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평판과 Turbo-B 표면에서 HFC32/HFC152a 혼합냉매의 풀 비등 열전달계수
강동규(Dong-Gyu Kang),장철한(Cheol Han Jang),최현주(H.J.Choi),이요한(Yohan Lee),정동수(Dongsoo Jung) 한국해양환경·에너지학회 2012 한국해양환경공학회 학술대회논문집 Vol.2012 No.11
Nucleate pool boiling heat transfer coefficients(HTCs) were measured with HFC32/HFC152a mixture. All data were taken at the liquid pool temperature of 7℃ on a various horizontal surface with heat fluxes of 10 ㎾/㎡ to 100 ㎾/㎡ with an interval of 10 ㎾/㎡ in the increasing order of heat flux. A smooth flat surface and Turbo-B surfaces are used to examine the effect of composition on pool boiling heat transfer coefficients (HTCs). HTCs are measured on a smooth square heater of 9.53 ㎜ × 9.53 ㎜ in a pool of the HFC32/HFC152a mixture. Test results on a smooth flat surface and Turbo-B surfaces showed a reduction of HTCs as much as 45%, 36%, 58% and 57% at 100 ㎾/㎡ from the ideal values on each surface. The reduction of Turbo-B surface in heat transfer were greater than a smooth flat surface.
수열원 히트펌프 용 HFC32/HFC152a 혼합냉매의 성능평가
강동규(Dong gyu Kang),김욱진(Wook-Jin Kim),정동수(Dongsoo Jung) 대한설비공학회 2012 설비공학 논문집 Vol.24 No.5
In this study, performance of HFC32/HFC152a mixture is measured in the composition range of 20 to 50% R32 with an interval of 10% for the comparison with the conventional HCFC22 in water-source heat pumps. Tests are carried out under the same capacity in a heat pump bench tester equipped with a variable speed compressor at the evaporation and condensation temperatures of 7/45℃ and -7/41℃ for summer and winter conditions, respectively. Test results show that the compressor power of the HFC32/HFC152a mixture is 13.7% lower than that of HCFC22 while the coefficient of performance(COP) the HFC32/HFC152a mixture is 15.8% higher than that of HCFC22. Hence, from the view point of energy efficiency, the HFC32/HFC152a mixture is excellent as compared to HCFC22. Compressor discharge temperatures of HFC32/HFC152a mixture are increased up to 15.4℃ as compared to that of HCFC22. The amount of charge for HFC32/HFC152 mixture decrease up to 27% as compared to that of HCFC22. Overall, HFC32/HFC152a mixture is an excellent long term candidate to replace HCFC22 in water-source heat pumps.
평판과 촉진관 표면에서 물의 유동 속도에 따른 풀 비등열전달 향상에 관한 실험 연구
강동규(Dong Gyu Kang),이요한(Yohan Lee),박기정(Ki-Jung Park),정동수(Dongsoo Jung) 대한설비공학회 2011 대한설비공학회 학술발표대회논문집 Vol.2011 No.7
In this study, pool boiling heat transfer coefficients (HTCs) and critical heat fluxes (CHFs) are measured on a smooth square flat copper heater of 9.53 x 9.53 ㎜ at 6 0℃ in a pool of pure water. For flat heater experiments, a smooth flat surface and 26 fpi low fin are used to see the change in HTCs and CHFs according to the surface characteristics. HTCs are taken from 10 ㎾/㎡ to critical heat flux for all surfaces. Test results with low-fin surface showed that CHFs are greatly improved, as compared to that of a plain surface as various fluid velocities, 0.00, 0.10, 0.15, 0.20 ㎧, in pure water. The HTCs of tested each surfaces are increased over 5% up to 112% as fluid velocities at 0.10, 0.15, 0.20 ㎧ as compared to that of stoped water. Judging from these results, it can be said that low-fin tube with the variation of flow velocity of water can be used in heat transfer applications at high heat fluxes.
