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From: Sam Nichols
Subject: Re: Help creating a heating element from resistor.
Date: Tue, 10 Dec 2002 14:46:53 -0800
User-Agent: MT-NewsWatcher/3.2 (PPC Mac OS X)
In article ,
> Sam Nichols wrote:
> > In article ,
> > wrote:
> >> Sam wrote:
> >> > In article ,
> >> > "George R. Gonzalez" wrote:
> >> >
> >> >> "Sam" wrote in message
> >> >> news:sizam-6B65B5.firstname.lastname@example.org...
> >> >> > Hello,
> >> >> > I'd like to create a small heating element running on as low a
> >> >> > voltage/current as possible and heats up to about 250 deg C. I'd like
> >> >> > to pump a fluid over it and have that fluid vaporize.
> >> >>
> >> >> We need a bit more info. How much fluid do you want to vaporize
> >> >> per unit time? What's the heat capacity of the fluid? What is its
> >> >> boiling point temperature? What is its heat of vaporization?
> >> >>
> >> >> Witht hat info we can calculate how many watts is required.
> >> > I'm not quite sure what the flow rate will be yet, pretty low, I'll be
> >> > using as small a pump as possible. Everything togeather should weigh
> >> > 3oz or less and another 2oz of liquid, the 3oz includes a battery to run
> >> > this on. The fluid is oil, don't konw what the heat capacity is, flash
> >> > point is 240 deg F, API gravity is 38.3. I was looking at a site that
> >> > carries Nichrome wire and they had some tables to help figure out what
> >> > you need (http://www.wiretron.com/nicrdat.html). It looks like if I
> >> > used AWG 40 wire I could get by with only needing to generate about 8
> >> > watts which I could get from 2 1.2V batteries at 3 amps. Is Nichrome
> >> > more efficient at generating heat from electricity then a resistor?
> >> No.
> >> Why do you want to evaporate oil?
> >> Off-hand, I'd say it's not going to happen, as the battery would be
> >> too heavy.
> > Sure it could happen, I have 1000 mAh NiMhs that weigh 0.75 oz each,
> > which leaves 1.5 oz for a pump which will be mostly plastic and a tiny
> > motor, and some Nichrome wire which seems like it'll weigh close to
> > nothing. I guess it might be closer to 4 oz which could still work. I
> > want to vaporize oil for a tiny smoke machine.
> > Anybody know a place that carries Nichrome in the Bay Area?
> Oh, it'll work.
> I'm just unsure as to for how many seconds.
> My gut says there is no way in hell you'r going to get enough energy from
> a battery that small to vapourise three times it's weight in oil.
> However, numbers are good.
> The first fog generator numbers I found were 20Kw evaporating 40l/hour,
> or 1Kw=2l/h. Maybe 1Kw/Kg/h.
> So, 60g of oil...
> Say you want to use it all in 6 mins.
> That's 600g/hour.
> So, you need a power source of 600W.
> That AA cell won't supply 500A, and it certainly won't do it for
> 6 minutes.
> The energy in an AA cell is about a watt hour, so you can evaporate a
> whole gram of fog. The oil container won't need to be very big.
> It'll produce about 20 cubic feet of fog a minute for 6 minutes.
Yah, you're right, I've come to the conclusion that a couple AA batts
won't do the trick, so I've modified the plan a little. Now I'll be
sucking off 1-2A from an already existing 8-cell battery pack which
gives between 10-12V. If anything it'll save me 1.5oz since I won't be
adding a 2nd battery pack for this smoke generator. Where are you
getting your numbers from btw? I was looking at some stats for Nichrome
wire and if I used 40 AWG wire looped around (probably a ceramic or
metal tube) the chart said I should get roughly 400 deg F out of about
13 watts. I only need 240 to smoke my oil so I imagine I could tone it
down to 10 watts or less which is well within (1-2A)*(10-12V).
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