Question

The extended heat transfer surfaces provided in heat exchangers are called as:

• A. Propellers
• B. Blades
• C. Fins
• D. Ribbons

Hint:

Fins are used to increase the surface area available for convective heat transfer. They are highly effective when the convective heat transfer coefficient (\(h\)) is small, such as when transferring heat to or from a gas.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
According to Newton's Law of Cooling, the rate of convective heat transfer from a surface is:
\[ q = h A_s (T_s - T_{\infty}) \]
To increase the heat transfer rate (\(q\)) when the heat transfer coefficient (\(h\)) is low (such as in gas-side heat transfer), we can increase the surface area (\(A_s\)).
This is achieved by extending the solid surface into the surrounding fluid.

Step 2: Detailed Explanation:
These extended solid surfaces are called fins.
- Fins conduct heat from the primary wall along their length while simultaneously transferring heat to the surrounding fluid by convection.
- They are widely used in compact heat exchangers, air-cooled engines, radiators, and dairy refrigeration systems to enhance heat transfer efficiency without increasing the overall size of the system.
- Let us examine the other options:
- Propellers are used to propel fluids or vessels.
- Blades are rotating aerodynamic surfaces used in turbines, compressors, or agitators.
- Ribbons are mixing or conveying elements.
Therefore, extended heat transfer surfaces are called fins.

Step 3: Final Answer:
The extended heat transfer surfaces are called fins. Hence, the correct option is (C).