Axial Flow Fan Design Parameter Affecting the Performance

Ankesh Kumar Pataskar, V.N. Bartaria and Abhishek Jain

University Institute of Technology, Barkatullah University, Bhopal, India.Lakshmi Narayan College of Technology, University Institute of Technology, Barkatullah University, Bhopal, India.

DOI : http://dx.doi.org/10.13005/msri/090212

ABSTRACT:

Axial flow fans are employed in heat exchangers and other engineering systems where the flow path around the fan becomes like a duct. The flow takes place along the axis of rotation of the rotor. The flow is essentially symmetrical to the axis. The design calculations are performed with presumption of flow through cascade of blade and it is the main governing factor of the design too. In this paper procedural calculation for an axial flow fan with profiled blade are presented. Calculations are tabulated for different parameter of radius and angles. On profiling, the increase of outlet angle has been shown which gives ultimate angle opening. The small corrections are therefore obtained. Different parameters used in the design are tabulated to get the calculation more accurately.

KEYWORDS: Axial Flow Fan; Airfoil Blade Design

Copy the following to cite this article: Pataskar A. K, Bartaria V. N, Jain A. Axial Flow Fan Design Parameter Affecting the Performance. Mat.Sci.Res.India;9(2)

Copy the following to cite this URL: Pataskar A. K, Bartaria V. N, Jain A. Axial Flow Fan Design Parameter Affecting the Performance. Mat.Sci.Res.India;9(2). Available from: http://www.materialsciencejournal.org/?p=1138

Introduction

Axial Fan designers are frequently faced with the problem of designing high-efficiency fans at a given flow rate and for a given pressure duty. Design techniques are typically based on engineering experience, and may involve much trial and error before an acceptable design is found. An axial flow fan stage consists of a rotor made up a number of blade fitted to the hub. When it is rotated by an electric motor or any other drive, a flow is established through the rotor. The action of the rotor cause in increase in the stagnation pressure of air or gas across it. A cylinderalcasing encloses the rotor. It receives the flow through well shaped converging passage (nozzle) and discharges it through a diverging passage or diffuser. The number of blade in rotor varies two to fifty. As in axial fan, the flow is generally in the axial direction, Guide blade to recover statics pressure from the swiral downstream of the rotor.

Fan engineers are frequently faced with the problem of designing high-efficiency fans at a given flow rate and for a given pressure duty. Design techniques are typically based on engineering experience, and may involve much trial and error before an acceptable design is found.

Fan Design

We take External Diameter d2= 0.795

Then wefind Value ϕ =0.22

We find Value this Equation Ψ =0.130

Take Equation of Ψ

Equating both value Ψ and ϕ

Then Find Value σ=2.16 & δ=1.28

After the value speed coefficient σ and diameter coefficient δ is calculated, specific diameter r is read from the graph given in Figure by Eck Specific speed coefficient

We take a formula d2=795 mm ,& d1= 795 .28 = 225 mm, η=73%

The meridional speed is obtained from

cm = V/(η/4)

cm = 15.122 m/sec

u2 = πd2n / 60

u2 = 60.73 m/sec

ϕ= cm / u2

ϕ = 0.24

Then,

Cu = ΔP/ηun

Figure 1

Click on image to enlarge

For t/ l, the best value of which range selects the first value are being at the tip of the blade. Thus we have take number of blade Z =9.

Z= (4π/ 1.5) [sin β2 /{1-(r1/r2)}]

Then find value β2 = 50.54° ≈ 50°

Then we take fig. blade pitch according to Zweifel by ECK

Take according to Zwifel β2= 30° Then we obtain value s/ l = 0.66 by fig. effect of Tip
clearance of Weining Draw Velocity triangle

cm=ω2sin β2

ω2 = 19.74 m/sec

Then we obtain value of ω2 and
u= ω2 cos β2

Then we obtain value of u =12.68 m/s General relationship angle cot
β∞= ½ (cot

β1+ cot β2)

Then we find value of β∞=37.87°

cm=ω∞ sin β∞

ω∞=24.63 m/s

υ∞ / 2 = ( β2 – β1)/2=10°

βm=(β1+ β2)/2=40°

And value of t/l

Then we take value of by graph t= l cos βm then take l = 0.085 m And we take a value of μ = 0.61 And (1-μ)/μ =.0639
And Value ν = (ϑ∞/2) { (1-μ)/μ}

υ = 6.393

β1´= β1´- υ

β1´=23.607°

β2´= β2- υ

β2´=56.393°

Δβ= Δβ1(l/t)2 according to Weining graph determining the increase of angle by profiling s, profile thickness , l chord length Δβ=2.39°

We take value of

βm+ Δβ =42.39°

Table : Impeller geometry parameters

Click on image to enlarge

 Table 2: Nomenclature

Click on image to enlarge

 Conclusion

In the present paper design procedure for an axial flow fan applicable in heat exchangers and other engineering systems has been presented. The design calculations are performed with presumption of flow through cascade of blade and it is the main governing factor of the design too. The profiled blade theory is used for designing. Calculations are tabulated for different parameter of radius and angles. On profiling, the increase of outlet angle has been shown which gives ultimate angle opening. The small corrections are therefore obtained. In this paper important design parameters with particular values as obtained through calculation are listed. The data of important design parameters can be used for design optimization  and energy conservation in application of axial flow fans.

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