Which type of heat exchanger transfers heat by direct physical contact in which heat and mass are transferred as the fluids mix?

Which type of heat exchanger transfers heat by direct physical contact in which heat and mass are transferred as the fluids mix?

• A. Direct Contact
• B. Indirect Contact
• C. Shell and Tube
• D. Plate and Frame

Answer: (A)

Direct-contact heat exchangers transfer heat through direct physical contact, so the two fluids actually mix as heat and possibly mass are exchanged. When the fluids come into contact, their temperatures move toward a common value dictated by the energy balance of the mixing streams, and any accompanying mass transfer (such as vapor into liquid or solute transfer) can occur because the phases are in direct contact. This makes the heat transfer coefficient often high due to vigorous mixing and intimate contact, but it also means the fluids are not kept separate, which can raise concerns about contamination or product purity and complicate downstream separation. In contrast, indirect-contact exchangers keep a barrier between the fluids (like walls, tubes, or plates), so heat transfer occurs through the barrier without any mixing. That distinction is what sets direct contact apart from the other common types, which rely on separation of streams while still facilitating heat transfer.

Direct-contact heat exchangers transfer heat through direct physical contact, so the two fluids actually mix as heat and possibly mass are exchanged. When the fluids come into contact, their temperatures move toward a common value dictated by the energy balance of the mixing streams, and any accompanying mass transfer (such as vapor into liquid or solute transfer) can occur because the phases are in direct contact. This makes the heat transfer coefficient often high due to vigorous mixing and intimate contact, but it also means the fluids are not kept separate, which can raise concerns about contamination or product purity and complicate downstream separation.

In contrast, indirect-contact exchangers keep a barrier between the fluids (like walls, tubes, or plates), so heat transfer occurs through the barrier without any mixing. That distinction is what sets direct contact apart from the other common types, which rely on separation of streams while still facilitating heat transfer.