• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.4
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• pp.158-162
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• 2014

A series of numerical simulation has been carried out to study thermo-hydraulic characteristics of a primary surface type heat exchanger, which is designed for the evaporator and condenser of a geothermal ORC. Working fluid is geothermal water at hot side and R-245fa, which is a refrigerant designed for ORC, at cold side. Amplitude ratio of the channel and Reynolds number are considered as design parameters. Nusselt number is presented for the Reynolds number ranging from 50 to 150 and compared to analytic solutions. The result shows that higher amplitude ratio channel gives better heat transfer performance within the range of investigation.

• Proceedings of the KIPE Conference
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• 2015.07a
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• pp.377-378
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• 2015

본 논문에서는 유기랭킨 사이클(organic rankine cycle: ORC) 발전 시스템에서 터빈과 발전기의 속도를 추정하는 방법을 제안한다. 다이오드 정류기에 의해 왜곡된 발전기 3상 단자 전압은 PLL 기법을 이용한 속도추정의 성능을 저하시키므로, 정상분 추출과 맥동성분 제거를 위한 상태관측기와 주파수 가변형 PR 제어기를 동기좌표계 PLL 기법에 적용하여 발전기의 속도를 추정한다. 제안하는 터빈과 발전기의 속도추정 방법은 실험 결과를 통해 그 성능을 검증한다.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.1
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• pp.8-14
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• 2014

This research designed Waste Heat Recovery System(WHRS) generation system of 250kW whose working fluid is R-245fa and studied on cycle characteristics by superheater organization. It simulated two conditions; series connection and parallel connection between superheater and evaporator. In simulation of series connection of superheater and evaporator, output of 4.7% could be improved because of the increase of enthalpy by overheating of working fluid. When setting 250kW for target output, cycle flux could be reduced by 4.1%. When setting 250kW as a target output of cycle In parallel connection simulation of superheater and evaporator, cycle flux was reduced as flux of heat source fluid for superheater was increased. So, the maximum 7.9% of working fluid pump's electric power was reduced and there was no big change in cycle efficiency and net efficiency by flux ratio.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.23 no.12
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• pp.776-781
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• 2011

The rapid increases in global energy demand and global warming need renewable energy sources such as solar thermal energy, biomass energy and waste heat. A ORC-based micro-CHP system(< 10 kWe) is one of the effective means to use renewable energy and solve energy problems because of its compactness, flexibilities and lower cost compared to other systems. The most important core components of the ORC is the expander which has a strong effect on the cycle efficiency. In the range of power output from 1 to 10 kW, the scroll expander is a good choice due to its performance and reliability. In this study, we have carried out an experimental study on an ORC equipped with oil-free scroll expander working with refrigerant R134a. We have measured power output and thermal efficiencies of the ORC and analyzed correlation between volumetric efficiencies of the expander and thermal efficiencies of the ORC.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.281-285
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• 2008

Effective use of available energy sources is of general concern along with the issues of global warming and unstable oil price. As one of the effort to recover waste heat from industrial facilities effectively, researchers have interest in a technology called organic Rankine cycle(ORC), in which the working fluid is some organic liquid instead of water. Known to have poor efficiency already, this old technology is considered to give an innovative solution to utilizing low grade energy sources, by improving the efficiency. Nano fluidics, coatings and the use of additives are the examples of these efforts. In the present study, we present simulated performance of a horizontal tube type condenser geometry. N-hexanr and isopentane are compared to water vapor case under 1 atm and the inet cooling water temperature of $20^{\circ}C$. EES(Engineering Equations Solver) is used for the present work.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.3
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• pp.276-284
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• 2014

The purpose of this study is to establish the designing method of ORC(Organic Rankine Cycle) radial inflow turbines. RTDM(Radial Turbine Design Modeler) Ver.2.1 which is a preliminary design program of radial inflow turbines was developed to achieve this purpose. The 200kW-class radial inflow turbine for OTEC(Ocean Thermal Energy Conversion) was designed by using the RTDM Ver.2.1 and CFD(Computational Fluid Dynamics) simulation was performed to verify the accuracy of RTDM Ver.2.1. With the result of simulation, the accuracy of RTDM Ver.2.1 was almost 94.6% based on the designed total enthalpy drop of the radial inflow turbine. Strategy of adjusting the mass flow rate was adopted on this study to satisfy the requirements of its power and rotor outlet's conditions for the designed radial inflow turbine. The mass flow rate was consequently increased to 21.2 kg/s for the designed 200kW-class radial inflow turbine for OTEC, and then Total to total and Total to static efficiency are 89.8% and 85.36% respectively.

