Global Power Technologies
APPENDIX B — PROCESS DESCRIPTION
05585 rev11 | Model 8550-SD
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APPENDIX B — PROCESS DESCRIPTION
A Thermoelectric Generator produces electrical power by directly converting heat energy to electrical
energy with the use of thermocouples. A thermocouple is formed by a P type and an N type
thermoelectric element joined electrically by a hot junction electrode. Adjacent thermocouples are
joined electrically by cold junction electrodes.
Electrical power will continue to flow through the circuit as long as the temperature difference
between the two ends of the thermocouple is maintained.
The Model 8550 Power Unit has a total of 325 thermocouples, each producing 87 mV at standard
conditions, connected in series to produce 590 Watts at 28 Volts and 21 Amperes.
Figure 30 – Design Illustration
The hot junction of the thermocouples is maintained at 1000°F (538°C) or by a burner that operates
on gaseous fuels. The burner operates at moderate fuel pressures, approximately 18 psi (124 kPa) for
propane and 9 psi (62 kPa) for natural gas. The cold junction of the thermocouples is maintained at
235°F (163°C) by an array of heat pipes that transfer the heat to the ambient air.
The cold junction of the thermocouples is maintained at a lower temperature (163°C or 235°F) by an
array of heat pipes that transfer the heat to the ambient air by natural convection. Each heat pipe is
hermetically sealed and contains a measured amount of fluid in equilibrium with its vapour. As heat is
applied to the fluid it, boils and then re-condenses
in the condenser tube
due to the cooling effect of
the cooling fins. In this way, heat is efficiently transferred to the cooling fin.
The power unit must always be in a loaded condition. This is because under extended open circuit or
high voltage conditions, the hot junction temperature may rise above the safe operating range. For
this reason, the power unit must always remain connected to a power conditioner which will keep
the power unit voltage within safe operating regions.
The temperature difference, and therefore the amount of power produced by the TEG, depends on
both the rate at which fuel is supplied to the burner and the amount of cooling supplied by the
ambient air. The operation of the TEG is controlled by the fuel pressure supplied to the burner.