• Journal of Environmental Science International
• /
• v.5 no.1
• /
• pp.93-102
• /
• 1996

Hydrodynamic characteristics such as gas holdup, liquid circulation velocity and bed expansion in a hexagonal inverse fluidized bed were investigated using air-water system by changing the ratio ($A_d$/$A_r$) of cross-sectional area between the riser and the downcomer, the liquid level($H_1$/H), and the superficial gas velocity($U_g$). The gas holdup and the liquid circulation velocity were steadily increased with the superficial gas velocity increasing, but at high superficial gas velocity, some of gas bubbles were carried over to a downcomer and circulated through the column. When the superficial gas velocity was high, the $A_d$/$A_r$ ratio in the range of 1 to 2.4 did not affect the liquid circulation velocity, but the maximum bed expansion was obtained at $A_d$/$A_r$ ratio of 1.25. The liquid circulation velocity was expressed as a model equation below with variables of the cross-sectional area ratio($A_d$/$A_r$) between riser to downcomer, the liquid level($H_1$/H), the superficial gas velocity($U_g$), the sparser height[(H-$H_s$)/H], and the draft Plate level($H_b$/H). $U_{ld}$ = 11.62U_g^{0.75}$${(\frac{H_1}{H})}^{10.30}$${(\frac{A_d}{A_r})}^{-0.52}$${(\frac({H-H_s}{H})}^{0.91}$${(\frac{H_b}{H})}^{0.13}$

• Journal of Environmental Science International
• /
• v.7 no.1
• /
• pp.41-45
• /
• 1998

The feasibility of foam separation to remove protein in aquacultural recirculating water was investigated. From the results of batch foam separation on protein removal, superficial air velocity and initial protein concentration in bulk solution were found to be important operational factors In determining removal rates of protein. The protein removal rate by batch foam separation was proportionally increased with the superficial air velocity. Performance characteristics of continous foam separator were highly dependent upon the operating parameters of superficial air velocity, hydraulic retention time(HRT) and foam height. Removal effeciency of protein increases with increasing superficial air velocity and HRT, and independent on foam height. As DO concentration was increased with superficial air velocity, foam separator is also used for oxygen addition. It could be confinned that foam separator might offer better perspective for protein removal in aquacuitural recirculating water.

• 한국신재생에너지학회:학술대회논문집
• /
• 2009.06a
• /
• pp.876-879
• /
• 2009

Fischer-Tropsch 합성 반응과 같은 slurry bubble column reactor에서는 반응 속도를 증진시키기 위해서는 서로 다른 상간의 접촉 면적을 최대화함으로써 물질 전달을 원활하게 유지하여야 한다. 특히 Fischer-Tropsch 합성 반응에서는 반응물인 기체가 촉매로서 기능하는 고체 표면으로의 external mass transfer가 효과적으로 이루어져야 하기 때문에 반응기 내의 기체의 거동뿐만 아니라 고체인 촉매의 분포에 대한 연구가 활발하게 이루어지고 있다. 따라서 본 연구에서는 반응기 내에 기체의 superficial velocity를 변화시키면서 기체의 hold up 뿐만 아니라 고체 입자의 분포특성에 대하여 관찰하였다. Superficial velocity가 증가함에따라 gas hold up의 경우, 일정하게 증가하다가 6 cm/sec 이상에서 그 증가폭이 감소하였다. 즉 6 cm/sec이상에서 turbulent flow regime을 형성하였다. 또한 고체입자의 분포 역시 기체의 superficial velocity가 증가함에따라 보다 균일하게 되는 것을 확인할 수 있었다.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.19 no.6
• /
• pp.441-446
• /
• 2007

An experimental study on the countercurrent two-phase flow in narrow rectangular channels has been peformed. Countercurrent flow limitation (CCFL) was investigated using air and water in 760mm long, 100mm wide, vertical test sections with 1 and 3mm channel gaps. Tests were systematically performed with downward liquid superficial velocities and upward gas velocities covering 0 to 0.125 and 0 to 3.5m/s ranges, respectively. As the gap width of rectangular channel increased the CCFL water superficial velocity decreased for the given air superficial velocity. Slight increase of the air superficial velocity resulted in the abrupt decrease of water velocity when $j_g=2{\sim}4m/s$. The critical superficial velocity of air, at which the downward flow of water was no longer allowed, also decreased with the increase of gap width. The experimental results were compared with the previous correlations, which were mainly for round tubes, and the qualitative trends were found to be partially acceptable. However the quantitative discrepancies were hardly neglected. New correlation of CCFL was developed and showed good agreement with the experimental data.

• Journal of Advanced Marine Engineering and Technology
• /
• v.29 no.4
• /
• pp.377-383
• /
• 2005

This paper deals with the flow characteristics of air-water two-phase flow in a vertical tube of 10mm I.D. and 600mm in length at an adiabatic condition. The obtained experimental data were covered with the liquid superficial velocity ranging from 0.095m/s to 2.56m/s. and the gas superficial velocity ranging from 0.032m/s to 21.08m/s. The effects of the gas and liquid superficial velocity on the flow pattern transitions, frictional pressure drop, and film thickness and gas-liquid interface roughness were also examined. It was found that the film thickness increased and the liquid film wave length was more longer with the liquid superficial velocity $j_L$ increasing at $j_G$ constant. It was also showed that the frictional pressure drops were experienced in three regions. namely increasing region(bubbly flow), decreasing region (Taylor bubble and slug flows) and re-increasing region (annular flow).

