Heat Transfer Equation

[bombardment]

I am looking to calculate the temperature of water inside a small pressure vessel. I have several thermocouples on the wall and have an average at different time increments. Purpose of this is so I can see how much heat the water absorbed. Thanks in advance.

 

[IRstuff]

Was there a question?

TTFN

FAQ731-376

 

[bombardment]

lol I apologize. What would be the best way to calculate the temperature of the water? I have the temperature of the outer surface of the vessel.

 

[IRstuff]

The steady state answer is that the water temperature will be roughly the average of your wall temperature, right?

TTFN

FAQ731-376

 

[bombardment]

The thermocouples are measuring the outerwall of the vessel.

 

[IRstuff]

Yes, and?

TTFN

FAQ731-376

 

[ivymike]

as irstuff noted, if the time involved is long enough then the outer wall of the vessel will be pretty close to the temperature of the inside.

If the outer wall temperature is constant then the vessel should be roughly in equilibrium with the surroundings.

The amount of heat absorbed or released by the internal fluid between steady condition 1 and steady condition 2 will be the change in temperature times mass times the heat capacity.

 

[bombardment]

The temperature never reaches a constant. Is it a correct assumption to assume that the change in temperature on the surface of the vessel will be the same as the internal fluid? Just seems like the heat absorbed by the internal fluid will be lower than what it really is by this assumption.

 

[IRstuff]

"Is it a correct assumption to assume that the change in temperature on the surface of the vessel will be the same as the internal fluid? "

NO. If the system never equilibrates, then, by definition, the internal fluid temperature change MUST be lower than the external temperature change.

But how do you know that the fluid temperature never stabilizes? If you already know the fluid temperature, then what's the issue?

TTFN

FAQ731-376

 

[bombardment]

I do not know the fluid temperature. I am measuring the outer wall of the vessel that the fluid is contained in.

Shouldn't the internal fluid temperature be higher than that of the outer vessel surface?

 

[ivymike]

depends on whether it is being heated or cooled. if the fluid is being heated, then the wall is hotter. if the fluid is being cooled, then the wall is cooler. if neither is happening, it's all at the same temp.

 

[IRstuff]

"Shouldn't the internal fluid temperature be higher than that of the outer vessel surface? "

Shouldn't you have told us that that the fluid was being heated internally or was hotter to start with?

TTFN

FAQ731-376

 

[Latexman]

Do you have any subsurface nozzles on this pressure vessel? If so, install a thermowell and thermocouple and measure it directly.

Good luck,
Latexman

 

[Twoballcane]

Not to be crass, but are you a Mechanical Engineer? Kind of give us a starting point on how to answer your question.

Tobalcane
"If you avoid failure, you also avoid success."