Pressure drop comparison – 1–2 versus 1–1 heat exchanger (tube side) For turbulent flow in the tubes, the tube-side pressure drop in a 1–2 exchanger is approximately how many times that in a 1–1 exchanger of the same size and tube count at the same liquid flow rate?

Introduction / Context:
Tube-side pressure drop affects pump sizing and operating cost. Changing pass arrangement (e.g., 1–1 to 1–2) alters the number of tubes in parallel and the velocity, hence the frictional losses. Knowing the scaling helps during thermal–hydraulic tradeoffs.

Given Data / Assumptions:

• Same shell, same total number of tubes, same total flow rate.
• Fully turbulent regime where ΔP ∝ L * v^2 (other factors roughly constant).
• No major entrance/exit losses difference considered.

Concept / Approach:
Going from 1–1 to 1–2 halves the number of parallel tubes per pass, doubling the average velocity in each tube. The flow path length per pass halves, but the fluid now traverses two passes. Net path length remains about the same, while velocity doubles. With ΔP scaling approximately with v^2, the pressure drop increases by about a factor of 4 (2^2). Minor variations occur due to return bends and distribution, but the rule-of-thumb answer remains ≈4 times.

Step-by-Step Solution:

Verification / Alternative check:
Detailed friction factor correlations show small corrections; the first-order estimate of 4× is standard in exchanger hydraulics.

Why Other Options Are Wrong:

• 2 or 8: Under/overestimates compared with v^2 scaling.
• 1/2: Contrary to increased velocity with more passes.

Common Pitfalls:
Comparing at equal velocity instead of equal total flow; forgetting the change in parallel flow area with passes.

Final Answer:
4