• Title/Summary/Keyword: fluid and flow

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A Numerical Study on the Effect of Coefficient of Restitution to Heat Transfer in a Conical Fluidized Bed Combustor (원추형 유동층 연소기 내의 열전달에 미치는 복원계수의 영향에 대한 수치해석 연구)

  • Kang, Seung Mo;Park, Woe-Chul;Abdelmotalib, Hamada;Ko, Dong Kuk;Im, Ik-Tae
    • Journal of the Semiconductor & Display Technology
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    • v.14 no.4
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    • pp.38-44
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    • 2015
  • In this paper, numerical simulations on conical fluidized bed combustors were carried out to estimate the effect of coefficients of restitution between particle and particle and particle to wall on hydrodynamics and heat transfer. The Eulerian-Eulerian two-fluid model was used to simulate the hydrodynamics and heat transfer in a conical fluidized bed combustor. The solid phase properties were calculated by applying the kinetic theory of granular flow. Simulations results show that increasing the restitution coefficient between the particle and particle results in increasing the bed pressure drop. On other hand, the increasing of particle to wall coefficient of restitution results in decreasing the bed pressure drop. It is found that the coefficient of restitution has little effect on heat transfer.

Evaluation of Energy Saving with Vector Control Inverter Driving Centrifugal Pump System (벡터 제어 인버터 구동 원심펌프시스템의 에너지 절감 평가)

  • Suh, Sang-Ho;Kim, Kyungwuk;Kim, Hyoung-Ho;Yoon, In Sik;Cho, Min-Tae
    • The KSFM Journal of Fluid Machinery
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    • v.18 no.2
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    • pp.67-72
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    • 2015
  • The purpose of this study is to achieve energy saving effect of inverter driving multistage centrifugal pump. For determining the operation points in the pump system, the system curves should be obtained experimentally. To get the system curves, three pumps combined in parallel and one pump operated with different rotational speeds. But for variable speed pump system, energy saving rates can not be evaluated from operation efficiencies. That is why operation efficiencies, system curves, duty cycles, and input powers of the pump system were measured by the constructed experimental apparatus. The duty cycle segmented into different flow rates and weighting the average value for each segment by the interval time. The system was operated with two different periods. The mean duty cycles were collected from apartment and found that the system operated at 40% and at 50% or below capacity. Measured energy saving rate was 58.16%. Estimating method of energy saving rate could be more effective operation index than that of operation efficiency.

A Study on Heat Transfer Characteristics of the Outside Surface of Ambient Vaporizer (액화가스용 대기식 기화기의 외측 열전달 특성에 관한 연구)

  • Kang, Seung Mo;Seo, Dongmin;Ko, Dong Guk;Choi, Jun-Ho;Park, Woe-Chul;Im, Ik-Tae
    • Journal of the Semiconductor & Display Technology
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    • v.16 no.4
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    • pp.5-10
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    • 2017
  • This paper analyzed the heat transfer characteristics on the outer surface of the ambient air vaporizer which received the heat from the air through natural convection by using numerical and experimental methods. The working fluid was a liquid nitrogen. The experimental variables were the length (2,000 mm, 1,800 mm, 1,600 mm) and width of the vaporizer fin and the fluid flow ($6.7m^3/h$, $7.1m^3/h$, $7.5m^3/h$). Based on the temperature data from the experiments, the heat transfer coefficient was calculated. Numerical analyses were also conducted in order to find the heat transfer coefficient for the range of Nusselt number which was difficult to get the data from experiments. The correlation equation between Nusselt number and Rayleigh number were suggested using both the experimental and numerical data.

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Study on noise prediction of non-cavitating underwater propeller with hull-appendages effect (선체-부가물 영향을 고려한 비공동 수중추진기의 소음예측 연구)

  • Choi, Jihun;Seol, Hanshin;Park, Ilryong;Lee, Soogab
    • The Journal of the Acoustical Society of Korea
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    • v.38 no.3
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    • pp.247-255
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    • 2019
  • In this study, to predict the noise of a submarine propeller which is going to become bigger and faster, the non - cavitating propeller noise was predicted based on the numerical analysis which considering the interaction of the hull - appendages - propeller. In order to predict the radiated noise of the propeller, the flow field for the entire region of hull-appendages-propeller was computed by CFD (Computational Fluid Dynamics). And the noise for the thickness noise and the load noise was numerically predicted using FW-H (Ffwocs Williams-Hawkings) acoustic analogy. Numerical noise prediction results were verified by model tests and showed good agreement with the measurement results in predicting total noise level and low frequency noise.

