Question

. You have two thermal couples. One thermal couple is fixed in space at (Xo,Yo,Zo) and the second thermal couple is moving in space. At time to, the second thermal couple moves to location (Xo,Yo,Zo). Assuming the temperature is not uniform in space.

Are the temperatures measured from the two thermal couples the same ?

Are the rate of changes of temperature the same?

Please be clear I really want to understand the concept, Thank you for your help (:

Answer 1

Let me just start by saying that the thermocouples are devices that use Peltier effect absorb and reject heat.

Now a thermocouple is just a joint made of two different material that can exhibit Seebeck effect, that is when one of the junction is heated and the other junction is left cool. A small electric current is produced by the thermocouple.

Peltier effect just uses the corollary of this concept. When an electric current is passed through a thermocouple, one end becomes heat rejecting (hotter) and one becomes heat absorbing (cold). So basically a thermocouple relies on how effectively the material covering the heat absorbing end of the thermocouple is transferring heat.

So, here in your problem, if the thermocouple moves to a new position then it will not show the same temperature because of various other effects associated with measuring temperature accurately. If we are talking about 1 degree Celcius accuracy then the thermocouples might show the same temperature. But if we talking about 0.1-degree accuracy or less the values might differ.

The thermocouple would need a relaxation time to attain thermal equilibrium between its measuring junction and space its measure it. So until and unless the time requirements are met and the temperature at X0Y0Z0 in the direction that the first thermocouple was facing is not varied at all, then if enough time is given for the second thermocouple then it would eventually reach the same temperature as the first.