Using concentric pipes as an inductive heater

[EzeTom]

Hi Everyone,

I am a mechanical Engineer, playing in the electrical word :)

I was thinking about creating an inductive heater, that was based on 2 concentric pipes, with a current flow path that is from the inside pipe, through to the outside pipe, and utilizing an induction power supply to do so. I saw this style of heater in a lead melting furnace on a recent trip to Europe, and I thought it might be a fun project for me to build at home. (the furnace was a crucible with a "heating stick" inserted into it.

Does anyone have any suggestions as to the math, and science behind this? I see on ebay there are many inductive heater power supplies for sale, however I am certain there will be some impedance matching/ Frequency/ Voltage parameters that will need to be optimized, I only tool a couple of electrical classes in school, and from what I gather, this sort of heater arrangement is basically a very "lossy" transmission line.

Any thoughts?

 

[Baluncore]

I think we need a better picture of the type of heater you suggest. Please post a link.
Are the concentric pipes the “heating stick” you refer to ?
Does conduction between tubes only take place at the tip of the tubes ?
Is the gap between the tubes used for water cooling ?

 

[EzeTom]

I think we need a better picture of the type of heater you suggest. Please post a link.
Are the concentric pipes the “heating stick” you refer to ?
Does conduction between tubes only take place at the tip of the tubes ?
Is the gap between the tubes used for water cooling ?

Thanks for the reply,

what I was thinking of is using something similar to this, but with 2 pipes - you can double the wattage (using transformer oil or something inside to conduct the heat from the inside to the outside. The below link is using a copper (non mag) conductor on the inside, and then using a magnetic pipe to create the "heater" via the return high frequency current that drives to the "skin" of the steel pipe. ( Induction-Resistance Heating)

http://www.valin.com/documents/Skin_Effect_Slides.pdf

I bought one of these on Ebay, http://www.ebay.com/itm/H-Voltage-Power-Supply-ZVS-Tesla-Coil-Driver-board-Marx-generator-Jacobs-ladder/141931226883?_trksid=p5411.c100167.m2940&_trkparms=aid%3D222007%26algo%3DSIC.MBE%26ao%3D1%26asc%3D20140131123730%26meid%3Dac08e617be664148bb7fa53db57effd4%26pid%3D100167%26rk%3D6%26rkt%3D15%26sd%3D172001795203

But I am not really sure how to calculate if this will be suitable, or if I need some sort of impedance matching transformer to ensure all of the power is dissipated in the steel pipe... Any ideas ?

 

[Baluncore]

The circuit board shown on eBay is printed with DC 12V-30V / 10A. The maximum power input is therefore 30V * 10A = 300W. The maximum output power available must therefore be less than 300 watt.

1. You have given us no idea of the physical size of the tubes involved, or the external thermal insulation and heat losses.

2. You have given us no idea of the temperatures you require. Even if transformer oil is cooled and circulated continuously, it will break down at temperatures that will melt lead.

You will need some form of output transformer, the secondary of that will be the load.

 

[EzeTom]

Id like to just try a proof of concept prototype - maybe using some pipes 1" and .625 OD? with 0.125" wall? and perhaps 6" long? The temperature I am looking for is around 300F. - for the initial test, It will just be in air, so I would suspect 300 ish watts should apply some significant heat...

I don't know what the frequency of the driver board from Ebay is, I guess I will have to wait to have it arrive to measure it...

Do you have any ideas how I can begin to calculate what I would need to do, to balance the load in the pipes, with the power supply?

 

[EzeTom]

Just thought I would bump this.