Microduct Fill Ratio and Cable Jetting Air
Computes cable-to-microduct fill (cable OD over duct ID, the manufacturers' basis), annulus, nominal duct air.
Example
You enter
- Microduct inside diameter (mm) 10
- Cable outside diameter (mm) 8.5
- Recommended minimum fill, OD/ID (%) 50
- Recommended maximum fill, OD/ID (%) 80
- Target fill, OD/ID (%) 65
- Nominal annulus air velocity (m/s) 25
- Duct pressure (bar absolute) 10
You get
- Cable fill (OD/ID) 85.0 % -- ABOVE WINDOW (72.2 % by area)
- Compressor free-air delivery 327 L/min
- Cable OD at target fill 6.50 mm
- Free air at target fill 680 L/min (108 % change)
Checked against published worked examples from: Corning Optical Communications.
Details, formula, and sources
ScopeComputes cable-to-microduct fill (cable OD over duct ID, the manufacturers' basis), annulus, nominal duct air, and compressor free-air delivery against an entered jetting window. An 8.5 mm cable in a 10 mm duct is an 85% fill, above Corning's 50% to 80% target. The arithmetic sizes air demand; manufacturer data and a trial shot, not a general formula, establish jetting distance.
Formula or tablefill = cable OD / duct ID (the manufacturers' basis); area fill = (OD/ID)^2 shown beside it; annulus = pi(ID^2 - OD^2)/4; nominal duct flow = annulus x velocity; free-air delivery scales by absolute pressure ratio.
Source and editionMicroduct fill and nominal air-demand screen. Jetting distance is deliberately not calculated.
Free accessCircle areas and a volumetric-flow conversion.
What governsEstimate. AHJ and licensed professional govern.
API field namesduct_id_mm, cable_od_mm, fill_min_pct, fill_max_pct, optimal_fill_pct, air_velocity_m_s, pressure_bar_absolute, fill_ratio_pct, free_air_l_min, optimal_cable_od_mm, optimal_free_air_l_min
- Nominal incompressible screen real duct flow is compressible and pressure falls along the runthe jetting-equipment supplier
- Fill window is entered cable and duct surface and stiffness alter itthe paired product data
- Distance excluded bends, elevation and surface friction prevent a general formulamanufacturer charts and a trial shot