• Journal of Advanced Marine Engineering and Technology
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• v.24 no.2
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• pp.24-30
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• 2000

The high-pressure natural refrigerant $CO_2$ is now being evaluated for use in the motor vehicle air-conditioning systems and for several types of unitary equipment. In this study thermodynamic properties of $CO_2$ is compared to those of R-22 and R-134a and the performance characteristics of $CO_2$ refrigeration cycle is analyzed. The results show that the optimum discharge pressure for the cycle performance exists. New design concept for the $CO_2$ refrigeration system should be developed due to the high-operating pressure of itself.

• Solar Energy
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• v.19 no.3
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• pp.101-113
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• 1999

Thermodynamic performance of a simple Rankine cycle, regenerative Rankine cycle, and Kalina cycle for Ocean thermal Energy Conversion(OTEC) is evaluated under the same condition with various working fluids. The evaporator and condenser are modeled by a UA and LMTD method while the turbine and pump are modeled by considering isentropic efficiencies. As for the working fluids, R22, R134a, R32, propylene, ammonia are used for the Rankine cycles while ammonia/water and R32/R134a mixtures are used for Kalina cycle. Calculated results show that newly developed fluids such non-ozone depleting refrigerants as R134a and R32 perform as well as R22 and ammonia. The regenerative Rankine cycle showed a 1.2 to 2.8% increase in energy efficiency as compared to the simple Rankine cycle while the Kalina cycle with ammonia/water mixture showed a 1.8% increase in energy efficiency. The efficiency of the Kalina cycle with R32/R134a mixtures is the same as that of a simple Rankine cycle using R22. Therefore, the regenerative Rankine cycle turns out to be best choice for OTEC applications.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.9
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• pp.881-889
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• 2015

Ocean thermal energy conversion is an organic Rankine cycle that generates power using the temperature difference between surface water and deep water. This study analyzes the thermodynamic efficiency of the cycle, which strongly depends on the working fluid and the cycle configuration. Cycles studied included the classical simple Rankine cycle, Rankine cycles with an open feedwater heater and an integrated regenerator, as well as the Kalina cycle. Nine kinds of simple refrigerants and three kinds of mixed refrigerants were investigated as the working fluids in this study. Pinch-point analysis that set a constant pinch-point temperature difference was applied in the performance analysis of the cycle. Results showed that thermodynamic efficiency was best when RE245fa2 was used as the working fluid with the simple Rankine cycle, the Rankine cycles with an open feedwater heater and an integrated regenerator, and when the mixing ratio of $NH_3/H_2O$ was 0.9:0.1 in the Kalina cycle. If the Rankine cycles with an open feedwater heater, an integrated regenerator, and the Kalina cycle were used for ocean thermal energy conversion, efficiency increases could be expected to be approximately 2.0%, 1.0%, and 10.0%, respectively, compared to the simple Rankine cycle.

• Journal of Advanced Marine Engineering and Technology
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• v.24 no.5
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• pp.76-85
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• 2000

Stirling cycle was actualized as so called ‘hot air engine’. It has been focused again lately as one of measures for exhaust gas emission problem, but as small power engine because of its method of heat addition. Recently marine power plants commenced to meet a stringent environmental restrictions by international convention, Marpol so that diesel engines as main and auxiliarly power plants are urged to be reformed to reduce NOx emission. Author devised a compression ignition engine as a large marine power plants combined with turbo charger based on stirling cycle, and analyzed the performance by means of basic thermodynamic calculation. Analyzed in this paper, were theoretical efficiency, mean effective pressure, required equivalence ratio, gas turbine power ratio, maximum pressure, states of turbo-charger inlet gas and exhaust gas, manifesting that the engine could be proposed as one of the future power plants of marine use.

