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Heat flux sensing using TC O8

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Heat flux sensing using TC O8

Postby tommaliacken » Mon Sep 20, 2010 10:53 am

could any one please tell me how to measure the heat flus using pico log TC 08..I have obtained the reading in mV..Do we have any equations to convert it into heat flux..
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Re: Heat flux sensing using TC O8

Postby ziko » Tue Sep 21, 2010 12:54 pm

Hi what kind of sensor are you using?

What is the voltage output proportional to?
Once you know what the formulae is you can then input that into the scaling options section for the individual channels, either by a look up table or an equation.

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Re: Heat flux sensing using TC O8

Postby GiladO » Mon Oct 25, 2010 8:35 am

Measurement of heat flux is simple once you understand Fourier's law:

q=-kGradT [W/m^2]

Or giving it a bit of hair styling (measuring the power):

P=-kAGradT [W]

Supposing that you are working in a single dimension:

P=-kA(T1-T2)/(x1-x2)

Given you know the thermal conductivity k (assuming it is isotropic) of the material which conducts the heat (hopefully you can find it because it may be far from trivial to measure it), all you need to do is place 2 thermocouples on two sides of the surface through which the flux passes (in the direction of the flow of the flux perpendicular to the surface) and measure the distance between them.

P.S. You need the temperature in degrees not mV readings.
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Re: Heat flux sensing using TC O8

Postby ziko » Thu Oct 28, 2010 10:25 am

Hi,

Without reasearching too much into Heatflux I cannot say for sure if this is possible, however I will have a go.

P=-kA(T1-T2)/(x1-x2)


This seems to be your equation for heat flux.

kA is a constant for thermal conductivity
T1-T2 is the temperature difference
x1-x2 is some kind of distance.

I assume you will be measuring two temperatures so that should be no problem incorporating that into a forumlae, the constant should also be find, however what exactly is x1 and x2? Are they variable?

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Re: Heat flux sensing using TC O8

Postby GiladO » Thu Oct 28, 2010 3:34 pm

kA is a constant for thermal conductivity

k is the thermal conductivity constant.
A is the area through which the heat passes.
T1-T2 is the temperature difference

correct
x1-x2 is some kind of distance.


Actually it is deltaT/deltaX x1-x2 is the distance between the thermocouples. x1 is the position of the first thermocouple x2 is the position of the second. By measuring the temperature drop on a certain distance you are actually measuring the temperature gradient. As in many physical phenomena, the amount of heat flowing from one point to the other depends on the temperature gradient. The larger it is more heat will flow from one point to the other. The minus sign states that it flows from the higher temperature to the lower one.
This formula is the basis of the whole field of heat transfer and is crucial in electronic component design as well as in many other fields of engineering.

Due to its design the TC08 is a very effective instrument for measuring heat transfer.
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Re: Heat flux sensing using TC O8

Postby ziko » Wed Nov 03, 2010 11:14 am

From what I can see then this is possible to do as a formulae as long as :

The values for

k
A
x1 and x2

are all fixed, T1 and T2 obviously can vary.

If you go into calculated parameters you can achieved this. It gives you a 5 variables A, B, C, D, E you would then assign each of your temperature channels onto each of those variables, for example put T1 is on A, and T2 on B you can then substiture T1 and T2 for A and B in your equation.

Calculated parameters can be found under Settings.

Hope this helps.
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Re: Heat flux sensing using TC O8

Postby GiladO » Thu Nov 04, 2010 10:05 am

That is a matter of preference and need. I prefer to get the raw data (well, almost raw as I do prefer that picolog or whatever program I'm using calculate the temperature. We still have some real old-timers here who actually use tables on a regular basis), and only then to manipulate it.

I don't know if the response was in time to help the guy as obviously he has not responded to the thread. However, I do hope that it will help someone in the future.
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Re: Heat flux sensing using TC O8

Postby ziko » Thu Nov 04, 2010 10:25 am

Ah I didn't realise that you were not the original poster! You are correct as long as you have the raw data you can always put it in excel and then do your calculations.

Anyway hopefully as you said it will be of use to someone. I also learnt something from it! :)
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