• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2154-2159
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• 2008

In conventional air-conditioning systems, when the circulated air from the air-conditioned space pass through the cooling coil in the air-conditioning system, the air is over-cooled to eliminate the moisture as well as to decrease the temperature. The purpose of this study is to test and evaluate performance of the cooling/reheating system which can save both cooling energy and reheating energy by exchanging heat between the cooled air and reheated air. Experimental apparatus consists of fan, ducts, polymer exchangers, cooling coil, electronic auxiliary heater and data acquisition system. Two types of polymer exchanger, plate type and dimple type, made of polypropylene for cooling/reheating system are designed. Heat transfer and dehumidification characteristics of system are tested. The results show that the energy saving is up to 40% in the range of present experimented conditions, and it decreases with increasing velocity, inlet temperature and specific humidity.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.3
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• pp.203-209
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• 1989

This paper is an experimental study on the pleasantly suitable cool/warm air conditioning system in order to minimize the energy consumption by attaching the electronic-controlled device to the heat pump air conditioning system.While the cool/warm air conditioning, the air temperatures in the entrance and exit of the indoor heat exchangers should be checked and when the surface of heat exchanger is reached to the dew point temperature, a speed of the compressor is to be automatically controlled by anti-dewing system in order to minimize the energy consumption.At the result of this study, the energy consuming amount is saved about 5% more than that of the conventional air conditioning system by prevent unnecessary dew forming.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.4
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• pp.109-121
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• 2004

A distributed nonlinear mathematical model for investigation of regenerative heat exchangers of both a continuous and periodic operation is described in the paper. The non-iterative numerical integration scheme for conjugate unsteady heat exchange problem of one dimensional flows and two dimensional matrix wall conductivity is developed. Case study of a regenerative heat exchanger with a rotary ceramic matrix is presented. The range of optimum rotation rates of the regenerator providing the greatest calorific efficiency is determined.

• Journal of the Korean Society of Visualization
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• v.17 no.1
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• pp.26-33
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• 2019

The rapid increase in the usage of energy in the fast-changing industries has led to resource depletion and environmental conflicts. Many types of research are available on heat exchangers that undergo simple energy conversion processes. The impingement rods discussed in this study improves the durability of the heat exchanger and ensure the stability of the operation. However, it is uncertain about selecting the installation location of the impingement rods. The commercially available CFD code, ANSYS CFX, is used for the impingement rods installation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.17 no.11
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• pp.1005-1013
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• 2005

The use of river water as a heat source of a heat pump has the advantage in the performance compared to the use of atmospheric air because the temperature variation of river water over the year is relatively small. In this study, the performance of the heat pump system using river water as a heat source was numerically investigated. A simulation model for the 2-stage compression heat pump system was developed with each component model composed of compressors, heat exchangers, a flash tank and electronic expansion devices. The peformance of the heat pump system using river water was improved by $50\%$ compared to that using atmospheric air in winter conditions.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.734-741
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• 2020

A new air-cooled waste heat removal system with a direct contact heat exchanger was designed for SMRs requiring 200 MW of waste heat removal. Conventional air-cooled systems use fin structure causing high thermal resistance; therefore, a large cooling tower is required. The new design replaces the fin structure with a vertical string type direct contact heat exchanger which has the most effective performance among tested heat exchangers in a previous study. The design results showed that the new system requires a cooling tower 50% smaller than that of the conventional system. However, droplet formation on a falling film along a string caused by Rayleigh-Plateau instability decreases heat removal performance of the new system. Analysis of Rayleigh-Plateau instability considering drag force on the falling film surface was developed. The analysis results showed that the instability can be prevented by providing thick string. The instability is prevented when the string radius exceeds the capillary length of liquid by a factor of 0.257 under stagnant air and 0.260 under 5 m/s air velocity.

• Transactions of the Korean hydrogen and new energy society
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• v.25 no.2
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• pp.183-190
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• 2014

Our lab designs a heat exchangers for air and carbondioxide gas. Coolant is water, thus it is very difficult to determine heat transfer parameters in this gas-liquid system. Repeated experiments gives overdesign value 35%, overall heat transfer coefficient $33.8(kcal/m2-hr-^{\circ}C)$ for carbondioxide. Another series of experiments determine overdesign 18.7%, overall heat transfer coefficient $21.4(kcal/m2-hr-^{\circ}C)$ for Air. These parameters are in same range of literature. Overdesign is increasing as tube length increases, also increases as wall thickness of heat exchanger increases. To get proper fluid linear velocity in heat exchanger, we change the diameter of tube and finally we can have optimum fluid linear velocity in the heat exchanger.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.12 no.4
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• pp.33-39
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• 2016

A ground source heat pump (GSHP) system is recommended as a heating and cooling system to solve the pending energy problem in the field of air conditioning, because it has the highest efficiency. However, higher initial construction cost works as a barrier to the promotion and dissemination of GSHP system. In this study, numerical analysis on the characteristics of high density polyethylene (HDPE) pipe with spiral inside was executed. The heat transfer and flow characteristics of it were compared with those of a conventional smooth HDPE pipe. The heat transfer coefficient and pressure drop of the spiral HDPE pipe were higher than those of the smooth HDPE pipes at the same fluid flow rate. By decreasing the flow rate, the spiral HDPE pipe represented similar values of heat transfer coefficient and pressure drop to the smooth HDPE pipe. The lower flow rate of the spiral HDPE pipe comparing with it of the smooth HDPE pipe is estimated to reduce the length of the ground loop heat exchanger.

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.1083-1090
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• 2005

Repeated ribs are used on heat exchange surfaces to promote turbulence and enhance convective heat transfer. Applications include fuel rods of gas-cooled nuclear reactors, inside cavities of turbine blades, and internal surfaces pipes used in heat exchangers. Despite the great number of literature papers, only few experimental data concern detailed distributions of friction factors and heat transfer coefficients in square channels varying the number of rough walls. This issue is tackled by investigating effects of different number of ribbed walls on heat transfer and friction characteristics in square channel. The rough wall have a 45$^{\circ}$ inclined square rib. Uniform heat flux is maintained on whole inner heat transfer channel area. The heat transfer coefficient and friction factor values increase with increasing the number of rough walls.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.3 s.234
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• pp.340-348
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• 2005

Repeated ribs are used on heat exchange surfaces to promote turbulence and enhance convective heat transfer. Applications include fuel rods of gas-cooled nuclear reactors, inside cavities of turbine blades, and internal surfaces pipes used in heat exchangers. Despite the great number of literature papers, only few experimental data concern detailed distributions of friction factors and heat transfer coefficients in square channels varying the number of rough walls. This issue is tackled by investigating effects of different number of ribbed walls on heat transfer and friction characteristics in square channel. The rough wall have a $45{\circ}C$ inclined square rib. Uniform heat flux is maintained on whole inner heat transfer channel area. The heat transfer coefficient and friction factor values increase with increasing the number of rough walls.