Question

Which of the following concentration processes consumes the maximum energy?

• A. Membrane concentration
• B. Evaporation
• C. Freeze concentration
• D. Fermentation

Hint:

Energy requirement ranking: Evaporation ($\approx 2260\,\text{kJ/kg}$) $>$ Freeze concentration ($\approx 334\,\text{kJ/kg}$) $>$ Reverse Osmosis (no phase change).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
The specific energy consumption of concentration technologies depends on the thermodynamic phase change required to separate water.

Step 2: Key Formula or Approach:
The latent heat requirements for phase change of water are:
- Latent heat of vaporization (Evaporation): $\Delta H_{\text{vap}} \approx 2260\,\text{kJ/kg}$ at $100^\circ\text{C}$
- Latent heat of fusion (Freeze concentration): $\Delta H_{\text{fus}} \approx 334\,\text{kJ/kg}$
- Membrane concentration (Reverse Osmosis): Requires only mechanical pumping energy ($\approx 10\text{--}30\,\text{kJ/kg}$) without phase change.

Step 3: Detailed Explanation:
Because water vaporization requires substantially greater thermal energy than ice crystallization or hydraulic pumping, thermal evaporation consumes the maximum energy per unit mass of water removed.

Step 4: Final Answer:
Thus, evaporation consumes the maximum energy.