Question

Excess insulation thickness for a steam pipeline will affect the heat loss due to change in

• A. Overall heat transfer co-efficient
• B. Area of heat transfer
• C. Temperature difference
• D. Cost of insulation

Hint:

Cylindrical Insulation Effect: In cylindrical pipes, increasing insulation thickness fundamentally INCREASES THE EXTERNAL SURFACE AREA OF HEAT TRANSFER ($A = 2\pi r L$).

Answer 1

The Correct Option is B

Step 1: Understanding the Concept:
Cylindrical radial geometry heat transfer physics: adding radial insulation to a pipe increases the outer radius ($r_2$), which increases the external surface Area of heat transfer ($A_o = 2\pi r_2 L$), directly altering external convective and radiative heat dissipation.
Key Formula or Approach:
\[ \text{Outer Surface Area } (A_o) = 2 \pi \cdot \mathbf{r_o} \cdot L \quad \implies \quad \text{Increasing Insulation Thickness} \longrightarrow \mathbf{\text{Area of Heat Transfer } (A_o) \uparrow} \]

Step 2: Detailed Explanation:
In heat transfer dynamics of insulated cylindrical conduits (steam and hot water lines):
- In flat planar walls, adding insulation only changes conduction thickness without changing surface area.
- In Cylindrical Steam Pipelines:
1. Adding excess insulation radially increases the outer radius ($r_o = r_i + \text{thickness}$).
2. The external convective heat transfer surface area is $A_o = 2\pi r_o L$.
3. Therefore, increasing insulation thickness directly increases the Area of heat transfer (B).
4. While the conductive thermal resistance increases, the expanded surface area lowers external convective resistance ($R_{\text{conv}} = \frac{1}{h_o A_o}$), which governs the net rate of heat loss.

Step 3: Final Answer:
Therefore, excess insulation thickness affects heat loss due to change in Area of heat transfer, corresponding to option (B).