When heat is conducted along the wires of a thermocouple which is carrying
no current, a uniform temperature distribution is established in each wire.
If a current now exists, the temperature distribution in each wire is
changed by an amount dT (delta T), which can not be accounted for by the
Joule heating effect alone. It is this additional change in the temperature
distribution which is known as the Thomson effect (first inderstood by Lord
Kelvin, a.k.a. William Thomson, 1824-1907). If one allows for the Joule
heating effect, the additional amount of heat which must be either supplied
or extracted along the entire length of the wires, such as to restore the
original temperature distribution, is called the Thomson heat. The Thomson
effect may be measured by exposing a small section of one of the wires and
producing a known temperature gradient in that region. If one now passes a
known current along the wire, either up or down the temperature gradient,
one can measure the Thomson Heat. The rate at which the Thomson heat is
transferred is equal to the rate at which electrical energy is dissipated,
minus the rate at which heat is conducted to (or extracted from) the wire
region. Since the Joule effect can be calculated and the conducted heat was
determined from previous experiments, it is possible to calculate the
Thomson Heat. The rate at which the Thomson heat is transferred into a small
region of the wire which is carrying a current I, and exhibiting a
temperature gradient dT, is equal to s.I.dT, where s is called the Thomson
coefficient.
    It should be noted that the Thomson heat is reversible, and depends on
material considerations.

K. Cazzini
Snr. Scientist
Alcon laboratories Inc.

----- Original Message -----
From: "Jun yao" 
To: 
Sent: Saturday, June 22, 2002 7:49 AM
Subject: [mems-talk] About Thomson coefficient


> Dear all,
>
> Does anybody know Thomson effect ( not Joule-Thomson effect) ? How can I
find the Thomson coefficient and what is the SI unit of Thomson coefficient?
>
> The important thing is that whether there is a formulation for Thomson
effect?
>
> Thank you very much.
>
>
>
> Jun
> Sign-up for Video Highlights of 2002 FIFA World Cup
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