Repeat problem $3\mathrm{.}6$ when the air outside the tube is at $21\backslash$deg C and has a relative humidity of $50$ percent. Also, determine the rate of heat transfer required to maintain the liquid water at $21\backslash$deg C$.$

$3\mathrm{.}6$ Consider water in a $25-$mm$-$diameter test tube evaporating into dry air at $1$ atm. The distance from the water$$air interface to the top of the tube is L $=15$ cm$.$ The mass fraction of the water vapor at the water$$air interface is $0\mathrm{.}0235,$ and the binary diffusivity for water vapor in air is $2\mathrm{.}6105$ m$2/$s$.$

A$.$ Determine the mass evaporation rate of the water.