Fan ovens are baked. They have a fan in the back... well, it's not really a fan in the traditional sense, more enthusiastic circular swirling. The point is to disrupt the normal convective currents that would be set up inside the oven.
I propose the reverse. Install a fan system to set up a nice powerful vertical cyclone. The denser, colder air will be on the outside, the hotter less-dense air will be in the middle. With a bit of calibration, you should be able to cook potatoes at 220C and beef at 190C in the same oven.
To be marketed heavily, by Dyson, since it's unnecessarily complicated.-- bs0u0155, Apr 05 2014 You sure the hotter air will be in the middle? http://en.wikipedia.org/wiki/Vortex_tubeNot that it's necessarily the same in an oven. [mitxela, Apr 05 2014] unnecessary complications [+]-- Voice, Apr 05 2014 There are no unnecessary complications, only unnecessary people.-- MaxwellBuchanan, Apr 05 2014 That's <link> a specialized system. This will be much more of a standard vortex. Way slower, much bigger diameter to height ratio, it should just act on density like a standard cyclonic separator.-- bs0u0155, Apr 05 2014 You may not need to go to such lengths; this is sort of how a cutting torch works, only with a jet of oxygen instead of a fan. Undoubtedly some clever pyromaniac could scale such an arrangement up to oven size.-- Alterother, Apr 05 2014 I've always wondered how you get the potatoes to do hotter than the beef without two ovens - I've normally had to resort to giving them more time at the end and turning the heat up when the beef is resting/turning to ice. This solves all of those problems. [+]-- TomP, Apr 06 2014 Shirley the solution would be to have no fan in the oven, and simply let the air stratify to give a hot top and cooler bottom, as ovens used to do?-- MaxwellBuchanan, Apr 06 2014 [TomP], it's because potatoes are better at holding their water than beef.-- Alterother, Apr 06 2014 random, halfbakery