• Journal of the Korean Society of Safety
• /
• v.8 no.4
• /
• pp.120-126
• /
• 1993

This work was carried out to investigate the effects of solid mass flow rate, mean particle diameter and mesh number of screen packing material on minimum carrying velocity, which defined as the superficial gas velocity of the upper limit of chocking phenomenon. Vertical pneumatic conveying was studied on a 4.6cm 1. D. pipe, 180cm in length. Experiments were performed in both the empty and the screen-packed pipe. It was also examined the effect of superficial gas velocity, solid mass flow, mean particle diameter, and mesh number of packing material on pressure drop. Minimum carrying velocity in screen packed-pipe was lower than that in an empty pipe. besides minimum carrying velocity was decreased with increase in mesh number of screen packing material. The pressure drop In vortical packed-pipe was Increased with superficial gas velocity, mean particle diameter, and mesh number of screen packing material.

• KSBB Journal
• /
• v.6 no.4
• /
• pp.345-350
• /
• 1991

The purpose of this study is to investigate biomass characteristics and organic removal efficiency by changing superficial upflow velocity and organic loading rate in treating alcoholic distillery wastewater. Since the biomass concentration and the thickness of biofilm are very sensitive to superficial upflow velocity, a high concentration of biomass could be achieved by decreasing superficial upflow velocity that lowered the organic removal efficiency. Therefore, superficial upflow velocity should be controlled as to give optimum conditions and removal efficiency. Generally, activated sludge system shows 70% COD removal efficiency at$1.5kgCOD/m^3{\cdot}day$, but the fluidized-bed biofllm reactor shows 80% COD removal efficiency even at 6kgCOD/$m^2{\cdot}day$.

• Journal of Aquaculture
• /
• v.16 no.4
• /
• pp.216-222
• /
• 2003

In a simulated seawater aquaculture system, effects of different operating factors like the superficial air velocity (SAY), hydraulic residence time (HRT), protein concentration and foam overflow height on the removal of total suspended solids (TSS) by a foam fractionator, with 20 cm diameter and 120 cm height, were investigated. This experiment was performed on batch and consecutive modes for different combinations of the tested factors, using synthetic wastewater. In 5 consecutive trials, TSS concentration in culture tank water decreased faster, when the foam fractionator was operated at higher SAV and lower HRT. In batch trials, with increasing SAV, TSS removal rate increased, but decreased with increasing HRT. Higher protein concentration in the bulk solution resulted in higher TSS removal rate. TSS concentration in the collected foam condensates increased but the foam overflow rate decreased with increasing foam overflow height. Foam fractionation was effective for removing TSS in seawater aquaculture systems and its performance largely depended on the operating parameters, especially superficial air velocity.

• Journal of Mechanical Science and Technology
• /
• v.17 no.3
• /
• pp.429-439
• /
• 2003

Counter-current two-phase flows of air- water in narrow rectangular channels with offset strip fins have been experimentally investigated in a 760 mm long and 100 mm wide test section with 3.0 and 5.0 mm gap widths. The two-phase flow regime, channel-average void fractions and two-phase pressure gradients were studied. Flow regime transition occurred at lower superficial velocities of air than in the channels without fins. In the bubbly and slug flow regimes, elongated bubbles rose along the subchannel formed by fins without lateral movement. The critical void fraction for the bubbly-to-slug transition was about 0.14 for the 3 mm gap channel and 0.2 for the 5 mm gap channel. respectively. Channel-average void fractions in the channels with fins were almost the same as those in the channels without fins. Void fractions increased as the gap width increased, especially at high superficial velocity of air. The presence of fins enhanced the two-phase distribution parameter significantly in the slug flow, where the effect of gap width was almost negligible. Superficial velocity of air dominated the two-phase pressure gradients. Liquid superficial velocity and channel gap width has only a minor effect on the pressure gradients.

• Journal of Environmental Science International
• /
• v.6 no.1
• /
• pp.25-31
• /
• 1997

The variations of gas hold-up, overall volumetric oxygen mass transfer coefficients and liquid circulation velocity in an internal loop reactor were investigated to manifest scale-up effect. The relationship between superficial gas velocity and gas hold-up were found as Ugr = 0.045 $\varepsilon$r in the pilot-scale and Ugr = 0.056 $\varepsilon$r in the bench-scale reactor. The overall volumetric oxygen mass tractsfer coefficient, KLa was slightly increased in the pilot-scale than in the bench-scale reactor. Flow regime was changed from the bubble flow to the churn-turbulent flow when the superficial gas velocity reached to 3.5 - 4 cm/sec in the pilot-scale.