• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 2000.11c
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• pp.639-646
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• 2000

Hot air heater with light oil combustion is the most common heater for greenhouse heating in the winter season in Korea. However, since the heat efficiency of the heater is about 80%, considerable unused heat in the form of exhaust gas heat discharges to atmosphere. In order to capture this exhaust gas heat a heat recovery system for plant bed heating in the greenhouse was built and tested in the hot air heating system of greenhouse. The system consists of a heat exchanger made of copper pipes, ${\phi}\;12.7{\times}0.7t$ located inside the rectangular column of $330{\times}330{\times}900mm$, a water circulation pump, circulation plastic pipe and a water tame The total heat exchanger area is $1.5m^2$, calculated considering the heat exchange amount between flue gas and water circulated in the copper pipes. The system was attached to the exhaust gas path. The heat recovery system was designed as to even recapture the latent heat of flue gas when exposing to low temperature water in the heat exchanger. According to performance test it can recover 45,200 to 51,000kJ/hr depending on the water circulation rates of 330 to $690{\ell}$/hr from the waste heat discharged. The exhaust gas temperature left from the heat exchanger dropped to $100^{circ}C$ from $270^{circ}C$ by the heat exchange between the water and the flue gas, while water gained the difference and temperature increased to $38^{circ}C$ from $21^{circ}C$ at the water flow rate of $690{\ell}$/hr. And, the condensed water amount varies from 16 to $43m{\ell}$ at the same water circulation rates. This condensing heat recovery system can reduce boiler fuel consumption amount in a day by 34% according to the feasibility study of the actual mimitomato greenhouse. No combustion load was observed in the hot air heater.

• Journal of Advanced Marine Engineering and Technology
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• v.38 no.9
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• pp.1021-1026
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• 2014

In this paper, among various systems applying hot-gas bypass control, outdoor temperature, outlet temperature of water cooler, superheating and subcooling degree, which are the factors affecting the performance of the system bypassing hot-gas to evaporator inlet were analyzed. The main results were summarized as following. Frist of all, performance of refrigeration system bypassing hot-gas to evaporator inlet was affected by outdoor temperature, outlet temperature of water cooler, superheating and sub cooling degree. Thus, providing basic planning date of refrigeration system obtained through optimization of variables is expectable. Thus, providing the basic design data of refrigeration system can be offered by performing the optimization of these variables. Also, the feasibility of this refrigeration system proposed in this paper was obtained by analyzing operating characteristics of the system bypassing hot-gas to evaporator inlet.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.3
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• pp.359-364
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• 2004

For the development of high efficiency and low emission combustion systems, high temperature air combustion technology has been tested by utilizing preheated air over 1100 K and exhaust gas recirculation. In this system, combustion air is diluted with large amount of recirculated exhaust gases, such that the oxygen concentration is relatively low in the reaction zone, leading to low flame temperature. Since, the temperature fluctuations and sound emissions from the flame are small and flame luminosity is low, the combustion mode is expected to be flameless or mild combustion. Experiment was performed to investigate the turbulent flame structure and NO$_x$ emission characteristics in the high temperature air combustion focused on coflowing jet diffusion flames which has a fundamental structure of many practical combustion systems. The effect of turbulence has also been evaluated by installing perforated plate in the oxidizer inlet nozzle. LPG was used as a fuel. Results showed that even though NO$_x$ emission is sensitive to the combustion air temperature, the present high temperature air combustion system produce low NO$_x$ emission because it is operated in low oxygen concentration condition by the high exhaust gas recirculation.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.20 no.2
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• pp.24-36
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• 2024

This study analyzed the feasibility of the air source heat pump in residential buildings based on operational performance and carbon emissions. The operational performance and carbon emissions were compared between a gas boiler and an air source heat pump by calculating the annual heating and hot water load based on the 21A and 36A models for actual residential buildings. For the operational performance of the air source heat pump, the lowest (2.3) and highest COP (5.9) were attained during the winter and summer seasons, respectively. The carbon emissions depend on the amount of energy consumed during operations. An air source heat pump consumed 65.10% and 65.4% less energy per year in the 21A and 36A models, respectively compared to the existing gas boiler. Consequently, for air source heat pump carbon emissions were also reduced by 13.3% and 15.1% per year for the 21A and 36A models, respectively. It shows the effectiveness of applying an air source heat pump compared to an existing gas boiler.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.4
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• pp.456-465
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• 1998

Effect of a non-absorbable gas on the absorption process in a vertical tube absorber was investigated numerically. The water vapor mined with air as the non-absorbable gas is absorbed into LiBr/water solution film. The flow is assumed to be laminar and fully developed in both liquid and gas phases. The diffusion and energy equations were solved in both phases to give the temperature and concentrations, from which heat and mass fluxes were determined. It was shown that the local absorption rate decreases as the mass fraction of air in water vapor increases. The vapor pressure of water at the liquid-vapor interface reduces significantly since the non-absorbable gas is accumulated near the interface. The effect of non-absorbable gases on absorption rate becomes larger as the mass flow rate of the vapor decreases. For small amount of non-absorbable gases the total absorption rate of water vapor increases as the mass flow rate of the vapor decreases. Total absorption rate increases as the mass flow rate of the vapor increases for large concentration of non-absorbables at the inlet of an absorber.

