  As power electronics shrinks down to sub-micron scale, the thermal transport
from a solid surface to environment becomes significant. Under circumstances
when the device works in rare gas environment, the scale for thermal transport
is comparable to the mean free path of molecules, and is difficult to
characterize. In this work, we present an experimental study about thermal
transport around a microwire in rare gas environment by using a steady state
hot wire method. Unlike conventional hot wire technique of using transient heat
transfer process, this method considers both the heat conduction along the wire
and convection effect from wire surface to surroundings. Convection heat
transfer coefficient from a platinum wire in diameter 25 um to air is
characterized under different heating power and air pressures to comprehend the
effect of temperature and density of gas molecules. It is observed that
convection heat transfer coefficient varies from 14 Wm-2K-1 at 7 Pa to 629
Wm-2K-1 at atmosphere pressure. In free molecule regime, Nusselt number has a
linear relationship with inverse Knudsen number and the slope of 0.274 is
employed to determined equivalent thermal dissipation boundary as 7.03E10-4 m.
In transition regime, the equivalent thermal dissipation boundary is obtained
as 5.02E10-4 m. Under a constant pressure, convection heat transfer coefficient
decreases with increasing temperature, and this correlation is more sensitive
to larger pressure. This work provides a pathway for studying both heat
conduction and heat convection effect at micro/nanoscale under rare gas
environment, the knowledge of which is essential for regulating heat
dissipation in various industrial applications.
