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Design Parameters for Venturi Tube to Obtain Variable Flow Mix of Air & O2

03/04/2008 8:09 AM

Hi !!! all the members

I have been asked a following subject by a student for which I have no answer to offer as subject is out of my purview , however I m sure with the help of experts on CR 4 I am hopeful of getting satisfactory answer for this young student

Query from the student is as under :

QUOTE :

I am currently doing my Biomedical Engineering from Manipal and presently doing my final semester project with a company in vadodara, who is into Manufacturing of Medical Ventilators.

Aim of my project - To come out with a Concept ( also a working model if possible) of a Light Weight, compact portable Ventilator

Current objective : To obtain constant/variable oxygen ( from a cylinder) and Air( from atmosphere) mixture to be given to a patient.
Methods by which i can achieve the above said : (a) Venturi Tube/ Mechanism - I have performed some tests and the results were satisfactory to some extent.
(b) Internal Compressor
(c) Piston
Query : The diameter of the orifice in the venturi and the width of the slit ( through which air can enter) are responsible in change of parameters such as Flow rate, mixing of the two gases etc.
With the present venturi tubes i have ( which are used in Medical Field to deliver a higher amount of oxygen to the Patient, known as a venturi Mask), I cannot obtain the desired flow rate and the pressure.
Having limited knowledge in this area can i have some guidance from you as to how to design a new one or make changes in the existing one so as to get desired results.

URL's for venturi mask: http://www.rcsed.ac.uk/journal/vol46_5/fig-3.gif
http://www.aic.cuhk.edu.hk/web8/venturi_mask.htm


Thanking you

Nirat Kothari

UNQUOTE

Looking for quick response from members

Udayan

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Guru
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#1

Re: Design Parameters for Venturi Tube to Obtain Variable Flow Mix of Air & O2

03/04/2008 8:52 AM

This is a very specialised field.
I worked on respiratory measuring instruments for several years. I don't think I'd want a studen messing with human ventilation. If you must then it would require an awfull lot of reading of medical journals, standards and such like just to understand the relevant terminology... It is difficult to gain 3years experience over a short project...

Sorry to sound negative, but this is also a field which is (quite rightly) subject to many regulations.
I would suggest finding an alternative project. If you want to play with venturis, maybe look at automatic dosing of detergents int a flow of water for cleaning applictions e.g filling buckets, trigger bottles, or car washing.

Del

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#5
In reply to #1

Re: Design Parameters for Venturi Tube to Obtain Variable Flow Mix of Air & O2

03/06/2008 11:56 PM

Sir,

I am the One who had asked the question to my teacher Mr Patel.

I would like to modify my question and seek your guidance.

Mixing of two gases is possible in a venturi tube having by having slits at the throat. But if there exists some positive pressure at the end ( having larger diameter ), how to get the desired concentration of the driving gas and the Driven gas ?

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Guru
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#6
In reply to #5

Re: Design Parameters for Venturi Tube to Obtain Variable Flow Mix of Air & O2

03/07/2008 3:36 AM

As I said in #1. I worked in measurement... so gas isn't my field.
I also suggested working with liquids... they are much easier to see, measure, contain, understand etc.(especially if one is brightly coloured)
The ideal project is one which can be broken down into small achievable steps and yet expanded into a meaningful whole.

Del

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#2

Re: Design Parameters for Venturi Tube to Obtain Variable Flow Mix of Air & O2

03/04/2008 9:36 AM

Ditto on Del's comments. I built a venturi to extract samples of flue gas and it took $5000 of a fluid professor's tutoring and a year or so of experimentation on my part to get it to work. And I still don't know even a tenth of what I would need to work on a patient ventilation device. When my devices didn't work right, it didn't hurt the power plant, but when a ventilator doesn't work right....Double Yoi!

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#3

Re: Design Parameters for Venturi Tube to Obtain Variable Flow Mix of Air & O2

03/05/2008 8:21 AM

As above... I have completed jobs at a couple of companies who make gas appliances, they use venturies (ii?) for the correct gas / air mix.

Whenever I've asked how they designed the venturi its always been a case of blank faces and a lot of hummming and errrring about "we fiddled until we got it right!!", even admitting that they still didn't know whether they had got it right after 40 years of manufacture!!

In fact I am doing a job at the moment for a well known company that produces tiny jets through which LPG passes into a venturi to mix with air before being burnt - they have no idea who designed it saying that we've always made them that size and shape!!

John (good luck!)

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#4
In reply to #3

Re: Design Parameters for Venturi Tube to Obtain Variable Flow Mix of Air & O2

03/05/2008 8:45 AM

A fine example of traceability

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#7

Re: Design Parameters for Venturi Tube to Obtain Variable Flow Mix of Air & O2

03/15/2008 12:10 PM

I have the feeling that your student already asked cr4 for this question with an other formulation and because he was send to look at other threads on same subject came to you. There are many discussions on this subject you can find under "venturi".

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