• 설비공학논문집
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• 제23권7호
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• pp.505-512
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• 2011

Recently, many researchers have analyzed the performance of the transcritical $CO_2$ refrigeration cycle in order to identify opportunities to improve the system energy efficiency. The reduction of the expansion process losses is one of the key issues to improve the efficiency of the transcritical $CO_2$ refrigeration cycle. In this study, the analytical study on the performance characteristics of $CO_2$ cycle with an ejector carried out with a variation of outdoor temperature, gascooler inlet air velocity, evaporator inlet air velocity, and evaporator inlet air temperature. As a result, the system performance could be improved over 85% by using an ejector for various operating condition because of the reduction of compressor work. Moreover, the cooling capacity increased about 18% for variable outdoor condition. Therefore, the high performance of an ejector system could be maintained for wide operating conditions and system reliability could be improved compared to that of a basic system.

• 설비공학논문집
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• 제21권1호
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• pp.55-62
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• 2009

Relatively low cycle performance of a conventional $CO_2$ system is partly due to significant increase in friction loss in the expansion process, since the pressure drop across the expansion device is considerably large compared to a conventional refrigeration cycle. To recover friction loss and increase refrigeration effect by providing isentropic expansion, a rotary vane type expander has been designed. Performance of the designed expander has been investigated by numerical simulation. With the pressure condition of 9 MPa/4.5 MPa and inlet temperature of $35^{\circ}C$, volumetric, isentropic, and mechanical efficiencies of the expander are calculated to be 58.1%, 101.1%, and 78.8%, respectively, resulting in total expander efficiency of 46.3%. With this expander, COP of a $CO_2$ refrigeration cycle is estimated to be improved by about 14%.

• 한국유체기계학회 논문집
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• 제18권1호
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• pp.37-43
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• 2015

A Beta-type Stirling engine is developed and tested on the operation stability and cycle performance. The flow rate for cooling water ranges from 300 to 1500 ml/min, while the temperature of heat source changes from 300 to $500^{\circ}C$. The internal pressure, working temperatures, and operation speed are measured and the engine performance is estimated from them. In the experiment, the rise in the temperature of heat source reduces internal pressure but increases operation speed, and overall, enhances the power output. The faster coolant flow rate contributes to the high temperature limit for stable operation, the cycle efficiency due to the alleviated thermal expansion of power piston, and the heat input to the engine, respectively. The experimental Stirling engine showed the maximum power output of 12.1 W and the cycle efficiency of 3.0 % when the cooling flow is 900 ml/min and the heat source temperature is $500^{\circ}C$.

• 동력기계공학회지
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• 제18권6호
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• pp.120-125
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• 2014

In this paper, suitable working fluid of 1MW Organic Rankine Cycle(ORC) with liquid-vapor ejector using effluent from power plant is selected. The results of comparison performance of 5 refrigerants are as follows; R600a, R134a, R1270, R236fa, R235fa. The operating parameters considered in this study include the condensation capacity evaporation capacity and efficiency. As a result of comparison of basic ORC system and with liquid-vapor ejector, with ORC system presents the higher system efficiency since the ejector makes the turbine outlet pressure lower than condensation pressure through its pressure recovery. Also, this ejector ORC system is advantageous in miniaturizing the size of components owing to decrease of evaporation capacity and condensation capacity.

• 한국구조물진단유지관리공학회 논문집
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• 제11권5호
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• pp.160-170
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• 2007

본 연구는 교량의 경제성 평가를 통해 교량 가설시 유용한 정보를 제공하기 위해, RC Slab교를 대상으로 유지관리수준에 따른 교량의 LCC를 예측하여 절감비용을 예측하고자 하였다. 본 연구의 수행 결과를 정리하면 다음과 같다. (1) 사례교량 LCC 분석 모델을 제안하였다. (2) 교량의 유지관리수준을 현행과 필요로 구분하고, 분석기간은 80년, 실질할인율은 4.5%로 가정하여 사례대상 교량에 대한 유지관리수준별 LCC를 예측하였다. (3) 사례교량의 LCC 예측결과를 통하여 절감비용을 예측하고 경제적인 절감효과를 파악하였다.

• 신재생에너지
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• 제20권3호
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• pp.12-19
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• 2024

This study uses exergy analysis to evaluate the fuel-saving potential of a waste heat recovery unit (WHRU) integrated with an Organic Rankine Cycle (ORC) system for marine applications. Data from the training ship HANBADA of the Korea Maritime University and the general cargo ship BBC CAMPANA, including their operational routes and main engine loads, were used in this study. Simulations indicated that the WHRU system could save approximately 27.5 metric tons of fuel per voyage, equivalent to approximately 2.1% of the total fuel consumption. The WHRU system demonstrated a higher efficiency during long-distance voyages, significantly enhancing fuel savings. In addition, higher engine loads increased the exhaust gas thermal energy, thereby substantially improving the WHRU output. This study emphasizes the importance of evaluating the applicability of the ORC system for marine vessels by closely examining their operational patterns, navigation duration, and main engine load variability.

