ABSTRACT
Many practical situations are not as simple as those mentioned above. Conduction heat transfer rate through a heat sink that is mounted on a smaller package is not one dimensional. Although, the concept of spreading resistance was introduced to account for this three-dimensional effect in a one-dimensional analysis, the underlying assumption of uniform heat flux on the fin side of the base is not completely accurate in most cases. Many electronic devices, such as notebook computers and power supplies, have complex shapes and are internally so congested that they may not be approximated as a flat plate or a duct. Besides, the assumption of uniform heat flux, uniform surface temperature, or even uniform ambient temperature may not be valid in many of these cases. For the radiation heat transfer, it is rare that we can assume the surrounding to be at constant temperature or only two or three radiating surfaces are involved. Therefore, radiation heat transfer calculations will involve calculating many view factors and solving a set of N simultaneous linear equations where N is the number of radiating surfaces. Again, similar to the convection heat transfer, the assumption of uniform surface temperature or uniform surface heat flux may not be accurate.
