  Frequently, the design of physicochemical processes requires screening of
large numbers of alternative designs with complex geometries. These geometries
may result in conformal meshes which introduce stability issues, significant
computational complexity, and require user-interaction for their creation. In
this work, a method for simulation of heat transfer using the diffuse interface
method to capture complex geometry is presented as an alternative to a
conformal meshing, with analysis and comparisons given. The methods presented
include automated non-iterative generation of phase fields from CAD geometries
and an extension of the diffuse interface method for mixed boundary conditions.
Simple measures of diffuse interface quality are presented and found provide
predictions of performance. The method is applied to a realistic heat transfer
problem and compared to the traditional conformal mesh approach. It is found to
enable reasonable accuracy at an order-of-magnitude reduction in simulation
time or comparable accuracy for equivalent simulation times.
