Fouling factor in heat exchanger design: On which parameters does the fouling factor chiefly depend?

Introduction:
Fouling adds thermal resistance, raises pressure drop, and shortens run length in heat exchangers. The “fouling factor” is a design allowance based on expected deposit formation. Recognizing what drives fouling helps select velocities, materials, and cleaning schedules.

Given Data / Assumptions:

• Conventional shell-and-tube or plate exchangers in process service.
• Fouling types include particulate deposition, chemical scaling, biofouling, and corrosion products.

Concept / Approach:
Fouling severity depends on the fluid’s chemical tendencies (e.g., scaling propensity), the amount and character of suspended matter, and hydrodynamics. Higher velocities can reduce settling and promote shear removal of deposits, while low velocities encourage deposition. Chemistry (pH, hardness, polymerization tendency) and solids load are equally important.

Step-by-Step Solution:
Assess fluid chemistry (a): dictates scaling/coking/biofouling mechanisms.Assess velocity (b): shear stress at the wall controls deposition vs. resuspension.Assess solids (c): more or stickier particulates increase fouling risk.Conclusion: fouling factor depends on all three.

Verification / Alternative check:
Industry fouling guidelines (e.g., TEMA/HEI) provide different allowances for different fluids and velocities, confirming the multi-factor dependence.

Why Other Options Are Wrong:

• Limiting to any one parameter misses the coupled nature of fouling.
• Wall material affects adhesion/corrosion but does not solely determine fouling resistance; fluid-side factors dominate the allowance.

Common Pitfalls:
Selecting a single “standard” fouling factor without considering service-specific chemistry and velocity can lead to under- or over-design.

Final Answer:
all (a), (b) and (c).