Net Energy and Waste Heat Recovery

[redsnapper]

I’m beginning to think zapkitty’s thermal number is (somehow) measured thermal output of the reactor core (i.e., thermal input to the high side of the conversion cycle), not thermal output of the low side of the conversion cycle. All along, I’ve been thinking (as is Brian H) the latter. In other words, zapkitty’s thermal number includes the electrical number. I suppose they’re well aware of the thermal output of the reactor core, and might choose to report that, just as they’re well aware of the total BTU’s of coal or oil or whatever that goes into a carbon-burning power plant. It’s simply a matter a making sure you read the footnotes in the report.

[zapkitty]

redsnapper wrote: I’m beginning to think zapkitty’s thermal number is (somehow) measured thermal output of the reactor core (i.e., thermal input to the high side of the conversion cycle), not thermal output of the low side of the conversion cycle.

I understand what you’re getting at but my numbers were indeed for the ganged output of the plant cooling towers, i.e.w(t) is the low temperature side of the thermal cycle, and the plant’s total electrical output as w(e). These are two things that can be measured external to the plant and are thus fair game for my manipulations.

The serious question is this: are the aardvark-banana hybrids a valid counter or are they merely a clever diversion?… 🙂

[redsnapper]

A diversion, I think.

So the electrical output leaves the power plant via the grid, and the thermal output via the cooling towers. One does not include the other, and they both came from the fission reaction. Neglecting any other significant losses, the total energy generated by the fission reaction is the sum of the two (1st law of thermodynamics). Efficiency is defined as useful energy output (electrical) divided by thermal input to the cycle, so you must do it the way Brian H has described: eff=w(elec)/(w(elec)+w(waste)).

[Tulse]

Of course, what counts as thermal “waste” in some contexts could be usable thermal energy in others (for example, captured for district heating or industrial applications).

[redsnapper]

Yes, I intentionally said “waste” because the term “thermal” had been used previously without adequate specificity. From the primary power generation cycle’s perspective, it’s waste – but certainly if you can do something else useful with the relatively low-grade heat, it’s not entirely waste.

[Brian H]

redsnapper wrote: Yes, I intentionally said “waste” because the term “thermal” had been used previously without adequate specificity. From the primary power generation cycle’s perspective, it’s waste – but certainly if you can do something else useful with the relatively low-grade heat, it’s not entirely waste.

A qualification necessary: “but certainly if you can do something else useful, at less expense than using ultra-cheap FF electric power for the task, with the relatively low-grade heat, it’s not entirely waste.”

If you spend $0.50/W for added “waste heat exploitation” equipment, 10X the capital cost of another FoFu, you’ll be a long time recovering your investment even with “free” heat. And typically getting much work out of diffuse, low-grade energy sources is very pricey. See wind turbines and solar farms for some of the more grotesque demonstrations.

[zapkitty]

redsnapper wrote: A diversion, I think.

So the electrical output leaves the power plant via the grid, and the thermal output via the cooling towers. One does not include the other, and they both came from the fission reaction. Neglecting any other significant losses, the total energy generated by the fission reaction is the sum of the two (1st law of thermodynamics). Efficiency is defined as useful energy output (electrical) divided by thermal input to the cycle, so you must do it the way Brian H has described: eff=w(elec)/(w(elec)+w(waste)).

… ah, but as external observers we don’t have the temperature or the watts of the thermal input to the cycle… so doesn’t that imply that we can’t get an actual efficiency rating for the plant using external observation and the standard equation?

(The aardnanas move into flanking positions…)

[redsnapper]

What you mean, “we”, Kemosabe? I expect the Japanese engineers know quite well what the temperature and watts of the thermal input is. And because “we” know the first law of thermodynamics, we do to (that is, apparently we do, since you’ve said the electrical and thermal output have been published). I’m not sure what you’re trying to get at here. There’s no mystery about the efficiency, there was only a small disagreement as to whether it was being calculated correctly – not if it could be.

[Brian H]

BTW, same “redsnapper” from the Tesla forums? Who lives in a DomeHome? Welcome!

