A study is presented for laminar natural convection heat transfer from isothermal, vertical disks with horizontal support cylinders, as found in annular-fin heat sinks. A distinction is made between the external and internal surfaces of the heat sink, and, hence, the heat transfer mechanisms which dominate in each of these surfaces can be more easily applied. A boundary layer solution for laminar natural convection, a fully developed flow solution, and a diffusive limit are successfully applied to this complex geometry to form the present model. The model shows good agreement with present experimental data and previous correlations.

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