Phase change material ...

[Dan Bloomquist]

thermate at india.com wrote:

> On Mar 8, 5:57 pm, "martinl" <goo... at mllengineering.ca> wrote:
> 
>>Hi All,
>>I'm looking for a substance that does a phase change at between 60 and
>>100 C.
>>
>>I need something with a high heat capacity so that when it cools
>>through the phase change, it stays at the freezing temperature for as
>>long as possible.
>>
>>Also it needs to be non toxic since it will be handled.
>>
>>Any thoughts?

I settled for hurricane wax. (IGI-1260). But that, because I felt it 
would suit my application, domestic heating. I have 3 thousand pounds of 
the stuff.

> If you want to arrest the temperature of your system using phase
> transformation, you probably need good thermal conductivity of the
> phase change material.

My biggest concern as I build the heat exchangers. Here is a photo at a 
previous state.

http://lakeweb.com/boiler/tubes.jpg

The tubes on the left are for steam condensation. I didn't think I would 
need to cover the volume that well with them because the wax will melt 
around them and convection currents will distribute the heat. But the 
heat sink tubing, (two rows on the right), are double and much longer 
with back and forth winding. When all the tubing is in there will be 
much vertical support, brazed, half inch EMT. The coefficient of 
expansion for wax is up there and I don't want the solid wax building on 
the tubes to sag the copper. And, more surface area for the exchanger. I 
had thought of running FEA on this but would have downloaded free 
software. I figured I lack the skill to make the time invested work out.

The average distance from far points to the heat exchanger will be some 
3-4 inches. And, the heat will be moved out on the scale of hours. The 
only time I could see having trouble is on the very coldest nights and 
having to bring the house back up to temperature in the morning.

The contingency plan for that is I load the boiler with some wood in the 
evening and it autostarts very early in the morning for those coldest 
nights.


Best, Dan.