065 Fans 2012 Presentation

8/12/2019 065 Fans 2012 Presentation

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Global Infrastructure & Industry

Use o f Grade 80 Steel in Fabric ated

Centr i fug al Impel ler

Authors:

Nicholas Brunck (American Fan Co.)Paul Okeley (Flkt Fan Group)

A. Geoff Sheard (Flktwoods)

April 18th, 2012


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Backward Curved Centrifugal Impeller

High efficiency

Lack of overloading horsepower

Stable performance throughout pressure range

Low noise levels near peak efficiency


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Methods to Increase Tip Speed

Intermediate shroud(s) (ring) per US Patent

3,306,528 (Eck, 1967) Widely used in practice today

Item 50

Blade Gussets

US Patent 4,028,005

(Eck, 1977)

Item 122

No discussion of effects on

performance.


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Historical Data

Inherently, an intermediate shroud is an obstruction in the airstream

Unpublished test results from Garden City Fan

November 1973

222BF flat backward inclined blades

565.2mm (22)

Comparison of impeller with and without

intermediate shroud 4 percentage point increase in efficiency

5-6% power savings

Plotted in non-dimensional form

Total efficiency vs. Specific diameter

Pressure coefficient (FTP/PVP) vs.

Specific diameter


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Historical Data (cont)

4%

headgravity

diameter

speed

flow

222

31

1

2

21

41

diameterspecific

Hg

D

N

Q

DN

gH

ND

Q

Dst

stD

speed

diameter

density

pressurefan total

2

pressurevelocityperipheral

pressurefan total

N

D

P

DN

P

PVP

FTP

PVP

FTP


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Application to Backward Curved Impeller

Duty Point

3363 Pa 4.6 m3/s

73% efficiency

Maximum 508mm

(20) impeller

Testing was conducted

on available impeller

381mm (15)

AMCA Std. 210-07

Type B

Data scaled via Fan

Laws Meets pressure and

flow duty requirements

Efficiency low by 3%

Efficiency

requirement

not met

w/ring

Max speed

w/out intshroud


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Backward Curved Impeller with & without intermediate shroud

381mm (15) scaled

to 508mm (20) viaFan Laws

With Int. Shroud:

3823 rpm

70% efficiency

W/out Int. Shroud: 3698 rpm

73% efficiency

Motivation to remove

intermediate shroud


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Mechanical Design Considerations

Removal of intermediate shroud increases stress

in impeller at given speed Imagine the blade as a beam, fixed at both ends

Max. stress is proportional to the moment, which is

proportional to the square of the beams length

By effectively doubling the length of the beam, the

moment & stress are quadrupled Maximum speed of standard 508mm Gr. 50

impeller without intermediate shroud is 2785 rpm

Much lower than required 3698 rpm

(1)

(2)


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Author: AAAA BBBBBBBBB

Business: Global Infrastructure &

Industry

Date: 10 Jan 2011

Ref: FWG-100111-rev1

Documents

065 Fans 2012 Presentation