Hydrogen is amazingly good for heat transfer. Rossi and Defkalion are both using H2 of 2.5-5MPa, and at 600°C that will have density of about 0.7kg/m³ or greater. At that density 4µm nickel powder particles (As defkalion are specifying) will need a hydrogen flow velocity of about 0.5m/s to pick it up against the force of gravity (from bernoulli's equation).
Please Note that the following calculations are very basic, and not that accurate, but give some indication about the size of flow speeds in the reactor. If the centre of the reactor is 600°C and the walls are 350°C then there is about 0.2kg/m³ hydrogen density difference between them, (about 2N/m³ in earths gravitational field). A reactor height of 50mm with that density difference would give about 2x0.05= 0.1Pa of driving force, and that pressure (from bernoullis equation again with 0.7kg/m³ density) would be equal to the dynamic pressure of hydrogen flowing at about 0.5m/s. So the powder is probably almost being picked up and circulated by the hydrogen. If the reactor was (taller) then the circulation of hydrogen would get faster and the powder would almost certainly start to get slowly blown around making a fountain in the hot middle of the reactor that would fall down the colder walls, gradually circulating the powder around the reactor. Also if the powder was smaller diameter then it would take less H2 flow speed to lift it up. But even without the particles moving you can see that the hydrogen will circulate (convect) in the reactor, fountaining up in the hot middle and dropping down the cool sides. Any hot spots will also increase the flow speed of the hydrogen locally in that spot due to reduced hydrogen density. The overall circulation of hydrogen will work to even out the temperatures throughout the powder very quickly, and if you want to increase the flow speeds and heat transfer then it is useful to have a taller reactor to increase the driving pressure (like a thermosiphon). http://en.wikipedia.org/wiki/Thermosiphon If you are very worried then you could also use a mechanical shaker to move the powder around and limit formation of hot spots. On 25 January 2012 21:20, mårten Sundling <mar...@krteknik.com> wrote: > Hello > Thanks for a great number of input. > My concern have been that the powder might just sit there as a pile > Be badly avaliable to the h2 and get > so hot by the bad cooling that it melts, I'm BTW using micrometer powders > at the moment by rossis specs, but it sounds like I will use nano powder.... > I thought that I might overcome those hurdles by using a conductive porous > substrate, but that might not be the case then. > What's your opinion about using acetylene and nickel instead of > nickel,carbon,h2 a idea that is floating around.. > Marten > > Skickat från min HTC > > ----- Reply message ----- > Från: "Robert Lynn" <robert.gulliver.l...@gmail.com> > Till: <vortex-l@eskimo.com> > Rubrik: [Vo]:Nickel honeycomb ? > Datum: ons, jan 25, 2012 22:00 > > > I think are a many potential downsides to using bulk material substrates > (foams, foils, wires) with nickel coatings. > - you might get large and non-homogenous transient temperature changes > throughout the reactor and this could lead to deformation and even breakup > of large continuous scaffolds. > - it prevents transport of powder throughout the reactor (which may be > important for continuous operation in terms of subjecting the nickel to > varying temperatures or physical impacts to create hydrogen flux through > the nickel surface) > - a foil type substrate may constrain or otherwise limit convective flow > of hydrogen (particularly if there is thermal deformation of the > substrate), allowing hot-spots to form and creating worse > temperature inhomogeneities throughout the reactor. > - thermal expansion and material crystalline structure phase changes > caused by temperature change or hydrogen loading can lead to large > dimensional mismatches and stresses between substrate and nickel - leading > to the nickel coating flaking off etc, at which point why not just use > powder anyway? > - the processes by which you apply the nickel coating to the substrate may > have limitations and so not be optimal for creating the exact chemical > alloy makeup and surface topologies required for best LENR performance. > - making nano-powder will almost certainly be cheaper than any plating > procedure. > - harder to recycle substrate with nickel coating > - very easy to replace nickel powder in a reactor. > - one or more of the above problems will probably impose a lower > temperature limit on the process than the nickel powder would have by > itself. > > Hydrogen convection driven by buoyancy will likely slowly agitate and > transport nickel nano-particles throughout the reactor, with radiation at > high temperatures and physical contact of the blowing nickel particles with > the walls also enhancing heat transfer. > > That does not mean nickel on a substrate won't work, but it appears to > come with more potential problems, temperature limitations and higher > fabrication and running costs than nickel powder, with few if any benefits > that I can see. So unless you have other compelling reasons for a > substrate I think you may as well just stick with the nano powder. > > On 25 January 2012 19:28, <mar...@krteknik.com> wrote: > >> Hello guys >> I have a q, i have been reading all the posts about the problems with >> energy transfer, core melts and so on . >> Why not embed the nickel / catalyst mix in a honeycomb, or other >> structure that gets easy acess for both H2 and >> heat trasnfer to the walls of the tube ? >> >> >> Is there any practical method of doing this? >> I have thought about covering steel or other material with nickel as so >> many other people, but in my mind that decrease the surface >> too much, a fungi or honeycomb like structure would maybe work, but how >> to make one ? >> >> Any ideas ? >> >> >> Marten >> >> >
