ANS:B - there is no risk of contamination.

Indirect contact heat exchangers are typically preferred over direct contact heat exchangers for several reasons:

1. No risk of contamination:
   • In indirect contact heat exchangers, the two fluids undergoing heat exchange are separated by a barrier, such as a tube wall or a plate. This prevents direct mixing of the fluids and eliminates the risk of contamination. This is especially important when dealing with sensitive processes or when one of the fluids needs to remain pure.
2. No mist formation:
   • Direct contact heat exchangers involve the physical mixing of the two fluids, which can sometimes lead to the formation of mist or droplets. This mist formation can be undesirable, especially in certain applications where maintaining a specific environment or controlling humidity is important. Indirect contact heat exchangers avoid this issue altogether as there is no direct mixing of the fluids.
3. Lower risk of corrosion and fouling:
   • In direct contact heat exchangers, the fluids are in direct contact with each other, which can increase the likelihood of corrosion or fouling, especially if the fluids are chemically aggressive or prone to scaling. Indirect contact heat exchangers mitigate this risk as the fluids are separated by a barrier, reducing the chance of corrosion or fouling on the heat transfer surfaces.
4. Versatility:
   • Indirect contact heat exchangers can handle a wider range of fluids, temperatures, and pressures compared to direct contact heat exchangers. This versatility makes them suitable for a variety of applications across different industries.

While it's true that indirect contact heat exchangers generally have higher heat transfer coefficients than direct contact heat exchangers, the primary reasons for their preference are the avoidance of contamination, mist formation, and lower risk of corrosion and fouling.