Internal Annular Flow Condensation and Flow Boiling: Context, Results, and Recommendations

Experimental investigations of temperature controlled innovative annular flow-boiling of FC-72 in millimeter scale ducts – steady and enhanced pulsatile realizations

“…It was decided that a more precise set of experimental results, when compared with a more precise set of results obtained from a precise suppressed nucleation modeling and its CFD-based solutions/simulations, can answer the question of significance of micronucleation to heat transfer rates -and that if it is the dominant mechanism, there is no need to expect that micro-convection effects which was observed to be dominant for flowcondensation [9] would also be equally dominant for flow-boiling. Despite the above clarity in hindsight, the existing literature's attempts at decomposing local HTC into nucleate and convective boiling contributions were confusing -and it was not clear whether such results (as reviewed in [13]) applied to this situation (and this is sorted out and discussed in section 4).…”

“…These are obtained from: Void-fraction and Heat Transfer Empirical Correlations [8][9][10][11][12][13][14],…”

Assessment of Annular Flow Boiling in the Context of Computational Fluid Dynamics (Cfd) Simulations, Experiments, and Existing Correlations

“…Above this critical heat-flux value, the flow displays instabilities which may result in time varying dry spots on the heating surface (typically experiencing higher qualities) or, in some cases, it may lead to inverted annular flow where the flow has liquid flowing in the core region -with vapor flowing in the annulus region. See [9][10][11] etc.…”

“…1.2a, is desired to be around 300 µm. This is, presumably, neither too thin nor too thick and it is important for subsequent and possible transitioning of the steady operations to pulsatile operations which were briefly discussed in Section 1.1 and discussed in detail elsewhere [9,13]. The control of inlet liquid film thickness by recirculating vapor is essential because, otherwise, the liquid film thickness may change abruptly to an undesirable range, as it exits the splitter plate in Fig.…”

“…This section discusses some of the constraints involved in the design of flowcondensers that may be required to operate in the thin liquid steady annular flowregime. Such condensers can, in principle, be converted to high heat-flux compact devices by superposing a pulsatile flow-physics -described in [9].…”