Literature on buoyancy driven flow in vertical channels have been reviewed in order to investigate formulas for Nusselt number and flow rate, which can be used in fast calculations of temperature rise in electrical apparatuses. The Rayleigh number range spans from fully developed duct flow to isolated plate boundary layer flow, and both uniform heat flux and uniform wall temperature boundary conditions are considered. Several heat transfer formulas are compared, and, for uniform temperature, an improved formula is presented that indicates the existence of an optimum plate separation. Flow rate formulas are proposed based on asymptotic estimates and adaptation to data available in the literature. Based on the flow rate formulas, the influence on flow rate of Rayleigh number and plate separation is discussed.

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