• 제목/요약/키워드: outer and inner diameter

검색결과 325건 처리시간 0.023초

Numerical Study of Turbulent Heat Transfer in Helically Coiled Tubes (나선형 튜브내의 난류 열전달에 대한 수치적 연구)

  • Yoon, Dong-Hyeog;Park, Ju-Yeop;Seul, Kwang-Won
    • Transactions of the Korean Society of Mechanical Engineers B
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    • 제36권8호
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    • pp.783-789
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    • 2012
  • In this study, turbulent flow and heat transfer characteristics in a helically coiled tube have been numerically investigated. Helically coiled tubes are commonly used in heat exchange systems to enhance the heat transfer rate. Accordingly, they have been widely studied experimentally; however, most studies have focused on the pressure drop and heat transfer correlations. The centrifugal force caused by a helical tube increases the wall shear stress and heat transfer rate on the outer side of the helical tube while decreasing those on the inner side of the tube. Therefore, this study quantitatively shows the variation of the local Nusselt number and friction factor along the circumference at the wall of a helical tube by varying the coil diameter and Reynolds number. It is seen that the local heat transfer rate and wall shear stress greatly decrease near the inner side of the tube, which can affect the safety of the tube materials. Moreover, this study verifies the previous experimental correlations for the friction factor and Nusselt number, and it shows that the correlation between the two in a straight tube can be applied to a helical tube. It is expected that the results of this study can be used as important data for the safety evaluation of heat exchangers and steam generators.

Measurement of Electron Temperature and Number Density and Their Effects on Reactive Species Formation in a DC Underwater Capillary Discharge

  • Ahmed, Muhammad Waqar;Rahman, Md. Shahinur;Choi, Sooseok;Shaislamov, Ulugbek;Yang, Jong-Keun;Suresh, Rai;Lee, Heon-Ju
    • Applied Science and Convergence Technology
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    • 제26권5호
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    • pp.118-128
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    • 2017
  • The scope of this work is to determine and compare the effect of electron temperature ($T_e$) and number density ($N_e$) on the yield rate and concentration of reactive chemical species ($^{\bullet}OH$, $H_2O_2$ and $O_3$) in an argon, air and oxygen injected negative DC (0-4 kV) capillary discharge with water flow(0.1 L/min). The discharge was created between tungsten pin-to pin electrodes (${\Phi}=0.5mm$) separated by a variable distance (1-2 mm) in a quartz capillary tube (2 mm inner diameter, 4 mm outer diameter), with various gas injection rates (100-800 sccm). Optical emission spectroscopy (OES) of the hydrogen Balmer lines was carried out to investigate the line shapes and intensities as functions of the discharge parameters such as the type of gas, gas injection rate and inter electrode gap distances. The intensity ratio method was used to calculate $T_e$ and Stark broadening of Balmer ${\beta}$ lines was adopted to determine $N_e$. The effects of $T_e$ and $N_e$ on the reactive chemical species formation were evaluated and presented. The enhancement in yield rate of reactive chemical species was revealed at the higher electron temperature, higher gas injection rates, higher discharge power and larger inter-electrode gap. The discharge with oxygen injection was the most effective one for increasing the reactive chemical species concentration. The formation of reactive chemical species was shown more directly related to $T_e$ than $N_e$ in a flowing water gas injected negative DC capillary discharge.

Preparation of Superflux Nickel Capillary Support with 3D Macropore Channel Network For Gas Separation and Liquid Filtration Membranes (기체/액체 분리막을 위한 3차원 Macropore 채널을 갖는 Superflux 니켈 모세관 지지체의 제조)

