• Journal of the Korean Society for Industrial and Applied Mathematics
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• 제2권2호
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• pp.97-109
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• 1998

A comparison of the two dimensional heat loss, computed using the analytical method and the finite difference method in two models(i.e. one is a parabolic fin whose parabolic curves meet at the fin center line and the other is a transformed parabolic fin whose tip cuts vertically), is made assuming the analytical method is correct. For these methods, the root temperature and surrounding convection coefficients of these fins are assumed as constants. The results show that the relative errors of the heat loss between the two methods for the parabolic fin whose tip cuts vertically are smaller than those for the one whose tip does not cut. In case of Bi=0.01, the values of the heat loss obtained using a finite difference method are close to those values obtained using the analytical method for both models. The values of the heat loss from both models calculated by using the analytical method are almost the same for given range of non-dimensional fin length in case of Bi = 0.01 and 0.1.

• Journal of Advanced Marine Engineering and Technology
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• 제31권1호
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• pp.51-57
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• 2007

In process of reinforced concrete (RC) box structure. the heat of hydration may cause serious thermal cracking. In order to eliminate hydration heat of mass concrete. this paper reports results of hydration heat control in mass concrete structure using the pulsating heat pipe. There were three RC box molds($1.2{\times}l.8{\times}2.4m^3$) which shows a difference as compared with each other. One was not equipped with pulsating heat pipe. The others were equipped with pulsating heat pipe. All of them were cooled with natural air convection. The pulsating heat pipe was composed of serpentine type copper pipe with 10 turns (outer diameter: 4mm. inner diameter: 2.8mm). The working fluid was R-22 and its charging ratio was 40% by volume. The conditions such as the number of turns. the length and the pitch of the pulsating heat pipe and the size of concrete structure were changed. Based on these experiments, it was confirmed that this construction method using pulsating heat pipe was effective to remove hydration heat of mass concrete structure and thus it was possible to prevent harmful thermal crack and construction Period and costs of concrete structure would be cut down.

• 한국식품저장유통학회지
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• 제23권1호
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• pp.27-33
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• 2016

본 연구에서는 신선편이 '로메인' 상추의 신선편이 가공 시 열수처리(45, 50, $55^{\circ}C/2min$)가 저장 중의 품질특성에 미치는 영향에 대하여 조사하였다. 각 처리구는 $5^{\circ}C$에서 5일간 저장한 후 관능품질, 호흡률, 에틸렌 발생량, 총균수, 갈변도, 총페놀, 비타민 C, 항산화 활성(DPPH, ABTS, FRAP)을 분석하였다. 본 연구에서 실시한 모든 열처리 조건은 총페놀 함량의 변화에 미치는 영향은 없었다. $45^{\circ}C$ 처리시에는 호흡과 에틸렌 발생이 증가하고 비타민 C 함량과 항산화 활성이 감소되었으며 갈변 억제 효과도 미미하였다. $55^{\circ}C$ 조건에서는 조직의 연화가 발생되는 문제가 발생하였다. $50^{\circ}C$ 열처리를 2분간 실시할 경우 조직감, 색, 미생물증식, 갈변도에서 가장 우수한 품질 상태를 나타내었으며, 저장 후 비타민 C 함량과 항산화 활성이 높게 유지되었다. 따라서 본 연구 결과 $50^{\circ}C$ 열처리 조건은 신선편이 '로메인' 상추의 저장 중 품질 및 항산화 활성을 유지시킬 수 있는 기술로 활용될 수 있을 것으로 판단되었다.

• 한국초전도ㆍ저온공학회논문지
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• 제22권1호
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• pp.24-28
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• 2020

Heat leakage is an important parameter to reflect heat insulated performance of cryogenic vessel. According to the current standard requirements, it needs to measure the daily evaporation rate to indicate heat leakage. The test needs-over 24h after cryogenic vessel in heat equilibrium as standard required, therefore test efficiency is poor and new efficient method is required to cut test time. First of all, the volume of instantaneous evaporated gas and heat leakage are calculated by the current standard corresponding to the maximum allowable daily evaporation rate of cryogenic vessel. Depending on the relationship between real daily evaporation rate and maximum allowable daily evaporation rate of cryogenic vessel, we designed a new test method based on the pressure changes over time in cryogenic vessel to determine whether its heat insulated performance meets requirements or not. Secondly, the heat transfer process was analyzed in measurement of cryogenic vessel, and the heat transfer equations of whole system were established. Finally, the test was completed in four hours; meanwhile the heat leakage and daily evaporation rate of cryogenic vessel are calculated basing on test data.

