I have been analyzing the latest design by Dr. Parkhomov and suspect that the new plan will demonstrate difficult stability problems. I understand that his latest model of Hotcat replication is much easier to measure and build, but there may be a major trade off with respect to COP and stability that will eventually force a return to the older version.
The inner core of the new system that contains the fuel is more isolated from the outer heater coil which will result in an increase in the thermal resistance from the core to ambient. Thermal power originating within the core will have to cross through a greater amount of thermal impedance before it escapes and will therefore cause a greater temperature drop between the core and the heater. The positive feedback will also increase due to the larger impedance and the onset of a negative resistance region due to that feedback will happen earlier. It is going to be difficult to operate in a stable fashion within the negative resistance region and entry into this mode of operation will likely result in thermal destruction without a lot of intervention. And, with the additional isolation between the core and the heater that needed intervention will be much more difficult to achieve. I suspect that the ideal design will be achieved with the heater coil tightly coupled to the fuel charge. In that case the thermal mass of the coil wire, fuel, and the ceramic components will behave more like one total item. That would allow the power modulation applied to the heater coil to have a more immediate effect upon any heat entering the net thermal mass. When the drive power is interrupted by the controller the entire system thermal mass begins to cool quickly and with the least amount of lag possible. The application of a PWM (pulse width modulated) drive could then be used to pull the system back toward stability assuming that the fuel response does not have too much lag. Rossi has long endorsed the use of a PWM drive waveform and there must be a good reason. The independent testers used static DC drive without witnessing a major stability issue which leads me to believe that Rossi adjusted the fuel charge to be somewhat less active than normal. The reduced fuel activity immediately resulted in a lower COP since there was no region of negative resistance observed, which multiplies that parameter. With these considerations I suspect that we are going to witness plenty of systems that exhibit thermal run away until we modify the device plan back to one that is more like the original Parkhomov device. With the latest design we should be able to reduce the fuel loading until stabile operation is obtained, but the COP will be too low to be practical. The good news is that it will be easy to build additional test samples since burned out cores are simple to replace. The bad news is that we might spend a great deal of time melting cores for that very reason. My opinion of the most recent Parkhomov design has changed dramatically since I have taken time to consider the thermal effects. At this point all we can do is to speculate about how our model system will perform and change should be expected when new ideas arise. The latest concepts will likely be replaced once proper measurements are obtained. We should all attempt to keep an open mind. Dave
