That will require using my mill. In fact I screwed up that base on the 19 jet block. My drill press isn't steady enough. I will try and get my mill this weekend if possible.

this will help to work out the heat tx for a given jet but i didnt know how to work out all the fields it needs.

http://www.coolingzone.com/Content/D...as/fcalc10.htm

Prandtl Number

Diameter (m) thats ones easy

Radius of the measurement area (2.5D <= r <= 7.5D) (m)

Height (2D <= H <= 12D) (m)

Kinematic viscosity (m^2/s)

Nozzle exit velocity (m/s)

Thermal conductivity (W/m.K)

if you can complete these fields it will tell you the average heat tx of the jet.

any thoughts ben ?

cathar told me the following is critical for the cascade to work.

copper between each cup needs to be a little as possible. Each jet only cools a small area.
the height of the tube above the cup base needs to be enough for the jets to form. IMO 3 * jet ID
jet orifice area should be around 26-30mm2 for all jets.

jet ID and cup ID should follow this guideline again ben can you add to this

http://www.lmnoeng.com/PipeDuct.htm


hope this helps some.

Yep, that's all the information that one needs.

A tad late for me to try to get into this math. Is there an interest?

What is the purpose of 'jet forming'?
What is the scientific background?
Will there be a special 'afterburner effect',
like a second acceleration after the water left the nozzle?

Or is its purpose just to minimise retroaction caused by the impingement?

flip

Seek and you shall find.

Jets develop fully over about a 4d distance. Less than this and what tends to occur is a concentrated "mash" of turbulent water striking the base.

Also, while the jet travelling down will lose a small amount of power due to the distance travelled, it also becomes more turbulent (or so it is hypothesised in scientific papers) and this leads to greater thermal efficiency. Again, search through google. There are many studies of the jet distance vs efficiency effect, and every single scientific paper I read found that getting less than 4d in height results in a performance drop off, hitting a peak plateau between 4-5d (different papers differ on the exact best distance) and then dropping off after that.

Very unspecific,
a link to one or more of your cited papers would be useful.
BTW, i've read enough papers to have a good overview.

Quote:

Jets develop fully over about a 4d distance. Less than this and what tends to occur is a concentrated "mash" of turbulent water striking the base.

What is wrt to kinetic energy the disadvantage of that 'mash'?

Quote:

Also, while the jet travelling down will lose a small amount of power due to the distance travelled, it also becomes more turbulent (or so it is hypothesised in scientific papers) and this leads to greater thermal efficiency.

While leaving the nozzle the jet has more turbulent flow,
while being a open jet it tends to develop a laminar flow
given the lesser friction in the free fluid.
Depends on different factors,
so this should not be in contradiction to your citations.

IMO the main turbulence is caused by fluid hitting the bottom,
not by the jets flow characteristic.
As long the fluid can escape with low restriction from
the impingment zone the design goal is reached.

Quote:

Again, search through google.

Sorry,
being myself a 'scientist' (graduated in biology),
it is common practise that the one who cites is in the due to give the origin of his citations.
Everything else is BillA-Style or Kindergarten. ;-)
(Means: I'm not a dumbas noob who has to be educated using the forum)

Quote:

There are many studies of the jet distance vs efficiency effect, and every single scientific paper I read found that getting less than 4d in height results in a performance drop off, hitting a peak plateau between 4-5d (different papers differ on the exact best distance) and then dropping off after that.

Ok,
accepting that as a fact for moment (or infinity ;-) ) ,
there are many factors to be included,
like secondary motion of the fluid after hitting the bottom,
the distance and heigth of the walls (if any there),
and wether the nozzle is a pipe-like structure like yours,
causing fluid can be flowing from 'behind'the nozzle
or a nozzle being 'build in' the upper plate.

I look forward for that paper which addresses the specific conditions like presented in th 'Cascade'-Design.
Keep in mind that i don't dipute your design
but looking for a good explanation of its characteristic dimensions.

flip

Like electrip_flip, I also interested in some specific references.
I am only aware of two from which this can be concluded :-
(1) the work of Suresh Garimella :- http://widget.ecn.purdue.edu/~eclweb...ht_results.xls from http://widget.ecn.purdue.edu/~eclweb/jet_benchmark/
(2) Calculating the "h" profiles using the Flomerics calculator http://www.coolingzone.com/Content/D...as/fcalc10.htm (referred to by leejsmith)
I am keen to add to my info pool.

leejsmith
An old example of the parameters I use at 20C..
http://www.jr001b4751.pwp.blueyonder.co.uk/Jeta.jpg
My interpreation of the consequences for the "best case"(probably no interference beteen Jets) on a flat surface of 9 Jet array compared to a Single Jet are shown in my post in the original Volenti thread http://<br /> <a href="http://forum...eadid=4650</a>
http://www.jr001b4751.pwp.blueyonder.co.uk/JetVole.jpg

Well guys, I've been searching Google and for the life of me I cannot find the two papers that I was using/basing the above comments on. I had saved them on my laptop, but then my laptop disk-drive died about a month ago, and so all data was lost.

