bluuebunny/crossref_metadata_2025_split huggingface dataset:
At Scale Development of Thermal Test Vehicles for Data Center Liquid Cooling Developments
Authors: Heydari Ali , Miyamura Harold , Chowdhury Uschas , Manaserh Yaman Mohammad Ali , Tradat Mohammad , Shahi Pardeep , Radmard Vahideh , Eslami Bahareh , Kalma Dwayne , Rodriguez Jeremy 
Published: November 2023

Abstract
High-performance computing with the latest generation of high-density chips and microprocessors in data centers requires advanced and efficient cooling technology to meet the challenging thermal requirements. Indirect liquid cooling with cold plates on top of the processor has become an attractive and efficient solution while transitioning from traditional air cooling inside the data center. Using a thermal test vehicle (TTV) can be a cost-effective and reliable methodology to commission liquid-cooled components successfully without risking actual IT equipment. TTVs can also be highly beneficial in testing and developing data center cooling technologies for future products with individual thermal requirements. In this paper, TTVs are created to replicate the thermal behavior of heat-generating components to characterize case-to-coolant thermal resistance, find hotspots, develop and test cooling technologies cost-effectively. Different design requirements influence the development and the intricacy involved in the construction, manufacturing, and telemetry of the TTV. In our study, TTVs for a 3U sled are discussed in detail, touching on different aspects such as proof of concept, design, verification, manufacturing, testing, and verification in a data center environment. The effects of choosing appropriate material properties, electrical requirements, form factors, stack-up method, type of heat-generating components, thermocouple placement, and nonuniform heat flux are also presented following analytical, numerical, and experimental results. The results and failure cases suggest some best practices in designing non-silicon TTVs while mimicking higher heat load in form factor of high heat density servers. Manufactured TTVs are placed in a chassis following the configuration and form factor of the 3U sled in high heat density servers and scaled up in a rack. In addition, a custom rack mount TTV server named “Olympus” is presented as an outcome of the study. Cold plates and cooling loops can be tested on the TTV server for thermal and hydraulic characterization with rack and row manifolds, Liquid-to-Liquid (L2L), and Liquid-to-Air (L2A) heat exchangers in a data center test environment. Later in the paper, the commissioning of liquid cooling technologies with TTVs is demonstrated in a data center environment. Real-time data for heater spreader temperature in TTVs are plotted with the help of a front-end application with boundary conditions on both primary and secondary sides. As a result, this paper provides complete guidelines on the development, verification, and application of TTV to determine critical performance parameters in commissioning (such as flow rate, temperature, pressure drop, cooling capacity, etc.) and simulate failure scenarios to ensure the reliability of components in the loop.
Evolution of Physical Properties of Liquid Film During Evaporation Process: Drying and Evaporation Process of Inkjet Liquid Film
Authors: Kichise Keisuke , Harada Yoshihiro , Kuramoto Shinichi , Kadonaga Masami , Fushinobu Kazuyoshi , Kato Koichi 
Published: November 2023

Abstract
In general, the evaporation and drying process of liquid film is a complex thermo-fluid phenomenon related to phase change and heat/mass transfer accompanied by changes in the physical properties of the liquid and understanding them is important in improving the performance of inkjet printers. In inkjet printers, ink droplets are ejected onto the media by an inkjet printhead to form a thin liquid film, which is then fixed by evaporation in a dryer. The dryer is one of the modules that consumes the most power among the inkjet printer components, and it is important to understand the evaporation behavior of the ink liquid film. One effective method to understand the evaporation behavior of ink film is to measure the temporal change in viscosity of the ink film surface. However, it has been difficult to measure the viscosity of thin liquid films formed by inkjet printheads using conventional methods. In this study, we propose to measure the temporal change of the viscosity of the liquid film surface by applying the Dynamic Light Scattering (DLS) method.
Boiling Limit on Textured Oil-Impregnated Surfaces
Authors: Zhou Yimin , Adera Solomon 
Published: November 2023

