Temp Measurement

[Brandon_Tyler]

Hey guys Brandon here..

I was just sitting here at my desk pondering something. How much modification would a single display CompuNurse and a 1/2 inch (14MM) Tee need to accurate get temps inside the loop?



-Brandon

[Jimbo Mahoney]

Hey there.

I used that same temp probe and just taped it to an exposed brass barb. Its temperature will be the same as the water temp and you won't affect the flow rate at all.

Hope that helps.

[Butcher]

Depends what you mean by "accurate"...

[Brandon_Tyler]

"LOL" just a rough ballpark idea. I dont need anything scientific here. Just always wanted to know. If I could get within 5-10 degrees I'd be satisfied.


-B

[Jimbo Mahoney]

You'd be within 3'C (IMO) if you taped the probe to a barb, and that includes the 'accuracy' of the compunurse.

[Brandon_Tyler]

Sweetness thanks man... Enjoy your evening....

B!

[Butcher]

Originally Posted by Jimbo Mahoney

You'd be within 3'C (IMO) if you taped the probe to a barb, and that includes the 'accuracy' of the compunurse.

Based upon?

[Jimbo Mahoney]

Guesstimation.

Although the given accuracy of the compunurse is +- 1'C and I can't see why a brass barb would be more than 1'C cooler than the water constantly flowing through it.

Do you really see it being out by more than that?

[MaxxxRacer]

the barb would be a few C cooler than the water i would think. the metal of the barb would disipate the heat faster than the water would so it would cool off. Feeling the brass barb on my rad right know I can confirm that it is noticably cooler than the water in the loop is..

Its best if you can get the probe to actually touch the water... but even then, the accuracty of the nurse is not.. well its just not accurate. A while back pH did some tests with the thermal probes compared to a calibrated high end measuring unit, and the temps varied from relatively accurate to 3-5C (if i recal correctly) off the mark... imo, i would call accurate within 1C of the actual temperature.. that being accurate only for the cheap probes that we purchase for computer related stuff.. the real probes are accurate within .1c...

[Althornin]

Originally Posted by MaxxxRacer

the barb would be a few C cooler than the water i would think. the metal of the barb would disipate the heat faster than the water would so it would cool off. Feeling the brass barb on my rad right know I can confirm that it is noticably cooler than the water in the loop is..

Lol, i bet not.
metal "feels" cooler than an insulating plastic like your hoses, even if both are at the same (below body) temperature. This is because of the much higher thermal conductivity of brass/metals in general.

What is the temperature gradient througha brass barb? If the inside of the bard is at water temp, i highly doubt the outside is a couple degree cooler. That implies that brass is a quite shitty heat conductor.

since brass has a thermal conductivity of 111 watts per meter per degree kelvin, lets look at a situation where the brass is a few degrees cooler on one side of the barb.
Lets assume that your cooling loop is dissipating 222Watts of heat through this brass barb alone (which is more than your entire cooling system disipates, but hey!), and the outside of the barb is 2 degrees cooler than the inside.
so, your brass barb is a meter thick?

[MaxxxRacer]

lol.. a few is 3 or more up to around 7max... thats what i think of as a few.. and im talking about C... 3C is alot and 7C is alot more for that matter. but thats a different story altogether..

anyway you got the point.

btw, bill just stated in another thread that the brass gives you messed up temps because it IS cooler... he just encountered the problem.. the brass feels cooler because it is...

"Metals are the best conductors. That is why we use them
for making such things as saucepans and radiators. It also explains why
metals usually feel cool to the touch. If a metal object is at a lower
temperature than your body, it will quickly carry heat away from your skin
when you touch it. The opposite is true if the metal is warmer then you
are. Then the metal will quickly give up its heat to your skin so that it
feels hot to the touch."

I grabbed that from a lab procedure off of google.. Anyway.. We can adapt that example to the barb situation.. imagine the warmer metal beign the barb and your finger being the water going through the barb... the barb is warmer than the barb, so the barb dumps its heat into the water, thus making it cool.. water doesnt have good heat conductivity (compared to metal), so it will take in the warmth from the barb.. Thus the barb is cooled (just like your copper waterblock on your cpu) and it IS cool to the touch...

And some more food for though.. the barb on the exit side of the rad should be slightly cooler than the one brining water into the rad.... try it.. i dont think it will be noticeable without a calibrated temp measruing device (oh pH where are you), but the difference will be there...

[Butcher]

I'd be more concerned about airflow over the barb causing your probe temps to fluctuate. At least if the probe is inside the barb it's not being air cooled.

[Risky]

If you've got a t-piece and the probe is ok in water (the thin ones are in my experience) then feet it in on the t untill its almostin the flow and seal up with goop.

[Butcher]

Not sure what sort of sensor the compunurse uses, but I'd be cautious about sumerging anything that wasn't properly sealed up in water. I've nuked a few thermistors from water immersion (they work fine for a while, but after a few months they just disintegrate).

[Althornin]

Originally Posted by MaxxxRacer

lol.. a few is 3 or more up to around 7max... thats what i think of as a few.. and im talking about C... 3C is alot and 7C is alot more for that matter. but thats a different story altogether..

anyway you got the point.

btw, bill just stated in another thread that the brass gives you messed up temps because it IS cooler... he just encountered the problem.. the brass feels cooler because it is...

