• 플랜트 저널
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• 제14권1호
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• pp.42-46
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• 2018

The flow and heat transfer characteristics inside a solar chimney power plant system are analyzed in this article. 3-D model with the $k-{\varepsilon}$ turbulence closure was developed. In this model, to solve the radiative transfer equation the discrete ordinates radiation model was implemented, using a two-band radiation model. To simulate radiation effects from the sun's rays, the solar ray tracing algorithm was coupled to the calculation via a source term in the energy equation. Simulations were carried out for a system with the geometry parameters of the Manzanares power plant. Based on the numerical results, the velocity and temperature distributions were illustrated and the results were validated by comparing with experimental data of the Manzanares prototype power plant. Moreover, temperature profile of the ground surface of the system was illustrated.

• 한국지열·수열에너지학회논문집
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• 제12권1호
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• pp.7-16
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• 2016

This paper presents the measurement and analysis results for the cooling performance of ground-coupled heat pump (GCHP) system using a cooling tower as a supplemental heat rejector. In order to demonstrate the performance of the hybrid approach, we installed the monitoring equipments including sensors for measuring temperature and power consumption, and measured operation parameters from May 1 to October 30, 2014. The results showed that the entering source temperature of brine returning from the ground heat exchanger was in a range of design target temperature. Leaving load temperatures to building showed an average value of $11.4^{\circ}C$ for cooling season. From the analysis, the daily performance factor (PF) of geothermal heat pumps ranged from 4.4 to 5.2, while the daily PF of hybrid GCHP system varied from 3.0 to 4.0 over the entire cooling season.

• Journal of Mechanical Science and Technology
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• 제14권3호
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• pp.350-357
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• 2000

Experiments were performed by using PF-5060 and water to investigate the influence of an aspect ratio of a horizontal rectangular channel on the cooling characteristics from an in-line $6{\times}1$ array of discrete heat sources which were flush mounted on the top wall of the channel. The experimental parameters were aspect ratio of rectangular channel, heat flux of simulated VLSI chip, and channel Reynolds number. The chip surface temperatures decreased with the aspect ratio at the first and sixth rows, and decreased more rapidly at a high heat flux than at a low heat flux. The measured friction factors at each aspect ratio for both water and PF-5060 gave a good agreement with the values predicted by the modified Blasius equation within ${\pm}7%$. The Nusselt number increased as the aspect ratio decreased, but the increasing rate of Nusselt number reduced as the aspect ratio decreased. A 5:1 rectangular channel yields the most efficient cooling performance when the heat transfer and pressure drop in the test section were considered simultaneously.

• 한국정밀공학회지
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• 제22권8호
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• pp.17-26
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• 2005

Dissimilar-metal welds(DHWs) are used widely in various industrial applications due to the pratical importance from the technical and economic aspect. However, DMWs have several fabricative and metallurgical drawbacks that can often lead to in-service failures. For example, the most pronounced fabrication faults are hot cracks. Recently, DMWs have used the various of heat source to decrease such as faults. In this paper, the weldability on dissimilar metal welds of Austenite stainless steel and Low carbon steel using a continuous wave Nd:YAG laser was experimentally investigated. Experiments were conducted to determine effects of welding parameters, on eliminating or reducing the extent welding zone formation at dissimilar metal welds and to optimize those parameters that have the most influence parameters such as focus length, power, beam speed, shielding gas, and wave length of laser.

• 한국산학기술학회논문지
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• 제15권9호
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• pp.5425-5433
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• 2014

본 연구에서는 발전용량이 20kW인 폐열회수용 칼리나 발전시스템의 설계 자료를 확보하기 위하여 EES프로그램을 사용하여 해석하였으며, 암모니아농도, 증기압력, 열원온도 및 냉각수온도가 발전효율에 미치는 영향을 분석하였다. 연구결과에서, 암모니아 농도는 낮을수록, 증기압력은 높을수록 발전효율은 증가하였다. 하지만 암모니아 농도가 너무 낮으면 발전효율이 감소하는 영역이 있었다. 터빈입구의 증기압력이 높아지면 발전효율도 높아지며, 암모니아 농도가 높을수록 증기압력의 영향을 더 많이 받는 것으로 나타났다. 최대의 발전효율을 얻기 위한 암모니아 농도, 증기압력, 열원온도 및 냉각수온도 조건이 존재한다는 것을 알 수 있었다. 20kW의 발전시스템에서는 증기압력은 25bar, 열원온도는 $160^{\circ}C$, 냉각수온도가 $10^{\circ}C$일때 암모니아 농도가 0.4에서 발전효율은 최고로 15%까지 가능하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2008년도 추계학술대회A
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• pp.690-694
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• 2008

In this presentation, we study numerically an optimization problem of a fire fighting robot cooling system. The governing equation for the system is the unsteady heat equation with source term. We use a multigrid method for numerical solutions in three-dimensional space. We investigated the effects of various parameters and the results will be presented.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 추계학술대회
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• pp.420-423
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• 2003

A low temperature difference model Stirling engine is a small Stirling engine running with several degree of temperature difference without power output. In this study, the design parameters to give maximum power are discussed. As results, the phase angle is about 100 degree, and compression ratio is 1.5% of the ratio of heat source temperatures at maximum power condition.

• 태양에너지
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• 제18권3호
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• pp.71-80
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• 1998

In thermal energy storage system, energy collected from many types of heat source is stored in a storage tank and then supply to load for demand. Lately, practical use of thermal energy storage system and attention to essential use of energy have been increased. From this point of view, especially, a study about the energy extraction process from a storage tank is necessary. So in this study, useful rate of hot water and hot water extraction efficiency was analysed respect to dynamic and geometric parameters dominating the hot water extraction process.

• 한국수소및신에너지학회논문집
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• 제21권6호
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• pp.570-579
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• 2010

Since the temperature of waste heat source is relatively low, it is difficult to maintain high level of efficiency in power generation when the waste heat recovery is employed in the system. In an effort to improve the thermal efficiency and power output, use of ammonia-water mixture as a working fluid in the power cycle becomes a viable option. In this work, the performance of ammonia-water mixture based Rankine cycle is thoroughly investigated in order to maximize the power generation from the low temperature waste heat. In analyzing the power cycle, several key system parameters such as mass fraction of ammonia in the mixture and turbine inlet pressure are studied to examine their effects on the system performance. The results of the cycle analysis find a substantial increase both in power output and thermal efficiency if the fraction of ammonia increases in the working fluid.

• 대한기계학회논문집B
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• 제31권7호
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• pp.581-587
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• 2007

At present time, LNG demand of the world is increasing and the piping line for NG transportation has been already installed in Korea. The air fm vaporizer is, however, required because of the transportation for remotely local areas. This paper numerically investigates on the heat transfer characteristics of relevant geometric variations of air-fin vaporizer which is heated by air not by sea water. This vaporizer must be designed in consideration of both efficiency and economics because air is relatively a little heat source. In this study, the pipe and the longitudinal fins are fundamental geometric considerations. Main parameters of geometry are the number, the thickness, and the length of the fins. Finally, the results of heat transfer effects are investigated with the characteristics of each parameter variation.