• Nuclear Engineering and Technology
• /
• 제31권6호
• /
• pp.548-560
• /
• 1999

An experimental investigation has been peformed to examine the effects of various geometrical parameters and an initial operating condition on the air-water countercurrent How limitation (CCFL) in a simulated PWR hot leg. A total of 118 experimental data for the onset of CCFL and zero liquid penetration were obtained for various combinations of test parameters. It was observe that the CCFL can be classified into three different categories: (the onset of CCFL, (the partial liquid delivery, and (r) the zero liquid penetration. The observed mechanisms of the onset of CCFL were different depending on the inlet water flow rate. The parametric effects of pipe diameter, horizontal pipe length, horizontal pipe length-to-diameter (L/D) ratio, and initial water level in the horizontal pipe of the test section on the onset of air-water CCFL were also examined. An empirical correlation for the onset of CCFL in a horizontal pipe connected to an inclined riser was developed in terms of Wallis flooding parameters for the low inlet water flow rate region. Comparisons of the present empirical correlation with the air-water CCFL data of large pipe diameters show that the present correlation agrees more closely with the experimental data than the existing CCFL correlations.

• 대한기계학회논문집
• /
• 제12권3호
• /
• pp.599-606
• /
• 1988

본 연구에서는 공기와 물을 사용한 근사수평 반류성층유동에서의 계면파 구조 를 측정하였다. 3차원파 영역내의 유동조건하에서 탐침접촉법을 이용하여 계면파의 액막분포도를 구하였으며 Gauss 모델과 비교분석하였다. 또 이 분포도에서 파의 구 조와 관련된 통계치, 즉 평균액막두께, 파진폭, 파고 교란강도등을 계산하여 유동조건 에 따른 경향을 분석하였다. 본 연구와 병행하여 계면전단응력과 계면마찰계수에 관 한 실험을 수행하였는데 이 결과와 계면파 구조와의 상호연관성도 고찰하였다.

• 한국환경보건학회지
• /
• 제22권1호
• /
• pp.57-64
• /
• 1996

The main objectives of this research program were to study the ozonation characteristics of phenol wastewater in the continuous packed colamn reactor(PCR) and the bubble column reactor (BCR) using ozone and to provide the fundamentals of ozonizing the phenol wastewater. Among various influencing factors that affect on phenol decomposition through the oxidation by ozone, contacting method, and ozone flow rate were chosen as reaction parameters. The results were obtained from two different types of contacting methods where the countercurrent flow was more efficient than the cocurrent flow in both the phenol removal efficiency and the ozone utilization efficiency. Furthermore, PCR showed the phenol removal efficiency 1.6 to 3% higher than that of BCR in both contacting methods, as well as the ozone utilization efficiency, suggesting that the countercurrent flow is more efficient than the cocurrent flow. The phenol removal efficiency and the ozone utilization efficiency were reduced in both reactors as the influent ozone flow rate increased. Upon varing flow rate from 0.5l/min to 2.0 l/min by 0.5 l/min, the phenol removal efficiency was reduced approximately from 8.5% to 10.5% and the ozone utilization efficiency was reduced approximately from 6% to 8% in both reactors. The performance of PCR was superior to that of BCR in the aspects of phenol removal and ozone utilization efficiency.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 1997년도 춘계학술발표회논문집(1)
• /
• pp.368-373
• /
• 1997

The transition from a statified wavy to a slug flow has been analyzed considering the mechanistic forces acting on the wave crest in a nearly horizontal air-water countercurrent flow. To verify the results of the analysis, a series of experiments have been performed changing the inclination angle of the test section. Comparisons of the theoretical predictions with experimental data show a good agreement and the results show that the present model gives similar results of Taitel and Dukler's in the case of inclined pipes. However, at high superficial liquid velocity, the results of present work agree more closely with data than that of Taitel and Dukler's. Also, predictions of the present model gives a very close agreement with the experimental data for various tube sizes obtained by others.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 1996년도 춘계학술발표회논문집(2)
• /
• pp.247-253
• /
• 1996

The Interfacial friction factor for the countercurrent stratified air-wafer flow has been experimentally investigated in nearly horizontal and inclined pipes. The presence of the hydraulic jump may significantly affect both the flow pattern and the interfacial friction factor. The measured values of f$_{i}$ in nearly horizontal and two inclined pipes are of the same order of magnitude but the dependencies of the air and water velocities are slightly different.t.

