수평 평활관과 내면 핀관 열교환기내에서 자연냉매인 프로판의 응축 전열

오후규,박기원 麗水水産大學校 産業技術硏究所 1998 産業基術硏究所 論文集 Vol.7 No.-

Worldwide energy consumption has been recently increasing enormously, especially in refrigeration and air-conditioning industries. As a result of this increase, atmospheric hydrocarbon and other gas levels have increased so that they may be a source of world environmental problems. Therefore, new research was started to overcome the environmental problems, like the destruction of the ozone-layer and the warming of Earth's temperature, by the use of natural refrigerants as substitutes for the freon refrigerant. A basic heat pump system was designed and manufactured, in which a pair of inner grooved tube was constructed as main heat exchanger. New natural refrigerant R-290 was used. In this paper, condensation heat transfer characteristic was studied and a basic data base for the optimum design of refrigeration and air-conditioning system was obtained. The local condensation heat transfer coefficient was increased according to the increment of mass flow rate. Comparing the condensation heat transfer coefficient between the experimental result and simulation data of other's, the Cavallini-Zecchin's equation was revealed more closed correlation to author's experimental results in the bare tube as well as grooved inner one.

수평 2중관 열교환기내에서 R-22와 그 대체냉매의 응축 열전달 특성

오후규,박기원,문정욱,노건상,이상훈 麗水水産大學校産業技術硏究所 1997 産業基術硏究所 論文集 Vol.6 No.-

Compared experimental results for forced convection condensation of R-22 and its alternative refrigerants inside a horizontal smooth tube are presented. The pure refrigerant, azeotropic refrigerant mixtures and binary and ternary non-azeotropic refrigerant mixtures are used as the test fluids and a double pipe heat exchanger is used. The refrigerant mass flow rate and temperatures were measured. Using the data, the heat flux, quality and local and mean heat transfer coefficients for the condensation have been obtained. Local heat transfer coefficients for R-22 and its alternative refrigerants were measured at top, side and bottom of the test tube. The results indicated that the heat transfer coefficient of pure and azeotropic refrigerant mixtures was higher than at top of the tube. Non-azeotropic refrigerant mixtures, however, were higher than side and top of the tube. Mean heat transfer coefficients for non-azeotropic refrigerant mixtures increased with refrigerant mass velocity and quality, but were considerably lower that of pure refrigerant and azeotropic refrigerant mixtures.

직렬과 병렬방식 이중효용 흡수식 냉동사이클의 성능 시뮬레이션

이윤환,오종택,오후규,박기원 麗水水産大學校産業技術硏究所 1998 産業基術硏究所 論文集 Vol.7 No.-

Condensing the global environmental problems such as CFCs, energy losses in heat recovery systems as well as summer peak time power demands, the development of high efficiency absorption refrigeration systems is one of the most promising method in this problems. In this study, simulation models of both series and parallel type, both using double-effect absorption cycle refrigeration systems. The results summarized as follows : ⑴ In the parallel type, the solution maximum temperature and the pressure of high temperature generator were adjusted by varing the distribution ratio of the solution, and the optimum value was found to be about 0.4. ⑵ The efficiency of the cooling cycle in both parallel and series systems were increased by decreasing the solution circulation ratio in the absorbers, while the solution maximum temperature and high temperature generator pressure were slightly increased.

Study on the evaporation Heat Transfer Characteristics of R-134a in Small Diameter Tubes

Roh, Geon-Sang,Oh, Hoo-Kyu The Korean Society of Marine Engineering 2007 한국마린엔지니어링학회지 Vol.31 No.3

Large diameter tubes have been used until comparatively lately. However, small diameter tubes are largely used because of their high efficiency in heat transfer and low cost, recently. This study focuses on the experimental research of the heat transfer coefficients during evaporation process of R-22 and R-134a in small diameter tubes. The evaporation heat transfer coefficients were measured in smooth horizontal copper tubes with ID 1.77, 3.36 and 5.35 mm. The evaporation heat transfer coefficients in the small diameter tubes (ID <7 mm) were observed to be strongly affected by the size of tube diameters and to differ from those of general predictions in the large diameter tubes. The heat transfer coefficients of ID 1.77 mm copper tube were higher by 20 and 30 % than those of ID 3.36 mm, ID 5.35 mm copper tubes respectively. Also, it was found that it was very difficult to apply some well-known previous predictions (Shah's, Jung's. Kandlikar's and Oh-Katsuda's correlation) to small diameter tubes. Based on the data, the new correlation is proposed to predict the evaporation heat transfer coefficients of R-22 and R-134a in small diameter tubes.

수평 내면 핀관내에서 R-22와 대체 냉매의 증발 열전달 비교

노건상,박기원,정재천,오후규 여수대학교 1998 論文集 Vol.12 No.2

Worldwide energy consumption has been recently increasing enormously, especially in refrigeration and air conditioning industries. As a result of this increase, atmospheric hydrocarbon and other gas levels have increased so that they may be a source of world environmental problems. Therefore, new research was started to overcome the environmental problems, like the destruction of the ozone layer and the warming of Earth's temperature, by the use of natural refrigerants as substitutes for the freon refrigerant. In this paper, evaporation heat transfer of global heat pump using grooved inner tube was studied. New natural refrigerants R-290 and HCFC refrigerant R-22 were used. The local heat transfer coefficient was decreased according to the evaporation process. Moreover, the increment of heat transfer coefficient was found in R-290 refrigerant. Average heat transfer coefficient was obtained the higher value in R-290 refrigerant than R-22. Comparing the heat transfer coefficient between experimental result and simulation data of other's, the Shah's correlated equation was closely assimilated to the author's experimental results.