Abstract
Boiling is an important heat and mass transfer process that has tremendous benefits in thermal management applications where timely and efficient heat removal is critical for operation. Boiling is inherently limited by the critical heat flux (CHF), which is the maximum heat flux that can be dissipated from the heated surface via liquid-to-vapor phase change. Heat fluxes that exceed CHF cause surface dry-out that initiates thermal runaway and eventual device failure or burnout. Past studies have used micro/nanoengineered surfaces to improve wicking and liquid replenishment mechanism to delay CHF and/or increase the CHF limit. In this work, we investigate the CHF limit of micro-nanotextured oil-impregnated surfaces in pool boiling. Pool boiling experiments in water were conducted for copper plates with different surface morphologies, including Krytox oil impregnation. The bubble nucleation, growth, and departure behaviors were captured using a high-speed camera at 1000 frames per second during nucleate boiling. Due to the presence of an annular wetting ridge, which forms near the base of the growing bubble, the bubble growth and coalescence mechanism on oil-impregnated surfaces was distinct from that on un-impregnated micro-nanostructured hydrophobized (i.e., superhydrophobic) surfaces. Our experimental results show that (a) the bubble departure diameter on the oil-impregnated surfaces was 1.6-times larger than that on the superhydrophobic surfaces and (b) the CHF on oil-impregnated surfaces was similar to that on the un-impregnated superhydrophobic surfaces (≈20–30 W/cm2), a result that we attribute to oil depletion. Results show that oil impregnation does not improve the CHF limit in boiling.
Experimental Validation of a Heuristic Control Strategy for a Transient Thermal Management System With Latent Thermal Energy Storage
Authors: Shanks Michael , Inyang-Udoh Uduak , Jain Neera 
Published: November 2023

Abstract
Hybrid thermal management systems (TMS) enable faster response to rapid transient heat loads by supplementing heat rejection through a primary heat sink with temporary heat storage in a thermal energy storage (TES) device. The TES is not a passive component; it must be actively controlled by a realtime controller to decide when the TES should be discharged or recharged. While various types of controllers have been developed for hybrid TMS architectures, controllers for hybrid TMS in transient electronics cooling applications have predominantly been demonstrated in simulation environments. One such controller developed previously is a heuristic logic-based controller that leverages a state of charge (SOC) metric and feedback from several thermocouples placed in the fluid loop to manage the operation of the TES. In that prior work, the controller was demonstrated in simulation only; this paper builds on that work by implementing and validating the controller’s performance in an experimental single-phase hybrid TMS testbed. A particular advantage of this controller is its low level of computational complexity, facilitated by its rule-based architecture, which makes it more amenable for industrial use. We present an experimental case study to demonstrate the heuristic controller’s ability to meet two objectives: reduce the peak temperature at the surface of the cold plate below an allowable threshold and manage the SOC so the thermal storage capacity is not depleted.
Development of Ceramic Pulsating Heat Pipes for Medium-Voltage Power Electronics
Authors: Abdelmaksoud Ramy , Diebold Jeffrey , Hota Sai Kiran , Lee Kuan-Lin , Sinha Shivangi , Maksimovic Dragan 
Published: November 2023

