Entrainment coefficient

The coefficients in the equations differ slightly in different references, depending on the entrainment coefficients used. The convective heat flux , in W or W/m from the heat source, can be estimated from the energy consumption of the heat source by... 

Froude number W1 /( bQ is nearly the same for the near and far field plumes, 1.60 0.1. The entrainment coefficients are much larger, which probably includes pressure effects near the base for the axisymmetric fires and tornado-flame filament effects for the line fire, which are actually three dimensional. It should be realized that the data corresponding to these correlations contain results for finite fires D > 0, not idealized sources. The correlations in Tables 10.1 and 10.2 are one set of formulas others exist with equal validity. 

Allow me now to call this tendency to entrain droplets K2, where K is a derived number, the entrainment coefficient, describing the tendency to entrain droplets of a randomly produced size distribution. We then... 

Y 1-2F) J where Cd is the drag coefficient inside the convective IBL 3/ is the lapse rate above the boundary layer or upwind conditions F is an entrainment coefficient, which ranges from 0 to 0.22 6>iand and 6>sea are the potential air temperatures over land and water, respectively and X is the distance or fetch downwind from the shoreline. The dependency of h on has been predicted by dimensional analysis and by the modynamic approaches. 

Entrainment coefficient A measure of the tendency of a flowing gas to carry droplets of liquid. 

In general, this equipment offers an economical heat-transfer area for first cost as well as operating cost. Capacity is hmited primarily by the air velocity which can be used without excessive dust entrainment. Table 12-32 shows hmiting air velocities suitable for various sohds particles. Usually, the equipment is satisfactory for particles larger than 100 mesh in size. [The use of indirect-heated conveyors eliminates the problem of dust entrainment, but capacity is limited by the heat-transfer coefficients obtainable on the deck (see Sec. 11)]. 

Jet interaction should not be taken into account when the jets are closely adjacent to each other, are propagated in confined conditions, and entrainment of the ambient air is restricted. This may be the case for concentrated air supply when air diffusers are uniformly positioned across the wall and the jets are replenished by the reverse flow, which decreases the jet velocity. This effect should be taken into consideration using the confinement coefficient discussed in Section 7.4.5. For the same reason, jet interaction should not be taken into consideration when air is supplied through the ceiling-mounted air diffusers and they are uniformly distributed across the ceiling. 

Wall temperatures drop after reaching the maximum in the case of the two highest heat flux levels in Fig. 8, and this is due to increasing convective heat transfer through the steam film, which now completely blankets the surface. The improved heat transfer is caused by the higher flow velocities in the tube as more entrained liquid is evaporated. Finally, at about 100% quality, based on the assumption of thermal equilibrium, only steam is present, and wall temperatures rise once more due to decreasing heat-transfer coefficients as the steam becomes superheated. 

The above model of settler flow behaviour, combined with entrainment backmixing was used by Aly (1972) to model the unsteady-state extraction of copper from aqueous solution, using Alamine 336 solvent. An identification procedure for the relevant flow parameters showed an excellent fit to the experimental data with very realistic entrainment backmixing factors, fL = fQ = 3.5 percent, the fraction of well-mixed flow in the settlers, (XX = ay = 5 percent and an overall mass transfer capacity coefficient, Ka = 25 s->. 

Instead of using a constant value of the mass transfer coefficient k at each pressure given by Harwell (Walley et al., 1973), Levy and Healzer (1980) developed an entrainment parameter p. GF and P are evaluated by solving the following two equations simultaneously ... 

In circumstances when entrained bubbles are present during devolatilization, considerable ambiguity can exist with regard to the physical significance of the mass transfer coefficients. If the mass transfer coefficient is defined, or measured, in the usual way [Eq. (43)], the rate at which mass is transferred is not in any way related to diffusional processes but instead is a measure of the rate at which bubbles are rupturing or being released from solution. Thus,... 

On the other hand, if bubble growth is diffusion controlled, then the mass transfer coefficient may be meaningful. However, in this case, the surface area for mass transfer is the surface area of the bubbles entrained in the solution and this depends on the volume of liquid in the extraction zone and not on the surface area of the extraction zone. Clearly, attempts to correlate experimental data for the extraction of a volatile component from a polymeric solution containing entrained bubbles using mass transfer coefficients can be misleading or totally erroneous. 

Annular orifices can also be used to advantage for gas metering when there is a possibility of entrained liquids or solids and for liquid metering with entrained gas present in small concentrations. Coefficient K was found by Bell and Bergelin [Trans. Am. Soc. Mech. Eng., 79, 593-601 (1957)] to range from about 0.63 to 0.67 for annulus Reynolds numbers in the range of 100 to 20,000 respectively for values of 2L/(D — d) less than 1 where L = thickness of orifice at outer edge, D = inside pipe diameter, and d = diameter of orifice disk. The annulus Reynolds number is defined as... 

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