Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

constitutive relations



Jim Green wrote:

I have been re-reading Clifford Truesdell "The Tragicomedy of Classical
Thermodynamics" at the suggestion of Steve Houk -- The guy (Truesdell not
Hoak) is really hard to read even after one gets around his megalomania --

What does he mean by "constitutive relation?

"Fourier stated this last assumption only in connection with the linear
constitutive relation H=K(theta)grad(theta)" where theta is the temp and H
is the "heat rate" [yuch] and K the conductivity.

"Like Fourier, Carnot could not operate without a special constitutive
relation." The equation in the previous paragraph is pv=R(theta), but I see
no connection.

Help anyone???

Jim Green
JMGreen@sisna.com

Constitutive relations are relations which are not strict laws of
physics (as e.g. Maxwell's laws), but which are inferred from
experiments and adequately represent the behaviour of certain classes of
materials. They are also sometimes referred to as "material equations",
which could be considered a more appropriate term but is nevertheless
seldom used.
I am familiar with this expression because all my colleagues in the
electronics department use the term when referring to the relation
between P (polarization) and E (electric field) for dielectrics.
Similarly, the equation pv=R(theta) can be considered to hold only for
ideal gases and to be inferred form experiment on very dilute gases (at
least in classical thermodynamics).
In my experience the term is seldom used in thermodynamics, I could find
only one reference to it in our library.


--
Willem Wieme
Professor of Physics
Department of Aplied Physics
University of Gent
Rozier 44, B-9000 GENT BELGIUM
Tel: +32 - 9 -2643823 Fax: +32 - 9 -2644198
e-mail Willem.Wieme@rug.ac.be