all windows of the apartments were opened, the heat island phenomenon was almost disappeared and the pleasant wind flow was more evenly distributed in the external spaces. If residents of apartments recognize the result of this study and practice in agrement on opening windows in summer, it is expected to contribute to minimizing the energy consumption for air conditioning.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.1
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• pp.1-7
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• 2005

The heat transfer characteristics of an internal heat exchanger for $CO_2$ refrigeration cycle are numerically investigated. The numerical model is verified using the published experimental results for the concentric tube type internal heat exchanger. The Hardy-Cross Method gives very good agreement between the calculation and experimental results on the heat transfer rates and exit temperatures. Also, appropriate combination of heat transfer correlations is found. The operating parameters of the heat exchanger are calculated at transcritical region of $CO_2.$ The heat transfer rate of the counter flow type heat exchanger shows the $32\%$ greater than that of the parallel flow type heat exchanger. The increase of heat exchanger length enhances the heat transfer rate. The thermodynamic characteristics and heat transfer coefficient of $CO_2$ in the internal heat exchanger are estimated.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.27 no.4
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• pp.220-227
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• 2015

Complex thermal hydraulic characteristics exist inside the reactor because the reactor internals consist of fuel assembly, internal structures and so on. In this study, to examine the effect of Reynolds-Averaged Navier-Stokes (RANS)-based two-equation turbulence models in the analysis of flow distribution inside a 1/5 scaled-down APR+, simulation was performed using the commercial computational fluid dynamics software, ANSYS CFX R.13 and the predicted results were compared with the measured data. It was concluded that reactor internal flow pattern was locally different depending on the turbulence models. In addition, the prediction accuracy of k-${\varepsilon}$ model was superior to that of other two-equation turbulence models and this model predicted the relatively uniform distribution of core inlet flow rate.

• The KSFM Journal of Fluid Machinery
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• v.15 no.6
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• pp.25-30
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• 2012

Renewable energy has been interested because of fluctuation of oil price, depletion of fossil fuel resources and environmental impact. Amongst renewable energy resources, hydropower is most reliable and cost effective way. In this study, to develop a new type of micro hydro turbine which can be operated in the range of very low specific speed, a cross-flow hydro turbine with simple structure is proposed. The turbine is designed to be used at the very low specific speed range of hydropower resources, such as very high-head and considerably small-flow rate water resources. CFD analysis on the performance and internal flow characteristics of the turbine is conducted to obtain a practical data for the new design method of the turbine. Results show that optimized arrangement of guide vane angle and inner guide angle can give contribution to the turbine performance improvement.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.3
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• pp.311-317
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• 2016

This paper presents the flow characteristics of a ball valve used for a gas pipeline. Understanding of the internal flow of a ball valve is an important to analyze the physical phenomena of the valve. Present experimental study was performed by IEC 60534-2-3, the international standard for an industrial control valve testing procedure. Pressure measured at upstream and downstream of the valve, flow-rate and gas temperature passing the inside of the gas pipeline were measured with respect to valve opening rates. Throughout the experimental measurement of the ball valve, empirical equation of the pressure drop between the ball valve according to the mass flow rates is successively obtained using a polynomial curve fitting method. In addition, flow coefficient for determining the valve capacity is also analyzed with respect to valve opening rates using the curve fitting method.

• Journal of Korean Society of Industrial and Systems Engineering
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• v.38 no.3
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• pp.95-99
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• 2015

The IRR(internal rate of return) is often used by investors for the evaluation of engineering projects. Unfortunately, it has serial flaws: (1) multiple real-valued IRRs may arise; (2) complex-valued IRRs may arise; (3) the IRR is, in special cases, incompatible with the net present value (NPV) in accept/reject decisions. The efforts of management scientists and economists in providing a reliable project rate of return have generated over the decades an immense amount of contributions aiming to solve these shortcomings. Especially, multiple internal rate of returns (IRRs) have a fatal flaw when we decide to accep it or not. To solve it, some researchers came up with external rate of returns (ERRs) such as ARR (Average Rate of Return) or MIRR (MIRR, Modified Internal Rate of Return). ARR or MIRR. will also always yield the same decision for a engineering project consistent with the NPV criterion. The ERRs are to modify the procedure for computing the rate of return by making explicit and consistent assumptions about the interest rate at which intermediate receipts from projects may be invested. This reinvestment could be either in other projects or in the outside market. However, when we use traditional ERRs, a volume of capital investment is still unclear. Alternatively, the productive rate of return (PRR) can settle these problems. Generally, a rate of return is a profit on an investment over a period of time, expressed as a proportion of the original investment. The time period is typically the life of a project. The PRR is based on the full life of the engineering project. but has been annualised to project one year. And the PRR uses the effective investment instead of the original investment. This method requires that the cash flow of an engineering project must be separated into 'investment' and 'loss' to calculate the PRR value. In this paper, we proposed a tabulated form for easy calculation of the PRR by modifing the profit and loss statement, and the cash flow statement.

