• 대한설비공학회지:설비저널
• /
• 제44권7호
• /
• pp.82-89
• /
• 2015

• 한국정밀공학회지
• /
• 제33권8호
• /
• pp.629-634
• /
• 2016

Laser-assisted machining (LAM) is one of the most effective methods of processing difficult-to-cut materials, such as titanium alloys and various ceramics. However, it is associated with problems such as the inability of the laser heat source to generate an appropriate preheating temperature. To solve the problem, thermally assisted machining with multiple heat sources is proposed. In this study, thermal analysis of multiple heat sources by laser and arc is performed according to power, heat source size, and leading heat source position. Then, the results are analyzed according to each condition. The results of this analysis can be used as a reference to predict preheating temperature in thermally assisted machining with multiple heat sources.

• 설비공학논문집
• /
• 제29권2호
• /
• pp.57-62
• /
• 2017

The heat transfer performance of a multi-heat-source fluidized bed heat exchanger was analyzed. The fluidized bed heat exchanger examined in this study can simultaneously recover the waste heat from gas, water vapor, and hot water. The effects of waste water flow rate, gas flow rate, and cooling water flow rate were examined to find their experimental correlations with the heat transfer coefficient. A computer program using the correlations was developed in this study to predict the thermal performance of the fluidized bed heat exchanger. The calculated heat transfer rates of gas, water vapor, waste water, and cooling water were compared with the measured values. It was found that the error of the calculated values was less than 12%.

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

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2008년도 추계학술대회B
• /
• pp.2053-2058
• /
• 2008

It was investigated thermal performances on two array types of a serial circulation and a two-way parallel circulation for six water-cooled cold plates covered with non-metallic material (polycarbonate, PC) to reduce weight of the cooling devices for humanoid robot cooling. Six cold plates attached on $10{\times}10\;mm^2$ copper base : $0.5{\times}0.5\;mm^2$ pin-finned surfaces of 1.5 mm high with 0.5 mm array spacing, was mounted on six copper heating blocks with isothermal conditions of $50{\sim}90^{\circ}C$, respectively. In order to compare thermal characteristics according to two circulation types, the surface temperatures of heating blocks and the cooling water temperatures at inlets and outlets of cold plates were measured. From the results, it was found that a two-way parallel circulation was better performance than a serial circulation in terms of total thermal resistance, total heat transfer rate, and surface temperature rises from $1^{st}$ heating block to last one for six multiple cold plates.

• 대한기계학회논문집B
• /
• 제22권3호
• /
• pp.303-315
• /
• 1998

Numerical and experimental studies on a heat pipe with two heat sources have been performed to investigate the operating characteristics. Numerical analysis was performed based on the cylindrical two-dimensional incompressible laminar flow for the vapor space and the conjugate heat transfer for the entire heat pipe. Experimental study with a 0.45 m length copper-water heat pipe was also performed to validate the numerical modeling for the heat input range from 29 W to 47 W on each heater. As results, the temperature profiles at the outer wall for the single active heat source as well as the temperature profiles for the switching operation between two heat sources are suggested. Due to the axial conduction, it is found that the temperature drop between the evaporator and the condenser appears small when the heat source closer to the condenser is turned on. For the switching operation in the present study, the transient time is about 700s and the temperatures at the locations of both heat source are same in 130s after switching.

• 대한전자공학회논문지
• /
• 제21권5호
• /
• pp.90-99
• /
• 1984

양면에서 텅스텐 램프를 조사하는 실리콘 재결정시의 SOI(silicon-on-insulator) 다층구조에 대한 1차원적 온도 및 열원(열원)의 분포를 SOR(successive over-relaxation)방법을 이용하여 정상상태의 열방정식의 해로부터 구하였다. 열원의 분포는 광원의 스펙트럼, SOI sample 내부 계면에서의 다중반사, 광흡수 계수의 온도, 주파수 의존성 등을 고려하여 구하였으며, 열 방정식의 경계조건이 되는 wafer의 전면과 후면의 온도는 혹체복사 조건으로부터 구하였다. 내부계면에서는 전도열속(conduction heat flux)과 복사열속(radiation heat flux)에 의한 연속조건을 만족하도록 하였다. 본 문제에서의 온도분포와 열원의 분포는 상호간에 큰 영향을 주게 되므로, 두가지 변수가 일치되는 값을 보일 때까지 iteration을 계속하였다. Pyrometer을 이용하여 측정한 wafer 전면의 온도는 약1200°K이었고 이때의 simulation 결과는 1120°K 정도로 나타났다.

• Journal of Biosystems Engineering
• /
• 제20권1호
• /
• pp.66-72
• /
• 1995

A numerical study for a two dimensional multi-impingement jet with crossflow of the spent fluid has been carried out. To study the flow characteristics especially in the jet flow region, three different distributions of mass flow rate at 5-jet exits were assumed. For each distribution, various Reynolds numbers ranging from laminar to turbulent flows were considered. Calculations drew the following items as conclusion. 1) A periodical fully developed flow was observed from the third protrusion. This was also observed from previous experimentally by Whidden at al. The Nessult number at the protrusion surface increased mildly as going downstream. 2) The low Reynolds number turbulence model of Launder and Sharma was found to be adequate for the prediction of fluid flow and heat transfer characteristics of two dimensional multi-jet configuration. 3) The Nusselt number at the protrusion surface was nearly proportional to the square root of the Reynolds number.

• 대한기계학회논문집B
• /
• 제34권6호
• /
• pp.607-613
• /
• 2010

도서지역에서 많이 사용하고 있는 소형 발전기의 폐열을 열원으로 이용하는 소용량 자급형 해수담수화장치의 설계 자료와 성능실험 결과를 제시하였다. 제안된 담수기는 조밀간격 수직형 평행평판이 복수단으로 구성된 다중효용방식으로서, 해수가 흐르는 윅(wick)이 부착되어 있다. 복수단의 평판에서 증발과 응축과정이 반복적으로 일어나므로 열에너지를 재이용하게 되어 담수생산량을 증가시킨다. 제안된 담수기의 성능실험 결과 5.6 kVA 발전기의 폐열이 담수화의 증발열원으로 사용될 수 있음을 알 수 있었고, 1중 효용만으로 최소 6.7 kg/day의 담수를 생산할 수 있었다. 이 결과는 10중 효용의 경우 약 35~44 kg/day를 기대할 수 있는 양으로서, 동일 전열면적의 태양열 증류기의 일일 최대 생산량보다 약 16~4배 많은 것이다.

• 대한기계학회논문집B
• /
• 제37권12호
• /
• pp.1061-1068
• /
• 2013

본 연구에서는 선행연구에서 제시된 태양열원식 해수 담수기 모델에 디젤 발전기 폐열을 적용하였을 때 설계변수에 따른 담수량을 수치해석을 통하여 예측하고, 최적설계를 위한 자료를 제시하고자 하였다. 선행연구를 기초로 수학적 모델을 설정하였고, 폐열 회수관으로부터의 열교환량을 고려하였다. 해석의 결과를 선행연구의 결과와 비교 분석하여 해석의 타당성을 확보하였고, 타당성이 검증된 해석모델을 적용하여 여러 가지 설계 변수에 따른 담수량을 예측하였다. 결과적으로 선행연구와 전반적으로 일치한 해석결과를 확인하였고, 디젤 발전기 폐열을 적용하였을 때 담수량 향상정도를 확인하였다. 또한 수치해석을 통하여 최적의 효용단 수, 유리덮개 경사각 등을 결정하였다.