• Journal of the Korea Institute of Military Science and Technology
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• v.6 no.3
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• pp.103-110
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• 2003

The present work was conducted to achieve the better understanding of the performance analysis technique for the expander type air turbo ramjet engine. For this purpose, the performance analysis was carried out using a small engine(8.0kN thrust) with two types of fuels. From this analysis, at the same input condition, the thrust of methane-fueled engine was 25% lower than that of hydrogen. In addition, the case of methane shows the inapplicable engine performance cycle.(i.e., The compressor work exceeds the turbine output power) These results come mainly from the different heating value of each fuel and specific heat. This analysis also shows that, to build a same performance cycle as the hydrogen case, the methane-fueled engine requires increased air and fuel flow rates, increased turbine expansion ratio, and decreased compressor pressure ratio.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.665-670
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• 2004

This paper reviews the latest studies of the expander cycle Air Turbo Ramjet engine (ATREX) conducted in JAXA. First, a system analysis including the vehicle and trajectory was conducted to optimize the engine cycle and turbo-machine configuration. We selected the precooled turbo-jet cycle for a prototype engine using the near term technologies. Second, a system ground-firing test was conducted to verify a defrosting system for the precooler. Methanol injection with its particles atomization could compensate 80 % of pressure loss caused by the frost. Thirdly, a feasibility of carbon/carbon composites for the engine components was investigated by making complex shapes such as a heat exchanger and a plug nozzle. Basic technologies on the gas leakage, the junction and bonding were also studied. The end of the paper, some basic studies such as wind tunnel tests of a new type air inlet and a plug nozzle are described.

• The KSFM Journal of Fluid Machinery
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• v.17 no.1
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• pp.12-21
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• 2014

An organic Rankine cycle was analyzed to work at the optimal operating point when the heat source is fluctuated. R245fa was adopted as a working fluid, and an axial-type turbine as expander on the cycle was designed to convert the heat energy to the electricity since the turbo-type expander works at off-design points better than the positive displacement-type expander. A supersonic nozzle was designed to increase the spouting velocity because a higher spouting velocity can produce more output power. They were designed by the method of characteristics for the operating fluid of R245fa. Three different cases, such as various spouting velocities, various inlet total temperatures, and various nozzle numbers, were studied. From these results, an optimal operating cycle can be designed with the organic Rankine cycle when the available heat source as renewable energy is low-grade temperature and fluctuated.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.742-748
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• 2004

In this paper are presented TSTO system analysis including some controlled variables on the engine operation such as a fuel flow rate and a pressure ratio of compressor, as well as variables on the trajectory. TSTO studied here is accelerated up to Mach 6 by a fly-back booster powered by air breathing engines. Three different types of engine cycle were treated for propulsion system of the booster, such as a turbo ramjet, a precooled turbojet and an EXpander cycle Air Turbo Ramjet (ATREX). The history of the controlled variables on the engine operation was optimized by Sequential Quadratic Programming (SQP) to accomplish the minimum fuel consumption. The trajectory was also optimized simultaneously. The results showed that the turbo ramjet gave the best fuel consumption. The optimal trajectory was almost the same except in the transonic range and just before reaching to Mach 6. The history of the pressure ratio of compressor considerably depended on the engine type. It is concluded that simultaneous optimization for engine control and trajectory is effective especially for a high-speed airplane propelled by turbojets like the TSTO booster.

• Transactions of the Korean hydrogen and new energy society
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• v.31 no.5
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• pp.429-435
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• 2020

This paper describes the experimental study of reverse-Brayton refrigeration system for application to high temperature superconductivity electric devices and LNG re-liquefaction. The reverse-Brayton refrigeration cycle is designed with operating pressure of 0.5 and 1.0 MPa, cooling capacity of 2 kW at 77 K, and neon as a working fluid. The refrigeration system is developed with multi scroll compressor, turbo expander and plate heat exchanger. From experiments, the performance characteristics of used components is measured and discussed for 77-120 K of operating temperature. The developed refrigeration system shows the cooling capacity of 1.23 kW at 77 K and 1.64 kW at 110 K.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2001.11b
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• pp.1026-1031
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• 2001

In this paper. the dynamic characteristics of a super high-speed tilting-pad air bearing(TPGB) used in a turbo expander with high expansion ratio are analyzed. The dynamic behavior and stability of a rotary system supported by two journal air bearings are investigated numerically. The transient response of the shaft is obtained by simultaneously solving the equation of motion of the shaft and the dynamic Reynolds equation. The stiffness and damping coefficients of the bearing are calculated from the loading coefficients of the bearing are calculated from the loading capacity. shaft velocity and displacement by using a curve fitting method. The natural frequencies of the 1st and 2nd rigid modes can be calculated from these coefficients. The theoretical method of a rigid rotor system is verified by experimentsut.

