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Open coil questions

Progen Member Posts: 2
edited October 2022 in THE MAIN WALL
The next frame and heating chamber for my home built coffee roaster has not been built yet but which will have better coil to air heat transfer?

Smaller and closer coils or larger and further ones? That's assuming I'm using the same length and gauge of nichrome.

Also, I couldn't find bushings of the size I wanted so I made around 80 of these from 25mm OD 15mm ID tubes. The intended gauge will be 1.2mm. Will I have hot spots because there'll be 3 per column and I'm thinking of a 2 x 8 array to give me around 10kW.

That means a total of 48 of these bushings quite close to each other in a tall narrow chamber.


  • MikeAmann
    MikeAmann Member Posts: 998
    All this to roast coffee?
    I wish I had the free time that you seem to have.
  • mattmia2
    mattmia2 Member Posts: 9,843
    The length you stretch the coil to will affect the temperature of the wire to some extent which will affect its resistance, further stretched coil will produce somewhat more heat because it will stay cooler and draw more current.
  • Progen
    Progen Member Posts: 2
    Mattmia, but I noticed a lot of open coil manufacturers tend to coil with smaller diameter and have more coils instead of larger ones. Why is that?

    I even saw a large open coil array that was like 2/3 the size of a single bed with perhaps only 20mm ID coils.