can we agree on the basis of "C" in C/W ?

[bobo5195]

Just a quicky, I need to get Incropera's heat and mass transfer from the library again grrr.

Has anyone attempted to use the NTU / effectiveness method?

[Cathar]

Originally Posted by Les

Have not seen any such curves or indications for radiators.

http://www.lytron.com/standard/he_6000_perform.htm

Lytron, a fairly serious radiator manufacturer, chooses to specify radiator performance in terms of C/W, and does not appear to differentiate with respect to the actual size of the heat-load.

Now we could argue for days on whether or not such is exactly correct, but perhaps we could agree that such is "good enough".

Are we prepared to say "If it's good enough for Lytron, then that makes it good enough for us"?

I don't know the answer to that question, and the absence of any heat-load specific corrections in the Lytron data does not necessarily mean that it is not a significant factor.

At the end of the day, it's something which could be investigated by those with the equipment to do so (i.e. very, very few), or we can run with a set of testing guidelines today that allows a wider range of testers to participate, which is what seems to me to be sorely needed in this day and age where there is an absolute dearth of radiator test data short of Bill's efforts.

So again I ask, "What is the goal here?". Are we here to define a way in which we can agree on what "C" should mean for each unit, and in a way that allows more testers to participate. Should we then leave more detailed discussion on the exact correctness of such, and calculating the necessary correction factors by those with the equipment to do so.

I'd like to see more independently verifiable data out there.

[Les]

Originally Posted by Cathar

Are we prepared to say "If it's good enough for Lytron, then that makes it good enough for us"?.

As you wish but exclude Les from the "we" and "us"

[Cathar]

Originally Posted by Les

As you wish but exclude Les from the "we" and "us"

It was purely a rhetorical question. Self-exclusion was therefore always an option.

[BillA]

for many years now I have been I have been providing data, procedures, materials, AND equipment to those individuals interested in the testing of WCing components, I do believe I am unmatched in the promotion of testing
I will take umbrage at suggestions that I am setting elitist 'standards'
I seek the best tool that I can afford for a task; yes there are always tools better yet

cost effectiveness is another measure which now includes the parameter of need or utility, this is a better evaluation but requires also a goodly amount of info to make a valid technical assessment
- those interested in testing may have observed the equipment evolution from TMT to Swiftech to the bench that is being built now for CoolingWorks; one thing is clear to me, greater accuracy and resolution produce more useful data for a product designer

"As for upholding a single absolute testbed procedure against which all other testbeds can be essentially described as being equal, I don't think that's ever going to be achieved."
I am not sure what is meant here; good engn, through a variety of paths, can achieve a goal - but optimization may continue so long as there are resources and inquisitive minds

Cathar's other point is clear, there is a consumer based desire for a somewhat accurate means of predicting system performance from a laundry list of components

my approach to such would be to use those products for which data is available
and to ignore those products w/o data

[bobo5195]

Im not to happy about it. Although this suggests otherwise
http://delphi.com/pdf/techpapers/2000-01-0579.pdf

SD = Q/dt = W/C

dt = water in temp - air in temp

Its applied to car heat cores so its applicable to water cooling. In summary coolant base line temps (in let conditions) are only a small effect but flow rate is very important.

Would do more analysis but have job applications to do.


EDIT: Should note that rads dont have 60kph air inputs and such high flow rates.

[Cathar]

Bill, no need to take offense (or did you? I'm unsure). Was certainly not meaning to suggest that your approach is elitist at all.

I think it's pretty clear you and I are on two separate paths with this one.

I want a "good enough" solution that's going to satiate the average consumer, that's easy to understand, and easy for them to plug in some values and spit out a figure at the end. Of course there's still a hundred and one variations and approximations and assumptions that have gone into that, and by no means am I suggesting that such should be ignored or left unexplored, but rather documented and made available for those who are interested to lead them towards the sort of stuff you're pursuing.

That's where we'd be leading into the sort of level that it appears to me that you want to operate at, and this really is necessary, but by the same token extremely involved and expensive.

If anything, I was just hoping that there could be some adequate degree of commonality between the two target criteria by agreeing at least upon the definition of "C".

[Les]

Originally Posted by bobo5195

Im not to happy about it. Although this suggests otherwise
http://delphi.com/pdf/techpapers/2000-01-0579.pdf

SD = Q/dt = W/C

dt = water in temp - air in temp

Its applied to car heat cores so its applicable to water cooling. In summary coolant base line temps (in let conditions) are only a small effect but flow rate is very important.

Would do more analysis but have job applications to do.


EDIT: Should note that rads dont have 60kph air inputs and such high flow rates.

