• 설비공학논문집
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• 제19권8호
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• pp.563-568
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• 2007

The air-side particulate fouling in the heat exchangers of HVAC applications degrades the performances of cooling capacity, pressure drop across a heat exchanger, and indoor air quality. Indoor and outdoor air contaminants foul heat exchangers. An empirical modeling equation has been derived from the experimental results using accelerated tests and it showed good predictions of the fouling characteristics of the slitted finned tube heat exchangers. However the modeling equation predicts only the fouling characteristics of new heat exchangers and it can not predicts fouling characteristics obtained from actual field data which contains the effect of hydrophilicity deterioration. Therefore an modified modeling equation is proposed and it shows good predictions of the actual fouling characteristics of finned-tube heat exchangers.

• Korean Chemical Engineering Research
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• 제44권3호
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• pp.270-276
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• 2006

본 연구에서는 전도열손실과 증발에 의한 열손실을 바탕으로 욕조의 자유표면에서 일어나는 온수의 열손실을 해석하고자 한다. 연구결과 욕조의 성능을 평가할 수 있는 식을 열전달 기본식으로 부터 관계식을 도출하였으며 이 식은 매우 시성적이며 정량적이었다. 특히 욕조 내 온수의 냉각은 증발에 의한 열손실이 지배적이었다. 또한, 온수의 온도 냉각 속도는 온수의 온도에는 크게 영향을 받지 않으나 욕실의 습도에 따라 크게 영향을 받는 것으로 확인되었다. 그러므로 욕조의 온도는 $41{\sim}45^{\circ}C$를 유지하며 욕실의 습도가 95％를 유지하는 것이 가장 효과적이라 판단된다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1119-1122
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• 2009

The use of cooling towers in the air conditioning systems of buildings is increasing. In closed wet cooling towers, the heat transfer between the air and surface tubes can be composed of the sensible heat transfer and the latent heat transfer. The latent heat transfer is affected by the air and spray water. This study provides a designing methodology of heat exchanger for closed wet cooling tower. The correlation equation was derived to interpret the mass transfer coefficient based on the analogy of the heat and mass transfer and the experimental results. The results from this correlation equation showed fairly good agreement with experimental data.

• 설비공학논문집
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• 제17권3호
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• pp.262-267
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• 2005

The air-side particulate fouling in the heat exchangers of HVAC applications degrades the performance of cooling capacity, pressure drop across a heat exchanger, and indoor air quality. Indoor and outdoor air contaminants foul heat exchangers. The purpose of this study is to investigate and to model the air-side particulate fouling characteristics of the heat exchangers using accelerated particle loading system. The main variables of the modeling equation are face velocity and dust concentration. The modeling equation shows good agreements with the experimental results at the face velocity of 0.5, 1.0, 1.5 m/s and the dust concentration of 1.28 and $3.84\;g/m^3$. It will be very useful to predict fouling characteristics such as variations of pressure drop and heat transfer capacity in finned-tube heat exchangers of air conditioners.

• 한국대기환경학회지
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• 제16권4호
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• pp.339-350
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• 2000

The three-dimensional new corrdinate system over a single hill double hills and complex terrain with a single hill and a rectangular obstacle was generated using a body-fitted coordinate system. Control of the coordinate line distribution in the field was executed by generalizing the elliptic generating system to Poisson equation. ▽2ξ=P. The new coordinate system was well fitted to the surface boundary of single hill and double hills. But in the case of complex terrain with hill and rectangular obstacle there was smoothing tendency around the rectangular obstacle. In order to show the validity of the body-fitted coordinate system the heat diffusion equation was transformed and the temperature distribution was calculated over the various terrain. The results showed the temperature distribution was very symmetrical and stable around hills and obstacle. As a result the couple of a body-fitted coordinate system and the heat diffusion equation were executed successfully. Wind field over complex terrain with hill and rectangular obstacle which represent urban area was simulated stably in body-fitted coordinate system. The qualitative result show the enhancement of wind speed at the upwind direction of a hill and a rectangular obstacle and the recirculation zone at the downwind direction.

