• 한국정밀공학회지
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• 제27권4호
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• pp.79-86
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• 2010

Mechanical structures with power sources experience repeated force produced by motors. In result, the life of the pipes reduces and ultimately, the pipes collapse. Such pipes are formed into several shapes and particularly, the U-shape pipe is damaged frequently. In most cases, the U-shape pipe is made with a straight pipe by complicated bending work. During this work process, plastic deformation of the pipe produces residual stress in the pipe. This residual stress significantly affects the fracture behavior of the pipe and induces the change of the stress ratio (min. stress/Max. stress = R). For this reason, residual stress has to be evaluated. In this paper, the residual stress of a U-shaped pipe was evaluated by FEM analysis. In addition, fatigue tests of the U-shaped pipe were performed by using a uniaxial fatigue testing machine. The results of the fatigue test were modified with the results of FEM (Finite Element Method) analysis for residual stress. The modified fatigue test results of the U-shaped pipe were compared with those of a straight pipe.

• 대한기계학회논문집B
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• 제25권12호
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• pp.1711-1720
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• 2001

In this study, the heat transfer characteristics of a U-shape heat pipes were investigated. Heat is supplied to the U heat pipe through its middle zone(evaporator), and is released to the environment through its both arms(condensers). Both heat transfer coefficients and heat transport limitations were measured and compared with correlations previously developed for straight type heat pipes. Special concerns were focused to the cases, when each of condensers were submitted to a different cooling conditions, relatively. As a result. the heat transfer limitation of a U-shape heat pipe was found out to be 10∼15% less than the value for a straight heat pipe with an equivalent size.

• 설비공학논문집
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• 제13권8호
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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}

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 추계학술대회 논문집
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• pp.819-820
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• 2010

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2003년도 춘계학술대회 논문집
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• pp.1630-1633
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• 2003

Hair pin bending machine is pipe forming machine consisting of heat exchanger product system. Hair pin produced by these machine is pathway of refrigerant and play a important role improving the performance and productivity of heat exchanger. The core technology of hair pin bending machine is forming the straight pipe into U-type without any defaults. Therefore, this paper study the relation between the pipe bending forming and the shape and position of mandrel using the elastic-plastic finite element analysis and provide a foundation technology for which developing the hair pin bending machine. The results are followed 1. Mandrel located in front of rotating center of bending die minimized the circular shape variation of copper pipe. 2. Diameter change of mandrel hardly effect the pipe shape.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 추계학술대회 논문집
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• pp.823-824
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• 2010

• 한국수자원학회논문집
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• 제38권7호
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• pp.527-535
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• 2005

등류수심의 산정은 수로 설계 및 흐름 해석에 있어 매우 중요하다. 하수관은 삼각형 또는 사각형의 인공 개수로와 달리 원형, U형과 같이 곡률을 갖는 경우가 일반적이며, 이 경우 수심에 따른 통수단면적 및 동수반경의 변화가 일정하지 않으므로 등류수심 산정 또는 수식 유도에 있어 상당한 어려움을 갖는다. 그러나 단면적과 관경의 비 또는 동수반경과 관경의 비를 수심대 관경의 비로 표기하여 지수형으로 나타내면 수식의 전개과정이 매우 용이해지며, 양해법 산정식의 개발이 가능해진다. 따라서 본 고에서는 우선 실무에서 가장 많이 사용하고 있는 원형 개수로와 U형 개수로에 대한 등류수심 양해법 산정식을 제시하며, 완난류 지수형 마찰계수 산정식과 더불어 실무에서 주로 사용되는 Hagen (Manning) 산정식을 이용한 등류수심 산정식도 제시하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2010년도 춘계 학술발표회
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• pp.229-239
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• 2010

Performing a series of in-situ thermal response tests, the effective thermal conductivity of six vertical closed-loop ground heat exchangers was experimentally evaluated and compared each other, which were constructed in a test bed in Wonju. To compare thermal efficiency of the ground heat exchangers in field, the six boreholes were constructed with different construction conditions: grouting materials (cement vs. bentonite), different additives (silica sand vs. graphite) and the shape of pipe-sections (general U-loop type vs. 3 pipe-type). From the test results, it can be concluded that cement grouting has a higher effective thermal conductivity than that of bentonite grouting, and the efficiency of graphite better performs over silica sand as a thermally-enhancing addictive. In addition, a new 3 pipe-type heat exchanger provides less thermal interference between the inlet and outlet pipe than the conventional U-loop type heat exchanger, which results in superior thermal performance.

• 한국지반공학회논문집
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• 제26권7호
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• pp.93-106
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• 2010

현장 열응답 시험을 통해 지중 유효 열전도도를 산출하여 각 보어홀의 성능을 비교하기 위해 강원도 원주 현장에 6개의 보어홀을 시험 시공하였다. 6개의 보어홀은 그라우트 종류와 첨가재 종류, 지중열교환기 파이프 단면에 따른 영향을 검토하도록 시공되었다. 그라우트 재료는 벤토나이트와 시멘트를 사용하였으며 첨가재는 천연규사와 흑연, 파이프 단면은 기존 U-tube 파이프 단면과 유입과 유출 파이프 사이에 파이프를 추가로 삽입한 새로운 3공형 파이프 단면을 적용하였다. 현장 열응답 시험으로 산정한 지중 유효 열전도도 결과는 시멘트 그라우트로 시공한 보어홀의 경우가 벤토나이트 그라우트로 시공한 경우에 비해 전열 성능이 향상됨을 보였으며 흑연을 추가로 사용한 경우가 천연규사만 사용한 경우보다 높은 효율을 보였다. 또한, 유입과 유출 파이프 사이에 물을 채워 부분적 단열 구간을 형성한 새로운 3공형 파이프 단면의 경우가 기존 U-tube 파이프 단면에 비해 높은 효율을 보였다. 가상 건물에 대한 지중열교환기 설계를 수행하여 지중열교환기 시공비를 비교한 결과, 시멘트 그라우트에 첨가재로 천연규사와 흑연을 함께 사용한 경우가 벤토나이트 그라우트에 첨가재로 천연규사를 사용한 기존의 시공방법 보다 낮은 시공비로 설계가 가능하였다. 마지막으로 본 현장 열응답 시험결과를 바탕으로 일련의 경제성 분석을 통하여 새로이 제시된 첨가제와 3공형 파이프 단면의 적용성을 평가하였다.

• 한국주거학회논문집
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• 제17권5호
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• pp.87-95
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• 2006

Building components have been deteriorated by various factors such as location, a building type, a surrounding environment and so on. In addition, each component has a peculiar characteristics, compared with other components in properties of matter an used part. Building components would be required to maintain its function and performance to provide the resident with a decent living condition. It is important to decide the repair time, scope and a required cost in repair plan, considering the each component's characteristics. In this parer, it aimed at providing the economic repair pattern to analyze the relation of the time-elapse and the cumulative repair cost in the apartment housing using 3rd quadratic function. Results of the study are as follows: First, the shape of the function for the economic repair is classified into two type. One is the continuous increase type of the cumulative cost which properly means the iterative repair type after built. The other is that the function has the maximum state at a point which means one-repair after its repair would be delayed to a scheduled time. Second, the iterative repair pattern would include window, roof proof, lighting and water supply pipe. The other repair pattern would include the paintings, heating pipe and sign board.