• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
• /
• v.16 no.2
• /
• pp.185-193
• /
• 1987

The heat transfer characteristics from a solid sphere in a fluctuating air flow is simulated numerically in the range of the Reynolds numbers, $1\;{\leqslant}\;Re\;{\leqslant}\;40.$ Such a situation may be encountered in forced convection from a heated spherical particle in a sound field or oscillat-ing flow. The amplitude and phase delay in the heat transfer response to the flow oscillation are computed for a small amplitude flow. The instantaneous response of heat transfer is simulated for the large amplitude oscillation and compared with the quasi-steady response. The effect of the oscillation on the time - mean value in the local and overall heat transfer rate is discussed along with the change in the flow .field.

• Journal of the Korean Electrochemical Society
• /
• v.14 no.4
• /
• pp.253-260
• /
• 2011

In this study, computational simulation was performed for thermal management of modules consisting of 10 batteries. Simplified structure and equivalent thermal resistance network was applied to maintain the thermal properties. Verification test of the mesh were in progress to ensure the reliability of 2.6 mm in the narrow gap between the battery, resulting in at least three divided mesh between the shape of the grid was required. Type of air from rear of the module, type of air from top of the module and type of air from bottom of the module were applied and effective cooling methods are discussed based on the location of fan and air intake of the modules. Maximum temperature and temperature differences of modules that directly affect the performance of the module were compared, and also behavior of the fluid was confirmed by comparing the air flow. The best maximum temperature is shown type of air from bottom of the module to $40.27^{\circ}C$ and type of air from top of the module shows smallest temperature difference $0.73^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.1
• /
• pp.68-74
• /
• 2000

Experimental investigation on flame spread along suspended droplet arrays have been conducted with various droplet spacings and ambient air velocities. Especially, an opposed air stream is introduced to simulate fundamental flame spread behaviors in spray combustion. High-speed chemiluminescence imaging technique of OH radicals has been adopted to measure flame spread rates and to observe various flame spread behaviors. The fuel used is n-Decane and the air velocity varies from 0 to 17cm/s. The pattern of flame spread is grouped into two: a continuous mode and an intermittent one. It is found that there exists droplet spcings, above which flame spread does not occur. The increase of ambient air velocity causes the limit droplet spacing of flame spread to become small due to the increase of apparent flame stretch. As the ambient air velocity decreases, flame spread rate increases and then decreases after taking a maximum flame spread rate. This suggests that there exists a moderate air flowing to give a maximum flame spread rate due to enhanced chemical reaction by the increase of oxidizer concentration.

• Nuclear Engineering and Technology
• /
• v.26 no.4
• /
• pp.516-525
• /
• 1994

Since the TMI and Chernobyl accidents, many passive safety features are suggested in advanced reactors in order to enhance the safety in future nuclear power plants. In order to verify the effectiveness and provide the data for detailed design of passive cooling system, in the present work, the effects of air inlet position and external condition on the natural circulated air flow rate and the natural and forced convective heat transfer coefficient have been investigated for the one-side heated closed path such as the passive containment cooling system of the Westinghouse's AP-600. A series of experiments have been peformed with the 1/26th scaled segment type test facility of the AP-600 passive containment. Under natural and forced convection, the air velocities and temperatures are measured at several points of the air flow path. The experimental result are compared with a simple one-dimensional model and it shows a good agreement.

• Proceedings of the KIEE Conference
• /
• 2008.05a
• /
• pp.139-140
• /
• 2008

Cooling systems for electronic equipments are becoming more important. Cooling technologies using natural and forced convection are limited and operated in very low efficiency. A corona discharge is utilized as the driving mechanism for anair pump, which allows for airflow generation with low noise and no moving parts. However they do not enhance the flow rate and overcome the control mechanism of the pump. In this study a point-mesh type air pump, with a third electro de installed near the corona point, has been proposed and investigated by focusing on elevating the ionic wind velocity and power yield. As a result, the significantly enhanced ionic wind velocity and tremendously increased power yield can be obtained with the proposed air pump system.

• International Journal of Air-Conditioning and Refrigeration
• /
• v.7
• /
• pp.45-54
• /
• 1999

In this study, condensation heat transfer experiments were conducted in two small diameter (ø17.5, ø4.0) tubes. Comparison with the existing in-tube condensation heat transfer correlations indicated that these correlations over predict the present data. For example, Akers correlation over predicted the data up to 104 %. The condensation heat transfer coefficient of the ø4.0 I.D. tube was smaller than that of the ø7.5 I.D tube; at the mass velocity of 300 kg/$m^2$s, the difference was 12 %. The pressure drop data of the small diameter tubes were highly (two to six times) over predicted by the Lockhart-Martinelli correlation. Sub-cooled forced convection heat transfer test confirmed that Gnielinski's single phase heat transfer correlation predicted the data reasonably well.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.10 no.1
• /
• pp.129-136
• /
• 1998

Pressure drop and heat transfer characteristics of a periodically fully developed flow in the flat channel with protrusions are investigated. The effects of shape and location of protrusion on the pressure drop and heat transfer are numerically analyzed in the present study. Taguchi method is used to optimize these parameters. It is found that the ratio of the height of protrusion to channel height shows larger influence on the pressure drop and heat transfer than the ratio of the length of protrusion to module length. As the height of protrusion increases, pressure drop and heat transfer increase, but if the height of protrusion exceeds 2/3 of the channel height, there is a substantial pressure drop. The results also show that the optimal length and height of protrusion are half of the module length and half of the channel height, respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.6 no.1
• /
• pp.20-28
• /
• 1994

A numerical study has been performed on enhancement of heat transfer in a forced convection of the modified driven-cavity flow which was previously found by the author to give a regular or chaotic stirring depending on the parameter value. It is found that for the present case wherein heat is transmitted between fluid and the surrounding walls, the chaotic stirring enhances the heat transfer at high Peclet numbers. The optimal condition of the flow modulation for the best heat transfer can be predicted by purely investigating the hydrodynamic facet, i.e. the stirring effect.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.10 no.5
• /
• pp.509-522
• /
• 1998

An experimental investigation is reported on the heat transfer coefficient from a rotating flat plate in a round turbulent normally impinging water jet. Tests were conducted over a range of jet flow rates, rotational speeds, jet radial posetions with various combinations of three jet nozzle diameter. Dimensionless correlation of average Nusselt number for laminar and turbulent flow is given in terms of jet and rotational Reynolds numbers, dimensionless jet radial position. We suggested various effective promotion methods according to heat transfer characteristics and aspects. The data presented herein will serve as a first step toward providing the information necessary to optimize in rational manner the cooling requirement of impingement cooled rotating machine components.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.3 no.3
• /
• pp.168-175
• /
• 1991

Experiments have been conducted to measure the overall heat transfer coefficient for gas-solid fluidized double pipe heat exchanger with finned tube. The average particle diameters of alumina are used in 0.4, 0.5, 0.6 and 0.9mm. And the effects of average particle diameter, static bed height and flow velocity on overall heat transfer coefficient have been investigated. Also the heat transfer effect of fluidized bed was compared with that of single phase forced convection and that of heat exchanger with smooth tube.