Editing Boiling (section)

== Influence of geometry ==

=== Pool boiling ===

"Pool boiling" refers to boiling where there is no forced convective flow. Instead, the flow occurs due to [[Density gradient|density gradients]]. It can experience any of the regimes mentioned above.

=== Flow boiling ===

"Flow boiling" occurs when the boiling fluid circulates, typically through pipes.<ref name="JamesHoldenFlowBoiling">{{cite journal | last1=Holden | first1=James B. | last2= Rowzee | first2= E. Ralph  | title=Adiabatic flow of boiling water through a horizontal pipe. | journal=Massachusetts Institute of Technology | publisher=Department of Chemical Engineering | year=1931}}</ref> Its movement can be powered by pumps, such as in power plants, or by density gradients, such as in a [[thermosiphon]] or a heat pipe. Flows in flow boiling are often characterised by a void fraction parameter, which indicates the fraction of the volume in the system that is vapor. One can use this fraction and the densities to calculate the [[vapor quality]], which refers to the mass fraction that is in the gas phase. Flow boiling can be very complex, with heavy influences of density, flow rates, and heat flux, as well as surface tension. The same system may have regions that are liquid, gas, and two-phase flow. Such two phase regimes can lead to some of the best heat transfer coefficients of any system.

=== Confined boiling ===

Confined boiling refers to boiling in confined geometries, typically characterized by a [[Bond number]] that compares the gap spacing to the capillary length. Confined boiling regimes begin to play a major role when Bo < 0.5. This boiling regime is dominated by "vapour stem bubbles" left behind after vapour departs.<ref name="Alsaati Warsinger Weibel Marconnet 2021 p=121520">{{cite journal | last1=Alsaati | first1=A.A. | last2=Warsinger | first2=D.M. | last3=Weibel | first3=J.A. | last4=Marconnet | first4=A.M.|author4-link=Amy Marconnet | title=Vapor stem bubbles dominate heat transfer enhancement in extremely confined boiling | journal=International Journal of Heat and Mass Transfer | publisher=Elsevier BV | volume=177 | year=2021 | issn=0017-9310 | doi=10.1016/j.ijheatmasstransfer.2021.121520 | page=121520| bibcode=2021IJHMT.17721520A | url=https://docs.lib.purdue.edu/coolingpubs/384 }}</ref> These bubbles act as seeds for vapor growth. Confined boiling typically has higher heat transfer coefficient but a lower CHF than pool boiling. CHF occurs when the vapor momentum force at the two-phase interface balances the combined surface tension and hydrostatic forces, leading to irreversible growth of the dry spot.<ref name="Alsaati Warsinger Weibel Marconnet 2023 p. 104542">{{cite journal | last1=Alsaati | first1=Albraa A. | last2=Warsinger | first2=David M. | last3=Weibel | first3=Justin A. | last4=Marconnet | first4=Amy M.|author4-link=Amy Marconnet | title=A mechanistic model to predict saturated pool boiling Critical Heat Flux (CHF) in a confined gap | journal=International Journal of Multiphase Flow | publisher=Elsevier BV | volume=167 | year=2023 | issn=0301-9322 | doi=10.1016/j.ijmultiphaseflow.2023.104542 | page=104542| bibcode=2023IJMF..16704542A }}</ref> Confined boiling is particularly promising for electronics cooling.