Jet impingement

I just did a thread on pattern spray nozzles that I found at mcmasters. I also found some reading material on impingement so I thought nozzles would fit in there somewhere. Seems DodgeViper's little nozzle idea is correct. I have found from reading that a flat base is better for what ever reason I have no idea. I think his idea would be better with more holes.

here's the link

Hopefully we can get some talk about it from others who are more educated in that area.

Well Cathar should know a thing or 2 about it. His block is really the first commercially available to use this technology and it does give amazing results.

A nice thread here:

http://forums.procooling.com/vbb/showthread.php?s=&threadid=5476

about a jet impingement design that contains my thoughts on the matter in a subsequent post.

It can be fairly easy to do as shown in that thread. I'm a bit hesitant to say that jet impingement alone is the way to go for anything except for direct-die applications, but there's no denying that for closed-blocks it's still has quite a ways to go before someone gets it right.

My block is a hybrid sort of thing. Not really a true jet impingement design, but does it's best to fake it and merge it with the fine-channel approach.

My interpretation of Jet v Channel is illustrated by these graphs*




*Used Flomeric** for Jet and Kyrotherm*** for Cnannel.
** http://www.coolingzone.com/Content/DesignCorner/Problems/formulas/fcalc10.htm
*** http://www.kryotherm.ru/soft.htm

Edit: Updated "h" v Pressure Drop graph using better nozzle PD calculations: http://www.pressure-drop.com/index.html.
Old "h" v"PD" is still here http://www.jr001b4751.pwp.blueyonder.co.uk/ChJet1.jpg

Les, could you specify what the "Micro" 58 channel stands for? Is this an actual block? I am a bit puzzled by it's line graphs. It seems to stay perfectly constant under a couple of conditions (lower velocity and LPM) and then suddenly undergo a big change, quite unlike the other lines. What is going on here?

FIZZ3 said:

1)Les, could you specify what the "Micro" 58 channel stands for? Is this an actual block?
2) I am a bit puzzled by it's line graphs. It seems to stay perfectly constant under a couple of conditions (lower velocity and LPM) and then suddenly undergo a big change, quite unlike the other lines. What is going on here?

Click to expand...

1) 58 refers to the number of Channels in a 33mm wide and 30mm long area. The Channel width is ~ 0.2mm with depths of 1 and 5mm.The fin width is ~ 0.35mm. It is an imaginary block. I consider these to be Micro-Channel blocks.
2) It is the change from conditions which are designated as "Laminar" and "Turbulent" by Kryotherm(Reynolds No. ~2,000).

Possibly some thoughts on the effect of "bp thickness and area" on the cooling are relevant here.The prediction is for a uniform heat Transfer Coeff over the bp areas and uses Waterloo*.


* http://www.mhtl.uwaterloo.ca/old/onlinetools/strip_source/strip2.html

Les56 said:

1) 58 refers to the number of Channels in a 33mm wide and 30mm long area. The Channel width is ~ 0.2mm with depths of 1 and 5mm.The fin width is ~ 0.35mm. It is an imaginary block. I consider these to be Micro-Channel blocks.
2) It is the change from conditions which are designated as "Laminar" and "Turbulent" by Kryotherm(Reynolds No. ~2,000).

Click to expand...

Interesting! Thanks for your insights.

Cathar said:

A nice thread here:

http://forums.procooling.com/vbb/showthread.php?s=&threadid=5476

about a jet impingement design that contains my thoughts on the matter in a subsequent post.

It can be fairly easy to do as shown in that thread. I'm a bit hesitant to say that jet impingement alone is the way to go for anything except for direct-die applications, but there's no denying that for closed-blocks it's still has quite a ways to go before someone gets it right.

My block is a hybrid sort of thing. Not really a true jet impingement design, but does it's best to fake it and merge it with the fine-channel approach.

Click to expand...

Thanks Cathar and Less for the cool graphs and links.

I think the distance from the face of the jet to the baseplate should be determined by head pressure and flow of the pump. With that said, it would be hard to get it "right" in a sense with all the different pumps we use. So what I though is to take a 3/8 npt threaded barb and take a half inch copper pipe and tin it inside the threaded part of the barb. Then I could take a normal 1/4 pipe tap and thread the inside of that. Then use a pipe with the same male thread to screw it in. The end of the pipe would be flared at the end to allow a 1/2 disk or more to be used with holes drilled in it. This would allow the jet impingement to be adjustable so one could just dial in the correct distance to get the best results with all the different pumps out there.

Another thing I thought about that would be best for a radial design microchannel. Make the radial channels but in the center leave a circle that is flat and dead center inside the radial. Ever see what happens when you take a water hose and stand the outlet against a flat surface? The velocity increases. Which I think would be a good idea for a radial design with a open pipe standing the same heigth as the channels.

Do the same thing with the channel design like in Cathar's and I think it would get better results. Then again with the normal pump we use would be effective enough to push that much pressure.

