Perimeter-average Nusselt number

Let us consider a tube of arbitrary shape and denote the contour of the cross-section by T. Generally speaking, the Nusselt number varies along the contour T. We define the perimeter-average Nusselt number Nu as follows ... 

For a tube of elliptic cross-section with constant temperature on the wall, the perimeter-average Nusselt number in the heat stabilization region (far from the input cross-section) is determined by [341]... 

Table 3.3 presents the perimeter-average Nusselt numbers for tubes with various shapes of the cross-section (according to [80]). 

By averaging the local Nusselt number along the heated perimeter, one can obtain the thermally fully developed mean Nusselt number ... 

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