A TIM C/W number.

[BillA]

as the wb is a heat exchanger, the LMTD is probably the most strictly correct
the LMTD is only ever so slightly different than the avg, with our deltaTs insignificant
where I have only one temp I'll use the intet temp

[Les]

Originally Posted by Incoherent

Question about your prediction Les. What water temperature are you calculating the delta T against? in, out or average.
.

Inlet,.or rather, have not included allowance for rise in temp.
Strictly an average should be used.
Probably, as Bill says, the LMTD .
I use the Wolverine series pdfs for my understanding of heat-exchangers.
ch1_3 covers LMTD.
When sorted out my Excels will post an allowance

[Incoherent]

Originally Posted by Les

Inlet,.or rather, have not included allowance for rise in temp.
Strictly an average should be used.
Probably, as Bill says, the LMTD .
I use the Wolverine series pdfs for my understanding of heat-exchangers.
ch1_3 covers LMTD.
When sorted out my Excels will post an allowance

I am very curious because of this:




++!

Wow.

[Les]

Yes "water out" is a bit.close to predicted "water in"
But sure is only accidental.

Have allowed for water temp rise and is with reference to inlet temperature
Used Kryotherm but not sure whether they use "average DeltaT" or LMTD

.

Will extend to below 1lpm when locate my original "h(effective)" sums - probably tomorrow

[Les]

The model:
The 281pin MCW6000 considered as 16channel(1.62x9mm) ,2mm fin on a 60x60x5mm bp with 6mm(ID) inlet.
Used Flomerics(D=0.006, H=0.009, r=0.015 to calculate "h(convection)"
Converted "h(convection)" to "h(effective)" using Kryotherm
Converted "h(effective)" to *C/W(isothermal)" using Waterloo
Converted *C/W(isothermal)" to C/W using Kryotherm

Originally Posted by Incoherent

.. it should be but mounting pressure is never going to be the same in terms of force/area...
.

Probably should only matter for C/W(TIM) values.

Edit Replaced the Hemisphere-wb data with the initial MCW6000 data

[Les]

Compared with your new data and eyeballed Billa's
Same 281pin modeling technique used for both.

[Incoherent]

I think I need to refine and further verify my flow-rate calculation.

I am trying to get the mounting pressure measurement incorporated and calibrated along with pressure drop. I am running out of DAQ channels, might need to sacrifice the fluxblock middle sensor.

[Incoherent]

Some data from the differential pressure measurement. Finally got it running, seems to be making sense. The sensor is not designed for water (I am skint) but I don't need the water in direct contact to get a reading and I am able to log it.







I am deliberately showing raw data, it gives a good idea of my noise levels. With averaging this can be cleaned up a bit. Note the increase in noise above 4lpm, this is the Hydor L30 which is rattling, it is very visible in the pressure drop measurement.

Also note that this (the dP) is not calibrated, it is the nominal transfer curve of the differential pressure sensor with an offset. I am using a low resolution DAQ channel for convenience, I think it is sufficient, gives me ~0.13kPa resolution (0.013m H2O).
No major clashes with existing data for this block I think.

[Incoherent]

Bumping this to make it easier to find. Will post some TIM data shortly.

[Incoherent]

I have been doing a bit of work. I have replaced some thermistors, recalibrated, remeasured the fluxblock after some lapping, fine tuned the placement of thermistors within the fluxblock and tweaked my realtime calculations to take into account the heat shadowing effects of the sensors and their holes.
I am now fairly confident that I am able to get reasonably consistant readings from the setup.
Since I generate a waterblock C/W number by extrapolation, I am able to get a number independent of the value of the TIM by assuming that the TIM joints at either end of the fluxblock are the same since I measure and calculate the joint between die and FB and remove it from the WB number.
This relies on me getting a good mount. Since I have made many mounts of this waterblock, I am now pretty familier with its performance so I am able to see if I have made a good mount by checking that my calculated C/W is correct. I tighten the mounting screws under power and am able to see the measured WB and TIM C/W in real time while I am doing this. When the WB C/W is correct and the TIM is at a minimum (within the mounting pressure limits, a spring compression distance) I know that I am either good on both TIM joints or equally bad on both. I choose to believe that it is unlikely that one would get both interfaces equally bad at the same time. I can see a difference - if the WB C/W is high, then the WB-FB interface is bad, if it is low then the Die-FB interface is at fault. This relies on a bad joint being caused by uneven pressure tilting one of the interfaces. Anyway, details...

