Graphite heat shield has a lower thermal conductivity relative to
tungsten rod. This makes the temperature of graphite higher than
tungsten (at same physical conditions) during Joule heating [19].
The contact of tungsten with heat shield at the contacting zone creates
a cooler temperature field different from the usual temperature
distribution field [20, 21] along the heat shield. Although the
graphite heat shield is homogenous, tungsten has more influence on the
part of heat shield closer to it within the temperature irregularity
zone (broken circular yellow line in Fig.5.4). Hence the cooling effect
of tungsten on the reference line within the temperature irregularity
zone is the reason for lower temperatures at the stagnation point within
the stagnation region in Fig.5.3.