• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.179-182
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• 2011

The purpose of this study is to evaluate a defrost model for the possibility of defrosting on wheelhouse window and the heat capacity if defrosting nozzle by using the commercial CFD solver FLUENT. A detailed simulation model has been created which contains the defrosting nozzle, window and the interior/exterior forced convection boundary. In this numerical study, the heat and mass transfer coupled during defrosting and investigated the defrost time for different hot gas temperature, external wind speed and temperature condition.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.195-200
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• 2001

An experimental study on critical heat flux (CHF) has been performed for water flow in a uniformly heated vertical 3 by 3 rod bundle under low flow and a wide range of pressure conditions. The objective of this study is to investigate the parametric trends of CHF with 3 by 3 rod bundle test section where three unheated rods exist. The general trends of the CHF are coincident with previous understandings. At low flow and system pressure above 3 MPa, some critical qualities are larger than 1.0 due to counter-current flow in test sections. Since there is a supply of water to the heated section from unheated section, the maximum CHFs at system pressure between 2 and 4 MPa are not shown.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.1
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• pp.25-33
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• 2005

When a circular tube with uniform heat generation within the wall was placed in a cross flow, heat flows by conduction in the circumferential direction due to the asymmetric nature of the fluid flow around the perimeter of the circular tube The circumferential heat flow affects the wall temperature distribution to such an extent that. in some cases, significantly different results may be obtained for geometrically similar surfaces. In the present investigation, the effect of circumferential wall heat conduction is investigated for forced convection around circular tube in cross flow of air and water Two-dimensional temperature distribution $T_w(r,{\theta})$ is calculated through the numerical analysis. The difference between one-dimensional and two-dimensional solutions is demonstrated on the graph of local heat transfer coefficients. It is observed that the effect of working fluid is very remarkable.

• Nuclear Engineering and Technology
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• v.38 no.8
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• pp.753-762
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• 2006

In this paper, works related to enhancement of the CHF are reviewed in terms of fundamental mechanisms and practical applications. Studies on CHF enhancement in forced convection are divided into two categories, CHF enhancement of internal flow in tubes and enhancement of CHF in the nuclear fuel bundle. Methods of enhancing the CHF of internal flows in tubes include enhancement of the swirl flow using twisted tapes, a helical coil, and a grooved surface; promotion of flow mixing using a hypervapotron; altering the characteristics of the heated surface using porous coatings and nano-fluids; and changing the surface tension of the fluid using additives such as surfactants. In the fuel bundle, mixing vanes or wire wrapped rods can be employed to enhance the CHF by changing the flow distributions. These methods can be applied to practical heat exchange systems such as nuclear reactors, fossil boilers, fusion reactors, etc.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.7
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• pp.599-606
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• 2002

uniform temperature. The surfaces of the block are taken at a constant higher temperature. The channel walls are assumed to be adiabatic. Results on the time-dependent temperature field are obtained and averaged over a cycle of pulsation. The effect of the important governing parameters, such as the Strouhal number on the flow and the heat transfer is investigated in detail. The results indicate that the recirculating flow behind the block are substantially affected by the pulsation frequency. These, in turn, have a strong influence on the thermal transport from the heated element to the pulsating flow. The frequency at which the enhancement is maximum is determined.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.7
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• pp.1770-1779
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• 1995

A combined convective heat transfer study for non-Newtonian fluids was experimentally performed in uniformly heated horizontal tubes with laminar flow in the thermal entry region. Velocity profiles were fully developed at the entrance of the heated sections in the tubes. Aqueous solutions of sodium carboxymethylcellulose(CMC ) were used; their behavior showed a reasonably good fit into the power-law model, .tau.=K.gamma.$^{n}$ . The test sections were made of copper with inside diameters of 3.23 cm and 5.042 cm and lengths of approximately 300 cm. Most experimental runs displayed noticeable secondary flows caused by buoyancy ; when present, secondary flows caused significant increase in the rate of heat transfer over the purely forced-convection case. A correlation, which relates the rate of heat transfer for flows with temperature-dependent properties, free convection effects, and non-newtonian effects, was suggested.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.4
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• pp.484-496
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• 1997

The fluid flow and heat transfer characteristics of conjugate forced and natural convection in the triple-glazed airflow window, where the outer air passes through a space contrived between the interior and exterior window panes, were studied numerically by a finite volume method for the elliptic form of the Navier-Stokes equations. The investigation focused on the influence of window geometry, ventilastion rate and solar energy on the temperature, velocity distribution and thermal performance of the airflow window. The comparison between the triple-glazed airflow window and the enclosed triple-glazed window was also made to evaluate the effect of buoyancy upon which the thermal performance of the window depended.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.2
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• pp.76-87
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• 1992

Flow and heat transfer characteristics in a horizontal electronic circuit board are studied numerically. The board has the arrays of heated blocks and the spaces between the plates and blocks are changed. Air in used as cooling fluid, of which prandt1 number is 0.7. The velocity distributions, temperature distributions, Nusselt numbers and dimensionless friction factors are obtained on the spaces between the plates and the blocks, for the cases of Rayleigh number, 0 and 10$^{5}$ . When Rayleigh number is so large, such as 10$^{5}$ , that the effect of bouyancy is not negligible, fluid friction and heat transfer is increased more than those of forced convection. This may be caused by the generation of secondary flow on the cross section of primary flow. The effect of bouyancy is of the most efficient, when the space of blocks is about block-width and the space of plates is about 1.7 times of block-height.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.4
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• pp.642-653
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• 1995

An analysis is made of the laminar fluid flow and heat transfer characteristics in a parallel-plate channel to whose walls are fitted with a series of equidistant staggered fins placed transversely to the flow direction. The governing equations are solved numerically by a finite-volume method for elliptic flows. Based on the obtained solutions of flow and temperature fields, the effects of Reynolds number and various geometric parameters on the heat transfer performance and pressure drop are evaluated. A comparson of the heat transfer characteristics between the channels with and without staggered fins is also made.

• Journal of Hydrogen and New Energy
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• v.34 no.5
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• pp.431-438
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• 2023

Recently, study on hydrogen is being conducted due to environmental pollution and fossil fuel depletion. High-pressure gas hydrogen commonly used is applied to vehicle and tube trailers. In particular, high-pressure hydrogen storage tank for vehicles must comply with the guidelines stipulated in SAE J2601. There is a charging temperature limitation condition for the safety of the storage tank material. In this study, numerical analysis method were verified based on previous studies and the nozzle angle was changed for thermal management to analyze the increase in forced convection effect and energy uniformity due to the promotion of circulation flow. The previously applied high-pressure hydrogen storage tank has a length/diameter ratio of about 2.4 and was analyzed by comparing the length/diameter ratio with 8. As a result, the circulation flow of hydrogen flowing into the high-pressure hydrogen storage tank is promoted at a nozzle angle of 30° than the straight nozzle and accordingly, the effect of suppressing temperature rise by energy uniformity and forced convection was confirmed.