In plate-and-frame filter presses used for solid–liquid separation, how does the thickness of the frame compare with the thickness of the plates? Provide the best practical comparison based on their functions (cake space versus drainage/support).

Introduction / Context:
Plate-and-frame filter presses are widely used in chemical, pharmaceutical, and mineral processes for batch solid–liquid separation. Understanding the geometry of the “plate” and the “frame” clarifies why their thicknesses differ and how that affects cake formation, filtrate flow, and mechanical strength.

Given Data / Assumptions:

• The plate provides drainage paths (grooves or cloth support) and mechanical rigidity.
• The frame primarily provides the void space in which the filter cake forms.
• The press operates at a pressure that compacts the cake inside the frame volume.

Concept / Approach:
The frame must be thick enough to accommodate the desired cake thickness at the selected cycle time and pressure drop. Plates, in contrast, are designed to be strong and sufficiently stiff while minimizing hydraulic resistance; their functional need is not to provide cake volume but to support cloths and convey filtrate through channels.

Step-by-Step Solution:

Verification / Alternative check:
Equipment catalogs show frames specified by “cake thickness” (e.g., 25 mm, 32 mm), while plate thickness is primarily a mechanical design parameter, commonly lower than frame thickness for the same press size.

Why Other Options Are Wrong:

• Less/same thickness: would restrict cake capacity or confuse plate and frame functions.
• Either less than or equal to: ignores the standard design intent to house cake in the frame.
• Varies randomly: design follows process requirements, not randomness.

Common Pitfalls:
Assuming thicker plates increase capacity; confusing recessed-plate (chamber) presses with true plate-and-frame designs.

Final Answer:
More than the plate thickness