• 한국태양에너지학회 논문집
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• 제31권5호
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• pp.140-145
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• 2011

In this study, the performance and behavior of solar heating system according to the system control scheme, variable flow control (proportional control) and constant flow control (on-off control) was carried out by experiment. The on-off control is used generally for solar thermal system by now. But the proportional control is used for the solar district heating system which is supplied the higher temperature of water than that of desired. The proportional control logic that pump speed is varied in an attempt to maintain a specified outlet temperature of solar heating system was developed and tested for the use widely for the small and medium solar thermal system. The results are as following. First, the proportional controller which is made here could be adopted the characteristics for setting temperature control. Second, the proportional control is better than the on-off control in the side of the performance of thermal stratification in storage tank. Third, the operating energy(electricity consumption by pump) of solar thermal system can be saved more than 60% using the proportional control comparing to the on-off control.

• 설비공학논문집
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• 제11권3호
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• pp.339-348
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• 1999

A computer model was developed in order to predict the temperature distribution and the performance of the vertical tube-in-tube ground coil heat exchanger. This model has been validated by experimental results conducted by ORNL. The heat exchanger performance with the variation of the length is calculated and compared. As results, the heat exchanger performance is proportional to the length but the performance per unit length decreases. The minimum performance of 70m - PVC heat exchanger during cyclic operation for a week is obtained 20,054kJ/h for cooling operation and 13,915kJ/h for heating operation. And minimum temperature difference is $4.64^{\circ}C$ for cooling operation and $2.64^{\circ}C$ for heating operation. In each case, it is noted that the temperature difference between the pipe and the far-field occurs within 0.8m from the heat exchanger.

• Current Photovoltaic Research
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• 제6권2호
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• pp.39-42
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• 2018

When the PV module is illuminated in a high temperature region, solar cells are also exposed to the high temperature external environment. The operating temperature of the solar cell inside the module is increased, which causes the power drops. Various efforts have been made to reduce the operating temperature and compensate the power of solar cells according to the outdoor temperature such as installing of a cooling system. Researches have been also reported to lower the operating temperature of solar cells by improving the heat dissipation properties of the backsheet. In this study, we conducted a test to measure the internal temperature of each module components and the external temperature when the light was irradiated according to the surrounding temperature. Backsheets with different thermal conductivities were compared in the test. Finally, in order to explain the temperature difference between the solar cell and the outside of the module, we proposed an evaluation method of the heat transfer characteristics of photovoltaic modules with different backsheet.

• 태양에너지
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• 제17권3호
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• pp.3-11
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• 1997

Recently the construction of atrium buildings has increased but along with it many problems in thermal environment have arised. since the exterior wall of glass, indoor temperature is greatly influenced by weather conditions and since the space volume is very large, the vertical air temperature is not uniform. So, in this study, a Vertical Temperature Distribution Model was developed to predict the vertical air temperature of an atrium and evaluate the effects of the design parameters on the air temperature distribution of an atrium. To consider the characteristics of the vertical air temperature distribution in an atrium, the Satosh Togari's Macroscopic Model was used basically for the calculation of the vertical air temperature distribution in large space and the solar radiation analysis model and natural ventilation analysis model in atrium. And to calculate the unsteady-state inside wall surface temperature(boundary condition), the finite difference method was used. For the verification of the developed temperature distribution program, numerical evaluation of air flow by the ${\kappa}-{\varepsilon}$ turbulence model and in-situ test was conducted in parallel. The results of this study, the developed temperature distribution program was seen to predict the thermal condition of the atrium very accurately.

• 자원환경지질
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• 제56권2호
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• pp.185-199
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• 2023

This study aimed to predict the effects of water ecology on the supply of hydrothermal energy to model a housing complex in Eco Delta Smart Village in Busan. Based on the results, engineering measures were recommended to minimize problems due to possible temperature variations on the supply of hydrothermal energy from the river. The current distribution of fish, benthic macroinvertebrates, and phytoplankton in the Pyeonggang Stream was monitored to determine their effects on water ecology. In the research area, five species and three families of fish were observed. The dominant species was Lepomis macrochirus, and the subdominant species was Carassius auratus. Twenty-five species and 21 families of benthic macroinvertebrates were found. The distribution of aquatic insects was poor in this area. The dominant species were Chironomidae sp., Lymnaea auricularia, Appasus japonicus, and Caridina denticulata denticulata in February, May, July, and October. Dominant phytoplankton were Aulacoseira ambigua and Nitzschia palea in February and May. Microcystis sp. was dominant in July and October. The health of the ecology the Pyeonggang Stream was assessed as D (bad) according to the benthic macroinvertebrate index (BMI). Shifts in the location of the discharge point 150 m downstream from intake points and discharge through embedded rock layer after adding equal amounts of stream water as was taken at the beginning were suggested to minimize water temperature variations due to the application of hydrothermal energy. When the scenario (i.e., quantity of water intake and dilution water, 1,600 m³/d and water temp. difference ±5 ℃) was realized, variations in water temperature were assessed at -0.19 ℃ and 0.59 ℃ during cooling and heating, respectively, at a point 10 m downstream. Water temperatures recorded at -0.20 ℃ and 0.68 ℃ during cooling and heating, respectively, at a point 10 m upstream. All stream water temperatures after the application of hydrothermal energy recovered within 24 hours. Future work on the long-term monitoring of ecosystems is suggested, particularly to analyze the influence of the water environment on hydrothermal energy supply operations.

