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pdpicasso
pdpicasso • Aug 2, 2009

In need of an idea to start designing a blowier system

hello everyone.
This is priyadharsan, Mechanical Engg.

Im struggling to start designing a blower system, hope i ll find a idea/solution to start and finish it up soon.

here it is.
requirements:

hope u all seen a artificial flames in bars/ restaurants (there is silky cloth dancing in the air and which is illuminated by electrical bulbs, so its look like a flame...)

actually this is what i exactly want...

Need to design on similar one but in very big size.

the flame need to be in 7.5mt diameter. (cloth has to be fixed in a circular fashion...)
the cloth has to be shoot up to 10 mt height.

this wat the requirement is. i don kno from where to start with?
and want to know
how to calculate the required air volume and pressure?
How to design the blower?
How to design/decide the size and shape of the duct?

anyone help me....
Rohan_sK
Rohan_sK • Aug 3, 2009
The Centrifugal Blower will be the best suited for the given requirement.

The Centrifugal Blowers function on the same theory of the Centrifugal Pumps where the Impeller Vanes rotate to produce a Centrifugal Force on the fluid and impart Energy to it which is Kinetic in case of liquids and Pressure energy if the fluid is gaseous.

Thus the Centrifugal Blower will produce High Pressure Air at discharge and this is what the application requires.

The Centrifugal Blowers follow the affinity laws applicable to the Centrifugal pumps ( for Pressure, Capacity, RPM, Power)

The things to be considered for designing the blower are :

1. The Pressure required to blow the cloth in air upto 10m and keep it waving there upright( it must not drop down).

2. The Capacity required.

3. The RPM and Power of the motor driving the blower.

4. The Pressure drops in the ducting, elbows, bends , etc.


Pressure:

The Pressure Head must be calculated from the height upto which the air needs to shoot up keeping the cloth upright.

As the fluid is air the density of the air along with the height will give the pressure head required.

But it is not only the air which needs to be forced up, the cloth needs to be lifted to that height and maintained there flairing upright without a sloppy fall under gravity. This must be considered when calculating the pressure head.

So the total weight of the cloth has to be lifted to the required height and how vigorously you need the cloth to sway will add to the head and Total Pressure Head calculation will include this factor.



Capacity :

The Capacity will indicate the Mass Flowrate of the air and will vary according to the RPM and Diameter of the blower. It will be corresponding to the value of the Pressure developed and can be easily found from the H v/s Q and Q v/s N curves.

Note that the Head v/s Capacity ( H v/s Q) curves are drawn for Constant Impeller Diameter and constant RPM.




Head Loss in Ducts and Bends :

The Pressure Head Loss in the Duct surfaces and the Elbows and Joints must be calculated and will directly vary with the Diameter of the duct and the number of joints or bends.



Power and RPM :

The Total Power required will depend on the Total Pressure head calculated

Total Pressure Head = P(total) = P(out) + P(fric. loss) + Mechanical losses

The mechanical losses in the rotating elements of the machinery must also be included in the total losses.

This will give the total power required.

The RPM must be calculated according to the standard formula for capacity and speed.



The Blower Vane Design :

The Centrifugal Blower can have either Open or Closed Impeller with Backward or Forward curved Vanes. There are also Airofoil tip designs with similar backward curves.
The vane profile design is available in any standard design book. The propper suction inlet eye diameter and outlet diameter play a great role in Impeller design and help to decide the Vane angles which are the most critical part of the Impeller design.

The size and shape of the duct will depend on the Flowrate ie Capacity ( Diameter directly varies as Capacity for same pressure) and the earlier discussed Head loss issues.

So the losses will be directly proportional to the diameter and length of the ducts and the number of bends. So to minimise the losses the above parameters must be optimised.

This is the basic line on which design is based and detailed formulae are not given here as detailed design can be refered to from any standard blower design book as said earlier.

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