Finding Parts for Sample Processing
Author: Rafael Estrella | Major: Mechanical Engineering | Semester: Spring 2022
My name is Rafael Estrella, and I am a senior mechanical engineering student and an aspiring researcher. At the end of the first semester of my sophomore year, I was invited to work in the lab of my Introduction to Materials professor and current honors mentor, Dr. David Huitink. Intrigued by the work of graduate student Reece Whitt on non-metallic heat spreaders for high-power electronics, I began analyzing the durability of the polymer materials used for these devices. I conducted an honors independent study on another part of the heat spreader project: improving the performance of a single jet nozzle during the 2021 fall grant term. During the 2022 spring grant term, I continued my research into the durability of non-metallic materials, culminating in my honors thesis. First, let’s contextualize heat spreaders and their application.
High-voltage power electronics are largely used to convert battery storage into useable power for electric motors and can suffer from deleterious heat concentrations during operation. One common thermal management solution, metallic cold plates, relies on conduction and convection via a liquid-cooled metallic block placed in direct contact with a power module to draw out excess heat. Concerns with this method are the inefficiencies with the metallic block cooling, the added weight, and the signal interference accentuated by the metal components. As such, this work is a sub-section of an effort to enable polymer AMHS (additively manufactured heat spreader) technology, which uses channels and jet impingement nozzles to direct coolant to known heat concentrations. This reduces the maximum device temperatures and allows fluid to come into direct contact with areas of concern, reducing thermal resistance.
The use of polymer materials for production means a lighter form factor and less signal interference. On the other hand, there are concerns about the durability of polymer AMHS devices at the temperatures and pressures of operation. The thermal performance of these devices is greatly influenced by the formation of the coolant jets as they leave the nozzles. As such, the integrity of these key geometric features is important to maintaining the performance of AMHS devices. Thus, this past semester my research, aided by graduate student Reece Whitt, comprised of an erosion study focused on the integrity of the impingement nozzles at elevated temperatures and pressures. The goal was to determine the coolant flow conditions under which a single nozzle would degrade and characterizing this degradation. To that end, we subjected single-nozzle samples to elevated flow rates and temperatures to accelerate erosion. In addition to these parameters, preliminary data suggested that cavitation, or vapor bubbles caused by low pressure areas, can quickly enlarge the nozzle diameter. Therefore, the effects of this phenomenon were studied alongside long-term effects of subtler forms of erosion.
We fabricated samples from nylon, high temperature epoxy, and ABS – polymer materials previously used for complete AMHS devices. The nylon and ABS were directly additively manufactured using multi-jet fusion and fused deposition molding, respectively. While the nylon were inherently waterproof, the ABS samples required post processing to achieve a watertight seal. For the epoxy samples, we printed the internal geometry out of a water-soluble material and cast the epoxy around it. The internal geometry was then dissolved out of the sample after the epoxy cured.
The presence or absence of cavitation naturally divided the study into two phases: testing under cavitating and non-cavitating flows. Damage to nozzles was quantified first by the change in pressure drop across the sample and second by the change in cross sectional area at the nozzle throat. In terms of results, both nylon and epoxy samples handled both testing environments quite well. These samples suffered minimal pressure drop or cross-sectional area changes in both flow conditions. On the other hand, ABS samples could not withstand even non-cavitating flow conditions for extend periods. High-intensity cavitation flows also greatly damaged the ABS nozzles. However, ABS samples provided similar results to the other samples when under cool, non-cavitating flows, or short durations of low intensity cavitating flows. Therefore, when considering materials for durable AMHS fabrication, this research supports nylon and epoxy as suitable candidates.
My research this semester provided an excellent opportunity for me to design an experiment in an academic setting and bring it to fruition. I am thankful for the guidance and mentorship provided by both Dr. Huitink and Reece Whitt throughout this study. This experience will serve me well as I pursue my master’s degree in mechanical engineering in the fall.