• Pediatric Gastroenterology, Hepatology & Nutrition
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• 제24권2호
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• pp.238-243
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• 2021

Caudal regression syndrome (CRS) is a rare neural tube defect that affects the terminal spinal segment, manifesting as neurological deficits and structural anomalies in the lower body. We report a case of a 31-month-old boy presenting with constipation who had long been considered to have functional constipation but was finally confirmed to have CRS. Small, flat buttocks with bilateral buttock dimples and a short intergluteal cleft were identified on close examination. Plain radiographs of the abdomen, retrospectively reviewed, revealed the absence of the distal sacrum and the coccyx. During the 5-year follow-up period, we could find his long-term clinical course showing bowel and bladder dysfunction without progressive neurologic deficits. We present this case to highlight the fact that a precise physical examination, along with a close evaluation of plain radiographs encompassing the sacrum, is necessary with a strong suspicion of spinal dysraphism when confronting a child with chronic constipation despite the absence of neurologic deficits or gross structural anomalies.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 추계학술대회
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• pp.1359-1364
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• 2004

An experiment was performed to study the evaporation heat transfer and the pressure drop characteristics of liquid nitrogen in a horizontal stainless steel tube with wire coil inserts. The inner diameter of test tube is 4.3mm and the length is 1.5m. Four wire coils having different pitch and thickness were inserted into the plain test tube. The wire coil length is 1.5m and the diameter is 3.65mm with thickness of 0.5mm and 0.9mm. Experiments were conducted at saturation temperature of $-191^{\circ}C$ mass flux from 200 to 370 $kg/m^{2}s$ and heat flux of 62 $kW/m^{2}$. Direct heating method was used to apply heat to the test section. Boiling heat transfer coefficients of both the plain and the enhanced tubes were calculated. Pressure drops between inlet and outlet side of test section were also measured, and they are used to estimate EPR(Enhancement Performance Ratio).

• 설비공학논문집
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• 제20권2호
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• pp.87-96
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• 2008

Flow condensation heat transfer coefficients(HTCs) of R123 and R245fa are measured in a horizontal plain tube. The main test section in the experimental flow loop is made of a plain copper tube of 9.52 mm outside diameter and 530 mm length. The refrigerant is cooled by passing cold water through an annulus surrounding the test section. Tests are performed at a fixed saturation temperature of $50\;{\pm}\;0.2\;^{\circ}C$ with mass fluxes of 50, 100, $150\;kg/m^2s$ and heat flux of $7.3{\sim}7.7\;kW/m^2$. Heat transfer data are obtained in the vapor quality range of $10{\sim}90%$. Test results show that the flow condensation HTCs of R245fa are overall 7.9% higher than those of R123 at all mass fluxes. The pressure drop of R245fa is smaller than that of R123 at the same heat flux. In conclusion, R245fa is a good candidate to replace ozone depleting R123 currently used in chillers from the view point heat transfer and environmental properties.

• 소성∙가공
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• 제9권6호
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• pp.631-637
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• 2000

The tube hydroforming technology is new key production technologies, which contribute to a light-weight cu. Because the tubes are used for hydroforming instead of the sheet materials formability test for tube is required to measure the formability of materials for hydroforming. In this Paper, a kind of formability test for tube, which can well represent the characteristics of tube hydroforming processes, is developed. Developed formability test method can consider not oかy the influence of material Properties but also contact with die and material. Some investigation was carried out to verify the effectiveness of developed formability test.

• 설비공학논문집
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• 제13권9호
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• pp.827-835
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• 2001

In this study, condensation heat transfer characteristics were conducted with special heat transfer tubes of SH-C type. Experiments were carried out the saturated vapor temperature of 334K and the wall subcooling of 1.5-4.5K. The refrigerant was R-113 and the enhanced tubes used in the present study were SH-CDR, SH-CYR and SH-CHR. The experimental results showed that the condensation heat transfer coefficients of SH-C type tubes were about 23-66% higher than those of a low integral-fin tube. It was visualized that the condensed liquid on the outer surface of SH-C type tubes flowed continuously down unlike a low integral-fin tube and a plain tube, due to a 3-D extending fin on the outer surface of SH-C type tubes. As a result, the thermal resistance of the condensed liquid decreased and the heat transfer coefficient increased. Also, the enhancement ratio of SH-CDR tube was the highest, and it was about 9-11 times as compared to that of a plain tube.

