• Journal of the Korean Solar Energy Society
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• v.34 no.4
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• pp.51-56
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• 2014

In this paper, OTEC(Ocean Thermal Energy Conversion) system with vapor-vapor ejector is newly proposed. And 6 wet refrigerants are applied into the proposed OTEC system for performance comparison. The results of comparison performance are as follows. In the view of system efficiency, R32/R744(90:10) has the highest efficiency among the 6 refrigerants. In case of evaporation capacity, pump work and mass flow rate of working fluid, R744, R717 and R717 is lowest value, respectively. As this results, the vapor-vapor ejector is able to increase the efficiency of system. And It is necessary to select the optimized working fluid considering environmental and economic factors.

• Solar Energy
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• v.17 no.4
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• pp.23-33
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• 1997

In this paper, performance of various working fluids is evaluated for the closed Ocean Thermal Energy Conversion(OTEC) power plant operating on Rankine cycle. The evaporator and condenser are modeled via UA and LMTD method while turbine and pump are modeled by specifying isentropic efficiencies. R22, Propane, Propylene, R134a, R125, R143a, R32, R410A and Ammonia are used as working fluids. Results show that newly developed fluids such as R410A and R32 that do not cause stratospheric ozone layer depletion perform as well as R22 and ammonia. The superheat at the evaporator exit and subcooling at the condenser exit do not affect the performance of the simple OTEC power cycle. Turbine efficiency and heat exchanger size influence greatly the performance of the Rankine cycle. Finally, it was shown that closed OTEC power plants can practically generate electricity when the difference in warm and cold sea water inlet temperatures is greater than $20^{\circ}C$.

• Proceedings of the KSME Conference
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• 2000.11b
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• pp.234-240
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• 2000

The Energy is the basis for almost all industrial activities and domestic needs. But recently there are increasing concerns internationally over environmental problems and consequent climate changes caused by the excessive use of fossil fuels. Furthermore the price of crude oil is increasing steadily with unstable supplies. In order to solve these national energy problems, the utilization of Ocean Energy is introduced as one of the best alternative technologies for the future. OTEC Power Plant has been installed at the West Inchon Power Plant Site. Temperature differences of $20{\sim}25^{\circ}C$ have been utilized for plant operations, where R22 is used as a working fluid. The system is composed of low pressure turbine, plate type heat exchanger, and pumps. In the present investigation the experimental results, such as gross power, net power and objective function, are analysed when temperature differences change from the reference design point.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.1
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• pp.46-52
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• 2011

A study on the improvement for cycle efficiency of closed-type ocean thermal energy conversion (OTEC) was studied to obtain the basic data for the optimal design of cycle. For that, OTEC cycle with a generator, a reheater and a multi-turbine was simulated and analyzed. The basic thermodynamic model for OTEC is Rankine cycle and the surface seawater of $26^{\circ}C$ and deep seawater of $5^{\circ}C$ were used for the heat source of evaporator and condenser, respectively. Ammonia is used as the working fluid. The cycle efficiency increased when generator is added with 0.9 generator effectiveness. When the reheater and multi-turbine are applied in the basic cycle, the cycle efficiency showed 3.14% and the capacity of heat exchanger decreased for same total cycle power. For the OTEC cycle with the generator, the reheater and the multi-turbine showed the highest cycle efficiency and increased the efficiency by more than 6.5% comparing with the basic OTEC cycle.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.9
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• pp.557-567
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• 2016

In this study, the optimal design of heat exchangers, including the evaporator and condenser of a solar-heating ocean thermal energy conversion (SH-OTEC), is investigated. The power output of the SH-OTEC is assumed to be 100 kW, and the SH-OTEC uses the working fluid of R134a and high-performance commercial tubes. The surface heat transfer area and the pressure drop were strongly dependent on the number of tubes, as well as the number of tube passes. To solve the reciprocal tendency between the heat transfer area and pressure drop with respect to the number of tubes, as well as the number of tube passes, a genetic algorithm (GA) with two objective functions of the heat transfer area (the capital cost) and operating cost (pressure drop) was used. Optimal results delineated the feasible regions of heat transfer area and operating cost with respect to the pertinent number of tubes and tube passes. Pareto fronts of the evaporator and condenser obtained from multi-objective GA provides designers or investors with a wide range of optimal solutions so that they can select projects suitable for their financial resources. In addition, the surface heat transfer area of the condenser took up a much higher percentage of the total heat transfer area of the SH-OTEC than that of the evaporator.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.5
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• pp.580-585
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• 2012

