• Fibers and Polymers
• /
• 제6권2호
• /
• pp.131-138
• /
• 2005

A theoretical model is proposed in order to investigate rheological behavior of bubble suspension with large deformation. Theoretical constitutive equations for dilute bubble suspensions are derived by applying a deformation theory of ellipsoidal droplet [1] to a phenomenological suspension theory [2]. The rate of deformation tensor within the bubble and the time evolution of interface tensor are predicted by applying the proposed constitutive equations, which have two free fitting parameters. The transient and steady rheological properties of dilute bubble suspensions are studied for several capillary numbers (Ca) under simple shear flow and uniaxial elongational flow fields. The retraction force of the bubble caused by the interfacial tension increases as bubbles undergo deformation. The transient and steady relative viscosity decreases as Ca increases. The normal stress difference (NSD) under the simple shear has the largest value when Ca is around 1 and the ratio Of the first NSD to the second NSD has the value of 3/4 for large Ca but 2 for small Ca. In the uniaxial elongational flow, the elongational viscosity is three times as large as the shear viscosity like the Newtonian fluid.

• 생명과학회지
• /
• 제12권5호
• /
• pp.577-583
• /
• 2002

$\beta$-glucuronidase 유전자를 형질전환한 담배에서 여러 조직중에서 가장 activity가 높은 줄기에서 현탁세포를 유도하여 생장 및 발현 양상을 조사하였다. Flask culture와 2.5 L bubble column culture시 세포의 성장에는 큰 차이가 없었지만 $\beta$-glucuronidase의 발현은 bubble column culture시 약 2850 U/mg으로 95배 향상되는 결과를 나타내었다. 하지만 두 경우 모두 $\beta$-glucuronidase의 생산량이 증가와 감소를 반복하는 양상을 나타내었다. 이것은 외래 단백질의 생산과 파괴가 반복적으로 일어나는 것으로 추정이 된다. 또한 bubble column culture의 생산성을 향상시키기 위해 중요한 영양분인 sucrose을 30 g/L로 두 번 첨가한 경우, 다른 영양분의 고갈로 인하여 세포의 최종 생산량은 향상되지가 않았고 $\beta$-glucuronidase는 안정적으로 생산되었지만 최종 생산량은 향상되지가 않았다. 하지만 세포의 크기가 감소하여 배양기 운전이 쉬워지는 장점이 있었고 이것은 세포의 고농도 배양을 통한 재조합 단백질 생산성을 향상시키는 유리하게 작용할 것이다.

• 한국섬유공학회:학술대회논문집
• /
• 한국섬유공학회 2003년도 The Korea-Japan Joint Symposium
• /
• pp.47-48
• /
• 2003

Dilute bubble suspensions are prepared by introducing carbon dioxide bubbles into polyol resin. The apparent shear viscosity is measured with a wide gap parallel plate rheometer. A numerical simulation for deformation of a single bubble suspended in a Newtonian fluid is conducted by using a finite volume method (FVM) where multigrid algorithms are incorporated. Transient and steady results of bubble deformation were obtained and were in good agreement with experimental results. At high capillary number, viscosity of the suspension increases as the volume fraction increases, while at low capillary number, the viscosity decreases as the volume fraction increases.

• Korea-Australia Rheology Journal
• /
• 제16권1호
• /
• pp.47-54
• /
• 2004

Low Reynolds number, dilute, and surfactant-free bubble suspensions are prepared by mechanical mixing after introducing carbon dioxide bubbles into a Newtonian liquid, polyol. The apparent shear viscosity is measured with a wide-gap parallel plate rheometer by imposing a simple shear flow of capillary numbers(Ca) of the order of $10^{-2}$ ~ $10^{-1}$ and for various gas volume fractions ($\phi$). Effects of capillary numbers and gas volume fractions on the viscosity of polyol foam are investigated. At high capillary number, viscosity of the suspension increases as the gas volume fraction increases, while at low capillary number, the viscosity decreases as the gas volume fraction increases. An empirical constitutive equation that is similar to the Frankel and Acrivos equation is proposed by fitting experimental data. A numerical simulation for deformation of a single bubble suspended in a Newtonian fluid is conducted by using a newly developed two-dimensional numerical code using a finite volume method (FVM). Although the bubble is treated by a circular cylinder in the two dimensional analysis, numerical results are in good agreement with experimental results.

• Nuclear Engineering and Technology
• /
• 제48권4호
• /
• pp.915-924
• /
• 2016

After a severe accident to the nuclear reactor, the in-vessel retention strategy is a key way to prevent the leakage of radioactive material. Nanofluid is a steady suspension used to improve heat-transfer characteristics of working fluids, formed by adding solid particles with diameters below 100nm to the base fluids, and its thermal physical properties and heat-transfer characteristics are much different from the conventional working fluids. Thus, nanofluids with appropriate nanoparticle type and volume concentration can enhance the heat-transfer process. In this study, the moving particle semi-implicit method-meshless advection using flow-directional local grid method is used to simulate the bubble growth, departure, and sliding on the downward-facing heating surface in pure water and nanofluid (1.0 vol.% $Al_2O_3/H_2O$) flow boiling processes; additionally, the bubble critical departure angle and sliding characteristics and their influence are also investigated. The results indicate that the bubble in nanofluid departs from the heating surface more easily and the critical departure inclined angle of nanofluid is greater than that of pure water. In addition, the influence of nanofluid on bubble sliding is not significant compared with pure water.

