Orientation effects on conjugate natural convection heat transfer from an LED bulb: A numerical study

Natural convection is a widely used cooling technique in LED bulbs. About 75–85% of input power to an LED package is being wasted as heat. Along with the LED packages, a notable amount of heat is generated by the LED driver. Thus, if this generated heat is not removed in a proper way, it can lead to decrease in life-span of the LED. Hence, the present study focusses on the numerical investigation of three-dimensional conjugate natural convection heat transfer from an LED bulb to elucidate the effect of orientation of the bulb on both momentum and heat transfer characteristics. Numerical computations are performed in a finite-volume based solver for the laminar flow regime of Rayleigh number spanning in the range 103 to 107 for various orientations of the LED bulb. Results are pictorially visualized in terms of temperature contours and streamlines to understand the thermal and flow fields, whereas both local and surface average Nusselt numbers are represented to expound the heat transfer from the bulb. The average Nusselt number is directly proportional to the Rayleigh number for all orientations of the bulb, and it is found to increase with an increase in the angle of orientation of the LED bulb from vertically upward to downward. The average Nusselt number at the vertically downward orientation of the bulb is higher than the vertically upward orientation by 86%, 77%, and 39% for Rayleigh number of 107, 105, and 103, respectively.