Flow and heat transfer performance of microchannel heat sinks with circular concave cavities and ribs for water cooling LEDs

Abstract

ABSTRACT The poor heat dissipation of LED light sources limits their applications in plant factories. This paper combines a microchannel heat sink (MHS) with circular concave cavities and ribs with the water irrigation system of an LED plant factory to develop water-cooled LEDs. By using this approach, four types of MHSs were designed: circular concave cavities (circular), circular concave cavities and single-sided ribs (circular-single), circular concave cavities and odd-symmetric ribs (circular-odd), and circular concave cavities and double symmetric ribs (circular-double). The influence of the arrangement of circular concave cavities and ribs on the flow and heat transfer performance was numerically investigated by ANSYS Fluent 21.0 R1. Corresponding MHSs with circular concave cavities and ribs were manufactured, and an experimental platform was built to experimentally verify the numerical results. The results showed that a circular concave cavity in the microchannel caused the fluid to form a secondary flow, which led to the continuous destruction and reconstruction of the flow and thermal boundary layer in the microchannel. This contributed to heat and mass transfer, while the presence of ribs altered the flow direction of the fluid and enhanced mass and heat transfer within the cavities. The pressure drop at the inlet and outlet of the MHS increased in the case of circular concave cavities and ribs as the inlet flow rate increased. Compared with MHSs with circular concave cavities, the ribs increased the pressure drop at the inlet and outlet. The inlet and outlet pressure drop of MHS with circular concave cavities and double-symmetric ribs was the highest, followed by MHS with circular concave cavities and odd-symmetric ribs, and the smallest was the MHS with circular concave cavities and single-sided ribs. As the inlet flow rate increased from 10 ml/min to 60 ml/min, the pressure drop between the inlet and outlet of the MHS with circular concave cavities increased from 22.54 Pa to 165.98 Pa (an increase of 143.44 Pa); the pressure drop of the MHS with circular concave cavities and single-sided ribs increased from 24.72 Pa to 187.31 Pa (an increase of 162.59 Pa); the pressure drop of the MHS with circular concave cavities and odd-symmetric ribs increased from 27.92 Pa to 212.12 Pa (an increase of 184.20 Pa) and that of the MHS with circular concave cavities and double symmetric ribs increased from 29.32 Pa to 221.21 Pa (an increase of 191.89 Pa). Under the same inlet flow rate and LED chip input power, the cooling water outlet temperature of MHS with circular concave cavities and double symmetric ribs was the highest, followed by MHS with circular concave cavities and odd-symmetric ribs, MHS with circular concave cavities and single-sided ribs, and MHS with circular concave cavities was the lowest. These results indicated that the heat transfer performance of MHS with circular concave cavities and double-symmetric ribs was the best, followed by MHS with circular concave cavities and odd-symmetric ribs, and MHS with circular concave cavities and single-sided ribs. The MHS with circular concave cavities had the worst heat transfer performance. The outlet temperature of the MHS with concave cavities and ribs reaches the highest value at the inlet flow rate of 30 ml/min. At this flow rate, the outlet temperature is 343.89 K for the MHS with circular concave cavities, 344.73 K for the MHS with circular concave cavities and single-sided ribs, 346.53 K for the MHS with circular concave cavities and odd-symmetric ribs; and 347.58 K for the MHS with circular concave cavities and double symmetric ribs.