• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.18 no.1
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• pp.55-65
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• 2006

The air and water flow distribution are experimentally studied for a round header - flat tube geometry simulating a parallel flow heat exchanger. The number of branch flat tube is thirty. The effects of tube outlet direction, tube protrusion depth as well as mass flux, and quality are investigated. The flow at the header inlet is identified as annular. For the downward flow configuration, the water flow distribution is significantly affected by the tube protrusion depth. For flush-mounted configuration, most of the water flows through frontal part of the header. As the protrusion depth increases, more water is forced to the rear part of the header. The effect of mass flux or quality is qualitatively the same as that of the protrusion depth. Increase of the mass flux or quality forces the water to rear part of the header. For the upward flow configuration, however, most of the water flows through rear part of the header. The protrusion depth, mass flux, or quality does not significantly alter the flow pattern. Possible explanations are provided based on the flow visualization results. Negligible difference on the water flow distribution was observed between the parallel and the reverse flow configuration.

• Nuclear Engineering and Technology
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• v.32 no.1
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• pp.1-9
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• 2000

Delayed hydride cracking (DHC) velocity and threshold stress intensity factor for DHC ($K_{IH}$) tests in the radial direction on M11 pressure tube material in Wolsong unit 1 were carried out following the Atomic Energy Canada Limited (AECL) standard test procedure in order to identify the effect of undercooling on DHCV and to acquire the $K_{IH}$ data. The results showed that $K_{IH}$ 's were 8.8$\pm$0.8 MPa√m in the back offcut and 11.4$\pm$0.7 MPa√m in the front offcut. The fact that $K_{IH}$ in the front offcut is about 20% higher than that in the back offcut is attributed to the microstructural difference between the materials of the front and back ends. $K_{IH}$ 's in M11 pressure tube appeared to be higher than the values from the tubes made of double melted ingot reported earlier. This can be interpreted by the fact that very small amounts of Chlorine (Cl) and Phosphorus (P) are contained in the ingot and that the content of the harmful elements in the M11 pressure tube is equivalent to that made of a quadruple melting process. DHC velocities at 25$0^{\circ}C$ in the front offcut in the radial direction are measured to be 5~8$\times$10$^{-8}$ m/s. The results show that the prior thermal history change the DHC velocity significantly. This effect was confirmed by the experiment of undercooling prior to the DHC tests.DHC tests.

• Journal of the Korean Society of Manufacturing Technology Engineers
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• v.22 no.6
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• pp.969-975
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• 2013

While accelerating, bicycle frames are subject to torsion forces and deformation. In this study, bicycle frame durability was evaluated by using structural, fatigue, and vibration experiments. Three types of models were designed by changing the frame configurations according to the shape and direction of a bicycle frame design. Because maximum equivalent stress was greatest at the saddle and at connected parts in Models 1, 2, and 3, these frame sections were most vulnerable to failure. Model 2 was the least safe, due to the increased total deformation and equivalent stresses in the top tube horizontal to the ground. Based on vibration and fatigue analysis results, Model 2 was also determined to be the least safe frame, because the head tube was placed slightly higher above the seat tube and inclined to $10^{\circ}$. These study results can be utilized in the design of bicycle frames by investigating prevention and durability against damage.

• Bulletin of the Korean Mathematical Society
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• v.49 no.5
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• pp.961-987
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• 2012

A compartment model of the flow driven by pumping without valves (valveless pumping) in an open tank system is proposed. By the open tank system, we mean that two rigid cylindrical tanks are connected with an elastic tube. An incompressible fluid fills this system up to a certain level in tanks under the gravity. The compartment model for analyzing such open system is derived from the energy principle which will be called the energy conserving compartment model or shortly the ECCM. Based on this ECCM of valveless pumping, we explore the occurrence of directional net flow or directional net power by a specific excitation at an asymmetric part of the elastic tube. The interaction between deformable elastic tube and the fluid inside is considered in the ECCM. The reliability of the ECCMis investigated through some physical examples. The ECCM shows the existence of directional net power of the valveless pump system with open tanks and confirms that the direction and magnitude of the net power depend on the pumping frequency as well. Furthermore, the phase synchronization in time between the fluid pressure difference and the external pinching force over the pumping region is highly related to the direction of energy storing or net power.