• Structural Engineering and Mechanics
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• 제75권6호
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• pp.643-657
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• 2020

This study presents experimental and numerical investigations on circular steel tube confined ultra high performance concrete (UHPC) columns under axial compression. The plain UHPC without fibers was designed to achieve a compressive strength ranged between 150 MPa and 200 MPa. Test results revealed that loading on only the UHPC core can generate a significant confinement effect for the UHPC core, thus leading to an increase in both strength and ductility of columns, and restricting the inherent brittleness of unconfined UHPC. All tested columns failed by shear plane failure of the UHPC core, this causes a softening stage in the axial load versus axial strain curves. In addition, an increase in the steel tube thickness or the confinement index was found to increase the strength and ductility enhancement and to reduce the magnitude of the loss of load capacity. Besides, steel tube with higher yield strength can improve the post-peak behavior. Based on the test results, the load contribution of the steel tube and the concrete core to the total load was examined. It was found that no significant confinement effect can be developed before the peak load, while the ductility of post-peak stage is mainly affected by the degree of the confinement effect. A finite element model (FEM) was also constructed in ABAQUS software to validate the test results. The effect of bond strength between the steel tube and the UHPC core was also investigated through the change of friction coefficient in FEM. Furthermore, the mechanism of circular steel tube confined UHPC columns was examined using the established FEM. Based on the results of FEM, the confining pressures along the height of each modeled column were shown. Furthermore, the interaction between the steel tube and the UHPC core was displayed through the slip length and shear stresses between two surfaces of two materials.

• 설비공학논문집
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• 제25권5호
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• pp.279-288
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• 2013

Heat transfer and pressure drop characteristics of fin-and-tube heat exchangers having sine wave fins and oval tubes were investigated. Oval tubes having an aspect ratio of 0.6 were made, by deforming 12.7 mm round tubes. Twelve samples, having different fin pitch and tube row, were tested. The effect of fin pitch on the j and f factors was negligible. The effect of the tube row on the j factor, however, was different from that of common fin-and-tube heat exchangers having plain fins and round tubes. The highest j factor was obtained for a two-row configuration, while the lowest one was obtained for a one-row configuration. A possible reason was attributed to the flow mixing characteristics of the sine wave channel of the present geometry. Comparison with a plain fin-and-tube heat exchanger having 15.88 mm O. D. round tube reveals that the present oval fin-and-tube heat exchanger shows generally superior thermal performance, except for the one-row configuration.

• 설비공학논문집
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• 제12권3호
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• pp.292-301
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• 2000

This study experimentally investigates an air-side performance of oval tube heat exchanger against round tube heat exchanger using scaled-up model experiment for home air conditioners. A plain fin and round tube heat exchanger with 21 FPI(fins per inch) was used as a reference heat exchanger, and these were applied equally to 4 oval tube heat exchangers. Oval tube samples were designed with the same perimeter as 7.5mm diameter round tube, and their aspect ratios were 1:2, 1:3, respectively. In this study, the heat transfer and pressure drop characteristics of oval tube heat exchangers against round tube heat exchanger were also compared to one another, and an optimal samples for home air conditioners was recommended. And, general performance characteristics for an optimum oval tube samples chosen in this work was compared with round tube heat exchanger.

• Journal of Advanced Marine Engineering and Technology
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• 제40권8호
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• pp.686-691
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• 2016

This paper employs numerical tools to obtain an optimal thermal design of a heat exchanger with plain-fins. This heat exchanger is located at the condensing section of a crevice-type heat pipe. The plain-fins in the heat exchanger are radically mounted to two tubes in the condensing section. To obtain the optimal design parameters, a computational fluid dynamics technique is introduced and applied to different placement configurations in a system module. Owing to its effects on the heat pipe performance, the temperature difference between the tube surfaces and ambient air is investigated in detail. A greater heat dissipation rate occurs when the plain-fin offsets change from 2 to 3 mm. When this temperature difference is ${\Delta}T=70^{\circ}C$, the upper part of the plain-fins undergoes an accumulation of heat. At below $70^{\circ}C$, the dissipation of heat is accepted. A rectangular plain-fin geometry with varying widths and heights does not have a significant impact on the heat dissipation through-out the overall system. In addition, the temperature distributions between different plain-fin pitches show an equal profile even with different fin pitches.

• 한국재료학회지
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• 제16권2호
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• pp.111-115
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• 2006

High-finned tubes have good thermal conductivity and have better cooling efficiency than plain tubes or low-fined tubes due to bigger air contact area. During high-fined tubes are manufactured by roll forming, the main technique is illustrated to optimizing primary material(copper pipe), optimized die matrix designing technique for roll forming, control manufacturing speed to develop productivity etc. In this study, a roll forming system was developed in oder to produce high-finned tube. Also a multi-step roll forming die was designed & built to produce high-finned tube that has over 10 mm fin height. And then, roll forming test using copper pipe was performed to produce high-finned tube. Roll forming process for producing highfinned tube was optimized by analyzing and adjusting misrostructure, hardness, and surface roughness of roll formed high-fined tube.