Effect of Bonding Structure and Heater Design on Performance Enhancement of FEEDS Embedded Manifold-Microchannel Cooling

Abstract

This work presents the design and characterization of a two-phase, embedded manifold-microchannel (MMC) system for cooling of high heat flux electronics. The study uses a thin-Film Evaporation and Enhanced fluid Delivery System (FEEDS) MMC cooler for high heat flux cooling of electronics. The work builds upon our group’s earlier work in this area with a particular focus on the use of an improved bonding structure and implementation of uniform heat flux heaters that collectively contribute to enhanced performance of the system. In many MMC systems targeted for high heat flux applications microchannels and manifolds are fabricated separately due to different dimensions and tolerances required for each. However, assembly of the system often leaves a gap between the channels and the manifold, thus causing the working fluid to leak through the top of the microfins leading to decreased cooler performance. The effect of this gap is parametrized and analyzed with ANSYS Fluent CFD simulations and discussed in this paper. The findings show that even a few microns wide gap can cause a noticeable degradation of the MMC system performance. Imperfect assembly and the deformation of a microchannel chip due to working fluid pressure can cause gaps, indicating the necessity of uniform and hermetic bonding between the manifold and the tips of the microfins. Furthermore, this work presents the need for better heater designs to enable uniform and high heat flux to the heat transfer surface. Serpentine heaters are often used to mimic electronics in a laboratory environment, but there is a lack of study on the performance characterization of the heaters themselves. In the current work, the performance of a conventional serpentine heater is characterized using ANSYS thermo-electric modeling software. The results show that conventional serpentine heaters are insufficient at providing uniform heat flux in applications where there is a lack of heat spreading-such as in the current embedded cooler — showing deviations ranging over 200 % of the nominal value. The deviations are caused by the many bends present in a serpentine pattern where current density concentrations vary significantly. Two alternate designs are proposed, and numerical simulations show that these new heater designs are capable of providing uniform heat flux, not deviating more than 20% from the nominal heat flux value. The conventional and newly proposed heaters are fabricated, tested, and analyzed with a working FEEDS system.

Embedded Two-Phase Cooling of High Flux Electronics Via Press-Fit and Bonded FEEDS Coolers

“…Braces were elongated in the direction of flow to minimize the disturbances to the flow. The alumina manifolds for the press-fit test section were lapped and polished to achieve 1 lm parallelism and 100 nm surface roughness in order to avoid microscopic gaps between the manifold and heat sink that could potentially adversely impact heat transfer and pressure drop [15,19]. The circuit boards were made of both glass, and the metal pattern screen-printed in the laboratory.…”

“…First, the header and manifold are 3D printed as one monolithic structure, and the microchannel fin tips and the manifold are directly bonded together, preventing the possibility of any flow bypassing the microchannels, which was shown in Refs. [15] and [19] to have a significant impact on pressure drop and heat transfer. Second, the use of additive manufacturing enables larger internal flow volume, which, in turn, improves intermicrochannel flow distribution.…”