• Korean Journal of Materials Research
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• v.30 no.3
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• pp.149-154
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• 2020

A powder-in-sheath rolling method is applied to the fabrication of a carbon nano tube (CNT) reinforced copper composite. A copper tube with outer diameter of 30 mm and wall thickness of 2 mm is used as sheath material. A mixture of pure copper powder and CNTs with a volume content of 3 % is filled in a tube by tap filling and then processed to an 93.3 % reduction using multi-pass rolling after heating for 0.5 h at 400 ℃. The specimen is then sintered for 1h at 500 ℃. The relative density of the 3 vol%CNT/Cu composite fabricated using powder in sheath rolling is 98 %, while that of the Cu powder compact is 99 %. The microstructure is somewhat heterogeneous in width direction in the composite, but is relatively homogeneous in the Cu powder compact. The hardness distribution is also ununiform in the width direction for the composite. The average hardness of the composites is higher by 8Hv than that of Cu powder compact. The tensile strength of the composite is 280 MPa, which is 20 MPa higher than that of the Cu powder compact. It is concluded that the powder in sheath rolling method is an effective process for fabrication of sound CNT reinforced Cu matrix composites.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.12
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• pp.943-949
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• 2002

The propagation of the impulse wave discharged from the Inclined exit of a pipe is investigated through shock tube experiment and numerical computations. The pressure histories and directivities of the impulse wave propagating outside from the exit of pipe with several different configurations are analyzed for the range of the incident shock wave Mach number between 1.1 and 1.4. In the shock tube experiments, the impulse waves are visualized by a Schlieren optical system for the purpose of validation of computational work. Computations using the two-dimensional. unsteady, compressible, Euler equations are carried out to represent the experimented impulse waves. Computed Schlieren images predict the experimented impulse waves with a good accuracy. The results obtained show that for the radial direction the peak pressure of the impulse wave discharged depends upon the Inclined angle of the exit of the pipe. but for the axial direction it is almost constant regardless of the inclined angle of the pipe exit.

• Journal of radiological science and technology
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• v.43 no.6
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• pp.489-494
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• 2020

The Law method is observing the temporal bone. There are two types of methods: the double angle method, which manipulates the center ray angle of the tube twice, and the single angle method, which manipulates once. The purpose is to increase the reproducibility of the image by making vertical incidence by making an assistive device using a 3D printer. Two assistive devices with a wedge-shaped 8.5 × 10 × 2.3 cm, an inclined surface of 7.5 cm, and an inclination angle of 15° were fabricated. Assistive devices can be combined with each other in the form of grooves, and PLA (Poly Lactic Acid) is used as a material. In the first experiment, 10 examiners operated the tube 15° in the caudad direction and 15° in the anterior direction, and measured it with a protractor to conduct a reproducibility experiment. Second, two examiners acquired vertically incidence images using the existing law method and assistive devices, and measured the distance between each measurement point to evaluate the reproducibility. The tube center ray angle reproducibility experiment was not statistically significant, but the angle difference was up to 9° between examiners. The reproducibility experiment of radiographic images was not statistically significant with the conventional method, and the method using an assistive device was statistically significant. Therefore, regardless of skill level, an image capable of securing reproducibility, which is the advantage of vertical incidence, could be obtained.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.6
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• pp.82-91
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• 2021

We compared the heat transfer characteristics of the parallel and the counterflow flow in the concentric double tube of the Al₂O₃/water nanofluids using numerical methods. The high- and low-temperature fluids flow through the inner circular tube and the annular tube, respectively. The heat transfer characteristics according to the flow direction were compared by changing the volume flow rate and the volume concentration of the nanoparticles. The results showed that the heat transfer rate and overall heat transfer coefficient improved compared to those of basic fluid with increasing the volume and flow rate of nanoparticles. When the inflow rate was small, the heat transfer performance of the counterflow was about 22% better than the parallel flow. As the inflow rate was increased, the parallel flow and the counterflow had similar heat transfer rates. In addition, the effectiveness of the counterflow increased from 10% to 22% rather than the parallel flow. However, we verified that the increment in the friction factor of the counterflow is not large compared to the increment in the heat transfer rate.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.1
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• pp.25-33
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• 2005

When a circular tube with uniform heat generation within the wall was placed in a cross flow, heat flows by conduction in the circumferential direction due to the asymmetric nature of the fluid flow around the perimeter of the circular tube The circumferential heat flow affects the wall temperature distribution to such an extent that. in some cases, significantly different results may be obtained for geometrically similar surfaces. In the present investigation, the effect of circumferential wall heat conduction is investigated for forced convection around circular tube in cross flow of air and water Two-dimensional temperature distribution $T_w(r,{\theta})$ is calculated through the numerical analysis. The difference between one-dimensional and two-dimensional solutions is demonstrated on the graph of local heat transfer coefficients. It is observed that the effect of working fluid is very remarkable.

• Proceedings of the KIEE Conference
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• 2007.04a
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• pp.29-31
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• 2007

In this paper we propose an directional analytic approach in image data space for X-ray image which is detected from the X-ray projection system. Such a radiographic nondestructive testing has long been used for steel-tube inspection and weld monitoring. The welded area and thickness of steel-tube are detected from gradient radiating mechanism based on the evaluation of biased X-ray source position. The welded area is an ellipse type on low contrast X-ray image including noise. Noise originates from most of elements of the system. such as shielding CCD camera, imaging screen, X-ray source, inspected object, electronic circuits and etc.. Projection incorrectness and noise influence on imaging quality is to be represented by vertical pixels' distribution. Space analysis due to vertical direction also shows the segmental possibility between regions by visual edge evaluation.