From Francesco
Dear Colleagues,
I am analyzing the latest results, made by Constantan (600L) and Pt wires (diameter 100micron).
More recently I made a mixture of H2(30%) and Ar (70%).
The total pressure was 3 bar ABS, slowing decreasing over time the amount of H2 (more permeable).
* I have the strong "feeling" that the most important parameter is the HIGH temperature.
I found a larger increase of performances when the Pt temperature, in mean, was >430°C.
My suggestion is to increase the temperature of the wire/cell as much as possible, with SOME H2 added.
My best,
Francesco
Comments
I'd say that this effect could account for a output heat overestimate of about 5% (ballpark figure).
My suggestions are:
(1) Do a thorough temperature sweep test with supposedly inert wires (NiCr). While keeping the same input power, vary the diameter and/or the number of wires in the calorimeter (i.e. you have to vary the radiating area, which is the total wire surface). Plot T_ext vs "total wire surface radiating area".
(2) Paint one of the copper bands that hold the thermocouples with an IR absorbing paint (just paint the internal-facing side), and see if this worsen the "temperature dependence behavior" of the thermocouple being held by the painted copper band.
(3) Switch to a 100% opaque calorimeter as soon as possible.
Although it's true that in general borosilicate glass is rather opaque to IR, it still allows a relevant amount of energy to leave the cell though that pathway, especially as temperatures get increased. Furthermore, the fact that the wires and the interior of the cell aren't ideal blackbodies adds much uncertainty to exactly how much emitted energy leaves the cell. I think this is a good reason to use 100% opaque tubes.
Here's a spectral radiance chart calculator, by the way:
wolframalpha.com/.../...
The borosilicate glass is very opaque to IR. I do not think much of the heat radiates out. It also is a rather good thermal conductor, so it will tent to lose heat that way pretty well.
The temperature/exc ess power behavior (yet to be confirmed - I have to stress this - but very promising) of the latest multi-wire CTC cell experiment indeed seems to point to this. This is why I've been telling to crank up input power to make temperatures increase to 500°C and beyond. The excess power rise with temperature seems exponential, but at lower temperatures you're basically playing with hard to measure sub-watt excess heat.
Unfortunately due to technical limitations increasing temperatures substantially just isn't possible in standard glass tube cells. Also, the very fact that they're transparent means that much input energy leaves the cell without heating the wires and that therefore it's wasted.
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