• 대한기계학회논문집B
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• 제21권5호
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• pp.670-678
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• 1997

A method to mitigate the thermal stratification phenomenon of pressurizer surge line is proposed by heating bottom outside of horizontal pipe. Unsteady two dimensional model has been used to numerically investigate an effect of heating the bottom of pipe. The dimensionless governing equations are solved by using the control volume formulation and SIMPLE algorithm. Temperature and streamline profiles of fluids and pipe walls with time are compared with the previous study result. The numerical result of this study shows that the outside heating can relaxate the thermal stratification flow of the pressurizer surge line. Maximum dimensionless temperature difference between hot and cold sections of the pipe inner wall which causes thermal stratification was reduced from 0.514 to 0.424 at dimensionless time 1, 632 and 1, 500 respectively.

• 에너지공학
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• 제20권4호
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• pp.330-337
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• 2011

난방장치로서 통상 가스 및 기름보일러가 많이 사용되어진다. 본 연구는 기존의 가스 및 기름 보일러에 의한 난방방식과 달리 밀폐된 X-L 파이프 내에 특수 제작된 전열선을 삽입하여 그 전열선에 전압을 인가함으로써 X-L 파이프 내 열매체의 온도를 상승시켜 난방하는 방법에 관한 것이다. 특수 제작된 전열선의 가닥수와 인가전압을 변화시켜 X-L 파이프 보일러의 특성과 발열 메카니즘을 파악하였다. 또한 X-L 파이프 보일러와 가스 및 기름보일러와의 난방비용을 객관적인 자료에 근거하여 서로 비교를 함으로써 그 경제성을 평가하였다. 그 결과 X-L 파이프 보일러는 기름(보일러등유)보일러의 28%, 가스(천연가스)보일러의 58%의 비용으로 난방이 가능함을 확인하였다.

• 한국안전학회지
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• 제14권1호
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• pp.66-72
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• 1999

Local heating transportation pipe has sensor and return lines to detect water-leakage. There are impulse and resistance comparison measurement types for a water-leakage detection. The impulse type shows large detection error within a measurement range. Since the resistance comparison type can find a comparative accurate single water-leakage point in the measurement range of heating pipe, it has been used to detect water-leakages these days. However if the multi water-leakages are happened in the measurement range of transportation pipe. the resistance comparison type shows a detection error point by the parallel resistance between a detection sensor line and ground. But the detection error will be minimized by the divided transportation pipe loops. In this research, it suggests the design of remote controlled detection system which can divide a large pipe loop and a possible single water-leakage measurement process in each divided loops.

• Corrosion Science and Technology
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• 제19권3호
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• pp.122-130
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• 2020

In this study, a corrosion failure analysis of a heat transport pipe was conducted, as the result of a pinhole leak. Interestingly, the corrosion damage occurred externally in the pipeline, resulting in severe thickness reduction near the seam line. Also, while a stable magnetite protective film formed on the inner surface, the manganese oxide formation occurred only on the outer surface. The interior and exterior of the pipe were composed of ferrite and pearlite. The large manganese sulfide and alumina inclusions were found near the seam line. In addition, the manganese sulfide inclusions resulted in grooving corrosion, which progressed in the seam line leading to the reduction in the thickness, followed by the exposure of the alumina in the matrix to the outer surface. To note, the corrosion was accelerated by pits generated from the boundaries separating the inclusions from the matrix, which resulted in pinhole leaks and water loss.

• 생물환경조절학회지
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• 제28권3호
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• pp.204-211
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• 2019

본 연구는 국내 온실의 환경설계 기준 설정에 필요한 기초자료 제공을 목적으로 온수난방 방식을 채택하고 있는 상업용 온실 2곳에서 난방 중 열환경 계측 실험을 실시하고, 온수난방 배관의 열전달 특성을 분석하여 난방배관의 단위길이 당 방열량 자료를 제시하였다. 실험 기간동안 두 온실의 평균기온은 각각 $16.3^{\circ}C$와 $14.6^{\circ}C$로 조절되었으며, 난방배관의 온수 온도는 평균 $52.3^{\circ}C$와 $45.0^{\circ}C$로 관측되었다. 실험결과 난방배관 표면의 자연대류열전달계수는 $5.71{\sim}7.49W/m^2^{\circ}C$의 범위로 분석되었다. 난방배관 내의 유속이 0.5m/s 이상일 때에는 관내의 수온과 관 외부의 표면온도 차이가 크지 않은 것으로 나타났다. 이를 바탕으로 난방배관의 관류열전달계수를 수평원통에서의 층류 자연대류열전달계수의 형태로 유도하였다. 유도된 관류열전달계수 식을 변형하여 관의 규격과 온수-실내공기의 온도차를 입력 변수로 하는 난방배관의 단위길이 당 방열량 산정식을 개발하였다. 본 연구 결과를 기존에 제공되고 있는 국내외 여러 자료와 비교한 결과 JGHA 자료와 가장 유사한 것으로 나타났다. 국내 온실의 설계에서 적용하고 있는 NAAS 자료와 국외의 BALLS 및 ASHRAE 자료는 값이 너무 큰 것으로 판단된다. 따라서 국내 온실의 환경설계기준을 제정하고, 고시하기 위해서는 추가적인 실험을 통해 이 부분에 대한 충분한 검토가 필요할 것으로 판단된다.

