Re: Candle fans in _Sun of Suns_

Wasn't it DJensen who wrote:
Mike Williams wrote:
Wasn't it DJensen who wrote:
In Karl Schroeder's _Sun of Suns_, Aerie is an air-filled megastructure x million kilometres wide, warmed internally by artificial suns and populate by unfortunate people clinging to wooden wheels and an asteroid or two orbiting the collective centre of gravity.

All that taken for granted, would the candle fans mentioned in the book really be necessary in microgravity? Candle sconces and the like are fitted with tiny fans to keep air feeding the flames. Wouldn't the candle's heat be enough to create a temperature gradient to expel the oxygen-starved air in the immediate vicinity and draw in negligibly-cooler O2-rich air to keep the light going? Fans imply the heated CO2/nitrogen would stay put/expand equally in all directions until the flame choked itself out.
In the absence of gravity, the temperature gradient doesn't cause any air movements.
In a gravity field, the lighter gasses near the flame are displaced by the heavier cold air from further away because the gravity pulls more strongly on the heavier air.

I suppose even in microgravity I was expected hot/energetic air to just /move/ and trigger convection. That is obviously not the case aboard the shuttle, but Aerie is basically a mini gas giant with enough gravitational pull to keep an asteroid or two orbiting the fake sun at the core. Central to the plot is the importance of light and heat of suns (there are multiple smaller artificial suns), and the frozen outermost extremes of the atmosphere (where inverted glaciers grow until their mass causes them to detach and sail inward). Is all of that >wrong?

I don't really follow your description, and have not read the book. If the dynamics of the whole thing are going to be reasonably stable over the medium term, then the atmosphere must rotate in a way that matches the orbit of the asteroids, otherwise they experience drag and spiral into the centre. And that in turn means that all the orbiting bodies must orbit in the same direction in the same plane.

If there's an outer envelope to the structure, then it also needs to rotate to match the rotation of the atmosphere. Ice that condenses at the equator of the envelope is stable and if any gets detached it orbits continues to orbit there. Ice that condenses at the poles of the envelope is not stable, if any gets detached then it falls straight down towards the centre. Ice that condenses at intermediate locations on the envelope will initially fall into an elliptical orbit, but atmospheric drag will circularize and equatorialize the orbit after a while.

If the envelope and asteroids are not in stable orbits, but maintain their position by being actively powered, then the atmosphere and envelope need not rotate and ice would fall straight down from any point on the envelope.

Thinking of glaciers probably isn't helpful because it suggests solid masses of ice, but that solid ice only exists because it was initially compressed by the weight of overlying layers of snow. In the absence of gravity, the ice might condense into soft light snow powder. Or it might form into a relatively solid mass like the frost in my freezer.

--
Mike Williams
Gentleman of Leisure
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