A TIM C/W number.

[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.

[BillA]

they must converge, eh ?

[Les]

Originally Posted by unregistered

they must converge, eh ?

Not when C/W is measured with reference to inlet temperature.
The lower Specific Heat of the Antifreeze mixture should keep its C/W vs LPM curve, as LPM approaches zero, above that of pure water.

[BillA]

I unnastan, but that difference approaches zero as well
is this difference measureable ?
the LMTD is better for this I think

[Les]

Originally Posted by unregistered

is this difference measureable ?
the LMTD is better for this I think

Dunno,but will do sums.
Not sure LMTD is better.
Anyone considering the theory will be aware that heating of coolant has to be taken into account.
For system calculations the use of inlet temperature is the most convenient.
So no, "C/W" with reference to inlet temperature is preferred.

[Roscal]

Agree with Les. LMTD is useless IMO and it's only another mathematical expression to show others things but don't change the reality. All we need is inlet T°, wattage and flowrate to describe perf (easily measured). A single description of the coolant used is enough to get (and understand) the whole thermal behaviour of any WB for a given fluid.