• Title/Summary/Keyword: Gap Flow

Search Result 986, Processing Time 0.025 seconds

ASSESSMENT OF CORE BYPASS FLOW IN A PRISMATIC VERY HIGH TEMPERATURE REACTOR BY USING UNIT-CELL EXPERIMENT AND CFD ANALYSIS (단위-셀 실험과 전산유체해석을 통한 블록형 초고온가스로의 노심우회유량 평가)

  • Yoon, S.J.;Jin, C.Y.;Kim, M.H.;Park, G.C.
    • Journal of computational fluids engineering
    • /
    • v.14 no.2
    • /
    • pp.59-67
    • /
    • 2009
  • An accurate prediction of the bypass flow is of great importance in the VHTR core design concerning the fuel thermal margin. Nevertheless, there has not been much effort in evaluating the amount and the distribution of the core bypass flow. In order to evaluate the behavior and the distribution of the coolant flow, a unit-cell experiment was carried out. Unit-cell is the regular triangular section which is formed by connecting the centers of three hexagonal blocks. Various conditions such as the inlet mass flow rate, block combinations and the size of bypass gap were examined in the experiment. CFD analysis was carried out to analyze detailed characteristics of the flow distribution. Commercial CFD code FLUENT 6.3 was validated by comparing with the experimental results. In addition, SST model and standard k-$\varepsilon$ model were validated. The results of CFD simulation show good agreements with the experimental results. SST model shows better agreement than standard k-$\varepsilon$ model. Results showed that block combinations and the size of the bypass gap have an influence on the bypass flow ratio but the inlet mass flow rate does not.

Numerical Analysis of a Turbine Rotor Cascade with Unsteady Passing Wakes (비정상 후류를 지나는 터빈 동익 주위의 유동장 수치해석)

  • Lee, Eun-Seok
    • 유체기계공업학회:학술대회논문집
    • /
    • 2006.08a
    • /
    • pp.153-156
    • /
    • 2006
  • A turbine stage consists of a stator and rotor. A stator provides the required inlet flow conditions so that a rotor can produce the necessary power. Passing wakes generated at the trailing edge of a stator make an interaction with a rotor. In the present study, this interaction flow mechanism is investigated using the numerical analysis. In case of the large gap distance between the stator and rotor, the stator and rotor flow analysis can be separated. First, only the stator flow field is solved. Second, the rotor flow field is solved including the passing wake information from the stator analysis. The passing wake experiences the shearing as it approaches to the rotor leading edge. And it is chopped when it strikes the rotor body. After that, the chopped wakes becomes the prolongation as it goes downstream. Also, the aerodynamic characteristics with the variation of the gap distance between a stator and rotor was investigated. Pressure jumps due to the passing wakes result in the pressure and lift loss and it gets stronger with the closer gap distance. This unsteady effect proves to be directly related to the fatigue and noise in turbomachinery and this study would be helpful to investigate such fields.

  • PDF

Empirical relationship between band gap and synthesis parameters of chemical vapor deposition-synthesized multiwalled carbon nanotubes

  • Obasogie, Oyema E.;Abdulkareem, Ambali S.;Mohammed, Is'haq A.;Bankole, Mercy T.;Tijani, Jimoh. O.;Abubakre, Oladiran K.
    • Carbon letters
    • /
    • v.28
    • /
    • pp.72-80
    • /
    • 2018
  • In this study, an empirical relationship between the energy band gap of multi-walled carbon nanotubes (MWCNTs) and synthesis parameters in a chemical vapor deposition (CVD) reactor using factorial design of experiment was established. A bimetallic (Fe-Ni) catalyst supported on $CaCO_3$ was synthesized via wet impregnation technique and used for MWCNT growth. The effects of synthesis parameters such as temperature, time, acetylene flow rate, and argon carrier gas flow rate on the MWCNTs energy gap, yield, and aspect ratio were investigated. The as-prepared supported bimetallic catalyst and the MWCNTs were characterized for their morphologies, microstructures, elemental composition, thermal profiles and surface areas by high-resolution scanning electron microscope, high resolution transmission electron microscope, energy dispersive X-ray spectroscopy, thermal gravimetry analysis and Brunauer-Emmett-Teller. A regression model was developed to establish the relationship between band gap energy, MWCNTs yield and aspect ratio. The results revealed that the optimum conditions to obtain high yield and quality MWCNTs of 159.9% were: temperature ($700^{\circ}C$), time (55 min), argon flow rate ($230.37mL\;min^{-1}$) and acetylene flow rate ($150mL\;min^{-1}$) respectively. The developed regression models demonstrated that the estimated values for the three response variables; energy gap, yield and aspect ratio, were 0.246 eV, 557.64 and 0.82. The regression models showed that the energy band gap, yield, and aspect ratio of the MWCNTs were largely influenced by the synthesis parameters and can be controlled in a CVD reactor.

