• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.112-121
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• 1992

A numerical analysis was carried out to study two-dimensional turbulent natural convection in a square enclosure containing fluid of Prandtl number 6.05 within internal energy sources. The square enclosure was bounded by four rigid planes of constant equal temperature. Inclination angles of 0, 15, 30 and 45 deg. from the horizon for Rayleigh numbers from 1 * 10$^{6}$ to 1 * 10$^{9}$ were studied. Local and average Nusselts numbers are obtained on all four walls. If inclination angle exists, the average Nusselt number appears in increasing order at bottom, left, right and top wall.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.6 no.2
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• pp.93-101
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• 1986

The behavior of a plane buoyant jet discharged vertically upward into a stagnant uniform environment is analyzed by continuity, momentum transport equation by numerical scheme. The governing equations are solved by finite difference method employing stream function and vorticity transport and Prandtl's turbulent model. Results for centerline velocities and temperatures, temperature distribution and flow pattern in receiving environment due to buoyant jet in the range of discharge densimetric Froude number of 4 to 32 show good agreement with published data. Spreading rate and dispersion ratio, which are required in integral type analysis of whole range of buoyant jet and have not been obtained yet, are derived in terms of discharge densimetric Froude number and vertical distance from source.

• Journal of the Korean Society of Propulsion Engineers
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• v.13 no.2
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• pp.54-63
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• 2009

Large eddy simulation was conducted for flow development in a chamber with wall injection which simulates the cold flow in an idealized hybrid rocket motor. It was found that a peculiar timescale, roughly corresponding to St~0.5, resides in the flowfield resulting from the interaction between the main oxidizer and wall injected flows. However, the fact that this time characteristics is absent in the temperature field in the vicinity of the wall indicates that even a small regression rate renders the passive scalar, such as temperature, dissimilar to the velocity field. This implies that a classical approach, which assumes that constant turbulent Prandtl number, should be replaced by a more sophisticated turbulence models to accurately predict the temperature field in the hybrid motor.

• Solar Energy
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• v.8 no.1
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• pp.33-40
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• 1988

The characteristics of thermal instabilities of natural convection in a horizontal fluid layer bounded below by a rigid plate and above by an interface with a passive gas is presented. The critical Grashof number decreases as the surface tension gradient effect (Marangoni effect) at the interface increases and the flow remains unstable for a critical Marangoni number depending on Prandtl numbers. These results are in substantial agreement with those of Smith and Davis.

• The Journal of Engineering Research
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• v.1 no.1
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• pp.23-30
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• 1997

Energy transfer by free convection arises in many engineering applications, such as a hot steam radiator for heating a room, refrigeration coils, electric transformers, heating elements and electronic equipments. Generally unsteady natural convection flow in a horizontal channel with arbitrary wall temperatures and the mathematical and physical basis of convection transport has been considered in general. A physically meaningful exact solution of the problem has been obtained in a closed form by the application of the standard finite sine transform technique. Influences of the governing parameters, the Prandtl number and the Rayleigh number, to bring the flow and heat transfer to final steady states have been discussed separately. For constant values of the arbitray wall temperatures and of the function, determining the average axial velocity, the final steady state is approached in different times respectively for the cases when the Prandtl number Pr>1 and Pr<1. It is also seen that the function, representing the axial temperature gradient, is influenced by none of the governing parameters : but the steady state flow is influenced only by the Rayleigh number. There are, of course, many applications. Free convection strongly influences heat transfer from pipes and transmission lines, as well as from various electronic devices. It is also relevant to the environmental sciences, where it is responsible for oceanic and atmospheric motions, as well as related heat transfer processes.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.11
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• pp.717-726
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• 2016

