I have simulated 3 different natural convection inside an enclosure. I put a heat source inside a closed chamber. My settings are Internal analysis, air, heat source 3W, gravity -9.81m/s^2,

Under Thermodynamic parameters i changed the pressure to 101325 Pa, 50,000Pa and 10,000 Pa. Theory if pressure increase, temperature increase.

The results show the lower the pressure, the heat source increase in temperature although i fix it to 3W and surrounding temperature increased as well.

Since the pressure is low (vacuum), convection is almost neglected.i expect the heat will only concentrated at the heat source.

What am i missing?