*) Reference junctions Ref1 and Ref2 are soaking in icewater,
so they are held at a constant temperature.
*) TC1, TC2, and R2 are all bonded together, so they are
at the same temperature, the so-called working temperature.
*) TC2, Ref2 and the voltmeter VM are used to measure
the working temperature.
*) R2 (driven by power supply PS2 is used as a heater,
to change the working temperature.
*) The adjustable regulated power supply PS is used to
control the so-called load voltage in the TC1/Ref1 circuit.
*) The idler resistor R1 is necessary so that there is
a positive current coming out of PS at all times. That's
important, because the typical laboratory-grade regulated
power supply has only one-quadrant regulation: the
regulator fails when loaded in such a way that negative
current would be required to maintain the desired voltage.
(The "quadrants" here refer to the graph of voltage versus
current. Most supplies will tolerate neither negative
voltage nor negative current. In a DC circuit, you can
simulate two-quadrant functionality with a one-quadrant
PS by reversing the leads when necessary, but four-quadrant
functionality is much trickier.)
You will have to substitute different R1 values to cover
different ranges of load voltage. In particular, you will
need a zero-ohm jumper to take the important zero-load-voltage
point.
*) Last but not least: TC1 and Ref1 constitute the heat
engine itself. The idea is to measure the current (using
the ammeter AM) as a function of voltage and temperature.
===============
Discussion:
In the Carnot cycle, there are four phases: Isothermal
expansion, adiabatic expansion, isothermal compression,
adibatic compression. These phases occur at separate
times.
In a turbine engine, seen as a whole, each of the basic
processes is happening all the time, not at its own
separate time. Instead, each process (expansion,
compression, etc.) happens at a different _place_.
Also, if you consider not the whole engine, but
rather just the fate of a particular parcel of fluid,
it does get exposed to different processes at different
times.
So it is with this thermoelectric engine. It's a
continuous-flow process like a turbine engine (as
opposed to the Carnot cycle which is a batch process).
The _principles_ of thermodynamics still apply. Rote
application of the textbook formulas will almost but
not quite suffice to describe the system; some tweaking
will be required.
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