A solution of organic colloids in water is to be concentrated from $10\%$ to $50\%$ solids in single effect evaporator. Steam is available at gauge pressure of $15(249F).$ A pressure of $4$ingHg absolute is to be maintained in the vapor space; this corresponds to a boiling point for water of $125F.$ The feed rate to evaporator is $55000I\frac{b}{h},$ the overall heat transfer coefficient can be taken as $500Bt\frac{u}{f}{t}^2.h.F.$ The solution has a negligible elevation in boiling point and a negligible heat of dilution. Calculate the steam consumption, the economy, and the heating surface required, if the temperature of feed is:

$($i$)125F.$

$($ii$)70F.$

Specific heat of feed solution $=0\mathrm{.}9Bt\frac{u}{\text{I}}b.F,$ and the latent heat of vaporization of the solution may be taken equal to that of water. Radiation losses may be neglected.