• Title/Summary/Keyword: non-uniform flow

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Exit Flow Measurements of a Centrifugal Pump Impeller

  • Hong, Soon-Sam;Kang, Shin-Hyoung
    • Journal of Mechanical Science and Technology
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    • v.16 no.9
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    • pp.1147-1155
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    • 2002
  • Discharge flows from a centrifugal pump impeller with a specific speed of 150 [rpm, m$^3$/min, m] were experimentally investigated. A large axisymmetric collector instead of a volute casing was installed to obtain circumferentially uniform flow, i.e. without interaction of the impeller and the volute. The unsteady flow was measured at the impeller exit and vaneless diffuser using a hot film probe and a pressure transducer. The flow at impeller exit showed pronounced jet-wake flow patterns. The wake, which was on the suction/hub side at high flow rate, became enlarged pitchwisely on both the hub and the shroud side as the flow rate decreases. The pitchwise non-uniformity of the flow rapidly decreased along the downstream and the non-uniformity almost disappeared at radius ratio of 1.18 for medium flow rate. The mean vaneless diffuser flow was reasonably predicted using a one dimensional analysis when an empirical constant was used to specify the skin friction coefficient. The data can be used for a centrifugal pump impeller design and validation of CFD codes and flow modeling.

Analysis of Coating Uniformity through Unsteady and Steady State Computer Simulation in Slot Coating (슬롯코팅에서 정상 및 비정상상태 컴퓨터해석을 통한 코팅의 균일성 분석)

  • Woo, Jeong-Woo;Sung, Dal-Je;Lyu, Min-Young
    • Polymer(Korea)
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    • v.38 no.5
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    • pp.640-644
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    • 2014
  • As a process of plat panel display production, slot coating is widely used for the coating of photoresist on a wide glass substrate. A uniform coating thickness is important, and the coating uniformity is divided into nozzle and machine directions. The machine and nozzle directions coating uniformities are influenced by the operation condition of coater and flow uniformity inside the die, respectively. Non-uniform coating during steady coating process occurs according to those factors, however, non-uniform coating along the machine and nozzle directions has been observed at the beginning of coating by unsteady flow. In this study, steady and unsteady state flow simulations have been performed and compared with experiment to examine the causes of non-uniform coating. Computational results exhibited that it took a time to get a uniform pressure distribution at whole inside the die, and during this period of time edge regions showed lower exit velocity compared with center region. Subsequently edge regions had thinner coated layers than center region. However edge regions showed higher exit velocity than center region after steady state, and this made edge regions had thicker coated layer than center region.

Effect of non-uniform magnetic field on the thermal behavior and mass transfer in magnetohydrodynamic Czochralski crystal growth of silicon (Magnetic Czochralski 실리콘 단결정 성장에서 열 및 유체유동과 질량전달에 미치는 비균일 자장의 효과)

  • 김창녕
    • Journal of the Korean Crystal Growth and Crystal Technology
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    • v.8 no.4
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    • pp.555-562
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    • 1998
  • Under the influence of non-uniform magnetic field, melt flow in steady state and oxygen concentration in unsteady state are numerically investigated. The strength of the applied characteristic magnetic fields are B=0.1T, 0.2T, and 0.3T, respectively. The buoyancy effects due to the crucible wall heating and the thermocapillary effects due to the surface tention at the free surface are suppressed differentially by the non-uniform magnetic fields. As the intensity of characteristic magnetic fields is increasing, the recirculation region in the meridional plane is moving toward the growing crystal, and is diminishing. The oxygen concentration on the growing surface of crystals is decreasing and the uniformity of the oxygen concentration is increasing as the intensity of the magnetic fields is increasing.

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Estimation algorithm of ocean surface temperature flow based on Morphological Operation (형태학적 연산에 기반한 해수면 온도 분포 추정 알고리즘)

  • Gu, Eun-Hye;Cho, Woong-Ho;Park, Kil-Houm
    • Journal of the Korean Institute of Intelligent Systems
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    • v.22 no.2
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    • pp.253-260
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    • 2012
  • Target detection is very difficult with complex clutters in IRST(Infrared Search and Track) system for a long distance target. Especially sea-clutter and ocean-surface with non-uniform temperature distribution make it difficult to detect incoming targets in images obtained in sea environment. In this paper, we propose a novel method based on morphological method for estimation of ocean surface with non-uniform temperature flow. In order to estimate the exact ocean surface temperature flow, we divided it into upper and lower bound flow. And after estimating it, the final ocean surface temperature flow is derived by a mean value of the estimated results. Also, we apply the multi-weighted technique with a variety of sizes of structure elements to overcome sub-sampling effect by using morphology method. Experimental results for ocean surface images acquired from many different environments are compared with results of existing method to verify the performance of the proposed methods.

