• Title/Summary/Keyword: Prandtl Number Effect

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The Effect of the Prandtl Number on Natural Convection in a Square Enclosure with Inner Cylinder of Various Positions (Prandtl 수 변화가 다양한 위치의 원형실린더가 존재하는 정사각형 밀폐계 내부 자연대류 현상에 미치는 영향)

  • Seong, Seon Yu;Choi, Changyoung;Ha, Man Yeong;Yoon, Hyun Sik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.38 no.11
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    • pp.943-950
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    • 2014
  • This paper presents a numerical study conducted for analyzing the effect of the Prandtl number on natural convection in a square enclosure with an inner circular cylinder in various positons. Several Prandtl numbers (Pr = 0.1, 0.7, and 7) and Rayleigh numbers (Ra = $10^3$, $10^4$ and $10^5$) are considered in the numerical study, along with different positions of the inner circular cylinder. The position of the inner circular cylinder is changed in steps of 0.1 in the range of -0.2 to 0.2. The effect of the Prandtl number on natural convection in the enclosure is analyzed on the basis of the thermal and flow fields and the distribution of the Nusselt number. Regardless of the position of the cylinder, when the Rayleigh number is $10^5$, the surface-averaged Nusselt number of the inner cylinder and the enclosure increases as the Prandtl number increases.

Effect of Prandtl Number on Natural Convection in Tilted Square Enclosure with Inner Circular Cylinder (Prandtl 수 변화가 내부 원형 실린더가 존재하는 기울어진 정사각형 밀폐계 내부의 자연대류 현상에 미치는 영향)

  • Mun, Gi Su;Choi, Changyoung;Ha, Man Yeong;Yoon, Hyun Sik
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.38 no.11
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    • pp.935-942
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    • 2014
  • A numerical analysis of the effect of the Prandtl number on the natural convection in a cold outer tilted square enclosure with an inner hot circular cylinder is presented. Several Prandtl numbers (Pr=0.1, 0.7, 7) are considered, with different angles($0^{\circ}$, $15^{\circ}$, $30^{\circ}$, $45^{\circ}$) for the enclosure and Rayleigh numbers ($Ra=10^3$, $10^4$, $10^5$). The effect of the Prandtl number on the natural convection is analyzed using isotherms and streamline and surface-averaged Nusselt numbers. The flow and heat transfer characteristics are found to be dependent on the time for $Ra=10^5$ and Pr=0.1 at angles of $0^{\circ}$ and $45^{\circ}$. However, in the other cases, the flow and heat transfer characteristics are independent of the time.The surfaceaveraged Nusselt number increases with an increase in the Prandtl number. As the Prandtl number increases, the Nusselt number becomes larger regardless of the angle for $Ra=10^5$. In particular, the Nusselt number steeply increases when the angle is $45^{\circ}$ for $Ra=10^5$ and Pr=0.1.

Thermo-Flow Analysis of Offset-Strip Fins according to Prandtl Number (Prandtl 수에 따른 옵셋 스트립 핀에서의 열 및 유동 분석)

  • Joo, Youn-Sik;Kong, Dong-Hyun;Lee, Kwan-Soo
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.21 no.6
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    • pp.340-346
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    • 2009
  • This paper numerically investigates thermo-flow characteristics of offset strip fins to obtain a correlation between heat transfer and pressure drop. The flow was divided into three regimes, i.e. laminar, transition and turbulent. The predicted j and f values from the SST k-$\omega$ turbulence model agreed with previous correlations with the error less than 20% in transition and turbulent regimes. Heat transfer and pressure drop were predicted by varying Prandtl number from 0.5 to 40. The Prandtl number showed little effects on pressure drop but had great effect on the heat transfer characteristics. An overall correlation to predict j was suggested by incorporating the effect of Pr and a new j correlation was suggested for each Pr.

