HEATSINK is a thermal analysis routine used to estimate the temperature of a
finned heatsink under natural convection air flows. Basic configuration data in
inputted by the user to define fin geometry, plate orientation, and ambient
conditions. Air flow rate are estimated based on buoyancy forces, friction
forces, and plate orientation. Heat transfer coefficients, fin efficiency, and
plate temperature are determined from air flow rates.
Heat radiates from the base plate and from each fin. The Effective Shape
Factor depends on the view factor of each fin with respect to each adjacent fin.
In our heatsink routine, emissivity is specified by the user then weighed by the
effective fin area and shape factor to calculate an overall radiation heat
transfer. Since heatsinks are fabricated of high conductive materials, the fins
tend to emit more energy at oblique angles than in a direction normal to the
surface. Consequently, shape factors have been weighed with a sinusoidal
function to approximate the characteristic.
Fin geometry is used to determine a minimum heat transfer coefficient based
on Limiting Nusselt Number. Buoyancy forces are balanced against friction forces
in a iterative technique to determine actual air velocity. Colburn number and
friction coefficient are determined and an air velocity established for each
iteration. A mass flow rate is also determined based on Grashof Number.
The heat transfer coefficient between the top of
the fin and the boundary layer is based on laminar flow. Heat transfer between
the fin and boundary layer is calculated using forced convection heat transfers
coefficients. This higher number (h) is required due to some mixing between the
After the air flows have been determined, all coefficients for our finite
difference routine are known and the temperature analysis is performed by
HEATSINK writing a heat flow equation for each node and solving these equations
simultaneously. The resulting temperatures are now used to calculate new
buoyancy forces. This procedure is repeated until new temperatures match old
temperatures. On micro computers, the whole calculation procedure only takes
milliseconds. We wish to thank Lockheed Electronics Corp. in Plainfield, New
Jersey for their generosity in providing test data to verify computer results.
Our software routines may be downloaded from this web site and are fully operational for your testing for about 30 days.