"Radius" by BigBen2k

[myv65]

Originally posted by unregistered
I do know Mike, he posts on OC and OCAU as Aesik

So the "has a solid grasp on all of this and didn't wish to bog down the readers" is the correct answer.

Thanks for chiming in, Bill.

[bigben2k]

For what it's worth...

What I got from Mike's article is that the boundary layer restricts the flow. In a circular cross-section, the flow is higher in the middle. I also deduced that this would be similar in non-circular channels. Turbulence is wanted for improved heat dissipation. Putting it all together, what we want is turbulence at, or near the boundary layer.

Upon closer examination, it seems that the turbulence provided by high speed flow alone, doesn't fit with what's needed to improve cooling.

[utabintarbo]

Originally posted by bigben2k
Putting it all together, what we want is turbulence at, or near the boundary layer.

Perhaps I've misinterpreted what I've read (or skimmed ), or perhaps I am merely saying what you said in a different way, but is turbulence not sought to reduce the boundary layer? I think one causes the other, no?

Bob

[bigben2k]

Originally posted by utabintarbo
Perhaps I've misinterpreted what I've read (or skimmed ), or perhaps I am merely saying what you said in a different way, but is turbulence not sought to reduce the boundary layer? I think one causes the other, no?

Bob

No, that's the whole issue.

If you look at the first graph in Mike's article, there's what is labelled as "Buffered Layer" and more importantly "Laminar sub layer".


This is why a rough surface (sandblasted?) is better, because it helps break up this laminar sub layer.

[bigben2k]

Incidentally...

The surface roughness adds to the flow restriction, as per this formula:

f=0.2083 (100 / C) ^ 1.812 * (Q^1.852 / d^4.8655)

Where
f = friction loss per 100 feet in feet of water
C=roughness coefficient (Hazen-Williams factor)
Q=flow rate (gpm)
d=inside diameter of pipe (inches)

Source: http://www.ppfahome.org/pdf/pvcpipewaterspec.pdf

For PVC piping, a value of 150 is used for C. A steel pipe would have a C value of about 100, and a rusty one about 80.

While on the topic, the optimal tubing size should allow a flow speed of no more than 8 fps (feet per second), otherwise the tubing becomes a significant restriction. A flow speed of 5 fps is the guideline for 1 inch ID and higher.

[myv65]

Originally posted by bigben2k
While on the topic, the optimal tubing size should allow a flow speed of no more than 8 fps (feet per second), otherwise the tubing becomes a significant restriction. A flow speed of 5 fps is the guideline for 1 inch ID and higher.

This guideline works fine for industrial pumps, but would cause most aquarium style pumps to struggle. Low speed is the weak pump's friend. Save the high speed for where it is needed, and that isn't in the tubing.

[bigben2k]

Agreed.

I ran the numbers last night, and 1/2 inch tubing will have a flow velocity of about 5 fps, with a 3 gpm flow rate.

If I shoot for 5 gpm, I will have to go to 3/4 inch tubing, because 5 gpm in 1/2 inch is 8 fps!!!

[bigben2k]

Well, it's official.

It's going to 3/4 inch tubing.

Now all I have to figure out is why my pump has 1/2 fittings... Otherwise, the pump is at its max P/Q curve with a flow of about 250 gph (4 gpm), at which point the head is 11 feet. That converts to 0.42 atmospheres, or 4.4 meters of water, or 323 mm of mercury, or 0.43 bars, or 43 kPa, or 6.25 psi.

I'm going to try to use PVC (CPVC) parts to construct that "cube-res", starting with this:

[bigben2k]

Here's a diagram:

As I explained it, the tee (1 1/2, threaded at all ends) is capped with 1 1/2 to 3/4 threaded adaptors at the in/outlet. The inside pipe could either be a 3/4 piece of PVC piping (which I'd bend with heat) or the tube (it's possible to mount a barb on both sides of the adapter). The branch, which goes to the block, would have a 1 1/2 barb screwed into it.

[bigben2k]

Here's an overview of it all (not to scale):

[edit]
(updated pic, with more details)
[edit]
(closer to scale)

[BillA]

so you would couple "fitting" and "high flow" ?
truly Ben, you do not listen (or are incapable of comprehending ??)
just post, and post, and post some more

have fun, too much for me (I'll leave you in peace)

[utabintarbo]

Originally posted by unregistered
so you would couple "fitting" and "high flow" ?
truly Ben, you do not listen (or are incapable of comprehending ??)
just post, and post, and post some more

have fun, too much for me (I'll leave you in peace)

I think what "Mr. Sunshine" is referring to is the barbs (allegedly) necessary at the intake side (to block) of the separator tee. If there is a way to perform the transition without "fittings", this would be preferable, no? I am referring only to the intake side - the "exhaust" side is less relevant due to your use of an air trap/reservoir.