• Journal of the Korean Solar Energy Society
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• v.27 no.3
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• pp.37-44
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• 2007

For the past few years, the concern for clean energy has been greatly increased. Ocean Thermal Energy Conversion(OTEC) power plants are studied as a viable option for the supply of clean energy. In this paper, the thermodynamic performance of OTEC cycle was examined. Computer simulation programs were developed under the same condition and various working fluids for closed Rankine cycle, regeneration cycle, Kalina cycle, open cycle and hybrid cycle. The results show that the regeneration cycle using R125 showed a 0.17 to 1.56% increase in energy efficiency, and simple Rankine cycle can generate electricity when the difference in warm and cold sea water inlet temperatures are greater than $15^{\circ}C$. Also, the cycle efficiency of OTEC power plant using the condenser effluent from nuclear power plant instead of the surface water increased about 2%.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.7
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• pp.711-719
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• 2012

A thermodynamic analysis and a feasibility study on the organic Rankine cycle (ORC) as a waste heat recovery system for a marine diesel engine were carried out. The ORC and its combined cycle with the engine were simulated, and its performance was estimated theoretically using R245fa. A parametric study on the performance of the ORC system was carried out under different temperature conditions of the heat transfer loop and specification of the heat exchanger. According to the thermodynamic analysis, ~10% of the thermal efficiency of the cycle was able to be realized with the low temperature heat source below $250^{\circ}C$. The electric power output of the ORC was estimated to be about 4% of the mechanical power output of the engine, considering additional pumps for cooling water and circulation of the heat transfer medium. According to the present study, the electric power generated by the ORC is about 59%-69% of the required power, and it is possible to reduce the fuel consumption under normal seagoing conditions.

• Advances in Energy Research
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• v.4 no.1
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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.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.9
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• pp.589-596
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• 2016

Recently organic flash cycle (OFC) has been proposed which is a vapor power cycle where heat addition occurs with the working fluid remaining in the liquid state. This study proposes a modified OFC with regeneration and carries out thermodynamic performance analysis of the system utilizing low-temperature heat source in the form of sensible energy. Effects of working fluid and flash temperature are systemically investigated on the system performance such as net power production and thermal efficiency. Results show that the net power production has a peak value with respect to the flash temperature but the thermal efficiency increases with the flash temperature. The regenerative system shows higher thermal efficiency compared to the original OFC and improved potential for recovery of low-temperature heat sources.

• Journal of Advanced Marine Engineering and Technology
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• v.39 no.7
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• pp.735-743
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• 2015

The major component with a significant impact on the thermodynamic efficiency of the organic Rankine cycle is the turbine. Many difficulties occur in the turbine design of an organic Rankine cycle because the expansion process in an organic Rankine cycle is generally accompanied by a dramatic change in the working fluid properties. A precise preliminary design for a radial inflow turbine is hard to obtain using the classic method for selecting the loading and flow coefficients from the existing performance chart. Therefore, this study proposed a method to calculate the loading and flow coefficient based on the number of rotor vanes and thermodynamic design requirements. Preliminary design results using the proposed models were in fairly good agreement with the credible results using the commercial preliminary design software. Furthermore, a numerical analysis of the preliminary design results was carried out to verify the accuracy of the proposed preliminary design models, and most of the dependent variables, with the exception of the efficiency, were analyzed to meet the preliminary design conditions.

• KEPCO Journal on Electric Power and Energy
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• v.2 no.2
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• pp.299-305
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• 2016

The High Temperature Superconducting power cables (HTS power cables) become increasingly longer to commercialize the HTS power cable system. Accordingly, demands on refrigerators of large cooling capacity per a unit system have been increased. In Korea, it is currently imported from abroad with the high price due to insufficient domestic technologies. In order to commercialize the HTS power cables, it is necessary to develop the refrigerators with large cooling capacity. The Brayton refrigerators are composed of recuperative heat exchangers, compressors and cryogenic turbo expanders. The most directly considering the efficiency of the Brayton refrigerator, it depends on performance of the cryogenic turbo expander. Rotating at high speed in cryogenic temperature, the cryogenic turbo expanders lower temperature by expanding high pressure of a helium or neon gas. In this paper, the reverse Brayton cycle is designed and the cryogenic turbo expander is designed in accordance with the thermodynamic cycle.