• 한국가스학회지
• /
• 제12권3호
• /
• pp.43-49
• /
• 2008

본 연구에서는 내경 4.3 mm와 6.4 mm의 수평동관내 R-22와 R-407C의 증발 열전달과 압력강하를 실험적으로 조사하였다. 냉매 순환루프의 주요구성품은 수액기, 압축기, 질량유량계, 응축기, 이중관식 증발기 (시험부)로 구성된다. 시험부는 내경 4.3 mm와 6.4mm의 평활 동관으로 이루어져 있다. 냉매질량유속은 $100\;kg/m^2s$에서 $300\;kg/m^2s$까지 변화시켰고, 증발기 냉매포화온도는 $5^{\circ}C$이다. R-22와 R-407C의 증발 열전달계수는 질량유속과 증기건도의 증가와 함께 따라 상승한다. 내경 4.3 mm와 6.4mm관내 R-22의 증발 열전달계수가 R-407C에 비해 각각 $7.3{\sim}47.1%$와 $5.68{\sim}46.6%$ 정도 높다.

• Journal of Mechanical Science and Technology
• /
• 제14권5호
• /
• pp.537-546
• /
• 2000

The heat transfer characteristics of refrigerant-oil mixture for horizontal in-tube evaporator have been investigated experimentally. A smooth copper tube and a micro-fin tube with nominal 9.5 mm outer diameter and 1500 mm length were tested. For the pure refrigerant flow, the dependence of the axial heat transfer coefficient on quality was weak in the smooth tube, but in the micro-fin tube, the coefficients were 3 to 10 times greater as quality increases. Oil addition to pure refrigerant in the smooth tube altered the flow pattern dramatically at low mass fluxes, with a resultant enhancement of the wetting area by vigorous foaming. The heat transfer coefficients of the mixture for low and medium qualities were increased at low mass fluxes. In the micro-fin tube, however, the addition of oil deteriorates the local heat transfer performance for most of the quality range, except for low quality. The micro-fin tube consequently loses its advantage of high heat transfer performance for an oil fraction of 5%. Results are presented as plots of local heat transfer coefficient versus quality.

• 설비공학논문집
• /
• 제28권11호
• /
• pp.428-433
• /
• 2016

The fin and tube heat exchanger using a two-port tube has in air-conditioner heat exchanger because heat transfer performance. This study investigates the feasibility of a fin and tube heat exchanger using two-port copper tube by mechanical expansion. The optimum size of the tube-expanding bullet for the heat exchanger using two-port tube was through numerical calculation. The heat exchanger using a two-port tube was fabricated by mechanical expansion, and the heat exchanger performance was evaluated condensation and evaporation experiments. Compared to the heat exchanger of a conventional circular tube, the pressure drop per unit length of the heat exchanger with a two-port tube decreased. Compared to the heat exchanger using a conventional circular tube, the overall heat transfer coefficient of heat exchanger with a two-port tube increased up to 13% in the case of condensation, and up to 25% in the case of evaporation. The two-port tube heat exchanger outperforms conventional heat exchanger for air conditioner with a inner grooved circular tube.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2007년도 동계학술발표대회 논문집
• /
• pp.247-251
• /
• 2007

Because of the ozone layer depletion and global warming, new alternative refrigerants are being developed. In this study, evaporation heat transfer characteristics of carbon dioxide flowing upward in a vertical micro-fin tube have been investigated by experiment. Before a test section, a pre-heater is installed to adjust the inlet quality of the refrigerant to a desired value. The micro-fin tube with outer diameter of 5 mm and length of 1.44 m was selected as the test section. The test was conducted at mass fluxes of 318 to $530\;kg/m^2s$, saturation temperature of -5 to $5^{\circ}C$, and heat fluxes of 15 to $30\;kW/m^2$. As the vapor quality increases, the heat transfer coefficients of carbon dioxide are increased, and the heat transfer coefficients increase when the heat fluxes and saturation temperatures increase, and there was not much of influence of mass flux on the heat transfer coefficients.

• 대한기계학회논문집B
• /
• 제26권2호
• /
• pp.269-277
• /
• 2002

Experiments on the evaporation heat transfer and pressure drop in the brazed type plate heat exchangers were performed using refrigerants R410A and R22. To investigate the geometric effect, plate heat exchangers with the same pitch and height but different 45$^{\circ}$, 35$^{\circ}$and 20$^{\circ}$chevron angles are used. Tests were conducted fur the ranges of the mass flux of refrigerant from 13 kg/m$^2$s to 34 kg/m$^2$s, the evaporation temperatures of 15$^{\circ}C$, 1$0^{\circ}C$ and 5$^{\circ}C$, vapor quality from 0.15 to 0.95 and the heat flux from 2.5 kW/m$^2$to 8.5 kW/m$^2$. The evaporation heat transfer coefficients and pressure drops were measured. Most of flow patterns are in the chum flow regime and become close to the annular flow for increasing the mass flux and the vapor quality. The heat transfer coefficient increases with increasing the evaporation temperature at a given mass flux in all plate heat exchangers. Also, the pressure drop increases with increasing the mass flux and the quality and decreasing the evaporation temperature and the chevron angle.

