3d induction heating model

I am new user of comsol and I am simulating the 3d induction heating . I was reffering to the the examples in model library. I reffered to the 3d eddy currents and induction heating of copper cylinder . I made all the physics settings according to examples but I am not getting the desired results.

First problem I am facing is in applying theSubdomain Settings in HT model. If I load the material properties from the library for air there is an error for the Density expression regarding the units.

Also I am Not getting which way to apply the current. Surface Current or Edge Current?? I tried both the ways but the solution is not converging

Please can anybody suggest any changes in the simulation .