A double effect evaporator has to concentrate $10,000$ Kg$/$h of caustic soda solution from $9\%$ to $47\%$ solid concentration by weight. For this purpose backward feed is used. The feed enters the evaporator at $36$ deg C $.$ Process steam at $7$ kg$/$cm$2($gauge$)$ is available and in the second effect a vacuum of $65$ cm Hg is maintained. Design a suitable forced circulation evaporator system with heat equal heating surface in both effects. Neglect boiling point rise. Specific heat of all caustic stream is $0\mathrm{.}9$ kcal$/$kg deg C The overall heat transfer coefficient in two effects are $2000$ and $1500$ kcal$/($h m$2$ deg C$)$ respectively.

Use absolute pressure to find temperature of steam and temperature in second effect using steam tables. Assume area in two effects are equal and find the area.