Thank you very much for the explanation Dave. That should add another tool for detecting and/or enhancing excess heat. My resistance wire is holding up quite well in an experiment I'm currently running affording a chance to try many different things to help determine what is going on.
On Thu, Nov 19, 2015 at 7:24 PM David Roberson <dlrober...@aol.com> wrote: > Jack, I would expect the output power to be greater for your first > case(1) due to the tendency of the core activity to 'stick' longer at the > highest temperature. This effect is mainly due to the time constant being > lengthened by the positive feedback acting like a negative resistance. > When you are operating at the lower temperature, the thermal time constant > is shorter and temperature changes occur at a more rapid pace. > > It appears to be the tendency to 'stick' that leads to the highest COP. > If your control system is capable of maintaining the temperature at very > nearly the level where the input power required becomes zero watts, the COP > will be enormous. I have simulated a system using negative feedback of a > traditional linear nature and it appears to work fairly well. And, of > course a PWM drive signal will also work. > > To answer your question, I would expect it to require less total input > power in the case of the PWM drive signal(1) operating between two > moderately separated core temperature levels than with input drive > producing a fixed temperature level at the average between them(2). This > effect will become much more pronounced as the highest power output level > approaches the point where the core generated power becomes close to the > power that is radiated and convected from the device. When those powers > are equal, the time constant approaches infinity and the temperature > 'sticks' at that level for a significant time while requiring very little > drive power. And, at that high level, when the PWM drive is zeroed the > temperature begins to move downwards with a time constant that is quite > long. > > As you might imagine, the effective time constant falls off rapidly as you > move away from the above mentioned balance point. It should be > significantly shorter by the time you reach the temperature level between > the two PWM turning points unless these temperatures are very close > together. The actual rate at which the time constant reduction falls off > with temperature depends upon the curves defining the core generation power > function and the output power escape function. > > Jack, I am assuming that you will have a type 3 system that is capable of > thermal run away. I make this assumption because it is difficult to adjust > the parameters of the defining equations necessary to achieve a type 2 > design. A 10% error is enough to completely miss type 2 behavior and I > find that I generally have to use Excel in order to obtain coefficients > that work well. It takes too much time to run simulations alone to obtain > that desired result. Excel however can be used to obtain the > characteristic curve quickly. Of course, a type 1 system is relatively > easy to test but the COP is limited to less than 3 which is not super > interesting. > > Dave > > > > -----Original Message----- > From: Jack Cole <jcol...@gmail.com> > To: vortex-l <vortex-l@eskimo.com> > Sent: Thu, Nov 19, 2015 1:16 pm > Subject: [Vo]:Questions about self-sustaining reactions > > I have been working on an algorithm to detect excess heat in a slightly > different way, but wanted to see if others could perhaps provide some > insight. > > Here are my thoughts: > > 1) utilize an on/off heating and cooling cycle within a specified range > (e.g., 1000-1200C) - input power turns off at 1200C and back on at 1000C > and repeats > 2) compare this to a steady state run at the average temperature from the > cycling range (let's say 1100C) > > If you have a theoretical excess heat running continuously at 20W in both > conditions would you expect the average input power in #1 to be greater > than #2. I suspect the answer may be no, unless the excess heat is truly > capable of self-sustaining the reaction for a period of time. > > I would welcome any thoughts on this process. I suspect Dave could speak > well to this from the perspective of his simulations. > > Thanks, > Jack >
