Thermal Design Research Articles

Correlation of heat transport mechanism and structural properties of GaN high electron mobility transistors

Grain sizes, impurities, and layer thicknesses in the nm-range affect the heat transport and, hence, hinder proper heat dissipation of GaN-based devices. To obtain a clear picture of heat dissipation, the mechanisms of heat transport must be linked to the structural properties of the nitride-based materials in the device. In this paper, a systematic investigation of the typical layers of GaN high-electron mobility transistor stacks was conducted by time-domain thermoreflectance analysis and Raman measurements. The analyzed layers are the AlN nucleation layer, the Al0.3Ga0.7N transition layer, the AlGaN/AlN superlattice, the C-doped GaN back-barrier, and the uid GaN layer. The results were interpreted using the Born–van Karman model, including the suppression function approach to describe the governing heat transport mechanisms. Investigation of this AlN nucleation layer showed that its phonon scattering is dominated by impurity and grain boundary scattering. The Al0.3Ga0.7N transition layer was shown to have a reduced thermal conductivity not only due to alloy scattering but also because of grain boundary scattering. The AlGaN/AlN superlattice showed a thermal conductivity lower than the Al0.3Ga0.7N transition layer, especially at higher temperatures (7.2 ± 0.2 W/mK vs 14.1 ± 0.4 W/mK at 300 °C). Caused by the enhanced AlGaN/AlN interface density, the thermal conductance was found to be 2 GW/m2 K. The AlGaN/AlN superlattice indicated an anisotropic thermal transport with a factor of ∼1.5. The C-doped GaN layers were analyzed in terms of their size-dictated thermal conductivity, resulting in a reduction of ∼66% from 1 μm to 250 nm at 30 °C. Raman spectroscopy revealed that the thicker the GaN layer, the higher the compressive stress in GaN, which additionally results in a higher thermal transport. The investigations of the heat transport depending on the structural properties enabled an accurate determination of the thermal conductivity of the layer stack. These thermal conductivities served as input parameters for 3D simulation to extract the temperature, in terms of the thermal resistance, of such high-electron mobility transistor stacks. This simulation shows the importance of the GaN layer in terms of thermal management. This work uncovers the thermal transport in GaN-based transistor stacks with the aim to improving the thermal design.

Quick Prediction of Complex Temperature Fields Using Conditional Generative Adversarial Networks

Abstract Qualified thermal management is an important guarantee for the stable work of electronic devices. However, the increasingly complex cooling structure needs several hours or even longer to simulate, which hinders finding the optimal heat dissipation design in the limited space. Herein, an approach based on conditional generative adversarial network (cGAN) is reported to bridge complex geometry and physical field. The established end-to-end model not only predicted the maximum temperature with high precision but also captured real field details in the generated image. The impact of amount of training data on model prediction performance was discussed, and the performance of the models fine-tuned and trained from scratch was also compared in the case of less training data or using in new electronic devices. Furthermore, the high expansibility of geometrically encoded labels makes this method possible to be used in the heat dissipation analysis of more electronic devices. More importantly, this approach, compared to the grid-based simulation, accelerates the process by several orders of magnitude and saves a large amount of energy, which can vastly improve the efficiency of the thermal management design of electronic devices.

Analytical model of the steady state temperature distribution in a single and multi-layer brake disc

This article focuses on the modeling and analyzing effort for the thermal analysis and design of disc brake for endurance braking scenario. Test cases of bike disc brake rotor are chosen as its unique double layered architecture has been recently proposed for thermal optimization especially. This work aims at the evaluation of the steady state temperature distribution during braking to be studied considering a constant rotation speed and localized heat sources at the brake pad area. The problem is solved analytically using variable separation and a double Fourier - Hankel transforms.The modelling strategy is developed for a single layered rotor as reference cases for various rotation speed and rotor thicknesses. The effect of the rotation speed is underlined using a representative constant heat exchange coefficient. For high rotation speed (greater than 50 rad s-1 for the studied geometry), an effective surface layer can be observed which limits the influence of the rotor thickness on the temperature level. The model is extended to a multi-layered material rotor architecture. The potential advantages of this composite structure for different layer thicknesses and materials are evaluated and discussed. It appears that the aluminium core provides the better results, yet the relative reduction of the temperature compared to a plain stainless steel disc is of about 1 % only.