• Journal of Power System Engineering
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• v.17 no.6
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• pp.102-107
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• 2013

In this paper, the performance analysis for evaporation capacity, total work and efficiency of the ocean thermal energy conversion(OTEC) power system using mixed refrigerant(R32,R152a) is conducted to find the effect of hot wasted water on OTEC power system. The system in this study is applied with two stage turbine, regenerator, cooler and separator on Organic Rankine Cycle. The commercial program HYSYS is used for the performance analysis. The main results were summarized as follows : The efficiency of the OTEC power cycle has a largely effect on the evaporation capacity and total work. As increasing temperature of heat source water, evaporator's capacity is decreased but total work increase. Otherwise, using hot wasted water bring effects not only increasing system efficiency but also declining evaporator's capacity. Thus With a thorough grasp of these effect, it is necessary to find way to use hot wasted water emitted by power plant and so on.

• Journal of Hydrogen and New Energy
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• v.26 no.3
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• pp.278-286
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• 2015

This paper presents the analytical results of the thermodynamic performance characteristics for a cogeneration system using regenerative organic Rankine cycle (ORC) driven by low-grade heat source. The combined heat and power cogeneration system consists of a regenerative superheated ORC and an additional process heater in a series circuit. Eight working fluids of R134a, R152a, propane, isobutane, butane, R245fa, R123, and isopentane are considered for the analysis. Special attention is paid to the effect of turbine inlet pressure on the system performance such as thermal input, net power and useful heat productions, electrical, thermal, and system efficiencies. The results show a significant effect of the turbine inlet pressure and selection of working fluid on the thermodynamic performance of the system.

• KEPCO Journal on Electric Power and Energy
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• v.5 no.3
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• pp.215-222
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• 2019

This work is experimental study of 10 kW specialized Combined Ocean Thermal Energy Conversion. We propose a C-OTEC technology that directly uses exhaust thermal energy from power station condensers to heat the working fluid (R134a), and tests the feasibility of such power station by designing, manufacturing, installing, and operating a 10 kW-pilot facility. Power generation status was monitored by using exhaust thermal energy from an existing power plant located on the east coast of the Korean peninsula, heat exchange with 300 kW of heat capacity, and a turbine, which can exceed enthalpy efficiency of 45%. Output of 8.5 kW at efficiency of 3.5% was monitored when the condenser temperature and seawater temperature are $29^{\circ}C$ and $7.5^{\circ}C$, respectively. The evaluation of the impact of large-capacity C-OTEC technology on power station confirmed the increased value of the technology on existing power generating equipment by improving output value and reducing hot waste water. Through the research result, the technical possibility of C-OTEC has been confirmed, and it is being conducted at 200 kW-class to gain economic feasibility. Based on the results, authors present an empirical study result on the 200 kW C-OTEC design and review the impact on power plant.

• Proceedings of the Korean Vacuum Society Conference
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• 2015.08a
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• pp.84.1-84.1
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• 2015

Recent years in particular in Korea see intensive interests in a deep geothermal engineering and its application in different uses as far as from direct uses to power generation sectors, that are achieved by harnessing hot energy sources from the earth. For instance widespread interest has been generated because the geothermal energy is the source that one extracts it for more than 20 hours per day and for about 30 years of an operation of the plant, which enables to give base load as for heating as well as an electric generation. In retrospect, shallow geothermal energy using heat pumps is commonplace in Korea while the deep geothermal is in the early stage of the development. Geothermal energies in view of the way of extracting heat are mainly categorized into several types such as a single well system, a hydrothermal system, an enhanced geothermal system (EGS) etc. In this talk, this speaker focuses on the thermo-fluid engineering of the single well system by introducing the modeling in order to harness hot fluid that is thermally balanced with the fluid of an injection well, which provides a challenge to assess the life time of the well. To avoid the loss of the temperature in producing the hot fluid, a specialized pipe or a borehole heat exchanger has been designed, and its concept is introduced. On the other hand, a binary system or an organic Rankine cycle, which provides the methodology to convert the heat into an electricity, is briefly introduced. Some experimental results of the binary system which has been constructed in our lab will be presented. Lastly as for the future direction, some comments for the industrialization of the deep geothermal energy in this country will be discussed.