• International Journal of Air-Conditioning and Refrigeration
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• v.7
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• pp.69-78
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• 1999

Effects of a non-absorbable gas on the absorption process in a vertical tube absorber has been investigated numerically. The water vapor mixed with air is absorbed into LiBr/water solution film. The flow is assumed to be laminar and fully developed in both liquid and gas phases. The diffusion and energy equations were solved in both phases to give the temperature and concentrations, from which heat and mass fluxes were determined. The local absorption rate has been shown to decrease as the mass fraction of air in the water vapor increases. The vapor pressure of water at the liquid-vapor is interface reduced significantly since the non-absorbable gas accumulates near the interface. The effects of non-absorbable gases on absorption rate become larger as the mass flow rate of the vapor decreases. For a small amount of non-absorbable gases, the total absorption rate of water vapor increases as the mass flow rate of the vapor decreases. The total absorption rate increases as the mass flow rate of the vapor increases for large concentrations of non-absorbable gases at the inlet of an absorber.

• Journal of Power System Engineering
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• v.18 no.5
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• pp.48-54
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• 2014

In this paper, three refrigeration systems bypassing hot-gas to compressor outlet, compressor and condenser outlet and evaporator inlet are theoretically compared to offer basic design data for performance depending on cooling load using a HYSYS program. The main results are summarized as follows : First, the COP of third system is the highest. Next, the COP of second system is higher than first one. And, the temperature of compressor inlet of third system is constant for all cooling load. Compared to first and second system, the compressor inlet temperature of the first system is higher than second one for all cooling loads. From the above results, third system, which is bypassing hot-gas to evaporator inlet, is more advantageous when considering the precise temperature control and excellent performance of oil and water cooler of industrial machine.

• Nuclear Engineering and Technology
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• v.37 no.6
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• pp.537-556
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• 2005

A primary-pipe rupture accident is one of the design-basis accidents of a High-Temperature Gas-cooled Reactor (HTGR). When the primary-pipe rupture accident occurs, air is expected to enter the reactor core from the breach and oxidize in-core graphite structures. This paper describes an experiment and analysis of the air ingress phenomena and the method fur the prevention of air ingress into the reactor during the primary-pipe rupture accident. The numerical results are in good agreement with the experimental ones regarding the density of the gas mixture, the concentration of each gas species produced by the graphite oxidation reaction and the onset time of the natural circulation of air. A hydrogen production system connected to the High-Temperature Engineering Test Reactor (HTTR) Is being designed to be able to produce hydrogen by themo-chemical iodine-Sulfur process, using a nuclear heat of 10 MW supplied by the HTTR. The HTTR hydrogen production system is first connected to a nuclear reactor in the world; hence a permeation test of hydrogen isotopes through heat exchanger is carried out to obtain detailed data for safety review and development of analytical codes. This paper also describes an overview of the hydrogen permeation test and permeability of hydrogen and deuterium of Hastelloy XR.

• Transactions of the Korean hydrogen and new energy society
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• v.27 no.5
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• pp.571-580
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• 2016

In this paper, performance of the gas turbine combined cycle(GTCC) using pre-combustion carbon capture technology was comparatively analysed. Steam reforming and autothermal reforming were used. In the latter, two different methods were adopted to supply oxygen for the reforming process. One is to extract air form gas turbine compressor (air blowing) and the other is to supply oxygen directly from air separation unit ($O_2$ blowing). To separate $CO_2$ from the reformed gas, the chemical absorption system using MEA solution was used. The net cycle efficiency of the system adopting $O_2$ blown autothermal reforming was higher than the other two systems. The system using air blown autothermal reforming exhibited the largest net cycle power output. In addition to the performance analysis, the influence of fuel reforming and carbon capture on the operating condition of the gas turbine and the necessity of turbine re-design were investigated.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.11
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• pp.41-46
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• 2015

This study was conducted to discover a substitute of $SF_6$ gas. $SF_6$ gas is widely used across the industries. Thanks to superior electrical properties, in particular, it has been commonly used in electrical industry. However, there have been a lot of studies on its serious effect on global warming. As a substitute of this synthetic gas, a mixture of dry air and $N_2/O_2$ was chosen in this study. In case of $N_2/O_2$, dielectric strength differs depending on the mixing ratio. This study examined dielectric breakdown and flashover after adjusting oxygen percentage in the dry air. This test was conducted in a quasi-uniform electric field depending on pressure, oxygen concentration and gas mixtures. The test results found that dielectric voltage and flashover voltage were the highest at a certain oxygen concentration. It is the results of this photoionization and electron attachment of oxygen.