A feed of 4535 kg/h of a 2.0-wt % salt solution at 311K enters continuously in a single effect evaporator and is being concentrated to 3.0 %. The evaporation is at atmospheric pressure and the area of the evaporator is 69.7 m2. Saturated steam at 383.2 K is supplied for the heating. Since the solution is dilute, it can be assumed to have the same boiling point of water. The heat capacity of the feed can be taken as cP = 4.10 kJ/kg-K. Calculate the amounts of vapor and liquid product and the overall heat transfer coefficient U.
A feed of 4535 kg/h of a 2.0-wt % salt solution at 311K enters continuously in a single effect evaporator and is being concentrated to 3.0 %. The evaporation is at atmospheric pressure and the area of the evaporator is 69.7 m2. Saturated steam at 383.2 K is supplied for the heating. Since the solution is dilute, it can be assumed to have the same boiling point of water. The heat capacity of the feed can be taken as cP = 4.10 kJ/kg-K. Calculate the amounts of vapor and liquid product and the overall heat transfer coefficient U.
Solution:
1. Use the Solute Balance to calculate for the liquid product L
2. Use the overall mass balance to calculate for the vapor product V
3. Calculate for the enthalpy of the feed hF and the enthalpy of the liquid product hL using the h = CPdT. Use a datum temperature T = ____________.
4. Get the enthalpy of the vapor product from the steam table at T = ___________ and the latent heat of condensation of steam at P = ____________ and T = ____________.
5. Using the enthalpy balance for the whole evaporator, calculate for the amount of steam needed.
6. Knowing the amount of steam needed for the heat transfer, calculate the heat q transferred through the heating surface A
7. Calculate the overall heat transfer coefficient using the general design equation for heat transfer equipment.
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