Convective heat transfer inside tubes – Location of thermal resistance When a hot tube wall transfers heat to a fluid flowing inside, where is the bulk of the convective thermal resistance located?

Introduction / Context:
Convective heat transfer involves fluid motion and thermal gradients. The velocity and temperature boundary layers near a wall strongly influence the overall resistance, which informs why surface enhancements (fins, roughness, inserts) and high turbulence intensities are used to improve heat transfer in exchangers and process tubing.

Given Data / Assumptions:

• Single-phase flow inside a tube with a hot wall and cooler fluid.
• Fully developed behavior conceptually; no phase change.
• Newtonian fluid; standard Prandtl numbers.

Concept / Approach:
Thermal and hydrodynamic boundary layers form at the wall. Most of the temperature drop occurs across the near-wall fluid layer where conduction dominates due to suppressed turbulence and low relative velocity. Thus, the dominant thermal resistance resides in the thin film adjacent to the surface, not in the well-mixed core.

Step-by-Step Solution:

Verification / Alternative check:
Classic correlations for h depend on near-wall behavior (e.g., friction factor analogy) and surface roughness effects, underscoring the dominance of the wall-adjacent film.

Why Other Options Are Wrong:

• Core/uniform distribution: Do not reflect the steep near-wall gradients observed experimentally and theoretically.
• None of these: Incorrect as the thin film description is standard.

Common Pitfalls:
Ignoring fouling layers; while separate from fluid film, deposits further increase effective near-wall resistance.

Final Answer:
mainly confined to a thin film of fluid near the surface.