Buoyancy control

This is consistent with data published by High (1968). Because liftoff is buoyancy-controlled, its relation to initial mass must have a power of 1/6, as shown by a fireball model of Fay and Lewis (1977). 

Thus, one observes that regardless of whether the fuel jet is momentum- or buoyancy-controlled, the flame height yF is directly proportional to the volumetric flow leaving the port exit. 

For large Froude numbers, the diffusion flame height is momentum-controlled and v = v0. However, most laminar burning fuel jets will have very small Froude numbers and v = vbj that is, most laminar fuel jets are buoyancy-controlled. 

Although the flame height is proportional to the fuel volumetric flow rate whether the flame is momentum- or buoyancy-controlled, the time to the flame tip does depend on what the controlling force is. The characteristic time for diffusion (tD) must be equal to the time (ts) for a fluid element to travel from the port to the flame tip, that is, if the flame is momentum-controlled,... 

Equation (6.31) shows the same dependence on Q as that developed from the Burke-Schumann approach [Eqs. (6.21)—(6.23)]. For a momentum-controlled fuel jet flame, the diffusion distance is r, the jet port radius and from Eq. (6.30) it is obvious that the time to the flame tip is independent of the fuel volumetric flow rate. For a buoyancy-controlled flame, ts remains proportional to (yF/v) however, since v = (2gyF)1/2,... 

Thus, the stay time of a fuel element in a buoyancy-controlled laminar diffusion flame is proportional to the square root of the fuel volumetric flow rate. This conclusion is significant with respect to the soot smoke height tests to be discussed in Chapter 8. 

The preceding analyses hold only for circular fuel jets. Roper [10] has shown, and the experimental evidence verifies [11], that the flame height for a slot burner is not the same for momentum- and buoyancy-controlled jets. Consider a slot burner of the Wolfhard-Parker type in which the slot width is x and the length is L. As discussed earlier for a buoyancy-controlled situation, the diffusive distance would not be x, but some smaller width, say xb. Following the terminology of Eq. (6.25), for a momentum-controlled slot burner,... 

Comparing Eqs. (6.34) and (6.37), one notes that under momentum-controlled conditions for a given Q, the flame height is directly proportional to the slot width while that under buoyancy-controlled conditions for a given Q, the flame height is independent of the slot width. Roper et al. [11] have verified these conclusions experimentally. 

The ratio of L/D (flame length to the gas exit diameter) is calculated and found to be 139, which is less than 200. Therefore, the jet flame is buoyancy-controlled and the calculated flame length of 13.9 m is appropriate. 

Heskestad, G. 1981. Peak Gas Velocities, and Flame Heights of Buoyancy-Controlled Turbulent Diffusion Flames. Eighteenth Symposium on Combustion. The Combustion Institute, Pittsburgh, PA. 

The hose couplings, buoyancy control (air pressure) and method of initiation (by Prima-cord) were the same as for the NOL Streamer in Use at that time. The only apparent weakness of the duPont streamer was that the pellets were broken to some extent by handling and countermining. The disadvantage of foe pellet load was largely eliminated by the EL development of a blend of flaked and grained TNT for use in the NOL canvas sock... 

Processing plants, holding spaces, living quarters, buoyancy control and navigation... 

Ryan MP (1994) Neutral-buoyancy controlled magma transport and storage in mid-ocean ridge magma reservoirs and their sheeted-dike complex a summaiy of basic relationships. Magmatic Systems 57 97-138... 

Flame type F. Long, luminous, lazy. No swirl, nor circulation. Low foef and air jet velocity. Laminar jet, buoyancy-controlled. Delayed, slow, diflusion mixing. Used for coverage in tong chambers, and to add luminous radiation. 

A sudden rapid decrease in barometric pressure. This may occur from loss of integrity of a pressurized aircraft cabin or recompression chamber, or in a diver who surfaces rapidly from depth due to a loss of buoyancy control. It may result in decompression sickness or pulmonary hyperinflation and air embolism. 

Schematic of extensional rheometer with a translating clamp and vertical buoyancy control bath. The temperature control fluid is circulated through a jacket around the buoyancy fluid. An outer vacuum jacket insulates the apparatus. Redrawn from Munstedt (1979).

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