How Efficient Is Split-Return Coil Design for Quenching in Induction Heating?

[ABrown123]

I am designing an induction heating rig to heat a strip on the surface of a steel sample with repeated quenching, through holes in the heating surface of the coil (shown in the third image). The rig should heat the sample to around 600C in 20 seconds, and quench to 30C in 20 seconds.

Firstly, could anyone comment on the current coil design (split-return rectangular copper pipe)
Secondly, there are two options for cooling, as shown in the image, one which quenches the sample from the centre leg and one which does so via the centre and return legs. Would the coil get too hot if it was only cooled during the quench cycle (half of the time) as in the second image?Thanks in advance

 

[Baluncore]

Firstly, could anyone comment on the current coil design (split-return rectangular copper pipe)

It looks to me like the magnetic fields of the three parallel conductors will produce two opposite poles. There must be an area between the poles, under the central feed conductors, where those three fields cancel. There will be little eddy current heating just where you want it.

 

[ABrown123]

It looks to me like the magnetic fields of the three parallel conductors will produce two opposite poles. There must be an area between the loops, under the central feed conductors, where those three fields cancel. There will be little eddy current heating just where you want it.

From what i understand, in the centre leg the current would be twice that and the power 4 times that of the return legs if they are the same thickness, even more if the return legs are thicker (in this design theyre twice as thick). I will also be using a flux concentrator focused around the centre leg. Hopefully this would suffice to prevent this flux interaction cancelling out below the centre legs?

 

[Baluncore]

I will also be using a flux concentrator focused around the centre leg. Hopefully this would suffice to prevent this flux interaction cancelling out below the centre legs?

You have a south pole on one side and a north pole on the other. There must be a line or zone between them where the opposite fields cancel.