Perhaps you could look into allowing the intake hose to go thru the separator tee, and simply sealing around it at its entrance point. Not the most reliable solution, I admit. Hmmm...


Bob

[bigben2k]

He he.

What "M. Sunshine" might have missed is that the tee is 1 and 1/2 (1.5) inch in size, which has an ID of about 1 7/8 (1.875) inch.

Last I checked, a tee of that size wasn't significantly restrictive, even theoretically, given a 4 gpm flow!

edit: calculated, the pressure drop across the run of a tee, 1 1/2 inch at 4 gpm is approximately the equivalent of a quarter inch of head.

Given that the expected head is about 11 feet, I'm not going to loose any sleep over it...

[bigben2k]

Originally posted by morphling1
As I know Reynolds number is v*d/kinematic viscosity

v.... velocity [m/s]
d... diameter [m]
kinematic viscosity [m2/s]

if the chanell isn't round you have to take the equivalent hidraulic diameter d' = 4*A/C
A... cross area [m2]
P... circumference [m]

so for bb2k rectangular chanell d'=2ab/(a+b)
So you can see that narrow rectangular chanell isn't realy too good for introducing turbolence round chanell is much better.... but with central nozzle and short paths I realy don't think that there would be lamilar flow in that kind of block

It's Saturday... I've tested my airtrap (with some success: the thin wall vynil tubing just collapses, otherwise all air is cleared within 10 seconds).

I'm recalculating the different radius' involved: boy was I off!

Doing a quick recalc of Reynolds# at center, assuming the last design posted (center square post):
-opening size (for trial): 5mm diameter, aka 3/16 inch.
(At 4 gpm, I loose 2 feet of head!)
-Velocity: 40 m/s
-4 openings measuring 1 by 5 mm (still not accurate)

if the chanell isn't round you have to take the equivalent hidraulic diameter d' = 4*A/C
A... cross area [m2]
P... circumference [m]

so for bb2k rectangular chanell d'=2ab/(a+b)

(I assume that the "C" in the equation is "P"?)

where
a=.001
b=0.005
A=0.000005
P(or C?)=0.031

so
d'=.00167 (using: 2ab/(a+b) )
multiply by 4 (4 channels)
d' becomes .0067

so Reynolds = ... What is "dynamic viscosity"?

[myv65]

Originally posted by bigben2k
-Velocity: 40 m/s

And just what pump do you think will manage this? How pray tell did you arrive at this number? You'd need at least 80 meters of static head to generate a velocity of 40 m/s. Maybe you missed this musing of mine a while back.

Water's dynamic viscosity varies with temperature (as do all liquids). At a reference temperature of 20°C, the dynamic viscosity is about 8.9*10-4 N-s/m^2.

[Alchemy]

Originally posted by myv65
Water's dynamic viscosity varies with temperature (as do all liquids). At a reference temperature of 20°C, the dynamic viscosity is about 8.9*10-4 N-s/m^2.

I think you misread. That's its viscosity at 25°C.

Rather big difference five degrees makes. Viscosity is incredibly temperature-sensitive.

Alchemy

[morphling1]

Wow being optimistic bb2k, for 40m/s to be pushed through 4*5mm2 openings you need 2880 L/h pump, and if you're thinking of pushing that kind of flow rate through 20mm2 opening , you'll need "slightly" different type of pump

[myv65]

Originally posted by Alchemy
I think you misread. That's its viscosity at 25°C.

Rather big difference five degrees makes. Viscosity is incredibly temperature-sensitive.

Alchemy

Could well be as my texts are at work and I was trying to recall from the top of my head. Details would appear to be like hair in that there is less up there with each passing day. LOL.

[bigben2k]

Ah yes, that was in feet per second, oops, my bad!


Anyways, I figured that the nozzle is either going to be 1/2 inch diameter, or 3/16:

3/16 nozzle: the opening of such an area is 17.8 mm^2, and that leaves an exit through the fins that can best be described as 8 channels (1 by 5) so 40mm^2, for a ratio of entrance to exit of 0.45 .

Flow speed is 14.2 m/s (46.5 fps). Pressure drop over one inch is 11.7 feet of head.


