Which of the following are examples of direct contact heat exchangers?

• A. Cooling Towers, Cooling Ponds/Rivers/Lakes, and Deaerators
• B. Shell and Tube Exchangers
• C. Plate and Frame Exchangers
• D. Crossflow Exchangers

Answer: (A)

Direct contact heat exchangers transfer heat by bringing the two fluids into direct contact, with no solid barrier separating them. In a cooling tower, hot water is dispersed into air, so water and air mix at the interface and heat flows directly from the water to the surrounding air. In a cooling pond, river, or lake, heat is exchanged directly between the water and the ambient environment (air) at the surface, without an intervening wall. In a deaerator, steam bubbles rise through and contact the feedwater, removing dissolved gases through direct steam-water interaction while transferring heat.

The other options rely on a separating wall between the fluids, so heat transfer occurs indirectly through that barrier rather than by direct mixing. Shell and tube, plate and frame, and typical crossflow exchangers all keep the fluids separate to exchange heat across walls or plates.