Consider this issue in the context of Dave Roberson's analysis. Suppose
there is a critical temperature where XH suddely appears in part of the
fuel. That heat pulse could propagate rapidly through the fuel, causing
the positive feedback Dave identified. Such a hot spot could increase
pressure and stress on the tube very quickly, leading to failure.
It seems likely that given a thermal time constant of several seconds or
more, negative feedback control of the heater by an external
thermocouple won't be fast enough to catch a runaway reaction. A
pressure sensor would be much faster, but there would still be
substantial delay as heat would continue to propagate through the tube
into the core, after heater power is cut. Bob's fan-assisted convection
cooling is a good safety measure, but will it be fast enough? I look
forward with great anticipation to his experiment.
This is a classic servo problem, and two other solutions come to mind.
The system could run open-loop, with an algorithm that reduces heater
power as the core approaches the critical temperature. Lots of research
and data collection are needed to fine tune the control parameters, and
those will vary between cores and fuel mixtures.
What if the reactor used induction heating rather than a resistance
coil. The heat is generated directly in the fuel mass, so the thermal
response time is much faster. With a pressure sensor, maybe the control
loop would be quick enough to correct for the positive feedback at the
critical temperature.
On 3/2/2015 10:57 AM, Bob Higgins wrote:
Yes, this is why I was worried about Alexander's new design that puts
an air gap and another ceramic around the reactor core - increasing
its thermal resistance to the lower temperature air around it and/or
the water in the calorimeter. He already showed that if he put alumina
powder insulating the reactor (to lower the input power to get it high
temp) that it failed catastrophically.
I am working on a large water volume calorimeter in which to test my
Parkhomov-like reactors. It will include a variable convection fan to
change the thermal resistance between the reactor tube and the cool
water in the surrounds. This convection will only be activated if the
heater coil power is turned off and the temperature of the reactor
continues to rise. The intent in this design is for the water to
never reach boiling. Also, the calorimeter will be a good shield for
any explosive shrapnel (primarily alumina shards). The calorimeter
also provides a port to measure radiations with low mass density
between the reactor core and the sensor. Here are 2 links to diagrams
of the calorimeter I am building:
https://drive.google.com/open?id=0B5Pc25a4cOM2R1RYemRlTEdZSEE&authuser=0
https://drive.google.com/open?id=0B5Pc25a4cOM2dWh5VXJFSU1uT1U&authuser=0
Here is the link to my planned ZDV plumbing that will allow me to
measure the pressure, sample the gas product, and vent the system
before opening the reactor post-experiment.
https://drive.google.com/open?id=0B5Pc25a4cOM2WU9MR3hyQ2NIWkE&authuser=0
As Bob Greenyer likes to do, he has dubbed this system in ASCII as
"{Garbage Can}".
Bob
On Mon, Mar 2, 2015 at 11:40 AM, Roarty, Francis X
<[email protected] <mailto:[email protected]>> wrote:
Thanks Bob, that is great information but I still have a nagging
concern that thermal loading is more important than anyone is
currently aware and that XH needs an environment that is robustly
subtracting heat away from an otherwise self destructing cell to
rise above the noise. IMHO researchers need to perform something
equivalent to an isometric where they are vigorusly fighting their
own heating effort via thermal loading and then repeatedly push
the drive thru the threshold temp while slowly increasing the
load..and …with luck..decreasing the drive [I think this what
Rossi has been doing]. The stories about life after death,
evaporating water and explosions where reactors were left leaning
in a bucket of water may have created a thermal gradient centered
about the waterline that eventually favored a particular area
within the tube and powders with just the right properties to run
away…. Shot gunning by accident.
Fran
