• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.6
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• pp.795-800
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• 1985

The ideal Brayton cycle has been analyzed with the heat exchange processes between the working fluid and the heat source and the sink while their heat capacity rates are constant. The power fo the cycle can be expressed in terms of a temperature of the cycle and the heat capacity rate of the working fluid. There exists an optimum power condition where the heat capacity rate of the working fluid has a value between those of the heat source and the heat sink, and the cycle efficiency is determined by the inlet temperatures of the heat source and the sink.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.34 no.5
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• pp.43-50
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• 2018

The temperature of underground water generally remains constant regardless of the season. therefore, it is possible to get plenty of energy if we use characteristics of underground water for both cooling and heating. This study evaluates efficiency of real size coaxial and U-tube type complex geothermal system which is combined with underground water well. This study also evaluates relative efficiency/adaptability through comparison with existing geothermal systems(vertical closed loop system, open loop system(SCW)). The heat exchange capacity of complex geothermal system according to temperature difference between circulating water and underground water shows very high significance by increasing proportionally. The temperature change of underground water according to injection energy, shows very high linear growth aspect as injection thermal volume heightens. As a result of evaluation of heat exchange volume between complex geothermal system and comparative geothermal system, coaxial type has 26.1 times greater efficiency than comparative vertical closed type and 2.8 times greater efficiency than SCW type. U-tube type has 26.5 tims greater efficiency than comparative vertical closed type and 2.8 times greater than SCW type as well. This means complex geothermal system has extremely outstanding performance.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2010.11a
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• pp.115-118
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• 2010

2 Types of heater (Vitiated Type, Clean Air Type) in order to increase the temperature for a test are used for industry. In this report, large capacity clean air type heater was designed. Heater capacity and LNG consumption rate can be calculated by the air mass flow and heater inlet/outlet temperature. The heater is composed by Burner, Furnace, Heat Exchanger, and Stack. The hot air from the burner and cold air from the tube inlet exchange their heat indirectly in the heat exchanger, so the desired temperature can be achieved at the exit of the tube.

• Journal of Bio-Environment Control
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• v.12 no.3
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• pp.107-113
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• 2003

This study was carried out to improve the performance of pre-developed heat recovery devices attached to exhaust-gas flue connected to combustion chamber of greenhouse heating system. Four different units were compared in the aspect of heat recovery performance; A-, B-, and C-types are exactly the same with the old ones reported in previous studies. D-type newly developed in this experiment is mainly different with the old ones in its heat exchange area and tube thickness. But airflow direction(U-turn) and pipe arrangement are similar with previous three types. The results are summarized as follows; 1. System performances in the aspect of heat recovery efficiency were estimated as 42.2% for A-type, 40.6% for B-type, 54.4% for C-type, and 69.2% for D-type. 2. There was not significant improvement of heat recovering efficiency between two different airflow directions inside the heat exchange system. But considering current technical conditions, straight air flow pattern has more advantage than hair-pin How pattern (U-turn f1ow). 3. The main factors influencing on heat recovery efficiency were presumably verified to be the total area of heat exchange surface, the thickness of ail-flow pipes, and the convective heat transfer coefficient influenced by airflow velocity under the conditions of allowable pipe durability and safety. 4. Desirable blower capacity for each type of heat recovery units were significantly different to each other. Therefore, the optimum airflow capacity should be determined by considering in economic aspect of electricity required together with the optimum heat recovery performance of given heat recovery systems.

• Journal of Soil and Groundwater Environment
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• v.22 no.5
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• pp.23-29
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• 2017

This study was conducted to evaluate performance of geothermal heat exchanger (GHE) in the combined well and open-closed loops geothermal (CWG) systems. The CWG systems were designed to combine open loop geothermal heat pumps and closed loop geothermal heat pumps for high energy efficiency. GHE of the CWG systems could be installed at pumping wells for agricultural usage. To get optimal heat exchange capacity of GHE of the CWG systems, 4 GHEs with various materials and apertures were tested at laboratory scale. Polyethylene (PE) and stainless steel (STS) were selected as GHE materials. The maximum heat exchange capacity of GHEs were estimated to be in the range of 33.0~104 kcal/min. The heat exchange capacity of STS GHEs was 2.4~3.2 times higher than that of PE GHE. The optimal cross section area of GHE and flow rate of circulating water of GHE were estimated to be $2,500mm^2$ and 113 L/min, respectively. For more complicated GHE of the CWG systems, it is necessary to evaluate GHEs at various scales.

