The historical box-wing blower is a centrifugal machine with enclosed sheet-metal wheel passages and rectangular discharge openings. This cutaway follows the arrangement in Hiscox figure 1206: a central inlet, rotating wheel and surrounding scroll outlet. Use the calculator to compare shaft power under two explicitly assumed static efficiencies.
Box-wing Blower Interactive Calculator
Compare shaft power at the same airflow and static pressure using assumed efficiencies A and B. These are hypothetical comparison values, not measured performance of the historical blower.
Equation Used
- One steady duty point, identical airflow and static pressure for both comparisons.
- Entered efficiencies are static efficiencies; defaults are illustrative.
- Shaft power equals static air power divided by the assumed static efficiency.
- No fan curve, RPM, noise, rotor stress or electrical consumption is calculated.
- Drawing proportions and eight passages illustrate the historical arrangement, not exact manufacturing geometry.
The enclosed wheel passages carry air from the central inlet toward the casing outlet. Compare shaft power using efficiency values appropriate to the operating point; the wheel geometry alone does not determine efficiency.
Enclosed passages inside a centrifugal blower
Hiscox’s historical drawing identifies a box-wing blower made of sheet metal, with enclosed sides and rectangular discharge openings. Its wheel sits in a scroll-shaped casing. Air enters near the shaft and is carried outward by the rotating passages before leaving through the surrounding outlet.
The illustration removes the outer cover so the wheel and inlet are visible. The rotating side plate, passage entrances and rectangular rim openings remain connected. Motion is deliberately slowed for inspection; neither rotational speed nor local streamlines are calculated.
Historical ventilation mechanism and modern power comparison
Hiscox places this blower among mining equipment. The illustration explains its construction; selecting a blower for ventilation also requires a measured performance curve and the system resistance.
The calculator remains useful for comparing assumed fan shaft powers at a chosen duty. A real selection requires applicable measured fan curves and an operating point consistent with the system resistance.
Static air power and shaft power
For Q in cubic feet per minute and SP in inches of water gauge, static air horsepower is Q×SP/6356. Multiplying by 0.7457 converts it to kW. Divide that static air power by the entered static efficiency, expressed as a fraction, to obtain required shaft power.
Compute each option at the same duty. The difference is shaft power B minus shaft power A. It may be negative if A is less efficient than B. This is not evidence that one wheel construction is inherently better. Static efficiency must not be substituted for total efficiency in a total-pressure calculation.
Worked comparison with assumed efficiencies
At 250,000 CFM and 6 in WG static pressure, static air power is 175.98 kW. Assuming 84% static efficiency gives 209.50 kW shaft power. Assuming 72% gives 244.42 kW. The difference is 34.92 kW.
Those efficiencies are hypothetical inputs. They are not test results for Hiscox’s blower. Electrical consumption would be larger than shaft power when motor or transmission losses are included.
Reading the cutaway and power comparison
The cutaway explains the physical arrangement: enclosed wheel passages, central eye and casing outlet. It does not calculate blade shape, pressure distribution or allowable speed. Flow and pressure controls change the power comparison; they do not resize the historical wheel or imply a particular RPM.
At fixed efficiency, doubling flow or pressure doubles calculated shaft power. Increasing efficiency reduces required shaft power. Actual fan efficiency depends on the operating point, so a constant-efficiency comparison cannot replace a performance curve.
Box-wing blower questions
How does air move through the blower?
Air enters near the shaft, moves outward through the enclosed wheel passages and exits through the surrounding casing outlet. The rectangular discharge openings are at the wheel rim.
Are the efficiency defaults measured values?
No. They are explicit assumptions for comparing power at one duty point. Enter appropriate static-efficiency data for the alternatives you are considering.
Why can the power difference be negative?
The result is B minus A. When the assumed efficiency of A is lower, A requires more shaft power and the difference is negative.
Does the animation run at the required fan speed?
No. It runs slowly to show the wheel construction. A real operating RPM requires a suitable fan curve; it cannot be inferred from these four inputs.
References
- Hiscox, Mechanical Movements: figure 1206, box-wing blower — historical arrangement and enclosed rectangular discharge passages.
- Hartzell Air Movement, Fan Engineering Data — fan static-efficiency and shaft-power relations, printed page 12.
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