Bubble process

The double-bubble process may be used to produce biaxiaHy oriented film, primarily polypropylene. In this process the first bubble formation is similar to the conventional blown film, except that the bubble is not coUapsed. Rather it is reheated to the orientation temperature and blown and drawn further in a second stage. It is then coUapsed, sUt, and wound. This process is generally limited to a final film thickness of less than 24 p.m. 

A variation of the preceding process is used to produce oriented vinyUdene chloride copolymer films. The plastic is extmded into tube form and then is supercooled and subsequently biaxiaHy oriented in a continuous bubble process. The supercooled tube is flattened and passed through two sets of pinch roUs, which are arranged so that the second set of roUs travels faster than the first set. Between the two sets, air is injected into the tube to create a bubble that is entrapped by the pinch roUs. The entrapped air bubble remains stationary while the extmded tube is oriented as it passes around the bubble. Orientation is produced in the transverse and the longitudinal directions, creating excellent tensile strength, elongation, and flexibiUty in the film. The commercial procedure has been described (157). 

Entrained liquids. Production of small droplets is inherent in the bubbling process, as shown by Fig. 14-90. Values range from near zero to 10,000/cm of vapor, depending on how the vapor breaks through the liquid and on the opportunity for evaporation of the small drops after entrainment. 

In their study on LLDPE resins containing 1-butene, 1-hexane, and 1-octene comonomers, Kalyon and Moy [30] found a significant variation in their film thickness when measured around the circumference of tubular bubbles processed under identical conditions. The samples blown with a blow-up ratio of two, exhibited more significant variation in thickness than those prepared with a blow-up ratio of three. However, film processed at a higher blow-up ratio has been found to have less variation in thickness. 

To prepare CO solution for the experimental purpose, it is recommended to bubble 20 ml of stock solution in a sealed glass tube with a stream of pure CO gas. The bubbling process lasts for 20 min under the pressure of 100 kPa at 37°C [3]. One microliter of this CO-saturated solution is estimated to contain 30 ng of the gas based on the solubility of CO at 37°C, the extent of dilution of the CO-saturated solution, and the assumption that the loss of the added CO from the bath solution at the time of experiments is negligible. The stock solution of CO should be freshly prepared before each experiment and then should be diluted immediately to the desired concentration with the bath solution or culture media. 

Bubble point calculation, 24 680, 685 Bubble process, 23 408 Bubble shapes, 11 776-777 in foams, 12 7—11... 

Biaxially oriented polypropylene (BOPP) films have higher stiffness than cast films and consequently can be used in much thinner gauges. Homopolvmers are used almost exclusively to provide maximum stiffness and water-vapor barrier. Oriented films are produced by the tenter frame and bubble processes. 

Entrainment E is inherent in the bubbling process and can stem from a variety of sources, as shown by Fig. 14-89. However, the biggest practical problem is entrainment generated by the kinetic energy of the flowing vapor rather than the bubbling process. As vapor velocity approaches the flooding limit [Eq. (14-168)], the entrainment rises approximately with (velocity)8. 

During the past 40 years, meteorologists and environment specialists have become increasingly aware of the importance of natural sea bubble processes. Their importance to meteorology stems in part from the fact that surface-active organic material in the sea, mainly biological surfactants, tends to concentrate at the surface (ref. 85). 

This expression (bubble velocities distribution) shows that two types of flows participate in the bubbling process the first type, introduced by the first term Eq. (4.256 ), is the regular flow the second flow type is called singular flow and is contained in the term where the Dirac function 5[1 + — (v — v)b] appears. The singular flow becomes unimportant when we have (i) a velocity distribution in a restricted domain around v (ii) a slow concentration of bubbles. Both cases are coupled when we can consider that y O in relation (4.256 ). If we multiply the left and right terms of equation (4.256 ) by v and then integrate it for all velocities of the bubbles, we obtain relations (4.257)-(4.258). Here we used... 

Orientation of styrene-based copolymers is usually carried out at temperatures just above T. BiaxiaUy oriented films and sheet are of particular interest. Such orientation increases tensile properties, flexibility, toughness, and shrinkability. PS produces particularly clear and sparkling film after being oriented biaxiaHy for envelope windows, decoration tapes, etc. Oriented films and sheet of styrene-based polymers are made by the bubble process and by the flat-sheet or tentering process. Eibers and films can be produced by uniaxial orientation (237) (see Eilmand SHEETING materials). 

The air-water flux model (Chapter 10, Eq. (10.24)) has a term for molecular exchange across the interface, Fawi. and one for bubble processes, Feub ... 

The gas transfer velocity is proportional to wind speed and can be estimated if this is known. The bubble terms, however, must be determined from a model of bubble processes (explained in Chapter 10) and the concentrations of the inert gases Ar, N2 and Ne. 

For the upper ocean, equations for the mass balance of DIG and DI G are similar to those used for the O2 mass balance however, there are two important differences. First, bubble processes can be neglected for gas transfer of GO2 because it is a much more soluble gas. At solubility equilibrium GO2 partitions about equally between the atmosphere and seawater whereas O2, Ar, N2, and Ne remain primarily... 

The fliox created by bubbles has been mathematically described in many ways, but all present theories are strongly dependent on assumptions regarding the nature of the bubble surface, the initial size spectra of the bubbles, and the distributions of bubbles with depth. A model that has been used to predict the effect of bubbles on gas saturation (Keeling, 1993, as modified from Fuchs et al, 1987) assumes that the full spectrum of bubble process can be described by a combination of two bubble transfer processes (Fig. 10.10). The first is the mechanism by which small bubbles, < 50 pim in diameter, completely collapse and inject their contents into the water. This mechanism has been called air injection or total trapping by bubbles. In this case flux of gas from the bubble depends only on the total volume of air transferred by these bubbles, which is described by an empirical transfer velocity, Vinj (mol m d atm ) and the mole fraction, X, of the gas in the air... 

A schematic diagram of steady-state gas supersaturation caused by bubble processes when there is no net flux at the air-water interface. The small symbols represent gas molecules in the air and dissolved in the water. The greater concentration of these symbols in the water relative to air on the left side of the diagram indicates that the dissolved gas is supersaturated in the water. The bubble-induced flux, Fb, into surface waters, illustrated on the right side of the diagram, is balanced by a diffusive flux across the air-water interface, Eawi. indicated on the left side. 

In this situation the degree of super saturation is highly dependent on the physicochemical properties of the gases (diffusion coefficient and solubility). Less soluble gases are more supersaturated than soluble ones at steady state because the water has lower relative concentrations of these gases to start with. For this reason, a small amount of air forced into the water by bubble processes has a much larger effect on the relative concentrations of Ne or N2 than it does on CO2. 

In the other extreme, when the exchange mechanism of bubble processes dominates (Vjnj = 0), and the bubble mechanism has the diffusion coefficient and solubility dependence prescribed for initial gas transfer across a clean bubble (m = 1 and n = 0.5), the gas supersaturation has no dependence on the physicochemical properties of the gases ... 

Table 10.3. I The relative degree of supersaturation 0/N2, Ar, and Ne at 20 °C created by bubble processes at steady state when there is no net gas flux across the air-water interface...

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