• Journal of Biosystems Engineering
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• v.25 no.4
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• pp.279-286
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• 2000

Most of the domestic cold storage rooms are inefficient for agricultural products because of temperature gradients inside the storage rooms. Temperature gradients are developed mainly by improper airflow pattern inside the storage room, which is a main cause of the spoilage of the agricultural products. There proper airflow pattern is essential to minimize these temperature gradients and the spoilage. The performance and characteristics of a cold storage room were determined as a function of airflow pattern and temperature distribution in forced circulation cold storage room. A commercial CFD(computational fluid dynamics) code was used to simulate 3-D airflow in the cold storage room. Solving the flow equations for the storage room, a standard k-$\varepsilon$ turbulent model was implemented to calculate steady state turbulent velocity distribution. The CFD prediction results were compared with temperature measurements inside the cold storage room. In case of pallet storage, Temperature gradients inside pallet storage was reduced because the contact area of cold air expanded through an alley of airflow in storage. But is case of bulk storage, the last temperature of storage considerably rose more than the initial temperature of storage. The reason was that bulk storage didn't include any alley of airflow in storage.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1997.10a
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• pp.66-69
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• 1997

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.8 s.227
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• pp.989-995
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• 2004

This paper presents a semi-empirical model to predict the frost growth formed on the cold cylinder surface. The model is composed of the correlations for frost properties including the various frosting parameters and local heat transfer coefficient. The effects of varying the correlations for local heat transfer coefficient on the frost growth are examined to establish the model. The numerical results are compared with experimental data obtained by the previous researchers. The results agree well with the experimental data within a maximum error of $13\%$. As the results, the frost thickness decreases with changing angular position from front stagnation to separation point. Also, the effects of air velocity on the frost growth are negligible, as compared to the other frosting parameters.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1546-1551
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• 2004

This paper presents a mathematical model to predict the frost properties and heal and mass transfer within the frost layer formed on a cold plate. The laminar flow equations for the air-side are analyzed. and the empirical correlations of local frost properties are employed in order to predict the frost layer growth. The correlations of local frost density and effective thermal conductivity of frost layer, obtained from various experimental conditions, are derived as functions of various frosting parameters (Reynolds number, frost surface temperature, absolute humidity and temperature of moist air, cooling plate temperature, and frost density). The numerical results are compared with experimental data and the results of various models to validate the present model, and agree well with experimental data within a maximum error of 10%. The heat and mass transfer coefficients obtained from the numerical analyses are presented, as the results, it is found that the model for frost growth using the correlation of heat transfer coefficient without solving air flow have a limitation in its application.

• Journal of the Korean Association of Geographic Information Studies
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• v.22 no.2
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• pp.133-151
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• 2019

This study aims to analyze cold air characteristics in the watershed areas and to suggest strategies for utilizing them in urban ventilation corridor plans. For this purpose, the Jungnangcheon watershed and Uijeongbu-si in the northern part of Gyeonggi province, and Anyangcheon watershed as well as Yangjaecheon Tancheon watershed and Gwacheon-si in the southern part were selected as study areas. We used KALM (Kaltluftabflussmodell), a cold air simulation model developed in Germany and identified both the cold air flow and the height of cold air layer generated during 6 hours at night. Uijeongbu City is located on the main stream of the Jungnangcheon watershed, and the local cold air from the southern outskirts is an important part of Uijeongbu-si's overall ventilation corridor planning. In addition, the cold air generated in the vicinity of Mt. Sapae flows into the central business district near the city hall and plays a major role in regulating the thermal environment of the city. But, the cold air flows in the eastern part of Uijeongbu-si was not smoothly. The cold air flow generated in the east of Gwanak Mountain and in the west of Cheonggye Mountain was the most active in the northern part of Gwacheon-si. This flow is also a major ventilation corridor in Anyangcheon watershed as well as Yangjaecheon Tancheon watershed. But, the southern part where the cold air flow is not smooth is planed to be developed as 'Gwacheon Knowledge Information Town Public Housing District', so rapid development is expected in the future. Hence, it is suggested that an additional ventilation corridor plan should be established based on the detailed local wind flow analysis.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.6
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• pp.86-95
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• 2002

This paper suggests the new technology to control metal flow in order to reduce the number of preforming and the machining for the cold forged product with complex geometry. This technology is the combined forming that consists of bulk and sheet forming with double action dies. To analyze the process, finite element simulation has been performed. The proposed technology is applied to hub model that is part of air conditioner clutch. The purpose of this study is to investigate the material now of hub through the relative-velocity control of punch and mandrel using the flow control forming technique.

• Journal of the Korean Society for Precision Engineering
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• v.7 no.4
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• pp.140-148
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• 1990

A mathemetical medel has been developed for the purpose of estimating the rolling force required for computer control of cold strip mills. The model consists of equations of rolling force. flow stress. friction coefficient and tension. By applying the model to a 6-High cold tandem mill, the computer simulation is then been possible for all kinds of steels except stainless steel and the effectiveness of the model has been confirmed in the practice.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.11a
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• pp.1-12
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• 2001

In cold forging of piston-pin for automobile parts, the flow defect appears by the dead metal zone. This appearance evidently happens in products with a thin piercing thickness for the dimension accuracy and the decrease of material loss. The best method that can prevent flow defect is removing dead metal zone. The purpose of this study is to investigate the material flow behavior of forward-backward extruded piston-pin through the relative velocity ratio and the stroke control of upper moving punch & container using the flow control forming technique. The finite element simulations are applied to analyse the flow defect, then the results are compared with the plasticine model material experiments. Finally, the model experiment results are in good agreement with the FE simulation ones.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1366-1375
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• 2002

In cold forging of piston-pin for automobile parts, the flow defect appears by the dead metal zone. This appearance evidently happens in products with a thin piercing thickness for the dimension accuracy and the decrease of material loss. The best method that can prevent flow defect is removing dead metal zone. The purpose of this study is to investigate the material flow behavior of forward-backward extruded piston-pin through the relative velocity ratio and the stroke control of upper moving punch & container using the flow control forming technique. The finite element simulations are applied to analyse the flow defect, then the results are compared with the plasticine model material experiments. The model experiment results are in good agreement with the FE simulation ones.

• Korean Journal of Environment and Ecology
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• v.33 no.3
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• pp.366-374
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• 2019

This study aims to analyze the characteristics of ventilation corridor and propose its utilization strategies in Jeonju city in order to discuss how to utilize urban ventilation corridors as a planning factor for reducing heat wave impact and fine particle pollution. For these purposes, cold air characteristics such as cold air flow and height of cold air in Jeonju area located in the Honam Jeongmaek were analyzed and major ventilation corridors were specified. Based on them, we proposed mountain management strategies for securing and utilizing ventilation corridors. We used KALM (Kaltluftabflussmodell), a cold air simulation model developed in Germany and identified both the cold air flow and the height of cold air layer generated during 6 hours at night. As a result, the cold air flow generated in the forests located in the northeast and east sides of the Jeonju city became clear and the height of cold air layer increased in the valley terrain and farmland areas with time. In particular, Jeonju City has an ideal structure of urban ventilation corridor. Based on the results, the area where the cold air generation is active was designated as the 'cold air conservation area', and the area requiring the management for the good cold air flow was as the 'cold air management area'. This study is expected to be used as basic data of policy making and research for reducing heat wave impact and fine particle pollution such as climate change adaptation policy and urban forest plans for ventilation corridor composition.