• Journal of Fisheries and Marine Sciences Education
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• v.6 no.1
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• pp.58-76
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• 1994

Heat transfer and pressure drop measurements are made on low integral-fin tubes in turbulent water flow condition. The integral-fin tubes investigated in this paper are nominally 19mm in diameter. Eight tubes have been used with trapezoidally shaped integral-fins having fin density from 748 to 1654 fpm and 10, 30 grooves. Plain tube having same diameter as finned tube is also tested for comparison. Experiments are carried out using R-11 as working fluid. The refrigerant condensates at a saturation state of $30^{\circ}C$ on the outside tube surface cooled by coolant. The amount of noncondensable gases present in the test loop is reduced to a negligible value by repeated purging. For a given heat input to the boiler and given cooling water flow rate, all test data are taken on steady state. The heat transfer loop is used for testing single long tubes and cooling water is pumped from a storage tank through filters and flowmeters to the horizontal test section where it is heated by steam condensing on the outside of the tube. The pressure drop across the test section is measured by means of pressure gauge and manometer. Each tube tested is cleaned with sodium dichromate pickling solution and well rinsed with water prior to installation in the test section. The results obtained in this study is as follows : 1. Based on inside diameter and nominal inside area, heat transfer of finned tube is enhanced up to 4 times as that of a plain tube at constant Reynolds number and up to 2 times at constant pumping power. 2. Friction factors are up to 1.6~2.1 times those of plain tube. 3. At a given Reynolds number, Nusselt number decrease with increasing pitch to diameter. 4. The constant pumping power ratio for low integral-fin tubes increase directly with the effective area to the nominal area ratio, and with the effective area diameter ratio.

• Journal of Korea Water Resources Association
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• v.54 no.spc1
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• pp.1023-1035
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• 2021

The electricity cost of a desalination facility was also predicted and reviewed, which allowed the proposed model to be incorporated into the future design of such facilities. Input data from 2003 to 2014 of the Korea Hydrographic and Oceanographic Agency (KHOA) were used, and the structure of the model was determined using the trial and error method to analyze as well as hyperparameters such as salinity and seawater temperature. The future seawater quality was estimated by optimizing the prediction model based on machine learning. Results indicated that the seawater temperature would be similar to the existing pattern, and salinity showed a gradual decrease in the maximum value from the past measurement data. Therefore, it was reviewed that the electricity cost for seawater desalination decreased by approximately 0.80% and a process configuration was determined to be necessary. This study aimed at establishing a machine-learning-based prediction model to predict future water quality changes, reviewed the impact on the scale of seawater desalination facilities, and suggested alternatives.

• Korean Journal of Agricultural Science
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• v.48 no.4
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• pp.1027-1037
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• 2021

This study aims to evaluate the performance of an electric multi-purpose cultivator through a simulation analysis. The simulation model was developed using commercial software, Simulation X, by applying the specifications of certain parts, such as an electric motor, a battery, and so on. The input parameter of the simulation was the engine load data according to the rotary tillage level using a conventional multi-purpose cultivator. The data were collected by configuring a load measurement system, and the load cycle was developed by repeating the data collection process under the most severe conditions. The average output engine torque values of conventional multi-purpose cultivator were 10.7, 13.0, 9.4, and 11.2 Nm in the D1P1, D1P2, D2P1, and D2P2 conditions, respectively. As a result of the simulation, the maximum values of the motor torque, rotational speed, and power of the electric multi-purpose cultivator were 16.8 Nm, 2,033.3 rpm, and 3.3 kW, respectively, and the motor was driven in sections within 70, 68, and 45% of the maximum output range. The rate of decrease of the battery state of charge (SOC) level per minute was approximately 0.6%, and it was possible to supply electric power to the motor for 9,550 sec. In the future study, research to verify and improve simulation models of electric multi-purpose cultivators should be conducted.

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.6
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• pp.85-96
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• 2000

It is necessary that fully differential operational amplifier circuit should drive an external load in the VLSI design such as SCF(Switched Capacitor Filter), D/A Converter, A/D Converter, Telecommunication Circuit and etc. The conventional CMOS operational amplifier circuit has many problems according to CMOS technique. Firstly, Capacity of large loads are not able to operate well. The problem can be solve to use class AB stages. But large loads are operate a difficult, because an element of existing CMOS has a quadratic functional relation with input and output voltage versus output current. Secondly, Whole circuit of dynamic range decrease, because a range of input and output voltages go down according as increasing of intergration rate drop supply voltage. The problem can be improved by employing fully differential operational amplifier using differential output stage with wide output swing. In this paper, we proposed new current mirror has large output impedance and good current matching with input an output current and compared with characteristics for operational amplifier using cascoded current mirror. To obtain large output swing and low power consumption we suggest a fully differential operational amplifier. The circuit employs an output stage composed new current mirror and two amplifier stage. The proposed circuit is layout and circuit of capability is inspected through simulation program(SPICE3f).