평판 표면에서 HFC32/HFC152a 혼합냉매의 풀 비등 열전달계수
강동규(Dong-Gyu Kang),이요한(Yohan Lee),정동수(Dongsoo Jung) 대한설비공학회 2013 설비공학 논문집 Vol.25 No.9
Nucleate pool boiling heat transfer coefficients (HTCs) are measured with HFC32/HFC152a mixture at several compositions. All data are taken at the liquid pool temperature of 7°C, on a horizontal plain square surface of 9.53×9.53mm, with heat fluxes of 10 kW/㎡ to 100 kW/㎡ with an interval of 10 kW/㎡, in the increasing order of heat flux. Test results show that the HTCs of these mixtures are up to 45% lower than those of the ideal HTCs calculated by a linear mixing rule with pure fluids’ HTCs, due to the mass transfer resistance associated with non-azeotropic refrigerant mixtures. Pool boiling data show the deduction in HTCs with an increase in GTD of the mixture. The present mixture data agree well with five well known correlations, within 20% deviation.
다양한 표면에서 유동 속도에 따른 풀 비등 열전달에 관한 연구
강동규(Dong-gyu Kang),이요한(Yohan Lee),서훈(Hoon Seo),정동수(Dongsoo Jung) 대한기계학회 2013 大韓機械學會論文集B Vol.37 No.4
본 연구에서는 열전달 표면의 형상과 그 위에서의 유동 속도의 변화에 따른 풀 비등 열전달계수의 변화를 살펴보기 위해 평판, 낮은 핀, Thermoexcel-E, Turbo-B 표면을 사용하여 유동 속도를 변화시켜가며 임계 열유속까지 열전달계수를 측정하였다. 작동 유체로는 증류수를 사용하였고 사각 평면 히터(9.53 x 9.53mm)를 이용하여 네 가지 표면에서 임계 열유속까지의 데이터를 얻을 수 있도록 장치를 제작하였고 60 에서 유동 속도를 0, 0.1, 0.15, 0.2m/s로 변화시켜가며 데이터를 취했다. 실험 데이터를 보면 모든 표면에서 유동이 있을 때의 임계 열유속은 유동이 없을 때에 비해 높은 것으로 나타났다. 또한 표면적의 증가와 기포 이탈에 충분한 핀 간격 등으로 인해 낮은 핀 표면의 임계 열유속은 평판이나 Turbo-B, Thermoexcel-E 표면보다 훨씬 놓았고 평판에 비해서는 무려 5배 정도의 향상을 보였다. 한편 대형 냉동기의 증발기용으로 개발된 Turbo-B와 Thermoexcel-E 표면은 물에서 기포의 이탈 지름이 크므로 열전달계수와 임계 열유속 모두 예상보다 큰 효과를 나타내지 않았다. 50kW/m2이하의 저열유속에서는 모든 표면에 대해 유동 속도 증가에 따라 열전달계수가 증가하였다. 결론적으로 핵발전소의 증기발생기에 적용하기에는 낮은 핀 형상의 표면이 가장 좋은 것으로 나타났다. In this study, a smooth flat surface, low fin, Turbo-B, and Thermoexcel-E surfaces are used to examine the effect of the flow velocity on the pool boiling heat transfer coefficients (HTCs) and critical heat fluxes (CHFs). HTCs and CHFs are measured on a smooth square heater of 9.53 × 9.53 mm2 at 60°C in a pool of pure water at various fluid velocities of 0, 0.1, 0.15, and 0.2 m/s. Test results show that for all surfaces, CHFs obtained with flow are higher than those obtained without flow. CHFs of the low fin surface are higher than those of the Turbo-B and Thermoexcel-E surfaces due largely to the increase in surface area and sufficient fin spaces for the easy removal of bubbles. CHFs of the low fin surface show even 5 times higher CHFs as compared to the plain surface. On the other hand, both Turbo-B and Thermoexcel-E surfaces do not show satisfactory results because their pore sizes are too small and water bubbles easily cover them. At low heat fluxes of less than 50 kW/m2, HTCs increase as the flow velocity increases for all surfaces. In conclusion, a low fin geometry is good for application to steam generators in nuclear power plants.
