• Title/Summary/Keyword: Reynolds number effects

Search Result 519, Processing Time 0.026 seconds

Effects of Nozzle Size and Height of Aluminum Foam Heat Sink on Jet Impingement Heat Transfer (충돌제트 열전달에 발포알루미늄 방열기의 높이와 노즐의 크기가 미치는 영향)

  • Kim, Seo-Yeong;Baek, Jin-Uk;Gang, Byeong-Ha
    • Transactions of the Korean Society of Mechanical Engineers B
    • /
    • v.25 no.9
    • /
    • pp.1263-1271
    • /
    • 2001
  • An experimental study is carried out for an aluminum foam heat sink attached to an isolated heat source to evaluate high potential of aluminum foam as a heat sink with impinging jets. The effects of the pore density and the height of the aluminum foam heat sink, the jet Reynolds number, and the nozzle diameter are delineated in comparison with a conventional pin type heat sink. It is found that the aluminum foam with small pores is inefficient for the heat transfer enhancement due to the large flow friction at the given porosity. In the parameter ranges of the present study, the change in the nozzle diameter shows no significant effects on the surface temperature of the aluminum foam heat sink at a given Reynolds number. The heat transfer enhancement is strongly dependent on the jet Reynolds number and shows a maximum value at a moderate Reynolds number.

Effects of Hub-to-Tip Ratio and Reynolds Number on the Performance of Impulse Turbine for Wave Energy Power Plant

  • Ajit Thakker;Khaleeq, Hammad-Bin;Manabu Takao;Toshiaki Setoguchi
    • Journal of Mechanical Science and Technology
    • /
    • v.17 no.11
    • /
    • pp.1767-1774
    • /
    • 2003
  • The objective of this paper is to present the performance comparison of the impulse turbines for different diameters. In the study, the investigation has been performed experimentally by model testing for some diameters, especially 0.3 m and 0.6 m. The experiment was performed for Reynolds number range of 0.17 ${\times}$ 10$\^$5/ -1.09 ${\times}$ 10$\^$5/ and for different values of hub-to-tip ratio ν ranging from 0.6 to 0.85. As a result, it was found that the critical Reynolds number is to be around 0.5 ${\times}$ 10$\^$5/ for ν=0.6 and 0.4 ${\times}$ 10$\^$5/ for ν=0.7. For the hub-to-tip ratio, the optimum value is 0.7 when the turbine is operated at lower Reynolds number. However, its value seems to be 0.6 at higher Reynolds number in the tested range.

Numerical Study for Mixing Characteristics of an Oscillating Micro-stirrer (미소진동교반기의 혼합특성에 대한 수치적 연구)

  • Kim, Yong-Dae;Maeng, Joo-Sung
    • 유체기계공업학회:학술대회논문집
    • /
    • 2006.08a
    • /
    • pp.309-312
    • /
    • 2006
  • Effective mixing is an important problem in microfluidics for chemical and biomechanical applications. In this study, the influences of the Reynolds number and the oscillating frequency on mixing characteristics of micro-stirrer are studied in a microchannel with single stirrer. The influence of fluid inertial effects in an active mixer is first discussed. It is found that the stirring effects by stirrer oscillation are promptly attenuated at low Reynolds number, which makes greatly difficult the rapid mixing. As the inertial effects are increased, the chaotic advection is generated and then developed. The mixing phase is finally developed some mushroom shaped structure. And the mixing efficiency is also studied as a function of the oscillating frequency. We found that the mixing efficiency does not always increase with higher oscillating frequency of stirrer. Consequently, we found the functional relation between the optimal frequency of a stirrer and the Reynolds number.

  • PDF

Reynolds Number Effects on the Near-Wake of an Oscillating Airfoil, Part 2: Turbulent Intensity (진동하는 NACA 4412 에어포일 근접후류에서의 레이놀즈수 효과 2: 난류강도)

