In a partially confined configuration, where the flow duct
is larger than the heat-sink cross sectional profile, there will
be a certain amount of flow bypass, and, as a result, the
flow velocity through the fins may be substantially different
from the approach velocity, The amount of flow bypass
is strongly related to the cross sectional geometry and the
pressure drop across the heat sink, and this must be determined
from the hydro-dynamic analysis before the thermal
analysis can be carried out.