- #1
rhenretta
- 66
- 0
I have a video on youtube about a crooke's radiometer, and one of the comments referred to a line from wikipedia about thermal transpiration:
I also found a thread about this very subject several years back, but the one link I was interested in (a paper in arxiv) was outdated, and I couldn't find the article. None of the links on Google were very trustworthy.
I have a problem with this, because the warmer area would create an area of slightly higher pressure, and that would flow to the area of low pressure - the cool side. The idea that the gas would flow from cold to hot would violate my understanding of physics. Is the idea of thermal transpiration accepted in academia, or is it nothing but an analogous urban legend?
The final piece of the puzzle, thermal transpiration, was theorized by Osborne Reynolds[3], but first published by James Clerk Maxwell[4] in the last paper before his death in 1879. Reynolds found that if a porous plate is kept hotter on one side than the other, the interactions between gas molecules and the plates are such that gas will flow through from the cooler to the hotter side. The vanes of a typical Crookes radiometer are not porous, but the space past their edges behaves like the pores in Reynolds's plate. On average, the gas molecules move from the cold side toward the hot side whenever the pressure ratio is less than the square root of the (absolute) temperature ratio. The pressure difference causes the vane to move, cold (white) side forward.
I also found a thread about this very subject several years back, but the one link I was interested in (a paper in arxiv) was outdated, and I couldn't find the article. None of the links on Google were very trustworthy.
I have a problem with this, because the warmer area would create an area of slightly higher pressure, and that would flow to the area of low pressure - the cool side. The idea that the gas would flow from cold to hot would violate my understanding of physics. Is the idea of thermal transpiration accepted in academia, or is it nothing but an analogous urban legend?