This study evaluated the effect of aspect ratio of an enclosure with a heated inner circular cylinder on three-dimensional natural convection. The immersed boundary method was used to model the inner circular cylinder based on the finite volume method. The Rayleigh number was varied between $10^5$ and $10^6$, and the Prandtl number was maintained at 0.7. The aspect ratio of the three-dimensional enclosure was changed in steps of 1 within a range of 1-4 by increasing the width of the enclosure. In this study, the flow and thermal fields in the enclosure reached the steady state, and showed a mirror-symmetric pattern with respect to the center plane (x=0). In addition, the surface-averaged Nusselt number of the inner circular cylinder increased, while the total surface-averaged Nusselt number of the enclosure walls decreased with increase in the aspect ratio of the enclosure.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.725-733
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• 1990

An analysis of laminar mixed convection flow adjacent to the inclined flat surface which is subjected to a uniform temperature in a uniform free stream is performed. Nonsimilar boundary layed equation are derived by using the mixed convection parameters such that smooth transition from the purely forced convection limit to the purely free convection limit is possible. The governing equations are solved by a finite difference method using the coupled box scheme of sixth order. Numerical results are presented for prandtl numbers of 0.7 and 7 with the angle of inclination ranging from 0 to 90 degree from the vertical. The velocity distributions for the buoyancy assisting flow exhibit a significant overshoot above the free stream value in the region of intense mixed convection and the velocity field is found to be more sensitive to the buoyancy effect than the temperature field. The separation point near the wall was obtained for the buoyancy opposing flow. The local Nusselt number increases for buoyancy assisting flow and decreases for opposing flow with increasing value of the local Grashoff number in the mixed convection parameter. For large Prandtl number, the Nusselt number and the friction factor decrease significantly near the separation point. Present numerical predictions are in good agreement with recent experimental results by Ramachandran.

• Journal of computational fluids engineering
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• v.22 no.1
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• pp.110-115
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• 2017

Natural convection of a fluid with the Prandtl number of 7(water) in a horizontal annulus with constant temperature walls is numerically investigated. The inner cylinder is hotter than the outer cylinder. The flows are classified by the number of eddies in a half annulus. It is found that dual or triple solutions exists above a critical Rayleigh number for an annulus with a aspect ratio $D_i/L=4$. Transitions of $3{\rightarrow}1$ and $2{\rightarrow}1$ eddy flow occur with decrease of Rayleigh number. However, reverse transitions of $1{\rightarrow}3$ and $1{\rightarrow}2$ eddy flow do not occur with increase of Rayleigh number, and no hysteresis phenomenon is observed. In the regime of triple solutions, the 3 eddy flow has the largest mean Nusselt number value and the 1 eddy flow has the smallest value.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.210-215
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• 2005

A three-dimensional numerical simulation is performed to investigate on a low Reynolds number mixed convection in a horizontal rectangular channel with the upper part cooled and the lower part heated uniformly. The three-dimensional governing equations are solved using a finite volume method. For convective term, the central differencing scheme is used and for the pressure correction, the PISO algorithm is used. Solutions are obtained for A=4, Pr=0.72, 10, 909, the Reynolds number ranging from $2.1{\times}10^{-2}$ to $1.2{\times}10^{-1}$, the Rayleigh number is $3.5{\times}10^4$. It is found that vortex roll structures of mixed convection in horizontal rectangular channel can be classified into three roll structures which affected by Prandtl number and Reynolds number.

• Solar Energy
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• v.6 no.1
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• pp.60-69
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• 1986

Two-dimensional finite difference numerical analysis is used to study conjugate natural convection heat transfer from a horizontal conducting tube with one vertical axial fin. By increasing dimensionless fin length ($L_F$), the mean total Nusselt number of the upward fin is slightly less than that of the downward fin at $L_F\;{\le}\;0.18$ and is higher than that of the downward fin at $L_F\;>\;0.18$. However comparing the upward fin and the downward fin with the no fin, the mean total Nusselt numbers of downward fin and upward fin at $L_F=0.30$ are increased approximately 4.01% and 5.51%, respectively. As Rayleigh number, Prandtl number and Biot number increase, the mean total and the mean tube Nusselt numbers are increased, but as wall thickness increases, the mean total and the mean tube Nusselt numbers are decreased. As the fin conduction parameter increases, the mean total Nusselt number is slightly increased because of increasing the mean fin Nusselt number.