Very annoying.

You will have to accept my apologies on the matter, as unsatisfactory as that may be.

As for the "jet in a cup" aspect though, there was not a single paper that I could find that exactly described this sort of behavior. To be honest, I experimented my way to the current implementation of the Cascade, rather than theorised my way there. It's one of BillA's favorite statements - observe the behavior and then assemble the theory to fit. I did take note of free-jet research to guide my initial steps, focusing on 2D to 6D mainly, and experimenting with cup widths ranging from 1.5D to 4D. However, and this must be stated, that structural strength plays as much of a role in the final Cascade base-plate design as the jet/height/width ratios. Given that the base-plate is essentially unsupported, I discarded any possibilities that would result in less than a 3mm base-plate thickness.

Information overload! :drool: :D

thanks for the info but how do i translate my system into the calcuator. Ie my pump , with it's flow and nozzel velocity.

what do i enter for the following

Prandtl Number

Kinematic viscosity (m^2/s)

Nozzle exit velocity (m/s)

for some more info i found the following pdf files.

http://homepage.ntlworld.com/lee_smith/Chapter1.pdf
http://homepage.ntlworld.com/lee_smith/Chapter4.pdf
http://homepage.ntlworld.com/lee_smith/1857.pdf

i have seen a paper on the jet's with cups but dont have it book marked.

just a note i am a noob that comes here to learn.

These are all variables depending on the flow rate.

I believe that the Prandtl number can be extrapolated from a Reynolds figure, not sure.

The kinematic viscosity is a constant. I can't find it right now, but Kryotherm will have it. Just enter: Water, 25 deg C.

so what about the nozzle exit velocity

At 20c
Prandtl No 7.02
Kinematic viscosity (m^2/s) 0.000001006
Thermal Conductivity (W/mK) 0.599
All values fro Kryotherm

Nozzle exit velocity (m/s)
48 x 0.8775 ID tubes
1LPM = 0.57m/s
2LPM = 1.14 m/s, etc

19 jets with a 0.06" ID for the tube... assuming a 1 gpm (60 gph) flow rate...

I've got 3.4 fps (feet per second) or 1 meter per second.

I just finished the cups in the base. I decided to do it on the engraver as it is the only thing I have readily available with precision enough to make the cups. Problem is it has a 22 degree bevel on the cups but the bottom is flat. Not great for optimal impingment, but don't have any other options at this point.

I'm not familiar with what works best in the cup arena... but the flat bottom cups MAY actually contribute to turbulance... At least in my twisted mind. :dome:

That's fine!

Now get yourself some small tubes, and make a top.:cool:

Top is already done:
http://www.customcooledpc.com/jet3b/001.jpg
http://www.customcooledpc.com/jet3b/002.jpg
See page 2 of this thread. ;) If I want the pipes to go INTO the holes a little I will have to mill the outside of the pipe peice down a little.

Yes the flat botton is the best for impingment, but the 22 degree beveled (chamfered) sides of the cups are not. I would have rather had them strait up and down instead of the angle. But this way should help flow rate a little. Will try to get this all together by this weekend. I think it will work out pretty good.

I also got the piece cut forthe 9 jet block that removed the jets as Tuff suggested. It is a 1/8" spacer peice in place of the jet peice. Will slap that together tonight and see what it does.

How deep were you able to make the dimples?

How deep is the side wall, before it starts angling out?

They are currently .050" deep. The bits used on the engraver are V shaped so the angle starts at the bottom of the pit. i will try it just as it is now, and later I will try and find a flat bottom endmill and make the holes a little deeper with it so it has some strait up and down sidewalls.

How did you make those cones? They look cool...

The acrylic piece with the pipes was done on a laser cutter/engraver and the cups in the copper base where done on a rotory engraver.

jaydee: why dont you just pop an end mill in there and turn the speed down to about 9000rpms? thats the usual max rpm for those.

could you take that engraver bit and make a tiny cone on the bottom? maybe give that a shot?


Jon

Endmills do not fit in the engraver. The bits in the engraver are 6.5" long and screw into place at the top of the 6.5". Nothing like a mill. They do make a couple endmill version but they are $32+ each and I am not going to pay for one when a $2.99 endmill for my mill will do the same thing. :D Just don't have access to my mill at the moment.

I have no clue what you mean about a cone? On the bottom of what?