이요한(Lee, Yo-Ha),강동규(Kang, Dong-Gyu),최현주(CHOI, Hyun-Joo),정동수(Jung, Dong-So) 한국태양에너지학회 2013 한국태양에너지학회 논문집 Vol.33 No.1
In this study, thermodynamic performance of R435A is examined both numerically and experimentally in an effort to replace HFC 134a used in the refrigeration system of domestic water purifiers. Even though HFC134a is used predominantly in such a system these days, it needs to be phased out in the near future in Europe and most of the developed countries due to its high global warming potential. To solve this problem, cycle simulation and experimental measurements are carried out with a new refrigerant mixture of 20%R152a/80%RE170 using actual domestic water purifiers. This mixture is numbered and listed as R435A by ASHRAE recently. Test results show that the system performance with R435A is greatly influenced by the amount of charge due to the small internal volume of the refrigeration system of the domestic water purifiers. With the optimum amount of charge of 21 to 22 grams, about 50% of HFC134a, the energy consumption of R435A is 11.8% lower than that of HFC134a. The compressor discharge temperature of R435A 8℃ lower than that of HFC134a at the optimum charge. Overall, R435A, a new long term environmentally safe refrigerant, is a good alternative for HFC134a requiring little change in the refrigeration system of the domestic water purifiers.
열전달 촉진 표면에서 임계 열유속까지의 물의 풀 비등 열전달계수
이요한(Yohan Lee),강동규(Kang Dong Gyu),정동수(Dongsoo Jung) 대한설비공학회 2011 설비공학 논문집 Vol.23 No.3
In this work, nucleate pool boiling heat transfer coefficients(HTCs) of pure water are measured on horizontal 26 fpi low fin, Turbo-B and Thermoexcel-E square surfaces of 9.53 ㎜ length. HTCs are taken from 10 ㎾/㎡ to critical heat flux for all surfaces. Test results show that critical heat fluxes(CHFs) of all enhanced surfaces are greatly improved as compared to that of a plain surface. CHFs of water on the 26 fpi low fin surface, Thermoexcel-E surface, and Turbo-B are increased up to 320%, 275%, and 150% as compared to that of the plain surface, respectively. CHF of the Turbo-B enhanced surface is lower than that of the 26 fpi low fin surface due to the surface geometry. The heat transfer enhancement ratios of the Thermoexcel-E surface, low fin surface and Turbo-B enhanced surface are 1.6~2.9, 1.6~2.1, 1.4~1.7 respectively in the range of heat fluxes tested. Judging from these results, it can be said that these types of enhanced surfaces can be used in heat transfer applications at high heat fluxes.
Low-fin 촉진 표면에서 임계 열유속까지의 분무 냉각 열전달 특성
이요한(Yohan Lee),강동규(Dong-Gyu Kang),정동수(Dongsoo Jung) 대한설비공학회 2013 설비공학 논문집 Vol.25 No.9
Spray cooling is a technology of increasing interest for electronic cooling and other high heat flux applications. In this study, heat transfer coefficients (HTCs) and critical heat fluxes (CHFs) were measured on a smooth square flat copper heater of 9.53×9.53 mm at 36℃ in a pool, with a smooth flat surface, and 26 fpi. Low-fin surfaces were used to see the change in HTCs and CHFs according to the surface characteristics, and FC-72 was used as the working fluid. FC-72 fluid had a significant influence on the heat transfer characteristics of the spray over the cooling surface. HTCs were taken from 10 kW/㎡ to critical heat flux, for all surfaces. Test results with Low-fin showed that the CHFs of all the enhanced surface were greatly improved. It can be said that the surface form affects the heat transfer coefficient and critical heat flux.