• Journal of Mechanical Science and Technology
• /
• v.18 no.6
• /
• pp.979-989
• /
• 2004

Numerical simulations have been performed to investigate tip clearance effect on through-flow and performance of a centrifugal compressor which has the same configuration of impeller with six different tip clearances. Secondary flow and loss distribution have been surveyed to understand the flow mechanism due to the tip clearance. Tip leakage flow strongly interacts with mainstream flow and considerably changes the secondary flow and the loss distribution inside the impeller passage. A method has been described to quantitatively estimate the tip clearance effect on the performance drop and the efficiency drop. The tip clearance has caused specific work reduction and additional entropy generation. The former, which is called inviscid loss, is independent of any internal loss and the latter, which is called viscous loss, is dependent on every loss in the flow passage. Two components equally affected the performance drop as the tip clearances were small, while the efficiency drop was influenced by the viscous component alone. The additional entropy generation was modeled with all the kinetic energy of the tip leakage flow. Therefore, the present paper can provide how to quantitatively estimate the tip clearance effect on the performance and efficiency.

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.65 no.11
• /
• pp.1919-1924
• /
• 2016

In general, Diode rectifier has been applied to DC traction power supply system. Diode has some characteristics which is voltage drop in inverse proportion of load because of non-controlled switch, and cannot flow a current in reverse bias. So, voltage drop occurs frequently, and regenerated power cannot use in substation. The PWM rectifier is able to control output voltage constantly to reduce voltage drop and to use regeneration power without additional inverter. This paper proposes analysis algorithm for DC traction power supply system with PWM rectifier.

• The Transactions of the Korean Institute of Electrical Engineers P
• /
• v.67 no.3
• /
• pp.155-159
• /
• 2018

Recently, the expansion or establishment of facilities for the logistics system is increasing. Conveyor facilities play a major role in sorting and transporting logistics. Induction motors are widely used for the operation of these conveyor systems. In the logistics system, a large number of induction motors are used. These motors have a considerable distance from the power source side and have a low power factor. The installation position for the power factor compensation of the induction motor is very important. Since the voltage drop depends on the length of the line, it is an important parameter in capacitor capacity determination for power factor compensation. The capacity of the capacitors installed to compensate the power factor of the inductive load should be designed to the extent that self-excitation does not occur. In this study, we analyze the method of compensating the proper power factor considering the voltage drop and the installation position of the induction motor in the logistics system.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.33 no.7B
• /
• pp.528-537
• /
• 2008

This paper proposes a dynamic job distribution algorithm in a hybrid NoC structure which can improve system network performance by reducing deadlock and packet drop rate for various multimedia applications. The proposed job distribution algorithm schedules every job to the sub-cluster where packet drop rate can be minimized for each multimedia application program. The proposed Job distribution algorithm and network topology targets multimedia applications frequently used in modern embedded systems, such as MPEG4 and MP3 decoder, GPS positioning system, and OFDM demodulator. Experimental results show that packet drop rate was reduced by about 13.0%, and chip area was increased by about 2.7% compared to the APSRA algorithm. When compared to the XY algorithm popularly used for benchmarking, the packet drop rate was reduced by about 23.9%, while chip area was increased by about 3.0%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.19 no.9
• /
• pp.622-629
• /
• 2007

Compact semi-center type automotive air handling system(AHS) is developed in this study and it's performance is compared with the conventional 3-pieces type air hand-ling system. The pressure drop is measured at component level and system level, and air flow rate and air distribution of discharge air through each ducts from air handling system are measured. System level characteristics of pressure drop at face and windshield discharge mode and air flow rate are investigated, and also temperature control linearities are tested. The volume of the air handling system package is reduced about 20%. And air flow rate increase about 5 to 20% compared to the conventional 3-pieces type air handling system at each discharge mode with significantly improved air pressure drop both component and system level. Also, air distribution and temperature controllability meet to evaluation criteria.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2012.10a
• /
• pp.769-770
• /
• 2012

• Journal of the Korean Society for Precision Engineering
• /
• v.34 no.3
• /
• pp.167-172
• /
• 2017

This study proposes a method for identifying correlations between tension and drop height for sessile droplets in a roll-to-roll processing system. The effect of tension and drop height on the contact angle of a sessile droplet is presented. Design of experiment (DOE) methodology and statistical analysis are used to define a correlation between the process parameters. The contact angle is decreased while increasing tension and drop height. The influence of the tension is less significant on the contact angle compared with the effect of the drop height. However, tension should be considered as a major parameter because it is not easy to fix with roll eccentricity and compensating speed of the driven roll. The results of this study show that the effect of tension on the contact angle of a sessile droplet is more important than drop height because the drop height is fixed when the process systems are determined.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.23 no.3
• /
• pp.237-242
• /
• 2014

Recently much research are has been done into the compositions of lead-free solders. As a result, there has been a rapid increase in the number of new compositions. In the past, the properties of these new compositions were determined and verified through drop-impact tests. However, these drop tests were expensive and it took a long time to obtain a result. The main goal of this study was to establish an analytical method capable of predicting the impact life-time of a new solder composition for board-level flip chips though the application of drop simulations using LS-DYNA. Based on the reaction load obtain with LS-DYNA, the drop-impact fracture cycles were predicted. The study was performed using a Sn-3.0Ag-0.5Cu solder (305 composition). To verify the reliability of the proposed analytical method, the results of the drop-impact tests and life-time analysis were compared, and were found to be in good agreement. Thus, the new analytical method was shown to be very useful and effective.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.8
• /
• pp.1021-1029
• /
• 2001

Rapid prototyping(RP) is a novel technology to create 3D products directly from CAD system. This study proposes a new RP method which uses the PZT ceramic plate to make a Drop-On-Demand liquid jet from the nozzle. The characteristic of drop formation in the new system is investigated both numerically and experimentally. The optimal drop for 3-D Printing can be obtained by the proper amplitude and frequency of the applied voltage. Also the process of the drop formation is analyzed using the pressure wave theory and verified by numerical simulation. First, the pressure wave generated by the deformation of the Piezo-plate at the nozzle is analyzed by solving the 2D axisymmetric wave equation via Finite Element Method. Finally, the drop formation process is simulated using a commercial software, FLOW 3D considering the pressure at the nozzle obtained by solving the wave equation as the boundary condition.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.13 no.10
• /
• pp.930-938
• /
• 2001

In this study, evaporation pressure drop experiments were conducted with two types of plate and shell heat exchangers (P&SHE) using R-22. An experimental refrigerant loop has been established to measure the evaporation pressure drop of R-22 in a vertical P&SHE. The flow channels were formed by adding three plates having a corrugated channel of a chevron angle of $45^{\circ}$. The R-22 flows down in one channel exchanging heat with the hot water flowing up in the other channel. The effect of the refrigerant mass flux, average heat flux, system pressure and vapor quality were explored in detail. During the experiment, the quality change between the inlet and outlet of the refrigerant channel ranges from 0.03 to 0.15. The present data showed that two types of P&SHE have similar trends. The pressure drop increases with the vapor quality for both types of P&SHE. At a higher mass flux, the pressure drop is higher for the entire range of the vapor quality. Also, the increase in the average heat flux increases the pressure drop. Finally, at a higher system pressure, the pressure drop is found to be slightly lower.