• Nuclear Engineering and Technology
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• 제53권2호
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• pp.677-687
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• 2021

The tendency to renewables is one of the consequences of changing attitudes towards energy issues. As a result, solar energy, which is the leader among renewable energies based on availability and potential, plays a crucial role in full filing global needs. Significant problems with the solar thermal power plants (STPP) are the operation time, which is limited by daylight and is approximately half of the power plants with fossil fuels, and the capital cost. Exergy analysis survey of STPP hybrid with PCM storage carried out using Engineering Equation Solver (EES) program with genetic algorithm (GA) for three different scenarios, based on eight decision variables, which led us to decrease final product cost (electricity) in optimized scenario up to 30% compare to base case scenario from 28.99 $/kWh to 20.27 $/kWh for the case study. Also, in the optimal third scenario of this plant, the inner carbon dioxide gas cycle produces 1200 kW power with a thermal efficiency of 59% and also 1000 m3/h water with an exergy efficiency of 23.4% and 79.70 kg/h with an overall exergy efficiency of 34% is produced in the tetrageneration plant.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2009년도 하계학술발표대회 논문집
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• pp.1288-1293
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• 2009

The TES (Thermal Energy Storage) cooling system utilizing cheaper off-peak electricity has been applied just for building air-conditioning currently and causes limitation of usage rate and inefficiency of national resources utilization. In this regard, more says the necessity to apply TES system in industrial cooling system which is longer using period and wider usage. In this study, we will approve the technical and economical improvement in efficiency of industrial cooling system applied TES system by utilizing cheaper off-peak electricity and it will attribute the promotion of TES system and stabilization of supply and demand of electric power by proving the necessity to develop more efficient industrial cooling system by combining TES system.

• 설비공학논문집
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• 제27권4호
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• pp.213-219
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• 2015

A thermal storage tank with internal heat exchange coils is commonly used in solar thermal systems with a collector area below $100m^2$. The coils are installed in the lower part of the tank because the temperature of the upper part of the tank can drop if the outlet temperature of the collector becomes lower than the upper temperature of the tank, which is a kind of temperature reversal. As an alternative to the well-mixed storage tank with lower coil only, we have proposed a tank with lower and upper coils and have achieved superior thermal stratification in the tank, which results in increased collector efficiency and solar fraction. But, the phenomenon of temperature reversal was often observed in the tank when the load or solar radiation changed rapidly. In the present work, revised control was successfully applied, i.e., to heat only the lower coil using a three way valve if temperature reversal occurs and to operate the collector at a low flow rate when the quality of solar radiation is not good.

• Advances in Energy Research
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• 제4권1호
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• pp.29-45
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• 2016

There has been a growing interest in the recent time for the development of solar power tower plants, which are mainly used for utility scale power generation. Combined heat and power (CHP) is an efficient and clean approach to generate electric power and useful thermal energy from a single heat source. The waste heat from the topping Brayton cycle is utilized in the bottoming HRSG cycle for driving steam turbine and also to produce process steam so that efficiency of the cycle is increased. A thermal storage system is likely to add greater reliability to such plants, providing power even during non-peak sunshine hours. This paper presents a conceptual configuration of a solar power tower combined heat and power plant with a topping air Brayton cycle. A simple downstream Rankine cycle with a heat recovery steam generator (HRSG) and a process heater have been considered for integration with the solar Brayton cycle. The conventional GT combustion chamber is replaced with a solar receiver. The combined cycle has been analyzed using energy as well as exergy methods for a range of pressure ratio across the GT block. From the thermodynamic analysis, it is found that such an integrated system would give a maximum total power (2.37 MW) at a much lower pressure ratio (5) with an overall efficiency exceeding 27%. The solar receiver and heliostats are the main components responsible for exergy destruction. However, exergetic performance of the components is found to improve at higher pressure ratio of the GT block.

• 대한설비공학회지:설비저널
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• 제7권1호
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• pp.13-19
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• 1978

An experiment has been performed of find a temperature distribution of the circulating fluid in a packed bed thermal storage system when the inlet fluid temperature is constant. The thermal storage system is a specific-heat type in which the circulating fluid, hot air, exchanges heat directly with the heat storage materials, glass balls, in a heat storage bin. An empirical equation which includes two dimensionless variables $t^*\;and\;T_f^*$, is obtained. Also, heat storage efficiency and heat storage capacity are calculated from this equation, The heat transfer coefficient calculated by the suggested equation was compared with the value determined by the existing empirical equation.

