• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.781-788
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• 2003

In the present study, the heat and flow characteristics of a parallel-flow heat exchanger are numerically analyzed by using three-dimensional turbulent modeling. Heat transfer rate and pressure drop are evaluated using the concept of the efficiency index by varying the locations, the shapes and angles of inlet/outlet, and the protrusion height of flat tube. It is found that negative angle of the inlet improves the heat transfer rate and pressure drop. Results show that the locations of the inlet and outlet should be toward the right side and the left side to the reference model, respectively, in order to enhance the heat transfer rate and pressure drop. Increasing the height of the lower header causes pressure drop to decrease and yields the good flow characteristics. The lower protrusion height of flat tube shows the improvement of the heat transfer rate and pressure drop. The heat transfer rate is greatly affected by the parameters of outlet side such as the location and angle of the outlet. However, the pressure drop is influenced by the parameters of inlet side such as the location and angle of inlet and the height of the header.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.186-193
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• 2001

In the high pressure state, the leakage flow rate of hydraulics is one of serious problems and the great reason to decrease the volume efficiency. In this paper, I tried to clarify tribology characteristics for the slipper hydrostatic bearing in swash plate type axial piston pumps and motors by means of experiment . I measured the leakage flow rate between swash plate and piston shoe with change the supply pressure and oil temperature at a swash plate angle of 0。 . And I also investigated the slipper pocket pressure and calculated oil film thickness for theoretical method. So. 1 have analyzed the tribology characteristics of hydrostatic bearing for leakage flow rate and oil film thickness with oil temperature and supply pressure.

• Journal of Korean Public Health Nursing
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• v.19 no.1
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• pp.5-17
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• 2005

This research was conducted to determine the actual condition of obesity and obese students' total cholesterol. blood glucose and blood pressure, and to analyze the relationship between the obesity rate and total cholesterol. blood glucose and blood pressure among the students at 7 middle schools in A city in Kyoung ki-do. The results were as follows: 1. Among 12,148 student participants in this investigation. students of normal weight range were $91.5\%$ and obese students were $8.5\%$, breaking down to mildly obese of $4.3\%$ $(boys,\;5.4\%;\;girls,\;3.0\%)$. moderately obese of $3.4\% (boys,\;4.6\%;\;girls,\;2.1\%)$ and severely obese of $0.7\%(boys,\;0.9\%;\;girls,\;0.5\%)$, The gender difference was statistically significant $(x^2=111.5830. p=.0001). 2. To analyze the 1.027 obese students. the average of total cholesterol was 166.9mg/dl, 171.0mg/dl and 182.1mg/dl in the mild, moderate and severe obesity groups, respectively. The results became more significant with increasing obesity rate (F=10.06, p=.0001). The average of systolic blood pressure (SBP) was 121.9mmHg, 123.2mm, and 127.5mm, respectively. The results became more significant with increasing obesity rate (F=6.29, p=.0019). The average of diastolic blood pressure (DBP) was 74.4mmHg. 76.0mmHg. and 78.4mmHg, respectively. The results became more significant with increasing obesity rate (F=8.15. p=.0003). The average of blood glucose was 83.3mg/dl, 84.5mg/dl, and 82.3mg/dl, respectively. There was no significant difference with obesity rate. 3. There were significant correlations between obesity rate and cholesterol(r=.11288, p=.0003), between obesity rate and DBP(r=.14209, p=.000l). and between obesity rate and SBP(r=.14081. p=.0001). However, there was no significant correlation between obesity rate and blood glucose (r=.00655, p=.8339).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.10 no.7
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• pp.1433-1438
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• 2009

The purpose of this study is to investigate how the ignition spark timing conversion influences the engine performance of LPG/Gasoline Bi-Fuel engine. We propose the control system which can advance the ignition spark timing in LPG fuel mode more than used in gasoline fuel mode. In order to investigate the engine performance during combustion, engine performance are sampled by data acquisition system, for example cylinder pressure, pressure rise rate and heat release rate, while change of the rpm(1500, 2000) and the ignition timing advance($5^{\circ}$,$10^{\circ}$,$15^{\circ}$,$20^{\circ}$) As the result, between 1500rpm and 2000rpm, the cylinder pressure and pressure rise rate was increased when the spark ignition was advanced but pressure rise rate at $20^{\circ}$was smaller value. Also, the heat release rate at 1500rpm was increased but it was lower around $20^{\circ}$at 2000rpm.

