The Low-Velocity Burn-Out Regime

The characteristic that has been called the low-velocity regime (M2) would have been observed at a much earlier stage if burn-out data had existed for experiments covering a very wide range of mass velocities with the other system parameters fixed. Even today there is no really good direct example of 

In Fig. 26, the dotted lines correspond to 100% quality at the tube exit and represent the 0/G ratios obtained from the following heat-balance equation for a uniformly heated tube (with k = 1)  

Because of the closeness of the low-velocity regime to the 100% quality line, it is to be expected that latent heat will be the dominant fluid property controlling burn-out in this regime. In fact, it has been found (M3) that latent heat alone can adequately represent all the low-velocity regime data, which includes pressures ranging from 15 to 2000 psia. For uniformly heated round tubes, for example, the appropriate burn-out equation obtained, based on Eq. (18), is  

Equation (21) fits the published data belonging to the low-velocity regime (Fig. 27), with an rms error of 5.5 %, and is applicable to any system pressure. 

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Fig. 27. Approximate boundary of the low-velocity burn-out regime for water flowing in round tubes. The low-velocity regime lies to the left of any given curve [from Macbeth (M2)].

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