• Proceedings of the KSR Conference
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• 2011.10a
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• pp.158-164
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• 2011

When a train passes a conventiaonl tunnel at high speed, external pressure variation problem arises. It is known that this issue can be reduced by control the tunnel length. We studied the variances of external pressure variation within the tunnel, by altering length of the dummy tunnel duct. We also studies the variances of micro-pressure waves at the exit of tunnel, by altering surface area of dummy tunnel duct. For analyzing this train-tunnel relation problem, axisymmetric steady compressible flow solver was used.

• Journal of computational fluids engineering
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• v.12 no.2
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• pp.46-52
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• 2007

An experimental and numerical investigation of the ejector-jets focusing on its geometric parameters that effect on thrust performance was carried out. The area ratio of the primary nozzle that was tested in the present study was 2.17 and 3.18, while the ratio of the length to the diameter of the duct downstream the primary nozzle inlet had values of 3.41, 6.82, and 10.23. Internal flow properties of ejector-jet were estimated by comparison experiment data and CFD analysis for basic study of ejector-jet thrust performance. For examination of thrust performance, the thrust ratios increased with increase in L/D. Especially at AR=2.17, the maximum thrust augmentation was 33 percent for the shortest L/D. It is expected that the increase of mixing duct length of ejector-jet will be helpful in a thrust performance by improving mixing efficiency.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.166-170
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• 2007

An experimental and numerical investigation of the ejector-jets focusing on its geometric parameters that effect on thrust performance was carried out. The area ratio of the primary nozzle that was tested in the present studywas 2.17 and 3.18, while the ratio of the length to the diameter of the duct downstream the primary nozzle inlet had values of 3.41, 6.82, and 10.23. Internal flow properties of ejector-jet were estimated by comparison experiment data and CFD analysis for basic study of ejector-jet thrust performance. For examination of thrust performance, the thrust ratios increased with increase in L/D. Especially at AR=2.17, the maximum thrust augmentation was 34 percent for the shortest L/D. It is expected that the increase of mixing duct length of ejector-jet will be helpful in a thrust performance by improving mixing efficiency.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.2
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• pp.17-23
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• 2000

Experimental investigations were conducted to study the forced convection of fully-developed turbulent flow in horizontal equilateral duct fabricated with the same length and equivalent diameter, but different surface roughness pitch ratio(P/e) of 4, 8 and 16 on the one side wall only. The experiments were performed with the hydraulic diameter based Reynolds number ranged from 70,000 to 10,000. The entire bottom wall of the duct was heated uniformly and the other surfaces were thermally insulated. To understand the mechanisms of the heat transfer enhancement, measurements of the heat transfer were done to investigate the contributive factor of heat transfer promotion, namely, the fin effect. And the results were compared with those of previous investigations for similarly configured channels, at which they were roughened by regularly spaced transverse ribs in the rectangular and circular channels.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.65-70
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• 2000

Experimental investigations were conducted to study the forced convection of fully-developed turbulent f)on· in horizontal equilateral duct fabricated with the same length and equivalent diameter, but different surface roughness Pitch ratio(P/e) of 4, 8 and 16 on the one side wall only The experiments were performed with the hydraulic diameter based Reynolds number ranged from 70.000 to 10,000 The entire bottom wall of the duct was heated uniformly and the other surfaces were thermally insulated. To understand the mechanisms of the heat transfer enhancement. measurements of the heat transfer were done to investigate the contributive factor of heat transfer promotion. namely the fin effect. And the results were compared with those of Previous investigations for similarly configured channels, at which they were roughened by regularly spaced transverse ribs in the rectangular and circular channels.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.7
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• pp.557-562
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• 2003

Flue gas from apartment heating gas boiler is exhausted outside through an exhaust duct mounted horizontally in a vertical row on the wall. The flue gas includes nitrogen-oxides (NOx) and carbon monoxide. To investigate the possible entrainment of the flue gas into the apartments through the windows, a large eddy simulation (LES) based numerical method is utilized. Distribution of the velocity intensity and temperature around the exhaust ducts is presented for three numerical parameters: exhaust velocity, temperature of the flue gas, and exhaust duct length. The flow field visualized with particles inserted at the ends of the ducts is also presented. The results clearly show that the exhausted flue gas may flow into the apartments when the windows are open.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.20 no.1
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• pp.91-102
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• 1990

