• Transactions of the Korean hydrogen and new energy society
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• v.34 no.6
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• pp.741-747
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• 2023

In this study, the heat transfer characteristics were numerically analyzed to investigate the possibility of utilizing cooling water using liquid nitrogen. From the study, as the mass flow rate of the hot fluid increased, the heat transfer rate increased by 8.9-81.7%. And lowering the inlet temperature of the hot fluid resulted in increase in the heat transfer rate by 33.8-71.5%. As for the filling level of liquid nitrogen, as higher filling level led to a decrease in the outlet temperature and an increase in the overall heat transfer coefficient.

• Transactions of Materials Processing
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• v.31 no.3
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• pp.143-150
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• 2022

The purpose of this study was to investigate an innovative hydroforming process for the cost-effective manufacturing of double layered tube with circumferentially corrugated patterns. Conventional double pipe heat exchanger has relatively poor heat transfer efficiency because of the limited contact area resulting from the concentrically arranged simple cylindrical structure. As a promising alternative to enhance heat transfer efficiency, double layered tube with corrugated internal pattern was considered in this study. To fabricate corrugated inner tube, innovative tube hydroforming system was developed. The customized loading paths were established using the simulated forming pressure and contracting stroke at various bar diameters. Experimentally obtained cross-sectional profiles were analyzed to evaluate the reliability and applicability of the hydroformed tube with various patterns. The results demonstrate that the proposed hydroforming process can be a feasible alternative for manufacturing high-performance double-tube heat exchangers.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.2
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• pp.183-189
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• 2012

Most of the domestic residential buildings have used the traditional radiant heating system, circulating hot water through the cross-linked polyethylene(PE-X) pipe buried in the floor panel of the heating space. New type of the heating panel was recently developed using heat pipes with double wicks. Some experiments were carried out in this study to verify the thermal characteristics of this heating system at the unit heating space which surrounded by outer space whose temperature of air be maintained scheduled value with time. Through the various experiments with several parameters, such as flow rate, inlet and outlet temperatures of hot water and the heating duration and so on, we found that the floor heating system with heat pipes was able to reduce the pumping power for hot water circulation by 4~31% compared with the conventional panel heating system using PE-X pipe. These results could be used for optimal design and efficient operation of the heating system as well as improvement of thermal comfort.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.511-516
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• 2005

This study is to investigate the pressure wave characteristics and the maximum pressure rise generated by instantaneous valve closure at the end of the straightening polybutylene double piping system with header. Experiments were conducted under the following conditions: initial pressure $1{\sim}5$ bar, flow velocity $0.5{\sim}3.0$ m/s and water temperature $25^{\circ}C$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.7
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• pp.380-385
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• 2009

This study is to investigate the pressure wave characteristics and the maximum pressure rise generated by instantaneous valve closure at the end of the straightening polybutylene double piping system with header. Experiments were conducted under the following conditions: initial pressure $0.1{\sim}0.5$ MFa, flow velocity $0.5{\sim}3.0$ m/s and water temperature $25^{\circ}C$.

• Journal of the Society of Naval Architects of Korea
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• v.35 no.1
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• pp.98-106
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• 1998

This paper shows the temperature distribution of double hull compartment and of cofferdam in a large LNG Carrier. In LNG Carrier, due to the lower cargo temperature($-163^{\circ}C$), structures are forced to lose their strength if additional heat is not supplied. So it is very important to estimate the temperature distribution and the heat flux needed to maintain the structure properly. The temperature of each compartment is obtained using 2-dimensional model analysis and compared with 3-dimensional results. And also this paper gives preliminary estimation of pipe length to supply necessary heat flux in bare pipe and finned pipe.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.4
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• pp.425-431
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• 2015

LNG (liquefied natural gas) is considered the best alternative eco-fuel, and many studies on the LNG fuel system have been performed to use LNG as the fuel for ships. For the LNG fuel supply system, natural gas transfers from the vaporizer to the engine in the gaseous state with a temperature of $50^{\circ}C$ and a pressure of 35MPa. Therefore, a structural safety evaluation of the double-walled pipelines considering thermal load is essential. In this article, an uniaxial tensile test for super duplex stainless steel, material for double-walled pipe, according to the annealing time was carried out to analyze the thermal effect. In addition, thermo-structural analysis of the high temperature-high pressure double-walled pipe with fixed supports that are now used widely was carried out to evaluate the structural safety. To minimize stress concentration of the connection point between the support and inner pipe, the shapes of the new type support that can slip through inner pipe were proposed, and the supports which has best structural performance was selected using the results from the thermo-structural analyses of new supports and an analysis of the whole double-walled pipeline was performed to ensure structural safety. These results can be used as a database for the design of double-walled pipelines and sliding support.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.3
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• pp.309-314
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• 2000

Experimental results for heat transfer characteristics of natural refrigerants R-290, R-600a and HCFC refrigerant R-22 during evaporating inside horizontal double pipe heat exchangers are presented. The experimental apparatus is basically a vapour heat pump system, composed of a compressor, a condenser, expansion devices, a evaporator, and some other peripheral devices. The test sections were horizontal double pipe heat exchangers, which were a pair of smoothed tube, having 10.07 mm ID, 12.07 mm OD, and grooved inner fin tube, having 12.70 mm OD, 0.25 mm fin height, and 75 fins. The local evaporating heat transfer coefficients of natural refrigerants were not much affected with the mass velocity than R-22 and it could be interpreted that the local evaporating heat transfer coefficients of R-22 were increased more than those of R-290, R-600a according to the increment of mass velocity. Moreover, the maximum increment of the heat transfer coefficient was found in R-290. The average heat transfer coefficient was obtained the maximum value in R-290 and the minimum value in R-22. It reveals that the natural refrigerant can be used as a substitute for R-22. In the grooved inner fin tube, 70% of the increment of the heat transfer coefficient was obtained compared to the smoothed tube.

• Journal of Korean Society of Water and Wastewater
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• v.28 no.4
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• pp.491-500
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• 2014

Due to rapid urbanization and industrialization, water supply and sewer line systems are also developed relevantly. Manhole is an essential component structure of the pipeline system. Manhole is a structure constructed to accommodate the direction, dimension, differences in level, and easy of maintenance in the pipeline system. In this paper we present the result of investigations pertaining to the structural behavior of PVC sewer manhole buried underground. In the paper mechanical properties of PVC material are reported. In addition, by the finite element analysis (FEA), we confirmed that a PVC double-wall corrugated pipe manhole, when it is buried underground, is safe for the stress as well as buckling strength if the manhole is constructed within the suggested limit of buried depth.

• Solar Energy
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• v.10 no.1
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• pp.38-46
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• 1990

For the optimal design and the efficient operation of the double pipe type latent heat storage equipment, the effect of the parameters of the system were analysed. The statistical analysis showed that the theoretical and the experimental results of the volume change rate and the temperature variations were well agreed. Therefore, this theoretical model is reasonable to analyze two dimensional moving boundary problems. In the analysis of the effects of the parameters, the heat extraction fraction and the water outlet temperature of the system as function of the time were analysed depending on the initial temperature of PCM, water inlet temperature, water mass flow rate and the dimension of the inner tube.