(This reads incoherently, I will fix it tomorrow)



This shows my performance over six mounts. (It's actually good over a damn sight more than just six) The Shin Etsu 765 grease (and 751 actually) is extremely viscous and seems to go hard when you move it or put it under pressure. A non-Newtonian dilatant behaviour. I had terrible difficulty in getting any decent mounts at all with it. This shows in the chart. Apart from this one thermal compound, I am pretty happy with the repeatability I am able to get.

The following numbers represent what I have been able to get from several different thermal greases. I would caution people not to draw too many conclusions from this. The numbers are Short term values and do not show effects of TIM settling over time and power cycles. They also represent only the behavior under a given pressure (~20kg over 144mm^2), NOT a given thickness. Meaning essentially that the more viscous the grease, the higher the thermal resistance. Depending on the application, the value will probably change. (Think IHS, where there might be a measurable gap between die and spreader)



A simple chart for what is tens and tens of mounts, megabytes of logfiles and repeated remounts.

Edit: Manners. Big thanks Colin at Arctic Silver for providing the Arctic Silver greases and Bill for the Shin Etsu and a pump, and the waterblock.

Excel sheet attached for those interested.

[Les]

Fascinating stuff as usual.
The overall values seem higher than those in preliminary investigation( ~0.04 for cheapo paste) :my memory or mounting pressure?
Note the grain of salt reappears , perhaps an actual salt crystal this time?
Will re-tune brain and scrutinise.

[bigben2k]

Originally Posted by Incoherent

... and tweaked my realtime calculations to take into account the heat shadowing effects of the sensors and their holes. ...

Can you expand on that? Not quite sure what you mean there.

[Incoherent]

Originally Posted by Les

Fascinating stuff as usual.
The overall values seem higher than those in preliminary investigation( ~0.04 for cheapo paste) :my memory or mounting pressure?...
Will re-tune brain and scrutinise.

Originally Posted by bigben2K

Can you expand on that? Not quite sure what you mean there.

Les, the MG Chemicals 680-4g paste I used before came with a heatsink or something I bought long ago, mounting pressure is definitely different, I was fully compressed with different springs so I think lower than before but the preliminary number of 0.04 is still reasonably valid although the latest measurements I have were affected by a noisy power supply. I have not included them here. It has changed a small amount due to mounting pressure and the changes I have made to the way I calculate a few things.
Notably, my measurement of the fluxblock earlier was incorrect, I stated that it's dimensions were under 12x12mm. This was due to me measuring with digital calipers outside in my workshop where the temperature was around 5C. I have since discovered that these calipers change value with temperature due I guess to expansion of the metal. A bit annoying but handleable. The true value is something like 12.02x12.03x12.89 (from memory) and I have also lapped the ends so the overall length is marginally less - that has no impact on the TIM value but is relevant for...

...Ben, the fluxblock and heat die have 1.5mm holes drilled into them from the side to accomodate the thermistors. This means the cross sectional area of the block around the thermistors is lower than in the rest of the flux path. This impedes the overall heat transfer and causes the temperature measured to be higher than what it should be in a solid block.

I overcome this by calculating the effect on the C/W of the changing CSA and generating an "effective length" for the thermistor position. The reduction in surface area creates an increase in effective length and these extended lengths are used in my Power calculation (Q=kAdT/L') and interface temperature extrapolation.
I have attached my correction sheet if you are interested. Note that the values are not the current ones but it shows what I am doing. The method is a bit primitive but works. It is also probably not strictly "heat shadowing" and the thermal conductivity of the thermistors, compound in the hole and the epoxy are unknown but I think it nudges me in the right direction.

[Les]

Am still acclimatising to the shadowing correction.
Also looking for signs of dP*Q being converted to Sensible Heat.( re. This and this hijack)
You found any signs?.

[Incoherent]

Originally Posted by Les

Am still acclimatising to the shadowing correction.
Also looking for signs of dP*Q being converted to Sensible Heat.( re. This and this hijack)
You found any signs?.