Experimental Study of Heat/Mass Transfer in Rotating Cooling Passages with Discrete Ribs (단락 요철이 설치된 내부 냉각유로에서 회전에 따른 열/물질전달 특성 연구)

  • Kim Kyung Min;Kim Sang In;Lee Dong Ho;Cho Hyung Hee
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.29 no.5 s.236
    • /
    • pp.590-598
    • /
    • 2005
  • The present study has been conducted to investigate the effect of discrete ribs and rotation on heat/mass transfer characteristics in a two-pass square duct with $90^{\circ}-rib$ turbulators. The rib turbulator has a square cross section of 1.5 mm. The rib height-to-hydraulic diameter ratio $({e/D_{h})$ is 0.056, and the rib pitch-to-rib height ratio (p/e) is 10. The gap width is the same as the rib height. The rotation number ranges from 0.0 to 0.2 while Reynolds number is fixed to 10,000. In a stationary duct, the heat/mass transfer on the surfaces with discrete ribs is enhanced because the gap flow promotes local turbulence and flow mixing near the ribbed surface. In a rotating duct, the gap flow affects differently the heat/mass transfer on leading and trailing surfaces with discrete ribs. On the leading surface of the first pass, heat/mass transfer is increased due to the gap flow. On the trailing surface of the first pass, however, heat/mass transfer is decreased because the gap flow disturbs reattachment of main flow. The phenomenon, that is, the difference of heat transfer between the leading and the trailing surfaces is distinctly presented by rotation.

Numerical Investigation on the Flow Pulsation of Two Parallel Channels with Different Cross-section Areas (크기가 다른 평행한 두 채널 간의 맥동유동에 관한 수치해석)

  • Seo, Jeong-Sik;Shin, Jong-Keun;Ahn, Deuk-Kuen;Choi, Young-Don
    • 한국전산유체공학회:학술대회논문집
    • /
    • 2008.03b
    • /
    • pp.601-604
    • /
    • 2008
  • The flow pulsation of two parallel channels is investigated using RANS and URANS approaches. The parallel channels are connected with a small gap and have different cross section areas. The ratio of a right side area and a left side area ($A_R$ / $A_L$) is 0.5. Computations are conducted using a CFX code. Turbulence models adopted for RANS are Reynolds stress model and Shear Stress Transport (SST) model. The bulk Reynolds number is 60,000. Predicted results are compared with the experimental result of Lee et al. and show the flow pulsation with the frequency of about 100 Hz at the center of the gap.

  • PDF

Numerical Prediction of Flow Field in a Hard Disk Drive (하드 디스크 드라이브 내부의 유동장에 관한 수치적 연구)

  • Lee, Jae-Heon;Back, Y.R.;Kim, K.S.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.3 no.3
    • /
    • pp.206-214
    • /
    • 1991
  • Flow field in a hard disk drive has been predicted numerically. Theoretical model was constructed based on a commercially available hard disk drive with 40 Mega byte capacity. Since the gap between disk tip and shroud is not homogeneous in real hard disk drive, three kinds of gap size have been tested as computational model. The discussion has been made on the circumferential velocity, radial velocity, and pressure fields. As a result, the average shear stress on the disk surface was reduced as the gap size decreased. This means that the shroud should be designed compactly to reduce power consumption of the spindle motor.