Interestingly that is the very paper Bill uses to introduce the discussion in his first article Radiator Heat Dissipation Testing

"Discussion of Results
This article is flirting with a thermal characterization known as Specific Dissipation (SD), which is defined as the heat transfer rate of a heat exchanger divided by the maximum temperature difference across the heat exchanger. As I have not the ability to display equations, nor most readers the inclination to view them, those interested in the “theory” are referred to an SAE paper, 2000-01-0579, on “The Effect of Changes in Ambient and Coolant Radiator Inlet Temperatures and Coolant Flowrate on Specific Dissipation” which can be found HERE. http://www.delphiauto.com/pdf/techpa...00-01-0579.pdf "

Will peruse again, slowly.
Yes, velocity in PC radiators possibly 2.5->25kph(1st guess)

[BillA]

B5 - welcome, I'm suspecting you may not be aware of how well-tilled is this field
of course I enjoy your participation ('cause you agree w/me, lol)

Cathar
the parametric data you must have for your or LHG's estimators MUST have some KNOWN relation to reality to be useful
this means describing the equip and procedures used
if you believe that it is not useful to outline some minimum test bench capability, reconsider the effects of multiple layers of uncertainty
killer for your calcs

re C: clever minds will find means to utilize the existing rad data as its basis is known
such being my assumption, I for one am content with C as it is
as soon as I have the ability to characterize the flow and temps on both sides I will change to the LMTD (and this is exactly where I'm headed but the air temps require an array of sensors)
all these minutiae are small wrt a general estimator, why try to change an existing component testing 'norm' for a semi-technical applications' related procedure ?

[BillA]

Cathar
another thought; you have some data (which I no longer have) and could see if the plot you want could not be generated from that which you have
if so just request such a graph, no biggie (actually you want the curve fitting equation, no ?)

[bobo5195]

I'm sorry if this old news but:

The more I think about it the more for radiators I move towards effectiveness as a way to measure radiator performance. For a customer it has the obvious problem that it is not compatible with C/W used by blocks. However if you say to your average joe that your rad is 40% he can understand that easily. Its less abstract.

Effectiveness is also quite easily measurable for the DIY crowd. Taken from the paper I linked to above

E =( Mflow,water*Cp,water*(Twater,in-Twater,out) ) / (Mflow,air * Cp,air * (Twater,in – T air,in)

If I am reading my notes and the paper right it can be then said that

Q= E* Mflow,air * Cp,air *(Twater,in-Tair,in).

As an side note that gives, so C/W is still valid. Its just a different form

SD = 1/bill C/W = E * Cp,air.

And if I am reading this right. My uni notes use a different approach and are tests for different applications. I believe the same method works.

All of these with the exception of Cp air, Cp water and Mflow,air are easy for the hobbyist. Cp’s can be roughly calculate from standard measurements. Measurement of the water vapor content of air might be troublesome but its do able. Mass flow of air is also quite inferable with some work. Either way flow does not need to be characterized on both sides.

More advanced users can easily convert effectiveness into more useful data with a set fan and such. Fan type might be problematic as it influences cooling performance but numbers are roughly constant.

I have a dislike of LMTD for radiators as it doesn’t really work LMTD needs to be corrected for the radiator geometry and temperature amounts.

[BillA]

very good comments, for me at least
the LMTD relies on assumptions, agreed
would prefer a datum to a derived value, but not all is possible

have to wait 'till I have some data to sort through
note that no rad air temps have (ever ?) been described, the ones I took and never published convinced me of the difficulty of accurately describing/averaging the air dT
so the wait may be a bit

we're not just sticking something into the airstream, though for the consumer estimator perhaps such would be better than nothing (or even sufficient ?)
I would not use my testing time that way however

[bobo5195]

Rad air input temps = ambient air temp.

[bobo5195]

should add that LMTD for cross flow heat exchangers needs a correction factor to use it. I'll email the stuff from my notes if you want Bill.

[BillA]

lost the damned post, grrrr

air temps from each fan quadrant <1/2" back from the blade midpoint
caution re room w/AC due to currents

several correction factors needed, not conventional 'cross flow'

Thanks, PM sent w/e-mail

ah, now consider the thermal shadow of the fan; input is easy,
-> for the output avg dT ??

3x3 sensors ?
edge/boundry effects ?
whew, my head hurts - not impossible, but some effort

and the fan heat ?

[jaydee]

Fan heat? What if you pulled instead of pushed. Fan heat would be irrelevant then?

Anyway I will forget rad testing. lol

[BillA]

how do you measure/model the non-isothermal heat dissipation (push or pull, apart from the fan heat) ?
consider this discussion applied also to HSFs ?
and a wind tunnel is on the front end to quantify the airflow

[bobo5195]

Fan heat input is ignored. Its small and not worth worrying to much about.

We are only after overall mass flow not mass flow at surface of rad with its distribution. Besides with a shroud (developed flow) and that restriction i would not be surprised if it is not approximately flat and will assume it is for making things easy. Ac and currents yes but assume well ventilated room with slow moving air at constant temperature.

