Combined convection and radiation heat transfer of the radially finned heat sink with a built-in motor fan and multiple vertical passages

Abstract This work proposed a novel finned heat sink with the air-driving device and vertical flow passages for LED lamp. The heat sink, made of aluminum alloy, was a cup-shaped cylinder with multiple externally radial fins. Various motor fans were mounted in the hollow chamber of the heat sink. Coupling with the multiple vertical passages in the ring wall of the heat sink and the separation board in the chamber of the heat sink, the air flow was driven through the internal of the heat sink. The measured air velocity within the vertical passages and the smoke flow visualization demonstrated that the present air-driving device did work. The heat-transfer experiments for the systems with the built-in motor fan and compressed air flow were performed, respectively. The overall heat transfer mechanism of the present cooling device was the combination of the internally forced convection and the externally natural convection coupling with radiation heat transfer. The overall Nusselt number of the heat sink with the built-in motor fan was 28–102% higher than that without motor fan. In general, bigger motor fan drove more air flow to enhance heat transfer. Finally, a theoretically empirical formula was proposed to predict the Nusselt numbers of the present combined convection and radiation heat transfer. The applied range was Grashof number Gr  = 2.37 × 10 5 –5.92 × 10 5 and Reynolds number Re  ≦ 343. The maximum deviation of the total Nusselt number between the predictions and the experimental data of the system with compressed air flow was ±11%.