  • PDF

Numerical Simulation and Experimental Research of the Flow Coefficient of the Nozzle-Flapper Valve Considering Cavitation

  • Li, Lei;Li, Changchun;Zhang, Hengxuan
    • International Journal of Fluid Machinery and Systems
    • /
    • v.10 no.2
    • /
    • pp.176-188
    • /
    • 2017
  • The nozzle-flapper valves are widely applied as a pilot stage in aerospace and military system. A subject of the analysis presented in this work is to find out a reasonable range of null clearance between the nozzle and flapper. This paper has presented a numerical flow coefficient simulation. In every design point, a parameterized model is created for flow coefficient simulation and cavitation under different conditions with varying gap width and inlet pressure. Moreover, a new test device has been designed to measure the flow coefficient and for visualized cavitation. The numerical simulation and test results both indicate that cavitation intensity gets fierce initially and shrinks finally as the gap width varies from small to large. From the curve, the flow coefficient mostly has experienced three stages: linear throttle section, transition section and saturation section. The appropriate deflection of flapper is recommended to make the gap width drop into the linear throttle section. The flapper-nozzle null clearance is optionally recommended near the range of $D_N/16$. Finally through simulation it is also concluded that the inlet pressure plays a little role in the influence on the flow coefficient.

Development of Model to Evaluate Thermal Fluid Flow Around a Submerged Transportation Cask of Spent Nuclear Fuel in the Deep Sea

  • Guhyeon Jeong;Sungyeon Kim;Sanghoon Lee
    • Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
    • /
    • v.20 no.4
    • /
    • pp.411-428
    • /
    • 2022
  • Given the domestic situation, all nuclear power plants are located at the seaside, where interim storage sites are also likely to be located and maritime transportation is considered inevitable. Currently, Korea does not have an independently developed maritime transportation risk assessment code, and no research has been conducted to evaluate the release rate of radioactive waste from a submerged transportation cask in the sea. Therefore, secure technology is necessary to assess the impact of immersion accidents and establish a regulatory framework to assess, mitigate, and prevent maritime transportation accidents causing serious radiological consequences. The flow rate through a gap in a containment boundary should be calculated to determine the accurate release rate of radionuclides. The fluid flow through the micro-scale gap can be evaluated by combining the flow inside and outside the transportation cask. In this study, detailed computational fluid dynamic and simplified models are constructed to evaluate the internal flow in a transportation cask and to capture the flow and heat transfer around the transportation cask in the sea, respectively. In the future, fluid flow through the gap will be evaluated by coupling the models developed in this study.

Drag Reduction Effect by a Self-Adjustable Splitter Plate on the Flow over a Circular Cylinder (원형실린더 후류내의 가동형 와류분할판에 의한 항력 감소효과)

  • 박운진
    • Transactions of the Korean Society of Mechanical Engineers
    • /
    • v.17 no.5
    • /
    • pp.1262-1275
    • /
    • 1993
  • The drag reduction effect of a freely-rotatable splitter plate was experimentally investigated in the 2-D wake behind a circular cylinder. By arranging the splitter plate to be aparted with a certain gap from the cylinder, the splitter plate was able to be aligned itself automatically to the flow direction in the tested range of 6.2$\times$$10^3$$\times$$10^4$. As a result, it was proven that the self-adjustable splitter plate always reduced effectively the drag imposed on the body against any arbitrary flow directions. In a specific range of Reynolds numbers, the drag reduction effect was dependent not only on the length of the splitter plate but also on the gap distance between the plate and the trailing edge of the body. For a splitter plate with a specific length, there existed a unique optimum range of gap distance to obtain successfully the drag reduction effect, however, the optimum range of gap distance was dependent on Reynolds number.

An Experimental Study on the Quenching Phenomena of Hemispherical Downward Facing Convex Surfaces with Narrow Gaps (반구형 소형 간극 내에서의 냉각과정에 관한 실험적 연구)

  • Ha, Kwang-Soon;Park, Rae-Joon;Kim, Sang-Baik;Cho, Young-Ro;Kim, Hee-Dong
    • Proceedings of the KSME Conference
    • /
    • 2001.06d
    • /
    • pp.447-452
    • /
    • 2001
  • Quenching phenomena of hemispherical downward facing convex surfaces with narrow gaps have been investigated experimentally. Experiments employed test sections having 1 and 2 mm in gap thickness and 1 atm in system pressure. From interpretations of the temperature and the heat flux history, it was found that the flooding inside the gap was restricted by CCFL phenomena and quenching process was propagated from lower to upper region of the internal copper shell. The ratio of the maximum heat fluxes at 1 mm to 2mm in gap thickness was the almost same that obtained by steady state experiments. The quenching scenario of the hemispherical downward facing surface with narrow gap has been suggested.

  • PDF