Although the thermo-couple with heat source is expanding, but the stresses are compressive as well as tensile. What causes this?

220^2 /2000 = 24.2 OHM HEATER 110^2 / 24.2 = 500W.

500 watts - half the voltage results in half the current across the same resistance so 1/4 the watts. Unless there is a fan 50 Hz makes no difference for 60 Hz.

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.