• Journal of Mechanical Science and Technology
• /
• 제18권3호
• /
• pp.513-525
• /
• 2004

This paper reports an experimental study on flow boiling of pure refrigerants R l34a and R l23 and their mixtures in a uniformly heated horizontal tube. The flow pattern was observed through tubular sight glasses with an internal diameter of 10㎜ located at the inlet and outlet of the test section. Tests were run at a pressure of 0.6 MPa in the heat flux ranges of 5-50㎾/㎡, vapor quality 0-100 percent and mass velocity of 150-600㎏/㎡s. Both in the nucleate boiling-dominant region at low quality and in the two-phase convective evaporation region at higher quality where nucleation is supposed to be fully suppressed, the heat transfer coefficient for the mixture was lower than that for an equivalent pure component with the same physical properties as the mixture. The reduction of the heat transfer coefficient in mixture is explained by such mechanisms as mass transfer resistance and non-linear variation in physical properties etc. In this study, the contribution of convective evaporation, which is obtained for pure refrigerants under the suppression of nucleate boiling, is multiplied by the composition factor by Singal et al. (1984). On the basis of Chen's superposition model, a new correlation is presented for heat transfer coefficients of mixture.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2005년도 동계학술발표대회 논문집
• /
• pp.268-273
• /
• 2005

Because of environmental issues caused by CFC, HCFC or HFC refrigerants, new alternative refrigerants has gained a significant attention. This paper presents experimental information on heat transfer coefficient and pressure drop behavior during evaporation process of R32/290 mixtures in a horizontal smooth tube. A smooth tube with outer diameter of 5 mm and length of 5 m was selected as a test tube. Heat transfer coefficients and pressure drop characteristics were measured for a range of mass fluxes from 497 to 994 $kg/m^2s$, heat fluxes from 12 to 20 $kW/m^2$ and for several mixture compositions(100/0, 75/25, 58.4/41.6, 2s/75, 100/0 by wt% of R32/290). The differences of measured heat transfer characteristics among various R32/290 refrigerant mixtures were analyzed for various compositions.

• 설비공학논문집
• /
• 제21권4호
• /
• pp.243-251
• /
• 2009

Refrigerant mixtures provide an opportunity to adjust their properties to fit design criteria and a possibility to create new blends that can improve heat transfer characteristics. Therefore, mixture of $CO_2$ and propane is chosen which may be a promising refrigerant and has good environmental compatibility. This paper presents measured heat transfer coefficient data during evaporation process of $CO_2$/propane mixtures flowing upward in vertical smooth and. micro-fin tubes. Smooth and micro-fin tubes with outer diameters of 5 mm and length of 1.44in were selected as test tubes. The tests were conducted at mass fluxes of 212 to $656kg/m^{2}s$, inlet temperatures of -10 to $30^{\circ}C$, heat fluxes of 15 to $60\;kW/m^2$ and for several compositions (75/25, 50/50, 25/75 wt%). Among $CO_2$/propane refrigerant mixtures, the heat transfer characteristics are much better than that of any compositions when the composition is 75/25 (wt%).

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2007년도 춘계학술대회B
• /
• pp.2217-2221
• /
• 2007

Because of the ozone layer depletion and global warming, new alternative refrigerants are being developed. In this study, evaporation heat transfer characteristics of carbon dioxide flowing upward in a vertical tube have been investigated by experiment. Before the test section, a pre-heater is installed to adjust the inlet quality of the refrigerant to a desired value. A smooth tube with outer diameter of 5 mm and length of 1.44 m was selected as a test tube. The test was conducted at mass fluxes of 212 to 530 kg/$m^2s$, saturation temperature of -5 to 20$^{\circ}C$, and heat fluxes of 20 to 45 kW/$m^2$. As the vapor quality and mass fluxes increase, the heat transfer coefficients of carbon dioxide are decreased, and the heat transfer coefficients increase when the heat fluxes and saturation temperatures increase.

• 설비공학논문집
• /
• 제12권12호
• /
• pp.1081-1089
• /
• 2000

Evaporating heat transfer coefficients of R-22 and R-134a were measured in smooth horizontal copper tubes with inner diameters of 1.77, 3.36 and 5.35mm, respectively. The experiments were conducted in a closed loop, which was driven by a magnetic gear pump. Experiments were performed for the following range of variables: mass velocity (200 to 400 kg/$m^2$.s), saturation temperature($0^{circ}C,; 5^{\circ}C$) and quality(0 to 1.0). Main results obtained are as follows: evaporating heat transfer coefficients in the small diameter tubes (ID<7mm) were observed to be strongly affected by various diameters and to differ from those in the large diameter tubers. The heat transfer coefficients of the small diameter tubes were higher than those of the large diameter tubs. And it was very difficult to apply some well-known previous predictions (Shah`s, Gungor-Winterton`s and Kandlikar`s correlation) to small diameter tubes.