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re: i want to build a simple steam generator..help reqd
27 jun 1996
gary rimmer wrote:
>i am trying to create in essence a smaller version of a steam
>generator used in the commercially available steam baths...
interesting problem...
>i am wishing to inject steam from this boiler in to a volume of air
>(35 cubic feet) to enable me to:-
>
> i) raise the environmental temperature to approx. 110 deg f from room
>temperature (65 deg f) within say 5/10 minutes,
hmmm. raising the temp of 35 ft^3 of air 45 f might take about 35/55x45
= 29 btu of heat.
> ii) raise the humidity from approx. 40% to near 100%.
hmmm. 65 f air at 40% rh has 0.4x0.0133 = 0.005 lb of water per pound of
dry air. 110 f saturated air has 0.06 #w/#da, and a pound of that air is
about 15 ft^3, so you want to add about 0.055x35/15 = 0.13 pounds of water
to that air, which takes another 128 btu or so.
>does the unit need to produce steam at atmospheric pressure...
sounds ok...
>i would like the unit to have a large enough water capacity to enable
>the unit to run continuously, without refilling, for up to 45 mins.
suppose the steam room is airtight, a 4' cube with r10 insulation and no
thermal mass, with a thermal conductance of 6x16ft^2/r10 = 9.6 btu/hr-f.
let's call this 10. then keeping it 45 f warmer than the surroundings for
45 minutes will take 45/60x45x10 = 338 btu, the energy needed to evaporate
about 1/3 pound of water.
>from some initial enquiries i believe i need a 3kw unit with a minimum
>water boiler capacity of approximately 5 litres. do these figures seem
>about right ?
maybe, if you are trying to heat a ceramic enclosure. if you heat one made
with very thin wood over foamboard, you might need closer to 100 watts and
a cup of water.
>as to the control side, i would also like to be able to regulate the
>amount of steam produced by means of a stepped on-off output switch
>with say, a 1...10 circular control dial apart from a stepped output
>control dial. i would also like to incorporate a cut-off switch for
>low water level.
how about a 240 v swan 3 kw 1.7 liter automatic teakettle, with a piece of
high temp plastic tubing pushed into the ~1/2" hole in the spout? you might
add some thermal mass to the auto shutoff thingie, eg a bit of copper wire
wound round it, so as to delay but not interfere with its operation. you'd
want to rig up some remote safe way to push on the start button...
nick
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