SD Type Perforated Plate Static Mixer

Product Overview

The SD type perforated plate static mixer is the general-purpose workhorse of the ywmixing plate-mixer family. Inside a cylindrical housing, multiple flat plates — each drilled or punched with a regular array of circular holes — are stacked at fixed spacing, typically 1.0-2.5 plate diameters apart. The hole pattern, plate thickness, open-area fraction, and number of plates are the four design parameters that the engineer tunes to match the process duty. The result is a robust, low-clag mixer that delivers 5-10 μm dispersion precision with σX ≤ 5% over a viscosity range of 1-10,000 cP and a pipe range of DN15 to DN600.

Where the SV corrugated plate model targets sub-5 μm precision in clean, low-μ fluids and the SDB dual-perforated-plate model handles fouling service with fibers and particles, the SD occupies the middle ground: it has larger flow channels (8-25 mm typical) than the SV but tighter geometry than the SDB, giving it a better dispersion precision than helical twist mixers of comparable L/D while remaining tolerant of occasional particulate excursions up to 2-3 mm. For most chemical-dosing, pH-adjustment, and oil-water blending applications in water treatment, fine chemicals, and refinery service, the SD is the first model specified.

Mechanically, the SD is also one of the simplest mixers to manufacture, inspect, and clean. Each plate is a flat disc that can be lifted out of the housing individually, so a fouled or damaged plate is replaced in minutes rather than the hours required to dismantle a corrugated-plate bundle. This has made the SD the preferred choice in plants where maintenance windows are short and where the unit must be opened for routine inspection every 3-6 months.

Working Principle

The mixing action of the SD is generated by the repeated radial and axial redirection of fluid as it passes through successive perforated plates. Each plate presents an array of circular orifices — typical diameters 4-15 mm, arranged in an equilateral-triangular pitch with an open-area fraction of 30-50%. As the fluid approaches a plate, the cross-section is suddenly reduced to the total hole area, accelerating the flow to 1.5-2.5× the upstream velocity. The jets exiting the orifices impinge on the downstream plate (or, at the end of the housing, on the bulk fluid), where the radial velocity component of each jet crosses the adjacent jets and produces a vigorous turbulent mixing zone. Subsequent plates repeat the process with the holes rotated by 45-90° to the previous plate, ensuring that streamlines are reoriented on every pass.

Quantitatively, the per-plate pressure drop is governed by the standard orifice equation Δp = ½·ρ·v²·K, where the loss coefficient K is in the range 1.5-2.5 for a single perforated plate. For a 6-plate housing the cumulative K is approximately 9-15, giving a total pressure drop of 0.15-0.35 bar at 2 m/s water service in a DN100 unit. In the turbulent regime (Re > 4,000 based on orifice diameter), the mixing is dominated by eddy breakup and the dispersion precision is 5-10 μm. In the laminar regime (Re < 2,300), the jets lose coherence quickly and the mixing mechanism shifts to the viscous folding of stream tubes between plates, producing dispersions of 8-15 μm but still adequate for most neutralization and dosing applications.

Two design ratios govern sizing. The first is the open-area ratio α = A_holes / A_pipe, typically 0.30-0.50. Lower α values give finer dispersion but higher pressure drop; higher α values allow larger particulates to pass but degrade mixing quality. The second is the plate spacing ratio β = s/d, where s is the inter-plate distance and d is the hole diameter, typically 1.0-2.5. Smaller β produces a more compact mixer with higher shear at each plate; larger β allows the jets to redevelop and is preferred when the bulk fluid is viscous. A correctly sized SD mixer will keep Re > 4,000 at the design flow rate to maintain turbulent operation; for Re between 2,300 and 4,000, the engineer should add 1-2 plates to compensate for the partial loss of eddy-driven mixing.

