• Journal of Mechanical Science and Technology
• /
• v.15 no.1
• /
• pp.98-107
• /
• 2001

Continuing efforts to achieve increased circuit performance in electronic package have resulted in higher power density at chip and module level. As a result, the thermal management of electronic package has been important in maintaining or improving the reliability of the component. An experimental investigation of thermosyphonic boiling in vertical tube and channel made by two parallel rectangular plates was carried out in this study for possible application of the direct immersion cooling. Fluorinert FC-72 as a working fluid was used in this experiment. Asymmetric heated channel of open periphery with gap size of 1, 2, 4 and 26mm and uniformly heated vertical tubes with diameter of 9, 15 and 20mm were boiled at saturated condition. The boiling curves from tested surfaces exhibited the boiling hysteresis. It was also found that the gap size is not a significant parameter for the thermosyphonic boiling heat transfer with this Fluorinert. Rather pool boiling characteristics appeared for larger gap size and tube diameter. The heat transfer coefficients measured were also compared with the calculation results by Chens correlation.

• Journal of the Korean Society for Aviation and Aeronautics
• /
• v.11 no.1
• /
• pp.41-55
• /
• 2003

A calibration jet system using separate blower is developed to calibrate a flow sensor effectively. Designed open circuit type mini calibration jet system, which has the dimension of $0.5m(W){\times}1.17m(H)$ is small compared with conventional calibration jet systems. The exit of nozzle has exchangeable contractions with a cross section area of $38.5cm^2$ , and a cross section area of $113.1cm^2$, respectively. The ranges of wind speed at exit of exchangeable nozzles are $7.5{\sim}42\;m/s$ and $1.8{\sim}16.5\;m/s$, respectively. The input power for the high pressure blower is 1.18kW. The turning vanes for corner was rolled flat plate parallel to the flow direction. The flow conditioning screen was located immediately downstream of the wide-angle diffuser. The honeycomb and two flow conditioning screens were located in the stagnation chamber. From the economical point of view and the simplicity of the calibration jet system set up and handling, it can be said that the developed calibration jet system is an effective calibration jet system. This system can also be used to calibrate the flow sensor with high resolution.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.15 no.6
• /
• pp.540-547
• /
• 2004

In this paper, a current - mode class D(CMCD) power amplifier over 70 % power added efficiency at 900 ㎒ is designed and implemented. Based on push-pull class B structure, main power loss due to charge and discharge of output capacitance in switching mode power amplifier is minimized by applying a parallel harmonic control circuit. Experimental CMCD amplifier with 73 % power added efficiency at 3.2 W and 72 % power added efficiency at 5 W are achieved respectively. In addition a characteristic of switching mode power amplifier whose output power is proportional to magnitude of U power is verified.

• Proceedings of the KIEE Conference
• /
• 1998.07f
• /
• pp.2067-2069
• /
• 1998

A prototype semiconductor switch for the command resonant charging system has been developed for a line type modulator, which charges parallel pulse forming network(PFN) up to voltage of 5 kV at repetition rates of 60 Hz. A phase controlled power supply provides charging of the 4.7 ${\mu}s$ filter capacitor bank to voltage up to 5 kV. A solid state module of series stack array of sixe matched SCRs(1.6 kV, 50 A) is used as a command charging switch to initiate the resonant charging cycle. Both resistive and RC snubber network are used across each stage of the switch assembly in order to ensure proper voltage division during both steady state and transient condition. A master trigger signal is generated to trigger circuits which are transmitted through pulse transformer to each of the 6 series switch stages. A pulse transformer is required for high voltage trigger or power isolation. This paper will discuss trigger method, protection scheme, circuit simulation, and test result.

• International Journal of Air-Conditioning and Refrigeration
• /
• v.6
• /
• pp.148-157
• /
• 1998

This study presents test results of a residential window air-conditioner using R22 and two potential alternative refrigerants, R407C and R410B. A series of performance tests has been carried out for the basic and liquid-suction heat exchange cycles in a psychometric calorimeter test facility. For R407C, the same rotary compressor was used as in the R22 system. However, compressor for the R410B system was modified to provide the similar cooling capacity. The evaporator circuit was changed to get a counter-cross flow heat exchanger to take advantage of zeotropic mixture's temperature glide, and liquid-suction heat exchange cycle was also considered to improve the system performance. Test results were compared with those for the basic R22 system. The modified system with a liquid-suction heat exchanger increased cooling capacity and energy efficiency by up to 5%.