• Transactions of the Korean Society of Automotive Engineers
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• v.9 no.1
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• pp.84-93
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• 2001

The aim of this study is to provide fundamental informations that make it possible to use a cool stream and a hot stream simultaneously. We changed the pressure of compressed air that flows into a tube, the inner diameter of orifice that a cold stream exits, and the mass flow rate ratio. And in each case, we measured the temperature of a cold stream and a hot stream in each exit of a tube. Also we measured the axial temperature distribution and the radial temperature distribution in internal space of a tube. From the study, following conclusive remarks can be made. Average flow rate that flows into a tube is in proportion to square root of inlet pressure. As inlet pressure increases axial and radial temperature distribution in the inner space of vortex-tube increase. As mass flow rate ratio change, separation point moves.

• 제어로봇시스템학회:학술대회논문집
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• 1992.10b
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• pp.235-239
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• 1992

The paper describes an approach for estimating unsteady flow rate through oil hydraulic pipelines and components in real time. Recently we have proposed following three unsteady flow rate measurement approaches; RIFM, QIFM and TPFM, in which hydraulic pipeline dynamics are made use of. In this paper, we firstly propose new approaches, i.e, an interpolation and an extrapolation methods in combination with RIFM and TPFM. In the interpolation method, unsteady flow rate at the arbitrary internal location along the pipeline between two points for measuring the two point pressure can be estimated. In this paper, the accuracy and dynamic response of interpolation method are mainly experimentally investigated in detail.

• The Journal of Korean Medicine
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• v.18 no.1
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• pp.456-469
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• 1997

The cerebral infarction arised from occulsion of cerebral artery has a high mortality rate and fatal sequelae. Sohabhyangwon(蘇合香元) is generally regarded to have a effect of walking up the patient from unconsiousness and promoting the flow of Qj(氣) by warming channel. METHOD The purpose of this study is to find out the effections of Sohabhyangwon(蘇合香元) on regional cerebral blood flow and relative cerebral infarction area in the experimentally induced infartion in rats In this experiment, 12 Spraque-Dawley rats weighting 280-350g were used. Cerebral ischemia induced by intraluminal suture technique of Kozumi's and Zea-Longer's method. $Co_{2},\;O_2$, pH, arterial blood pressure in rats were checked by Blood Gas Analyzer every 30 minutes for 2 hours. And regional cerebral blood flow were checking by hydrogen clearance technique, cerebral infarcted area was megsured by Image Analysis System. RESULTS 1. During the experiment, $CO_{2},\;O_2$, pH, arterial blood pressure in rats had no change in both sample group and control group. 2. Cortical cerebral blood flow decreased at same rate in both sample group and control group after inducing cerebral infarction. 3. On comparison of relative cerebral infarcted area, Sohabhyangwon(蘇合香元) perfused group showed a significant decrease. CONCLUSION According to the result above, Sohabhyangwon has a protection effect on cranial nerve and-has no effect on cerebral blood flow.

• Journal of Korean Society on Water Environment
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• v.26 no.1
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• pp.81-88
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• 2010

This study was conducted to find the capability of comparison of overall oxygen transfer coefficient in the membrane coupled high performance reactor (MPHCR) in treating high organic loading wastewater. Effluent quality had been analyzed while the influent organic loading rate was changed from 2 to $7kg\;COD/m^3{\cdot}day$. The oxygen transfer coefficients had been investigated using two-phase nozzle for operating variables which were internal circulation flowrate (5~8 L/min), air flow rate (0.0125~0.2 L/min), liquid temperature ($10{\sim}20^{\circ}C$), and pure-oxygen flow rate (0.0125~0.2 L/min). The overall oxygen transfer coefficient was increased with flowrate of internal circulation and air and high temperature. Especially, internal circulation flow rate showed distinct effect on overall oxygen transfer coefficient due to an increase of gas holdup and air-liquid contract area by two-phase nozzle. In the high range of organic loading rate from 4 to $7kg\;COD/m^3{\cdot}day$, the removable efficiency of COD was 91%. Conventional activated sludge process usually treat organic loading from 0.32 to $0.64kg\;COD/m^3{\cdot}day$ however, the MPHCR can treat 10 to 20 times higher if it would be compared to the conventional activated sludge process. Foaming problem often happened and caused biomass wash out of the reactor, therefore, the foaming should be controlled for the enhanced operation.