• Nuclear Engineering and Technology
• /
• 제28권1호
• /
• pp.1-16
• /
• 1996

축소한 격납용기 내부 핵연료재장전수저장탱크의 안쪽에 설치한 열교환기 튜브의 주요 매개변수들이 풀핵비등 열전달에 미치는 복합적인 영향을 극명하기 위해 튜브 외경, 표면 거칠기, 그리고 튜브 설치 방향에 대한 다양한 조합들을 환용하여 열유속 q'quot;와 과열 온도 차이 $\Delta$T 간의 관계에 대한 총 1,966 개의 실험값을 취득하였다. 이 실험 결과들에 의하면, (1) 표면 거칠기 증가는 수평 및 수직 튜브 모두에 대해 열전달을 향상시키고, (2) 기포 생성에 따른 두가지 열전달 기구인 주변 액체 운동증가에 의한 열전달 향상과 기포층 및 기포 군집 형성에 의한 열전달 감소는 50㎾/$m^2$의 열유속을 경계로 낮은 열유속과 높은 열유속 영 역 에서 서로 다르게 관찰되는데, 이것은 튜브 설치 방향과 표면 거칠기의 크기와 관련이 있으며, (3) 튜브 외경 증가는 수평 및 수직 튜브 모두에 대해 열전달을 감소시키는데, 그 영향정도는 수평보다 수직구조에서 더 크다. 수평 및 수직 튜브들에 대해 열유속 q'quot;와 표면 거칠기 ($\varepsilon$) 및 튜브 외경 (D) 사이의 관계를 결정하는 두 가지 실험식을 개발하였다. 그리고, q'quot;만의 함수로된 풀핵비등 열전달계수( $h_{b}$ 에 대한 간단한 실험식도 부가적으로 개발하였다. 실험식도 부가적으로 개발하였다.'quot;만의 함수로된 풀핵비등 열전달계수($h_{b}$ 에 대한 간단한 실험식도 부가적으로 개발하였다.

• 설비공학논문집
• /
• 제25권3호
• /
• pp.143-149
• /
• 2013

In this work, nucleate pool boiling heat transfer coefficients (HTCs) of R134a and R1234yf are measured, on flat plain, 26 fpi low fin, Turbo-B, Turbo-C and Thermoexcel-E surfaces. All data are taken at the liquid pool temperature of $7^{\circ}C$, on a small square copper plate ($9.53mm{\times}9.53mm$), at heat fluxes from $10kW/m^2$ to $200kW/m^2$, with an interval of $10kW/m^2$. Test results show that nucleate boiling HTCs of all enhanced surfaces are greatly improved, as compared to that of a plain surface. Nucleate pool boiling HTCs of R1234yf are very similar to those of R134a, for the five surfaces tested.

• 동력기계공학회지
• /
• 제14권4호
• /
• pp.11-16
• /
• 2010

The evaporation heat transfer characteristics of propane(R-290) in horizontal small diameter tubes were investigated experimentally. The test tubes have inner diameters of 1 mm and 4 mm. Local heat transfer coefficients were measured at heat fluxes of 12, $24\;kW/m^2$, mass fluxes of 150, $300\;kg/m^2s$, and evaporation temperature of $15^{\circ}C$. The experimental results showed that the evaporation heat transfer coefficient of R-290 has an effect on heat flux, mass flux, tube diameter, and vapor quality. The evaporation heat transfer of R-290 has an influenced on nucleate boiling at low quality and convective boiling at high quality. The evaporation heat transfer coefficient of R-290 increases with decreasing inner tube diameter. And the evaporation heat transfer coefficient of R-290 is about 1~3 times higher than that of R-134a.

• International Journal of Air-Conditioning and Refrigeration
• /
• 제14권4호
• /
• pp.156-165
• /
• 2006

Convective boiling heat transfer coefficients were measured in a horizontal minichannel with R-l34a. The test section was made of stainless steel tube with an inner diameter of 3.0 mm and a length of 2m. It was uniformly heated by applying electric current directly to the tube. Local heat transfer coefficients were obtained for heat fluxes from 10 to $40kW/m^2$, mass fluxes from 200 to $600kgT/m^2s$, qualities up to 1.0, and the inlet saturation temperature of $10^{\circ}C$. The experimental results were mapped on Wojtan et $al.'s^(7)$ and Wang et $al.'s^(8)$ flow pattern maps. The nucleate boiling was predominant at low vapor quality whereas the convective boiling was predominant at high vapor quality. Laminar flow appeared in the flow with minichannel. The experimental results were compared with six existing two-phase heat transfer coefficient correlations. A new boiling heat transfer coefficient correlation based on the superposition model for refrigerants was developed with mean and average deviations of 10.39% and -3.66%, respectively.

• Journal of Advanced Marine Engineering and Technology
• /
• 제10권4호
• /
• pp.67-77
• /
• 1986

The information on the heat transfer characteristics, flow pattern and pressure drop, are very important for the desing of general heat exchanger, refrigerating system, air conditioning system and energy recovery system. In these systems, water or lubricating oil contained in working fluid affects greatly the flow and heat transfer condition and this phenomena must be considered in the practical design. An experiment has been performed for studying the flow and heat transfer characteristics of the forced convective horizontal flow of R-113 under the range of the liquid single phase state to the boiling flow state. Basic experimental results are obtained in the case that water or lubricating oil does not contaminate in the test fluid. Experimental results are as follows; (1) The local heat transfer coefficients in the nucleate boiling region and transition boiling region are almostly ten times as large as that of liquid single phase flow. (2) The measured heat transfer coefficient in the present experimental range is relatively agreed well with the predicted value from the various experimental results for the boiling flow.

