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조홍현(Honghyun Cho) 대한기계학회 2021 대한기계학회 춘추학술대회 Vol.2021 No.11
Recently, many plants use a lot of energy and various efforts are being made to reduce it. Techniques for reducing heat energy used in plants and improving heat transfer performance in the heat exchanger are being applied. Some methods for improving heat transfer in the heat exchanger including heat transfer improvement through changes in the structure and shape of the heat exchanger and improvement through enhancement of thermal properties of the working fluid. When the thermal properties of the working fluid are improved by using various ionic liquids, the performance of heat transfer can be improved. In this review, performance improvement technology using these ionic liquids is presented.
R1234yf와 R134a 냉매의 이젝터를 적용한 냉동사이클 성능에 대한 해석적 연구
조홍현(Honghyun Cho),박차식(Chasik Park) 대한설비공학회 2015 설비공학 논문집 Vol.27 No.7
This paper presents a numerical study on the performance of a vapor compression cycle equipped with an ejector as an expansion device to improve the COP by reducing the expansion loss and compressor work. The simulation is carried out using a model based on the conservation of mass, energy and momentum in the ejector. From the results of the simulation, the vapor compression cycle equipped with an ejector showed a maximum COP improvement of 14.0% when using R134a refrigerant and 16.8% when using R1234yf. In addition, the performance of the system with an ejector represents the increased performance as the temperature difference between condensing and evaporating increased.
이산화탄소 급탕 열펌프의 난방 성능에 관한 실험적 연구
조홍현(Honghyun Cho),조성욱(Sungwook Cho),백창현(Changhyun Baek),이응찬(Eungchan Lee),강훈(Hoon Kang),김용찬(Yongchan Kim) 대한설비공학회 2008 대한설비공학회 학술발표대회논문집 Vol.2008 No.2
In this study, experimental study on the heating performance of a CO₂ heat pump water heater with a variation of operating conditions such as refrigerant charge amount, outdoor temperature, compressor frequency, EEV opening and water mass flow rate. Based on the test results, the optimum charge amount was 1800 g. At the water mass flow rates of 75, 85, 95 ㎏/hr, the water heating temperature was 62, 67, 74℃ and COP was 2.6, 2.8, 3.0, respectively. Besides, the water mass flow rate and compressor frequency were varied to maintain above the water heating temperature of 60℃ with the decrease of outdoor temperature. So, The compressor frequency increased beyond 65 Hz and the water mass flow rate was 45 kg/hr at the outdoor temperature of -13℃, 65 ㎏/hr at -8℃, 75 ㎏/hr at -3℃ and 85 ㎏/hr at 2, 7℃. As the outdoor temperature decreased, the heating COP decreased by 2.5-39.8%.
이산화탄소를 적용한 상분리 사이클의 최적운전에 관한 실험적 연구
조홍현(Honghyun Cho),이호성(Hoseong Lee),김용찬(Yongchan Kim) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
The cooling performance of a transcritical CO₂ cycle can be significantly improved by using a multi-stage compressor because the CO₂ cycle has a large pressure difference. In this study, the performance of a phase-separate CO₂ cycle was measured and analyzed by varying the refrigerant charge amount, 1<SUP>st</SUP>-2<SUP>nd</SUP> EEV opening, and 1<SUP>st</SUP>-2<SUP>nd</SUP> compressor frequency. The cooling performance of the phase-separate CO₂ cycle was improved over 6.4% by optimizing the operating conditions, and the reliability of system increased significantly.
냉매 R1234yf 적용 자동차용 에어컨 Drop-in 성능 특성
조홍현(Honghyun Cho),이호성(Hoseong Lee),박차식(Chasik Park) 대한설비공학회 2012 설비공학 논문집 Vol.24 No.12
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℃ 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.
대체냉매 R1234yf를 적용한 자동차용 에어컨 시스템의 성능향상에 관한 연구
조홍현(Honghyun Cho),이호성(Hoseong Lee),박차식(Chasik Park) 대한설비공학회 2013 설비공학 논문집 Vol.25 No.4
The performance of automobile air conditioning systems of R1234yf was evaluated and compared with that of R134a. In particular, the performance evaluation was carried out by installing an internal heat exchanger in order to improve the performance of the system used in R1234yf. A performance comparison between the R1234yf and R134a for automotive air conditioning revealed that the cooling capacity and COP of the 1234yf system without the IHX decreased by up to 7% and 4.5%, respectively, but those with the IHX decreased by up to 1.8% and 2.9%, respectively.
이단압축을 이용한 이산화탄소 사이클의 냉방성능에 관한 연구
조홍현(Honghyun Cho),류창기(Changgi Ryu),김용찬(Yongchan Kim),조성욱(Sungwook Cho) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
To improve of the cooling performance of a CO₂ cycle, a CO₂ air-conditioner using two-stage compression cycle was tested with a variation of compressor frequency ratio. The cycle options include a basic cycle, a cycle with an intercooler, a cycle with an IHX(internal heat exchanger), and a cycle with an intercooler and IHX. The results show that the cycles with the intercooler, IHX, and intercooler and IHX improved the cooling performance significantly at all frequency ratios. The cycle with the intercooler, the cycle with the IHX and the cycle with the intercooler and IHX improved the cooling COP by 7, 12, and 15% over the basic CO₂ cycle.