냉동ㆍ공조 장치에서 R-22와 자연냉매 R-290의 열전달과 사이클 특성

정재천,박기원,노건상,오후규 여수대학교 1998 論文集 Vol.12 No.2

A basic heat pump system was designed and manufactured, in which a pair of bare tube was constructed as main heat exchanger. New natural refrigerants R-290 and HCFC refrigerant R-22 were used. In this paper, cycle characteristics of global heat pump, evaporation and condensation heat transfer characteristics were studied and a basic data base for the optimum design of refrigeration and air-conditioning systems was obtained. On the condensing and evaporating heat transfer characteristics, the average heat transfer coefficient was obtained the higher value in R-290 than R-22 refrigerant. Characteristics of heat pump cycle were researched based on the compressor shaft power, cooling capacity and coefficient of performance. From these results, the heat pump cycle characteristics were more affected from the refrigerant properties and operating conditions. Considering the results, R-290 refrigerant has a sufficient ability to substitute R-22 due to its higher performance.

Study on Condensation Heat Transfer Characteristics of Hydrocarbons Natural Refrigerants

Oh, Hoo-Kyu,Park, Seung-Jun,Park, Ki-Won,Roh, Geon-Sang,Jeong, Jae-Cheon The Society of Air-Conditioning and Refrigerating 2001 International Journal Of Air-Conditioning and Refr Vol.9 No.3

This study investigated the condensation heat transfer coefficients of R-22, R-290 and R-600a inside horizontal tube. Heat transfer measurements were performed for smooth tube with inside diameter of 10.07 mm and outside diameter of 12.07 mm and inner grooved tube having 75 fins whose height is 0.25 mm. Condensation temperatures and mass velocity were ranged from 308K to 323 K and $51kg/m^2s$ to $250kg/m^2s$, respectively. The test results showed that the local condensation heat transfer coefficients increased as the mass flux increased, and also the effects of mass velocity on heat transfer coefficients of R-290 and R-600a were less than those of R-22. Average condensation heat transfer coefficients of natural refrigerants were superior to that of R-22. The present results had a good agreement with Cavallini-Zecchin's correlation for smooth and inner grooved tubes.

Heat transfer characteristics of supercritical CO₂ in a helical coil gas cooler on the change of coil diameter

Hoo-Kyu Oh(오후규),Tae-Guen Yu(유태근),Geon-Sang Roh(노건상),Hak-Keun Ku(구학근),Jiating Yan 한국마린엔지니어링학회 2007 한국마린엔지니어링학회 학술대회 논문집 Vol.2007 No.-

The heat transfer characteristics of supercritical CO₂ during gas cooling process are investigated experimentally. The test section is a helically coiled tube with I.D. of 4.55, O.D. of 6.35 and length of 10000 [㎜]. The helical coil diameter is 41.35 and 26.75 [㎜], respectively. The apparatus consist of a receiver, a variable-speed pump, a mass flow meter, a pre-heater, a gas cooler (test section) and an isothermal tank. The range of the refrigerant mass fluxes is from 200 to 800 [㎏/㎡s] and the pressure in the gas cooler varies from 7.5 to 10.0 [㎫]. The main experimental results are summarized as follows; as the gas cooling pressure decreases gradually, the heat transfer coefficient increases greatly. The mass flux has a positive effect on heat transfer like constant property condition. The heat transfer coefficient at coil diameter 26.75 [㎜] is larger than that of coil diameter 41.35 [㎜]. The data is compared with the existing correlations, which generally under-predict the measured data. However the experimental data show a relatively good agreement with correlations by Pitla et al. except for pseudo critical temperature.

Study on Condensation Heat Transfer Characteristics of Hydrocarbons Natural Refrigerants

Hoo Kyu Oh,Seung Jun Park,Ki Won Park,Geon Sang Roh,Jae Cheon Jeong 대한설비공학회 2001 International Journal Of Air-Conditioning and Refr Vol.9 No.3

This study investigated the condensation heat transfer coefficients of R-22, R-290 and R-600a inside horizontal tube. Heat transfer measurements were performed for smooth tube with inside diameter of 10.07 ㎜ and outside diameter of 12.07 ㎜ and inner grooved tube having 75 fins whose height is 0.25 ㎜. Condensation temperatures and mass velocity were ranged from 308 K to 323 K and 51 ㎏/㎡s to 250 ㎏/㎡s, respectively. The test results showed that the local condensation heat transfer coefficients increased as the mass flux increased, and also the effects of mass velocity on heat transfer coefficients of R-290 and R-600a were less than those of R-22. Average condensation heat transfer coefficients of natural refrigerants were superior to that of R-22. The present results had a good agreement with Cavallini-Zecchin's correlation for smooth and inner grooved tubes.

Heat Transfer Characteristics of R-134a in a Capillary Tube Heat Exchanger

Hoo Kyu Oh,Masafumi Katsuta,Kohichi Shibata 대한기계학회 1998 Heat transter conference Vol.6 No.1