• Journal of Biosystems Engineering
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• v.26 no.5
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• pp.441-448
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• 2001

Hot air heater with light oil combustion is used as the most common heater for greenhouse heating in the winter season. However, exhaust gas heat discharged to atmosphere through chimney reaches up to 10~20% of total heat capacity of the oil burred. In order to recover the heat of this exhaust gas and to use for greenhouse heating, the heat pipe type exhaust heat recovery system was manufactured and tested in this experiment. The system consisted of a heat exchanger made of heat pipes, ø15.88${\times}$600mm located in the rectangular box of 675(L)${\times}$425(W)${\times}$370(H)mm, an air suction fan and air ducts. The number of heat pipe was 60, calculated considering the heat exchange amount between exhaust gas and air and heat transfer capacity of a heat pipe. The working fluid of heat pipe was acetone because acetone is known for its excellent heat transfer capacity. The system was attached to the exhaust gas path. According to the performance test it could recover 53,809 to 74,613kJ/h depending on the inlet air temperature of 12 to -12˚at air flow rate of 1.100㎥/h. The temperature of the exhaust gas left the heat exchanger dropped to 100$^{\circ}C$ from 270$^{\circ}C$ after the heat exchange between the suction air and the exhaust gas.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.15 no.4
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• pp.46-54
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• 2019

In this study, the performance of a shell and tube heat exchanger (STHE) and welded plate heat exchanger (WPHE) was measured experimentally. The pass numbers of the STHE was changed by 1, 2 and 4. As a result, the WPHE showed 2.1 times higher heat exchange capacity than that of the STHE. In case of pressure drop, the STHE with 1 and 2 pass number has a lower pressure drop than the WPHE, while the STHE with 4 pass presented higher pressure drop than the WPHE. The performance index considering the heat exchange capacity and pump consumption power, showed in oder of STHE_Pass1 > STHE_Pass2 > W PHE > STHE_Pass4 under the same flow rate. Therefore, when the WPHE was designed optimally under same operating condition with STHE, the maintenance fee and space can be reduced effectively by using the WPHE.

• Journal of Energy Engineering
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• v.10 no.4
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• pp.357-362
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• 2001

A bench type ammonia-water absorber heat exchange cycle was tested by varying the system charging concentration, refrigerating valve opening and weak solution flow rate. It was observed that the cooling capacity was increased as the system charging concentration was increased. Optimum system charging concentration was found for the coolong capacity of the system. The opening rate of refrigerant expansion valve had a direct influence on the refrigerant sub-cooling at the condenser outlet. Optimum sub-cooling was found to be 0~4$^{\circ}C$. As the weak solution flow rate increased the concentration of strong solution and the evaporating pressure decreased. There existed a optimum weak solution flow rate which maximized the cooling capacity and COP.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.477-480
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• 2007

Inlet fluid temperature of the BRE in the geothermal heat pump system depends on heat exchange rate between the refrigerant of the heat pump and the leaving fluid from the BRE. Because the outlet fluid temperature of the BHE varies with time, inlet fluid temperature has to vary with time. In this study, the module to calculate inlet fluid temperature is developed, which can consider the time-varying outlet fluid temperature and the heat exchange capacity of the heat pump. It is assumed that heat loss or gain of the leaving fluid from outlet to inlet of the BHE is negligible, except when the fluid contacts with the refrigerant of the heat pump. This module is combined with TOUGHREACT, a widely accepted three-dimensional numerical simulator for heat and water flow and geochemical reactions in geothermal systems and is applied to data analyses of the thermal response test.

• Journal of the Korean Ceramic Society
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• v.21 no.1
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• pp.41-50
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• 1984

The ion-exchange porous glasses were prepared by heat treating and subsequently acid treating the (95-y) $SiO_2$.$yB_2O_3$.$5Na_2O+xAl_2O_3$ glasses with y=55, 45, 35, 25. mole% and x=0, 2, 5, 9 mole% It was then investigated how the cation exchange capacity was affected by the phase separation in these glasses. For that matter such quantities as alkali extraction amount pore volume and specific surface area of the glasses were measured. The phase separation in these glasses was in general suppressed by the addition of $Al_2O_3$ maximally around the composition of 5 mole% $Al_2O_3$ This may be because the micro-phase separation prevailed in the glass of that composition over the macro-phase separation increasing thereby the specific surface area as well as the residual amount Al of after acid-treatment and accordingly the cation exchange capacity. The maximum values of the cation exchange capacity was observed to be about 150meq/100g for the glasses of (40-50) $SiO_2$ (55~45)$yB_2O_3$. $5Na_2O+5Al_2O_3$.