Analysis of mixed convective laminar flow and heat transfer about a sphere (혼합대류에 의한 구 주위의 충류유동 및 열전달 해석)

  • 이준식;김택영
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.11 no.2
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    • pp.345-353
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    • 1987
  • An analysis is performed to study flow and heat transfer characteristics of mixed free and forced convection about a sphere. Nonsimilar boundary layer equations which are valid over the entire regime of mixed convection are derived in terms of the mixed convection parameter, Gr/Re$^{2}$, through a dimensional analysis. The transformed conservation equations are solved by a finite difference method for the whole range of mixed convection regime. Numerical results for fluids having the Prandtl number 0.7 and 7 are presented. As the mixed convection parameter increases, the local friction coefficient and local heat transfer coefficient increases as well. For small Prandtl number, the friction coefficient is larger, while for large Prandtl number, the heat transfer coefficient is larger. Natural convection effect on the forced flow is more sensitive for small Prandtl number fluid. Flow separation migrates rearward as an increase in the mixed convection parameter. For small Prandtl number, the buoyancy effect is relatively small so that the flow separation occurs earlier.

NUMERICAL STUDY FOR PRANDTL NUMBER DEPENDENCY ON NATURAL CONVECTION IN AN ENCLOSURE WITH SQUARE ADIABATIC BODY (사각 단열체가 존재하는 밀폐계 내부에서 Pr수 변화에 따른 자연대류 현상에 대한 수치적 연구)

  • Lee, Jae-Ryong
    • Journal of computational fluids engineering
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    • v.16 no.3
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    • pp.29-36
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    • 2011
  • The natural convection in a horizontal enclosure heated from the bottom wall, cooled at the top wall, and having a square adiabatic body at its centered area was studied. Three different Prandtl numbers (0.01, 0.7 and 7) were considered for an effect of the Prandtl number on natural convection. A two-dimensional solution for unsteady natural convection was obtained, using Chebyshev spectral methodology for different Rayleigh numbers varying over the range of $10^4$ to $10^6$. It had been experimentally and numerically reported [1,2] that the heat transfer mode becomes oscillatory when Pr is out of a specific Pr band beyond the critical Ra. In this study, we reproduced this phenomenon numerically. The variation of time- and surface-averaged Nusselt numbers on the hot and cold walls for different Rayleigh numbers and Prandtl numbers was presented to show the overall heat transfer characteristics in the system. And also, the isotherms and streamline distributions were presented in detail to compare the physics related to their thermal behavior.

NUMERICAL ANALYSIS FOR PRANDTL NUMBER DEPENDENCY ON NATURAL CONVECTION IN AN ENCLOSURE HAVING A VERTICAL THERMAL GRADIENT WITH A SQUARE INSULATOR INSIDE

  • Lee, Jae-Ryong;Park, Il-Seouk
    • Nuclear Engineering and Technology
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    • v.44 no.3
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    • pp.283-296
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    • 2012
  • The natural convection in a horizontal enclosure heated from the bottom wall, cooled at the top wall, and having a square adiabatic body in the center is studied. Three different Prandtl numbers (0.01, 0.7 and 7) are considered for the investigation of the effect of the Prandtl number on natural convection. Adiabatic boundary conditions are employed for the side walls. A two-dimensional solution for unsteady natural convection is obtained, using an accurate and efficient Chebyshev spectral methodology for different Rayleigh numbers varying over the range of $10_3$ to $10_6$. It had been experimentally reported that the heat transfer mode becomes oscillatory when Pr is out of a specific Pr band beyond the critical Ra. In this study, we reproduced this phenomenon numerically. It was found that when Ra=$10_6$, only the case for intermediate Pr (=0.7) reached a non-changing steady state and the low and high Pr number cases (Pr=0.01 and 7) showed a periodically oscillatory fashion hydrodynamically and thermally. The variation of time- and surface-averaged Nusselt numbers on the hot and cold walls for different Rayleigh numbers and Prandtl numbers are presented to show the overall heat transfer characteristics in the system. Further, the isotherms and streamline distributions are presented in detail to compare the physics related to their thermal behavior.

