An effort to find out what is needed for a special laminar jet

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An effort to find out what is needed for a special laminar jet

Post  Jurrien on Sun Jun 12, 2011 4:05 pm

Hi all of you,

this is my first post on this wonderful forum. Since I have seen this forum, I like to play with nozzles every summer. You can see some photographs and documentation (in dutch) on my personal website

Now, I have done some study on the dimensions of a nozzle in order to understand what is needed to get a water arch of some height and distance. I have written down the results in a document that you can download here:

http://www.roerei.nl/Dimensions-waterjet-nozzle.pdf

I hope it helps you with your designs and I that some of you can review and improve this document. Comments are welcome! Of course, I will make new nozzles in this summer!

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Re: An effort to find out what is needed for a special laminar jet

Post  Jurrien on Wed Jul 06, 2011 4:41 pm

I have discovered a number of errors in my document and I have replaced it with a new version using the same name. You will notice that the values for arch heights have changed considerably. Now , I like to find out more about what is happening inside the nozzle and especially what the pressure drop is at the exit side of the nozzle.

Today, I have done my first experiemnets with a new 4'' nozzle and a 1'' line between the pump and the nozzle. The result was spectacluar. The arch was much much bigger than I was used to with the 0.5'' lines, and the nozzle broke into parts that had not been glued together yet. Tomorrow is for new experiments.

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Re: An effort to find out what is needed for a special laminar jet

Post  Jurrien on Thu Jul 07, 2011 2:07 pm

Today I have managed to some some experiments with a new 4'' nozzle. The biggest change this year was not the biiger nozzle but the use of a waterline with a 1'' diameter, instead of the standard 0.5''. The result was unexpected and spectacular: much higher archs (and almost wet people passing by)

This is the result with a 10 mm diameter for the exit


This is the result with a 11.5 mm diameter for the exit


and finally the result with a 13 mm diameter for the exit


In the previous years, I have used the same pump and I never had arch's like this. The largest one, for 10 mm, was about 4 m heigh and 6 meters wide.

However, the quality was bad. .
I have created the exit nozzles from a sheet of aluminium that I attached to the plastic closures that come with the tubes. A circular piece of wood was used to make this construction stiff. It is easy for experimentation but it appeared to be not so easy to make nice perfect circular holes.


This picture shows the difference between the latest version of the old tubes and the new one.

The next step is to find a way to reduce the flow.


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Re: An effort to find out what is needed for a special laminar jet

Post  Jurrien on Tue Aug 02, 2011 10:52 am

Because I have to wait for a "ball tap?" that can control the flow, I decided to do one more experment. This time I created a nozzle with an exit diameter of 16 mm. The quality of the jet is still not very good.



Next week , I hope to receive the "ball tap". I also hope to lay my hands on a ""column drill" for making better holes in my aluminium sheets.


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Re: An effort to find out what is needed for a special laminar jet

Post  jetty on Tue Aug 02, 2011 12:53 pm

Hi Jurrien,

It's all about the nozzle, needs to be razor sharp and well, pretty much perfect. If it's not, small amounts of turbulence are created which break up the stream further along. I found it pretty much impossible to make a perfect nozzle via drilling or grinding. Anything using a sheet (even the thinest brass sheet i could find), ended up not great, because it didn't have a perfect razor edge. I ended up resorting to a mini lathe to achieve this.

Here are some conclusions I came to:

1. Exit nozzle must be perfect, it's the biggest contributing factor

2. Designing the components of the tube is important, but getting it exact is less important
than the nozzle. Better tube design will enable the jet to be laminar further.

3. Reducing water flow ends up with less distance / height, but if say you get laminar for half the distance,
reducing the pressure so that the whole jet is half the distance will result in laminar flow for pretty much the whole length.

It's pretty easy to tell if the nozzle is the cause. Do you have a closeup picture of the water tube exiting the jet for about 5 inches? Imperfection in the exit nozzle show up as striations in the stream on exit and are rotating along the length. This turbulence that is introduced causes breakup in the laminar flow the further you get from the exit nozzle and undoes the handwork done creating a laminar flow in the tube.
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Re: An effort to find out what is needed for a special laminar jet

Post  Jurrien on Wed Aug 03, 2011 3:33 am

Hi Jetty,

thank you for your comments. The theory on the working of the laminar jet also confirms that the shape of the orrifice has an extremely big unfluence. There were lots of striations in the beginning of my jets. The quality of the holes was realy bad. My first concern was to find out what size I needed and what the influence would be of a bigger inlet. (and that was a big surprise for me). (I have found the right name for "ball tap": globe valve)

I have found your reply on the post "Nozzel Construction question from a new guy" with the story of your own experiments. I think it's worthwile to have a special topic on the creation of orrifices with different methods, materials and tools. I try to find a cheep solution and that's why I like to experment with sheets. The people in this forum who want to have the best and biggest jets, realy need to think of special tools like mini lathe's and mills, and materials like copper, brass, aluminium, stainless steell and probably coating of materials? I am tempted now to buy a mini lathe myself (the Unimat Classic). That will also allow for experiments with other shapes like slits.

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