RE: [Vo]:Linear Operation of ECAT Modeled
Dave, Did you consider a negative differential resistance scenario for the input? This would make for nonlinear operation but it is closer to what Rossi is suggesting. It implies a sweet spot in the parameters which should be easier to control since there would be both positive and negative feedback. From: David Roberson Subject: [Vo]:Linear Operation of ECAT Modeled I have been toying with a new computer model of the ECAT that I constructed the other day. The concepts that are being presented are based upon a simple model of the ECAT that has many assumptions since Rossi has not released many of the detailed technical information required to construct a truly accurate one. This particular model run assumes that the internally generated heat power follows a forth order function in the region around the thermal run away temperature. It can be adjusted to include any polynomial or other function once that has been verified. The main idea at work is that the ECAT must use positive feedback in order to operate at a reasonable COP. Negative internal feedback or no reinforcing heat from the powder will not work to a useful degree. The model suggests that Rossi must carefully set the thermal resistance into which heat is delivered by the device. If the coolant flow rate is excessive, which would represent someone attempting to extract too much heat from the system, the positive feedback can be defeated and the temperature would collapse. This implies that there must be a tradeoff between the variables which is most likely where a lot of Rossi's time is being expended. I did notice that under the ideal conditions operation slightly below the run away core temperature can be theoretically controlled and the gain large. My model demonstrates this is possible, but the control system is subjected to a positive feedback behavior which it must overwhelm. Operation at these types of location are tricky since any error in temperature of either direction tends to compound and the device heads ever stronger in that direction. If the core experiences a slight increase in temperature it heads toward thermal run away and must be reversed by the control loop. On the other hand a tiny drop in core temperature leads to total cooling unless compensated. The control loop has to contend with environment changes such as input coolant temperature and flow rate, or for example changes to the activity of the powder with time. I am confident that there are many other factors which attempt to influence the instantaneous balance required at the chosen operation temperature and all of these require an excess of control range for proper allowance. The time constants associated with the device must also be contended with and of course these are not being revealed by Rossi at this time either. Any delays built into the heat generation mechanism itself further complicate the control system. For all of these reasons, a model such as the one I have constructed makes assumptions that will likely be found in error, but at least the trends should be revealed. One of the model runs that I conducted assumed that an input power set to a constant 1000 watts(modified by the loop) could control a total output power of 1 watts for a net COP of 10. Other drives can of course be used which yield higher or lower values of COP, but this value has a nice ring to it! The thermal run away trip point is within 5% of the absolute temperature of operation in this particular case. I have noticed that most any other polynomial relationship between core power generation and temperature work in a similar fashion to the forth order where the higher ordered functions tend to be more critical. This is to be expected. Dave
Re: [Vo]:Linear Operation of ECAT Modeled
The model I constructed is fairly simple in form. In this particular case I used a forth order function of power internally generated versus core internal temperature. I also tried many other functions, but felt that the magnitude of the nonlinearity was within reason with the forth order function. The assumed internally generated power begins at 0 watts and then rapidly increases with temperature as would be expected with the forth order relationship. Could you offer a simple description of the behavior of the negative differential resistance function that you mention? My model also generates a negative resistance once a certain internal temperature is reached. The exact level at which this is reached depends also upon the thermal impendence that the core works into. I can adjust this factor fairly easily in the model and in real life I suspect that Rossi would likely reduce the coolant flow rate and hence raise its associated thermal resistance value at startup to reduce the power input required to enter into the positive resistance dominated region. Once this region is breeched, the positive feedback, as evidenced by the negative resistance calculation, takes over and brings the ECAT