• The KSFM Journal of Fluid Machinery
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• v.18 no.3
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• pp.12-19
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• 2015

As a means of improving cycle performance of a R410A air-conditioning system, a combined structure of compressor and expander was introduced. A vane rotary type expander was designed to share a common shaft with twin type rolling piston rotary compressor in a housing. Numerical simulation on the performance of the combined compressor and expander was carried out. At ARI condition, the volumetric and total efficiencies of the designed vane expander were 69.37% and 30.23%, respectively. With the application of this expander, the compressor input was reduced by 3.91%, and the cooling capacity was increased by 3.98%. As a result, COP of the air-conditioning system was improved by 8.2%. As the pressure difference between the condenser and the evaporator becomes large, COP improvement increases unless the mass flow rate in the expander exceeds that in the compressor.

• Journal of Energy Engineering
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• v.13 no.3
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• pp.214-218
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• 2004

In the present study, the variation of input power and efficiency improvement of a scroll compressor applying PWM method are experimentally investigated. The cooling capacity, input power and COP are measured under the cooling operation. The input power due to the change of the condenser and the coil addition in a main current part is measured to enhance the compressor efficiency. Measured results show that the input power and COP increase with increasing the tooling capacity. And the minimum input power of the compressor is observed. By the adoption of the double system, the consumption of compressor input power is reduced, compared with the existing system.

• 한국신재생에너지학회:학술대회논문집
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• 2008.05a
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• pp.626-629
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• 2008

In this study, a geothermal power generation system using the Kalina cycle was investigated by the simulation method. The Kalina cycle system can be used for the utilization of a low-temperature heat sources such as geothermal and industrial waste heat that are not hot enough to produce steam. The sea/river water can be considered as a cooling media. A steady-state simulation model was developed to analyze and optimize its performance. The model contains a turbine, a pump, an expansion valve and heat exchangers. The turbine and pump were modelled by an isentropic efficiency, while a condenser, an evaporator and a regenerative heat exchanger were modeled by UA-LMTD method with a counter-flow assumption. The effect of the ammonia fraction at the separator inlet on the cycle performance is investigated in detail.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.8
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• pp.567-572
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• 2010

Air shift type heat pump is combined heat recovery ventilator and refrigerator, and it is installed an air shifter changing air flow. And so it is an perfect AHU(Air Handling Unit) capable to cooling, heating, ventilation and heat recovery. Therefore, an experimental study has been carried out to investigate the operating performance in winter for this system. An experimental data are room temperature, inlet/outlet temperature of condenser, evaporator and heat exchanger. They have been measured as the variation of outdoor temperature. The results, in case of rising above freezing, the air shift type heat pump system is operated normally, and the heating COP is 3.0~4.2 by varying outdoor temperature from $-3^{\circ}C$ to $15^{\circ}C$.

• Proceedings of the IEEK Conference
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• 2001.06e
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• pp.215-218
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• 2001

A pulsed Nd:YAG laser is used widely for materials processing and medical instrument. It's very important to control the laser energy density in those fields using a pulsed Nd:YAG laser. A pulse repetition rate and a pulse width are regarded as the most dominant factors to control the energy density of laser beam. In this paper, the alternating charge and discharge system was designed to adjust a pulse repetition rate. This system is controlled by microprocessor and allows to frequence an expensive condenser for high frequency to cheap one for low frequency. In addtion, The microcontroller monitors the flow of cooling water, short circuit, and miss firing and so on. We designed Nd:YAG laser firmware with smart microcontroller, and want to explain general matters about the firmware from now.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.5
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• pp.431-438
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• 2000

The major irreversibilities in absorption chillers are associated with the transfer of heat into and out from the machine and irreversible process inside the machine. By modeling only external irreversibilities(endo-reversible), a model was formulated to predict the ideal performance of a single-effect absorption chiller. Its actual performance including both external and internal irreversibilities was calculated with a in-house simulation program. The optimization of heat transfer area distribution was performed for both endo-reversible cycle and actual cycle. The equation of endo-reversible modeling was found to give about 2times higher cooling capacity than the simulation program. At optimal distribution, it was found that heat transfer area of the evaporator was about 30% of total area, that of the generator was 20%, and the rest 50% was for the absorber and condenser. The system COP for endo-reversible cycle was slightly higher than that for actual cycle. In the case of LiBr-water single-effect absorption chiller, the maximum cooling capacity was obtained near the condition that LMTD is same at all heat exchangers.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.6
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• pp.369-374
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• 2010