With my cheap Al block I did a 3/4 round hole in the center but with a two stepped taper. Kind of like an upside down cone with the point dead center over the core. Inside I carved radial channels that swirl upwards. More for directing the flow of water than anything else. I tried a 1/4npt barb and got better temps with it. So I tried the same barb after making a new top which makes sit further away from the base and the temps were worse. So my next step is using the idea above with an adjustable jet but with an adjustable cone, although it wont be as good as a multiple jet since my base is not flat but coned. Sort of like carburater jet. With the jet stream hitting dead center and the water rushing up the side like one big channel. Make sense? lol

for the 58 channel block did you model it as if the flow was going from side to side or like cathar's block.

The reason I ask this is that I put the numbers into a program I wrote in excel that could calculate side to side flow and the 5mm deep one would only work at flow rates greater than 1900gph or 119L/Min. because the water would absorb too much heat and then would be warming the block instead of cooling it.

EDIt:Sorry I didn't look at the Reynolds # which is 13000 @ 1900gph and my prggie only accurately calculates lamiar flow. I am working of the turbulent flow calcs.:EDIT

Following up Les's graphs, 1 PSI =~ 6900Pa.

Looking at BillA's charts 1mH20 =~ 10000Pa

So an Eheim 1250 pushes at best around 20000Pa.

Now I can look at those charts a little better and figure what's being said.

The graphs are good - but I still wonder what the effect of the combined jet/channel approach is over the pure jet/pure channel as indicated by those graphs...

Cathar said:

Following up Les's graphs, 1 PSI =~ 6900Pa.

Looking at BillA's charts 1mH20 =~ 10000Pa

So an Eheim 1250 pushes at best around 20000Pa.

Now I can look at those charts a little better and figure what's being said.

The graphs are good - but I still wonder what the effect of the combined jet/channel approach is over the pure jet/pure channel as indicated by those graphs...

Click to expand...

So we're looking at maybe a measely 3PSI?

Here's another link. Take notice the temperature drop versus distance.

link here

From reading that article, jet impinement works because the increased velocity increases the reynolds # which is a measurement of turbulence which increases thermal conductivity.
Since the velocity and turbulence is caused by going through small channels technicly the temps would be the same if the water was put in from the side and not the top and make it go through a similar group of holes to increase turbulence.

My idea is to do a cathar like block mixed with a spiral. YOu will see it after I designed it.

Okay, getting close to the outer limits of my understanding of this, so I could be off. Impingement creates a "stagnation" region under the jet of extremely high turbulence, which to my knowledge, exceeds what's typically predictable just by looking at Reynold's number for flow through channels.

What is clear (through my testing) is that given the ability to make channels of a certain size, in side-to-side mode vs middle-impingement mode, that the middle-in mode offers superior cooling ability.

If the ability to make finer channels is there, then the middle-in mode would still be superior if applied to those finer channels, than using them in side-to-side mode.

Cathar said:

What is clear (through my testing) is that given the ability to make channels of a certain size, in side-to-side mode vs middle-impingement mode, that the middle-in mode offers superior cooling ability.

If the ability to make finer channels is there, then the middle-in mode would still be superior if applied to those finer channels, than using them in side-to-side mode.

Click to expand...

Because the distance from the jet impingement to the end of a given channel is shorter in the middle-in mode compared to the side-to-side mode where velocity and turbulant flow would decrease before it reach the end of the channel.

Not only that but underneath the jet impingement like you said is where the stagnation point is which is where the core heat is. The boundery layer acting like an insulator would be thinner if not eliminated right under that stagnation point which increases the heat transfer to the water hitting the base inside that stagnation point. The further you get from the center of the stagnation point the boundary layer gradually gets thicker to it's original thickness. How far that distance is would be determined by the amount of pressure the jet is hitting the base(that is where your micro-channels come into play Cathar). So, more pressure we make the further our jets need to be from each other to avoid them interupting each other. Am I right in that last sentence?

Question that I keep asking is - Do I have enough pressure to do that with my pump. Also, we can't forget the variable of gravity. A jet shooting straight down will need less pressure than a jet shooting horizontally. Horizontally we would need a bit more pressure to overcome gravity. With the pumps we use that have a small pressure, that can be over come with making the distance of the jet to the base smaller. The further the distance the less effect the jet has unless it is shooting straight down.

I just tried a single 3/16 jet 2mm from the base using a 3/8 copper tube. It didn't make one bit of difference that could see anyways using on board sensors. Far cry from being scientific. Air still isn't completely bled so maybe tomorrow I'll give it another shot after remounting the block.

Here is a neat website with a good pic showing jet impingement over a pedastle(sp?). What I find interesting is that there is a cooler circle outside of the pin. maybe four pins in a square with the jets over them. O O and the cool circles would overlap and cool the core. O O



Wonder how a block like this would do?

gulp35 said:

Here is a neat website with a good pic showing jet impingement over a pedastle(sp?). What I find interesting is that there is a cooler circle outside of the pin. maybe four pins in a square with the jets over them. O O and the cool circles would overlap and cool the core. O O



Wonder how a block like this would do?

Click to expand...

That little pedestal effects the stagnation point. I'm still learning this stuff. Your idea might work. I still have the question if the pumps we use can generate enough PSI for it to be effective.

Les
I sent an email to my dad @ work about the first site you linked to make sure it is valid. He emailed me back and said that he found that if using the sites calculator there is an error and the final answer is off by a factor of about 1000.
Just a warning. If you used their formulas on the previous pages you could get the correct answers