• 한국수소및신에너지학회논문집
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• 제30권1호
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• pp.58-66
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• 2019

Static compound parabolic collectors (CPCs) have advantages such as ease for fabrication and lower cost compared with other concentrating collectors. In this study, thermal performance analysis of CPC employing heat storage tank was carried out. The clearness index and capacity of heat storage tank are taken as the main parameters for numerical simulation. The effects of the parameters on the hourly and daily system performances ncluding the useful energy, heat loss, and collector efficiency were numerically investigated. Results showed that the system has a potential for efficient recovery of solar thermal energy.

• 대한기계학회논문집 C: 기술과 교육
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• 제2권1호
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• pp.65-72
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• 2014

본 연구에서는 지역난방 공사에서 사용하고 있는 성층 축열조의 불가용 에너지를 줄이기 위해 단열층을 설계하였다. 단열층은 추가적인 장치 없이 고온수와 저온수의 밀도차이로 생기는 부력으로 운용된다. 축열조의 내부 온도분포를 모사할 수 있는 해석모델을 Matlab Simulink 를 이용하여 제작하고 해석 결과를 이용하여 단열층의 소재와 두께를 결정하였다. 또한 축열조의 축소실험을 통하여 단열층의 운용 가능성을 확인하였다. 실험 결과, 단열층이 축열 방열과정에서 고온수와 저온수의 혼합과 열전도로 인한 온도 경계층형성을 효과적으로 억제할 수 있다는 것을 확인하였다. 단열층을 설치한 축소실험에서는 단열층이 없는 축열조보다 약 1540 J 의 추가 가용에너지가 보존되었고 이를 실제 축열조에 적용할 경우 약 6%의 축열효율이 증가될 것으로 예상된다.

• 터널과지하공간
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• 제23권4호
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• pp.308-318
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• 2013

열저장소 내 열성층화는 에너지저장 시스템의 효율을 향상시키고 수요 발생시 더 많은 유효에너지를 공급하기 위해 필수적인 기술이다. 일반적으로 저장소의 종횡비(폭에 대한 높이의 비)와 크기에 따라 열성층도가 달라지는 것으로 알려져 있다. 본 논문은 열수 저장을 위한 암반공동의 종횡비와 저장용량이 저장공동 내 열성층화와 외부로의 열손실에 미치는 영향을 조사하는 데 연구 목적이 있다. 이를 위해 전산유체역학 코드인 FLUENT를 이용하여 암반공동의 종횡비와 저장용량에 따른 열전달 시뮬레이션을 수행하였다. 성층도 정량화 지수를 이용하여 시간경과에 따른 열성층화의 변화를 분석하였으며, 저장공동 외부로의 열손실을 평가하였다. 분석 결과, 종횡비가 증가함에 따라 공동 내 열성층화가 향상되는 경향을 보였으나, 종횡비 3-4 이상부터는 이러한 영향이 크지 않은 것으로 분석되었다. 저장용량이 작은 암반공동에 비해 용량이 큰 암반공동에서 상대적으로 긴 시간 동안 열성층화가 높게 유지되는 것으로 분석되었으나, 종횡비 증가에 따라 저장용량이 다른 공동들간의 성층화 차이가 줄어드는 경향을 나타냈다. 암반공동의 종횡비가 커질수록 공동의 표면적이 늘어나 종횡비의 증가에 따라 주변 암반으로의 열손실이 증가하는 경향을 보였으며, 단위 저장용량을 줄여 소규모 다중공동을 적용하는 경우, 총 저장용량이 동일한 단일공동에 비해 전체 열손실량이 증가하는 것으로 분석되었다.

• 설비공학논문집
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• 제28권1호
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• pp.15-20
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• 2016

Phase change materials (PCM) are able to store a large amount of latent heat, and can be applied to thermal energy storage systems. In a PCM, it takes a long time to store heat in the storage system because of the low thermal conductivity. In this study, a finned-tube-in-tank heat exchanger was applied to a PCM thermal energy storage system to increase heat transfer efficiency. The effects of geometric and operating parameters were investigated, and the results were compared with those of the tube-in-tank heat exchanger. The finned-tube-in-tank heat exchanger showed higher heat transfer effectiveness than the tube-in-tank heat exchanger. The heat exchange effectiveness of the storage tank was determined as a function of the average NTU.

• KIEAE Journal
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• 제9권5호
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• pp.39-46
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• 2009

Most Plastic Green Houses in Korea are made according the European weather condition, which lead to have very low solar energy efficiency. Moreover, the function of green houses, as well as the structure of them, has not changed for Korean weather condition. Therefore, the structure and function of them should adopt the regional weather condition in order to improve the energy efficiency. This paper investigates the current plastic green housesin Korea, and presents an alternative for improving the energy efficiency. The elements of green houses were investigated. When using a partial opaque insulation with a thermal storage body, the difference of indoor air temperature became 20C during daytime, and 5C during night, which will save massive fossil fuels.