up to an active core temperature near the thermal runaway level. The control loop must rapidly begin to extract any excess power once this temperature is reached. A failure at that time will cause the ECAT to melt. It is evident from the model runs and common sense that the thermal runaway temperature can be modified on the fly by the settings of the coolant flow rate and input temperature. This was demonstrated in one of Rossi's earlier test runs where he upped the flow rate significantly to pull the early model into safe turn off. I suspect that even an intervention such as this has limitations unless applied soon enough. Rossi has numerous variables at his disposal that he can modify at startup, operation, and turn off. I hope that we can get more information from him before one of his final designs is thrown into our laps via production in volume. Dave -Original Message- From: Jones Beene jone...@pacbell.net To: vortex-l vortex-l@eskimo.com Sent: Thu, Jan 2, 2014 12:47 pm Subject: RE: [Vo]:Linear Operation of ECAT Modeled Dave, Did you consider anegative differential resistance scenario for the input? This would make fornonlinear operation but it is closer to what Rossi is suggesting. It implies a “sweetspot” in the parameters which should be easier to control since therewould be both positive and negative feedback. From:David Roberson Subject:[Vo]:Linear Operation of ECAT Modeled I have been toying with a new computer model of the ECAT that Iconstructed the other day. The concepts that are being presented arebased upon a simple model of the ECAT that has many assumptions since Rossi hasnot released many of the detailed technical information required to construct atruly accurate one. This particular model run assumes that the internally generated heat powerfollows a forth order function in the region around the thermal run awaytemperature. It can be adjusted to include any polynomial or otherfunction once that has been verified. The main idea at work is that theECAT must use positive feedback in order to operate at a reasonable COP. Negative internal feedback or no reinforcing heat from the powder will not workto a useful degree. The model suggests that Rossi must carefully set the thermal resistance intowhich heat is delivered by the device. If the coolant flow rate isexcessive, which would represent someone attempting to extract too much heatfrom the system, the positive feedback can be defeated and the temperaturewould collapse. This implies that there must be a tradeoff between thevariables which is most likely where a lot of Rossi's time is being expended. I did notice that under the ideal conditions operation slightly below the runaway core temperature can be theoretically controlled and the gain large. My model demonstrates this is possible, but the control system is subjected toa positive feedback behavior which it must overwhelm. Operation at thesetypes of location are tricky since any error in temperature of either directiontends to compound and the device heads ever stronger in that direction. If the core experiences a slight increase in temperature it heads towardthermal run away and must be reversed by the control loop. On the otherhand a tiny drop in core temperature leads to total cooling unlesscompensated. The control loop has to contend with environment changessuch as input coolant temperature and flow rate, or for example changes to theactivity of the powder with time. I am confident that there are manyother factors which attempt to influence the instantaneous balance required atthe chosen operation temperature and all of these require an excess of controlrange for proper allowance
RE: [Vo]:Linear Operation of ECAT Modeled
From: David Roberson Could you offer a simple description of the behavior of the negative differential resistance function that you mention? Looks like you are already doing something similar. Wiki has an entry for the electronic version. The image of the curve is an ascending double hump, so if your model accommodates that already, then that may be why it is so intuitive. If one is plotting P-in vs. P-out then there is good control functionality to the top of the first hump, where the negative feedback would start to show itself. https://www.google.com/search?q=negative+differential+resistanceclient=firefox-ahs=bBTrls=org.mozilla:en-US:officialtbm=ischtbo=usource=univsa=Xei=JKTFUo6jBcvxoASVpoCABwved=0CDwQsAQbiw=1146bih=675
RE: [Vo]:Linear Operation of ECAT Modeled
