• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.4
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• pp.997-1008
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• 1994

Heat transfer by laminar oscillating flow in a circular pipe has been studied analytically. The general solution with respect to the arbitrary wall boundary condition is obtained by superposing the fluid temperatures with the sinusoidal wall temperature distributions. The fulid temperature distributions are two dimensional, but uniform flow assumption is used to simplify the velocity distribution. The heat transfer characteristics in the thermally developing regions are analyzed by applying the general solution to the two cases of thermal boundary conditions in which the wall temperature and wall heat flux distributions have a square-wave form, respectively. The results show that the length of the thermally developing region becomes larger in proportion to the oscillation frequency at slow oscillation and eventually approaches to the value comparable to the swept distance as the frequency increases. The time and cross-section averaged Nusselt number in the developing region is inversely proportional to the square root of the distance from the position where the wall boundary condition is changed suddenly. In the developed region, Nusselt number is only determined by the oscillation frequency.

• Nuclear Engineering and Technology
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• v.56 no.7
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• pp.2524-2533
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• 2024

When analyzing containment thermal-hydraulics, computational fluid dynamics (CFD) is a powerful tool because multi-dimensional and local analysis is required for some accident scenarios. According to the previous study, neglecting steam bulk condensation in the CFD analysis leads to a significant error in boundary layer profiles. Validating the condensation model requires the experimental data near the condensing surface, however, available boundary layer data is quite limited. It is also important to confirm whether the heat and mass transfer analogy (HMTA) is still valid in the presence of bulk condensation. In this study, the boundary layer measurements on the vertical condensing surface in the presence of air were performed with the rectangular channel facility WINCS, which was designed to measure the velocity, temperature, and concentration boundary layers. We set the laminar flow condition and varied the Richardson number (1.0-23) and the steam volume fraction (0.35-0.57). The experimental results were used to validate CFD analysis and HMTA models. For the former, we implemented a bulk condensation model assuming local thermal equilibrium into the CFD code and confirmed its validity. For the latter, we validated the HMTA-based correlations, confirming that the mixed convection correlation reasonably predicted the sum of wall and bulk condensation rates.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.4
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• pp.1071-1082
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• 1995

Numerical analyses have been performed to obtain the absorption heat and mass transfer coefficients and the absorption mass flux from a falling film of the LiBr aqueous solution which is cooled by cooling air. Heat flux at the wall is specified in terms of the heat transfer coefficient of cooling air and the cooling air temperature. Effects of operating conditions, such as the heat transfer coefficient, the cooling air temperature, the system pressure and the solution inlet concentration have been investigated in view of the local absorption mass flux and the total mass transfer rate. Effects of film thickness and film Reynolds number on the heat and mass transfer coefficients have been also estimated. Analyses for the constant wall temperature condition have been also carried out to examine the reliability of present numerical method by comparing with previous investigations.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2006.04a
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• pp.820-827
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• 2006

The convection heat transfer coefficients on the top surface of a large liquid petroleum liquid injection(LPLi) engine piston are analyzed by solving an inverse thermal conduction problem. The heat transfer coefficients are numerically found so that the difference between analyzed temperatures from the finite element method and measured temperatures is minimized. Using the resulting heat transfer coefficients as the boundary condition, temperature of a large LPLi engine piston is analyzed.

• Journal of Ocean Engineering and Technology
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• v.15 no.2
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• pp.39-45
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• 2001

With uniform heat generation from the inner surface of the cylindrical heater placed in a cross flow boundary condition, heat flow that is conducted along the wall of the heater creates a non-isothermal surface temperature and non-uniform heat flux distribution. In the present investigation, the effects of circumferential wall heat conduction on convection heat transfer is investigated for the case of forced convection around horizontal circular tube in cross flow of air. The wall conduction number which can be deduced from the governing energy equation should be used to express the effect of circumferential wall heat conduction. It is demonstrated that the circumferential wall heat conduction influences local Nusselt numbers of one-dimensional and two-dimensional solutions.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.4
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• pp.1-6
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• 2002