Flow Simulation of Simulant Gel Propellant with $Al_2O_3$ Nano Particles in A U-Type Duct (U-자형 덕트에서의 $Al_2O_3$ 나노 입자를 포함한 모사 Gel 추진제의 유동 특성 수치해석)

  • Oh, Jeong-Su;Park, Ji-Hoon;Jang, Seok-Pil;Moon, Hee-Jang
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2010.05a
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    • pp.377-382
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    • 2010
  • The Present study uses non-Newtonian simulant gel propellant mixed by Water, Carbopol 941, and NaOH solution in order to analyze the gel propellant flow behavior. Rheological data have been measured and obtained prior to the analysis of flow characteristics where water-gel propellant as well as water-gel propellant with $Al_2O_3$ nano particles are both used. The critical Dean number were examined by numerical simulation of gel propellant in the U-shape duct flow. It is found that though gel-nano propellants have higher apparent viscosity, the critical Dean number did not showed notable difference with respect to the water-gel propellant. It is believe that this is due to the fact that the power law index of both propellants have close value, as was demonstrated by Fellouah et al.[1]

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An experimental study on the thermal entrance lengths for viscoelastic polymer solutions in turbulent tube flow (점탄성 특성을 가진 폴리머용액의 난류유동 열적입구길이에 관한 실험적 연구)

  • 유상신;황태성;엄정섭
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.12 no.5
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    • pp.1189-1196
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    • 1988
  • Thermal entrance lengths of turbulent tube flow for viscoelastic polymer solutions are investigated experimentally in the recirculating flow system with tubes of inside diameters 8.5mm(L/D=710) and 10.3mm(L/D=1158), respectively. In the present system, the hydrodynamic and thermal boundary layers develop simultaneously from the beginning of the test section. To provide the boundary condition of constant heat flux at the wall, the test tubes are heated directly by electricity. The polymer solution used in the current study is 1000 wppm aqueous solution of polyacrylamide(Separan AP-273). The apparent viscosity of the polymer solutions circulating in the flow system are measured by the capillary tube viscometer at regular time intervals. Thermal entrance lengths vary due to the rate of degradation. The entrance lengths of degraded polymer solutions are about 500~600 times the diameter. However, the entrance lengths of fresh polymer solutions are greater than the lengths of the test tubes used in this study suggesting that thermal entrance lengths for viscoelastic polymer solutions are greater than 1100 tube times the diameters. Friction factor is almost insensitive to the degradation, but the heat transfer $j_{H}$-factor is affected seriously by degradation. Based on the present experimental data of fresh solutions a correlation for the heat transfer $j_{H}$-factor is presented.ted.

Prediction of the turning and zig-zag maneuvering performance of a surface combatant with URANS

  • Duman, Suleyman;Bal, Sakir
    • Ocean Systems Engineering
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    • v.7 no.4
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    • pp.435-460
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    • 2017
  • The main objective of this study is to investigate the turning and zig-zag maneuvering performance of the well-known naval surface combatant DTMB (David Taylor Model Basin) 5415 hull with URANS (Unsteady Reynolds-averaged Navier-Stokes) method. Numerical simulations of static drift tests have been performed by a commercial RANS solver based on a finite volume method (FVM) in an unsteady manner. The fluid flow is considered as 3-D, incompressible and fully turbulent. Hydrodynamic analyses have been carried out for a fixed Froude number 0.28. During the analyses, the free surface effects have been taken into account using VOF (Volume of Fluid) method and the hull is considered as fixed. First, the code has been validated with the available experimental data in literature. After validation, static drift, static rudder and drift and rudder tests have been simulated. The forces and moments acting on the hull have been computed with URANS approach. Numerical results have been applied to determine the hydrodynamic maneuvering coefficients, such as, velocity terms and rudder terms. The acceleration, angular velocity and cross-coupled terms have been taken from the available experimental data. A computer program has been developed to apply a fast maneuvering simulation technique. Abkowitz's non-linear mathematical model has been used to calculate the forces and moment acting on the hull during the maneuvering motion. Euler method on the other hand has been applied to solve the simultaneous differential equations. Turning and zig-zag maneuvering simulations have been carried out and the maneuvering characteristics have been determined and the numerical simulation results have been compared with the available data in literature. In addition, viscous effects have been investigated using Eulerian approach for several static drift cases.

