Asri-unix.930
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utcsrgv!utzoo!decvax!ucbvax!C70:sri-unix!DIETZ@USC-ECL
Tue Mar 9 12:22:38 1982
Sodium heat engine - SPS application?
The following appeared in a recent (Feb. 27) Science News:
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Electricity from a sodium heat engine
Scientists at the Ford Motor Company are developing a new device
capable of converting heat directly into electrical energy. This
device, called a sodium heat engine, has no moving parts and uses a
small quantity of liquid sodium as its working fluid.
Hot liquid sodium fills one side of a closed container divided into
two parts by a ceramic wall of the compound beta''-alumina. The wall
allows passage of sodium ions but not electrons or sodium atoms.
Thus, sodium ions go through the solid, ion-conducting electrolyte,
while electrons travel an external circuit to provide a low voltage,
high current electrical output. A sodium vapor pressure difference
across the electrolyte generates the driving voltage. In the low
temperature part of the system, the sodium vaporizes from the
electrode surface and then condenses on a cooled wall. An
electromagnetic pump returns the condensed sodium to the hot region.
The device can use any source delivering heat at 700 degrees C or
more. Its efficiency, potentially in the range of 30 to 40 percent,
is independent of the heat engine's size. A model designed for
long-term testing has reached 19 percent efficiency at an output of 22
watts. The pump siphons off less than 0.1 percent of the energy
output. The major problem with the system is deterioration of the
electrodes after several hundred hours of operation, which lowers the
voltage and decreases power. Despite this problem, the sodium heat
engine looks good more promising than many earlier thermionic devices.
The researchers say, "An efficient, durable, low maintenance,
thermoelectric energy converter with good power density, made of
readily available materials and with efficiency independent of size
would have substantial implications for solution of some of the
nation's energy, transportation and defense problems."
Potential applications include use in total energy systems for
residences and factories, in remote locations and as part of solar
energy installations the concentrate light. Even the rejected heat at
the low temperature end of the cycle can be used.
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If they can solve that electrode problem this thing could be useful in
solar power satellites.
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