• 한국정밀공학회지
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• 제32권12호
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• pp.1023-1029
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• 2015

Laser-assisted machining (LAM) is one of the most effective methods for enhancing the machinability of difficult-to-cut materials, such as titanium alloys and various ceramics, and has been studied by many researchers. LAM is a method that facilitates machining by softening a workpiece using a laser heat source. The advantages of the LAM process are decreases in tool wear, cutting force, and surface roughness. However, when the material is over-heated, melting or burning can occur. This study analyzed the heat source distribution with regard to overlapping of preheating on the laser heating path with an acute angle, a right angle and obtuse angles. Then, a power reduction method was proposed to reduce the melting and burning of the workpiece.

• 한국환경과학회지
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• 제3권1호
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• pp.17-29
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• 1994

An one dimensional atmosphere-vegetation interaction model is developed to discuss of the effect of vegetation on heat flux in mesoscale planetary boundary layer. The canopy model was a coupled system of three balance equations of energy, moisture at ground surface and energy state of canopy with three independent variables of $T_f$(foliage temperature), $T_g$(ground temperature) and $q_g$(ground specific humidity). The model was verified by comparative study with OSUID(Oregon State University One Dimensional Model) proved in HYPEX-MOBHLY experiment. As the result, both vegetation and soil characteristics can be emphasized as an important factor iii the analysis of heat flux in the boundary layer. From the numerical experiments, following heat flux characteristics are clearly founded simulation. The larger shielding factor(vegetation) increase of $T_f$ while decrease $T_g$. because vegetation cut solar radiation to ground. Vegetation, the increase of roughness and resistance, increase of sensible heat flux in foliage while decrease the latent heat flux in the foliage.

• 한국공작기계학회논문집
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• 제10권1호
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• pp.30-35
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• 2001

Nickel-based heat resisting alloys are commonly used for high temperature application such as in aircraft engines and gas turbines. In this paper, the machinability of Nickel-based heat resisting alloys was investigated with respect to the wear and the chip formation by tool type and cutting condition. Relationship between three types of tool and chip formation was experimentally investigated. Among the three types of tool tested, coated tools(CVD, PVD) ara available for the difficult-to-cut-materials such as Nickel-based heat resisting alloys and etc.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2000년도 춘계학술대회논문집 - 한국공작기계학회
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• pp.264-269
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• 2000

Nickel-based heat resisting alloys are commonly used for high temperature applications such as in aircraft engines and gas turbines. In this paper, the machinability of Nickel-based heat resisting alloy was investigated with respect to the wear and the chip formation by tool type and cutting condition. Relationship between three types of tool and chip formation was experimentally investigated. Among the three types of tool tested, coated tools(CVD, PVD) are available for the difficult-to-cut-materials such as Nickel-based heat resisting alloy and etc..

• Journal of Advanced Marine Engineering and Technology
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• 제24권5호
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• pp.119-124
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• 2000

A finite element method is applied to investigate the characteristics of the fluid flow and heat transfer performance in a channel in terms of the various effects of baffle cuts, baffle angles, and leakages. The results show that the decrease of a baffle cut gives a good heat transfer enhancement. However, it also increases pressure drop. In the case of an inclined baffle, the result shows that the pressure drop decreases with a reasonable heat transfer performance. But a steeply inclined baffle gives adverse effects on the performance of the channel. The clearances between baffle-to-shell and tube-to-baffle affect the overall performance. The effects of these parameters are discussed in details.

• 한국기계가공학회지
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• 제18권10호
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• pp.93-98
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• 2019

Recently, with the development of the aerospace and automotive industries, the demand for high-melting-point materials has increased. However, high-melting-point materials are difficult to cut through conventional machining methods. Thermally assisted machining (TAM) is a method for improving the machinability by preheating the materials. A laser, the most commonly used device for TAM, has high efficiency through local preheating but is not sufficient for maintaining a high preheating temperature due to rapid cooling. However, the use of multi-heat sources can supplement the disadvantage of a single heat source. The high preheating temperature can be maintained with a wide and deep heat-affected zone (HAZ) by multi-heat sources. The purpose of this study is to analyze the preheating effects of multi-heat sources using laser plasma. Thermal analysis and preheating experiments were carried out. As a result, the high preheating effect of multi-heat sources compared with a single heat source was verified.