• Proceedings of the SAREK Conference
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• 2007.11a
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• pp.358-363
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• 2007

In this study, experimental study on the heating performance of a $CO_2$ heat pump with gas injection was performed varying gas injection ratio and outdoor temperature to improve the heating performance of $CO_2$ heat pump. The twin rotary compressor having volume ratio of 0.7 was adopted in the $CO_2$ heat pump. From the test results, the heating capacity and COP were increased and the compressor discharge temperature was decreased with the increase of injection ratio. At the outdoor temperature of $-8^{\circ}C$, the heating capacity and COP with the injection were increased by 45% and 24%, respectively, compared with non-injection condition.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.5
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• pp.249-258
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• 2017

This paper provides an economic analysis of a new geothermal heat pump system that reuses condenser waste heat from a Ground Source Heat Pump ($GSHP_{ch}$) to provide energy for a hot water Ground Source heat pump ($GSHP_{hw}$). After conducting feasibility tests using GLD and TRNSYS simulations, the proposed system was effectively installed and thoroughly tested. We observe that 1) the Coefficient of Performance (COP) of the $GSHP_{hw}$ and the $GSHP_{ch}$ during cooling mode improves by up to 62% and 7%, respectively; 2) the number of bore holes can be reduced by two; and 3) the hot water supply temperature of the $GSHP_{hw}$ increases by up to $60^{\circ}C$. We further conclude that 1) the reduction of two bore holes can save approximately ten million Won from the initial cost investment; and 2) the increased COP of the $GSHP_{hw}$ can save approximately one million Won in annual electricity costs.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.24 no.12
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• pp.823-829
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• 2012

In this study, the performance of mobile air conditioner(MAC) systems to which the refrigerants R134a and R1234yf were used was evaluated to compare the characteristic of automotive refrigeration cycles with refrigerant. The experimental setup of a MAC consists of an belt driven compressor, a condenser, an evaporator and a block type thermal expansion valve. The drop-in test on MAC were carried out under variable compressor speed from 800 to 2500 rpm. Performance test by using R1234yf and R134a in the same system revealed low the charge amount and mass flow rates for using R1234yf, that is, up to 10% and 17%, respectively. The compressor discharge temperature of R1234yf is $8^{\circ}C$ lower than that of R134a. The cooling capacity with R1234yf system decreased by 4~7% compared with R134a system. In addition, The COP of R1234yf system is lower 3~4% than that of R134a system.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.1
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• pp.55-62
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• 2009

Relatively low cycle performance of a conventional $CO_2$ system is partly due to significant increase in friction loss in the expansion process, since the pressure drop across the expansion device is considerably large compared to a conventional refrigeration cycle. To recover friction loss and increase refrigeration effect by providing isentropic expansion, a rotary vane type expander has been designed. Performance of the designed expander has been investigated by numerical simulation. With the pressure condition of 9 MPa/4.5 MPa and inlet temperature of $35^{\circ}C$, volumetric, isentropic, and mechanical efficiencies of the expander are calculated to be 58.1%, 101.1%, and 78.8%, respectively, resulting in total expander efficiency of 46.3%. With this expander, COP of a $CO_2$ refrigeration cycle is estimated to be improved by about 14%.

• Proceedings of the KIEE Conference
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• summer
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• pp.1281-1284
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• 2004

본 논문에서는 백라이트로 사용되는 CCFL의 점등을 위한 인버터를 연구대상으로 하였다. CCFL의 고전압 점등을 위해 다층 longitudinal 모드구조의 압전세라믹을 이용하였다. CCFL의 점등은 공진특성을 이용하는 것이므로 기계적인 공진주파수와 스위칭 주파수가 거의 일치할 수 있도록 L-C공진회로를 설계하였다. 인버터의 토플로지는 플라이백 기법을 적용하였으며 이를 위해서 권선의 배치에 의해 손실을 고려한 고주파 트랜스포머를 설계하였다. 시뮬레이션 및 실험 결과를 통하여 이에 대한 타당성을 입증하였다. 이로부터 공진주파수 48[kHz], 점등전압 600[V] 및 점등전류 6[mA] 얻었으며, 적용된 CCFL 램프사양은 관직경 $2.2{\phi}$와 관길이 314[mm], 압전세라믹 $43{\times}5.5{\times}2.3[mm]$를 이용하였다.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.42 no.4
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• pp.259-266
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• 2006

In this study, the 2-way condensation system was designed applying air-to-air heat pump to dry a marine product such as squid in the winter. And to be made the drying apparatuses by this system, there are two kinds of type, A type, was set a compressor outside of the drying apparatus, B type, was set a compressor in the drying room. And then the variations of temperature in drying room were measured to compare the heating performance of the drying apparatuses between A type and B type at $-6.5^{\circ}C$, outdoor temperature. The temperature of the drying room for B type was increased to $36^{\circ}C$ but the temperature of the drying room for A type was not increased to $36^{\circ}C$, to be increased to $20^{\circ}C$.

