Venturi pump design

[sampi]

I am busy designing a venturi pump. the venturi works with air. The objective is to create a lowered pressure in the throught of the venturi to have some "suction" on another pipe that ends in the throught. The pipe contains a gas mixture of N2, H2 and SiH4 (108m3/hr) at about 86.5kPa (1atm) pressure, diameter=75mm=3". I want the pressure in the throught to be about 85.5-84.5kPa. The end of the venturi is open to the atmosphere, thus pressure ~86.5kPa. I am having problems with the calculations of fluid speeds (in the throught and there after) and pressure drops in order to calculated diameters...

 

[katmar]

Hi Sampi,

Venturi pumps are tricky to design yourself because there is a lot of empirical knowledge required. Even though you could do an overall energy and momentum balance to get the flowrates and pressures, this would not tell you how long the throat needs to be to get good momentum transfer, or what angle the diffuser should be to get maximum pressure recovery. These are things that the manufacturers have learned through trial and error over the years.

Fabrication technique is also important because the internals need to be polished smooth to achieve high efficiencies.

If you want to get a rough idea of the dimensions required there is a design chart in Perry 4th Ed pg 6-31. It may be in later editions as well, but I don't have them to hand right now. Look under "Ejectors" in the index.

My recommendation would be to hand the problem over to a competent supplier.

regards
Katmar

 

[sampi]

Can you maybe name suppliers based in South Africa?

If not, thanks anyway!
Greetings
Sampi

 

[katmar]

Try Geoff Levy at Applied Vacuum

http://www.appliedvacuum.co.za

The big international companies like Croll-Reynolds or Graham Manufacturing have probably got agents in SA - try their web pages for contact addresses.

 

[Torricelli]

Sampi,
specify the absolute pressure for each of the 3 connections (Inlet / Outlet / motive)
and specify the suction flow (mass flow and Molecular weight).

Suppliers in South Africa:

http://www.vacuum-guide.com/firmenlisten/laender/southafrica.htm

vacuum ejector manufacturers:

http://www.vacuum-guide.com/firmenlisten/produkte/vacuum_ejector_europe.htm

regards