I'm currently in the process of winding a new induction coil for a project, and was thinking about ways to increase the efficiency of the magnetic coupling.
The coil is heating a metal wire that's continually pulled through it, but the wire OD (1mm) is relatively small compared to the ID of the coil (25mm) due to the size of copper tubing I needed to use. This induction heater flows coolant through the coil, and I needed to get a decent flow rate. The coil is currently 25 turns, but to get better heating, I was thinking about putting a ferrite jacket around it.
My question is a couple fold. The induction heater is around 50KHz output frequency, and I'm uncertain if higher or lower initial magnetic permeability would be better for this jacket. The other question is whether I need a largish air gap between the coil and the ferrite torroid. The OD of the coil is around 40mm (and around 200mm long), so going larger significantly increases the weight of the torroid.
Open to any input or ideas. If the ferrite torroid jacket is a poor idea, it would be great to know why.