• Proceedings of the KIEE Conference
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• 2005.07c
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• pp.2175-2178
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• 2005

During normal machine operation, partial discharge(PD) measurements were performed with turbine generator analyzer(TGA) in five high voltage motors(rated 6.6kV). These high voltage motors were installed with 80pF capacitive couplers at the terminal box. The PD patterns were displayed two dimensional and three dimensional. TGA summarizes each plot with two quantities such as the normalized quantity number(NQN) and the peak PD magnitude(Qm). Off-line PD measurements were conducted on five motors. These motors were energized to 3.81kV. The PD levels in pC were measured with a conventional digital PD detector. The comparison of positive to negative PD indicates whether the defect elements of PD are within the insulation or on the insulation surface. Internal discharges were generated in phase A, B and C of COP-B and pulv.-B, in phase B of Pulv. C and in phase C of Pulv.-D motor. Discharge at conductor surface was discovered in phase A of Pulv. D motor. Slot discharges occurred in three phases of Pulv. E motor.

• International Journal of Air-Conditioning and Refrigeration
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• v.16 no.2
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• pp.44-50
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• 2008

This study presents test results of a mobile air-conditioning system using a potential alternative refrigerant, R152a. A series of performance tests have been carried out and cycle characteristics such as cooling capacity, energy efficiency ratio, suction and discharge pressures, and temperatures are presented, compared to those for the baseline R134a system. Tests were conducted with evaporation temperature of $5^{\circ}C$, condensation temperature of $45^{\circ}C$, subcooling temperature of $5^{\circ}C$, superheating temperature of $5^{\circ}C$, and compressor speed of 500-1500 rpm. The performance of R152a system with readjustment of an expansion valve showed better than those of R134a. The effect of oil on the pressure drop in the evaporator was also addressed.

• Journal of the Korean Association of Oral and Maxillofacial Surgeons
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• v.43 no.5
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• pp.305-311
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• 2017

Objectives: TNM staging, especially for lymph node metastasis, is the scoring system most widely used among prognostic factors for cancer survival. Several biomarkers have been studied as serologic markers, but their specificity is low and clinical applications are difficult. This study aimed to establish a scoring system for patients with oral squamous cell carcinoma (OSCC) using platelet (PLT) and mean platelet volume (MPV) levels measured postoperatively and to evaluate their significance as prognostic factors. Materials and Methods: We studied 40 patients admitted to the Department of Oral and Maxillofacial Surgery of Dankook University Hospital who were diagnosed with primary OSCC histopathologically between May 2006 and May 2012. Clinical pathological information obtained from the medical records of each patient included age, sex, height, weight, tumor location, degree of differentiation, tumor diameter, lymph node metastasis, TNM stage, and other test values including white blood cell, MPV, PLT, C-reactive protein (CRP), and albumin obtained through a test conducted within 7 days before surgery. Count of platelet (COP)-MPV Score: Patients with both PLT and MPV values below the cut-off values were defined as score 0 (group A). Patients with at least one of the two higher than the cut-off value were defined as score 1 (group B). Results: Univariate analyses showed N-metastasis, COP-MPV (A vs B), PLT, platelet-lymphocyte ratio, and CRP were statistically significant prognostic factors. A multivariate Cox proportional hazards model showed N-metastasis (hazard ratio [HR] 6.227, P=0.016) and COP-MPV (A vs B) (HR 18.992, P=0.013) were independent prognostic factors with a significant effect on survival. Conclusion: COP-MPV score is a simple and cost-effective test method and is considered a more effective prognostic factor than other considered factors in predicting the prognosis of OSCC patients.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.4
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• pp.324-331
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• 2013

All evacuated tube collector is being constantly studied since it can reduce the conductive heat loss in absorber by using vacuum technology and has advantage of heat transport capacity and quick thermal response in comparatively small temperature difference. This study investigated the dynamic thermal performance of the solar collector with the control condition of solar irradiance and fluid temperature by using performance experimental apparatus which is combined with solar collector and refrigerator, examined the thermal characteristics in definite temperature range of fluid in constant temperature tank by simultaneously measuring refrigerating performance. As a result of it, I deducted the related equation of collector efficiency and found that mean collector efficiency has increased through quick heat transfer characteristics according to increase of outdoor temperature and irradiance in case of outlet temperature of constant temperature tank $22^{\circ}C$ when set outlet temperature of solar collector $25^{\circ}C$ with outlet temperature of constant temperature tank $18^{\circ}C$ & $22^{\circ}C$. Also COP of refrigerator was acquired value of 6.2~7.1 at outlet temperature of constant temperature tank $18^{\circ}C$.