  • Song, Ju-Seob;Cho, Churl-Hee
    • Membrane Journal
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    • 제28권3호
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    • pp.214-219
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    • 2018
  • In the present study, superflux nickel capillary supports for gas and vapor separation membranes were prepared by a combined process of NIPS and sintering. Nickel capillary precursors were prepared by NIPS process from PSf-Ni-DMAC-PEG400 dope solution and was sintered at various temperatures in $H_2$ atmosphere to reliably produce Ni capillary support. The optimized Ni capillary support has an outer and inner diameters of 722 and $550{\mu}m$, and its thickness was $94{\mu}m$. It has 3-dimensional pore channel network and its porosity and mean pore diameter was 26% and $4{\mu}m$, respectively. Also, its mechanical strength was tested in tensile mode: its fracture load was 2.84 kgf and the fracture elongation was 13%. Finally, its single gas permeance was measured: He, $N_2$, $O_2$, and $CO_2$ permeance was 432,327, 281,119, 264,259, and 193,143 GPU, respectively. The superflux behavior could be explained from viscous flow through the macropores having a diameter of $4{\mu}m$ and narrow thickness. It could be concluded that the superflux behavior of the Ni capillary support was from the 3-D pore channel network and the small thickness.

Changes in Growth and Yield of Strawberry (cv. Maehyang and Seolhyang) in Response to Defoliation during Nursery Period (딸기 '매향'과 '설향'의 육묘기 자묘 적엽이 생육 및 수량에 미치는 영향)

  • Kim, Dae-Young;Kim, Tae-Il;Kim, Woon-Seop;Kang, Yun-Im;Yun, Hyung-Kweon;Choi, Jong-Myung;Yoon, Moo-Kyung
    • Journal of Bio-Environment Control
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    • 제20권4호
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    • pp.283-289
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    • 2011
  • This study was conducted to examine the effects of defoliation treatment on the growth and yield of strawberry ($Fragaria{\times}ananassa$ cv. Maehyang and Seolhyang) during nursery period. Leaves of strawberry plantlet had been removed except two, three and four fully expanded leaves until planting date. As the intensity of defoliation was strong, the petiole length was reduced and overgrowth of strawberry plantlet was suppressed. Outer diameter of crown in defoliation treatments significantly decreased but inner diameter of crown was not significant. Number of primary roots of the 3 leaves or 4 leaves defoliation treatment generally tended to increase, but there was not significantly different among treatments. Fresh weight and leaf area in the defoliation treatments significantly decreased and the root weight were higher in partial 3 leaves or 4 leaves defoliation treatment but was not significantly different among treatments. Because T/R ratio decreased significantly as growth inhibition of above-ground part compared to underground part, it is considered easy to take rooting after plantlet plating. As the intensity of defoliation was strong, chlorophyll contents tended to decrease significantly. Reduction of the endogenous nitrogen by defoliation effectively led to promote floral differentiation at low temperature and short day condition. This promoted timing of budding and flowering and also induced uniform flowering after plantlet planting. Marketable fruit yield of 3 leaves defoliation treatment tended to be higher than the control.

Fabrication of a sterling silver ring with folding process (폴딩 기법을 이용한 스털링실버 링 제조 공정)

  • Kim, Ik gyu;Kim, Kwangbae;Kim, Eun-Seok;Song, Ohsung
    • Journal of the Korea Academia-Industrial cooperation Society
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    • 제20권9호
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    • pp.382-389
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    • 2019
  • A novel folding process is proposed using a repeated cold-die forging and annealing to form a sterling silver ring. Sterling silver plate was cut into a doughnut shape, and lattices with 0.43-mm line-width were imprinted on it. The sample was folded by forging using dies with slopes of $45^{\circ}$, $60^{\circ}$, and $75^{\circ}$ and annealing. For comparison, samples were also fabricated without annealing. Strain was identified by measuring the length of lattices. Vernier calipers, a Vickers hardness tester, an optical microscope, and a UV-VIS colorimeter were used to determine the size, hardness, microstructure, and body color. Without annealing, cracks occurred. However, successful deformation was possible when annealing was used. The results of macro strain measurements show that the outer diameter and width decreased, while the inner diameter and thickness increased after the final process. The maximum strain was increased 0.128 toward the parallel direction. The Vickers hardness decreased after annealing and increased after the folding process. The microstructure results showed that the grain size increased after annealing but decreased after folding. The color difference based on the Lab index was under 10 for all processes. Eventually, a doughnut-shaped silver plate was successfully deformed into a ring shape by the folding process.