[zapkitty]

redsnapper wrote: What you mean, “we”, Kemosabe? I expect the Japanese engineers know quite well what the temperature and watts of the thermal input is. And because “we” know the first law of thermodynamics, we do to (that is, apparently we do, since you’ve said the electrical and thermal output have been published). I’m not sure what you’re trying to get at here. There’s no mystery about the efficiency, there was only a small disagreement as to whether it was being calculated correctly – not if it could be.

Just poking around the issue a bit… I can screw up as well as the next neko or even more so 🙂

But the parameters discussed are actually relevant to one of the potential issues that you raised in your initial posts: the local effect of the thermal output of a plant when air cooling is used. I wanted to be sure that the terms I was working with were ones others could agree on.

The solution is a sort of chimney, almost certainly fan-driven. The amount of air moved at a given temp, the chimney height and the chimney diameter would govern the extent of the local heating effect, if any.

Of course it isn’t technically a “chimney” as no combustion products would be expelled… and it would not be a “smokestack” or a “flue” nor would it even be a “cooling tower”… so what would be an benign yet accurate name for this column poking up over the neighborhood rooftops?

As for the stats, in general local ordinances are concerned almost solely with an appropriate flue height for dispersing specific pollutants before they reach the ground… something that is utterly inapplicable to an FF installation… and there are very few mentions of heat. Apparently 99% or more of heat regulation concerns thermal pollution of water… something else that would be inapplicable to a standalone FF station.

But I believe that the dispersion models used to determine standard stack heights would be a good starting point for a cooling system that fits in with the “plug n play” and “zero-impact” attributes of FF… but the varying ordinances in varying localities specify varying models…

[redsnapper]

Personally, I favor the term “cooling tower,” because that’s what it is and does. (Chimney works for me, too – if a chimney is something that moves air from the ground to a higher altitude by virtue of the “chimney effect”, i.e., hot air rises.) I do recall studying (back in grad school) large-scale cooling towers that were entirely natural-convection driven – probably in the context of fission-based power generation. I don’t see why that existing technology wouldn’t be directly adaptable to any power plant, FF in particular.

[Brian H]

Blow hole? Ventilation tower? Convection outlet?
😉

redsnapper — see my question above. Did you come here from TM Forums?

[redsnapper]

Brian H – sorry, missed the previous post! Yes, the very same redsnapper. Sorry it took me so long to check out FF – it was serendipity that I went back a couple of months ago and was rereading posts on the TM Forum from last September, and saw the link (which I’d totally missed the first time around – guess I’m becoming fairly predictable that way :-)). Fusion power has been another lifelong dream of mine. I’d wanted to get into that line of work when I graduated from Caltech, but there weren’t any good jobs in the field for an MSME. Thanks for the connection!

[Brian H]

rs;
you might like to hook up with Rezwan here, or Aaron. (Or, for that matter, Derek or Eric.) LPP is starving for competent hands-on; budgets don’t yet permit hiring the half-dozen or so more people they’d like to have, but if you are enough into the hardware or physics pushes, and want to lend a hand pending the flood of investment that will follow “sci-break-even”, :cheese: I’d guess they’d try hard to make it work.

Just opining. Or saying. Or WAGging. 😉

And, of course, if you are a “qualified investor” type of dude they’d be even more eager to talk to you.

[zapkitty]

Universal Generic FF 5MWe Power Plant

First numbers: keeping things cool with the neighbors…

Plot of land: 24 meters on a side.

Building: 6 meters square, interior height 3 meters, exterior height 4 meters. The height difference is made up of the intakes, fans and ducts of the cooling system.

air cooling

Sufficient volume on intake grills to handle high-altitude/high-temperature locales. More temperate climes can reconfigure to suit.

exhaust duct – probable overkill – double-walled aluminum 7 meters high and 2 meters wide. total duct height from ground level 11 meters.

exhaust air: 46 cubic meters/sec at 250 c
duct diameter: 2 meters at exit
duct flow: 14.6 meters per second

Given the low emissivity of aluminum and the very low emissivity of air this should bring sensible heat outside the fence close to never mind.

Practical examples show that conduction and convection from similar plant heat outputs aren’t a problem for their surroundings with suitable exhaust stacks but still want to run models for insurance.

Thoughts?
Glaring errors?
Musings on the fate of a 50s vintage pickup arbitrarily rescaled to the size of a modern large pickup?

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