--- Jed Rothwell wrote: > 15% efficient thermoelectric generators would be > fine for small > machines such as wristwatches, cell phones and > implantable heart > boosters (VAD) but I expect larger machines such as > home generators > and automobiles will use more efficient, > conventional heat engines.
Perhaps I did not make the example clear enough. There is no conventional heat engine, no matter how large, which will approach the high "device efficiency" which might be feasible with nanowires. Consequently, the problem is not size. In fact, for thermoelectric nanowires, like the ones presented in the previous News release, there is evidence that smaller is better, due to heat transfer limitations or larger geometries. It is the Carnot "spread" or the temperature differential between the hot side (in Kelvin) and the sink- which is all-important. In my example the efficiency of the converter was optimistic at 80%, but nothing can change the low "spread" except a higher hot side. The problem there is that metal hydrides like Pd are limited in loading at higher temperatures and you need the full loading for the CF effect (apparently). That loss in loading is a similar reason why hydrogen storage tanks (using metal hydrides) can release the gas simply by heating the tank. With a diesel heat engine, for instance the high Carnot spread is due to the fuel ignition temperature- roughly 2,400 F, versus ambient. This will allow an engine with a device efficiency of only 50% to achieve about a 35% net Carnot efficiency. But that high spread in unavailable with liquid electrolytes and/or with electrodes which demand full loading. Lets say the LENR cell is working at 200 degrees F, so that a liquid electrolyte will not boil. This is ~367 K and room temperature is ~300, so your spread is 67. The ratio of the spread to the sink is 67/300 or ~22%. This is the maximum net efficiency for any heat engine at that temperature, no matter how large the heat engine is... and that is the maximum, even if the device itself is 100% efficient as a no-loss converter. If the device itself, like the nanowire example, is 80% efficient on its own, then you might get the net up to 17-18%, but that must include the parasitic energy which is fed back to the electrodes, in order to keep the cell running. Therefore a net efficiency of 15% would be absolutely fabulous, with ANY size LENR cell, from the smallest to the largest ... unless you can find an electrode which works at low loading. AFAIK there is zero evidence for any such electrode in the literature ... and conversely, the net efficiency would most likely go down, not up, with a larger machine (for automotive)... this is due to the problem of getting adequate heat transfer at the sink. Of course, if you can safely let the electrolyte boil or become superpressurized to maintain high loading, then that feature will raise the bar ... but then the added pressurization becomes the issue which keeps this from use with smaller devices. Jones
