Re: solar cars revisited
Posted by:
Peter Brow (IP Logged)
Date: May 10, 2002 08:53AM
<HTML>Hi Tom,
Interesting idea. The Robert McElroy system, described on the "Solar Steam Car" page at my website, does seem to use latent heat of fusion, in that the "thermal liquid" was described as an asphalt-like material which underwent a phase change (between solid and liquid) during heating or cooling. However, the latent heat of fusion of metals might be higher per pound. Sodium in sealed pellets might be nice -- until the pellets wear and leak. Then the steam generation rate would really take off! Or perhaps molten lead inside of steel pellets. Some calculations on the recoverable heat per pound of weight of various heat-storage media would be useful.
I've done some math on bead-type heat exchangers, and yes, the weight/volume per unit of heat-exchange area can be amazingly low with small beads -- esp around the size of BB's. Then again, most heat battery systems operate with much lower temperature differentials than steam generators fired with hydrocarbon fuels, so much more heat exchange area is needed for a given steam output.
Bead-handling systems tend to be noisier and more prone to wear than liquid-handling systems, but there may be ways to reduce wear and noise to acceptable levels.
Small size and light weight have been claimed with phase-change molten salts as heat storage media, but these tend to be toxic, costly, and/or highly corrosive.
Peter</HTML>