• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.457-462
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• 2005

In this study, the performance of automatic thermostatic valves according to each heating method of a large scale residential building were researched by simulation. The flow characteristics of the entire pipe networks of the hot water radiant heating system is analized by using linear analysis method. For the analysis of unsteady heat transfer phenomena in each household, the method of using electric equivalent R-C circuit is applied.

• Journal of Biosystems Engineering
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• v.31 no.5 s.118
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• pp.430-435
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• 2006

Greenhouse horticulture in South Korea covered about 52,000 ha in 2005. Greenhouse area of about 12,000 ha has been heated during winter season with heating cost of $20{\sim}40%$ of total Production cost. Farmers engaged in greenhouse horticulture were changed into aged people. Therefore the laborsaving of working process and the saving of greenhouse heating cost should be accomplished simultaneously to increase income of greenhouse horticulture. The best method for saving of greenhouse heating cost is to install thermal tunnels into greenhouse. Then hot air heaters using fossil fuel should be changed into hot water heaters. In other words air heating using forced convection should be changed into natural convection system. In this research coil tube made of flexible PE pipe was designed as hot water heat exchanger and its heat exchanging characteristics were analyzed. This new heat exchanger has been adopted as a natural convection system for hot water heating of greenhouse horticulture.

• Nuclear Engineering and Technology
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• v.50 no.7
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• pp.1079-1087
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• 2018

There are many parameters that affect the natural circulation flow, such as height difference, heating power size, pipe diameter, system pressure and inlet temperature and so on. In general analysis the heating power is often regarded as a uniform distribution. The ANSYS-CFX numerical analysis software was used to analyze the flow heat transfer of supercritical water under different heating power distribution conditions. The distribution types of uniform, power increasing, power decreasing and sine function are investigated. Through the analysis, it can be concluded that different power distribution has a great influence on the flow of natural circulation if the total power of heating is constant. It was found that the peak flow of supercritical water natural circulation is maximal when the distribution of heating power is monotonically decreasing, minimal when it is monotonically increasing, and moderate at uniform or the sine type of heating. The simulation results further reveal the supercritical water under different heat transfer conditions on its flow characteristics. It can provide certain theory reference and system design for passive residual heat removal system about supercritical water.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.311-316
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• 2005

The experimental study for an operational characteristics and performance of the sodium heat pipe were carried out. For an experiment. the heat pipe which is 1000mm length and 25.4mm diameter of stainless steel container with 50 mesh of screen wick using sodium as a working fluid is manufactured and tested as functions of heat flow rate, inclined angle and operating temperature. The test results are as follows. During the start-up. frontal start up was observed because of the vapor density increasing as increased the hot zone. Also, the heat pipe showed uniform temperature over than $420^{\circ}C$ of the operating temperature. The average heat transfer coefficient increased as the heat flux and the vapor temperature increase, and the range of the total thermal resistance was 0.075-0.04 $^{\circ}C/W$ at the 12-53.55 $kW/m^2$ of heat flux and $500-750^{\circ}C$of operating temperature. The maximum heat flow rate was 750W at the 10 degree of top heating mode.

• Journal of Biosystems Engineering
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• v.35 no.2
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• pp.108-115
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• 2010

This study was conducted to estimate the optimum temperature and required time for soil sterilization when heated water was circulated through underground heating pipes in the greenhouse which solar heat was influenced to the temperature of soil during the summer day. Two different types of heating pipes were used for the experiment. One was a polyethylene pipe(XL) and the other was a corrugated ring shaped stainless steel pipe(STS). The results of the studies were summarized as follows; By measuring the thermal characteristics of the XL and STS, it was examined that the average temperature differences of the inlet and outlet were $8.5^{\circ}C$ and $13.3^{\circ}C$, the average flowrates were 15.3 L/min and 5.6 L/min, and the average radiation powers were 9.1 kW and 4.1 kW, respectively. As results of the regression analysis of underground temperatures, when average soil temperature was$35^{\circ}C$, an average water temperature was $80^{\circ}C$, and XL was used, it was estimated that the possible heat transfer distance, the required time for heat transfer and heat flux to reach the underground temperature of $60^{\circ}C$ were 300 mm, 230 hours, and $7.57kW/m^2$, respectively.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.8
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• pp.456-461
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• 2009

Recently, an increasing interest in district heating system has emerged rapidly, In this paper, the physical measurements and data to be monitoring through the internet were carried out with regard to hot water heating energy consumption at the three apartment housings with district heating system in Sang-am district of Seoul, Korea, Measurements were made of the thermal factors such as the pressure of heating pipe, flow rates, hot water temperature and etc, The objective of this study is to compare the design capacity of reheat exchanger with that of preheat exchanger in order to evaluate for the number of plates of two exchangers to be distributed properly.

• Journal of Welding and Joining
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• v.21 no.6
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• pp.64-70
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• 2003

Multipass welds of the 316L stainless steel have been widely employed in the pipes of Liquid Metal Reactor. Owing to localized heating and subsequent rapid cooling by the welding process, the residual stress arises in the weld of the pipe. In this study, the residual stresses in the 316L stainless steel pipe welds were calculated by the finite element method using ANSYS code. Also, the residual stresses both on the surface and in the interior of the thickness were measured by HRPD(High Resolution Powder Diffractometer) instrumented in HANARO Reactor. The experimental data and the calculated results were compared and the characteristics of the distribution of the residual stress discussed.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.13 no.8
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• pp.796-802
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• 2001

The purpose of the present study is to examine the heat transfer characteristics of the U-shape heat pipe for the cooling of semiconductor in subway train. Perflouro-carbon(PFC) was used as working fluid. Temperature distribution on the surface and heat transfer coefficients were investigated according to the working fluid volume percent and heating rate. The results were as follows; Optimum volumetric percent of working fluid was from 80% to 90%, and hat transfer coefficients of evaporation and condensation were as follows, respectively. $\hbar_ie=0.37\times(\frac{P_i}{P_O})$l_c}^0.3$,$\hbar_ic-4.2(\frac{\kappa_l^3p_l^2gh_fg}{\mu_lq_c_l_c}^\frac{1}{3}

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1225-1230
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• 2004

In this paper, the pressure drops were investigated according to the sintered porous wick structure in loop heat pipe(LHP) by theoretical analysis. LHP has the wick only in evaporator for the circulation of working fluid, so utilizes porous wick structure which pore diameter is very small for large capillary force. This paper investigates the effects of different parameters on the pressure drops of the LHP such as particle diameter of sintered porous wick, wick porosity, vapor line diameter, thickness of wick and heating capacity. Working fluid is water and the material of sintered porous wick is copper. According to the these different parameters, capillary pressure, pressure drop in wick were analized by theoretical design method of LHP.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.493-497
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• 2002

In the part industry, pipe has required high accuracy in surface roughness and size. Especially, when producing the high frequency welding pipe, cutting process is very important as the finishing process that remove the hot welding bead. The objective of this paper is to investigate the hot machining high frequency welded pipe by simulation and experimental tests. To test the cutting process as hot machining, all cutting environment is reproduced in turning with heating system, and the test is accomplished by comparing with room temperature machining and hot machining in consideration of cutting force, tool wear and cutting temperature.