SDB Type Dual-Perforated Plate Static Mixer

Product Overview

The SDB type dual-perforated plate static mixer is the ywmixing model designed specifically for fouling service. Where the SD single-plate mixer handles clean-to-moderately-dirty fluids and the SV corrugated-plate mixer demands cleanliness, the SDB is built around paired perforated plates that face each other with a 5-15 mm inter-plate gap and offset hole patterns. The two plates together behave as a single thick barrier with wide, oblique flow channels, rather than as a thin barrier with a fine hole array. The result is a mixer that passes fibers, pulp, and 5-10 mm particulates without clogging, while still delivering 5-15 μm dispersion precision in clean media and 20-50 μm in heavy slurry service.

This geometry gives the SDB two distinct advantages over its siblings. First, the wide, oblique channels are self-cleaning: the bulk flow continuously sweeps fibers and particulates past the plate surface, and the offset hole pattern means there is no flat stagnation face where debris can accumulate. Second, the dual-plate construction provides structural rigidity that allows the housing to operate at viscosities up to 100,000 cP (10⁵ cP) without plate deflection under viscous drag — a problem that limits the SD above about 10,000 cP and the SV above about 100 cP. The trade-off is dispersion precision: the wider channels produce coarser dispersions than the SD's single-plate geometry, and the engineer must accept 5-15 μm (clean) or 20-50 μm (fouling) in place of the SD's 5-10 μm and the SV's 1-2 μm.

Across the ywmixing family, the SDB occupies the fouling-service niche between the helical twist models (SK, SH) and the single perforated-plate model (SD). For applications involving pulp, paper-mill broke, primary sludge, mineral slurries, polymer-flocculated wastewater, and similar streams, the SDB is typically the first mixer specified because it is the only plate-type mixer in our range that can sustain continuous operation in fouling service without routine plate removal for cleaning.

Working Principle

The mixing action of the SDB is generated by the tortuous-path flow through successive dual-plate stages. Each stage consists of two parallel plates separated by a 5-15 mm gap, with the hole patterns offset so that fluid entering a hole on the upstream plate must make a 30-60° turn before it can exit through the nearest downstream-plate hole. The tortuosity of the path is the principal source of mixing; the change in flow direction at each hole exit produces a local jet that impinges on the opposite plate, generating a small mixing zone of intense turbulence. Over the full housing length, with 3-8 dual-plate stages in series, the cumulative effect is several hundred jet-impingement events that redistribute the fluid in the radial and azimuthal directions.

Quantitatively, the per-stage pressure drop is governed by Δp = ½·ρ·v²·K_s, where the loss coefficient K_s for a dual-plate stage is in the range 2.0-3.5 — somewhat higher than the SD's single-plate value of 1.5-2.5 because the offset geometry adds a turning loss. For a 6-stage housing the cumulative K is approximately 12-21, giving a total pressure drop of 0.2-0.5 bar at 2 m/s water service in a DN100 unit. The open-area fraction is typically 35-55% (higher than the SD's 30-50%) because the wide channels and large holes are needed to pass fibers and particulates.

Three design parameters govern the SDB sizing. The first is the offset ratio γ = δ/d, where δ is the lateral offset between the upstream and downstream hole centers and d is the hole diameter, typically 0.3-0.8. Smaller γ produces a more direct flow path with lower pressure drop but weaker mixing; larger γ forces the flow to turn more sharply and produces more vigorous mixing at the expense of higher Δp. The second is the dual-plate gap g, typically 5-15 mm, set by structural spacers that maintain the gap under thermal and mechanical load. The third is the inter-stage distance s, typically 1.0-2.0 × the housing diameter, which provides space for the jets to redevelop and the velocity profile to relax before the next stage.

In the turbulent regime (Re > 4,000 based on hole diameter), the SDB achieves 5-15 μm dispersion with σX ≤ 5%. In the laminar regime (Re < 2,300) — common in pulp and high-viscosity polymer service — the mixing mechanism shifts to viscous folding of stream tubes and the dispersion coarsens to 20-50 μm with σX in the 8-12% range. The SDB is unusual among plate-type mixers in that this laminar-fouling combination is exactly the duty for which it is designed, so the 20-50 μm / 8-12% σX performance is considered adequate rather than a limitation.