1/2 nozzle: the opening is 126.7 mm^2, with an exit of 16 channels, 80mm^2, for a ratio of 1.6 .

Flow speed is 8 m/s (26.1 fps). Pressure drop over one inch is 0.1 foot head (1.2 inch).

The above ratios are the smallest and largest, respectively.


Here's the bug: what am I trying to achieve with this inpingement? Since the flow rate is the same everywhere, the exit speed will be higher than the entrance, with a 1/2 nozzle. Using a 3/16 nozzle, the entrance speed is higher, but the exit speed is lower.

So if I go with a 3/16 nozzle, I'll have high-speed (and turbulent) flow within a very small area, which has a diameter of about 5 mm. The nozzle will have to be kept short, given the very high pressure drop.

Note that the turbulence that occurs due to the 90 deg flow bend hasn't been accounted for, yet.


Other progress:

Round saw blades:
The 20mm saw blade, if used to cut 5mm deep, will extend 13.2mm beyond the point of cut, in either direction.
25mm: 15 mm
32mm: 17.2 mm

Which makes the blades pretty useless except for the central cuts, which leaves a center square post.


Turbulator thoughts:

Turbulators at the bottom of the channel: using a 1.0mm drill bit, drill a hole every other 1.0mm, to a depth of 0.5 mm.

Turbulator at the fin: don't leave the fin tips at an angle, cut them off at 90 degrees. Necessary?

[edit]: added depth-of-cut to bottom-of-channel turbulator.

[myv65]

Still seems awfully optimistic. Make it and measure it. Reality is the best and most objective means of determining true flow rates. Once you've tested both options to determine true flow and performance, the better one will be clear.

[Dix Dogfight]

@BB2K
Why not use a straight inlet?????
To eliminate a bend in the piping where the water velocity is high.

Nice to see you are making progress with your design.
I'm looking forward too see it in action.


cheers

EDIT: It might not matter but you are aiming for a top performer right?

[bigben2k]

Originally posted by Dix Dogfight
@BB2K
Why not use a straight inlet?????
To eliminate a bend in the piping where the water velocity is high.

EDIT: It might not matter but you are aiming for a top performer right?

The problem is that this 1 1/2 (1.5) tee is about 3.5 inch wide, at the branch. Since there's only 8 inches in width in the case (which I assume is typical), that would only leave a couple of inches for a tube to bend, with a "straight inlet". That bend would make it all much worse for flow (I'll be using thick braided 3/4" tubing).

The inner tube would be bent in the largest radius possible. I'm even considering using a drain trap tee, which has a nice curve from the branch to one of the runs (ends).

The only thing I have to add about it is that the water return should exit downward, to make draining this thing easier.

I am aiming for a top performer, yes, but I have A LOT of calculations to go through! I was hoping to do that Saturday, but I got caught up in all of the other calculations:

Fin set #2 starts (the pointy tip) at radius 2.5 mm
Fin set#2 taper ends at 3.3mm.

Fin set #3 starts at radius 4.6mm, and the taper ends at 6.4 mm.

fin set #4 does not appear in this design, because it starts at radius 9.0 mm, and the whole fin pattern has been reduced (temporarily) to 7.5, pending my thermal calculations.

I made a number of drawings (which I'll try to post this week), so that I can visualize the inpingement. I have more work to do on that too, using some info found here:
http://www.electronics-cooling.com/h...01_may_a2.html

and
http://widget.ecn.purdue.edu/~eclweb/jet_benchmark/

To be explored: using 4 nozzles/holes, instead of one.

Myv65: I'm not done with the numbers yet, to even say that I'm redy to experiment. I'd rather spend more time going through the numbers, until I get this thing to a point where I have a fair idea of how well it will cool. I know that ya'll just can't wait to see it in action, but unless someone is going to run the thermals for me, ya'll are going to have to wait!


I still need help on the Reynolds calculation.

[bigben2k]

Reynolds calculation

v=14.2 m/s
a=0.001 m
b=0.005 m
A=0.000005 m^2
P(or C)=0.031 m

d'=0.00167 by 8 channels= .0134

So Reynolds = 14.2 * .0134 / 8.9*10-4

= 107 ?

(didn't I say I needed help )

[bigben2k]

Originally posted by bigben2k
2" outer hose ugly? I don't think so... I'll pick up a foot of the stuff this weekend. We can apply our artistic interpretations then!

Originally posted by morphling1

Ok, I'll be waiting

Well, here it is, in all it's glory...

[bigben2k]

And the pic (DOH!)

(If you look REAL close, you can see me!)