A numerical heat transfer analysis and the structural analysis were performed for the design of sub-scale combustion chamber's coolant passage. The heat flux through the combustion chamber wall was estimated by 2-D heat transfer analysis of compressible hot gas and the result was applied as a thermal boundary condition of 3-D analysis. The heat flux estimated by the present method agreed well with the experimental correlation and proved to be insensitive to cooling condition. So the same thermal boundary condition was applied for various operating conditions. The maximum temperature of combustion chamber wall was predicted by 3-D analysis for single coolant passage and the result will be used for the development of a regeneratively cooled combustion chamber. Also estimated were the stress distribution and structural safety of coolant passage through the static structural analysis.

• KIEAE Journal
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• v.15 no.4
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• pp.29-35
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• 2015

Purpose: Double skin facade is a representative advantageous passive technology of building skin in the aspect of energy saving and environment improvement, reduces heat loss with buffer space in winter season and enhances indoor air and comfort of residents by activating natural ventilation in mid-season. However, in summer season, temperature increase in the intermediate space due to solar energy from exterior transparent skin could be a potential problem; also, relatively weak buoyancy of air caused by low density difference between double-skin facade could increase cooling load as air of intermediate space in high temperature hangs. However, proof data is insufficient to objectify such phenomenon. Method: In this study, researchers surveyed air temperature of intermediate space and airflow and diagnosed its cause targeting on applied multistory facade in the building which gives thermal uncomfort to residents. Also, the researchers produced Solar-air heat transfer coefficient meter, measured thermal boundary condition of double-skin facade, and presented the result of measurement as an objectified verification material regarding overheating phenomenon in the intermediate space of double-skin facade in summer season. Result: Inefficient condition was verified that total heat increases and overheating due to insufficient natural ventilation in multistory facade. In addition, logic behind preceding research was objectified and verified regarding high temperature phenomenon in the intermediate space which could increase cooling load in summer season.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.16-23
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• 2005

The objective of this research is to estimate two dimensional ablating and charring of heat shield materials in severe aero-thermal heat transfer. This estimation requires an accurate and rapid technique for its serious heat transfer with a moving boundary. Aerodynamic heating is obtained by an explicit relation which is a function of Mach number and air condition, while a fully implicit method is used for heat transfer calculations. Moving boundary is captured by FLIAR method which is a subgroup of VOF. Thickness of ablating and charring of heat shield, temperature of the moving surface and rate of radiation heat are calculated and compared with references. The results are in good agreement with other calculations.

• Journal of the Korean Society for Precision Engineering
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• v.16 no.7
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• pp.158-167
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• 1999

Heat and moisture transfer associated with porous materials are investigated. The heat and moisture transfer in porous materials caused by the interaction of moisture gradient, temperature gradient, conduction, and evaporation are considered. The variations of temperature and moisture not only change the volume but also induce the hygro-thermal stress. The finite element formulation for solving the temperature and moisture transfer as well as the associated hygro-thermal stresses is developed. In order to verify the finite element formulation, the heat and moisture moving boundary problem in a half space and the hygro-thermo-mechanical problem in an infinite plate with a circular hole are analyzed. Temperature profile, moisture profile, and hygro-thermal stresses are compared with those of analytic solution and other investigator. Good agreements are examined

• Membrane and Water Treatment
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• v.11 no.5
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• pp.353-361
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• 2020

The present study deals with a numerical investigation of heat and mass transfer in a Sweeping Gas Membrane Distillation (SGMD) used for desalination. The governing equations expressing the conservation of mass, momentum, energy and species with coupled boundary conditions were solved numerically. The slip boundary condition applied on the feed saline solution-hydrophobic membrane interface is taken into consideration showing its effects on profiles and process parameters.The numerical model was validated with available experimental data and was found to be in good agreement particularly when the slip condition is considered. The results of the simulations highlighted the effect of slip boundary condition on the velocity and temperature distributions as well as the process effectiveness. They showed in particular that as the slip length increases, the permeate flux of fresh water and process thermal efficiency rise.