$6.$ A continuous single effect evaporator is used to concentrate a dilute salt solution entering the vessel at salt concentration of $5$wt$\%$ and temperature $370$K$.$ The level inside the evaporator is $1\mathrm{.}3$m and the concentrated product exits at $15$ wt$\%$ salt. The vapour space inside the evaporator is at $101\mathrm{.}3$kPa $($abs$).$ Steam is supplied at $250$kPa $($abs$)$ and the heat transfer area is $30$m$2.$ Assume no subcooling of steam condensate.

a$.$ Calculate the rate at which the concentrate exits the evaporator.

b$.$ Calculate the steam consumption. $($Do consider boiling point elevation due to hydrostatic head$)$

c$.$ Calculate the heat transfer are required.

d$.$ Calculate the steam economy.

e$.$ If the tube dimensions are $5$m high and $50$mm diameter, how many tubes in the evaporator?