• 한국세라믹학회지
• /
• 제51권5호
• /
• pp.511-515
• /
• 2014

The thermodynamic instability of bubbles in wet-foam colloidal suspension is due to the substantial area of their gas/liquid interface. Several physical processes lead to gas diffusion from smaller to larger bubbles, resulting in a coarsening and Ostwald ripening of wet foam. This includes a narrowing of the bubble size distribution. The distribution and microstructure of porous ceramics, the adsorption free energy and Laplace pressure of $Al_2O_3$ particle-stabilized colloidal suspension, and $SiO_2$ content were investigated for tailoring the bubble size. Wet-foam stability of more than 80% is related to the degree of hydrophobicity with contact angles of $62-70^{\circ}$ achieved from the surfactant. The contact angle replaces part of the highly energetic interface and lowers the free energy of the system. This leads to an apparent increase in the surface tension (26-33 mN/m) of the colloidal suspension.

• 자원리싸이클링
• /
• 제5권3호
• /
• pp.56-64
• /
• 1996

탄산칼슘의 다형 제어를 목적으로 합성 음료, 의약품 등으로서도 폭넓게 이용되고 있는 ${C_2}{H_4}{OH}$계에서 수산화칼슘을 현탁시키고 감미제, 의약품 등의 용도로서도 이용되고 있는 에틸렌글리콜을 첨가하면서 탄산칼슘 생성 및 탄산칼슘 다형결정화 특성에 대해 연구하였다. 세라믹 bubble plate를 부착 제작한 반응기를 사용하여 $CO_2$gas와 반응 진행시 전기전도도의 연속 측정을 통해 변화시점에서 일부 현탁액을 분리 분말화하여 X선 회절 및 전자현미경을 통해 중가 생성물과 이들이 각각 Vaterite, Aragonite, Calcite로 전이됨을 확인하였다. ${C_2}{H_4}{OH}$에 대한 에틸렌글리콜 첨가를 10 vol%로 하여 500ml의 반응 현탁액에 10~50g의 수산화칼슘 첨가 변화에 따른 생성물을 조사하였다. 결정화단계에서 수산화칼슘 10g 첨가시를 제외하고는 모든 조건에서 겔화(gelation)가 일어나며 그 생성 유지시간은 수산화칼슘 양이 많아질수록 짧아짐을 관찰할 수 있었다. 상온 상압하에서 생성되기 어려웠던 Vaterite가 $Ca(OH)_2$의 30g 첨가반응계에서 구형으로 생성됨을 확인할 수 있었다. 이는 칼슘계, 흡착제 등의 가능성을 부여한 복합재료로서의 Vaterite 합성을 상온 상압화에서${C_2}{H_4}{OH}$ 계에서 다형제어 할 수 있음을 보여주었다. 탄산칼슘의 동질이상중 Vaterite는 준안정상이고 분말화 과정에서 이미 Calcite로 전이되기 쉬우나 G5 glass filter와 vacuum drier를 사용하여 안정적인 구형의 Vaterite을 확인할 수 있었다.

• 원예과학기술지
• /
• 제33권2호
• /
• pp.251-258
• /
• 2015

Eurycoma longifolia is an important rare medicinal plant that contains valuable bioactive compounds. In the present study, cell suspension culture of E. longifolia was established for the production of biomass and phenolic compounds. Various medium parameters, such as concentration of auxin, salt strength of the medium, and sucrose and nitrogen concentrations, were optimized for the production of biomass at the flask-scale level. Full strength Murashige and Skoog (MS) medium supplemented with $3.0mg{\cdot}L^{-1}$ naphthaleneacetic acid (NAA), 3% (w/v) sucrose, 0:60 $NH{_4}^+:NO{_3}^-$ was found suitable for biomass accumulation. Based on the optimized flask-scale parameters, cell suspension cultures were established in balloon-type bubble bioreactors, and bioprocess parameters such as inoculum density and aeration rate were optimized. Inoculum density of $50g{\cdot}L^{-1}$ and increasing aeration rate from 0.05 to 0.3 vvm, with increases every 7 days, were suitable for the accumulation of both biomass and phenolic compounds. With the optimized conditions, $14.70g{\cdot}L^{-1}$ dry biomass, $10.33mg{\cdot}g^{-1}$ DW of phenolics and $3.89mg{\cdot}g^{-1}$ DW of flavonoids could be achieved. Phenolics isolated from the cell biomass showed optimal free radical scavenging activity.

• 한국세라믹학회지
• /
• 제48권5호
• /
• pp.463-466
• /
• 2011

Wet foams formed through direct foaming were stabilized using various concentrations of amiphiphilic particles that could control pore size and porosity. These porous materials showed moderate strength upon compression with high porosity. Bubble size and wet foam stability were tailored by amphiphile concentration, particle concentration, contact angle, and pH of the suspension to obtain crack-free porous solid after sintering. Closed and open pores were obtained with sizes of 30~300 ${\mu}m$ and porosities of over 80%.

• 한국세라믹학회지
• /
• 제56권5호
• /
• pp.513-520
• /
• 2019

This study reports the improvement of mechanical properties of Al₂O₃ porous ceramics from colloidal suspension with the addition of carbon fiber by direct foaming. The initial colloidal suspension of Al₂O₃ was partially hydrophobized by surfactant to stabilize wet foam with the addition of carbon fiber from 2 to 8 wt% as stabilizer. The influence of carbon fiber on the air content, bubble size, pore size and pore distribution in terms of wet foam stability and physical properties of porous ceramics were discussed. The viscosity of the colloidal suspension was increased giving solid like properties with the increased in carbon fiber content. The mechanical properties of the sintered porous samples were investigated by Hertzian indentation test. The results show the wet foam stability of more than 90% corresponds to compressive loading of 156.48 N and elastic modulus of 57.44 MPa of sintered sample with 8 wt% of carbon fiber content.