Abstract
Due to the rapid increase of electric vehicles in the market, a corresponding significant increase in fast chargers will be needed. However, expanding the adoption of fast chargers such as direct current fast chargers is challenging with the current grid infrastructure. Medium-voltage (MV) electronics are an essential component in grid-tied applications. However, thermal management of such components presents a barrier to pushing the boundaries of high-power density, while maintaining high efficiency and reliability. Thermal management is further complicated by the need to maintain sufficient voltage isolation. Under a Small Business Innovative Research (SBIR) Phase I program funded by the U.S. Department of Energy (DOE), Advanced Cooling Technologies, Inc. (ACT), in collaboration with the University of Colorado, Boulder (UC Boulder) developed innovative ceramic Pulsating Heat Pipes (PHP)s, which significantly improved the thermal management and provided voltage isolation. Different flat ceramic PHPs were fabricated for the lab-scale testing. The thermal performance and voltage isolation were evaluated through both experimental testing and numerical modeling. The effect of different parameters, such as the fill ratio, gravity-aided and against-gravity orientations, and heat input, on the thermal performance of the ceramic PHP, was investigated. It was found that at the optimal fill ratio, a thermal resistance reduction of 41%–67% was achieved for different gravity-aided orientations (0–90°) when compared to the uncharged ceramic PHP (i.e., the ceramic PHP without fluid in it). The ceramic PHP was able to efficiently transport up to 6 W/in2 with a thermal resistance reduction of 58% at the horizontal position. The voltage isolation testing showed that the ceramic PHP can provide electrical insulation when exposed to a voltage of 28 kV. In addition, the effect of different working fluids and fill ratios, on the voltage isolation capability of the ceramic PHP, was investigated.
Evolution in Lead-Free Solder Alloys Subjected to Both Mechanical Cycling and Aging
Authors: Maruf Mahbub Alam , Mazumder Golam Rakib , Chakraborty Souvik , Suhling Jeffrey C. , Lall Pradeep 
Published: November 2023

Abstract
Solder joints in electronic packaging often experience failure due to cyclic thermo-mechanical loading. For example, electronic components in the automotive engine compartment or a giant turbine of a power plant may encounter both thermal cycling as well as mechanical cycling due to vibration. At the same time, electronic components can undergo thermal cycling due to frequent power switching, e.g., turning a car engine on and off. Thus, the solder materials used to attach electronic components are often subjected to cyclic stresses and strains due to temperature changes and the CTE mismatches of the assembly materials, as well as due to vibration and other time-varying loadings. In the literature, recent studies by our group have been carried out to examine the mechanical behavior and property evolutions (e.g., modulus, yield stress, ultimate tensile strength, and creep rate) occurring due to either isothermal aging or due to isothermal mechanical cycling. In the case of aging, microstructure changes are the primary reason for changes in the mechanical response. In the case of mechanical cycling, both microstructural evolution and damage accumulation (e.g. microcrack growth) lead to the observed changes. Currently, there are no prior investigations on the effects of both isothermal aging and mechanical cycling on the mechanical property and microstructural evolution of lead-free solder alloys.
In this study, we have evaluated the changes in mechanical properties and microstructure that occur due to mechanical cycling followed by isothermal aging at high temperature. Uniaxial samples of SAC305 lead-free solder alloy were first prepared by solidification in glass tubes under a controlled reflow profile. The samples were first mechanically cycled under strain control for various durations (e.g., 0, 50, 100, 200, 300 cycles), and then subsequently aged for 20 days at T = 125 °C. All of the preconditioned specimens were then subjected to nanoindentation testing to evaluate mechanical properties. Results for the various tests were compared to characterize the effects of combined effects of aging and mechanical cycling on the deterioration of the elastic modulus, hardness, and creep properties relative to the results for pristine specimens. As expected, exposure to both cycling and aging greatly influenced the results, with the samples that were cycled 300 times followed by aging showing the greatest degradations. Optical microscopy was also used to evaluate the microstructural evolution which demonstrates microstructural coarsening occurred in the samples due to the combination of mechanical cycling aging.
Repairability of SMDs on 3D Printed Circuitry for Sustainable Electronics Utilizing Direct Write Technique
Authors: Lall Pradeep , Sarwar Md Golam , Soni Ved , Miller Scott 
Published: November 2023

