TL;DR

I have a question about heat transfer in a vacuum chamber.

Assume the chamber is not externally heated. Instead, its outer surface is exposed only to ambient air at about 30°C, so the stainless steel walls gradually reach approximately the ambient temperature.

In a vacuum, there is essentially no convective heat transfer. My understanding is that the chamber walls, having absorbed heat from the surroundings, will emit thermal radiation into the chamber.

My questions are:

1. Will all the inner stainless steel surfaces (side walls, bottom, and top lid) radiate heat toward the product?
2. Will the top lid, being directly above the tray of fruit slices, also radiate heat downward onto the product?
3. Is the thermal radiation from the chamber walls sufficient to transfer a meaningful amount of heat to the fruit slices, or would the effect be negligible at an ambient temperature of only 30°C?

TL;DR: I have a question about heat transfer in a vacuum chamber.

Suppose I have a vacuum chamber made entirely of stainless steel and it is completely enclosed on all sides. Inside the chamber, fruit slices are placed on a tray for vacuum drying.

Assume the chamber is not externally heated. Instead, its outer surface is exposed only to ambient air at about 30°C, so the stainless steel walls gradually reach approximately the ambient temperature.

In a vacuum, there is essentially no convective heat transfer. My understanding is that the chamber walls, having absorbed heat from the surroundings, will emit thermal radiation into the chamber.

My questions are:

1. Will all the inner stainless steel surfaces (side walls, bottom, and top lid) radiate heat toward the product?
2. Will the top lid, being directly above the tray of fruit slices, also radiate heat downward onto the product?
3. Is the thermal radiation from the chamber walls sufficient to transfer a meaningful amount of heat to the fruit slices, or would the effect be negligible at an ambient temperature of only 30°C?

I would appreciate an explanation based on the principles of thermal radiation and heat transfer in a vacuum.

The earth has an atmosphere after all. :)

It's also why frost can form even when the air temperature is a few degrees above freezing.

This discussion also reminds me of the sudden temperature drop often observed during a solar eclipse.

TL;DR: I have a question about heat transfer in a vacuum chamber.

Now suppose the tray with the fruit slices manifests somehow. The cavity's radiation will heat or cool it to 30 ℃.

That temperature will also tend to evaporate whatever water is in the fruit. The partial pressure of water at 30 ℃ is 4.24 kPa, so the evaporation will continue until your cavity's vacuum becomes filled with water vapor up to that pressure assuming there's enough water in the fruit. If so, the drying may not be complete as some water may remain in the fruit. If not, the drying will be essentially complete and the final pressure in the cavity will be less or equal to 4.24 kPa. (I say "essentially" because water vapor in the fruit at 4.24 kPa or less is essentially dry.)

Of course, if your vacuum is being maintained with a pump then all the water will be pumped out as vapor and the fruit will eventually be perfectly dry.

So if your goal was to completely dry the fruit, either maintain the vacuum with a pump, or size the cavity large enough for the expected amount of water in the fruit.

TL;DR: I have a question about heat transfer in a vacuum chamber.

Suppose I have a vacuum chamber made entirely of stainless steel and it is completely enclosed on all sides. Inside the chamber, fruit slices are placed on a tray for vacuum drying.

Assume the chamber is not externally heated. Instead, its outer surface is exposed only to ambient air at about 30°C, so the stainless steel walls gradually reach approximately the ambient temperature.

In a vacuum, there is essentially no convective heat transfer. My understanding is that the chamber walls, having absorbed heat from the surroundings, will emit thermal radiation into the chamber.

My questions are:

1. Will all the inner stainless steel surfaces (side walls, bottom, and top lid) radiate heat toward the product?
2. Will the top lid, being directly above the tray of fruit slices, also radiate heat downward onto the product?
3. Is the thermal radiation from the chamber walls sufficient to transfer a meaningful amount of heat to the fruit slices, or would the effect be negligible at an ambient temperature of only 30°C?

I would appreciate an explanation based on the principles of thermal radiation and heat transfer in a vacuum.

However, radiation intensity depends on temperature. At only 30 °C, the radiant heat flux is relatively low. The thermal input from the chamber wall is small and often negligible for vacuum drying processes.

[Moderator's note: Off topic personal theory content deleted.]

The 'Gazebo Effect' is just like the Greenhouse effect. The roof will be not far from 0C whereas the deep sky will be well be at a much lower temperature with only clear air in the way so the re-radiated heat will hit your face and you will feel it. (Albeit still pretty damn chilly)

A lot of this stuff is far from intuitive (as many climate deniers have found out).

TL;DR: I have a question about heat transfer in a vacuum chamber.

Suppose I have a vacuum chamber made entirely of stainless steel and it is completely enclosed on all sides. Inside the chamber, fruit slices are placed on a tray for vacuum drying.

Assume the chamber is not externally heated. Instead, its outer surface is exposed only to ambient air at about 30°C, so the stainless steel walls gradually reach approximately the ambient temperature.

In a vacuum, there is essentially no convective heat transfer. My understanding is that the chamber walls, having absorbed heat from the surroundings, will emit thermal radiation into the chamber.

My questions are:

1. Will all the inner stainless steel surfaces (side walls, bottom, and top lid) radiate heat toward the product?
2. Will the top lid, being directly above the tray of fruit slices, also radiate heat downward onto the product?
3. Is the thermal radiation from the chamber walls sufficient to transfer a meaningful amount of heat to the fruit slices, or would the effect be negligible at an ambient temperature of only 30°C?

I would appreciate an explanation based on the principles of thermal radiation and heat transfer in a vacuum.