Air, entrained

Defoamers. Foam is a common problem in papermaking systems (27). It is caused by surface-active agents which are present in the pulp slurry or in the chemical additives. In addition, partially hydrophobic soHd materials can function as foam stabilizers. Foam can exist as surface foam or as a combination of surface foam and entrained air bubbles. Surface foam usually can be removed by water or steam showers and causes few problems. Entrained air bubbles, however, can slow drainage of the stock and hence reduce machine speed. Another serious effect is the formation of translucent circular spots in the finished sheet caused by permanently entrained air. 

The vapor pressure may be dependent on the amount of the dissolved, not the entrained, air in the Hquid. This issue is important to appHcations of cooling-water double-suction pumps (58,59). Because of the unknowns, a safety margin is always recommended for use to minimise the effects of cavitation. 

Flotation. Flotation (qv) is used alone or in combination with washing and cleaning to deink office paper and mixtures of old newsprint and old magazines (26). An effective flotation process must fulfill four functions. (/) The process must efficiently entrain air. Air bubble diameter is about 1000 p.m. Typically air bubbles occupy 25—60% of the flotation cell volume. Increa sing the airRquid ratio in the flotation cell is said to improve ink removal efficiency (27). (2) Ink must attach to air bubbles. This is primarily a function of surfactant chemistry. Air bubbles must have sufficient residence time in the cell for ink attachment to occur. (3) There must be minimal trapping of cellulose fibers in the froth layer. This depends on both cell design and surfactant chemistry. (4) The froth layer must be separated from the pulp slurry before too many air bubbles coUapse and return ink particles to the pulp slurry. 

Phenomena at Liquid Interfaces. The area of contact between two phases is called the interface three phases can have only aline of contact, and only a point of mutual contact is possible between four or more phases. Combinations of phases encountered in surfactant systems are L—G, L—L—G, L—S—G, L—S—S—G, L—L, L—L—L, L—S—S, L—L—S—S—G, L—S, L—L—S, and L—L—S—G, where G = gas, L = liquid, and S = solid. An example of an L—L—S—G system is an aqueous surfactant solution containing an emulsified oil, suspended soHd, and entrained air (see Emulsions Foams). This embodies several conditions common to practical surfactant systems. First, because the surface area of a phase iacreases as particle size decreases, the emulsion, suspension, and entrained gas each have large areas of contact with the surfactant solution. Next, because iaterfaces can only exist between two phases, analysis of phenomena ia the L—L—S—G system breaks down iato a series of analyses, ie, surfactant solution to the emulsion, soHd, and gas. It is also apparent that the surfactant must be stabilizing the system by preventing contact between the emulsified oil and dispersed soHd. FiaaHy, the dispersed phases are ia equiUbrium with each other through their common equiUbrium with the surfactant solution. 

Solids addition entrains air into inerted head space, creates flammable... 

Two wooden beams are butt-jointed using an epoxy adhesive (Fig. A1.3). The adhesive was stirred before application, entraining air bubbles which, under pressure in forming the joint, deform to flat, penny-shaped discs of diameter 2fl = 2 mm. If the beam has the dimensions shown, and epoxy has a fracture toughness of 0.5 MN mT , calculate the maximum load F that the beam can support. Assume K = cT Tra for the disc-shaped bubbles. 

Pressure Surge. Not enough NPSHa. Air aspirated or air pockets at the suction line. Entrained Air. Plugged impeller. 

Inadequate sump design leads to entrained air bubbles and turbulenee. This will damage the pump (Figure 17-6). 

After combustion, the rich burning mixture leaves the combustion zone and flows between the rows of air jets entering the liner. Each jet entrains air and burning fuel and carries it toward the combustor axis, forming torroidal recirculation patterns around each jet that result in intensive turbulence and mixing throughout the combustor. 

In most gas turbines, liquid fuel is atomized and injeeted into the eom-bustors in the form of a fine spray. A typieal low-pressure fuel atomization nozzle is shown in Figure 10-10. The fuel spray entrains air beeause of the... 

Imagine that we enclose the plume, as shown in Fig. 7.74. The plume still entrains air from the surroundings, but the available fresh air is limited. This means that fresh air will surround the plume only up to a certain level. Above this level, the entrained air has to be recirculated from the plume itself. This leads to a two-zone flow model, wirh a layer of fresh air at the borrorn, and warmer air from the plume at the top. The interface between the two layers is located at the height at which the entrained air in the plume equals the supplied air. rhis can be found from the volume-flow formulae of Section 7.5.2. 

The theory for plane jets is similar to descriptions of circular jets (see Section 7.4) and many derived equations describe both two-dimensional (plane) and three-dimensional (round) jets. The principle is to generate such high air velocity that a shield against pressure difference, temperature difference, and wind velocity is sustained. Howeveg it is not possible to have complete separation by an air curtain. The main reason for this, is that the jet entrains air... 

This entrained flow rate is normally many times the original flow race and it is the total flow rate that the receiving opening must be designed to exhaust. At the same time the entrained air must be available to both sides of the jet,... 

The rate of combustion is set equal to the rate of heat applied to warm the entrained air plus the radiative heat losses ... 

Based on handling pure liquids, without entrained air or other non-condensable gases, which adversely affect the pump performance. 

Submergence of the inlet pipe column or bell inlet below the water level is necessary for good operation and to prevent vortexes and entrained air. The minimum submergence as recommended by the manufacturer must be maintained at all Limes. Generally, for 70°F w ater, each 1000 feet of elevation above sea level adds 14 inches to the... 

Any high spot in the suction line can become filled with air or vapor, which, if transported into the impeller, will create an effect similar to cavitation, and with the same results. Services that are particularly susceptible to this situation are those where the pump volume contains a significant amount of entrained air or vapor, as well as those operating on a suction lift, where it can also cause the pump to lose its prime. A concentric reducer can cause a similar effect. The suction of a pump should be fitted... 

In addition to providing storage for the reserve fluid needed for the system, the reservoir acts as a radiator for dissipating heat from the fluid. It also acts as a settling tank where heavy particles of contamination may settle out of the fluid and remain harmlessly on the bottom until removed by cleaning or flushing the reservoir. Also, the reservoir allows entrained air to separate from the fluid. 

Large reservoirs are desirable for cooling. A large reservoir also reduces re-circulation, which helps settle contamination, and separates entrained air. As a mle of thumb, the ideal reservoir should be two to three times the pump outlet per minute. However, due to space limitations in mobile and aerospace systems, the benefits of a large reservoir may have to be sacrificed. But they must be large enough to accommodate thermal expansion of the fluid and changes in fluid level due to system operation. 

The hydraulic oil must provide adequate lubrication in the diverse operating conditions associated with the components of the various systems. It must function over an extended temperature range and sometimes under boundary conditions. It will be expected to provide a long, trouble-free service life its chemical stability must therefore be high. Its wear-resisting properties must be capable of handling the high loads in hydraulic pumps. Additionally, the oil must protect metal surfaces from corrosion and it must both resist emulsification and rapidly release entrained air that, on circulation, would produce foam. 

Ice-cream must be kept at low temperature right up to the point of final consumption. If it is allowed to soften, the entrained air bubbles may escape and the original texture will be lost. If it softens and is then re-frozen, a hard, solid skin forms, making the product inedible. Ice-cream must always be handled quickly when passing through transit stages from the factory to consumer. 

If the air in a horizontal jet is warmer or cooler than the surrounding air, it will tend to rise or fall. This effect will lessen as the jet entrains air, but may be important if wide temperature differences have to be used or in large rooms [58, 59]. 

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