• 대한기계학회논문집
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• 제13권5호
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• pp.952-961
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• 1989

본 연구에서는 널리 사용되는 핀-관 직교류 열교환기의 정상 상태를 예측 하기 위하여 냉매의 상변화에 따른 유체의 물성치, 열전달계수 및 마찰계수의 변화와 관벽에서의 축방향 열전도를 고려한 모형을 세우고 이를 분석하여 열교환기의 종합적 인 특성을 규명하고자 한다.

• Journal of Mechanical Science and Technology
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• 제20권1호
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• pp.158-166
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• 2006

Extended Graetz problem in microtube is analyzed by using eigenfunction expansion to solve the energy equation. For the eigenvalue problem we applied the shooting method and Galerkin method. The hydrodynamically isothermal developed flow is assumed to enter the microtube with uniform temperature or uniform heat flux boundary condition. The effects of velocity and temperature jump boundary condition on the microtube wall, axial conduction and viscous dissipation are included. From the temperature field obtained, the local Nusselt number distributions on the tube wall are obtained as the dimensionless parameters (Peclet number, Knudsen number, Brinkman number) vary. The fully developed Nusselt number for each boundary condition is obtained also in terms of these parameters.

• Journal of Advanced Marine Engineering and Technology
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• 제10권2호
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• pp.156-164
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• 1986

In the case of boiling on high temperature wall, vapor film covers fully or parcially the surface. This phenomenon, film boiling or transition boiling, is very important in the surface heat treatment of metal, design of cryogenic heat exchanger and emergency cooling of nuclear reactor. Mainly supposed hydraulic-thermal accidents in nuclear reactor are LCCA (Loss of Coolant Accident) and PCM (Power-Cooling Mismatch). Recently, world-wide studies on reflooding of high temperature rod bundles after the occurrence of the above accidents focus attention on wall temperature history and required time in transient cooling process, wall superheat at rewet point, heat flux-wall superheat relationship beyond the transition boiling region, and two-phase flow state near the surface. It is considered that the further systematical study in this field will be in need in spite of the previous results in ref. (2), (3), (4). The paper is the study about the fast transient cooling process following the wall temperature excursion under the CHF (Critical Heat Flux) condition in a forced convective subcooled boiling system. The test section is a vertically arranged concentric annulus of 800 mm long and 10 mm hydraulic diameter. The inner tube, SUS 304 of 400 mm long, 8 mm I.D, and 7 mm O.D., is heated uniformly by the low voltage AC power. The wall temperature measurements were performed at the axial distance from the inlet of the heating tube, z=390 mm. 6 chromel- alumel thermocouples of 76 .mu.m were press fitted to the inner surface of the heating tube periphery. To investigate the heat transfer characteristics during the fast transient cooling process, the outer surface (fluid side) temperature and the surface heat flux are computed from the measured inner surface temperature history by means of a numerical method for inverse problems of transient heat conduction. Present cooling (boiling) curve is sufficiently compared with the previous results.

• 태양에너지
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• 제6권1호
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• pp.60-69
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• 1986

Two-dimensional finite difference numerical analysis is used to study conjugate natural convection heat transfer from a horizontal conducting tube with one vertical axial fin. By increasing dimensionless fin length ($L_F$), the mean total Nusselt number of the upward fin is slightly less than that of the downward fin at $L_F\;{\le}\;0.18$ and is higher than that of the downward fin at $L_F\;>\;0.18$. However comparing the upward fin and the downward fin with the no fin, the mean total Nusselt numbers of downward fin and upward fin at $L_F=0.30$ are increased approximately 4.01% and 5.51%, respectively. As Rayleigh number, Prandtl number and Biot number increase, the mean total and the mean tube Nusselt numbers are increased, but as wall thickness increases, the mean total and the mean tube Nusselt numbers are decreased. As the fin conduction parameter increases, the mean total Nusselt number is slightly increased because of increasing the mean fin Nusselt number.

• 대한기계학회논문집B
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• 제39권2호
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• pp.119-124
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• 2015

반도체 생산에 사용되는 액체용 극소 질량유량계측기의 새로운 설계 안에 대하여 수치해석적으로 연구하였다. 내경 0.3mm 정도인 원관 외부에 히터선을 일정 폭 권선하고, 히터로부터 일정거리 떨어진 후류에 온도계측용 써미스터선을 권선하는 형상이다. 히터에 단일펄스 가열을 하면 일정시간 경과 후 써미스터가 최고온도를 겪는다. 최고온도까지 걸리는 시간은 질량유량과 거의 반비례하며, 이를 이용하여 질량유량을 계측할 수 있다. 관벽을 통한 전도열전달과 액체유동에 의한 대류열전달이 복합적으로 작용하므로 관내유동의 평균속도와 관벽을 통한 최고온도의 이동속도는 큰 차이를 나타내며, 상호 비선형적인 특성을 보인다. 본 연구에서는 센서관의 내 외경, 히터의 권선폭 및 히터와 써미스터 사이의 거리를 설계변수로 고려하여 수치해석적으로 제안한 설계사항을 분석하였으며, 설계인자의 최적화에 대한 검토를 수행하였다.