Prediction of Device Temperatures
with Depth-Averaged Models of the Flow Field
over Printed Circuit Boards

Gerald W. Recktenwald
Department of Mechanical Engineering
Portland State University
Portland, Oregon
gerry@me.pdx.edu

Convective heat transfer from electronic devices mounted on a printed
circuit board is simulated with an efficient Computational Fluid
Dynamics (CFD) model.  The computer time necessary to calculate a
solution to the flow field is greatly reduced by solving the
depth-averaged (DA) flow equations for the fluid flowing above the
devices.  The DA flow field is then coupled to the full,
three-dimensional energy equation in the fluid and in the solid
materials comprising the circuit board and the electronic devices.
Because the temperature is determined by solving the conjugate problem,
no heat transfer coefficient needs to be specified on the outer surface
of the devices. This paper provides an overview of the theory behind
the depth-averaged and three-dimensional energy equation models.
Incorporation of the essentially two-dimensional depth-averaged flow
fields in the three-dimensional energy equation is described. The
combination of the DA flow field and the three-dimensional energy
equation does not yield the same level of detail as a conventional
three-dimensional CFD code.  The advantage of this approach, however,
is that it makes significantly lower demands on the computational
hardware and it obtains useful solutions in much less time than
conventional CFD codes.

------------------------------
presented at the 1995 International Mechanical Engineering
Congress and Exposition in San Francisco, November 1995