Very very little. I would say nothing actually. There is no visible trend in the heat absorbed by the water relative flow rate.
However, I need an accurate flowmeter. The technique of using the in-out dT is very noisy at higher rates, and sqrt(Pd) * K factor is inaccurate at low rates and is flawed in that I am generating the k-factor from the in-out dT method. I should perhaps establish the k-factor for a given block by the bucket method.
Still, I am pretty sure there is no visible increase (or decrease) in "heat to water" vs flow or pressure drop.
Could additives make a difference? I am running only de-ionised water... unlikely.

[Les]

This is good, well worth a bump.http://forums.procooling.com/vbb/sho...2&postcount=60
"Strong Flow " jumped well in his build up to the "Gold Cup" ;
Worth a bet at~ !0-1
"Harchiibard" for the the Champion Hurdleat ~ 4-1 seems a bit skinny

[BillA]

agreed, #60 is a pip
Inchoerent, this is probably a pita but your methodology and data would make one hellish good article
anywhere

http://www.oddschecker.com/betting/m...5/mbid/1554734

[Les]

Maybe worthy of a skirmish here(re. article):
http://www.coolingzone.com/index.html

Not forgetting the bump:
http://forums.procooling.com/vbb/sho...2&postcount=60

[Incoherent]

The part I really dislike - presentation.
I have the beginnings of something, an outline of the calibration method and stuff but I have been distracted from it recently. I'll poke away a bit at it and try and work up some focus.

Been trying to come to grips with FEMLab , pretty cool stuff, need to get up to speed to do some simulations at work but there are some interesting cooling problems that it lends itself well to. I am a little confused about what my models of submerged jet impingement are saying... GIGO mostly I think. A steep learning curve...

[Les]

Originally Posted by Incoherent

The part I really dislike - presentation.
..

Presentation is a problem. I am no wordsmith.
It is a couple of years since the term "h(effective)"( linked,by you, to definition) was introduced .
Think only 3/4 people understand what we are talking about.

[Incoherent]

An interesting chart. I did a quick test of how the MCW6000 behaves with increasing proportions of coolant additive.
I have no idea of the exact properties of this, it is simply automotive antifreeze, ethylene-glycol. I have included standard deviations to give an idea of the noise levels. They are quite high, I did not spend too much time on this.



I will now definitely need to do some flow rate tests to try and establish the new Cp.
Tested with the Hydor S30 (a lower, more controllable flowrate to save spraying antifreeze all over my desk). Premixed by tapping off some of the water already in the loop and re-adding the solution to the reservoir. There is undoubtedly some inaccuracy due to insufficient mixing. Take it or leave it.


Attached some numbers vs flowrate.

[Les]

Perhaps further testimony to "good instrumentation AND good technique "
Bill: "viscosity changes, and with good instrumentation AND good technique the changed performance is readily apparent" from this wrangle

[BillA]

but Incoherent demonstrated it in detail
now if we could get temp on the third axis . . . .
j/k

[Les]

Added thumbnail:-

A little surprised at the apparent convergence as flow rate is decreased..
Although the influence viscosity on h(conv) may be less at low values(eg, think have better illustrations somewhere among st my Excels)
would expect the effect of Heat Capacity to become apparent with departure from Isothermal(see 55 ). Will try some numbers.

[Incoherent]

Originally Posted by Les

Added thumbnail:-

A little surprised at the apparent convergence as flow rate is decreased..
Although the influence viscosity on h(conv) may be less at low values(eg, think have better illustrations somewhere among st my Excels)
would expect the effect of Heat Capacity to become apparent with departure from Isothermal(see 55 ). Will try some numbers.

Am also a little put out by it. Could simply be the noise at these (very) low flowrates.
I did a check of my flow rate calculation last night. Expected to see the effects of the reduced Cp but did not. Max error in averaged flow rate calculation from Watts and Tin-Tout versus bucket test was ~0.05 lpm @~3.5lpm. Note that I did not confirm the water only numbers before adding glycol. Wish I had, do not want to do it again but I think I need to. It's a finicky three handed process of starting logging, stopwatch and transfering hoses without flooding the proceedings.