• Journal of computational fluids engineering
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• v.9 no.3
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• pp.49-56
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• 2004

A heated and expanded helium is used to pressurize liquid propellants in propellant tanks of propulsion system of liquid propellant launch vehicles. To produce a heated and expanded helium, an hot-gas heat exchanger is used by utilizing heat source from an exhausted gas, which was generated in a gas generator to operate turbine of turbo-pump and dumped out through an exhaust duct of engine. Both experimental and numerical approaches of hot-gas heat exchanger design were conducted in the present study. Experimentally, siliconites - electrical resistance types - were used to simulate the full heat condition instead of an exhausted gas. Cryogenic heat exchangers, which were immersed in a liquid nitrogen pool, were used to feed cryogenic gaseous helium in a hot-gas heat exchanger. Numerical simulation was made using commercially utilized solver - Fluent V.6.0 - to validate experimental results. Helically coiled stainless steel pipe and stainless steel exhausted duct were consisted of tetrahedron unstructured mesh. Helium was a working fluid Inside helical heat coil and regarded as an ideal gas. Realizable k-』 turbulent modeling was adopted to take turbulent mixing effects in consideration. Comparisons between experimental results and numerical solutions are Presented. It is observed that a resulted hot-gas heat exchanger design is reliable based on the comparison of both results.

• 한국신재생에너지학회:학술대회논문집
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• 2008.10a
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• pp.166-166
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• 2008

• Proceedings of the SAREK Conference
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• 2004.06a
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• pp.207-207
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• 2004

• Proceedings of the Korean Society of Marine Engineers Conference
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• 2005.06a
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• pp.216-221
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• 2005

The heat transfer coefficient and pressure drop during gas cooling process of carbon dioxide in a helically coiled tube were investigated experimentally. The experiments were conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable speed pump, a mass flowmeter, a pre-heater, a gas cooler(test section) and an isothermal tank. The test section is a double pipe type heat exchanger with refrigerant flowing in the inner tube and water flowing in the annulus. It was made of a copper tube with the inner diameter of 4.85 [mm], the outer diameter of 6.35 [mm] and length of 10000 [mm]. The refrigerant mass fluxes were 200${\sim}$600 [kg/$m^2$s] and the average pressure varied from 7.5 [MPa] to 10.0 [MPa]. The main results were summarized as follows: The heat transfer coefficient of supercritical $CO_2$ increases, as the cooling pressure of gas cooler decreases. And the heat transfer coefficient increases with the increase of the refrigerant mass flux. The pressure drop decreases in increase of the gas cooler pressure and increases with increase the refrigerant mass flux.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.5
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• pp.576-581
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• 2011

In this paper, the prediction of adiabatic capillary tube of heat pump using carbon dioxide is investigated theoretically and experimentally to offer the basic design data for the operating parameters of this system. The operating parameters considered in this study include evaporation temperature, cooling pressure of gas cooler, mass flowrate, and the length and diameter of capillary tube. Based on study results of several researchers, the correlation predicting the length of capillary tube of $CO_2$ heat pump was proposed. And the experimental results of evaporation temperature, mass flowrate and cooling pressure in adiabatic capillary tube have an good agreement to those calculated from Eq. (3) within 0.63~10.9%. Therefore, the prediction calculating the length of adiabatic capillary tube of $CO_2$ heat pump was proposed at the given conditions such as cooling pressure, evaporation temperature and capillary tube diameter.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.11 no.3
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• pp.369-376
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• 1999

Experiments were carried out to study the heat transfer characteristics of a disrober for 150 RT LiBr-water absorption heat pump. An experimental apparatus was divided into four sections, a combustion chamber area, two bare-tube areas, and finally a finned-tube area to quantify the heat transfer rate of each section by measuring the generation rate of vapor. Dividing plates was installed at the upper inside part of deserter to prohibit the moving of vapor generated at heating tubes of a section to another section near. In the first bare-tube area, the generation rate of vapor was the largest among the four sections. The finned-tube area only contributed to give sensible heat increase of solution to the saturation temperature. The heat transfer area of the finned-tube area was 52.2%, which absorbed only 9.2% of the total heat from the combustion gas. On the contrary, the heat transfer area of the first bare-tube area was 16.6%, but it absorbed 52.4% of the total absorbed heat. The temperature of the solution at upper part at the finned-tube area was lower than that of the lower part, because weak solution came in upper part of the finned-tube area. But, this tendency was changed at the first and second bare-tube area due to the vigorous heat transfer and fluid flow enhanced by vapor generation through heating tubes. The overall heat transfer coefficient and heat flux were the largest at the first bare-tube area among the other sections.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.2
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• pp.71-78
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• 2009