• Biotechnology and Bioprocess Engineering:BBE
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• 제8권6호
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• pp.349-353
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• 2003

The physiological characteristics of cultures of very high cell mass (e.g. 10g cell mass/L), termed“ultrahigh cell density cultures”is reviewed. A close relationship was found between the length of the optical path (OP) in flat-plate reactors and the optimal cell density of the culture as well as its areal (g m$\^$-2/ day$\^$-1/) productivity. Cell-growth inhibition (GI) unfolds as culture density surpasses a certain threshold. If it is constantly relieved, a 1.0cm OP reactor could produce ca. 50% more than reactors with longer OP, e.g. 5 or 10cm. This unique effect, discovered by Hu et al. [3], is explained in terms of the relationships between the frequency of the light-dark cycle (L-D cycle), cells undergo in their travel between the light and dark volumes in the reactor, and the turnover time of the photosynthetic center (PC). In long OP reactors (5cm and above) the L-D cycle time may be orders of magnitude longer than the PC turnover time, resulting in a light regime in which the cells are exposed along the L-D cycle, to long, wasteful dark periods. In contrast, in reactors with an OP of ca. 1.0 cm, the L-D cycle frequency approaches the PC turnover time resulting in a significant reduction of the wasteful dark exposure time, thereby inducing a surge in photosynthetic efficiency. Presently, the major difficulty in mass cultivation of ultrahigh-density culture (UHDC) concerns cell growth inhibition in the culture, the exact nature of which is awaiting detailed investigation.

• 대한기계학회논문집B
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• 제26권9호
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• pp.1241-1248
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• 2002

Performance extension of the absorption refrigerator with LiBr solution is often faced to operate very close to the crystallization limit. Especially in the development of an air-cooled cycle, the crystallization of working solution in the system is a very difficult problem to overcome. This paper describes the cycle of hot water driven absorption system using a new working absorption solution instead of LiBr solution to improve the efficiency. In this study, we found out the characteristics of new working absorption solution through the cycle simulation and compared LiBr solution to evaluate. The effect of cooling water temperature, weak solution flow rate, hot water temperature and hot water flow rate were also examined. The COP is increased 22% higher in the case of LiBr＋Li1＋LiC1＋LiNO$_3$＋$H_2O$, 2% LiBr＋HO(CH$_2$)$_3$OH＋$H_2O$ than that of LiBr solution for the same operation condition.

• 신재생에너지
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• 제10권4호
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• pp.36-46
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• 2014

Low-grade heats are wasted even though an amount of their energy is huge. In the small and medium industrial complex sites, large amount of low-grade thermal energy generated during the manufacturing process is wasted if it is not used directly for building heating or air-conditioning. In order to utilize this waste thermal energy more efficiently, organic Rankine cycle (ORC) was adopted. The range of operating temperature of ORC was set to $60^{\circ}C$ from $30^{\circ}C$ applicable low-temperature waste heat. A study was conducted to select an appropriate organic working fluid based on these operating conditions. More than 60 working fluids were screened. Eleven working fluids were selected based on the requirements as working fluid for ORC such as environmentally friendly, safety, and good operation on the expander. Finally, six working fluids were selected by considering the operating temperature ranges. Then, a cycle analysis was conducted with these six working fluids. As a results, R-245fa and R-134a appeared as appropriate working fluids for ORC operating at low-temperature condition based on the system efficiency and the turbine output power.

• 한국수소및신에너지학회논문집
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• 제24권5호
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• pp.461-466
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• 2013

In this research, the diesel cycle was thermodynamically interpreted to evaluate the possibility of high efficiency by converting diesel engine to the atkinson cycle, and general cycle features were analyzed after comparing these two cycles. That an experimental single cylinder and a long stroke diesel-atkinson engine, of which S/B ratio was more than 3, were manufactured. After evaluating the engine through basic experiments, a diesel engine was converted into the atkinson cycle by constituent VCR (variable compression ratio) device and VVT (variable valve timing) system. The experimental method was to observe compression work reduction effects due to low compression effects from delayed intake valve closing of the early stage atkinson engine. The result, the possibility of increasing compression ratio about each engine load was confirmation by constructing compensate expansion-compression ratio in accordance with the delayed intake valve close.