Electro heat - How much heat can I generate?

[Joffre]

Housing batteries in an enclosed aluminum tube. Batteries will need to heat up the housing to 80-100 decC for 40-50 minutes. Dimensions of housing are 2 inch diameter by 24 inches long. Question - Is there a battery that could generate enough heat over that time period and fit in the housing described? Or am I asking to much?

 

[JimB]

Too many unknowns.

Is the tube thermally insulated?
What is the U value of the insulation?
What is the ambient temperature outside the tube?

JimB

 

[Joffre]

The batteries need to heat the aluminum tube to melt through wax plugs in a steel pipe. There could be insulation between the batteries and housing but need to use the battery power to heat the housing to melt the wax. Temp outside the tube is ~20 degC

 

[Les Jones]

You will need to provide the following information.
1 The initial temperature of the wax
2 The melting point of the wax.
3 The specific heat of the wax (In it's solid state.)
4 The latent heat of fusion of the wax
5 The mass of the wax that needs to be melted
6 The rate of heat loss from the steel tube when it is at about 100 Deg. C

This information needs to be uses to calculate the number of calories (Or BTUs) required to first raise the temperature of the wax to it's melting point an then to actually change the state of the wax from solid to liquid. This quantity of heat will then have to be convered to watt hours of electrical energy. The batteries will need to have a capacity to provide somewhat more than this amount of energy.

Les.

 

[spec]

If you could fill the whole of the tube with Litium Iion (LiIon) electrolyte, you would get 783 watt/hours, according to my rough calculation. In practical terms you may be able to achieve half of that= 391 W/H. At a guestimate the aluminum tube would have a thermal resistance of 0.1 DegC/W so that would give a delta tube to ambient of 39 Deg C. So if the ambient temperature were 25 Deg C nominal, the surface temperature of the tube would be 25 Deg C + 39 Deg C = 64 Deg C.

This is all very notional just to give a rough feel for the situation.

But the overriding factors are as Jim says in post #2. For example if the tube were in a vacuum you could more of less heat it to any temperature you liked.

In addition to the above factors, there are practical considerations. Batteries do not like operating at high temperatures and worse still they become dangerous above a certain temperature.

So in summary, my feeling, for what it is worth, is that what you are considering is not viable. NASA may be able to do it though.

spec

PS: I would love to know what you are using the tube for.

 

[alec_t]

You would also need to be sure that the batteries could withstand 100C for 45 minutes.
Why must the device be battery powered?

 

[Les Jones]

Hi alec,
I have noticed recently that some new forum members appear and just make pointless comments on old posts. There was one recently where the new member just copied some text from a previous post on the thread and just posted the copied text without even a comment about it. (I think it was a different new member.)

Les.

 

[JimB]

I have noticed recently that some new forum members appear and just make pointless comments on old posts.

Usually an indication of a potential future spammer.
The moderators have a fix for that.

JimB

 

[Joffre]

I appreciate the feedback, sorry for not replying sooner. The initial temp of the wax is 10-20 degC, meting point of the wax is 60-70 deg C, pressure inside the pipe is 1-2MPa. Spec, your comments are very interesting; I'm also trying to heat this tube using a exothermic reaction but pressure buildup is getting in the way of that idea.
I honestly can't answer all the question because every situation would be different. My goal though would be to maintain 80 degrees of heat on this tool for 40-50 minutes. The heat transfer to melt the wax would have to be estimated.