• 공업화학
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• 제8권4호
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• pp.667-672
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• 1997

고용량 Nickel/Metal hybride 전지의 온도 거동을 3차원 유한요소법 software인 NISA를 사용하여 해석하였다. 전지 내부의 열전도에는 미분형 에너지 수지식을, 외부 대기와의 접촉면은 대류 열전달 방식을 사용하였다. 전지 온도에 영향을 미치는 요소인 열발생량과 대류 열전달계수에 대한 실험을 행하였고, 이 결과로부터 일반식을 도출하였다. 금속 재질의 cooling fin을 사용하므로써 급속한 충전이나 방전시 야기될 수 있는 온도 상승을 상당 부분 방지할 수 있었다. 전지 외벽에 열전도도가 낮고 얇은 절연물질을 부착하여도 최고온도의 상승에 미치는 영향은 미미하였다.

• Journal of applied mathematics & informatics
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• 제7권3호
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• pp.787-800
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• 2000

In this paper we consider an optimal control system described by n-dimensional heat equation with a thermal source. Thus problem is to find an optimal control which puts the system in a finite time T, into a stationary regime and to minimize a general objective function. Here we assume there is no constraints on control. This problem is reduced to a moment problem. We modify the moment problem into one consisting of the minimization of a positive linear functional over a set of Radon measures and we show that there is an optimal measure corresponding to the optimal control. The above optimal measure approximated by a finite combination of atomic measures. This construction gives rise to a finite dimensional linear programming problem, where its solution can be used to determine the optimal combination of atomic measures. Then by using the solution of the above linear programming problem we find a piecewise-constant optimal control function which is an approximate control for the original optimal control problem. Finally we obtain piecewise-constant optimal control for two examples of heat equations with a thermal source in one-dimensional.

• Journal of Advanced Marine Engineering and Technology
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• 제23권5호
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• pp.687-694
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• 1999

This study was conducted to develop new drying process for automatic control and marine engi-neering system. Air-water tests were carried out to investigate dryer performance. The dispersed flow in he dryer test apparatuses was also simulated by using a numerical code which solves the Dittus-Boelter equation for continuous liquid phase and the Reynolds equation of droplet motion for continuous liquid phase and the Reynolds equation of droplet motion for dispersed phase to predict droplet removal efficiency. Proper conditions for dehumidification were optimized by response ambient conditions. When the selected indexes were constrained in the range of 85-98% moisture content above $15^{\circ}$ and more than mass flow rates of moist air 750kg/h. The numerical results were compared with the experimental data pertaining to the removal effi-ciency at chamber stage and overall pressure drop along concentric tubes Good agreement was obtained as for the efficiency while relatively poor agreement was obtained for the relative humidity. The results also showed that the efficiency depended strongly on the relative humidity at the inlet condition which indicated the importance of estimating the heat exchanger length. Effects of some design parameters in both removal efficiency and breakthrough onset condition are discussed.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 C
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• pp.2315-2317
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• 2005

In this paper, an iterative method to model the electromagnetic heating of electrically large lossy dielectrics is presented. Frequency domain finite element (FEM) solutions of the wave equation are determined for the lossy inhomogeneous dielectric as the material properties are change with temperature and time. The power absorbed from microwave losses is applied to a finite element time domain (FETD) calculation of the heat diffusion equation. Time steps appropriate for updating the piecewise material properties in the wave equation and the time stepping of the heat equation are presented. The effects of preheating and source frequency are investigated.

• 에너지공학
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• 제15권4호
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• pp.250-255
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• 2006

원자력 분야에서 중성자 수송계산을 위해 개발되어 널리 사용되는 방향차분법을 시간 종속 복사 열전달식의 해를 구하는데 적용하였다. 광자의 방향별 밀도를 자체수반형 2계 편미분방정식으로 나타내어 해의 안정성을 높였고 매질의 온도방정식의 비선형성은 다단계 선형화법을 사용하여 근사하였다. 본 연구에서 개발된 해법을 전형적인 Marshak wave 문제에 적용하였고 계산 결과를 기존의 Monte Carlo의 계산결과와 비교하여 그 우월성을 보였다.