Hi Joe,

The orifice plate is similar, but you measure the pressure difference on each SIDE of the plate, rather than the method used in a venturi, where your vacuum port is within the high velocity stream, within the restriction iself.

It's the venturi effect which causes the suction in this case.

My design is crude enough to be a sort of hybrid, because it doesn't offer the smooth flow narrowing gradient of an efficient venturi.

Both use the same basic Bernoulli principal.

As to the formulas, there is a wide variety of venturi designs, no one formula will conveniently suit all design requirements.

Some venturis are intended to act as flow meters, whereby you measure the pressure difference and can determine flow rate from that. This means there is no net flow into or out of the vacuum port. It is simply a static pressure.

The venturi vacuum pump, on the other hand, expects flow to be drawn in thru the vacuum port and this flow volume is added to the total flow.

This makes the design somewhat different, as you may want to design for maximum suction, or for minimum flow restriction, or a combination of suction level and flow restriction values.

It also depends what you are sucking thru the vacuum port.

A liquid is incompressible, so will affect the output throat angle differently to a gas. The important factor here is the ratio of prime flow to vacuum inlet flow.

You can have a liquid or a gas as the main flow medium causing the vacuum, and you can suck in a liquid or a gas. You can even suck in a powder mixed with a gas.

Different densities of materials cause different turbulences also, which again affects the calculations.

The inlet on a static venturi often has a cone angle twice the outlet cone angle, but for a mixing venturi, or a venturi vacuum pump, the inlet and outlet throat angles can be quite similar.

A wealth of information concerning eductors, injectors, and pumps.

http://www.penberthy-online.com/jet.asp

quote:

Some venturis are intended to act as flow meters, whereby you measure the pressure difference and can determine flow rate from that. This means there is no net flow into or out of the vacuum port. It is simply a static pressure.

So with an accurate enough vacuum gauge, and some calibration, this sort of venturi of yours could be made into a flow rate meter? And with a little electronic manipulation, a cheap flow volume meter? Hmmmm....

I have made Venturis for antique Motorcycles.
They start with a radius and taper down (get larger). I don't know if something like that would work the same with two liquids.

Hi Ryan and Mack

If you add a U-tube to the venturi, it makes a great flowmeter. Very common in industry - simple and therefore fairly reliable.

Here's how you would arrange the venturi as a simple flow meter...



You can isolate the u-tube liquid from the process liquid by using an air loop of tubing going up, then down to the liquid u-tube.

You would probably want a larger diameter orifice if you're using the venturi as a flowmeter, rather than a pump, to reduce the vacuum - you'd not want to draw the u-tube liquid up into the process.

You could fit a differential pressure sensor to the tubes if you wanted an electronic signal, but the response is not at all linear - you'd need to linearize it. This is also true for the markings against the u-tube.

The curve crudely approximates to a square-law, so if you double the flow rate, you get roughly 4 times the pressure difference. Or, if you see a doubling in pressure, you know your flow has increased by around 41%, because the square root of 2 is around 1.41

Hi Rick G

This site has some handy calculators for venturi
performance ...

http://www.pipeflowcalculations.com/venturi/index.htm

Hope that helps,

Made some changes to the venturi - big performance leap. See 1st post for link.

Sucks up methoxide and mixes it very nicely into the oil.

Venturi is on the outlet of the pump, just before the pipe enters the processor.

New processor plans coming soon...

A few new ideas near the end of page, showing how to make a venturi by bashing copper pipe.

http://www.graham-laming.com/bd/venturi/venturi.htm


This is simple to make, with just 2 components soldered together, and metal bashing copper is a lot easier than you might think! I tried it for the 1st time last night and have 2 of my best performing venturis to show for it.

Give it a try!

This message has been edited. Last edited by: GrahamLaming,

Your forged copper venturi looks nice. It may go faster if you anneal it every three or four passes around with the hammer. Just crank up your torch and heat the copper till it is glowing a dull red heat, or at least until it has a full dark oxide color and then quench in water. Should be much softer and will be less likely to crack as your swaging down progresses.

BTW I forged myself a nice one of 1" steel pipe this weekend and have been plumbing it into my reactor. Anxious to try your new methods out.

GL,

Now I'm really impressed!!

Question -- is copper a suitable material for BD processors -- everyone seems to be recommending use of black iron and brass valves (unless you are Bill Gates and can afford stainless )?

Thanks,
Kurt

A reamer is designed to remove small amounts of material, same goes for a tapered reamer, they are not designed to hog out material. You can drill a tapered hole by step drilling and finishing up with a tapered reamer but you need to do the steps in very small increments. Easier if you use a very soft material. You need a tapered hole, generate it on a lathe.

Hi cstoker,

Thanks, good idea, I'll give annealing a try this evening, let you know how it goes. Even without it, the work is reasonably easy and a ding in the wrong place doesn't make too much of a dent

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Hi Kurt,

If you can make it all in steel, great.

My entire system is copper, including the reactor tank, and has done many a batch without problems. It may affect shelf life, but I use my biodiesel pretty soon after it's made.

However, steel would be better.

If just the venturi is made in copper, I don't think you'll have any problems at all.

Regards,

Graham, I have a program that calculates pressure drop on venturis, if you will give me the diameter of the entering port and the restriction diameter and degrees of taper, whether 15* or 30*. I follow your threads and they are quite informative and helpful. jack

Graham , Interesting thread , will try this on my reactor . A little information for you . When attaching one copper tube to another solder is not strong enough ,can be snapped off with little force , silver solder is what should be used . It takes more heat to silver solder than to soft solder . and if you can a lip around the hole you solder the tube into will make the joint stronger also . I will post some instructions on how to anneal the tube and make the lip tonight . Dan

Hi jacmac

That's a nice offer!

Here's a rough guess at the dimensions and angles, should be pretty close...

Assume a flow rate of 40 litres per minute.




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Hi Lu47Dan,

Thanks, yes, you're right, simple plumbing solder is risky with a butt joint like that.

I'm working on a wrap-around joint for the next prototype, and plan to use silver solder. I'm making a simple blowpipe to direct the flame more precisely than my current wide blast.

I tried annealing some pipe last night, but made a big mess of the job. The copper was so soft, I really made a dreadful shape. And the compression fitting I tried wouldn't hold - I need to be more precise on which parts I anneal and which parts I leave solid. A damp cloth around the ends would probably do. All part of the fun of learning a new trick.

Looking forward to your info on annealing and creating a more sturdy joint.

This message has been edited. Last edited by: GrahamLaming,

Graham , the wet rag will keep the heat from migrating and making the copper soft too far away . Another way to handle it is to use couplings and two stub pieces of tube soldered on to your venturi or use two unions . I am going to put the information on silver soldering over on the biodiesel pictures site , I will come back and place a link to it . Dan

Graham here is the Link to the thread on silver soldering and making a "pulled" tee . Hope you find it interesting . Dan

Hi Dan,

Many thanks for that! How would you go about re-hardening the copper? After annealing, I found the copper extremely soft, and would want to re-harden it somehow, for durability.

The only way I know to re-harden copper is to beat it, but if I'm already at the shape I want, what do I do?

Thanks again,

You're right Graham, there's no easy way to re-harden the copper other than cold-working it. It will get hard fairly quickly (10 to 20 cycles of gentle bending back & forth).

ultrasonic hardening?

http://snipurl.com/1d673

many hits, low amplitude.

(I might use one of these in a glycerine fired heater...hee-hee!)