Thermo-Flow Analysis of Offset-strip fins according to Prandtl Number (Plandtl 수에 따른 옵셋 스트립핀에서의 열 및 유동 분석)

  • Joo, Youn-Sik;Kim, Min-Soo;Lee, Kwan-Soo
    • Proceedings of the SAREK Conference
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    • 2008.11a
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    • pp.233-238
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    • 2008
  • This paper numerically investigates thermo-flow characteristics of offset strip fins to obtain a correlation between heat transfer and pressure drop. The flow was divided into three regimes, i.e. laminar, transition and turbulent. The predicted j and f values from the SST k-$\omega$ turbulence model agreed with previous correlations with the error less than 20% in transition and turbulent regimes. Heat transfer and pressure drop were predicted by varying Prandtl number from 0.5 to 40. The Prandtl number showed little effects on pressure drop but had great effect on the heat transfer characteristics. An overall correlation to predict j was suggested by incorporating the effect of Pr and a new j correlation was suggested for each Pr.

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Effect of axial rotation on oscillatory thermocapillary flow in half-zone of high Prandtl number fluid (높은 Prandtl 수 유체에서 축회전이 열모세관 유동의 진동에 미치는 영향)

  • Jeon, Seung-Won;Lee, Kyu-Jung
    • Proceedings of the KSME Conference
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    • 2008.11b
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    • pp.2248-2253
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    • 2008
  • A numerical study on oscillatory thermocapillary flow in half-zone has performed to understand the effect of axial rotation. 2d unsteady code is developed to observe the onset of oscillation. 2cs Silicone oil with Prandtl number of 26.5 is used as a working fluid. The critical temperature difference at onset of oscillation is investigated under the different aspect ratios and rotation modes. It is shown that the onset of oscillation is delayed when aspect ratio reduces and rotating speed increases. The oscillatory flow is strongly reduced under top rotation and co-rotation modes, while it is augmented under bottom rotation and counter-rotation modes. It is thought that interaction between return flow and bottom wall is important to explain the oscillatory flow.

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Numerical Analysis of Turbulent Flow and Heat Transfer in a Rectangular Duct with a 180° Bend Degree (직사각단면을 갖는 180°곡관내의 난류 유동및 열전달에 관한 수치해석적 연구)

  • Choi, Y.D.;Moon, C.
    • Korean Journal of Air-Conditioning and Refrigeration Engineering
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    • v.6 no.4
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    • pp.325-336
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    • 1994
  • A numerical simulation of velocity and temperature fields and Nusselt number distributions is performed by using the algebraic stress model (ASM) for the velocity profiles and low Reynolds number ${\kappa}-{\varepsilon}$ model and the algebraic heat flux model(AHFM) for turbulent heat transfer in a $180^{\circ}$ bend with a constant wall heat flux. In the low Reynolds number ${\kappa}-{\varepsilon}$ model, turbulent Prandtl number is modified by considering the streamline curvature effect and the non-equilibrium effect between turbulent kinetic energy production and dissipation rate. Every heat flux term presented in the transport equation of turbulent heat flux is reduced to algebraic expressions in a way similar to algebraic stress model. Also. in the wall region, low Reynods number algebraic heat flux model(AHFM) is applied.

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A Numerical Study for Natural Convective Heat Transfer by Finite Element Method (유한요소법을 이용한 자연대류열전달 수치해석 연구)

  • ;Ashley F. Emery
    • Journal of Energy Engineering
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    • v.7 no.1
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    • pp.113-121
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    • 1998
  • In natural convection flows, the fluid velocities are highly dependent on the thermal field and property variations can have a strong effect on both the flow and thermal fields. To examine the effect of property variations, at first, numerical analyses covering wide range of the Prandtl number under the same Rayleigh numbers have been carried out. Next, we have modeled the viscosity and thermal conductivity as parabolic functions of temperature and a comprehensive set of numerical solutions have been obtained to understand the effect. The Prandtl number dependence of Nusselt number is fairly strong even though the effect is still weak compared to the Rayleigh number dependence. When thermophysical properties are dependent on temperature, the flow field showed a fairly weak variation except near boundaries, whereas the temperature field is strongly affected, especially by the temperature dependent thermal conductivity.

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