• Nuclear Engineering and Technology
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• v.52 no.12
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• pp.2771-2788
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• 2020

Experiments are conducted to study bubble flow behavior during the instability of subcooled boiling under uniform and non-uniform transverse heating. The non-uniform heat distribution introduces nonuniform bubble generation and condensation rates on the heated surface, which is different from the uniform heating. These bubble generation and condensation characteristics introduce a non-uniform local pressure distribution in the transverse direction, which creates an extra non-uniform pressure on the flowing bubbles. Therefore, different bubble flow behavior can be observed between uniform and non-uniform heating conditions. In the uniform heating, bubble velocity fluctuations are low, and the bubbles travel straight along the axial direction. In the non-uniform heating, more fluctuation in the bubble velocity occurs at low mass flow rate and high subcooled inlet temperatures, and reverse flow is observed. Additionally, the bubbles show a zigzag trajectory when they pass through the channel, which indicates the existence of cross flow in the transverse direction.

• 한국정보디스플레이학회:학술대회논문집
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• 2007.08a
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• pp.930-932
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• 2007

In order to understand the doping control for the belt source evaporation, the Alq3 and NPB were codeposited on the Ta plate to re-sublimate. The very slow heating $(0.1^{\circ}C/s)$ of the Ta plate shows the separated rate signals of Alq3 and NPB sublimated from the Alq3-mixed NPB organic film on Ta plate. The ratio of the vapor rates of Alq3 and NPB was measured as same as that of each sublimation rates. Therefore, the doping control of the belt source evaporation is of the ratio of the vaporization rates of host and dopants.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.10
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• pp.725-731
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• 2016

This study numerically investigates the thermal performance of a 2.0-kW butane-based combustion heating system for an electric vehicle under cold conditions. The system is used for cabin space heating and coolant-based battery thermal management. ANSYS CFX 17 software was used for parametric analysis. The mass flow rates of cold air and coolant were varied, and their effects were compared. The numerical results were validated with theoretical studies, which showed an error of 0.15%. As the outside air mass flow rates were increased to 0.005, 0.01, and 0.015 kg/s, the cabin supply air temperature decreased continuously while the coolant outlet temperature increased. When the coolant mass flow rates were increased to 0.005, 0.01 and 0.015 kg/s, the air temperature increased while the coolant outlet temperatures decreased. The optimal mass flow rates are discussed in a consideration of the requirements for high cabin heating capacity and efficient battery thermal management.

• 한국태양에너지학회:학술대회논문집
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• 2009.04a
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• pp.109-114
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• 2009

The dominant heating system used in Korean residential apartment buildings is a hydronic radiant floor heating system, known as the Ondol system. The most common control strategy applied to this traditional hydronic radiant system is a simple on-off control that intermittently supplies "hot water of a fixed temperature" at a "constant flow rate" to each room. However, the current problems with the aforementioned control are as follows: (1) since the simple on-off control is usually based on a one point measured temperature (a signal from a thermostat installed in a living room) in each dwelling unit, heating energy use for unoccupied rooms as well as a difference in temperatures between spaces (master bedroom, living room, bedroom1, bedroom2) can occur occasionally. (2) the most widely used residential water splitter has static valves, and is thus not able to change the flow rate to each room depending on the space heating load. In other words, the ratio of flow rates to rooms is fixed after construction, resulting in over- or under-heating and an improper use of energy. The aim of this paper is therefore to investigate the differences in the system's performance between control strategies in terms of the flow rate control and sensor location. It is shown that energy savings of control strategies are strongly influenced by occupant schedule.

• 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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.10 no.6
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• pp.773-783
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• 1998

The heating system for apartment complex may be classified as old systems including central system with steam boiler(S1), gas engine driven heat pump system(S2), system using waste heat(S3) and new systems including mechanical vapor re-compression system with flashing heat exchangers(S4), system using methanol(S5), system using metal hydride (S6). The purpose of the present study is to suggest optimal heating system by technically, economically and environmentally evaluating old and new heating systems of apartment complex from 500 to 3,000 households. Economic evaluation based on the technical evaluation results which estimated heat transfer area of heat exchangers and capacity of equipments was estimated initial investment cost, annual operating cost and relative payback period by considering annual increasing rates of energy cost and interest. Environmental evaluation provided annual generation rate of carbon dioxide. Initial investment cost was cheap in the order of S6, S5, S3, S2, S4, S1, annual operating cost was cheap in the order of S1, S2, S4, S5 and relative payback period was short in the order of S6, S5, S2, S3 and S4. Relative payback period was within 8 years for all scenarios of 3,000 households, and was increased as annual increasing rates of energy cost and interest were increased. As transportation pipe length was increased twice, payback period was increased by 1.4~2.6 time. The effect of temperatures of waste gas and waste water on the relative payback period was small within 0.8 years. The annual generation rate of carbon dioxide was big in the order of S4, S2 and S1. S4 was the most economic system among whole scenarios when S1 was replaced with other scenarios.