Methodology to Characterize Row Manifolds for High Power Direct to Chip Liquid Cooling Data Centers

Abstract Demand is growing for the dense and high-performing IT computing capacity to support artificial intelligence, deep learning, machine learning, autonomous cars, the Internet of things, etc. This led to an unprecedented growth in transistor density for high-end CPUs and GPUs, creating thermal design power (TDP) of even more than 700 watts for some of the NVIDIA existing GPUs. Cooling these high TDP chips with air cooling comes with a cost of the higher form factor of servers and noise produced by server fans close to the permissible limit. Direct-to-chip cold plate-based liquid cooling is highly efficient and becoming more reliable as the advancement in technology is taking place. Several components are used in the liquid-cooled data centers for the deployment of cold plate based direct to chip liquid cooling like cooling loops, rack manifolds, CDUs, row manifolds, quick disconnects, flow control valves, etc. Row manifolds used in liquid cooling are used to distribute secondary coolant to the rack manifolds. Characterizing these row manifolds to understand the pressure drops and flow distribution for better data center design and energy efficiency is important. In this paper, the methodology is developed to characterize the row manifolds. Water-based coolant Propylene glycol 25% was used as the coolant for the experiments and experiments were conducted at 21 °C coolant supply temperature. Two, six-port row manifolds' P-Q curves were generated, and the value of supply pressure and the flow rate were measured at each port. The results obtained from the experiments were validated by a technique called Flow Network Modeling (FNM). FNM technique uses the overall flow and thermal characteristics to represent the behavior of individual components.

Analysis of unsteady flow of [formula omitted] based nanoparticle of different shapes in the presence of joule heating over stretching surface

This work investigates the unsteady flow behavior of variously shaped Cunanoparticles based EG-nanofluid in the presence of Joule heating across a stretched surface. The study's objective is to comprehend and explore how the geometry of nanoparticles affects the thermal behavior and velocity field of a nanofluid flow. The matter is significant because it has an impact on industrial processes, thermal management systems, and cooling technologies. Moreover, the influence of joule heating on convective heat transfer is examined. In order to account for unsteadiness and shape-dependent nanoparticle features, numerical solutions are derived for the major equations of corresponding thermal phenomenon of nanofluid flow. The acquired results shed important light on how the form of nanoparticles and Joule heating affect the properties of heat transfer across the stretching sheet. Meanwhile, friction coefficient and local Nusselt number are calculated numerically and tabulated for discussion. Cu nanoparticles in various forms and other relevant parameters are investigated for their effects on flow, joule heating properties, and heat transmission. Significant evidence shows that using spherical nanoparticles instead of cylindrical or platelet-shaped ones results in a 15 % boost in heat transmission rates. Moreover, Joule heating has significant effect over thermal boundary layer and can generally boost heat transfer by up to 20 %. It is argued that the thermal efficiency of nanofluid systems can be greatly increased by optimizing the form of nanoparticles and taking Joule heating into account. This work is novel due to it fully examines the combined impact of Joule heating and nanoparticle morphology on unstable nanofluid flow, offering new perspectives beyond previous studies that mostly focused on steady-state conditions or disregarded the shape aspect. Through a deeper comprehension of nanofluid behavior in dynamic environments, our work opens the door to more efficient thermal management system design.

Are airports like cities? Affordances and people’s micro embodied interactions during the arrival experience

Airports are designed to work efficiently. Specifically, they seek to efficiently process and ‘control’ people’s movements across landside and airside spaces, as well as to entice consumption through the architectural engineering of atmospheres and passenger experiences using architecture (Adey 2008; Fuller and Harley 2004; Hubregtse 2020). However, studies of the design and human sensorial perception of spaces of mobilities have shown that the way people move through and inhabit such spaces transcends the intended functionality of their design (Jensen and Lanng 2017). This includes work that considers airports as not only machines of movement, control and profit, but also city-like spaces (Hernandez-Bueno 2021; Nikolaeva 2013). Based on the conceptualisation of the airport as an ambiguous and city-like space, this paper uses thermal camera video recordings, ethnography, and design mappings to analyse the passenger movements, practices, embodied interactions, and mobile affordances of Copenhagen Airport’s meet and greet area. Focusing on a micro scale, the analysis shows the comparability of people’s practices and ways of inhabiting the airport with practices common to urban public spaces. This facilitates broader reflection on how to speculatively re-design and re-imagine the airport like an urban ‘public’ space.