Assume conventional crossflow (don’t make work for yourself) it’s a close enough model to real life. You could try and be swish my modeling each step as a thin radiator and integrating but really theres no point. Similar with edge and boundary conditions don’t worry, it will make your head hurt and not improve the quality of the results.


HSFs are a different kettle of fish.

[Long Haired Git]

Originally Posted by unregistered

the parametric data you must have for your or LHG's estimators MUST have some KNOWN relation to reality to be useful
this means describing the equip and procedures used

My tool is just a collation of results posted by others, and I link to them for perusal of their techniques and equipment. I don't do modelling of radiators/blocks/pumps using mega tricky, brain implosion formulae like those in this post. I just use published PQ graphs to derive a PQ equation (flow vs head), and a published C/W graph to make a CW formulae (liq flow vs delta-T). For pumps, I assume 60% to 80% of the rated wattage goes into the coolant as heat depending on flow rate except if pump is submersed, then 100%. I've seen a recent pump test including wattage info, so this may be refined.

For radiator data, I use one tester (there is only one!) but was looking to combine two era's of testing until a single block of data is published (waiting with abaited breath).
For block data, I use one tester and will link to that review once I confirm they're "happy" (ie: not going to sue etc).
For pump PQ, currently using manufacturer (marketing dept?) graphs, but hopefully this will change "any minute now" as per previous.

I don't see the problem with combining a single set of block results with a single set of rad results and, ideally, a single set of pump results.

[Les]

Originally Posted by bobo5195

The more I think about it the more for radiators I move towards effectiveness as a way to measure radiator performance. .

I like it Bobo
When previously discussed I was quibbling about the difference between "sensible heat" and "energy of coolant"(link)
Since this is possibly detected in data at low fannage(eg link andlink) maybe this should be addressed together with (for completeness) the air-side's energy/"sensible heat"

[bobo5195]

Les: hmm maybe I need to look over my notes and such. Personally i prefer the KISS approach.

After a night on it I still prefer efficiency but the fact eff and SD (aka C/W) is related is extremely useful. It means that there are two ways of getting the same result, which helps check for errors. Also generally speaking a good review already has the data in it as fan specs are known and ambient temp should really be measured. Two measured results with some accurate (differential based) errors should give you highly accurate results for less cost. It also helps eliminate mistakes as you know something’s wrong if the two do not overlap.

For a proper fan mass flow rate test you would want a long tube (10d) where d is your radiator size. This gives fully developed flow. Cutting down tube length is possible as it might not take to long for a good distribution to develop. If you have fully developed flow then you can guess mass flow rate as the velocity distribution is known. Measuring velocity at a point is tricky. Best way would be a hot wire anemometer ($$$ -$375 for one on ebay) but a pito static tube with some colour liquid is quite acceptable and DIYable in your shed.

[Marci]

So let's throw it back and ask what are we trying to achieve here, who is the audience, what do they want, what are they (the wider audience) capable of understanding, and what is an acceptable degree of accuracy for them?

Suggest settling the above in a separate thread then throwing the outcome into this one...

And in a sudden spark of brainpower have finally just worked out what Twi, Tai, Two and Tao are/mean! Man do I feel thick.... shutting up now

[Les]

Originally Posted by bobo5195

Im not to happy about it. Although this suggests otherwise
http://delphi.com/pdf/techpapers/2000-01-0579.pdf.

Further perusal
They looked at Water-Air differentials of 60-80c
Only studied effect of change in Water-Air differential at different Air Velocities(4-14m/s) by changing Air(ambient) Temperature
Results indicate that SD %error ^ with decreasing air velocity(Figs 5,6 and7).Turbulent water predictions giving largest error

Attachment
Used turbulent and taken the liberty of considering the change in Air(ambient) Temperature at fixed(100c) Water(in) Temperature to be a change in differential "Water(in)-Air(in)"

"SD %error" vs Va, illustrates that extrapolation to lower velocities could go nearly anywhere

"Error to 70c Diff Values" vs "Differential Twi-Tai".
Illustrates extrapolation could, again, go nearly anywhere
Shows,for example, that at Va =4m/s when operating with (Twi-Ta)=60c application of "(Twi-Tai)=70c test data" will give ~2% error(I think?)
Additionally suggests* that at 6c differential there will be ~2% error if applying 7c differential test results(???) Think may have this wrong but dunno

All above suggest that errors >2% will occur for lower Va (?)

Think Va of interest for 120x120mm radiator are: 0.1m/s(passive) to ~ 3.5m/s(2xDelta AFB 1212 VHE @12v)

* In conjunction with the lower "SD %error" exhibited by the " 80°C to 70°C" curve

[Les]

Of course the Delphi paper can be completely ignored if you believe in a dP*Q correction to the Heat Dissipated measurements.They take no account and give no pressure drop data with which to attempt a correction...
I choose to completely ignore.

[BillA]

groan