Differences in Fouling During Concentration and Crystallization Between Narrow- and Wide-Flow-Channel Plate Heat Exchangers

I. Narrow Material Flow Channels (Conventional Standard Plates, Small Gaps)

Blockage occurs rapidly, leading to rapid localized blockage

Due to the narrow flow channels, suspended salt crystals, silica gel flocs, and flocculation residues are highly prone to becoming lodged in the corrugation corners and flow-guiding zones; even a small amount of solid-phase accumulation can immediately cut off the flow cross-section, causing a rapid decline in flow rate and forming a dead zone on one side.

Prone to bridging and material blockage

Salt crystals interlock to form stable bridges within the narrow channels; even low-concentration slurries can rapidly cause permanent blockages that cannot be cleared by circulation flushing alone.

Extremely pronounced rise in pressure differential

Even minor salt accumulation causes a steep increase in the inlet-outlet pressure differential, increasing the load on the circulation pump and reducing the overall flow velocity within the chamber—which, in turn, exacerbates sedimentation and crystal deposition, creating a vicious cycle.

Uniform Scale Deposition Adhering to the Plate Surface, Rapid Decline in Heat Transfer Efficiency

In narrow gaps, crystals grow tightly against the plate surface, completely covering the heat transfer corrugations. This causes a sharp increase in thermal resistance, leading to uncontrolled evaporation temperatures and vacuum fluctuations.

Difficult to Clean

Solid salt crystals become lodged in the narrow corrugated gaps; acid washing penetrates slowly, and manual flushing is difficult to perform thoroughly. Residual crystal nuclei will quickly cause re-blockage upon the next startup.

II. Wide Material Flow Channels (Wide Gaps, Free-Flow Plates)

Tolerates higher solids content and is less prone to complete blockage in the short term

With ample channel space, salt crystals can pass smoothly with the fluid, making bridging and jamming less likely. The flow area will only gradually narrow with long-term, continuous concentration and significant accumulation of solid phase.

Blockage primarily occurs as sedimentation and accumulation at the bottom

The flow channel is not completely blocked; instead, a layer of salt sludge deposits on the underside of the plates in low-velocity stagnation zones, while fluid continues to flow in the upper section. The pressure difference rises gradually and does not spike suddenly.

Hard bridging scale is unlikely to form

Crystals have ample space to move and are unlikely to interlock and form bridges; they mostly form loose sediment layers. High-flow circulation flushing can remove most of the accumulated crystals.

Significant localized flow deviation occurs

Salt accumulation at the bottom raises the liquid level, causing all fluid to flow at high speed through the narrow gaps at the top of the plates. This halves the effective heat transfer area, creates a large temperature difference between the top and bottom, and results in uneven thermal stress.

Silica gel and viscous flocs still form extensive coatings

For soft, sticky sludge such as silica gel colloids and organic flocs, wide flow channels offer no advantage. The viscous substances spread across the corrugated surface in large patches, gradually narrowing the channels; however, the blockage cycle is simply longer than in narrow flow channels.

III. Summary of Key Differences in Core Blockage Mechanisms Between the Two

Blockage Speed: Narrow flow channels become completely blocked in a short time; wide flow channels experience gradual sedimentation and channel narrowing, without an instantaneous flow interruption.

Blockage Pattern: Narrow channels form hard blockages due to particle bridging; wide channels accumulate loose salt sludge at the bottom.

Pressure Drop Changes: Pressure drops in narrow channels spike abruptly; in wide channels, they rise gradually and smoothly.

Self-Cleaning Ability: Wide channels can rely on high flow rates to flush away loose deposits; narrow channels cannot self-clear once bridging occurs.

Compatible Media: Narrow flow channels are suitable only for low-salt, colloid-free clear liquids; wide flow channels are suitable for high-salt, concentrated mother liquors containing trace amounts of flocs.

Cleaning Difficulty: Narrow flow channels harbor deposits in crevices, resulting in short cleaning cycles and poor cleaning results; salt deposits in wide flow channels are easily flushed away, allowing for longer maintenance intervals.