Heat exchange

Heat exchange occurs through three mechanisms:

• Conduction
• Convection
• Radiation

In a vacuum evaporator, heat necessary for liquid evaporation comes primarily through conduction, where the liquid contacts a heated metal surface directly. The heat transfer depends on factors such as surface area, thermal gradient (delta T), material properties, fouling, and surface geometry, inversely proportional to surface thickness.

Transitioning 1 kg of water from room to boiling temperature and vapor phase under atmospheric pressure (101 kPa) demands about 2500 kJ (approximately 700 Wh) , typically lost without condensation heat recovery. Vacuum evaporation systems recycle this energy within the cycle, minimizing water evaporation energy consumption. Various technologies achieve this:

• Vacuum evaporation with heat pumps
• Multiple effect vacuum evaporation
• Mechanical vapor recompression

Such approaches can reduce energy consumption by around 25 times compared to atmospheric evaporation.