Sounds like one of Rossi's controllability issues may come from the temperature stability of the cooling fluid itself. Dave's explanation sounds as if the control loop is expecting a rather consistent cooling fluid inlet temperature... and that may be the case if running off the city water supply (at least no major differences in water temp for a running faucet), but if one gets a sudden drop of several degrees on inlet water temp, what will that do to the control loop??? -Mark Iverson On Thu, Jan 2, 2014 at 10:33 AM, Jones Beene wrote: From: David Roberson Could you offer a simple description of the behavior of the negative differential resistance function that you mention? Looks like you are already doing something similar. Wiki has an entry for the electronic version. The image of the curve is an ascending double hump, so if your model accommodates that already, then that may be why it is so intuitive. If one is plotting P-in vs. P-out then there is good control functionality to the top of the first hump, where the negative feedback would start to show itself. https://www.google.com/search?q=negative+differential+resistanceclient=firefox-ahs=bBTrls=org.mozilla:en-US:officialtbm=ischtbo=usource=univsa=Xei=JKTFUo6jBcvxoASVpoCABwved=0CDwQsAQbiw=1146bih=675
Re: [Vo]:Linear Operation of ECAT Modeled
I suspect that a change of the temperature of the incoming water will cause a disturbance to the loop. Rossi must allow sufficient margin for his drive to account for this behavior since it will no doubt be encountered. It would be a good idea for him to control the coolant flow rate on the fly as a means to compensate for this type of change. Rossi now discusses having the internal temperature at around 1000 C while the coolant is heated up to 500 C. I have long waited for him to make such a statement since the earlier testing did not indicate this situation. Of course, he allowed radiation to cool the hot cats which now must be designed to work at a reasonable cooler output temperature. The thermal resistance of this heat flow path directly impacts the positive feedback loop and must be controlled for a reliable product. As I mentioned previously, he would be wise to keep the coolant at a zero flow rate condition at startup to enable the positive feedback to begin at a lower net temperature and input power. The coolant could be heated quickly under this condition at the lower input power level. The thermal masses of the system components and the coolant itself would retard the temperature rate of rise which would give him time for his control loop to initially stabilize. It is not clear whether or not the coolant should be rapidly allowed to resume flow at its design value. The shape of the flow transition might be used to his advantage. The mention of negative resistance is a subject that I am comfortable with. I have used this type of analysis for many years in the design of oscillator networks. In the ECAT case, it is required in order for the COP to be much greater than unity. Positive resistance appears in the form of heat transferring into the coolant. At a given temperature, the thermal resistance can be expressed in a differential form. The slope of the curve that defines core node temperature as a function of heat output power being absorbed by the load is one of the important factors in determining the net resistance of the system. This slope at a given temperature yields the positive load thermal resistance seen by the core. The internal power generation process of the core itself yields the other resistance term. That one is negative since heat power is being generated by the core in greater quantities as the temperature rises. The slope again is also important and represents the instantaneous negative resistance at a given core temperature. The interaction of the input heating power with the balance of the system is a bit complex but important. It determines the temperature at which the positive feedback takes control. It likewise allows control of the complete system as discussed in previous posts. Dave -Original Message- From: MarkI-Zeropoint zeropo...@charter.net To: vortex-l vortex-l@eskimo.com Sent: Thu, Jan 2, 2014 1:44 pm Subject: RE: [Vo]:Linear Operation of ECAT Modeled Sounds like one of Rossi's controllability issues may come from the temperature stability of the cooling fluid itself. Dave's explanation sounds as if the control loop is expecting a rather consistent cooling fluid inlet temperature... and that may be the case if running off the city water supply (at least no major differences in water temp for a running faucet), but if one gets a sudden drop of several degrees on inlet water temp, what will that do to the control loop??? -Mark Iverson On Thu, Jan 2, 2014 at 10:33 AM, Jones Beene wrote: From: David Roberson Could you offer a simple description of the behavior of the negative differential resistance function that you mention? Looks like you are already doing something similar. Wiki has an entry for the electronic version. The image of the curve is an ascending double hump, so if your model accommodates that already, then that may be why it is so intuitive. If one is plotting P-in vs. P-out then there is good control functionality to the top of the first hump, where the negative feedback would start to show itself. https://www.google.com/search?q=negative+differential+resistanceclient=firefox-ahs=bBTrls=org.mozilla:en-US:officialtbm=ischtbo=usource=univsa=Xei=JKTFUo6jBcvxoASVpoCABwved=0CDwQsAQbiw=1146bih=675
