• Fibers and Polymers
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• v.6 no.2
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• pp.131-138
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• 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.

• Journal of Life Science
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• v.12 no.5
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• pp.577-583
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• 2002

The growth kinetics and the production of $\beta$-glucuronidase from transgenic tobacco's suspension culture was investigated in the flask culture and a 2.5 L bubble column reactor. The growth of bubble column reactor was similar to that of flask culture. However, in the bubble column reactor, the production of $\beta$ -glucuronidase reached 2850 U/mg (85-fold higher than that of flask culture). In both case, the production level of $\beta$ -glucuronidase was fluctuated, which was resulted from periodical degradation of the protein. Sucrose is important component in plant culture medium. Twice addition of sucrose in bubble column reactor could not improve cell growth, since other components in a medium were already depleted. However, the addition of sugar decreased cell size, which facilitated the operation of bioreactor. The production of $\beta$ -glucuronidase was continuously increased, however final concentration of $\beta$ -glucuronidase was similar to that without sucrose addition.

• Proceedings of the Korean Fiber Society Conference
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• 2003.10a
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• pp.47-48
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• 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
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• v.16 no.1
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• pp.47-54
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• 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
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• v.48 no.4
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• pp.915-924
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• 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.

• Journal of the Korean Ceramic Society
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• v.51 no.5
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• pp.511-515
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• 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.

• Resources Recycling
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• v.5 no.3
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• pp.56-64
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• 1996

C,H,OH system is widely used for producing synthetic beverages and pharmaceuticals. Calcium hydroxide suspension was used to callhol the morphology of calcium carbonate, and the charactenstics of the formahan and crystsllizatian of calcium cilrbonate by adding ethylenc glycol were determined A reaclor was made with attaching a ceramic bubble plate, and lhe eleclrical conductivity was continously monitored during the rcaction with CO, gas. A part of the suspension was separated and powdered at the transition point. XRD and electron microscopic observation showed that the intermedmte and final products were vilterite, ;~r;lganite and calcite. In this study, the volumc of the ethylene glycol added to CH,OH was fixed a1 10 vol\ulcornerh. The valumc of the suspension was 500 ml, and the changes oi characteristics were shdied along with variims cnntents(l0-50 g) of calcium hydroxide. Except m the case of 10 g of calcium hydroxide at the crystallization stagc, all of products showed gelation. Tne marc the calcium hydroxide the shorter the formation time. Alsa. the farmalion of spherical valcrile ivas obsemcd when 30 g Ca(OH), was added. Tne vaterite(a compound material) can bc synthesised under alnbienl pressure and lempcmhre m a C,H,OH system by morphology control. Even though the vateritc was meta-stable phasc and could bc changed to calcitc easily, the stable and spherical vateritc was observed by using G5 glass fillers and vacuum dricrs.

• Horticultural Science & Technology
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• v.33 no.2
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• pp.251-258
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• 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.

• Journal of the Korean Ceramic Society
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• v.48 no.5
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• pp.463-466
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• 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%.

• Journal of the Korean Ceramic Society
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• v.56 no.5
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• pp.513-520
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• 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.