  • Jang,Jo-Won
    • Journal of the Korean Society for Aeronautical & Space Sciences
    • /
    • v.31 no.8
    • /
    • pp.8-18
    • /
    • 2003
  • An experimental study is carried out to investigate the Reynolds number effects on the near-wake of an airfoil oscillating in pitch. An NACA 4412 airfoil is sinusoidally pitched about the quarter chord point between the angle of attack -6$^{\circ}$ and +6$^{\circ}$. A hot-wire anemometer is used to measure the turbulent intensity in the near-wake region of an NACA 4412 airfoil. The freestream velocities of present work are 3.4, 12.4, 26.2 m/s, and the corresponding Reynolds numbers are $5.3{\times}10^4,\;1.9{\times}10^5,\;4.1{\times}10^5$ and the reduced frequency is 0.1. Axial turbulent intensity profiles are presented to show the Reynolds number effects on the near-wake region behind an airfoil oscillating in pitch. All the cases in these measurements show that the turbulent intensities by the change of the Reynolds number are very large at the lowest Reynolds number $R_N=5.3{\times}10^4$; and are small at the other Reynolds number $(R_N=1.9{\times}10^5\;and\;4.1{\times}10^5)$ in the near-wake region. The significant difference of turbulent intensity between $R_N=5.3{\times}10^4,\;and\;1.9{\times}l0^5$ is observed. A critical value of the Reynolds number in the near-wake of an oscillating NACA 4412 airfoil which indicates laminar separation, no separation or turbulent separation exists in the range between $R_N=5.3{\times}10^4\;and\;1.9{\times}10^5$.

A flow characteristic of non-newtonian fluid in coutte flow of concentric cylinder (동심원통속의 Coutte flow에 있어서 비 Newton 유체의 유동특성)

  • 권혁칠;이성노;부전유사
    • Journal of the korean Society of Automotive Engineers
    • /
    • v.14 no.3
    • /
    • pp.109-114
    • /
    • 1992
  • The purpose of this study is to experimentally research the effects of polymer additives on turbulent transition of Couette flow between concentric cylinders when outer one is rotating and inner one is at rest; the diameter ratio being 0.2. Aqueous polymer solution generate the degradation phenomena in machine forming work, but this is not effected in about 10 minute at 5ppm. aqueous polymer solution testing. The Reynolds number, referred to the gap distance and rotation velocity of the outer cylinder, of turbulent transition is about 20000 for water flow. In the laminer region, the torque value is as same as theoretical one in the region of low Reynolds number, but becomes high with an increase in the Reynolds number. The polymer additives reduce the Reynolds number for turbulent transtition. In the turbulent region, the torque is remarkably reduced by the polymer additives, soluble polymer take down effect of turbulent transition boundary torque.

  • PDF

Numerical Study on Combined Heat Transfer in NIR Dryer for Agricultural and Marine Products (근적외선 농수산물 건조기의 복합열전달특성에 관한 수치적 연구)

  • Choi, H.K.
    • Journal of Biosystems Engineering
    • /
    • v.31 no.5 s.118
    • /
    • pp.395-402
    • /
    • 2006
  • Mixed heat transfer in an indirected NIR (Near Infrared Ray) dry chamber was investigated numerical analysis. It is Important that the miked heat transfer effects on double parameters which the Reynolds number and the position of emit lamp. Reynolds number are based on the outer diameter of the cylinder range from 103 to $30{\times}105$. Four difference heat transfer regimes of behavior are apparent: forced convection and radiation on the outer surface of the cylinder, pure conduction, pure natural convection and radiation between lamp surface and inner surface of the cylinder. The temperature and flow patterns are illustrated by iso-contour lines for the double parameters. Also presented are results on the convective heat transfer flux and the radiative heat transfer flux as increased with Reynolds number.

REYNOLDS NUMBER EFFECTS ON MASS TRANSFER IN TURBULENT PIPE FLOW: PART II. INSTANTANEOUS CONCENTRATION FIELD, HIGHER-ORDER STATISTICS AND MASS TRANSFER BUDGETS (난류 파이프 유동 내 물질전달에 대한 레이놀즈 수 영향: Part II. 순간농도장, 고차 난류통계치 및 물질전달수지)

  • Kang, Chang-Woo;Yang, Kyung-Soo
    • Journal of computational fluids engineering
    • /
    • v.17 no.3
    • /
    • pp.59-67
    • /
    • 2012
  • Large Eddy Simulation(LES) of turbulent mass transfer in fully developed turbulent pipe flow has been performed to study the effect of Reynolds number on the concentration fields at $Re_{\tau}=180$, 395, 590 based on friction velocity and pipe radius. Dynamic subgrid-scale models for the turbulent subgrid-scale stresses and mass fluxes were employed to close the governing equations. Fully developed turbulent pipe flows with constant mass flux imposed at the wall are studied for Sc=0.71. The mean concentration profiles and turbulent intensities obtained from the present LES are in good agreement with the previous numerical and experimental results currently available. The effects of Reynolds number on the turbulent mass transfer are identified in the higher-order statistics(Skewness and Flatness factor) and instantaneous concentration fields. The budgets of turbulent mass fluxes and concentration variance were computed and analyzed to elucidate the effect of Reynolds number on turbulent mass transfer. Furthermore, to understand the correlation between near-wall turbulence structure and concentration fluctuation, we present an octant analysis in the vicinity of the pipe wall.

