• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.3 s.246
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• pp.238-245
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• 2006

This paper proposes appropriate conjugate parameters and dimensionless temperatures to analysis the conjugate problem of heat conduction in solid wall coupled with laminar film condensation flow adjacent to horizontal flat plate. An efficient methods for some fluids are proposed for its solution. The momentum and energy balance equations are reduced to a nonlinear system of ordinary differential equations with four parameters: the Prandtl number, Pr, Modified Jacob number, $Ja^*/Pr$, defined by an overall temperature difference, a property ratio $\sqrt{\rho_l{\mu}_l/{\rho_v{\mu}_v}$ and the conjugate parameter $\zeta$. The obtained similarity solution reveals the effect of the conjugate parameter, and the results are compared with the simplified solution. The variations of the heat transfer rates as well as the interface temperature and frictions along the plate are shown explicitly.

• Nuclear Engineering and Technology
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• v.23 no.2
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• pp.200-209
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• 1991

A new semi-empirical average heat transfer correlation applicable for both laminar and turbulent film-wise condensation on a vertical surface has been presented. Re functional form of the present correlation is based on the representative existing correlations for laminar and turbulent film flows, whereas the numerical coefficients of the present correlation have been determined by the least squares method using experimental data obtained from the open literatures. In addition, the performance of the present as well as the seven existing correlations (four for laminar and three for turbulent film flow regimes) were evaluated for their accuracy and the range of application. The result shows that for laminar film filow regimes Zazuli's and the present correlations give the samllest values of mean error, whereas for turbulent film How regimes Kirkbride and Badger's and the present correlations produce the smallest values of mean error.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05b
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• pp.88-94
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• 1996

The dependence of the node size in the condensation heat transfer coefficient for an inclined surface is eliminated and two correlations applicable for laminar and turbulent regimes are implemented in RELAP5/MOD3.1. The newly implemented correlations are used according to their applicable ranges of the film Reynolds numbers Reps which are calculated recursively to track the condensate film thickness along the condensation length. The modified version is compared with the original one through comparison with an analytical solution and the simulation of the Secondary Condensers (SC). It turns out that the simulation results by this modified version are independent of the node size and are better agreement with the analytical solution than those by the original one.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.11
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• pp.1169-1176
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• 2011

Liquid film flows are classified into waveless laminar, wavy laminar, and turbulent flows depending on the Reynolds number or the flow stability. Since the wavy motions of the film flows are so intricate and nonlinear, studies on them have largely been experimental. Most numerical approaches have been limited to the waveless flow regime. The various free surface-tracking schemes adopted for this problem were used to more accurately estimate the average film thickness, rather than to capture the unsteady wavy motion. In this study, the wavy motions in laminar wavy liquid film flows with Reynolds numbers of 200-1000 were simulated with various numerical schemes based on the volume of fluid (VOF) method for interface tracking. The results from each numerical scheme were compared with the experimental results in terms of the average film thickness, the wave velocity, and the wave amplitude.

• Journal of the korean Society of Automotive Engineers
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• v.2 no.1
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• pp.21-31
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• 1980

Two phase boundary layer equations of laminar filmwise condensation are solved by an approximate integral method under the following condition; saturated vapour flows vertically downward over a cooled surface of uniform temperature, the condensate film is so thin that the inertia and convection terms are neglected. The following conclusions are drawn under the above assumptions. 1. free convection In case of the linear temperature profile in a liquid film, numerical results for the average coefficients of heat transfer may be expressed as N $u_{m}$=4/3,(G $r_{l}$ /4.H)$^{1}$4/ and in case of the quadratic profile, numerical results may be expressed as N $u_{m}$=2/1.682,(G $r_{l}$ /H)$^{1}$4/. 2. Forced convection When the temperature profile is assumed to be linear in a liquid film, numerical results fir the average heat transfer coefficients may be expressed as N $u_{m}$=(A, R $e_{l}$ /H)$^{1}$2/. This expression is compared with the experimental results hitherto reported; For theoretical Nusselt number (N $u_{m}$)$_{th}$<2*10$^{4}$, the experimental Nusselt number (N $u_{m}$)$_{exp}$ is on the average larger than theoretical Nusselt number (N $u_{m}$)$_{th}$ by 30%. For (N $u_{m}$)$_{th}$>2*10$^{4}$, experimental Nusselt number (N $u_{m}$)$_{exp}$ is about 1.6 times as large as theoretical Nusselt number (N $u_{m}$)$_{th}$. These large deviation may be caused by the presence of turbulence in the liquid film. In case of the quadratic temperature profile in a liquid film, numerical results for the average coefficients of heat transfer may be expressed as N $u_{m}$'=(2,A,Re/H)$^{1}$2/. This formular shows that theoretical Nusselt number (N $u_{m}$)$_{th}$ is larger than experimental Nusselt number (N $u_{m}$)$_{exp}$ by 60%. It is speculated that when the temperature difference between cooled surface and saturated vapour is small, temperature profile in a liquid film is quadratic.quadratic.. quadratic.quadratic..atic..

• Proceedings of the Korean Nuclear Society Conference
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• 1997.10a
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• pp.585-590
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• 1997

The condonation models in the standard RELAP5/MOD3.2 code are assessed and improved based on the database, which is constructed from the previous experimental data on various condonation phenomena The default model the laminar film condonation in RELAP5/MOD3.2 does not give any reliable predictions, and its alternative model always predicts higher values than the experimental data Therefore, it is needed to develop a new correlation based on the experimental data of various operating ranges in the constructed database. The Shah correlation, which is used to calculate the turbulent film condensation heat transfer coefficients in the standard RELAP5/MOD3.2, well predicts the experimental data in the database. The horizontally stratified condonation model of RELAP5/MOD3.2 overpredicts both cocurrent and countercurrent experimental data The correlation proposed by H.J.Kim predicts the database relatively well compared with that of RELAP5/MOD3.2 The RELAP5/MOD3.2 model should use the liquid velocity for the calculation of the liquid Reynolds number and be modified to conifer the effects of the gas velocity and the film thickness.

• Journal of Mechanical Science and Technology
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• v.16 no.7
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• pp.966-974
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• 2002

An analytic approach has been employed to study condensate film thickness distribution inside cave-shaped cavity of a flat plate heat pipe. The results indicate that the condensate film thickness largely depends on mass flow rate and local velocity of condensate. The increasing rate of condensate film for circular region reveals about 50% higher value than that of vertical region. The physical properties of working fluid affect significantly the condensate film thickness, such as the condensate film thickness for the case of FC-40 are 5 times larger than that of water. In comparison with condensation on a vertical wall, the average heat transfer coefficient in the cave-shaped cavity presented 10∼15% lower values due to the fact that the average film thickness formed inside the cave-shaped cavity was larger than that of the vertical wall with an equivalent flow length. A correlation formula which is based on the condensate film analysis for the cave-shaped cavity to predict average heat transfer coefficient is presented. Also, the critical minimum fill charge ratio of working fluid based on condensate film analysis has been predicted, and the minimum fill charge ratios for FC-40 and water are about Ψ$\_$crit/=3∼7%, Ψ$\_$crit/=0.5∼1.3% respectively, in the range of heat flux q"=5∼90kW/㎡.