Editing Nusselt number (section)

====Free convection from enclosure heated from below====
Cited<ref name="bejanauth">{{cite book |author-link=Adrian Bejan |last1=Bejan |first1=Adrian|title=Convection Heat Transfer |url=https://www.researchgate.net/profile/Gamal-Abdelaziz-2/post/How_to_calculate_Nusselt_number_if_an_enclosure_is_heated_from_two_sides_horizontally_and_vertically/attachment/5f511b80ed60840001ca5842/AS%3A931720878649344%401599150976439/download/Adrian+Bejan%28auth.%29-Convection+Heat+Transfer%2C+Fourth+Edition+%282013%29.pdf?_tp=eyJjb250ZXh0Ijp7ImZpcnN0UGFnZSI6InB1YmxpY2F0aW9uIiwicGFnZSI6InF1ZXN0aW9uIn19 |url-access=limited |edition=4th |publisher=Wiley |year=2013 |isbn=978-0-470-90037-6 }}</ref> as coming from Bejan:

:<math>\overline{\mathrm{Nu}}_L \ = 0.069\, \mathrm{Ra}_L^{1/3}Pr^{0.074} \, \quad 3 * 10^5 \le \mathrm{Ra}_L \le 7 * 10^{9}</math>

This equation <i>"holds when the
horizontal layer is sufficiently wide so that the effect of the short vertical sides
is minimal."</i>

It was empirically determined by Globe and Dropkin in 1959:<ref>{{Cite journal |last1=Globe |first1=Samuel |last2=Dropkin |first2=David |date=1959 |title=Natural-Convection Heat Transfer in Liquids Confined by Two Horizontal Plates and Heated From Below |url=https://asmedigitalcollection.asme.org/heattransfer/article-abstract/81/1/24/397579/Natural-Convection-Heat-Transfer-in-Liquids?redirectedFrom=fulltext |journal=Journal of Heat Transfer |volume=81 |issue=1 |pages=24–28 |doi=10.1115/1.4008124 |via=ASME Digital Collection}}</ref> <i>"Tests were made in cylindrical containers having copper tops and bottoms and insulating walls."</i> The containers used were around 5" in diameter and 2" high.