• Land and Housing Review
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• v.3 no.2
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• pp.169-175
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• 2012

In recent, there are many studies associated with energy piles to save initial construction cost for ground source heat pump system. In this study, to evaluate geothermal exchange rates two types (a connection type and a slinky type) of cast-in-place energy piles (PRD, 4.5m in depth, 1,200 mm in diameter) were constructed for the tests and their efficiencies were compared with numerical analysis results. As a result, starting with operation, geothermal exchange rate gradually decreases due to exchange of lower ground temperature. In the case of connection type, temperature difference is $0.37^{\circ}C$ in heating mode and $0.34^{\circ}C$, in cooling mode, respectively. In addition, in case of a connection type, geothermal exchange rate in heating mode is 2,314W/m and in cooling mode, 252.2W/m whose value is 9% higher than in heating mode. In the case of slinky type, the average geothermal exchange rate in heating mode is 168.0W/m, which is about 27% lower than that of connection type.

• Proceedings of the Korean Society For Composite Materials Conference
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• 1999.11a
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• pp.251-257
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• 1999

Smart structure that contains sensors, which are either embedded in a composite material or attached to a structure, is currently receiving considerable attention. Fiber Bragg grating sensor, one of the optical fiber sensors, has been widely used to sense strain and temperature for smart structures since both parameters change the resonant frequency of the grating. In this paper, according to the various heating and cooling conditions the thermal behavior of unidirectional composite material was monitored by embedding the fiber Bragg grating sensors in the longitudinal and transverse directions of unidirectional composites. The thermal behavior of unidirectional composite material was monitored for various heating and cooling rates and applied pressure. It was found that the thermal behavior was unaffected by pressure variations and heating and cooling rates applied to the composites. The thermal strains were measured by considering the shift in Bragg wavelength that was generated by the thermal expansion of composite specimen. The longitudinal and transverse C.T.E.'s were also obtained from the corresponding temperature-thermal strain curves.

• Journal of the Korean Wood Science and Technology
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• v.23 no.4
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• pp.33-38
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• 1995

The rates of fixation of CCA-Type B and CCFZ in blocks of radiata pine sapwood were compared at various temperatures and conditioning methods (drying and nondrying conditioning). Also the time required to proper fixation of preservative components in the treated wood was estimated. Fixation was monitored by the rates of depletion of free hexavalent chromium in the cell lumens in the teated blocks. The rate of preservative fixation in wood was highly temperature dependent. The fixation rate was considerably accelerated by means of heating and complete fixation of hexavalent chromium was achieved within about 12 hours by heating at $60^{\circ}C$. The moisture content of treated wood during fixation apparently played an important role in the fixation process. The fixation rate of treated wood conditioned in nondrying conditions was much more faster than that of treated wood conditioned in drying conditions. particularly when the moisture content of treated wood was below fiber saturation point. Time required to full fixation could be predicted successfully using the fixation temperatures applied since the correlation between the fixation temperature and the fixation time was excellent. regardless of conditioning methods.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.74.1-74.1
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• 2010

Using two-dimensional numerical hydrodynamic simulations, we investigate the regulation of star ormation rates in turbulent, multiphase, galactic gaseous disks. Our simulation domain is xisymmetric, and local in the radial direction and global in the vertical direction. Our models nclude galactic rotation, vertical stratification, self-gravity, heating and cooling, and thermal onduction. Turbulence in our models is driven by momentum feedback from supernova events ccurring in localized dense regions formed by thermal and gravitational instabilities. Self-onsistent radiative heating, representing enhanced/reduced FUV photons from the star formation, s also taken into account. Evolution of our model disks is highly dynamic, but reaches a quasi-teady state. The disks are overall in effective hydrostatic equilibrium with the midplane thermal ressure set by the vertical gravity. The star formation rate is found to be proportional pproximately linearly to the midplane thermal pressure. These results are in good agreement with the predictions of a recent theory by Ostriker, McKee, and Leroy (2010) for the thermal/dynamic equilibrium model of star formation regulation.