Filter medium resistance control: in practice, the resistance attributed to the filter medium (cloth plus embedded particles) varies primarily with which operating influences?

Introduction / Context:
Total filtration resistance comprises the clean medium resistance (cloth, screens) plus resistance due to particles embedded within the medium structure and the external cake. Although often treated as a constant, the effective medium resistance in real operations can vary with hydrodynamic conditions.

Given Data / Assumptions:

• Medium: woven cloth or porous septum.
• Operation: pressure or vacuum filtration with evolving embedment.
• Cake resistance considered separately from medium resistance.

Concept / Approach:
Pressure drop influences how fines are driven into the medium pores (depth blinding), changing the effective porosity and thickness of the “internal” deposit. Flow rate affects shear at the medium surface and within pores, which can dislodge or further compact embedded solids. Therefore, the effective medium resistance is sensitive to both ΔP and superficial velocity, while external cake thickness primarily affects cake resistance, not the inherent medium term.

Step-by-Step Solution:
Identify mechanisms: embedment and pore constriction under ΔP.Acknowledge shear/flow effects: flow rate alters fouling or partial cleaning.Conclude that both ΔP and flow rate modulate the effective medium resistance.

Verification / Alternative check:
Pilot tests commonly show different “clean cloth” resistances after multiple cycles at different ΔP regimes due to varying degrees of depth blinding.

Why Other Options Are Wrong:
Pressure alone or flow alone: incomplete; both factors matter.Cake thickness: governs cake resistance, not the medium’s intrinsic term.

Common Pitfalls:
Treating Rm as constant across campaigns; fouling history and operating profile can shift Rm materially.

Final Answer:
both pressure drop and flow rate