For 1.5 inch shell-and-tube heat exchanger tubes, how does the inside flow area change as BWG (Birmingham Wire Gauge) decreases (i.e., wall gets thicker)?

Introduction / Context:
Tube wall thickness is commonly specified by BWG. A lower BWG number corresponds to a thicker wall. The internal diameter determines the flow area and therefore velocity and pressure drop for a given volumetric flow rate.

Given Data / Assumptions:

• Nominal outside diameter fixed at 1.5 inch.
• BWG decreases → wall thickness increases.
• No corrosion allowance changes considered; focus is purely geometric.

Concept / Approach:
Inner diameter ID = OD − 2 * t. Increasing the wall thickness t reduces ID linearly. Flow area A = (π/4) * ID^2 therefore decreases with decreasing BWG (thicker wall).

Step-by-Step Solution:
Start with fixed OD = 1.5 in.Decrease BWG → increase t.ID = OD − 2t decreases as t increases.A ∝ ID^2; hence the inside flow area decreases.

Verification / Alternative check:
Sample numbers: If t increases by 0.05 in, ID drops by 0.10 in, which reduces area roughly proportionally to the square of ID, confirming the trend.

Why Other Options Are Wrong:
Increases / Remains the same: contradict geometry.Cannot be determined: basic geometry determines it.Increases only at high Reynolds number: flow regime does not reverse the geometric effect.

Common Pitfalls:
Confusing BWG numbering (lower number means thicker wall).Mixing up OD and ID when applying thickness changes.

Final Answer:
Decreases