Development of conduction optimized heat sinks with enhanced fluid flow path for passive cooling applications

Abstract

Passive cooling, which utilizes natural convection and thermal radiation as the heat removal mechanisms, offers the advantages of high reliability, compactness, noise-free and low-energy-cost for thermal management of electronics. Unfortunately, existing passive heat sinks have limited geometrical variation to take advantage of the heat dissipation mechanisms, leading to large air flow paths and conduction resistances. To overcome these shortcomings of conventional passive heat sink designs, this study proposes three categories of passive heat sinks including parameter optimized cross-shaped plate fins (CF), topology optimized tree-shaped fins (TF) and hybridized cross-shaped and tree-shaped fins (CF-TF). While the CF heat sinks aim to reduce the air flow resistance to increase the average air velocity in the heat sinks and the TF heat sinks simultaneously reduce the fin conduction resistance and increase the wetted area for enhanced heat transfer, the CF-TF heat sinks synergize the advantages of both CF and TO topology to further enhance cooling performance. Using selective laser melting (SLM), a laser powder bed fusion (LPBF) process, we showed that the complex geometries of the heat sinks can be readily fabricated with short production time and at low cost, thus demonstrating the potential of utilizing LPBF for full scale production for these heat sinks. Furthermore, using Fourier transform infrared spectroscopy (FTIR), we showed that the SLM-fabricated heat sinks made from AlSi10Mg have the added advantage of significantly higher spectral emissivity, thus enhancing radiation heat dissipation as compared to conventionally casted aluminum alloy, Al6061. To evaluate the passive cooling performance of the new heat sinks, they were experimentally characterized in an environmental chamber. Our results showed that the best hybridized heat sink (CF0-TF16), cross-shaped heat sink (CF2), and topology optimized heat sink (TF16-R) exhibited 10.6 % 10.5 % and 10.0 % reduction in thermal resistance as compared to the best conventional plate fin heat sink, respectively. More importantly, the thermal enhancements of CF0-TF16, CF2 and TF16-R were achieved at the weight reductions of 14.8 %, 18.7 % and 20.7 %, respectively, as compared to the conventional heat sink. This research demonstrates the advantage of synergizing new thermal design strategy and additive manufacturing technique to develop passive cooling devices with simultaneous thermal efficiency enhancement and weight reduction.