Technical Specifications

Parameter	Value
Internal Structure	Stacked flat plates with circular-hole arrays; plates rotated 45-90° between stages
Hole Diameter Range	4-15 mm standard; custom 2-25 mm available
Open-Area Fraction	30-50% (typical); 25-60% (extended range)
Plate Spacing	1.0-2.5 × hole diameter
Plate Count	4-10 standard housings
Dispersion Precision	5-10 μm (turbulent) / 8-15 μm (laminar)
Viscosity Range	1-10,000 cP (kinematic), 10⁴ cP upper limit
Pressure Drop	0.15-0.35 bar typical at 2 m/s water in DN100; scales with v²
Non-Uniformity Coefficient	σX ≤ 5% (standard design); ≤ 3% with extended L/D
Material Options	SS304, SS316L, Carbon Steel (PTFE/rubber lined), PVC, PP
Connection Types	Flange (ANSI / DIN / JIS), Threaded (NPT / BSP), Welded
Temperature Range	-50°C to +300°C (metallic) / -10°C to +80°C (PVC/PP)
Pipe Diameter Range	DN15 to DN600
Flow Rate Range	0.1 to 1,800 m³/h (model and pipe-size dependent)
Clogging Risk	Low to moderate; channel width 8-25 mm; particulate tolerance 2-3 mm

Material Options

The SD plate is available in five standard material grades, with the housing matched to the plate selection unless otherwise specified. SS304 (1.4301, AISI 304) is the default for potable water, dilute acid and base service below 60°C, and food-grade applications. It tolerates chloride concentrations up to 200 ppm continuous without pitting risk and is the lowest-cost stainless option. SS316L (1.4404, AISI 316L) is the chemical-industry workhorse: improved chloride resistance to 1,000 ppm continuous, low-carbon formulation that eliminates carbide precipitation at welds (critical for plate-to-rod welded assemblies), and broad compatibility with organic solvents, weak acids, and most process chemicals.

Carbon steel (A516 Gr.70 plate / SA-106 pipe) is specified when the fluid is non-corrosive but the line size is large (DN300 and above) or the cost of stainless would be prohibitive. Carbon steel SD plates are almost always supplied with an internal lining — PTFE, ETFE, or rubber — to provide chemical resistance while retaining the structural economics of mild steel. Lined carbon-steel SD mixers are a common choice for chlor-alkali service, mineral acid dosing, and large-diameter wastewater neutralization lines.

PVC (Type I, Cell Classification 12454) is used for aggressive inorganic acids (HCl up to 30%, H₂SO₄ up to 50%, sodium hypochlorite up to 12% available chlorine) at temperatures up to 60°C. The upper pressure rating at 60°C is approximately 6 bar for DN100 and falls to 3 bar at DN300. PP (polypropylene, homopolymer) extends the operating envelope to 80°C and provides better resistance to organic solvents than PVC, but at reduced mechanical strength above 60°C. For temperatures above 80°C in corrosive service, the engineer must move to metallic construction with PTFE lining.

Gasket and seal selection follows the housing material. EPDM is standard for water and dilute bases; FKM (Viton) for hydrocarbons, oils, and solvents; PTFE envelope gaskets for high-temperature acid service above 150°C; and graphite-clad stainless for steam and high-temperature hydrocarbons above 200°C. For PVC and PP housings, EPDM or FKM O-rings are used; PTFE is preferred for chemical dosing where the gasket will see prolonged contact with the process fluid.

Installation Methods

SD mixers are installed in-line in the process pipe using one of three standard connection types, each suited to a different service environment. Flanged connections (ANSI B16.5 Class 150, DIN PN16, or JIS 10K) are by far the most common. They allow the entire mixer to be removed for plate inspection without cutting the pipe, and they accommodate the thermal expansion of the housing when the process sees more than 80°C differential. Flanged SD mixers are specified for DN50 and above, or whenever the unit will see periodic maintenance, which is the typical case in water-treatment and chemical-dosing service where the unit is opened every 6-12 months for plate inspection.

Threaded connections (NPT or BSP) are used for small-diameter SD mixers (DN15 to DN50) in low-pressure service — typically instrument-air lines, water-treatment skid packages, and lab-pilot installations. They are quick to install and disassemble, but limited to about 16 bar at DN50 and 40 bar at DN15. Above DN50 the threaded joint becomes impractically large for the pressure rating and the engineer should default to flanged. Welded connections are specified for high-pressure or high-temperature service where threaded joints would be a leak risk, and for permanent installations where the mixer is not expected to be removed during the plant's lifetime.