The Improvement of Weldline and Flow mark Defection by using Injection Molding Analysis (사출성형 해석을 통한 Weldline 및 Flow mark 개선사례)

  • Lee, Yeong Chang
    • Journal of the Korean Society for Precision Engineering
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    • v.30 no.12
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    • pp.1295-1301
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    • 2013
  • The cause of flow mark defect is known as non-uniform temperature of mold surface when the flow front meets the cold cavity. The exact definition and classification of Flow mark is not clear because the mechanism of flow mark is not figured out till now. Any injection molding analysis software can not predict the flow mark phenomena. To solve weldline and flow mark defects, the gate thickness is reduced to increase the melt front velocity and the melt front velocity of the flow mark area is increased from 82.3mm/s to 104.7mm/s. In addition, the bulk temperature of the flow mark area is increased from $178.3^{\circ}C$to $215.2^{\circ}C$ by adding a cold slug well. The flow mark phenomena can be greatly reduced by increasing the flow front velocity and elevating the bulk temperature.

COMPUTATIONAL STUDY FOR PERFORMANCE EVALUATION OF FLOW CHANNELS INSIDE CDI UNIT CELL (수치모사를 이용한 CDI Unit Cell 내부의 유로성능 평가)

  • Sohn, D.Y.;Choi, Y.H.;Park, D.W.;Jung, C.H.
    • Journal of computational fluids engineering
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    • v.15 no.1
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    • pp.31-36
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    • 2010
  • In the present study, computations for flow fields inside the CDI unit cells with electrodes and spacers have been made to evaluate their performance. Three types of unit cells that include a planar type, a serpentine channel type, and a spiral wound type were considered and their flow characteristics were compared. From the computational results, it is found that the serpentine channel type has a large flow resistance and can not guarantee the outflow flux for industrial applications. On the other hand, the planar type can sustain a large enough outflow flux but it's efficiency is low for the electrode-use because of the non-uniform velocity distribution inside the cell and dead zones in every corner. Finally, The spiral wound type has not only a large outflow flux as much as the planar type has, but also a high efficiency for the electrode-use because of uniform velocity distribution. From this comparison, we can expect that the spiral wound type of CDI unit cell would have a high performance deionization capability.

A Study for Optimal Design of the AIG to Improve the Performance of DeNOx Facilities Installed in Combined Cycle Plant (복합화력 탈질설비 성능향상을 위한 암모니아 주입 그리드의 최적설계 방안에 관한 연구)

  • Kim, Kwang-Chu;Park, Man-Heung;Yoon, Jun-Kyu;Lim, Jong-Han
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.19 no.12
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    • pp.811-820
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    • 2007
  • A Study on the optimal design of the AIG(Ammonia Injection Grid) to improve the performance of DeNOx facilities in the HRSG(Heat Recovery Steam Generator) was performed using the CFD analysis. On the basis of the flow analysis results in the case that the AIG in the HRSG was not installed, the numerical analyses according to the positions of AIG, injection angles of nozzle and the control of ammonia injection quantity were carried out. The standard deviation according to factors was calculated for quantitative comparison. As the results, the AIG in the HRSG should be installed in the position that the uniform flow field shows through the exact flow analysis in the previous of the AIG design and installation. In the case the AIG has already been installed and non uniform flow distribution shows, it is recommended that flow correction device or KoNOx catalyst should be used. Otherwise, the control of ammonia injection angle or the ammonia injection quantity using the velocity profile analysis is demanded to accomplish the optimal performance.

Rotordynamic Forces Due to Rotor Sealing Gap in Turbines (비대칭 터빈 로터 실에 기인한 축 가진력)

  • Kim Woo June;Song Bum Ho;Song Seung Jin
    • Proceedings of the KSME Conference
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    • 2002.08a
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    • pp.545-548
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    • 2002
  • Turbines have been known to be particularly susceptible to flow-induced self-excited vibration. In such vibrations, direct damping and cross stiffness effects of aerodynamic forces determine rotordynamic stability. In axial turbines with eccentric shrouded rotors, the non-uniform sealing gap causes azimuthal non-uniformities in the seal gland pressure and the turbine torque which destabilize the rotor system. Previously, research efforts focused solely on either the seal flow or the unshrouded turbine passge flow. Recently, a model for flow in a turbine with a statically offset shrouded rotor has been developed and some stiffness predictions have been obtained. The model couples the seal flow to the passage flow and uses a small perturbation approach to determine nonaxiymmetric flow conditions. The model uses basic conservation laws. Input parameters include aerodynamic parameters (e.g. flow coefficient, reaction, and work coefficient); geometric parameters (e.g. sealing gap, depth of seal gland, seal pitch, annulus height); and a prescribed rotor offset. Thus, aerodynamic stiffness predictions have been obtained. However, aerodynamic damping (i.e. unsteady aerodynamic) effects caused by a whirling turbine has not yet been examined. Therefore, this paper presents a new unsteady model to predict the unsteady flow field due to a whirling shrouded rotor in turbines. From unsteady perturbations in velocity and pressure at various whirling frequencies, not only stiffness but also damping effects of aerodynamic forces can be obtained. Furthermore, relative contributions of seal gland pressure asymmetry and turbine torque asymmetry are presented.

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