• Proceedings of the IEEK Conference
• /
• 2002.07c
• /
• pp.1535-1538
• /
• 2002

The flexibility of content addressable mem-ory (CAM) can greatly be extended through the use of trits (ternary digits) Trits consist of binary logical values “0” and “1” with addition of “x” (“dont’t care”). The “dont’t care“is extremely useful for providing com- pact representation of sets of bit strings. In this paper, we propose a new ternary CAM with Hamming distance search functions. Each memory cell in the CAM consists of a pair of lambda diodes which can store trits, namely, a logical “0”, “1” and “x” (“dont’t care“). The CAM can compare stored data and an input data in parallel, and find stored data with Hamming distance within a certain range (“near match“). Also, the interrogation characteristics of the ternary CAM are analyzed in detail. Furthermore, the results obtained these analyses are fully confirmed by simulation using the circuit analysis program HSPICE.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.37 no.5
• /
• pp.33-41
• /
• 2000

In this paper, a symmetric QMSA(Quarter-wavelength Microstrip Antenna) loading a capacitor to spread the electric flux lines is proposed. It was found that the bandwidth of this symmetric QMSA is broader than that of the asymmetric QMSA having a right-side Parallel plate only to load a capacitor. It was also found that this antenna could receive both vertically and horizontally polarized waves at 2.13GHz, and would be useful as a small antenna for wireless telephones and for indoor communication. A transmission line circuit model of this antenna was obtained and used to compute the resonant frequency and the return loss of the antenna accurately.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.8 no.7
• /
• pp.1506-1511
• /
• 2004

The error control of digital transmission system is a very important subject because of the noise effects, which is very sensitive to transmission performance of the digital communication system It employs a modified Euclid's algorithm to compute the error-location polynomial and error-magnitude polynomial of input data. The circuit size is reduced by selecting the Modified Euclid's Algorithm with one Euclid Cell of mutual operation. And the operation speed of Decoder is improved by using ROM and parallel structure. The proposed Encoder and Decoder are simulated with ModelSim and Active-HDL and synthesized with Synopsys. We can see that this chip is implemented on Xilinx Virtex2 XC2V3000. A share of slice is 28%. nut speed of this paper is 45Mhz.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.31 no.7
• /
• pp.515-520
• /
• 2018

A large number of lithium-ion batteries are arranged in series and parallel in battery packs, such as those in electric vehicles or energy storage systems. As battery packs age, their output power and energy density drop because of voltage deviation, constant and non-uniform exposure to abnormal environments, and increased contact resistance between batteries; this reduces application system efficiency. Despite the balancing circuit and logic of the battery management system, the output of the battery pack is concentrated in the most severely aged unit cell and the output is frequently limited by power derating. In this study, we implemented a cell imbalance detection algorithm and selected parameters to detect a sudden decrease in battery pack output. In addition, we propose a method to increase efficiency by applying the measured testing values considering the operating conditions and abnormal conditions of the battery pack.

• Journal of Power Electronics
• /
• v.1 no.2
• /
• pp.78-87
• /
• 2001

A new high-power step-up based on the two-module parallel-input (PISO) modular dual inductor-fed push-pull converter is proposed. The proposed converter is operated at a constant duty cycle and employs and auxiliary circuit to control the output voltage with a phase-shift between two modules. It shows a high efficiency due to the greatly reduced switch turn-off stress. It also shows a high and linear voltage conversion ratio, low current stress in the output capacitor, and fast control-to-output dynamics. The operation principles and the mathematical models of the proposed converter are presented. Features of the proposed converter are discussed in comparison with the two-module PISO modular dual inductor-fed push-pull converter. Also, experimental results from a 50kHz, 800W, 350 Vdc prototype with an input voltage range of 20-32 Vdc are provided to confirm the validity of the proposed converter. The new converter compares favorably with the conventional counterpart, and is considered well siuted to high-power step-up applications.