Thermal analysis of portable electronic products

As an ever-increasing diversity of portable electronic products enter the market with smaller sizes and greater functionality, thermal analyses are becoming more important much earlier in the design cycle. Many electronic products are passively cooled with little or no internal air motion between printed circuit boards and the external housing. For these applications, thermal analyses can be greatly simplified by modeling heat transfer through air gaps using linear finite element analysis (FEA), including radiation exchange, without resorting to more involved computational fluid dynamic (CFD) simulations. Experimental temperature measurements made in a narrow cavity enclosure show that heat is transported across air gaps by thermal conduction, as evident from the linear temperature profile. CFD predictions made for the same geometry and boundary conditions indicate that internal flow velocities are extremely low, less than 0.006 m/s. Finally, an example of the air gap conduction model is illustrated by building a FEA model directly from a computer aided design (CAD) solid model of a hand-held radio. Transient temperatures predicted from a FEA model agree with measurements made on a radio while running a transient duty cycle consisting of transmit and dwell intervals.