• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.534-542
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• 2012

Vertical closed-loop ground source heat pump systems(GSHP) have been installed widely in Korea since it can extract moderate temperature level of geothermal heat in a small area. As a ground heat exchanger, a vertical closed-loop type with brine circulation is mostly preferred since it is simple and less harmful to ground environment. However, it requires a secondary heat exchange loop between the refrigerant in a heat pump and the brine. By adding a geothermal heat exchanger in the secondary heat exchange loop, circulation pumps should be attached and the temperature difference between refrigerant and ground is increased, which are important parts of performance degradation. In this paper, annual and seasonal performances of direct expansion(DX) geothermal heat pump were estimated mathematically as an alternative of classical indirect geothermal heat pump based on the annual performance evaluation. As a result, DX geothermal heat pump showed 43% higher annual performance than the classical U-tube geothermal heat pump.

• Current Photovoltaic Research
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• v.9 no.3
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• pp.106-109
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• 2021

In order to perform photovoltaic (PV) operation and management (O&M) efficiently, individual PV module monitoring is becoming more important. In this research, we developed wireless IoT sensor which can monitor individual photovoltaic modules. This IoT sensor can detect the output voltage, current and module temperature of individual modules and provide monitored data by wireless communication. Measured voltage error was 1.23%, and it shows 16.6 dBM, 0.42sec and 7.1 mA for voltage, transmittance output, response time and mean power consumption, respectively. IoT sensors were demonstrated in the test field with real climate environment condition and each of 5 sensors showed precise results of voltage, current and temperature. Also, sensors were compared with commercial power-optimizers and showed result difference within 5%.

• 한국태양에너지학회:학술대회논문집
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• 2012.03a
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• pp.543-548
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• 2012

The use of glass applied to curved surface as a building material has increased in recent years. However, the curved glass is difficult to guarantee the quality in process of making it into double glazing, So it is vulnerable to thermal breakage. In this paper, when the glass broken during experiments, surface temperature difference on curved double glazing was compared to that of heat strengthened glass and flat glass. As a result, flat single glass was broken at temperature difference of 100~140 degrees but curved double glazing was broken at that of 40~60 degrees. Therefore, curved double glazing is more vulnerable than flat double glazing to thermal breakage, so it should be considered when applied to building facade.

• KSBB Journal
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• v.5 no.4
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• pp.403-410
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• 1990

Application of the Rheocatch Hotwire Monitoring System for food biotechnology process was evaluated. The growth of microogranism, E coli (JM 83 and Sigma) and Corynesccfertun glutamicum, were monitored. in the fermentor. The cell growth could not be detected the temperature differences between the hotwire and samples($\Delta$T) as indicated by the monitoring system during the fermentation processes. The cell concentration of less than 2g/dl was not sufficient to generate the measurable temperature difference in the fermentor. In order to calibrate the Rheocatch Monitoring System, the temperature difference as a function of solute concentration (microbial cells, sodium cholide, sucrose and dextran) was studied. The relationship between $\Delta$T and the concentration of microbial cells, sucrose and dextran can be expressed in a power series. Further studied with dextran indicated that viscosity and/or kinematic viscosity increase exponentially with an increase in $\Delta$T This is regardless of the concentration and molecular weight of dextran. $\Delta$T linearly increases with the logarithm of molecular weight, while the logarithm of viscosity and the logarithm of kinematic viscosity increase with the logarithm of molecular weight.

• Solar Energy
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• v.7 no.2
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• pp.37-53
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• 1987

This study has been prepared for the purpose of developing the system performance prediction method of natural circulation solar hot water system. The storage tank of the natural circulation solar hot water system equipped with flat-plate solar collector is located at higher elevation than the solar collectors. Therefor, the storage tank temperature distribution formed accordance with configuration of storage tank by flow rate of circulating fluid affect system collection efficiency. In this study measure the storage tank temperature distribution with various experimental system under real sun condition and present the theoretical prediction method of the storage tank temperature. Moreover measure the flow rate not only day-time but also night-time reverse flow rate with die injection visual flow meter. Main conclusion obtain from the present study is as follows; 1) The storage tank temperature distribution above the connecting pipe connection position is the same as that of the fully mixed tank and below the connection position is the same as that of stratified tank. 2) The system performance sensitive to the storage tank temperature distribution. Therefore detailed tank model is necessary. Average storage tank temperature can be calculate 3% and storage tank temperature profile can get less than 10% difference with this model system.