The aim of this study was to establish the diagnostic criteria of normal parotid glands in adults revealing the anatomical shape, its variations and the postitional relationships of the gland. Materials included 96 lateral and anterior-posterior sialograms of selected person from 23 to 28 years of age. Results were as follows: 1. The average length and lateral displacement of main duct was 48.43㎜ and l6.88㎜. The mean lumen diameter of that was 0.91㎜ in distal end and 1.40㎜ in hilar end in parotid glands. 2. The average angle of main duct to the inferior border of mandib was 34.32 degree. In configurations of main duct, modified curvilinear type was. most prevalent and followed by curvilinear, reverse sigmoid, sigmoid type. 3. The mean caliber of parotid gland was the longest in superior-inferior. 4. The interlobar ducts showed relatively well defined in all cases, its average number was 5.72. Arrangement of these ducts showed at random. Accessory lobe showed 87.5% in the all cases, its average number was 1.7. 5. There were no difference between the well and poorly defined acinar fillings in the glandular parenchyme. 6. There were no differences between right and left parotid glands in size and shape of main duct and parenchymal portion, but there were great variations in each individuals.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.13 no.1
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• pp.127-137
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• 1983

The aim of this study was to establish the diagnostic criteria of normal submandibular glands in adults. Materials included 132 sialograms of selected person from 23 to 28 years of age. In subjects each variable was measured and evaluated statistically introducing 18 items respectively. Conclusions from this study were as follows. 1. The mean diameter of main duct was 1.96㎜ in distal end and 2.71㎜ in hilar end, so the diameter of distal end was smaller than that of hilar end in submandibular glands. 2. The mean length of main duct was 42.02㎜ in submandibular glands. 3. The mean angle of main duct was 35.67 degrees with inferior border of mandible and 103.05 degrees at posterior mylohyoid portion. 4. In configurations following shape of main duct, those revealed that 39.39% of cases of the curvilinear type, 16.67% of cases of the linear type, 22.73% of cases of the sigmiod type and 21.21% of cases of the angular type. And in configurations following course of main duct, those revealed that 83.33% of cases of the smooth type and 16.67% of cases of the tortuous type. 5. The mean caliber of submandibular glands was 45.59㎜ in superoinferior height, 43.56㎜ in anteroposterior width, 28.85㎜ in mediolateral width and 33.65㎜ in extent below mandibular angle. 6. Well-delineated acinar parenchyme was observed in 77.28% of cases and well-defined tertiary ducts in 50.06% of cases. 7. There were no differences between right and left submandibular glands in size and shape of main duct and parenchymal portion, but there were great variations in each individual.

• Journal of the Institute of Convergence Signal Processing
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• v.22 no.3
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• pp.116-121
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• 2021

A lot of research is being done to develop a high-efficiency heat pump to save energy, and research to reduce or eliminate the phenomenon of frost occurring in the outdoor unit coil is also being conducted at the same time. A curved constant temperature chamber was constructed that can be tested under the same conditions as in the natural state so that the research can be conducted in which frost does not occur on the outdoor unit of the heat pump regardless of the season. Simulations were performed to verity whether such a curved constant temperature chamber has feasibility as an experimental device. For CFD conditions, the length of the straight duct in front of the outdoor unit located in the duct-type constant temperature chamber was 1, 5, 10 and 15 times the diameter of the duct. As a result, it was found that a straight space must be secured 10 times the diameter of the duct.

• International Journal of Air-Conditioning and Refrigeration
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• v.15 no.3
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• pp.122-128
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• 2007

Heat transfer distributions and friction factors in square channels (3.0 ${\times}$ 3.0 cm) with twisted tape inserts and with twisted tape inserts plus interrupted ribs are respectively investigated. The rib height-to-channel hydraulic diameter ratio, $e/D_h$, is kept at 0.067 and test section length-to-hydraulic diameter ratio, $L/D_h$ is 30. The square ribs are arranged to follow the trace of the twisted tape and along the flow direction defined as axial interrupted ribs. The twisted tape is 0.1 mm thick carbon steel sheet with diameter of 2.8 cm, length of 90 cm, and 2.5 turns. Two heating conditions are investigated for test channels with twisted tape inserts and rib turbulators: (1) electric heat uniformly applied to four side walls of the square duct, and (2) electric heat uniformly applied to two opposite ribbed walls of the square channel. Results show that the twisted tape with interrupted ribs provides a higher overall heat transfer performance over the twisted tape with no ribs.