• Chronological Sequence of Evaporator Operations:
• In dairy and food engineering, the operational procedure for a falling film or forced circulation evaporator follows a rigorous thermodynamic sequence:

• Step 1: Preheating the feed solution: Raw liquid feed is preheated close to the boiling temperature using regenerate heat exchangers to conserve energy.
• Step 5: Heating the feed solution to its boiling point: The liquid is brought to its saturation boiling point within the evaporation chamber/calandria tubes.
• Step 2: Vaporization of the solvent from the feed solution: Latent heat of vaporization causes rapid water evaporation, concentrating the non-volatile milk solutes.
• Step 3: Condensation of the vaporized solvent to produce distillate: Separated water vapor passes to a condenser (or mechanical vapor recompressor, MVR) to produce condensate.
• Step 4: Removal of concentrated solution or residue: The concentrated product (condensed milk/dairy syrup) is continuously discharged through the bottom extraction pump.
  • Conclusion: The correct chronological sequence is 1 - 5 - 2 - 3 - 4 (Option 1).

• Modes of Heat Transfer in Industrial Evaporators:
• (I) Conduction: Occurs through the solid metallic walls of the evaporator tubes separating condensing steam and boiling liquid.
• (II) Convection: Convective condensation of steam on outer tube surfaces and convective boiling (nucleate boiling) of milk/liquid film on inside tube surfaces.
• Radiation (III): Negligible because dairy evaporators operate at modest vacuum temperatures ($45 - 100^\circ\text{C}$), where radiative flux is inconsequential.
• Conclusion: (I) and (II) only (Option 2).

Correct option: (2) (I) and (I!) only