Experimental Study of Reynolds Number Effects on Heat/Mass Transfer and Pressure Drop Characteristics in a Rotating Smooth Duct (매끈한 벽면을 가진 회전덕트 내 레이놀즈 수에 따른 열/물질전달 및 압력강하 특성 연구)

  • Kim, Kyung-Min;Park, Suk-Hwan;Lee, Dong-Hyun;Cho, Hyung-Hee
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.18 no.11
    • /
    • pp.888-895
    • /
    • 2006
  • The present study has been conducted to investigate the effects of Reynolds number on heat/mass transfer and pressure drop characteristics in a rotating smooth two-pass duct. For stationary cases, the heat/mass transfer and pressure drop Is decreased on turning region of both leading and trailing surfaces as Reynolds number increases. For rotating cases, increment of Reynolds number affects differently the heat/mass transfer and pressure drop on the leading and trailing surfaces. In the first pass, for example, the heat/mass transfer on the leading surface is greatly increased, though the heat/mass transfer on the trailing surface is almost the same. The reason is that effect of the main flow is more dominant than effect of secondary flow. In particular, it gave decrement of the heat/mass transfer and the pressure drop at turning region and upstream region of second pass for both non-rotating and rotating cases.

Thermal performance of the spherical capsule system using paraffin as the thermal storage material (파라핀 축열재를 사용한 구형캡슐 시스템의 전열성능)

  • Cho, K.N.;Choi, S.H.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
    • /
    • v.9 no.3
    • /
    • pp.354-363
    • /
    • 1997
  • The purpose of the present work is to show the best thermal storage material and the sensitivity of the parameters on the thermal performance by experimentally investigating the effects of the parameters on the thermal performance of the spherical capsule system using paraffins superior to the commercial one. The paraffins were n-Tetradecane and the mixture of n-Tetradecane 40% and n-Hexadecane 60%. The experimental parameters were the Reynolds number of 8, 12, and 16 and the inlet temperature of-7, -4, -1, and $2^{\circ}C$. The charging and the discharing time, the dimensionless thermal storage amount, and the averge heat transfer coefficient in the tank were obtained by utilizing the local temperature variation in the tank. The local charging and discharging time in the tank was axially and radially different a lot. The effects of the inlet temperature on the charging and the discharging time were larger during the charging process than during the discharging process, but the effects of the Reynolds number on the charging and the discharging time were in reverse order. The paraffins were better by 11~72% than the water with the inorganic material in the charging time aspect, but no difference in the discharging time aspect. The effects of the Reynolds number on the dimensionless thermal storage amount were smaller than the effects of the inlet temperature during the charging process, but in reverse order during the discharging process within the working range of the experimental parameters. The effects of the inlet temperature and the Reynolds number on the average heat transfer coefficient were larger during the discharging process than during the charging process. The average heat transfer coefficient for the paraffins was larger by 40% maximum than that for the commercial material during the charing and the discharging process.

  • PDF

Effects of Reynolds Number and Shape of Manifold on Flow Rate in Separator for Polymer Electrolyte Fuel Cell (ICCAS 2004)

  • Huang, Chaii;Ozawa, Yoshikuni;Ennoji, Hisayuki;Iijima, Toshio
    • 제어로봇시스템학회:학술대회논문집
    • /
    • 2004.08a
    • /
    • pp.68-71
    • /
    • 2004
  • Recently, a great deal of research and development of a fuel cell have been carried out to solve problems on the drain of fossil fuel, air pollution and global warning. In order to improve the efficiency of a fuel cell, it is necessary to clarify the flow in separator. In this study, distributions of velocity flow rate and pressure, and streamlines are examined in detail from numerical analysis with CFD code. In the experiment the distribution of flow rate is measured and flow in the each grooves of the separator is visualized by dye method changing Reynolds number. Furthermore, effects of size of the inlet and outlet manifolds and shape of ribs near the inlet outlet on the distributions of flow and pressure are examined.

  • PDF