Shear-sensitive liquid

The optical-based shear stress sensor can be classified into two categories based on the measurement principle oil-film interferometry and shear-sensitive liquid crystal. These techniques are discussed in the following sections. 

Shear Stress Sensors, Fig. 6 Schematic showing (a) the principle of shear-sensitive liquid crystal and (b) the experimental setup for shear stress measurement using shear-sensitive liquid crystal... 

Shear-sensitive liquid crystal coatings applied to a solid surface consist of helical aggregates of long planar molecules arranged in layers parallel to the coated surface. This molecular... 

The schematic showing (a) the principle of shear-sensitive liquid crystal and... 

In an airlift fermenter, mixing is accomplished without any mechanical agitation. An airlift fermenter is used for tissue culture, because the tissues are shear sensitive and normal mixing is not possible. With the airlift, because the shear levels are significantly lower than in stirred vessels, it is suitable for tissue culture. The gas is sparged only up to the part of the vessel cross section called the riser. Gas is held up, fluid density decreases causing liquid in the riser to move upwards and the bubble-free liquid to circulate through the down-comer. The liquid circulates in airlift reactors as a result of the density difference between riser and down-comer. 

In this chapter, we study various correlations for gas-liquid mass transfer, interfacial area, bubble size, gas hold-up, agitation power consumption, and volumetric mass-transfer coefficient, which are vital tools for the design and operation of fermenter systems. Criteria for the scale-up and shear sensitive mixing are also presented. First of all, let s review basic mass-transfer concepts important in understanding gas-liquid mass transfer in a fermentation system. 

Torque rheometers are multipurpose instruments well suited for formulating multicomponent polymer systems, studying flow behavior, thermal sensitivity, shear sensitivity, batch compounding, and so on. The instrument is applicable to thermoplastics, rubber (compounding, cure, scorch tests), thermoset materials, and liquid materials. 

Mechanically stirred hybrid airlift reactors (see Fig. 6) are well suited for use with shear sensitive fermentations that require better oxygen transfer and mixing than is provided by a conventional airlift reactor. Use of a low-power axial flow impeller in the downcomer of an airlift bioreactor can substantially enhance liquid circulation rates, mixing, and gas-liquid mass transfer relative to operation without the agitator. This enhancement increases power consumption disproportionately and also adds other disadvantages of a mechanical agitation system. 

The optimal configuration depends on numerous factors, including the required gas transfer and mixing rates, and an acceptable range of shear rates. Some factors may be mutually contradictory as in a crystallizer where the required gas-liquid transfer rate is best achieved by increasing turbulence and shear yet the crystals are shear sensitive. In these cases, successful design carefully balances the contradictory factors. 

Osmotic distillation is unique among concentration processes in that feeds containing thermally labile or shear-sensitive components, and those with appreciable volatility, can be concentrated with little or no loss of product integrity. This characteristic is particularly important for the concentration of fruit juices and other liquid foodstuffs, such as vegetable juices, and tea and coffee extracts. These feeds contain a complex mixture of essential volatile hydrophilic flavor, and fragrance components in very low concentrations. Substantial depletion of these components by direct destruction or evaporation may render the product... 

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