• 한국신재생에너지학회:학술대회논문집
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• 한국신재생에너지학회 2010년도 춘계학술대회 초록집
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• pp.238.2-238.2
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• 2010

Recently, environmental pollution and energy depletion problems have been issued over the world. For this reason, many renewable systems have been developing. Of these, the Ocean Thermal Energy Conservation(OTEC) is drawing attention as the upcoming alternative energy source. In this paper, the efficiency of each of OTEC which harness the effluent from nuclear power plant was analyzed by using computer calculation. The result, shows that Ul-jin Nuclear Power Plant is the best place geographically and the regenerative cycle is most outstanding performance cycle for OTEC. The difference of temperature between surface water and deep water temperature should be greater than $20^{\circ}C$ in order to increase the efficiency.

• 한국태양에너지학회:학술대회논문집
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• 한국태양에너지학회 2009년도 추계학술발표대회 논문집
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• pp.320-323
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• 2009

Weather data is an important variable for the estimation value of the program for evaluating energy performance. The difference in data value of major weather elements used in weather data (temperature, insolation amount) were compared and analyzed. It was found that temperature showed similar values but insolation amount took different values. Especially in Ulsan, since the Meteorological Association does not measure insolation amount. To optimize the incident solar radiation, the solar azimuth angles are needed for solar photovoltaic systems. Test results shows that the $60^{\circ}$installation angel higher efficient than the $30^{\circ}$ installation angel in winter.

• 한국수소및신에너지학회논문집
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• 제12권1호
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• pp.65-73
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• 2001

Carbon nanotubes were prepared by catalytic decomposition of $CH_4$ using Ni-MgO catalyst at various temperatures. $H_2$ effect on crystallinity and morphology during the synthesis of carbon nanotubes was investigated. The crystallinity and morphology were characterized by SEM, TEM, XRD, TGA, and Raman spectroscopy. In addition, the hydrogen adsorption properties were evaluated by PCT measurement in a hydrogen pressure range between 1 and 120 bar. The optimal synthesis temperature of carbon nanotubes was elevated in the presence of $H_2$, although significant difference of carbon nanotube morphology was not found. It is believed that hydrogen served as self-cleaner mops the amorphous carbon on the catalyst surface. It is proved that the carbon nanotubes have multi-walled structure, short length with a outer diameter of 20 ~40nm and open tips after elimination of the catalyst. The amount of hydrogen adsorbed in carbon nanotubes is increased as the pressure of hydrogen is increased and reaches 1.3 wt % under the hydrogen pressure of 120 bar at room temperature.

• Journal of Biosystems Engineering
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• 제21권4호
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• pp.436-448
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• 1996

An earth tube soil air heat exchange system was designed, installed and operated as a single pass heat exchanger to utilize the geothermal energy as an natural energy source. This study was undertaken to investigate the potential of the heating and cooling, energy gain, heat exchange efficiency and coefficient of performance of the system. The system consisted of 30m in length and 30cm in diameter polyethylene pipes buried 2m deep in soil. Maximum heating and cooling performance were 2.51㎾ and 1.26㎾ at the air mass rate of 21cmm. Energy gain and coefficient of performance were the function of temperature difference between outside air and soil temperature. They were expressed as Q=0.33$ imes$$Delta T_{max}$+0.134(㎾) for energy gain and COP=0.44$ imes$$Delta T_{max}$+0.178 for coefficient of performance with correlation factor of 0.95. The mean of heat exchange efficiencies was 85.6%.

• 한국수소및신에너지학회논문집
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• 제19권4호
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• pp.299-304
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• 2008

Thermal decomposition of Ammonia Borane have been investigated with various analytical methods including TGA, TP-MS, DSC. By-products such as aminoborane and borazine were identified during hydrogen release by TGA, TP-MS analysis. $H_2$ release amount was measured at each temperature isothermally, which resulted in 7 wt% $H_2$ release at 130$^{\circ}C$. Moreover, higher temperature enhanced hydrogen release kinetics leading to shortened induction period from 20 min at 95$^{\circ}C$ to 0 min at 130$^{\circ}C$. Melting and decomposition at close temperature (4$^{\circ}C$ difference) caused the formation of thin foam during hydrogen release. Suppression of by-products and thin foam formation during hydrogen release is suggested as critical issues to realize chemical hydrogen storage system with ammonia borane.