Evaluation of Additively Manufactured Microchannel Heat Sinks

Abstract

Microchannel heat sinks allow removal of dense heat loads from high-power electronic devices at modest chip temperature rises. Such heat sinks are produced primarily using conventional subtractive machining techniques or anisotropic chemical etching, which restricts the geometric features that can be produced. Owing to their layer-by-layer and direct-write approaches, additive manufacturing (AM) technologies enable more design-driven construction flexibility and offer improved geometric freedom. Various AM processes and materials are available, but their capability to produce features desirable for microchannel heat sinks has received limited assessment. Following a survey of commercially mature AM techniques, direct metal laser sintering (DMLS) was used in this work to produce both straight and manifold microchannel designs with hydraulic diameters of 500 µm in an aluminum alloy (AlSi10Mg). Thermal and hydraulic performance were characterized over a range of mass fluxes from 500 kg/m 2 s to 2000 kg/m 2 s using water as the working fluid. The straight microchannel design allows these experimental results to be directly compared against widely accepted correlations from the literature. The manifold design demonstrates a more complex geometry that offers a reduced pressure drop. A comparison of the measured and predicted performance confirms that the nominal geometry is reproduced accurately enough to predict pressure drop based on conventional hydrodynamic theory, albeit with roughness-induced early transition to turbulence; however, the material properties are not known with sufficient accuracy to allow for a priori thermal design. New design guidelines are needed to exploit the benefits of additive manufacturing while avoiding undesired or unanticipated performance impacts.

A permeable-membrane microchannel heat sink made by additive manufacturing

“…A flow loop identical to that described in Ref. [19] The test section presses the heat sink onto the heater, positions thermocouples for temperature measurements, and contains pressure taps to measure the pressure drop; slight modifications were made compared to Ref. [19].…”

“…[19] The test section presses the heat sink onto the heater, positions thermocouples for temperature measurements, and contains pressure taps to measure the pressure drop; slight modifications were made compared to Ref. [19]. Due to the lack of an incorporated lid on both heat sinks due to a desire to visualize the heat transfer features, a silicone rubber gasket was used to seal the interface between the heat sink and a polycarbonate block that has features to route flow into and out of the heat sink.…”

“…Studies of microscale heat exchangers made by additive manufacturing, specifically powder bed fusion processes, frequently highlight issues associated with material properties and high surface roughness. The authors' previous work [19] demonstrated AM fabrication of straight microchannel and manifold microchannel heat sinks in an aluminum alloy having channel hydraulic diameters of 500 µm and monolithic construction. The pressure drop was well-predicted by conventional hydrodynamic theory, with a roughness-induced early transition to turbulence at low Reynolds numbers (Re < 800).…”

“…After fusion, another thin layer of powder is deposited on top and the process repeats; in this way, parts build up layer by layer. Based on our previous work[19] and the literature[24], a microchannel width of 500 µm is near the lower limit of what can be commercially fabricated; even though laser spot sizes of 50-100 µm are common, the significant heat-affected zone prevents finer widths from being fabricated. Therefore, the membrane pores in the PMM cannot be directly printed; rather, the material must be rendered porous during the powder fusion process to achieve these small pore features.…”

2022 roadmap on 3D printing for energy

“…Electrochemical fabrication, a group of processes based on photolithography and electrodeposition of metals, may fabricate minimum features around (4-25) µm with 2 µm tolerances, but supports only a limited set of materials and small build volumes [99]. On the other hand, SLS processes are less expensive and may fabricate minimum features around (200-400) µm with 50 µm tolerances [99]. A high surface area to volume ratio is essential for improved forced convection heat transfer in confined spaces.…”