Abstract
Sustainable conductive ink for 3D-printed flexible electronics is needed to enable lower-impact waste print processes. The ability to undertake reparability is an additional method to achieve sustainable products through the extension of electronic components’ lifespan and reduced e-waste. However, repairability studies are scarce for sustainable, flexible electronics in the literature. This study assessed the repairability potential of Surface Mount Devices (SMD) on 3D-printed full wave rectifier circuits for sustainable flexible electronics. Full wave rectifiers are commonly used in power supplies, battery chargers, and other applications requiring a steady DC voltage. The direct-write printing technique used stretchable silver ink and interconnects composed of electrically conductive adhesive (ECA) for component attachment to create conductive traces. The circuit’s electrical characteristics are assessed using a high-frequency impedance analyzer, which analyzes the circuit’s resistance, capacitance, and inductance at various frequencies. The circuit is deliberately damaged by removing SMDs, and the research looks into the efficiency of direct write repair procedures. Direct write repair entails printing a conductive pad onto the circuit surface selectively using the same direct-write technique that was used for manufacturing the circuit. The repaired circuits are evaluated using an impedance analyzer, and the results are compared to the original circuit to determine the influence of the repair procedure on the circuit’s electrical performance.
Component Attach Process Recipe and Performance on Aerosol Printed Sustainable Silver Ink
Authors: Lall Pradeep , Bimali Sabina , Narangaparambil Jinesh , Miller Scott 
Published: November 2023

Abstract
The advancement of flexible printing technology in electronics has raised the demand for compact, lightweight, and stretchable printed electric circuits. The viability of environmentally friendly water-based inks with low-impact waste requires the development of process recipes for component attachment on flexible substrates. The processes required for component attachment on the newer generation of inks are not well understood. This paper aims to demonstrate process parameter study and component attachment in the aerosol jet printer (AJP) platform with water-based silver nanoparticle ink. The process parameter study includes printing parameters such as UAMFC, SMFC, stage speed, several passes, and sintering analysis, including sintering time and temperature. Print quality is evaluated using white light interferometry (WLI) and optical microscopy images. By integrating the bell-shaped cross-section area (CSA) acquired by the WLI test, the CSA of the printed lines is computed. The electrical and mechanical properties of the printed lines are quantified in terms of resistivity and shear load to failure, respectively. Optimized parameters from the printing and sintering process are used to print traces on which different components are attached with the help of ECA (Electrically Conductive Adhesive). The effect of using sustainable ink and ECA on passive components was analyzed by comparing their performance before and after being attached. Components that fall within the acceptable range of the rated value are deemed to be functioning properly.
Performance Analysis of Liquid-to-Air Heat Exchangers of High-Power Density Racks
Authors: Heydari Ali , Gharaibeh Ahmad R. , Tradat Mohammad , Soud Qusai , Manaserh Yaman , Radmard Vahideh , Eslami Bahareh , Sammakia Bahgat , Rodriguez Jeremy 
Published: November 2023

Abstract
The ability of traditional room-conditioning systems to accommodate expanding information technology (IT) loads is limited in contemporary data centers, where the storage, storing, and processing of data have grown quickly as a result of evolving technological trends and rising demand for online services, which has also led to an increase in the amount of waste heat generated by IT equipment. Through the implementation of hybrid air and liquid cooling technologies, targeted, on-demand cooling is made possible by employing a variety of techniques, which include but are not limited to in-row, overhead, and rear door heat exchanger cooling systems. The ongoing trends of rising power densities of microprocessors and the presence of hot spots present a considerable challenge to the air-cooling system, which pushes it to its limits. As a result of the significant rise in IT power densities, single-phase cold plate cooling is becoming increasingly popular. However, the limited availability of a source of chilled water or constrained air distribution routes and the unavailability of raised floors are the main obstacles to the adoption of single-phase cooling technologies in many old data centers, which led to the use of liquid-to-air cooling distribution units (CDUs). These types of CDUs effectively cool servers by distributing liquid coolant into cooling loops that are installed on top of each server. The CDU pumps cold liquid to cooling loops attached to servers or chips, where they absorb heat. After returning the heated fluid to the CDU, the heat exchanger (HX) uses the cold air to eject the by the use of fans.
One of the most common liquid cooling techniques will be examined in the current study based on different conditions for high power density racks (+50 kW). This paper investigates the cooling performance of a liquid-to-air in-row CDU in a test rack containing seven thermal test vehicles (TTVs) under various operational conditions, focusing on cooling capacity, HX effectiveness, and TTV case temperatures under different supply air temperatures (SAT). This test rig has the necessary instruments to monitor and analyze the experiments on both the liquid coolant and the air sides. Moreover, another experiment is conducted to assess the performance of the CDU that runs under different control fan schemes, as well as how the change of the control type will affect the supply fluid temperature and the TTV case temperatures at 10%, 50%, and 100% of the total delivered power. Finally, suggestions for the best control fan scheme to use for these systems and units are provided at the conclusion of the study.
Enhancing Mechanical Reliability of Silver Sintered Joints With Copper Nanowires in High-Power Electronic Devices
Authors: Medina Garcia Alicia , Harris John , Huitink David R. 
Published: November 2023