• Natural Product Sciences
• /
• 제24권4호
• /
• pp.288-292
• /
• 2018

High-performance countercurrent chromatography (HPCCC) coupled with reversed-phase highperformance liquid chromatography (RP-HPLC) method was developed to isolate dihydrophaseic acid 3'-O-${\beta}$-D-glucopyranoside (DHPAG) from the extract of Nelumbo nucifera seeds. Enriched DHPAG sample (2.3 g) was separated by HPCCC using ethyl acetate/n-butanol/water system (6:4:10, v/v/v, normal-phase mode, flow rate: 4.0 mL/min) to give 23.1 mg of DHPAG with purity of 88.7%. Further preparative RP-HPLC experiment gave pure DHPAG (16.3 mg, purity > 98%). The current study demonstrates that utilization of CCC method maximizes the isolation efficiency compared with that of solid-based conventional column chromatography.

• Nuclear Engineering and Technology
• /
• 제31권6호
• /
• pp.618-630
• /
• 1999

An analytical model that includes the steam condensation effect has been derived and a parametric study has been performed. In addition, a series of experiments were performed and a total of 34 experimental data for the onset of CCFL in nearly horizontal countercurrent two-phase How have been obtained for various flow rates of water. Comparisons of the present CCFL data with slug formation models show that the agreement between the present as well as the existing model and the data is about the same. However, the deviation between the Taitel and Dukler's model predictions and the data is the largest when if j$_{f}$<0.04 m/s. A parametric study of the effect of the steam condensation using the present model shows that, when all local conditions are similar, the model predicted local gas velocities that cause the onset of flooding are slightly lower when condensation occurred. Based on the visual observation and the evaluation of the present work, it has been concluded that the criterion derived for the onset of slug flow can be directly used to predict the onset of inner flooding in nearly horizontal two-phase flow within the experimental ranges of the present work.

• Nuclear Engineering and Technology
• /
• 제37권6호
• /
• pp.557-564
• /
• 2005

Air-water countercurrent flow limitation at perforated plates with four holes was investigated in a vertical tank to see the effects of the plate thickness, the number of hole, and the diameter of the hole on the onset of CCFL. The thickness of plates was 1 cm and 4 cm, with a relatively large hole diameter of 5 cm. The collapsed water level formed on the perforated plate and its distribution in the upper plenum were measured. The gas flow rate in the multi-hole plate is relatively higher than one in the single tube because some of holes in the multi-hole plate provide a flow path fur liquid with less air-liquid resistance than in the single tube. The onset of CCFL occurred at nearly the same air flow rate regardless of the plate thickness. The negligible effect of the plate thickness on CCFL means that the flooding is initiated at the top of the plate rather than at its bottom. It turns out that $j_k$ and $K_k$ better fit the data than $H_k$ when hole diameter is greater than 2.86 cm. In our experimental ranges, the collapsed water levels at the onset of CCFL ranged from 7.5 cm to 10.5 cm. There was no three dimensional distribution of water level before and after the onset of CCFL.

• Nuclear Engineering and Technology
• /
• 제28권4호
• /
• pp.379-389
• /
• 1996

To experimentally investigate the several wave patterns for the horizontal countercurrent stratified air-water flow, a series of systematic experimental studies have been performed. The experiments are carried out in a horizontal pipe with 4m in length and 102mm in inner diameter. The oater and air superficial velocities vary from 0.0004 to 0.0204 and from 0 to 6m/s, respectively. The instantaneous water thickness is measured by parallel-wire conductance probes, and the wave field is recorded by high speed video camera. Also, to evaluate the wave effect on interfacial friction factor, the pressure drop is measured. Statistical data anal)sis is accomplished in order to obtain the fundamental wave parameters such as un amplitude, length and velocity, and spatial growth factor. By using these statistical parameters, the wave regime boundaries can be verified.

• 한국원자력학회:학술대회논문집
• /
• 한국원자력학회 1998년도 춘계학술발표회논문집(1)
• /
• pp.565-570
• /
• 1998

An interfacial condensation heat transfer phenomenon in a steam/water countercurrent stratified flow in a nearly horizontal pipe has been experimentally investigated. The present study has been focused on the measurement of the temperature and velocity distributions within the water layer. In particular, the water layer thickness used in the present work is large enough so that the turbulent mixing is limited and the thermal stratification is established. As a result, the thermal resistance of the water layer to the condensation heat transfer is increased significantly. An empirical correlation of the interfacial condensation heat transfer has been developed. The present correlation agrees with the data within $\pm$15%