• 태양에너지
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• 제8권2호
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• pp.57-65
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• 1988

The coefficients of convective heat transfer were investigated when air is jetted to surface of the heated side-wall. The temperature on the side-wall was measured when the offsets changed from 1.5 to 10.5 as 7 steps at the state of fixed Reynolds numbers that were 35000, 29000 and 23000. The experimental results are as follows: 1. The mean Nusselt number is very high on the surface of reattached flow region. 2. The offset and the recirculation flow region decreased, while the mean Nusselt number increased between the outlet of nozzle and the region of reattachment flow. 3. The local Nusselt number is not concerned with Reynolds number on the recirculation flow and on the reattached flow region when the offset decrease. But the Nusselt number increased only when Reynolds numbers on the wall jet flow region increased. 4. The mean and the maximum Nusselt number decreases linearly, and in particular its values rapidly decrease in accordance with changing of the offset from 1.5 to 3 in inverse proportion.

• 대한설비공학회지:설비저널
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• 제14권2호
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• pp.138-149
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• 1985

The heat diffusion equation for an annular fin is analyzed using Laplace transformations. The fin has a uniform thickness with its edge heat loss and two temperature profiles at the base such as a step change in temperature or heat flux. To obtain the exact solutions for temperature distribution, this paper can detect the eigenvalues which satisfy the roots of transcendental equations in above two cases during inverse Laplace transformations. The exact solutions for temperature and heat flux are obtained with the infinite Series by dimensionless factors. The solutions are developed for small and large values of times. These series solutions converge rapidly for large values of time, but slowly for small.

• 한국정밀공학회지
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• 제29권11호
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• pp.1190-1198
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• 2012

A hot forming of large thick Al plate using a grid-type hybrid die is a process to make a shell plate for the production of a spherical LNG tank. This process is characterized by using a grid-typed die with an additional air cooling system for reducing the cooling time of the heated plate after hot forming. The process consists of the plate's feeding, heating, forming and cooling in detail and each of them is continuously performed along the rail. This paper was designed to propose the analytical and experimental methods for determining the convection and interfacial heat transfer coefficients required in hot forming analysis of Al plate. These values in the analysis are to reproduce numerically the cooling performance of grid-typed die and cooling device. Interfacial heat transfer was obtained from the heat transfer experiments for different pressures and inverse analysis method. To verify the efficiency of the coefficient values obtained from above methods, FE analysis and experiment of the hot spherical-forming process were conducted for a small-scaled model. The convection coefficient was also calculated from flow analysis of air released by cooling device within grid-typed die using ANSYS-CFX.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.444-445
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• 2010

Predictive modeling schemes have been developed to characterize the heat Transfer and thermo-mechanical behavior for the plasma display panel (PDP) in operation. The inverse approach was adopted to predict the accurate temperature distribution and deformation in PDP. The predictive models were validated with the measurements from real panel. The developed models could be utilized to predict and/or improve the product quality of PDP.

• 대한기계학회논문집B
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• 제38권9호
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• pp.747-755
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• 2014

광자(Photon)이나 전자기파(Electromagnetic Wave) 등의 형태로 직접 열을 전달하는 특징을 가지고 있는 복사열전달은 중간 매질의 열전달 관여여부에 따라 표면복사(Surface Radiation)와 기체복사(Gas Radiation)의 형태로 구분될 수 있다. 본 연구에서는 원통 형상에서의 표면복사에 대해 미지의 복사물성치들을 역해석 방법을 이용해 역추정하였다. 이때, 효율적인 역해석을 위해 반발 입자 군집 최적화(Repulsive Particle Swarm Optimization, RPSO) 알고리즘을 역해석 기법으로 채택하였다. 이로부터 얻은 해의 수렴성과 정확도 등을 기존의 유전알고리즘(GA) 결과와 비교해 봄으로써, 표면복사 현상에 대한 역해석의 적용 가능성을 고찰하고자 하였다.

• 한국주조공학회지
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• 제16권6호
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• pp.550-555
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• 1996

A stochastic model, based on the coupling of the finite volume(FV) method for macroscopic heat flow calculation and a two-dimensional cellular automaton(CA) model for treating microstructural evolution was applied-for the prediction of microstructural evolution in squeeze casting. The interfacial heat transfer coefficient at the casting/die interface was evaluated as a function of time using an inverse problem method in order to provide a quantitative simulation of solidification sequences under high pressure. The effects of casting process variables on the formation of solidification grain structures and on the columnar to equiaxed transition of an Al-4.5wt%Cu alloy in squeeze casting were investigated. The calculated solidification grain structures were in good agreement with those obtained experimentally.

