In reply to David Roberson's message of Fri, 18 Jan 2013 14:10:12 -0500 (EST): Hi, [snip] >I was thinking of a system that appears to take thermal energy and convert it >into mechanical energy in a useful manner. The net effect is that the system >cools down in response. > > >Suppose that a group of hot heads lives within a world that is at a very high >temperature, so hot in fact that everything radiates visible light instead of >the long wavelengths associated with our environment.
That would be us, on a hot day. ;) > I guess it would resemble the surface of the sun to produce our standard > spectrum. > > >These guys construct a photoelectric cell that takes some of the ever present >light and converts it into DC voltage that is used to drive a motor. I have suggested several times in the past that a solar cell effectively "rectifies" sunlight, producing DC current. Since DC has a frequency of zero, it represents a body that doesn't radiate, i.e. it is effectively at absolute zero. IOW, ideally, heat/light goes in and is stored (in a battery). Nothing comes out (depends on your definition of system boundaries). > The motor is used to transport material from the surface of their world into > a higher location thereby producing gravitational energy. This is the equivalent of storing the energy in a battery. > > >Since light energy has been converted into mechanical work, less of it is >present within the system so the world gets a bit cooler. Every body radiates and gets cooler all the time. Most of the time however it receives just as much energy as it radiates, so it is in thermal equilibrium with it's environment (the exception being active cooling/heating devices). >There is little doubt that the overall energy is conserved, but it does not >seem to require a low temperature heat sink for this engine to exhaust the >high temperature heat into. Correct. Low temperature heat sinks are only required where the energy remains in the form of molecular kinetic energy throughout the process. Conversion to potential rather than kinetic energy can remove the requirement for a low temperature heat sink. Which BTW is why wind chill is capable of cooling water below ambient temperature. Energy is stored as potential energy when the hydrogen bonds between water molecules are broken. Only a very tiny fraction of the energy required to create the temperature differential is supplied by the wind. This is because the wind only removes the molecules once thermal energy has separated them. Once they are separated they are effectively "at infinity" relative to one another, so the attractive force between them is only a minute fraction of what it was when they were bound together by Hydrogen bonds in the liquid. It is only this remaining minute attraction that needs to be broken by the wind. > > >It appears that the cold space surrounding a system can be used as the cool >sink if another is not available. ??????? >In principle this suggests that it should be possible to take any system that >is above absolute zero temperature and extract heat from it which can be >converted into another form of energy. For some reason, this seems to be >getting a free lunch and I must be missing something. You fear you may be violating the second law of thermodynamics. ;) > > >Support for this hypothesis is evident by observing the radiation of thermal >energy from hot bodies into free space. The body cools down as it loses >energy as would be expected, but perhaps there are other ways to cool it down >besides radiation as the hot heads discovered. The process I proposed is very >much like the conversion of gravitational energy of a gas into heat as the >cloud collapses; only in reverse. > > >Is this assumption wrong? Expanding gasses often cool down. That's how refrigerators work. :) Unfortunately, all you have really shown is that solar cells can harvest energy, which we already knew. ;) Regards, Robin van Spaandonk http://rvanspaa.freehostia.com/project.html
