Transition boiling regime

Operation in the transition boiling regime is normally avoided in the design of heat transfer equipment, and thus no major attempt has been made to develop general correlations for boiling heal transfer in this regime. 

Ramilison, J. M., and J. H. Lienhard, 1987, Transition Boiling Heat Transfer and the Film Transition Regime, Trans. ASME. J. Heat Transfer 109 146. (2)... 

Various boiling regimes during boiling of methanol on a horizontal l-cm-diametet Steam-healed copper tube (n) nucleate boiling, (fc) transition boiling, and (c) film boiling. 

Nucleate boiling is the most desirable boiling regime in practice because high heat transfer rates can be achieved in this regime with relatively small values of A7 c, ss typically under 30"C for water. The photographs in Fig. 10-7 show the nature of bubble formation and bubble motion associated with nucleate, transition, and film boiling. 

This ratio is a comparison of convective effects in the liquid layer (causing a to increase with x) and bubble dynamics at the wall (causing a to increase with q). Thus Xcv/Xb is proportional to Bo and a function of vapour quality so that the boiling number is the appropriate dimensionless number to study the transition between these two boiling regimes. 

In convective vaporization, the same boiling regimes are encountered, but modified by the net motion of the two-phase fluid past the surface. At low velocities or high heat fluxes, the convection effect is small, and nucleate boiling dominates. At higher velocities, the heat-transfer rate is dominated by the two-phase mixture sweeping across the surface. It is still important to avoid transition and film boiling, but the onset of these phenomena is complicated by many factors. (See [1, 34].)... 

Typical heat transfer results to monodisperse sprays impacting on a heated surface are shown in Fig. 18.24. The liquid flow rate is varied over a wide range, while the droplet diameter is kept almost constant [136]. The heat flux versus surface temperature trends are similar to those of conventional boiling curves (see Chap. 15 of this handbook), and the heat fluxes are very high. The available experimental data [133, 134,137-140] show that the volumetric spray flux V (m3/m2 s) is a dominant parameter affecting heat transfer. However, mean drop diameter and mean drop velocity and water temperature have been found to have an effect on heat transfer and transitions between regimes. Urbanovich et al. [141], for example, showed that heat transfer is not only a function of the volumetric spray flux but also of the pressure difference at the nozzle and the location within the spray field (Fig. 18.25). 

Heat transfer coefficients (HTCs) between melt and water fields are provided via a boiling curve, which describes nucleate, transition, and film boiling. (In the present problem, only the film boiling regime occurs.) At high vapor volume fractions, a transition is made between film boiling heat transfer to water and convective heat transfer to vapor from the melt. 

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