• International Journal of Air-Conditioning and Refrigeration
• /
• 제8권2호
• /
• pp.23-28
• /
• 2000

In this study, pool boiling performance of a structured enhanced tube for a flooded refrigerant evaporator was experimentally investigated. Tests were performed for three different refrigerants(R-11, R-123, R-l34a). Compared with the heat transfer coefficients of the smooth tube, the heat transfer coefficients of the enhanced tube were 6.6 times larger for R-11, 6.0 times larger for R-123 and 3.5 times larger for R-l34a, which are comparable with the performance of foreign products. The heat transfer coefficients of R-l34a was higher than those of R-11 or R-123, both for the enhanced tube and for the smooth tube. At 4.4$^\circ$C saturation temperature, however, the heat transfer coefficients of R-l34a was approximately the same as those of R-11. The effect of the saturation pressure on the boiling performance was similar to that of the smooth tube-the heat transfer coefficient increased as the saturation pressure increased.

• 대한기계학회논문집B
• /
• 제29권5호
• /
• pp.643-652
• /
• 2005

Saturated nucleate pool boiling experiments for binary mixtures, which are consisted of refrigerant R11 and R113, were performed with constant wall temperature condition. Results for binary mixtures were also compared with pure fluids. A microscale heater array and Wheatstone bridge circuits were used to maintain the constant temperature of the heating surface and to obtain heat flow rate measurements with high temporal and spatial resolutions. Bubble growth images were captured using a high speed CCD camera synchronized with the heat flow rate measurements. The departure time for binary mixtures was longer than that for pure fluids, and binary mixtures had a higher onset of nucleate boiling (ONB) temperature than pure fluids. In the asymptotic growth region, the bubble growth rate was proportional to a value between $t^{\frac{1}{6}}$ and $t^{\frac{1}{4}}$. The bubble growth behavior was analyzed to permit comparisons with binary mixtures and pure fluids at the same scale using dimensionless parameters. There was no discernable difference in the bubble growth behavior between binary mixtures and pure fluids for a given ONB temperature. And the departure radius and time were well predicted within a ${\pm}30{\%}$ error. The minimum heat transfer coefficient of binary mixtures occurred near the maximum ${\mid}y-x{\mid}$ value, and the average required heat flux during bubble growth did not depend on the mass fraction of R11 as more volatile component in binary mixtures. Finally, the results showed that for binary mixtures, a higher ONB temperature had the greatest effect on reducing the heat transfer coefficient.

• 한국생산제조학회지
• /
• 제8권4호
• /
• pp.65-65
• /
• 1999

Heat transfer performance is studied for boiling and condensation of R-11 on integral-fin tubes. Nine tubes with trapezoidal integral-fins having fin densities from 748 to 1654fpm and 10,30 grooves and finned tubes with caves of 0.55 and 0.64 mm height respectively are tested. in case of condensation CFC-11 condensates at saturation stat of 32℃ on the outside surface cooled by inside cooling water flows. And in case of boiling the refrigerant evaporates at a saturation state of 1 bar on the outside tube surface and heat is supplied by hot water which circulates inside of the tube,. The tube having fin transfer coefficient concerns fin tubes with caves show higher valve than low fin tube having find density of 1299fpm and 30grooves. The overall heat transfer coefficient of fin tube with caves is about 5155 W/mK at 2.8m/s of water velocity, The value is abuot 2.7 times higher than plain tube and 1.3 times higher than low fin tube having fin density of 1299fpm and 30 grooves.

• Nuclear Engineering and Technology
• /
• 제34권4호
• /
• pp.269-285
• /
• 2002

Water heat transfer experiments were carried out in a uniformly heated annulus with a wide range of pressure conditions. The local heat transfer coefficients for saturated water (low boiling have been measured just before the occurrence of the critical heat flux (CHF) along the length of the heated section. The trends of the measured heat transfer coefficients were quite different from the conventional understanding for the heat transfer of saturated flow boiling. This discrepancy was explained from the nucleate boiling in the liquid film of annular flow under high heat flux conditions. The well-known correlations were compared with the measured heat transfer coefficients. The Shah and Kandlikar correlations gave better prediction than the Chen correlation. However, the modified Chen correlation proposed in the present work showed the best agreement with the present data among correlations examined .

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 추계학술대회논문집B
• /
• pp.330-336
• /
• 2001

Water heat transfer experiments were carried out in a uniformly heated annulus with a wide range of pressure conditions. The local heat transfer coefficients for saturated water flow boiling have been measured just before the occurrence of the critical heat flux (CHF) along the length of the heated section. The trends of the measured heat transfer coefficients were quite different from the conventional understanding for the heat transfer of saturated flow boiling. This discrepancy was explained from the nucleate boiling in the liquid film of annular flow under high heat flux conditions.