• 대한기계학회논문집A
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• 제35권10호
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• pp.1161-1170
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• 2011

이 논문은 촉매 담체에서 열유동 및 구조해석의 실동경계조건에 대한 역문제 해법을 나타낸다. 촉매 담체의 배기가스 정화효율은 열유동 매개변수와 촉매 성분 등에 영향을 받고 열유동 균일도에 의해 평가된다. 역문제의 정식화-열유동 매개변수(입구 온도, 속도, 반응열, 대류열전달계수)를 얻고-와 직접 문제-주어진 출구 온도 분포로부터 평가-를 설명하였다. 실험계획법과 반응표면 최적화 기법은 제안된 역문제 해결을 위해 이용하였다. 촉매 담체의 온도 분포는 예측된 열유동 매개변수에 대한 열유동해석에 의해 얻었다. 열응력과 내구성 평가는 이 온도 분포에 기반해서 수행하였다. 역문제 접근 방법의 유효성과 정확성은 반응표면모델과 측정된 실차 시험과 좋은 일치를 달성함으로써 설명하였다.

• 한국농공학회지
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• 제18권1호
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• pp.4038-4051
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• 1976

This study was intended to provide the basic design creteria for the refrigerated storage, and to estimate the required optimum capacity of refrigerator for the different sizes and kinds of the existing fruit storage. The structural characteristics of the existing fruit storages in Pyungtaek-khun of Kyungki-do were surveyed. The average out-door air temperature during the expected storage life after harvesting, was obtained by analyzing the weather information. The heat transfer rates through the different models of storage walls were estimated. The refrigerating load required for different models of fruit storage was analyzed in the basis of out-door air temperature. The results obtained in this study are summarized as follows: 1. The fruit storages surveyed were constructed on-ground, under-ground and sub-ground type buildings. The majority of them being the on-ground buildings are mostly made of earth bricks with double walls. Rice hull was mostly used as the insulating materials for their walls and ceilings. About 42% of the buildings were with the horizontal ceiling, 22% with sloped ceiling, and about 36% without ceiling. About 60% of the storage buildings had floor without using insulated material. They were made of compacted earth. 2. There is no difference in heat transfer among six different types of double walls. The double wall, however, gives much less heat transfer than the single wall. Therefore, the double wall is recommended as the walls of the fruit storage on the point of heat transfer. Especially, in case of the single wall using concrete, the heat transfer is about five time of the double walls. It is evident that concrete is not proper wall material for the fruit storage without using special insulating material. 3. The heat transfer through the storage walls is in inverse proportion to the thickness of rice hull which is mostly used as the insulating material in the surveyed area. It is recommended that the thickness of rice hull used as the insulating material far storage wall is about 20cm in consideration of the decreasing rate of heat transfer and the available storage area. 4. The design refrigerating load for the on-ground storages having 20 pyung area is estimated in 4.07 to 4.16 ton refrigeration for double walls, and 5.23 to 6.97 ton refrigeration for single walls. During the long storage life, however, the average daily refrigerating load is ranged from 0.93 to 0.95 ton refrigeration for double walls, and from 1.15 to 1.47 ton refrigeration for single walls, respectively. 5. In case of single walls, 50.8 to 61.4 percent to total refrigerating load during the long storage life is caused by the heat transferred into the room space through walls, ceiling and floor. On the other hand, 39.1 to 40.7 percent is for the double walls. 6. The design and average daily refrigerating load increases in linear proportion to the size of storage area. As the size increases, the increasing rate of the refrigerating load is raised in proportion to the heat transfer rate of the wall. 7. The refrigerating load during the long storage life has close relationship to the out-door air temperature. The maximum refrigeration load is shown in later May, which is amounted to about 50 percent to the design refrigerating load. 8. It is noted that when the wall material having high heat transfer rate, such as the single wall made of concrete, is used, heating facilities are required for the period of later December to early February.

• 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.

• Steel and Composite Structures
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• 제24권3호
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• pp.297-307
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• 2017

A unified mathematical model of phase-lag Green-Naghdi magneto-thermoelasticty theories based on fractional derivative heat transfer for perfectly conducting media in the presence of a constant magnetic field is given. The GN theories as well as the theories of coupled and of generalized magneto-thermoelasticity with thermal relaxation follow as limit cases. The resulting nondimensional coupled equations together with the Laplace transforms techniques are applied to a half space, which is assumed to be traction free and subjected to a thermal shock that is a function of time. The inverse transforms are obtained by using a numerical method based on Fourier expansion techniques. The predictions of the theory are discussed and compared with those for the generalized theory of magneto-thermoelasticity with one relaxation time. The effects of Alfven velocity and the fractional order parameter on copper-like material are discussed in different types of GN theories.