"Metals are the best conductors. That is why we use them
for making such things as saucepans and radiators. It also explains why
metals usually feel cool to the touch. If a metal object is at a lower
temperature than your body, it will quickly carry heat away from your skin
when you touch it. The opposite is true if the metal is warmer then you
are. Then the metal will quickly give up its heat to your skin so that it
feels hot to the touch."

I grabbed that from a lab procedure off of google.. Anyway.. We can adapt that example to the barb situation.. imagine the warmer metal beign the barb and your finger being the water going through the barb... the barb is warmer than the barb, so the barb dumps its heat into the water, thus making it cool.. water doesnt have good heat conductivity (compared to metal), so it will take in the warmth from the barb.. Thus the barb is cooled (just like your copper waterblock on your cpu) and it IS cool to the touch...

And some more food for though.. the barb on the exit side of the rad should be slightly cooler than the one brining water into the rad.... try it.. i dont think it will be noticeable without a calibrated temp measruing device (oh pH where are you), but the difference will be there...

lol, your quote from the lab procedure supports my argument, not yours.
If the temperature is off, it is because of air flow past the probe, not because the outside of the barb is 3-7 (LOL, this makes the barb multiple meters thick) degrees cooler than the water. Oh and for your edification - 1 degree change kelvin is the same as one degree change C.

[MaxxxRacer]

i know one degree kelvin is one degree C.. known that for many many years....

and actually the quote supports exactly what I was saying... you say that the metal just feels cooler, not that it is cooler.. you think this because the metal will conduct the heat from our bodies much faster (pulling the heat away from us), which is true to an extent, but if you put a thermal probe on that piece of brass even with no airflow over it (just the water in it) it will show that its cooler than the water inside.

you can test it even with one of the laser temp sensors where there will be no change in temp from airflow over the sensor.. or you can take a thermistor and cover it in goop and neoprene so there is no airflow over it at all.


what your saying about the thermal conductivity properties of brass I am not arguing. "since brass has a thermal conductivity of 111 watts per meter per degree kelvin"

I am not arguing that.. but... when you apply water to the equation, the brass does not have to be thick at all to be cooled. in that example where it is several meteres thick you are saying that if you apply a heat source to one side of it and for the temp to be differet on the other side it has to be N meters thick.. well that example DOES NOT apply in this situation..

The barb is being cooled all around.. the barb will be as cool as it is on the outside as it is on the inside. so if you strap the sensor to the inside of the brass barb with the water, it will still give you low temps because of the lower temperature of the brass. So you see, the barb is not jsut cool on the outside, its cool on EVERY side... I hope this makes sense to you now...


Butcher: Im pretty sure the compunurse uses a thermistor.. Pretty much all the inexpensive temp gaugues use them.

[talcum]

Take a brass hose mender of the correct diameter and a couple of Omega's precision RTD's http://www.omega.com/ppt/pptsc.asp?r...0KN&Nav=temc13 . Drill holes to fit to insert the RTDs into the hose mender in the middle and then insert the RTDs with Artic epoxy. After letting everything setup, solder wires to the RTD and then strain relieve the wires by potting with RTV in a 3/4" tubing sleeve as a form. After all is done you can calibrate your sensors to .1 or better using an ice bath and boiling water and then insert into any line in your system to get a pretty good reading at that point

[Nickd]

Maxx,
perhaps there's a different way of thinking about it?
If you were outside and the air temp was at 1 deg C, and you had a bucket of water at 1 deg C too, which would feel the coldest to have your hand in? Obviously the cold water would conduct heat away from your hand much faster than the air, reducing the temp of your hand much faster.
With the brass T in your loop the water would conduct heat to the brass fitting pretty quickly, wheras the brass T would dissipate heat to the air much more slowly. Its the principle on which a radiator works. Lots of fins on the air side to give a large surface area for heat transfer, smooth passage for the water as it conducts heat to the radiator very efficiently.
In reality the temp of the brass fitting would have to be somewhere between the water temp and the internal case temp, but due to the above it would be very close to the water temp.
If brass Ts were so good at removing heat from the loop we'd have radiators made out of them.
Hope this makes sense.

[MaxxxRacer]

I see what you are saying and I know that. but as you stated yourself the brass barb will be cooler... thats what my point was in the first place. Im not saying it will be a HUGE difference, but the barb will make the results rather useless... actually having the sensor touching the water would make it a heck of alot more accurate.

[Nickd]

Yes that sounds right too, though I don't think it would make much difference as the conductivity of brass (~109W/m.K??) is much higher than that of the TIM (~5W/m.K??) you normally use to mount sensors . It would be interesting to actually make one to find out. Depends on what order of accuracy you were after I guess. From what I've read around here the accuracy of the sensors would be the major stumbling block. I suppose at least it would give you a relative temp should you change a pump or block, so that you know whether your temps had improved or not.

[MaxxxRacer]

yah, but having it on the outside of the fitting, it would insulate it even more and minor temp fluxuations would take longer to be read, that is if they were read at all..

True that the biggest stubling block is the sensor itself, but there is no sense and not giving it the best enviornment you can to get accurate temps..

[Incoherent]

If the brass fitting and temp sensor are properly insulated there will be no temperature difference across the barb wall.

[Blackeagle]

Originally Posted by Incoherent

If the brass fitting and temp sensor are properly insulated there will be no temperature difference across the barb wall.

Reading this thread I could not believe that no one was pointing out to just insulate the stupid thing, with the thermister between the insulation & the metal fitting.