Influence of the Amount of Conductive Paste on the Electrical Characteristics of c-Si Photovoltaic Module (전도성 페이스트 도포량 변화에 따른 결정질 태양광 모듈의 전기적 특성에 대한 영향성 분석)

  • Kim, Yong Sung;Lim, Jong Rok;Shin, Woo Gyun;Ko, Suk-Whan;Ju, Young-Chul;Hwang, Hye Mi;Chang, Hyo Sik;Kang, Gi-Hwan
    • Korean Journal of Materials Research
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    • 제29권11호
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    • pp.720-726
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    • 2019
  • Recently, research on cost reduction and efficiency improvement of crystalline silicon(c-Si) photovoltaic(PV) module has been conducted. In order to reduce costs, the thickness of solar cell wafers is becoming thinner. If the thickness of the wafer is reduced, cracking of wafer may occur in high temperature processes during the c-Si PV module manufacturing process. To solve this problem, a low temperature process has been proposed. Conductive paste(CP) is used for low temperature processing; it contains Sn57.6Bi0.4Ag component and can be electrically combined with solar cells and ribbons at a melting point of $150^{\circ}C$. Use of CP in the PV module manufacturing process can minimize cracks of solar cells. When CP is applied to solar cells, the output varies with the amount of CP, and so the optimum amount of CP must be found. In this paper, in order to find the optimal CP application amount, we manufactured several c-Si PV modules with different CP amounts. The amount control of CP is fixed at air pressure (500 kPa) and nozzle diameter 22G(outer diameter 0.72Ø, inner 0.42Ø) of dispenser; only speed is controlled. The c-Si PV module output is measured to analyze the difference according to the amount of CP and analyzed by optical microscope and Alpha-step. As the result, the optimum amount of CP is 0.452 ~ 0.544 g on solar cells.

Ultrastructure of Spermatozoa in the Bagrid Catfish, Pseudobagrus fulvidraco (Teleostei, Siluriformes, Bagridae) (동자개 Pseudobagrus fulvidraco (경골어강, 메기목, 동자개과)의 정자의 미세구조)

  • Lee, Young-Hwan
    • Applied Microscopy
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    • 제28권1호
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    • pp.39-48
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    • 1998
  • The spermatozoa of bagrid catfish, Pseudobagrus fulvidraco are approximately $76{\mu}m$ in length, and a relatively simple and elongated cell composed of a spherical head, a short middle piece and a tail. The ultrastructure of spermatozoa of P. fulvidraco is characterized by the following features. The acrosome is absent as in most teleost. The round nucleus measuring about $1.67{\mu}m$ in length and diameter is depressed with a deep nuclear fossa. The nuclear fossa, the length of which is about three-fifths of the nuclear diameter, contains the proximal and distal contrioles. The two centrioles are oriented approximately $160^{\circ}$ to each other. The filamentous materials give rise to satellite appendages arranged tangentially from the triplets of the distal centriole and the doublets of the anterior end of the axoneme toward the nuclear envelope. The mitochondria are not fused and their number is 20 or more. They are arranged in two or three layers and two rings within the cytoplasmic collar and surround the axoneme. They are separated from the axoneme by the cytoplasmic canal. The axoneme is of the 9+2 microtubular pattern and has inner but no outer dynein arms. The two lateral fins are in the same plane with the two central microtubules, the doublets 3 and 8, which are ultrastructural characteristics of the sperm tail unlike other siluroids lacking the lateral fins.

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A Characteristic Analysis of Glass Beads in Geumgwan Gaya, Korea (I) (금관가야 유리구슬의 특성 분석 (I))