• Journal of radiological science and technology
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• v.35 no.2
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• pp.109-117
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• 2012

The purpose of this work was to evaluate an amorphous silicon cesium iodide based indirect flat-panel detector (FPD) in terms of their modulation transfer function (MTF), Wiener spectrum (WS, or noise power spectrum, NPS), and detective quantum efficiency (DQE). Measurements were made on flat-panel detector using the International Electrotechnical Commission (IEC) defined RQA3, RQA5, RQA7, and RQA9 radiographic technique. The MTFs of the systems were measured using an edge method. The WS(NPS) of the systems were determined for a range of exposure levels by two-dimensional (2D). Fourier analysis of uniformly exposed radiographs. The DQEs were assessed from the measured MTF, WS(NPS), exposure, and estimated ideal signal-to-noise ratios. Characteristic curve in the RQA3 showed difference in the characteristic curve from RQA5, RQA7, RQA9. MTFs were not differences according to x-ray beam quality. WS(NPS) was reduced with increasing dose, and RQA 3, RQA5, RQA7, RQA9 as the order is reduced. DQE represented the best in the 1mR, RQA 3, RQA5, RQA7, RQA9 decrease in the order. The physical imaging characteristics of FPD may also differ from input beam quality. This study gives an initial motivation that the physical imaging characteristics of FPD is an important issue for the right use of digital radiography system.

• The Journal of Bigdata
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• v.8 no.2
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• pp.165-175
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• 2023

LNG is a representative imported cargo at Incheon Port and has a relatively high contribution to the increase/decrease in overall cargo volume at Incheon Port. In addition, in the view point of nationwide, LNG is the one of the most important key resource to supply the gas and generate electricity. Thus, it is very essential to identify the factors that have impact on the demand fluctuation and build the appropriate forecasting model, which present the basic information to make balance between supply and demand of LNG and establish the plan for power generation. In this study, different to previous research based on macroscopic annual data, the weekly demand of LNG is converted from the cargo volume unloaded by LNG carriers. We have identified the periodicity and correlations among internal and external factors of demand variability. We have identified the input factors for predicting the LNG demand such as seasonality of weekly cargo volume, the peak power demand, and the reserved capacity of power supply. In addition, in order to predict LNG demand, considering the characteristics of the data, time series prediction with weekly LNG cargo volume as a dependent variable and prediction through an artificial neural network model were made, the suitability of the predictions was verified, and the optimal model was established through error comparison between performance and estimates.

• The Proceedings of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.11 no.4
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• pp.82-91
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• 1997

In this paper, a design method of the boiler-turbine control system in the coal fired power plant is proposed. We need to control electric output and drum pressure and water level in drum to guarantee stable operation and save energy for generating electricity and decrease air pollution in the boiler-turbine system. This boiler-turbine control system is composed of reference model part and model following part. The multivariable boiler-turbine system is separated into 3 SISO(Single Input Single Output) systems applying the concept of relative gain matrix. Each 3 reference models for separated boiler-turbine system are composed of 1st order nominal plant and hysteresis integral control system and they make good dy¬namic response with no overshoot and fast rising time. Each fuzzy controller to follow as close as possible to the response of each reference model is designed. The robustness and the good tracking property can be achieved using 5150 fuzzy controllers when there are modeling errors, disturbances and parameter pertur¬bations. The effectiveness of the proposed design method is verified through simulations.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.8 no.5
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• pp.1134-1140
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• 2004

In this paper, we investigated the effect of cross phase modulation(XPM) on compensation for WDM channel distortion due to chromatic dispersion, self phase modulation and XPM as a function of fiber dispersion coefficient and modulation format in 320 Gbps WDM systems. The considered WDM transmission system is based on mid-span spectral inversion(MSSI) compensation method, which has highly nonlinear dispersion shifted fiber(HNL-DSF) as nonlinear medium of optical phase conjugator (OPC) in the mid-way of total transmission line. We confirmed that the maximum channel input power resulting 1 dB eye opening penalty is reduced due to XPM effect on channel distortion, even if MSSI method was applied to WDM system. But, we confirmed that the effect of XPM on channel distortion becomes decrease as fiber dispersion coefficient of WDM system becomes larger. Futhermore, we confirmed that NRZ is better than RZ as a modulation format for similarly compensating overall WDM channels in WDM system with large fiber dispersion coefficient in order to minimize the effect of the XPM on channel distortion.

• Journal of IKEEE
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• v.17 no.3
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• pp.275-283
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• 2013

In this paper, a 8bit 10Ms/s CMOS Folding and Interpolation analog-to-digital convertor is proposed. The architecture of the proposed ADC is based on a Folding & Interpolation using FR(Folding Rate)=8, NFB(Number of Folding Block)=4, IR(Interpolation Rate)=8. The proposed ADC adopts a preamplifier sharing method to decrease the number of preamplifier by half comparing to the conventional ones. This chip has been fabricated with a 0.35[um] CMOS technology. The effective chip area is $1.8[mm]{\times}2.11[mm]$ and it consumes 20[mA] at 3.3 power supply with 10[MHz] clock. The INL is -0.57, +0.61 [LSB] and DNL is -0.4, +0.51 [LSB]. The SFDR is 48.9[dB] and SNDR is 47.9[dB](ENOB 7.6b) when the input frequency is 100[kHz] at 10[MHz] conversion rate.

• Journal of IKEEE
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• v.14 no.2
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• pp.82-89
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• 2010

In this paper, a buck-boost converter using three DTMOS(Dynamic Threshold Voltage MOSFET) switching devices is presented. The efficiency of the proposed converter is higher than that of conventional buck-boost converter. DTMOS with low on-resistance is designed to decrease conduction loss. The threshold voltage of DTMOS drops as the gate voltage increases, resulting in a much higher current handling capability than standard MOSFET. In order to improve the power efficiency at the high current level, the proposed converter is controlled with PWM(pulse width modulation) method. The converter has maximum output current 300mA, input voltage 3.3V, output voltage from 700mV to 12V, 1.2MHz oscillation frequency, and maximum efficiency 90%. Moreover, the LDO(low drop-out) is designed to increase the converting efficiency at the standby mode below 1mA.