• Electrical & Electronic Materials
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• v.9 no.2
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• pp.188-195
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• 1996

The AlSi etching process using the MERIE type reactor carried out with different process parameters such as C1$_{2}$ and N$_{2}$ gas flow rate, RF power and chamber pressure. The etching characteristics were evaluated in terms of etch rate, selectivity, uniformity and etched profile. As the N2 gas flow rate is increased, the AlSi etch rate is decreased and uniformity has remained constant within .+-.5%. The etch rate is increased and uniformity is decreased, according to increment of the C1$_{2}$ gas flow rate, RF power and chamber pressure. Selective etching of TEOS with respect to AlSi is decreased as the RF power is increased while it is increased by increment of the C1$_{2}$ gas flow rate and chamber pressure, on the other hand, selective etching of photoresist with respect to AlSi is increased by increment of the C1$_{2}$ gas flow rate and chamber pressure, it is decreased as the N$_{2}$ gas flow rate is increased.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 1999.10a
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• pp.411-416
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• 1999

The measurement of unsteady flow rate is of vital importance to clarify and improve the dynamic characteristics in pipeline, hydraulic components and system. There is also demand for a real time flow sensor of ability to measure unsteady flow rate with high accuracy and fast response to realize feedback control of flow rate in fluid power systems. In this paper, we propose an approach for estimating unsteady flow rate through a pipeline and components under high pressure condition. In the method, unsteady flow rate is estimated by using hydraulic pipeline dynamics and the measured pressure values at two distant points along the pipeline. The distributed parameter model of hydraulic pipeline is applied with consideration of frequency dependent viscosity friction and unsteady velocity distribution at a cross section of a pipeline. By using the self-checking functions of the method, the validity is investigated by comparison with the measured and estimated pressure waveforms at the halfway section on the pipeline. The results show good agreement between the estimated flow rate waveforms and theroetical those under unsteady laminar flow conditions. the method proposed here is useful in estimating unsteady flow rate through an arbitray cross section in hydraulic pipeline and components without installing an instantaneous flowmeter.

• Journal of the Korean Home Economics Association
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• v.36 no.6
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• pp.85-94
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• 1998

In this study we tested the physiological influence on human-body according to clothing pressure with reduction rate and varied posture using three kinds of belt with different width. The width of belts were 2.5cm, 3.5cm and 4.5cm, and reduction rates of belts were 0%, 2.5% and 5% of the subject/s waist size respectively. the measured postures were standing state and sitting stste in the chair. The reasults are as follows; 1. Clothing pressure was high in the order of Side part>Front part>Back part and the rate fo change in the side part was highest, according to the reductio rate of belts. The more the width of belt was wide, the less the clothing pressure was small, and this kind of phenomenon could be explained by "The Principle of the power". 2. Both the rate of reduction of belt and the change of average skin temperature in accordance with the width of belt is small, however, the more the width of belts is wider and the reduction rate is bigger, the more the skin temperature at the waist part is increased. 3. The blood pressure and pulse was influenced when the width of belt was narrow and the reduction rate was high. 4. A sense restraining was much influenced by the width of belt, especially when the width of belts was wide, the significant difference was permitted.permitted.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2007.04a
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• pp.152-156
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• 2007

It is very important to understand about mass flow rate variations of propellants generated by pressure fluctuation in the combustion chamber. Therefore, we have studied quantifying the variation of mass flow rate generated by pressure fluctuation. The flow velocity in orifice is acquired through theoretical approach after measuring the pressure in orifice and the flow area in orifice is measured by film thickness measuring device. Our results agreed with it in the very small error range comparing our results with velocity and mass flow rate in steady state. Thus, our result based on theoretical approach will help about measuring mass flow rate in non-steady state.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.10a
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• pp.191-191
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• 2003

It is well-known that the mechanical behavior of fiber-reinforced composites under hydrostatic pressure environment is different from that of atmospheric pressure environment. It is also known that the mechanical behavior of fiber-reinforced composites is affected by strain rate. In this work, we investigated the effect of strain rate on the compressional elastic modulus and fracture stress of fiber-reinforced composites under hydrostatic pressure environment. The material used in the compressional test was unidirectional carbon/epoxy composites and the hydrostatic pressures applied was 250 MPa. Compressional tests were performed applying various strain rates of 0.05 %/sec, 0.25 %/sec, 0.45 %/sec, and 0.75 %/sec. The results showed that the elastic modulus increased with increasing strain rate while the fracture stress was little affected by the strain rate.

• Journal of Biosystems Engineering
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• v.25 no.1
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• pp.11-18
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• 2000

In precision chemical application increment of biological efficacy with less chemical is the virtue. spraying rate and droplet size is closely related to biological efficacy. this study was performed to develope a spray-control-system that could control spraying rate and droplet size independently. Twin-fluid nozzles were selected and tested to certify if the nozzles were suitable for the objective of this study. Characteritics of the nozzles i.e., spraying rte and droplet size change u8nder the changes of spraying pressure and air pressure were statistically modeled. The model had I to 1 matching property between dependent variables and independent variables. Using the property and the model, inverse relationship could be determined between variables. A feedback spray control system was developed and tested with predetermined error of 5 % in pressure. The system showed 4 % error in spraying rate and 9 % error in droplets size. Performance of the system could be upgraded by fine tuning but, in practical sense keeping air pressure in the field sprayer was the bottle neck of commercialization of the spray system.