• Proceedings of the Korea Concrete Institute Conference
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• 2000.04a
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• pp.645-650
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• 2000

In the prestressed concrete structures, the effective prestressing force of tendon is basically most important item for structural safety and serviceability. The frictional loss is one of the major items for determinating the effective prestressing force and depend on the construction accuracy of the structures. In this thesis, it will be analyzed and found through measured hydraulic jack pressure, tendon elongation and prestressing control system that the tendancy of apparent curvature friction coefficient, the ratio of jacking force and required prestressing force, the ratio of initial jacking force and required prestressing force and compatibility of specified friction loss coefficient. The specified control limit for curvature friction coefficient of prestressing control system is about 0.25 and wobble friction coefficient 0.005. Thus, the control limit should be modified according to changed vale of friction coefficient.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11a
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• pp.282-287
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• 2001

The test facility has been manufactured to predict the dynamic insertion loss and the pressure drop for ducted silencers based on ISO 7235. The qualification test of the test facility is necessary for determining the dynamic insertion loss and the pressure drop of the test silencer, and is surveyed the reflection coefficient for an anechoic termination, the velocity profile near the upstream connection to the test silencer, the reduction of the system silencer and the limiting insertion loss due to the flanking sound transmission along the duct walls.

• Journal of Drive and Control
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• v.12 no.4
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• pp.48-53
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• 2015

This paper deals with the flow characteristics of a reed valve analyzed using computational dynamics(CFD) for optimal design. The seat sizes of the valve are modeled asØ6[mm] and Ø8[mm] to compare the flow characteristics. The inlet boundary condition is entered at 10[kPa], 15[kPa], 20[kPa], and 30[kPa] and the outlet boundary condition is set to the atmospheric pressure. The flow coefficient(C) and pressure loss coefficient(K) are calculated from the results of flow analysis. From the analysis results, it was confirmed that the flow coefficient of a reed valve having a seat size of Ø6[mm] is greater than that having a seat size of Ø8[mm], and the coefficient of pressure loss of a valve with a seat size of Ø6[mm] is lower than the Ø8[mm] size valve.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.8 no.4
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• pp.550-560
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• 1996

Recently, fluidized bed heat exchangers with circulating liquid are widely used in a number of places-chemical, process, food concentration, waste water treatment facilities, etc. In a circulating heat exchanger, solid particles circulate with the liquid, thereby increase the heat transfer and reduce the fouling potential of the heat exchanger. In this study, glass beads were circulated through a vertical tube. The pressure loss and the heat transfer coefficient were measured. At low flow velocities, glass beads enhanced the heat transfer considerably. The enhancement increased as the volume fraction of the glass beads increased. The pressure loss showed a similar trend. From the observed particle behavior near tube wall, a possible explanation of the trend is provided.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1996.04a
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• pp.121-131
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• 1996

Recently, circulating liquid fluidized bed heat exchangers are widely used in a number of places - chemical, process, food concentration, waste water treatment facilities, etc. In a circulating heat exchanger, solid particles circulate with the liquid, thereby increase the heat transfer and reduce the fouling potential of the heat exchanger. In this study, glass beads were circulated through a vertical tube. The pressure loss and the heat transfer coefficient were measured. At low flow velocities, glass beads enhanced the heat transfer considerably. The enhancement increased as the volume fraction of the glass beads increased. It also increased as the particle diameter increased. The pressure loss showed a similar trend. From the observed particle behavior near tube wall, a possible explanation of the trend is provided.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.240-243
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• 2008

In this paper, the design of Centrifugal Compressor which is used in sizes 50 horse power has 8 pressure ratio and numerical analysis of the flow within compressor varying tip clearance length are performed. To get high pressure ratio with low power the exit height of impellers is low but compressor has very high speed of revolution. So compressor has high specific speed although mass flow rate is very small. The shape of impellers at the first stage is carried out. Flow and performance characteristics of impellers has been analyzed by using a commercial CFD program, $Fine^{TM}$/turbo. The result shows that loss coefficient is affected by tip clearance length and compressor has proper tip clearance length. It is possible to decrease loss by selecting apt tip clearance length.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.7
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• pp.366-372
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• 2017

The objective of this study was to characterize Waveguide-Blow-Cutoff (WBC) array for Electromagnetic Pulse (EMP) shield in air duct or water pipe, the typical pathway of pulse in indoor space with critical electronic device. A numerical investigation with three different WBC designs (circular, rectangular, and hexagonal or honeycomb) was conducted to satisfy recommended shielding effectiveness (SE) levels from 80 dB to 140 dB. Pressure drop between upstream and downstream of EMP shields based on WBC arrays was also investigated to understand air flow feature in air duct of HVAC system. Results showed that honeycomb geometry outperformed other shapes in terms of reducing the depth of EMP shield, thus providing better air flow in duct path with lower local loss coefficient in HVAC system under SE requirements.

• Journal of the Korean Solar Energy Society
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• v.39 no.6
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• pp.27-40
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• 2019

Kitchen hoods are limited in discharging all contaminants produced during cooking. Contaminants that have not been discharged can rise to the upper part of the kitchen and become stacked. To solve this problem, there is a way to increase the air volume of the kitchen hood, but there are limits, so a new system is required. This study proposes the Duct System (IADK : Inducing Airflow Duct system for Kitchen hood )through 3D printers and experiments. To do this, the pressure is measured to verify the three levels of air volume provided by the kitchen hood. To check the degree of loss of flow in the existing kitchen hood system, install flexible ducts alone to measure the pressure. Change the internal diameter and type of connection of the IADK and measure the pressure. The air pressure, static pressure difference, and loss factor are calculated and analyzed using the pressure measured through the experiment.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.2
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• pp.115-120
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• 2014

To enhance the performance of an automobile turbocharger compressor, the circumferential inlet heights of the volute were modified and the flow field for the combined region of the diffuser and volute was numerically investigated using commercial software. Basically, a well-designed volute should have a high pressure recovery coefficient and a low loss coefficient for the total pressure. In this study, two circular volutes with the same cross sectional shape and tongue angle, but circumferentially different volute inlet heights, were selected. One volute had the middle inlet in the cross-section at the circumferential angle of $90^{\circ}$ but gradually lower inlet heights for the angles between $90^{\circ}$ to $360^{\circ}$ with respect to the cross sectional center of the volute, while maintaining the same height between the tangential line connecting the lowest positions of the cross section and the line connecting the volute inlets in the circumferential direction (case 1 volute). The other volute has an inlet height that is 2 mm lower than in case 1 volute such that the tongue section has a tangential inlet (case 2 volute). The results showed that the case 2 volute had a higher total pressure ratio because of its higher pressure recovery coefficient and higher isentropic efficiency, resulting from the lower loss coefficient along the circumferential position than the case 1 volute.

• Applied Chemistry for Engineering
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• v.29 no.6
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• pp.789-798
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• 2018

The role of empirical equation to predict the performance of polymer electrolyte membrane fuel cell is important. The activation, ohmic and mass transfer losses were separated in a polarization curve, and the curve fitting according to each region was performed using Kim's model and Hao's model. Changes of each loss were compared according to operation variables of the temperature, pressure, oxygen concentration and membrane thickness. The existing model showed a good fitting convergence, but less fitting accuracy in the separated loss region. A new model using the convergence coefficient was suggested to improve the accuracy of performance prediction of fuel cells of which results were demonstrated.