• 한국기계기술학회지
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• 제13권2호
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• pp.63-70
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• 2011

In the present study, we developed optimal heat supply algorithm which minimizes the heat loss through the distribution pipe line in group energy apartment. Heating load variation of group energy apartment building in accordance with outdoor air temperature was predicted by the correlation obtained from calorimeter measurements of whole households of apartment building. Supply water temperature and mass flow rate were conjugately controlled to minimize the heat loss rate through distribution pipe line. Group heating apartment located in Hwaseong city, Korea, which has 1,473 households divided in 4 regions, was selected as the object apartment for verifying the present heat supply control algorithm. Compared to the original heat supply system, 10.4% heat loss rate reduction can be accomplished by employing the present control algorithm.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 춘계학술발표회논문집(1)
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• pp.304-309
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• 1997

A method to mitigate the thermal stratification flow of a horizontal pipe line is proposed by heating external bottom of the pipe with electrical heat tracing. Unsteady two dimensional model has been used to numerically investigate an effect of the external Denting to the thermally stratified flow. The dimensionless governing equations are solved by using the control volume formulation and SIMPLE algorithm. Temperature distribution, streamline profile and Nusselt numbers of fluids and pipe walls with time are analyzed in case of externally heating condition. no numerical result of this study shows that the maximum dimensionless temperature difference between the hot and the cold sections of pipe inner wall is 0.424 at dimensionless time 1,500 ann the thermal stratification phenomena is disappeared at about dimensionless time 9,000. This result means that external heat tracing can mitigate the thermal stratification phenomena by lessening $\Delta$ $T_{ma}$ about 0.1 and shortening the dimensionless time about 132 in comparison with no external heat tracing.rnal heat tracing.

• 설비공학논문집
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• 제23권5호
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• pp.334-341
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• 2011

In the present study, optimal heat supply algorithm which minimize the heat loss through the distribution pipe line in group energy apartment was developed. Variation of heating load of group energy apartment building in accord with the outdoor air temperature was predicted by the heating load-outdoor temperature correlation. Supply water temperature and mass flow rate were controlled to minimize the heat loss through distribution pipe line. District heating apartment building located in Hwaseong city, which has 1,473 households, was selected as the object building for testing the present heat supply a1gorithm. Compared to the previous heat supply system, 10.4% heat loss reduction can be accomplished by employing the present method.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2130-2135
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• 2007

Operating characteristics of a loop heat pipe (LHP) having a bypass line was investigated experimentally. The LHP had a sintered metal wick as a capillary structure and methanol as a working fluid. The sintered metal wick was made of stainless steel of which the average pore size was 5 ${\mu}m$and porosity of 47%. A bypass line of a small diameter was attached between the vapor escape passage and the liquid reservoir. The dimension of the flat evaporator was $50(L){\times}40(W){\times}30(H)$ mm and that of the condenser was $50(L){\times}40(W){\times}11(H)$ mm. Wall and pipe material of the LHP was stainless steel and heating area was 35(W) mm${\times}$35(L) mm. The inner diameters of vapor and liquid transport lines were 4.0 mm and 2.0 mm, and the lengths of the two lines were both 0.5 m. The LHP was tested for three different tilt angles of horizontal, favorite tilt, and adverse tilt. The thermal load range was up to 290 W at the condenser above evaporation position. Furthermore, the effect of a bypass line on the start-up transient as well as steady-state operation was presented and discussed.

• 에너지공학
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• 제6권2호
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• pp.119-128
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• 1997

수평배관의 열성층 유동을 완화하기 위하여 아래부분에 Heat Tracing을 한 수평배관의 외부 가열에 의한 열성층 유동과 열전달 특성을 수치적으로 해석하기 위하여 비정상 2차원 모델을 이용하였다. 무차원 지배방정식은 제어체적방법과 SIMPLE 알고리즘을 사용하여 해를 구하였다. Heat Tracing이 있는 수평배관 내부 열성층 유동의 등온선, 유선분포, Nusselt수, 온도 분포를 해석하였다. 무차원 시간 1,500에서 최대 무차원 온도차가 0.424로 계산되어졌고 무차원 시간 9,000 이후에는 열성층 현상이 없어졌다.