Abstract
This study investigated the mechanical reliability of silver-sintered die attachment under harsh operating conditions, and explored the advantages of adding copper nanowires to improve the bond’s mechanical properties. Samples were prepared using a template-assisted electrochemical deposition process to coat the substrate surface with copper nanowires, and were subjected to thermal aging at various temperatures to assess their mechanical reliability. Results showed that the incorporation of copper nanowires in the substrate interface significantly reduced degradation in shear strength as a result of thermal aging, acting as mechanical reinforcement and improving the interfacial resilience against mechanical shear stress. The addition of copper nanowires also reduced the void formation in the thermal aging, resulting in a more robust and reliable bond. The study demonstrates the potential of using copper nanowires as a reinforcing agent to enhance the mechanical properties of silver-sintered die attachment, particularly for high-temperature applications.
Finite Strain Sensing via Additively Manufactured CNF/TPU Strain Gauges
Authors: Hernandez Julio A. , Maynard Cole , O’Brien Corey , Rodriguez David , Newell Brittany , Tallman Tyler N. 
Published: November 2023

Abstract
Multifunctional additive manufacturing (AM) has opened the door to exciting new possibilities for highly customizable and on-demand printable sensors and actuators for application in areas such as embedded structural sensing, robotics, and, among other examples, human healthcare and monitoring technology. In particular, strain or deformation sensors printed via fused filament fabrication (FFF) methods typically make use of the piezoresistive effect, which can be achieved by modifying the base polymer with conductive micro-to-nanoscale fillers. However, sensors of this type often suffer from challenges such as limited flexibility due to the use of comparatively hard polymers and additives and highly inconsistent electrical properties. To overcome these challenges, we herein present the preliminary results of a study of carbon nanofiber (CNF)-modified thermoplastic polyurethane (TPU) sensors produced via FFF printing. The CNF/TPU filament used to print these sensors was produced using a novel wet mixing process, wherein the TPU is first dissolved in dimethylformamide (DMF) solvent prior to dispersing the CNFs. To demonstrate the strain sensing properties of this material, simple dog bone-shaped sensors were printed out of TPU modified with 7.5 and 10 wt.% CNFs. And to showcase the potential of this material for large deformation sensing, resistance changes were measured for finite strains up to 50%. The CNF/TPU sensors showed non-linear but monotonically increasing resistance up to approximately 35% strain, beyond which point resistance rapidly became immeasurable. The results of this study are an important step towards the realization of next-generation printable plastics with functional and consistent properties for applications such as strain sensing.
An Investigation on the Effectiveness of Cross-Sectional Tapering for Broadband Non-Reflective Traveling Waves Generation in Beams With Passive Discontinuities
Authors: Omidi Soroor Amirhossein , Tarazaga Pablo A. 
Published: November 2023

Abstract
Inspired by the dynamic behavior of the basilar membrane in the mammalian auditory system, the non-reflective traveling wave phenomenon is studied in a finite tapered cantilever beam. The goal of this study is to investigate the effectiveness of tapering the geometry to relax the design sensitivity to achieve such behavior as compared to the uniform geometry. The Galerkin method is used to derive the discretized form of the equation of motion. The results of this study suggest that tapering can be effective in improving the robustness of the design space in which traveling waves can be obtained.