Bubble generating devices

In the present research, we study two fundamental properties of bubble columns liquid hold-up and mixing. Both of these properties depend on the flow rates of the gas and liquid phases. These two properties may be considered response variables in the sense that their values depend on the way bubbles are formed. We present results for two types of bubble generating devices (or, for short, spargers) i.e. perforated rigid plates and perforated rubber sheets. An advantage of the rubber-sheet sparger is the self-cleaning feature. This is... 

Figure 8.7 Axisymmetric flow focusing bubble generation device.

Figure 8.8 Planarflow focusing bubble generation device without nozzle, (a) Sketch of the device showing the expected shape of the free surface (b) picture of bubble-liquid suspension obtained. From [67].

The flow patterns of single-phase liquids in tanks agitated by various types of impeller have been reported in the literature. The experimental techniques used include the use of coloured tracer liquid, mutually-buoyant particles, hydrogen bubble generation and mean velocity measurements using pitot probes, hot-rdm devices and lasers. 

Figure 8.9 Planar flow focusing foam generation device with gas nozzle, (a) Schematic diagram (b) optical micrograph of the production of a foam comprising monodisperse bubbles.

The specific surface area of an industrial-sized continuous stirred tank reactor (CSTR) can be calculated from the reactor dimensions. However, it is difficult to estimate the effect of the formation of bubbles and of the stirrer-induced vortex at low melt viscosity. The calculation of the characteristic length of diffusion in a high-viscosity finishing reactor with devices for the generation of thin films with respective high specific surface areas is more complex. 

It is clear then, that the measurement of non-Newtonian materials presents special challenges for a viscometer. Many industrial viscometers designed to give a single point determination have a deceptively simple operating principle. Examples include the speed at which a liquid flows out of a container through a known orifice, a bubble rises in a column of fluid, or a ball falls in a column of fluid. These simple devices are actually very complex in terms of the shear field that is generated. The shear field is the variation of shear stress or shear rate as a function of position within the... 

Devices such as ultrasonic flow equipment use the Doppler frequency shift of ultrasonic signals reflected from discontinuities in the fluid stream to obtain flow measurements. These discontinuities can be suspended solids, bubbles, or interfaces generated by turbulent eddies in the flow stream. The sensor is mounted on the outside of the pipe, and an ultrasonic beam from a piezoelectric crystal is transmitted through the pipe wall into the fluid at an angle to the flow stream. Signals reflected off flow disturbances are detected by a second piezoelectric crystal located in the same sensor. Transmitted and reflected signals are compared in an electrical circuit, and the corresponding frequency shift is proportional to the flow velocity. 

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