Up until recently, the energy and the economic analysis of a cogeneration system have been implemented by a manual calculation that is based on monthly thermal loads of buildings. In this study, a cogeneration system modeling validation with a detail building energy simulation, eQUEST, for a building energy and cost prediction has been implemented. By analyzing the hourly building electricity and thermal loads, it enables users to decide proper cogeneration system capacity and to estimate more accurate building energy consumption. eQUEST also verified the energy analysis when the heat pump system is integrated with the cogeneration system. The mechanical system configuration benefits from the high efficiency heat pump system while avoiding the building electricity demand increase. Economic analysis such as LCC (Life Cycle Cost) method is carried out to verify economical benefits of the system by applying actual utility rates of KEPCO(Korea Electricity Power COmpany) and KOGAS(KOrea GAS company).

• New & Renewable Energy
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• v.5 no.3
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• pp.40-48
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• 2009

Recovered heat has been considered as a renewable energy in Europe since 2008 because its great effect on energy saving and carbon decreasing in plant process. Energy saving and decreasing green gas are critical issue today, so various technologies to save energy and decrease carbon dioxide in plant process have been applied to many industrial area. In this paper, the feasibility of condenser heat recovery by heat pump in power plant for district heating and fuel line preheating were reviewed by verifying energy (heat) balance and mass balance of power plant model. Some ways to compose proper system to recover heat of condenser are suggested and their possibilities are also reviewed. Limitations on heat recovery in power plant are also reviewed. The results are verified by calculating input/output energy based on actual performance test data of Taean Thermal Power Plant in Korea. There is noticeable improvement of plant performance in some cases which demand low temperature (<100 C) heat like distrcit heating, fuel line heating, and so forth.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.23 no.4
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• pp.29-38
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• 2009

The GHP(Gas Heat Pump) is an efficient cooling;11eating system in which a compressor is driven by a gas engine and is brodening its application to the facilities such as schools and office buildings. It is difficult to control the GHP system because of slow response, big time constant and time variant system. These nonlinear loads generate harmonic currents and create distortions on the sinusoidal voltage of the power system Harmonic field measurements have shown that the harmonic contents of a waveform varies with time. A cumulative probability approach is the most commonly used method to solve time varying harmonics. This paper provides an in depth analysis on harmonics field measurement of the GHP loads, harmonic assessment by me 61000-3-2, and harmonic simulation and harmonic filter application using EDSA program for the case study system.

• KIEAE Journal
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• v.17 no.4
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• pp.67-74
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• 2017

Purpose: As the recent climate environment changes so rapidly, environmental problems such as hot weather and fine dust have occurred, and interest in environmental policies and technology development is increasing in countries around the world. Similarly in the Architecture, researches to reduce greenhouse gas emissions and to reduce energy application are actively conducted. Looking at previous studies, it is analyzed that the electric VRF is more energy efficient than the gas engine VRF. However, energy costs have changed due to recent price hikes and discounts on gas charges due to high electricity consumption in summer. Method: In this study, the actual building of Gas Engine VRF system was modeled using SketchUp program, and EnergyPlus was used to simulate actual building. Also, Electric VRF system was simulated, and compared with Gas Engine VRF system. Result: The total secondary energy requirement of Electric VRF system was 19.6% less than that of the Gas Engine VRF system, But when analyzing with primary energy requirement, EHP used 15.8% more energy. CO2 emissions were also estimated to be 16.9% more EHP. Energy costs were 14.8% more in Electric VRF systems, because their electricity charges are 0.6 to 160% more expensive than gas charges.