you can get tremendous thermal conductivity by using smaller tubes. hypodermic stainless steel tubing is made cheaply and in very large quantities. Alternatively (and more easily) use a pump to actively circulate the fluid. But having heat sink fluid close to same temperature of reaction with low thermal resistance between the two is key to getting rock-steady control. Forms a much harder wall against run-away thermal events.
Above the critical point of water 374°C and 22MPa you do not get steam bubbles forming - as is a supercritical fluid (single state). in nearly 3 years with many flawed demos Rossi has not demonstrated any particular talent for practical management of engineering thermodynamics, (defkalion showed more much more sensible approaches, even if their heat generation may not be working as well) so I do not expect the seeming control-freak Rossi to do anything particularly clever or even sensible in this respect now or in near future. On 9 October 2013 19:54, James Bowery <[email protected]> wrote: > A lot of this depends on the internal heat conductivity structure of the > device not developing hot-spots that runaway. Is there a good model of > this conductivity structure? > > > On Wed, Oct 9, 2013 at 1:42 PM, Robert Lynn < > [email protected]> wrote: > >> That would be a very simple means of providing excellent high temperature >> control. >> >> A coil of tube inside the reactor containing water with a pressurised >> cold reservoir attached to one end to keep it filled with water and a >> pressure relief valve at the other end to release steam above a certain >> pressure. The pressure release setting could control the temperature very >> accurately, at any point from 100°C to 6-700°C, and the steam from the >> pressure relief valve could be sparged into a water tank for simple >> calorimetry. >> >> The water filled tube would absorb relatively little energy until the >> rector temperature rose above it's set point, at which point it would >> absorb a huge amount of energy with small temperature increase. >> >> Would give safe reliable hot-cat operation without danger of thermal >> run-away. >> >> >> On 9 October 2013 16:18, <[email protected]> wrote: >> >>> On 9/10/2013 12:20 PM, David Roberson wrote: >>> >>> I finally got around to checking my ECAT model performance with active >>> cooling control and the results were very interesting. First, I applied >>> normal heating to the device which leads to thermal run away conditions if >>> allowed to go beyond a certain critical core temperature. As expected, >>> the model showed that the ECAT began a path toward melt down. >>> >>> The path to destruction would proceed even when the original drive is >>> removed since the critical temperature was exceeded. Then, I allowed the >>> model to continue heating for a period of time and applied the brakes >>> quickly with a new load that withdraws a significant amount of extra heat >>> power from the system. This might be possible in real life if for instance >>> a phase change coolant were sprayed onto the core directly. The extra >>> cooling must be applied continuously while the temperature drops and >>> until an optimum trip temperature is reached. The turn around point must >>> be above the normal critical temperature since no additional heating is >>> required to achieve a condition where thermal run away can begin anew. >>> >>> The model demonstrated that this type of cycle could be repeated >>> indefinitely while the total power being generated by the device is >>> significantly above that safely obtained by heating control alone. I would >>> assume that a cooling method similar to that suggested above would take >>> less input power than the standard heating process that I have modeled >>> earlier so this type of control would result in a higher COP for the system. >>> >>> The model also demonstrated that a continual application of the extra >>> cooling resulted in the cores return to room temperature as desired. >>> Actually, the powerful cooling was not required to be applied once the >>> critical run away point was passed. In this case, the core would be >>> subjected to positive feedback that forces it toward turn off by itself. >>> >>> It is evident that a hybrid type of control system that uses both power >>> resistive heating as well as active cooling would perform the function. If >>> both techniques were available it might be possible to keep the ECAT >>> temperature very near the critical point in which case the COP would be >>> extremely high. For this type of tight control to work the loading as well >>> as all the other parameters which cause the critical temperature to vary >>> must be kept under tight control. This might be possible. >>> >>> >>> Good to see someone thinking! In fact I think the problem is really >>> simple. (And there should be no "extremely high" for overunity devices - >>> if they are not beyond infinity then you haven't got an engineer worth his >>> salt working on it). There should be no need even for an active system. >>> You simply need a passive system that presents a steeper load onset with >>> temperature (cooling effect) than the (expected) exponential power increase >>> with temperature produced by the reaction. >>> >>> With a few moments thought you can come up with a really simple one:- >>> Put the reactor into a stainless thermos flask, cover it with water, and >>> heat it up with its internal heater until the overpressure release of the >>> flask starts to leak steam. Disconnect the power and it should >>> self-regulate and hiss away for hours or days and there is your demo (until >>> it runs out of coolant). If you want a continuous system, then you might >>> need to put it on an electronic scale and organise a little pump to inject >>> more coolant very slowly to just keep the weight constant. >>> >>> Consider a Thermos flask that is capable of keeping tea hot for maybe 6 >>> hours. If we have a 2 liter flask and the temperature drops from 100 down >>> to 70 degrees in 6 hours, then that represents an total heat loss of >>> 4.2kJ/kg/K * 2kg * 30K => 250kJ or an average heat loss rate of >>> 2.5*10^5J/(6h*3600s/h) => 12watts. If we do the calculation a little bit >>> better and assume that it is an exponential decay which is heading for 20C >>> after infinite time then we get a time constant of 12.8h, and the rate of >>> heat loss at the start is simply the total heat divided by the time >>> constant (4.2*10^3*2*(100-20)/(12.8*3600)) => 14.6watts. So this means >>> that if we supply 15 watts of power by some means, then whatever is in the >>> flask will eventually reach boiling point and stay there. >>> >>> So if the reaction can produce more than 15 watts of power while it is >>> held at 100C, then it must remain at this temperature because as soon as it >>> rises above 100C, the water will boil and steam will exit the flask >>> providing an almost infinite heat sink capability (boiling water can easily >>> consume kilowatts of power without allowing the temperature to rise >>> significantly). If 100C is not hot enough then we can either pressurise it >>> (with a simple overpressure valve), or go to a lot more trouble and use a >>> higher boiling point fluid. The sort of silicone oil that they use in >>> diffusion pumps comes to mind. You would need to have a closed system (at >>> least not allow oxygen to get to it I think) but you could easily get >>> boiling points around 300C which could be further raised by pressure. >>> Mercury would be an excellent boiling point coolant for 360C and up. (It >>> used to be used and worked very well in diff pumps before people got all >>> paranoid about it). >>> >>> Rossi's "December Test" suggested a power generation capability of ~2kw >>> while being held at a peak core temperature of approx 500C. The "March >>> Test" suggested a power generation capability of 530w while being cycled >>> around a temperature of approx 320C at the core. Provided the core reactor >>> in the two cases is very similar, we can use these two points to solve >>> Arrhenius' equation for the temperature dependence of the reaction rate. >>> We get a pre-exponential factor of 1.6*10^5 and exponential (activation >>> energy / R) factor of 3380. Arrhenius' equation thus suggests a power >>> generation rate dependent on temperature given by Power = >>> 1.6*10^5Exp-(3380/Temp in K). Using this equation to see what happens at >>> 100C tells us that it should generate a power output of 18.6 watts. >>> >>> So Rossi's reactor should in fact work and generate steam continuously >>> if simply put in a thermos flask and warmed up to 100C! If we were to >>> pressurise a well insulated container to a reasonably easy to obtain >>> pressure of say 10 atmospheres (giving a water boiling temperature of 180C) >>> we would expect to be able to generate 92 watts in a continuous manner. If >>> we were to set up a mercury cooling loop, then we could run it continuously >>> at kilowatt levels with no active control and just a small pump to inject >>> the condensed mercury back into the pressure chamber. >>> >> >> >
