Bubble formation control

BWRs do not operate with dissolved boron like a PWR but use pure, demineralized water with a continuous water quality control system. The reactivity is controlled by the large number of control rods (>100) containing burnable neutron poisons, and by varying the flow rate through the reactor for normal, fine control. Two recirculation loops using variable speed recirculation pumps inject water into the jet pumps inside of the reactor vessel to increase the flow rate by several times over that in the recirculation loops. The steam bubble formation reduces the moderator density and... 

Wedlock, D.J. (ed.), 1994. Controlled particle, droplet and bubble formation. Oxford Butterworth-Heinemann. 

In bubbling, the control of the bubble diameter is a little easier. In these methods bubbles are made at an orifice or a multitude of orifices. If there is only one orifice, of radius r, and if bubble formation is slow and undisturbed, the greatest possible bubble volume is 27rry/gp] y is the surface tension of the liquid, p the difference between the densities of liquid and gas (practically equal to the density of the liquid), and g is acceleration due to gravity. Every type of agitation lowers the real bubble size. On the other hand, if there are many orifices near enough to each other, the actual bubble may be much larger than predicted by the above expression. 

Borstar A catalytic process for polymerizing ethylene. Use of two reactors, a loop reactor and a gas-phase reactor, allows better control of molecular weight distribution. The loop reactor operates under super-critical conditions to avoid bubble formation. Either Ziegler-Natta or metallocene catalysts can be used. The first commercial unit was installed in Porvoo, Finland, in 1995. 

Schurmann (S6) and Davidson and Schuler (D8) used extremely small orifices, so that the downward surface-tension force was negligible, and viscosity was the controlling factor in bubble formation Hence these investigators concluded that viscosity has a great influence on the bubble formation. 

Bubbles are critical in manufacturing in the food industry. The stability and size of the bubbles determines the taste and the looks of the product. In industry, much research has been done on the factors that control bubble formation and stability. This is of special interest in the production of ice cream, where air bubbles are trapped in frozen material. 

E Matijevic. In DJ Wedlock, ed. Controlled Particle, Droplet and Bubble Formation. London Butterworth-Heinemann, 1994, pp 39-59. 

In a related experimental study, the relative effectiveness of all the above-mentioned decompression tables in reducing bubble formation within aqueous gels was evaluated quantitatively under rigorously controlled conditions specifically, visual counts were conducted of the bubbles formed in highly purified agarose gels (ref. 49,139) subjected to the different decompression schedules. 

Temperature has often been suggested as a useful control variable for HPLC to make a changes and to speed equilibrations leading to faster separations. The problem has been that both bonded-phase hydrolytic cleavage and solubility of silica in aqueous solvents are accelerated at elevated temperatures. Mobile phase boiling within the column can cause bubble formation and vapor locking if the critical point of the solvent is exceeded. Finally, thermal-labile compounds can suffer degradation at elevated temperatures. 

It was found that Sylgard 184 provided a higher tensile strength and elongation than RTV 615, and so the former was selected for fabrication of the microvalve control layer [449]. Moreover, the control channel must be filled with water before use, in order to prevent bubble formation in the fluidic channel due to the gas permeability of PDMS [449]. 

Interconnection of expanded interlayers, control the bubble formation in the char, control of the rheology up to high temperature... 

Since epoxy formulations are generally good thermal insulators, the exotherm will depend on the mass of the system. A high rate of exotherm is needed with some epoxy adhesive systems to achieve practical curing rates. However, excessively high exothermic temperatures can result in bubble formation, thermal degradation, and even a potentially hazardous situation. Control of the exotherm is, therefore, a very important factor in formulating epoxy adhesives. 

Borstar A catalytic process for polymerizing ethylene or propylene, subdivided into Borstar PE and Borstar PP. Use of two reactors — a loop reactor and a gas-phase reactor — allows better control of molecular weight distribution. The loop reactor operates under supercritical conditions to avoid bubble formation. Either Ziegler-Natta or metallocene catalysts can be used. The latest version, Borstar PE 2G, uses a single, multizone gas-phase reactor to make polymers that have bimodal molecular weight distributions. Developed by Borealis A/S. The first commercial unit, for polyethylene, was installed in Porvoo, Finland, in 1995. The first polypropylene plant was operated by Borealis in Schwechat, Austria, in 2000. In 2005, Borstar s total capacity for PE and PP was 1.3 million tons. 

A study of the effect of pore geometry on foam formation mechanisms shows that snap-off" bubble formation is dominant in highly heterogeneous pore systems. The morphology of the foams formed by the two mechanisms are quite different. A comparison of two foam injection schemes, simultaneous gas/surfactant solution injection (SI) and alternate gas/surfactant solution injection (GDS), shows that the SI scheme is more efficient at controlling gas mobility on a micro-scale during a foam flood. 

Figure 27.8 Domains of bubble formation Domain A bubble volume is controlled by the size of orifice, Domain B bubble volume is controlled by the interfacial tension.

In the bubble formation from an inclined surface, however, the bubble development and the bubble detachment processes are decoupled because a developing bubble could drift out of the orifice due to the component of the buoyancy parallel to the inclined surface. Once a sessile bubble drift out of the orifice, the bubble development ceases because no air is fed into a sliding bubble. Since the bubble development and detachment are decoupled, the flow rate of air becomes an important factor, which controls the frequency of sliding bubble... 

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