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Abstract
Zero-length loss coefficients were calculated for controlled bends of 45° and 90° in nonmetallic flexible ducts under fully stretched conditions for dimensionless bend radii of r/D = 1 and r/D = 1.5. The nominal duct diameters were 203, 305, and 356 mm (8, 12, and 14 in.). A regression analysis was performed on the measured data, and the uncertainties in the pressure loss coefficients were calculated. Correlations of loss coefficient data appropriate for insertion into a duct fitting database are presented.
Nomenclature
| A | = | duct cross-section, m2 (ft2) |
| C | = | loss coefficient, dimensionless |
| C′ | = | pressure loss coefficient, Pa·sn/m·Ln (in. water/100 ft·cfmn) |
| D | = | diameter, mm (in.) |
| L | = | length, m (ft) |
| L′ | = | helical wire pitch, mm (in.) |
| m | = | slope, dimensionless |
| n | = | exponent, dimensionless |
| N | = | number of data points, dimensionless |
| pv | = | velocity pressure, Pa (in. water) |
| Q | = | flow rate, L/s (ft3/min) |
| R2 | = | coefficient of determination, dimensionless |
| r/D | = | radius-to-diameter ratio, dimensionless |
| S2xx | = | sum of squared deviations of C about the curve, dimensionless |
| syx | = | standard error of C about the curve, dimensionless |
| V | = | velocity, m/s (ft/min) |
| x, y | = | linearized variables |
| = | mean values | |
| ΔC | = | loss coefficient uncertainty |
| Δpf | = | frictional pressure loss, Pa (in. water) |
| Δps | = | static pressure loss, Pa (in. water) |
| Δpt | = | total pressure loss, Pa (in. water) |
Subscripts
| 1 | = | plane 1 |
| 2 | = | plane 2 |
| 7 | = | plane 7 |
| 8 | = | plane 8 |
| i | = | data point i |