• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.701-705
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• 2009

After revision of law of architecture in 2006, all houses which have more 100 households must has ventilation unit for the indoor air quality. Optimal design of the natural and the mechanical ventilation has being considered. In this paper, it is carried out about optimal design for airflow distribution of total heat exchanger in houses using CFD. As the result, first design of ventilation has some problem in porch area. Adding diffusers in porch area and changing diffuser schedule make more efficient ventilation than original design.

• Korean Chemical Engineering Research
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• v.59 no.1
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• pp.60-67
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• 2021

This study presented techno-economic analysis of a 500 MWe oxy-coal power plant with CO2 capture. The power plant included a circulating fluidized-bed (CFB), ultra-supercritical steam turbine, flue gas conditioning (FGC), air separation unit (ASU), and CO2 processing unit (CPU). The dry flue gas recirculation (FGR) was used to control the combustion temperature of CFB. One FGR heat exchanger, one heat exchanger for N2 stream exiting ASU, and a heat recovery from CPU compressor were considered to enhance heat efficiency. The decrease in the temperature difference (ΔT) of the FGR heat exchanger that means the increase in heat recovery from flue gas enhanced the electricity and exergy efficiencies. The annual cost including the FGR heat exchanger and FGC cooling water was minimized at ΔT = 10 ℃, where the electricity efficiency, total capital cost, total production cost, and return on investment were 39%, 1371 M$, 90 M$, and 7%/y, respectively.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.349-354
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• 1991

The power output behavior of the binary cycle composed of two Carnot cycles is analyzed with considering heat transfer processes, in which the finitely constant temperature differences between heat sources and working fluids exists. The power output has the maximum value as an extremum for cycle temperatures and capacities of heat exchangers. In the internally reversible cycle, the power output is independent of the cycle temperature in the intermediate heat exchanger. In this case when the total capacities of heat exchangers are given, three heat exchangers have the same capacities at the maximum power output condition. In addition, when the cycle is not extremum for cycle temperatures and capacities of heat exchangers. At the maximum power output condition, the capacity of heat exchanger at the cold side is slightly more than the hot side as the cycle effectiveness decreases.

• Solar Energy
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• v.10 no.1
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• pp.14-21
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• 1990

The entropy generation rate in a fin-tube heat exchanger is investigated as a basis for thermodynamic optimization associated with single fin-tube heat exchanger. The entropy generation (irreversibility)analysis is used to find the optimum design factor and investigate total entropy generation, optimum dimensions of fin length, tube inner and outer diameters, and fin spacing on the variation of design factors. The results of this study are as follows: As the outer diameter increases, optimum !in spacing and fin length increase but the entropy generation and optimum inner diameter decrease; As fin thickness increases, the entropy generation of system and optimum fin spacing increase; As fin length increases, entropy generation and optimum outer diameter increase.

• 연구논문집
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• s.29
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• pp.5-15
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• 1999

Present study deals with performance analysis of an inert gas generator (IGG) which is to be used as an effective mean to suppress the fire. The IGG uses a turbo jet cycle gas turbine engine to generate inert gas for fire extinguishing. It is generally known that a lesser degree of oxygen content in the product of combustion will increase the effectiveness of fire suppressing. An inert gas generator system with water injection will bring advantages of suffocating and cooling effects which are considered as vital factors for fire extinguishing. As the inert gas is injected to the burning site, it lowers the oxygen content of the air surrounding the flame as well as reduces the temperature around the fire as the vapour in the inert gas evaporates during the time of spreading. Some important aspects of influencing parameters, such as, air excess coefficient. $\alpha$, compressor pressure ratio, $ pi_c$, air temperature before combustion chamber, $T_2$, gas temperature after combustion chamber, $T_3$, mass flow rate of water injection, $M_w$, etc., on the performance of IGG system are investigated. Calculations of total amount of water needed to reduce the turbine exit temperature to pre-set nozzle exit temperature employing a heat exchanger were made to compare the economics of the system. A heat exchanger with two step cooling by water and steam is considered to be better than water cooling only. Computer programs were developed to perform the cycle analysis of the IGG system and heat exchanger considered in the present study.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.8
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• pp.1001-1008
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• 2011

This paper describes an analysis on performance and exergy of R744-R404A cascade refrigeration system with internal heat exchanger to optimize the design for the operating parameters of this system. The operating parameters considered in this study include subcooling and superheating degree, internal heat exchanger and compression efficiency, evaporation and condensation temperature in the R744 low- and R404A high- temperature cycle, respectively. The main results are summarized as follows : As the evaporation temperature of cascade heat exchanger increases, the COP of R404A high-temperature cycle increases. But the COP of R744 low-temperature cycle decreases, and the COP of total cascade cycle is almost constant. As cascade evaporation temperature increase, the exergy loss in the R404A condenser and the R744 internal heat exchanger is the largest and the lowest among all components, respectively. Therefore, the exergy loss in the condenser and compressor of R404A must be decreased to enhance the COP of R744-R404A cascade refrigeration system.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.11
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• pp.2196-2202
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• 1992

The optimum size combination of heat exchangers in a Joule-Thomson(J-T) circuit for small cryogenic systems has been sought analytically, when the circuit is combined with a two-stage Gifford-McMahon(GM) cooler. Full thermodynamic cycle analysis was carried out to predict the performance of the combined refrigeration system. Relevant convective heat transfer coefficients, the computerized properties of helium, and the refrigeration capacity curve of a typical GM cooler have been used in the analysis. The result showed that, by changing the configuration(heat exchanger area ratio) of the system, the performance of the commonly-used GM/J-T refrigerators could be optimized. For the maximum refrigeration performance, the optimum mass flow rate of the refrigerant and the relative size between the heat exchangers have been obtained, when the cooling load was 0.1W at 3.995K with the total heat exchanger area being given.

• Journal of the Korean Society for Geothermal and Hydrothermal Energy
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• v.12 no.4
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• pp.27-32
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• 2016

It is estimated that only heating and cooling take about one third of the total energy consumption worldwide. However, the conventional heating and cooling systems have low efficiencies. Also, boilers and electric heaters that are mostly used to generate both domestic and industrial hot water are inefficient and high energy consumers. For this reason, cascade heat pumps which are known to be very energy efficient and have less environmental impact are being promoted to replace conventional heating, cooling and hot water systems. In this study, a newly designed cascade heat pump by two-stage water heating method has been experimentally investigated. By adopting the auxiliary heat exchanger, the performance of the system was increased. The performance enhancement rate of the system could be maximized by adjusting the low stage compressor speed rather than the high stage compressor speed. The performance of the system with the auxiliary heat exchanger was enhanced by 16.5%.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.26 no.11
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• pp.504-511
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• 2014

The objective of this study is to theoretically analyze the performance of an open wet air-cycle refrigeration system, which nowadays is increasingly generating environmental concern. The temperature and relative humidity of the outside air are selected as the most important parameters. As the temperature and relative humidity of the outside air increase, the pressure ratio of the ACM compressor is determined to be nearly constant, the air temperature at the exit of the system increases, and the amount of condensed water, the cooling capacity, the COP, and the total entropy production rate increase overall. The effects of the effectiveness of the heat exchanger and the efficiency of the turbine on the performance are greater than that of the efficiency of the ACM compressor. Also, the performance of the wet air-cycle refrigeration system with two heat exchangers is enhanced, with a high COP and low total entropy production rate, compared to the system with a single heat exchanger.

• 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.