Natural convection heat transfer along vertical cylinder heat sinks with longitudinal fins

• Edge of thermal boundary layer is expressed as a sinusoidal function.
• Average Nu along z coordinate is approximately an exponential function of z.
• A Nu correlation within ±10% error is proposed by introducing finned ratio.

Heat sinks appearing as one vertical cylinder with longitudinal fins are widely used in heat dissipation of LED bulbs and other electric devices. Numerical models of natural convection heat transfer are built based on CFD method. Thermal boundary layers are discussed along with the air flow patterns. Numerical results disclose that the edge of thermal boundary layer can be fitted into a sinusoidal function in 2D polar coordinate system. The local Nu distributions on both cylinder and fin surfaces are presented and analyzed. It is found that average Nusselt number along the fin length is approximately proportional to an exponential function of z. A new correlation is proposed by introducing finned ratio, achieving a deviation within ±10%.