A refrigerant-subcooling refrigeration system consisted of a typical single vapor-compression refrigeration cycle, a subcooler, and an ice storage tank. The degree of subcooling at the exit of the condenser can be increased by the heat exchange between the subcooler and the ice storage tank. The cold heat in the ice storage tank was stored by using the refrigeration cycle during night time and then used to absorb the heat from the subcooler during daytime. The performance of the refrigerant-subcooling refrigeration system was measured by varying the degree of subcooling. In addition, the performance characteristics of the present system were compared with those of a conventional refrigeration system. The mass flow rate of the present system was higher than that of the conventional system due to the increase in the degree of subcooling. Generally, the refrigerant-subcooling system showed superior performance to the conventional refrigeration system.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.54 no.2
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• pp.94-100
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• 2005

Korea Electrotechnology Research Institute(KERI) has successfully developed a 100hp-1800rpm-class high temperature superconducting(HTS) motor with high efficiency under partnership with Doosan Heavy Industries & Construction Co. Ltd. This motor has a HTS field winding and an air-cooled stator. The advantages of HTS motor can be represented by a reduction of 50% in both losses and size compared to conventional motors of the same rating. The cooling system is based on the heat transfer mechanism of the thermosyphon by using GM cryocooler as cooling source. The cold head is in contact with the condenser of a Ne-filled thermosyphon. Independently, the rotor assembly was tested at the stationary state and combined with stator. The HTS field winding could be cooled into below 30K. Test of open-circuit characteristics(OCC) and short-circuit characteristics(SCC) and load test with resistive load bank were conducted in generator mode. Also, load tests in motor mode driven by inverter were finished at KERI. Maximum operating current of field winding at 30K was 120A. From OCC and SCC test results synchronous inductance and synchronous reactance were 2.4mH, 0.49pu, respectively. Efficiency of this HTS machine was 93.3% in full load(100hp) test. This paper will present design, construction. and experimental test results of the 100hp HTS machine.

• The Journal of the Acoustical Society of Korea
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• v.14 no.6
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• pp.13-20
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• 1995

In this paper, the thermoacoustic refrigerating system was implemented and its operation was experimentally verified. The system is composed of several parts ,4 inch midrange speaker, speaker housing, chamber, stack housing, stack of plates, heat exchangers, thin pipe and cavity. The system is filled with He gas at 10 bar and contains T-type thermocouples and condenser microphone for measuring the temperature and pressure inside, respectively. In addition, cooling water is used for protecting speaker from thermal destruction and cooling down the hot heat exchanger. For the experimental verification of the implemented refigerating system, electrical impedance and resonance characteristics were measured. The results showed that it was most efficient to drive the system at 340 Hz. When operated at 340 Hz, $30^\circ{C}$ environments and 50 electical watts, the temperature of the cold region decreased by $16^\circ{C}$. The dissatisfaction mainly comes from the incomplete thermal insulation of the cold region. We also pointed out some guidelines to improve the performance for later study.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.6
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• pp.337-344
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• 2010

Good plant-growth conditions can be achieved by means of using greenhouses. One of the main issues in greenhouse cultivation is energy savings through the development of high efficient heating and cooling system. GSHPs are one of the recommended systems to cope with this pending need. The aim of this study is to investigate the heating performance of ground source multi-heat pump system installed in a greenhouse under part load conditions. Daily average heating COP of the heat pump unit was very high by at least 7.4, because of relatively large condenser, evaporator, and mass flow rate through ground loop heat exchanger. However, the system COP, overall heating coefficient of the performance of the system with heat pump unit and GLHX, decreased drastically due to relatively large power consumption of circulating pump under part load condition. It is suggested that the technology to enhance the performance of the ground source multi-heat pump system for a greenhouse under part load conditions should be developed.