Problem $2$ In a flow boiling experiment, saturated water at a temperature of $300$degC flows within a horizontal tube. At one visualization section, the interface was captured from the side as shown below. $1)$ Please explain what makes this regular interfacial pattern $2)$ For water at $300$degC, density$1=712$ kg$/$m$^3.,$ density$2=46\mathrm{.}2$ kg$/$m$^3,$ surface tension $=0\mathrm{.}0144$ N$/$m$,$ thermal conductivity k$1=0\mathrm{.}541$ W$/$mK$,$ k$2=0\mathrm{.}0752$ W$/$mK$,$ and latent heat $=1367$ kJ$/$kg$.$ you may refer to the attached table for other properties. The tube internal diameter is $15$mm$,$ please estimate the vapor velocity relative to water liquid.