Air $(1$ atm$)$ enters into a $5-$cm$-$diameter circular tube at $20$C with an average velocity of $5$ m$/$s$.$ The tube wall is maintained at a constant surface temperature of $180$C$,$ and the outlet mean temperature is $80$C$.$ Estimate the length of the tube. Is the flow fully developed? The properties of air atPG$19$ To$=($T; $+$T$)/2=50$C are cp $=1007$ J$/$kg$.$K$,$ K $=0\mathrm{.}02735$ W$/$m$.$K$,$ p $=1\mathrm{.}092$ kg$/$m$3,$ p$=1\mathrm{.}963$ x $10-5$k kg$/$m$-$s$,$ v$=1\mathrm{.}798$ x $10-5$ m$2/$s$,$ and Pr$=0\mathrm{.}7228.$ The length of the tube is m$.$ The flow $($Click to select$)$ fully developed.