i have just made an explanation diagram, but first have a look at this link. see the video:
http://study.com/academy/lesson/how...c-heat-capacity-for-different-substances.html


when you are done. see this:

 

Go home "proper sensor attachment" thread, you're drunk.

 

I think that just because heat losses are higher through the metal shell of the tank than through the insulated attached sensor, doesn't mean that their temperatures would be significantly different at a given moment.
Once the system reaches thermal stability the temperature will practically be evenly distributed throughout it.
And yes, if you're looking for laboratory quality results in your readings, then there might be a difference of a few hundredths, or maybe thousandts of a degree due precisely to the rate of heat loss or gain.
But who's to say which part of the tank at an arbitrarily given time is most representative of the entire sistem? Why not try to measure temperature at its center of mass instead?
Personally, I think it's impractical, and also a waste of resources (mainly time) to try to reach that level of perfection in this issue.

 

The insulated temp area will not be accurate to that of the rest of the tank or to that of the water

Even so the insulated area temperature will be closer to the water temp than the uninsulated area and under no circumstances higher than that of the water (unless the tank is externally heated and the probe is injudiciously near the burner -- as I assume you are aware, practical boilers are heated via internal 'fire-tubes' or their 'electrical equivalent'...)

Best regards
HP

 

I can't believe there would be a 9C temperature difference between a steel tank and the water contents, especially if the tank has an insulating jacket.

 

I can't believe there would be a 9C temperature difference between a steel tank and the water contents, especially if the tank has an insulating jacket.

i didnt calculate the exact temp difference. it is just an example....

 

Even so the insulated area temperature will be closer to the water temp than the uninsulated area and under no circumstances higher than that of the water (unless the tank is externally heated and the probe is injudiciously near the burner -- as I assume you are aware, practical boilers are heated via internal 'fire-tubes' or their 'electrical equivalent'...)

Best regards
HP

Excellent point. And we must also keep in mind that (assuming the tank is made of metal) the temperature difference between the insulated and non-insulated areas would quickly equalize, since heat would easily travel between both.
Ever heard the term "splitting hairs"?

 

I can't believe there would be a 9C temperature difference between a steel tank and the water contents, especially if the tank has an insulating jacket.

what is this? A naked tank in an Alaskan winter enduring a fierce, snowy gale?

 

Relax, friends. I set the thermostat on my residential (electric) water heater at 125F, four years ago, then I closed up the insulation layer, put the metal covers back on, and built a wooden laundry table over the top of the tank. I checked the water at the kitchen faucet and found that it was 125F.

I checked it again today. It's still 125F. The laws of thermodynamics have not been repealed. Thermostats still work. Temperature can still be measured. Insulation still keeps the thermostat measuring the tank instead of the air around it.

 

The laws of thermodynamics have not been repealed

Well... you let me know if that ever changes... I know of an excellent priest that can perform exorcisms on demand in case Maxwell's Demon ever shows up and half your water heater suddenly freezes while the other half boils...

 

Well... you let me know if that ever changes... I know of an excellent priest that can perform exorcisms on demand in case Maxwell's Demon ever shows up and half your water heater suddenly freezes while the other half boils...

I'm not sure about you. You recently posted something that suggests the Speed Limit for light has been repealed.

http://forum.allaboutcircuits.com/threads/the-d-wave-2x-quantum-computer.114660/

All I ask is that the water in my heater stratifies so the boiling half will be adjacent to the safety valve, otherwise, I will have to deal with the consequences illustrated on Mythbusters.

 

I'm not sure about you. You recently posted something that suggests the Speed Limit for light has been repealed.

yeah... I've been a bit of a naughty boy as of late... I just hope Santa doesn't hear about it until Christmas has passed!

 

I'm not sure about you. You recently posted something that suggests the Speed Limit for light has been repealed.

http://forum.allaboutcircuits.com/threads/the-d-wave-2x-quantum-computer.114660/

All I ask is that the water in my heater stratifies so the boiling half will be adjacent to the safety valve, otherwise, I will have to deal with the consequences illustrated on Mythbusters.

Good Lord!... that was an excellent video. Thanks for sharing!

 

guys. I might be wrong. but why did everyone dash to bash me, but almost non considered explaining? i might have been too extreme, i might have forgotten some things (such as that the temperatures equalizing).

In the end i learned one thing: that school doesnt give the complete picture
however. No one bothered to explain why what i am saying is wrong.
I have already said that i dont have much experience with boilers, heck i live in UAE where temps approach 55 C. but was talking about what we learned in the lab.

Just a small thing. would this whole conversion happen if the replying was left to the OP? and could we agree that IF he does want extreme precision submerging the sensor would be best?

 

guys. I might be wrong. but why did everyone dash to bash me, but almost non considered explaining? i might have been too extreme, i might have forgotten some things (such as that the temperatures equalizing).

In the end i learned one thing: that school doesnt give the complete picture
however. No one bothered to explain why what i am saying is wrong.
I have already said that i dont have much experience with boilers, heck i live in UAE where temps approach 55 C. but was talking about what we learned in the lab.

Just a small thing. would this whole conversion happen if the replying was left to the OP? and could we agree that IF he does want extreme precision submerging the sensor would be best?

Yes, if you want extreme precision, then submerging the sensor would be best. But then you'd have to ask yourself where.

If the tank were in thermal equilibrium, then it wouldn't matter where you placed the sensor, or if it were covered with insulation or anything else. But, in the real world, almost nothing is ever in thermal equilibrium. Even inside the tank there are important thermal variations between water at the top and water at the bottom.
So, for extreme precision, you'd have to use not just one, but many sensors distributed inside the tank, to build an accurate thermal map of what's happening inside. But then you'd have to ask yourself, is it worth it?

In all honesty, for such a mundane application it is certainly not. This is one of the many, many cases in which experience (with knowledge) is far more important than knowledge alone. I'd seriously reconsider #12's initial suggestion if I were you.

 

First off -- I'm genuinely sorry you felt 'set upon' Speaking for myself, I got the impression your mind was closed to explanation - my bad!

Just a small thing. would this whole conversion happen if the replying was left to the OP?

The function of public fora is discussion - carrying with it the advantages of 'peer review', as it were -- if, as you said, you learned something then the process is working! - Even as it does for all of us despite level of expertise/experience

Sincerely
HP