Venturi injector suction not adequate

[kdv1988]

Hey guys, we've been tasked with providing solutions for reducing coolant consumption by our client using automation. One of those is a system to reclaim the coolant dripped off of the chips from a Chip Trolley in a CNC Machine. Around 15-20 Litres of coolant+water emulsion is wasted everyday, even more on certain machines. And this data is for one machine. Considering the total number of machines in our client's Machine Shop, we believe this would go some way in solving coolant consumption issues for them.

So basically we have designed a Venturi Injector. This was designed by taking some inspiration from existing Venturi designs from the internet. I am in no way an expert on Fluid Mechanics or CFD. The motive liquid in the injector is the Coolant pumped by the Coolant Pump (The unit is connected to the discharge of the pump by a Tee). In the suction port, we have connected a 6mm OD PU Tube and at the other end of the tube is a Suction Block with filters. This block is to be placed on the Chip Trolley. Please see attached file for the drawings.

So in this lockdown, since it is difficult to visit clients, we took trials with our own small pump used for transferring water in our office. We connected the flexible hose from the discharge of the pump into the inlet of the Venturi with a Hose Nipple & Clamp. Our small pump is a 0.5 HP domestic pump that discharges approx. 35 LPM. We placed the Suction Cup into a box with some amount of water.

What we saw was the venturi worked to some extent, as in it sucked the water through the cup, but it would stop sucking liquid after a point. And this happened in multiple trials. We even changed the 6mm OD tube into a 8mm OD tube, but the result was the same. We need the system to reclaim all the water (or coolant). Also we noticed that the outlet of water from the venturi would fluctuate i.e the flow-rate of water kept varying as the suction was taking place. Maybe the flow-rate from the pump is not constant, I need to verify that.

Yes I know I would probably need to take more trials with a bigger pump, but I was wondering if you guys could let me know if I am going wrong anywhere and if there were some immediate changes I can make to achieve this goal. I have filmed one of the trials which can be found on this link -

https://photos.app.goo.gl/LLWaS6m3QR4aEqPp6

Maybe that might help you'll get a better idea of what I am doing.

Any advice would be great. Thanks.

 

[EdStainless]

Go out and buy a manufactured eductor. The inside shapes are critical, and yours is wrong.
Try these guys

https://www.foxvalve.com/liquid-eductors/stock-units/

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P.E. Metallurgy, consulting work welcomed

 

[Latexman]

Fox valves!

Good products. I have no association to them.

Good Luck,
Latexman
Pats' Pub's Proprietor

 

[hydtools]

Look for an old waterbed water removal venturi to test your idea. Or an aquarium venturi.

https://www.chewy.com/python-aquari...PfXZ2ePxpHod7lUCP5TyOiJSziD3N9ARoCO_gQAvD_BwE

Ted

 

[kdv1988]

@EdStainless , Yes i will check out Fox Valves. Could you tell me why my design is wrong though? I made this prototype based on a cross-sectional view of another brand's Venturi. I accept it could be wrong, would be nice if you could tell me where I can improve the design though

 

[Compositepro]

You need a converging taper on the right side nozzle. Your jet will expand somewhat after leaving the left hand nozzle and then you are trying to get it to enter a hole that is smaller than the jet diameter. Also your "suction chamber" is the same diameter as the jet nozzle so the walls of your chamber are interfering with the jet.

 

[EdStainless]

So typically you allow abrupt expansion and have the side branch in the contracta just after the flow leaves the nozzle.

https://www.foxvalve.com/liquid-eductors/introduction/

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P.E. Metallurgy, consulting work welcomed

 

[kdv1988]

@Compositepro, I have had a look at some Fox Valve Venturi designs again and I do see your point. The right side nozzle where the liquid enters after leaving the left nozzle does have a much larger diameter which converges and then increases again.

Regarding the suction chamber, I can see the suction chamber diameter is also larger than the nozzle dia. Is it safe to assume the suction chamber diameter should be just about be equivalent to the motive fluid inlet dia?

Also, the Fox Valves website is under construction guys!

 

[kdv1988]

@EdStainless, I will change my design to allow abrupt expansion. But regarding the entry of suction into the chamber, I have noticed that the left nozzle extends past the entry point of the suction. Please see attached picture. I have marked the centre of the suction chamber with a red line that runs across the nozzle. You can see that the nozzle goes past the red line. Kindly clarify.

 

[EdStainless]

So the flow out of the nozzle will actually contract slightly after flow leaves the nozzle.
The suction branch needs to be able to deliver the needed flow and keep the pressure low.
This is why you have the 'well' around the nozzle.
I have made ones from pipe parts, a "T" with a smaller line in one end. but they are not efficient as they don't have correct tappers. The size and taper for each are engineered for the flow rate, pressure drop, and so on. They change a lot depending on the drive fluid (liquid or gas) and the suction fluid (again liquid or gas).
But in all cases the less outlet back pressure the better.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed

 

[kdv1988]

Hi @EdStainless, my second design (based on a Fox Valve venturi) is almost ready for trials. I will take my trials and comment here soon.

Meanwhile I was wondering if you'll could shed some light on the Vacuum Cup. This cup shall stick to the bottom of the Swarf Bin. It has slots on its bottom for allowing the liquid to enter. I am attaching the design of the Cup in this post.

Would be great if you'll could comment on this. I'm spending so much time on developing a venturi. I'd hate it if the problem actually was in the Vacuum Cup.

As described, the function of the Cup is to attach itself to the bottom of the Bin. Due to the vacuum created by the venturi, the liquid from the Bin is sucked through this cup. Let me know if you'll need any more info. Thanks

 

[EdStainless]

You want the least suction height possible and as little restriction as possible.
Use gravity to assist as much as possible.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy, consulting work welcomed