  • Kim, Eun A;Lee, Je Hyun;Kim, Gyu Ho
    • Journal of Conservation Science
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    • 제37권3호
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    • pp.232-244
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    • 2021
  • This study examined the physical attributes and heat treatment characteristics of glass beads excavated from the Gimhae area, which is the location of Geumgwan Gaya. This enabled classification of surface characteristics of the beads based on the investigation of the color, size, and shape. The glass beads were classified into eight color systems, with purplish-blue beads as the representative color. Bead size was categorized into three types depending on the outer diameter and how it increased over time. Bead shapes were categorized as round, tubular, or doughnut-shaped based on the inner diameter and length, with round being the typical shape. According to the degree of heat treatment, there are three types of cross-section for glass beads that are manufactured by the drawing technique, most of which are the HT-III type. In addition, it is estimated that the heat treatment technology has more considerable effects than other methods. Through non-destructive analysis, the chemical composition was obtained and categorized as flux, stabilizer, and colorant. Analysis confirmed the presence of 63 and 9 pieces in the potash and soda glass groups, respectively. Overall findings from the study highlighted a correlation between the chemical composition and the external factors such as color, size, shape, and manufacturing technology of glass beads recovered from Geumgwan Gaya, revealing characteristics related to that time and region.

Research on the Development of Microneedle Arrays Based on Micromachining Technology and the Applicability of Parylene-C (미세가공 기술 기반의 마이크로니들 어레이 개발 및 패럴린 적용 가능성에 관한 연구)

  • Dong-Guk Kim;Deok-kyu Yoon;Yongchan Lee;Min-Uk Kim;Jihyoung Roh;Yohan Seo;Kwan-Su Kang;Young Hun Jeong;Kyung-Ah Kim;Tae-Ha Song
    • Journal of Biomedical Engineering Research
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    • 제44권6호
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    • pp.404-413
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    • 2023
  • In this research, we studied the development of a SUS304 microneedle array based on microfabrication technology and the applicability of Parylene-C thin film, a medical polymer material. First of all, four materials commonly used in the field of medical engineering (SUS304, Ti, PMMA, and PEEK) were selected and a 5 ㎛ Parylene-C thin film was deposited. The applicability of Parylene-C coating to each material was confirmed through SEM analysis, contact angle measurement, surface roughness(Ra) measurement, and adhesion test according to ASTM standards for each specimen. Parylene-C thin film was deposited based on chemical vapor deposition (CVD), and a 5 ㎛ Parylene-C deposition process was established through trial and error. Through characteristic experiments to confirm the applicability of Parylene-C, SUS304 material, which is the easiest to apply Parylene-C coating without pretreatment was selected to develop a microneedle array based on CNC micromachining technology. The CNC micromachining process was divided into a total of 5 steps, and a microneedle array consisting of 19 needles with an inner diameter of 200 ㎛, an outer diameter of 400 ㎛, and a height of 1.4 mm was designed and manufactured. Finally, a 5 ㎛ Parylene-C coated microneedle array was developed, which presented future research directions in the field of microneedle-based drug delivery systems.

Adsorption Characteristics of Hydrogen in Regular Single-Walled Carbon Nanotube Arrays at Low Temperature (저온에서 규칙적인 단일벽 탄소나노튜브 배열의 수소 흡착 특성)

  • Yang Gon Seo
    • Clean Technology
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    • 제29권3호
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    • pp.217-226
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    • 2023
  • The amount of hydrogen adsorbed in arrays of single walled carbon nanotubes (SWNTs) was studied as a function of nanotube diameter and distance between the nearest-neighbor nanotubes on square arrangements using a grand canonical Monte Carlo simulation. The influence of the geometry of a triangle array with the same diameters and distances was also studied. Hydrogen-carbon and hydrogen-hydrogen interactions were modeled with Lennard-Jones potentials for short range interactions and electrostatic interactions were added for hydrogen-hydrogen pairs to consider quantum contributions at low temperatures. At 194.5 K, Type I isotherms for large-diameter SWNTs and Type IV isotherms without hysteresis between adsorption and desorption processes for wider tube separations were observed. At 200 bars, the gravimetric hydrogen storage capacity of the SWNTs was reached or exceeded the US Department of Energy (DOE) target, but the volumetric capacity was about 70% of the DOE target. At 77 K, a two-step adsorption was observed, corresponding to a monolayer formation step followed by a condensation step. Hydrogen was adsorbed first to the inner surface of the nanotubes, then to the outer surface, intratubular space and the interstitial channels between the nanotube bundles. The simulation indicated that SWNTs of various diameters and distances in a wide range of configurations exceeded the DOE gravimetric and volumetric targets at under 1 bar.