Review on Phlegm in Hyungsang medicine (담음에 관한 형상의학적 고찰)

  • Kim Min Jung;Kim Kyung Chul;Lee Yang Tae
    • Journal of Physiology & Pathology in Korean Medicine
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    • v.16 no.3
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    • pp.435-442
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    • 2002
  • Phlegm is defined as the static fluid in excess in one or more parts of the body. It is not only a pathologic product but also a pathogen itself. However, as it says Phlegm is another title for the body fluid. phlegm can be physiological. In Hyungsang medicine. since the Hyungsang which an individual shows determines his or her illness. the principle to treat phlegm also varies according to the individual's Hyungsang. Thus, the author reviewed ‘Jisan’s Special Lectures for Clinicians’ and summarized the concepts and diagnostics of phlegm, and treatment and regimens by Hyungsang medicine. The concepts of phlegm : Phlegm is not only a pathologic product of disharmony of Jung(精), Ki(氣), Shin(神) and Hyul(血) but also a driving force to mature and transform these constituents. Phlegm is another designation for the Fluid. Phlegm can act as an alternative substance or buffering agent. If we describe our body as the habitat of worms. phlegm could be the inhabitant. Diagnostics of phlegm : The infraorbital areas have a dark-gray or blackish coloring. A man who is feminine or a woman who is masculine tends to develop phlegm. One of the major signs of phlegm is pain in Chungwan(中脘). The color of the skin does not change. Treatment of phlegm by Hyungsang medicine. For the Jung type(精科) and the Hyul type(血科), phlegm treatment is to supply Jung and Blood or eliminate Damp-phlegm. The man needs tonifying herbs and the woman needs herbs which promote the flow of Ki(氣). Children and the aged are. tegardless of the nature of disease, to be warmed and supplemented. For the heavy man. treatment is to supplement Ki and eliminate Damp; for the slim man. treatment is to supplement Yin(陰) and purge Heat.

EFFECTS OF SUPPORT STRUCTURE CHANGES ON FLOW-INDUCED VIBRATION CHARACTERISTICS OF STEAM GENERATOR TUBES

  • Ryu, Ki-Wahn;Park, Chi-Yong;Rhee, Hui-Nam
    • Nuclear Engineering and Technology
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    • v.42 no.1
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    • pp.97-108
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    • 2010
  • Fluid-elastic instability and turbulence-induced vibration of steam generator U-tubes of a nuclear power plant are studied numerically to investigate the effect of design changes of support structures in the upper region of the tubes. Two steam generator models, Model A and Model B, are considered in this study. The main design features of both models are identical except for the conditions of vertical and horizontal support bars. The location and number of vertical and horizontal support bars at the middle of the U-bend region in Model A differs from that of Model B. The stability ratio and the amplitude of turbulence-induced vibration are calculated by a computer program based on the ASME code. The mode shape with a large modal displacement at the upper region of the U-tube is the key parameter related to the fretting wear between the tube and its support structures, such as vertical, horizontal, and diagonal support bars. Therefore, the location and the number of vertical and horizontal support bars have a great influence on the fretting wear mechanism. The variation in the stability ratios for each vibrational mode is compared with respect to Model A and Model B. Even though both models satisfy the design criteria, Model A shows substantial improvements over Model B, particularly in terms of having greater amplitude margins in the turbulence-excited vibration (especially at the inner region of the tube bundle) and better stability ratios for the fluid-elastic instability.

Flow Noise Analysis of Ship Pipes using Lattice Boltzmann Method (격자볼츠만기법을 이용한 선박 파이프내 유동소음해석)

  • Beom-Jin Joe;Suk-Yoon Hong;Jee-Hun Song
    • Journal of the Korean Society of Marine Environment & Safety
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    • v.29 no.5
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    • pp.512-519
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    • 2023
  • Noise pollution poses significant challenges to human well-being and marine ecosystems. It is primarily caused by the flow around ships and marine installations, emphasizing the need for accurate noise evaluation of flow noise to ensure environmental safety. Existing flow noise analysis methods for underwater environments typically use a hybrid method combining computational fluid dynamics and Ffowcs Williams-Hawkings acoustic analogy. However, this approach has limitations, neglecting near-field effects such as reflection, scattering, and diffraction of sound waves. In this study, an alternative using direct method flow noise analysis via the lattice Boltzmann method (LBM) is incorporated. The LBM provides a more accurate representation of the underwater structural boundaries and acoustic wave effects. Despite challenges in underwater environments due to numerical instabilities, a novel DM-TS LBM collision operator has been developed for stable implementations for hydroacoustic applications. This expands the LBM's applicability to underwater structures. Validation through flow noise analysis in pipe orifice demonstrates the feasibility of near-field analysis, with experimental comparisons confirming the method's reliability in identifying main pressure peaks from flow noise. This supports the viability of near-field flow noise analysis using the LBM.