John Baymore on tue 18 jun 96
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3) How come the outside of the tank frosts up as it's being used? .......
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Propane in compressed form is a liquid. Most pottery burner systems burn
propane in the gaseous form. To get from a liquid to a gas, the propane
evaporates. The evaporation process cools the liquid in the tank (it is an
endothermic process....it takes heat energy). The more quickly you evaporate
the propane the more quickly it cools the remaining liquid. The smaller the
"store" of liquid propane, the less available heat energy is stored in its
"thermal mass". If there is little liquid gas storage and the draw rate is
high, (typical portable raku setup) the liquid propane can get QUITE cold.
Below the freezing point of water. Hence the "frost" on the outside.
Interestingly, and of consequence to the potter, as the liquid propane cools,
the ability to evaporate gas off of it decreases. So if the store of liquid gas
gets too low a temperature relative to the desired evaporation rate, the gas
can't evaporate fast enough to keep up with demand. The burner "chokes" (runs
out of gas to burn). Your kiln stops climbing.
.........................john
John Baymore
River Bend Pottery
Wilton, NH
76506.3102@Compuserve.com
http://www.CraftWEB.com/org/jbaymore
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