DeltaV wrote:A constant-RPM Stirling driving a generator, steadily charging a powerpack, would have gentler waste heat transients than an IC engine driving the unpredictable primary load. Buffered by being one step further removed from the accelerator pedal. Figure one cycle per driving session.
Do notice that the linked article says that even rapidly pulsed heat flow, unless above 1 kHz, causes thermal fatigue in Peltier devices. I suspect, though, that a little modification of the materials and configuration might get around that.
The question for me is, would current TEGs be worth using to scavenge heat from a Stirling-generator device? Efficiencies of Bi-Te chips commonly available are in the 4-7% range. Pb-Te are getting up to 12% and may push to 18% per an earlier thread. But if a Stirling is run at optimal conditions, its converting far better than that, and generators can be extremely efficient. Maybe we're talking 40% or a little better overall. Adding a TEG to the heat flow path would reduce thermal conductivity, and I'd expect it to reduce the overall efficiency of the Stirling engine.
And then there's the prospect of graphene TEGs, in the lab but apparently not yet practical. Theory says 65% or higher may be possible. In which case you pitch the mechanical marvel in the recycle bin.
Meanwhile I'm messing around with an old Peltier cooler I've had since the last millennium, a MPJA surplus unit pulled from a picnic cooler. I stacked a similar chip, calibrated as a heat flow sensor, on it yesterday, in order to try to make some sense of the heat flow curves available for the device. In principle, the ability of a Peltier device to move heat should be symmetrical. Reverse polarity and it should work about as well in one direction as the other. This one is not doing it. It has developed different resistance in the two directions, and the heat flow changes by about a factor of 2. It is producing higher heat flow in the direction with lower current. I'm baffled. I suspect a malfunction. But this particular unit has a history in the Polywell effort, as it kept my lunch cold on the drive to San Diego.