In this paper, the cycle performance analysis for condensation and evaporation capacity, total work and efficiency of ocean thermal energy conversion power system using R744 ($CO_2$) is presented to offer the basic design data for the operating parameters of this system. The operating parameters considered in this study include superheating and subcooling degree, evaporation and condensation temperature, pump and turbine efficiency. The main results were summarized as follows : The evaporation capacity of R744 increases with superheating and subcooling degree, but decreases with the increasing condensation temperature. The total work increases with superheating and subcooling degree of R744, but decreases with the increasing evaporating temperature. And, the efficiency increases with subcooling and superheating degree, but decreases with the increasing condensation temperature. Therefore, superheating and subcooling degree, evaporation and condensation temperature and pump and turbine efficiency of R744 OTEC power system have an effect on the evaporation and condensation capacity, total work and efficiency of this system. With a thorough grasp of these effect, it is necessary to design the OTEC power cycle using R744.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.9
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• pp.1101-1105
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• 2014

Ocean Thermal Energy Conversion(OTEC) which uses the temperature difference between warm surface sea-water and cold deep sea-water to produce electric power is the promising technology. OTEC is able to be utilized as the $CO_2$ reducing technology by using the consistent temperature differential, while the system efficiency is very low. Thus, the design and development of a efficient turbine is essential to improve the system efficiency for OTEC. In this study, a 100kW-class radial inflow turbine using R32 was designed for OTEC and this turbine's performance was estimated by analysis of CFD. According as the simulation results, turbine's geometry was corrected. The radial inflow turbine satisfying the requirements is designed by the repeated attempts.

• 한국신재생에너지학회:학술대회논문집
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• 2010.11a
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• pp.170-170
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• 2010

The energy conversion from the temperature difference between hot and cold source like ocean thermal energy conversion (OTEC), requires a long and large-diameter pipe (about 1000 to 10,000 meters long) to reach the deep water. The pipe diameter ranges from 2.8 meter for proposed early test systems, to 5 meter for large, commercial power generation systems. The pipe must be designed to resist collapsing pressures produced by water temperature and density differences, and the reduced pressure required to induce flow up the pipe. Other design considerations include the external-drag effect on the pipe due to ocean currents, and the wave-induced motions of the platform to which the pipe is attached. Various approaches to the pipe construction have been proposed, including aluminum, steel, concrete, and fiberglass. More recently, a flexible pipe construction involving the use of fiberglass reinforced plastic has been proposed. This report presents the results of a scaled fixed cold water pipe (CWP) model test program performed by EES(Engineering Equation Solver) to demonstrate the feasibility of this pipe approach.

• Solar Energy
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• v.19 no.2
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• pp.37-44
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• 1999

Experimental investigation has been carried out to determine drag reducing effects of polymer additives for a plate type heat exchanger(evaporator or condenser) in OTEC power plant applications, where the pressure drop in the heat exchangers takes up $70{\sim}80%$ of the total pumping power in the existing system. The rate of drag reduction was investigated with various polymer concentrations and mass flow rates. Experiments were undertaken for a test section in Alfa-Laval plate heat exchanger utilizing Poly Ethylene Oxide(Mw $5{\times}10^6$) as polymer additives. Concentrations of polymer additives were 5, 10, 20, 30, 40, 50, 100, 200, 400 wppm at $25^{\circ}C$ and mass flow rates were 0.6kg/s, 0.7kg/s, 0.8kg/s and 0.9kg/s in normal operating ranges for a 15kW Alfa-Laval plate heat exchanger. The maximum effects of drag reductions were found at approximately 0.7kg/s of mass flow rate. The results show that there exists the optimum mass flow rate for the plate heat exchanger to obtain maximum drag reductions. Drag reduction of 20% means considerable savings in pumping power for a large size of OTEC plant.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.1
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• pp.22-28
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• 2015

The design on a riser in 1MW OTEC system is performed. The minimum diameter of the riser is decided depending on intake quantity of deep-sea water to supply an OTEC cycle. An applicable pipe material is selected from analyzing the properties of commercial pipes. The selected HDPE pipe with the low density and strength is reinforced with a lumped block attached at the end of and wire ropes along the riser. A lumped block, connected to a floating structure by wire ropes, with 25% and 50% weight of a GFRP riser is designed to be attached the end of a riser. The structural safety of the HDPE riser with wire rope supporting axial loads induced by a lumped block is analyzed under the harsh ocean environmental condition near Hawaii ocean with the numerical method. The final dimension of the riser and accessories is determined considering the economic point of view. The designed riser will be applicable to the construction of the 1 MW OTEC pilot plant.