0
$\begingroup$

I am designing an electric kiln just for fun and I found myself not knowing how to answer this scenarios.

The main constant is power. The final power must be the same in each case. My question is about the effects of differents approach in order to get the best result.

Previous info

  • Coil: Kanthal A1
  • Diameter: 1.3mm
  • Resistance: 1.09Ω/m
  • Resistivity at 1300°C: 1.508Ωmm2

First scenario: Single element (or series, should be the same keeping the equivalent resistance)

  • Voltage: 220V
  • Power: 3000W
  • Circuit current: 13.33A
  • N° of elements: 1
  • Element resistance: 16.88Ω
  • Equivalent resistance: 16.88Ω
  • Element current: 13.33A
  • Lenght of heating element: 14.853m
  • Element surface area: 606.614cm2
  • Element surface load: 4.945W/cm2

Second scenario: Two elements in parallel

  • Voltage: 220V
  • Power: 3000W
  • Element power: 1500W
  • Circuit current: 13.33A
  • N° of elements: 2
  • Element resistance: 33.75Ω
  • Equivalent resistance: 16.88Ω
  • Element current: 6.67A
  • Lenght of heating element: 29.706m
  • Element surface area: 1213.228cm2
  • Element surface load: 2.473W/cm2

Both circuits have the same power. The parallel ones has to double each resistance in order to get half the total power. We can see that the distance of the resistance has doubled and the current halved. This gets us more area in each coil with less surface load, that would benefit the lifespan of the coil.

If isolation is good in each case the energy would stay inside the kiln independent of the length and current of each heating element as my understanding. The heat would keep rising until get to an equilibrium with the kiln or reach the desired temperature.

  1. Is there a difference in the heating of the kiln? Maybe it heat faster because of the bigger surface of the heating element but at the cost of less current per distance (I don't know if this is a thing)

  2. Does current has an effect in the maximum temperature of each element? (at same power)

  3. Would be the same if there were 2 in series with half the resistance?

To me seems more beneficial to use the parallel one if everything its the same and it would extend the lifespan of the coils because of the lower surface load.

Thermodynamics is not my forte. Correct me if my assumptions are incorrect.

--- edit ---

Some additional info about the kiln

  • Interior size 30x30x30cm
  • Insulation is made with K23 fire bricks and an additional ceramic cloth outside
  • I am planning on using PID controller with two relays in the parallel scenario that would control the duty cycle
$\endgroup$
4
  • $\begingroup$ From reading you question I get the impession that you think that two parallel elements will give half the power of one. It won't. It will give twice the power of one. Series connection will give twice the resistance, half the current and 1/4 the power (since $P = I^2R$. Can you clarify? $\endgroup$
    – Transistor
    Nov 5, 2022 at 15:07
  • $\begingroup$ In order to keep the same power output each element in parallel will have 2 times the original resistance in order to get to 1500Watts each. These scenarios are changing the resistance in order to keep the output power the same. $\endgroup$ Nov 5, 2022 at 16:09
  • $\begingroup$ "In order to keep the same power output each element in parallel will have 2 times the original resistance in order to get to 1500Watts each." Correct. $\endgroup$
    – Transistor
    Nov 5, 2022 at 17:00
  • $\begingroup$ Don't use Kanthal; ( iron base) it becomes very brittle and weak after it is used. Use Nichrome ( Ni base), several very similar alloys. There are service ratings for permissible power density, like watts / square mm; $\endgroup$ Nov 7, 2022 at 21:56

1 Answer 1

0
$\begingroup$

If you were to consider each element as a lightbulb then this is a good reference to help your understanding. I found it through an internet search.Light Bulb demonstration

Materials and the size of the kiln are important factors in answering your question. Having temperature control in the kiln will be of great use since you are designing it, it will ensure your heating elements do not melt as it seems you have few means of dissipating heat. There are probably other methods of course to mitigate for it, e.g. if your resistance is sensitive to temperature you could potentially detect overheat by measuring current.

Say if you did have a particular temperature in mind for the kiln then I would say that the larger surface area would be a good option to ensure evenness in your heat distribution at a lower power as it is heating up. One factor to consider is that having a large temperature gradients is generally considered a bad thing from a stress point of view.

$\endgroup$
2
  • $\begingroup$ I read the link, it's an interesting article on the effects of series and parallel. The main difference with my problem is that mine is considering same output power. My main variable is the resistance (that I am making myself). I added some additional info about the materials and size. I am planning on using PID controller and k23 firebricks. The size is 30x30x30cm. $\endgroup$ Nov 7, 2022 at 13:08
  • $\begingroup$ Great, I also though it was a good analogy I'm glad you thought it was interesting. $\endgroup$ Nov 7, 2022 at 16:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.