• Imaging Science in Dentistry
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• v.51 no.1
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• pp.63-71
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• 2021

Purpose: The aim of this study was to assess the artefacts of 12 fixed orthodontic appliances in magnetic resonance images obtained using 1.5-T and 3-T scanners, and to evaluate different imaging sequences designed to suppress metal artefacts. Materials and Methods: In vitro, study casts of 1 adult with normal occlusion were used. Twelve orthodontic appliances were attached to the study casts and scanned. Turbo spin echo (TSE), TSE with high readout bandwidth, and TSE with view angle tilting and slice encoding for metal artefact correction were used to suppress metal artefacts. Artefacts were measured. In vivo, 6 appliances were scanned: 1) conventional stainless-steel brackets; 2) nickelfree brackets; 3) titanium brackets; 4) a Herbst appliance; 5) a fixed retainer; and 6) a rapid maxillary expander. The maxilla, mandible, nasopharynx, tongue, temporomandibular joints, and cranial base/eye globes were assessed. Scores of 0, 1, 2, and 3 indicated no artefacts and minor, moderate, and major artefacts, respectively. Results: In vitro, titanium brackets and the fixed retainer created minor artefacts. In vivo, titanium brackets caused minor artefacts. Conventional stainless-steel and nickel free brackets, the fixed retainer, and the rapid maxillary expander caused major artefacts in the maxilla and mandible. Conventional stainless-steel and nickel-free brackets caused major artefacts in the eye globe (3-T). TSE with high readout bandwidth reduced image artefacts in both scanners. Conclusion: Titanium brackets, the Herbst appliance, and the fixed retainer caused minor artefacts in images of neurocranial structures(1.5-T and 3-T) when using TSE with high readout bandwidth.

• The KSFM Journal of Fluid Machinery
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• v.19 no.6
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• pp.34-42
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• 2016

The organic Rankine cycle (ORC) has been used to convert thermal energy to mechanical energy or electricity. The available thermal energy could be waste heat, solar energy, geothermal energy, and so on. However, these kinds of thermal energies cannot be provided continuously. Hence, the ORC can be operated at the off-design point. In this case, the performance of the ORC could be worse because the components of the ORC system designed based on a design point can be mismatched with the output power obtained at the off-design point. In order to improve the performance at the off-design point, a few components were replaced including generator, bearing, load bank, shaft, pump and so on. Experiments were performed on the same facility without including other losses in the experiment. The experimental results were compared with the results obtained with the previous model, and they showed that the system efficiency of the ORC was greatly affected by the losses occurred on the components.

• Journal of the Korean Institute of Gas
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• v.19 no.3
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• pp.9-17
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• 2015

Almost all of the natural gas consumed in South Korea is compressed into very high pressure for the transportation through the underground pipelines, then reduced in pressure regulation stations before delivery to the consumer. For pressure reduction, expansion valves have been used due to the simple and effective installation, but recover none of the energy in the gas during compression. Hence, turbo-expanders are proposed instead of the valves to accomplish the same pressure letdown function and recover some of the compression energy in the form of shaft work converting into electric powers. Here we have theoretically calculated the electric powers at the pressure reduction from 68.7 bar to 23 bar (which are the average values taken at the inlet and outlet points of the expansion valve in medium-pressure regulation stations) according to the inlet conditions of temperature and flow rate. The natural gas is considered as two cases of a pure methane and the mixture of hydrocarbons with a very small amount of nitrogen, and the Peng-Robinson equation of state is employed for the calculation of required thermodynamic properties. The electric energy is recovered as much as 1596 MW(methane) and 1567 MW(mixture) based on the total supply of natural gas in 2013.