• Journal of the Korean Solar Energy Society
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• v.35 no.5
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• pp.21-29
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• 2015

In this study, the performance of hybrid solar air-water heater when the heated air was used as inlet air was investigated during air and liquid were heated simultaneously. Temperature difference between inlet air and ambient was set as $0^{\circ}C$, $13^{\circ}C$ and $22^{\circ}C$ and it was maintained during the daily operation. As a result, thermal efficiency of liquid heating was increased when the inlet air temperature was increased and heat gain of the water in heat storage tank was also increased with increment of temperature difference between inlet air and ambient temperature. On the contrary to this, the decrement of air heating efficiency and total efficiency of collector was confirmed with increment of inlet air temperature and it is considered that heat gain of liquid side is lower than heat loss of air side that occurring by using heated air as inlet air of collector. So, from these results, maximum temperature that the liquid in heat storage tank can reach was expected to increase if the return air or any heated air was used as inlet air. But air and total efficiency of hybrid solar air-water is decreased, so using outdoor air as inlet air is considered as better way on perspective of using of solar thermal energy by hybrid solar collector. However, it is hard to conclude that using outdoor air is better than heated air on the perspective of energy saving of building because the performance of heat storage performance was increased even air and total thermal efficiency was decreased, so the necessity of more profound consideration about these result in further research was confirmed for putting the hybrid solar air-water heater to practical use.

• Journal of the Korean Solar Energy Society
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• v.26 no.3
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• pp.71-78
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• 2006

Thermodynamic irreversibility analysis of an air-to-water heat pump system is analyzed in this study. This analysis shows the distribution of irreversibilities(true losses in thermodynamic sense) through the system components and informs us of a potential improvements with the irreversibility factor decreases. The results show that the largest irreversibilities occur in the motor-compressor unit. The remaining irreversibilities are distributed relatively uniformly through the other parts including utilization system. The increase of performance can be attained through either the improvement of adiabatic efficiency of motor-compressor unit(${\eta}_{mc}$) or the reduction of temperature difference(${\Delta}T$). With the decrease of utilization temperature($T_u$) COPH also increases but the exergetic efficiency decreases. The increase of COPH of about 0.05 can be accomplished with 1K decrease of ${\Delta}T$ or $T_u$.

• Nuclear Engineering and Technology
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• v.28 no.4
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• pp.405-414
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• 1996

In this paper, the unsteady 2-dimensional turbulent flow model for thermal stratification in a pressurizer surge line of PWR plant is proposed to numerically investigate the heat transfer and flow characteristics. The turbulence model is adapted to the low Reynolds number K-$\varepsilon$ model (Davidson model). The dimensionless governing equations are solved by using the SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm. The results are compared with simulated experimental results of TEMR Test. The time-dependent temperature profiles in the fluid and pipe nil are shown with the thermal stratification occurring in the horizontal section of the pipe. The corresponding thermal stresses are also presented. The numerical result for thermal stratification by the outsurge during heatup operation of PWR shows that the maximum dimensionless temperature difference is about 0.83 between hot and cold sections of pipe well and the maximum thermal stress is calculated about 322MPa at the dimensionless time 28.5 under given conditions.

• Journal of the Korean Society of Safety
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• v.13 no.4
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• pp.9-18
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• 1998

The vortex tube is a simple device for separating a compressed gaseous fluid stream into two flows of high and low temperature without any chemical reactions. Recently, vortex tube is widely used to local cooler of industrial equipments and air supply system. The phenomena of energy separation through the vortex tube was investigated experimentally. This study is focused on the effect of the diameter of cold end orifice diameter on the energy separation. The experiment was carried out with various cold end orifice diameter ratio from 0.22 to 0.78 for different input pressure and cold air flow ratio. The experimental results were indicated that there are an optimum diameter of cold end orifice for the best cooling performance. The maximum cold air temperature difference was appeared when the diameter ratio of the cold end orifice was 0.5. The maximum cooling capacity was obtained when the diameter ratio of the cold end orifice was 0.6 and cold air flow ratio was 0.7.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.9
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• pp.1780-1787
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• 1992

Experiments have been performed on the thermal behavior in a liquid saturated porous medium in a system to simulate a single well aquifer thermal energy storage system. The principal interests in this study are the combined effects of forced and natural convection. Significant buoyancy flow due to natural convection is developed quickly as the temperature difference between the injection and original aquifer temperature increases. Theoretical model under simplified assumptions (called simple buoyancy flow model in this study) has been developed. The results of this model agree well with the experiments. The effects of buoyancy flow on the recovery factor are also examined in this study.