The installation geometry follows the standard static-mixer practice: 3D of straight pipe upstream and 3D downstream of the housing, with the additional recommendation that the upstream section include any injection quill or injection port that feeds the secondary stream. For multi-stream injection (such as acid + base + polymer into a wastewater stream), the engineer should design the injection quills so that all secondary streams enter the pipe within 2D of the mixer inlet; this prevents the secondary streams from stratifying along the pipe invert before they reach the first plate.

For gas service, the SD mixer is typically installed vertically with downward flow, so that any condensate drains through the housing rather than pooling on the upper surface of the plates. A drain port at the bottom of the housing is standard for gas applications. For steam or hot-gas service above 200°C, allow 50 mm of thermal expansion clearance between the mixer flanges and the mating pipe flanges, and use graphite gaskets rated for the maximum cycle temperature.

Typical Applications

Municipal water treatment chemical dosing. Drinking-water plants dose coagulants (polyaluminum chloride at 5-15 mg/L, ferric chloride at 5-25 mg/L) and pH-adjustment chemicals (lime slurry, sodium hydroxide, sulfuric acid) into raw-water streams of 50-5,000 m³/h. The SD mixer installed immediately downstream of the injection quill achieves σX ≤ 5% distribution within 0.5-1.5 seconds (5-10 mixer diameters of travel), eliminating the streak floc formation that occurs with diffusion mixers or static mixers with wider channels. Compared to the SV, the SD accepts the occasional sand grain or sediment particle that breaks through the screens, reducing unplanned maintenance by a factor of 3-4 in plants with variable raw-water quality.

Industrial wastewater pH adjustment. Continuous neutralization of acidic or alkaline wastewater streams requires intense, rapid mixing to prevent localized pH excursions that would corrode downstream piping or overload the biological treatment stage. The SD mixer's 5-10 μm dispersion eliminates pH swings greater than ±0.3 units at the mixer outlet, allowing the operator to control the neutralization reaction by a single pH probe located 2-3D downstream. A DN200 SD housing processing 200 m³/h of wastewater at 1.5 m/s is a typical sizing for a 50,000 m³/d plant.

Oil-water blending in refinery desalter service. Crude oil desalters inject wash water (1-5 vol% of the crude) into the incoming charge to dissolve entrained salts. An SD mixer installed upstream of the desalter mixing valve produces a 10-50 μm water-in-oil dispersion that dramatically improves salt extraction efficiency, reducing the residual salt content of the desalted crude from 50-100 PTB to 5-15 PTB. The SD plate geometry is preferred over the SV here because the wash water often contains 50-200 μm suspended solids that would foul the smaller SV channels.

Polymer solution make-up and dilution. Emulsion polyacrylamide and other water-soluble polymers are supplied at 30-50% active concentration and diluted to 0.1-0.5% working concentration at the point of use. The SD mixer provides the rapid, uniform dilution required to avoid gel formation and fish-eyes; the dispersion precision of 5-10 μm is more than adequate and the unit handles occasional undissolved polymer particles that would clog an SV. A DN80 SD housing is typical for 30 m³/h of diluted polymer solution.

Flue-gas conditioning. In SO₂ scrubbers and selective catalytic reduction (SCR) systems, the SD mixer is installed in the gas duct to blend the reagent (lime slurry, ammonia, or urea solution) with the flue gas. The plate geometry handles the two-phase flow without significant fouling, and the open area of 30-50% prevents pressure excursions if the reagent injection is temporarily interrupted. SD mixers in flue-gas service are typically fabricated in SS316L with alloy reinforcement at the injection quill to resist chloride-induced stress-corrosion cracking.

Model Comparison

Parameter	SD	SV	SDB	SK	SX
Internal Structure	Perforated plates	Corrugated plates	Dual perforated plates	Helical twist	Crossed bars
Dispersion Precision	5-10 μm	1-2 μm	5-15 μm	≤ 10 μm	2-5 μm
Max Viscosity (cP)	10,000	100	100,000	1,000,000	10,000
Pipe Diameter	DN15-DN600	DN15-DN1000	DN25-DN600	DN15-DN500	DN25-DN800
Clogging Risk	Low-moderate	High	Lowest	Lowest	Moderate
Particulate Tolerance	2-3 mm	< 0.5 mm	5-10 mm	5-10 mm	2-3 mm
Best For	General medium-μ	Fine dispersion	Fouling service	High-viscosity	Mid-range reactions

Frequently Asked Questions

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