Energy transfer, conversion and mechanical regulation in graded piezoelectric semiconductor bipolar junction transistor

While the effective regulation of carrier redistribution in piezoelectric semiconductor devices by mechanical loads through piezoelectric polarized electric fields is well-studied, there is a scarcity of reported research on the influence of energy transfer and conversion characteristics in a non-thermal equilibrium state of these devices. This paper establishes a nonlinear multi-field coupling model for piezoelectric semiconductor graded bipolar junction transistor (PS-GBJT) and proposes a corresponding multi-gradient iterative algorithm. We regard the product of current and built-in electric field as the work done by electric field force on carriers. By incorporating the energy absorbed/released during carrier recombination/generation process, we observe that non-equilibrium carriers act as a medium that facilitates energy conversion between these two mechanisms. Additionally, the non-uniformly distributed doping extends the influence of space charge region throughout entire transistor. In terms of external input electrical energy, the emitter, base, and collector regions play roles of input energy, transfer energy, and output energy, respectively. The study concludes by demonstrating the regulation of energy transfer or conversion efficiency in emitter, base, and collector regions through mechanical loads, thereby altering the heating behavior of entire GBJT and reshaping its energy transfer path. This leads to the significant finding that distinct energy transfer paths fundamentally define the various operational states of GBJT. The novel insights gained from this research hold reference value for thermal design and energy management of electronic devices.

Computational Fluid Dynamics-Based Systems Engineering for Ground-Based Astronomy

This paper presents the state-of-the-art techniques employed in aerothermal modeling to respond to the current observatory design challenges, particularly those of the next generation of extremely large telescopes (ELTs), such as the European ELT, the Thirty Meter Telescope International Observatory (TIO), and the Giant Magellan Telescope (GMT). It reviews the various aerothermal simulation techniques, the synergy between modeling outputs and observatory integrating modeling, and recent applications. The suite of aerothermal modeling presented includes thermal network models, Computational Fluid Dynamics (CFD) models, solid thermal and deformation models, and conjugate heat transfer models (concurrent fluid/solid simulations). The aerothermal suite is part of the overall observatory integrated modeling (IM) framework, which also includes optics, dynamics, and controls. The outputs of the IM framework, nominally image quality (IQ) metrics for a specific telescope state, are fed into a stochastic framework in the form of a multidimensional array that covers the range of influencing operational parameters, thus providing a statistical representation of observatory performance. The applications of the framework range from site selection, ground layer characterization, and site development to observatory performance current best estimate and optimization, active thermal control design, structural analysis, and an assortment of cost–performance trade studies. Finally, this paper addresses planned improvements, the development of new ideas, attacking new challenges, and how it all ties to the “Computational Fluid Dynamics Vision 2030” initiative.

Recent Advancements in Geothermal Energy Piles Performance and Design

Geothermal energy piles or ground heat exchange (GHE) systems embrace a sustainable source of energy that utilizes the geothermal energy naturally found inside the ground in order to heat and/or cool buildings. GHE is a highly innovative system that consists of energy loops within foundation elements (shallow foundations or piles) through which a heat carrier fluid circulates, enabling heat extraction or storage in the ground. Despite the innovation and potential of GHE systems, there are significant challenges in harmonizing their thermal and mechanical designs due to the complex interactions involved. This review critically examines state-of-the-art design methodologies developed to address these complexities, providing insights into the most recent advancements in GHE performance and design. Key findings include innovative techniques such as advanced numerical modeling to predict thermomechanical behavior, the use of different pipe configurations to optimize heat transfer, and strategies to minimize thermal stress on the foundation. Additionally, this review identifies research gaps, including the need for more comprehensive full-scale experimental validations, the impact of soil properties on system performance, and the long-term effects of thermal cycling on pile integrity. These insights aim to contribute to a better understanding of the thermomechanical behavior of energy piles, ultimately facilitating more accurate and effective design solutions.

A coupled modeling framework for investigating flow maldistribution in cross-flow-corrugated plate heat exchangers

Accurate prediction of the impact of flow maldistribution on the thermo-hydraulic behavior of plate heat exchangers is important for thermal design and optimization in a number of practical applications. In this paper, a coupled modeling framework, consisting of a heat transfer model and a hydraulic model, is proposed for quantitatively evaluating the impact of maldistribution on the thermo-hydraulic performance of a cross-flow-corrugated plate heat exchanger. The numerical results of the proposed approach are validated by comparison with experimental data. Using the coupled model, the flow distribution nonuniformity, heat exchanger effectiveness deteriorations, and pressure drop deviations are analyzed. Furthermore, the combined effects of side stream maldistribution are investigated for different inlet Reynolds numbers and inlet temperatures. The results demonstrate that when the inlet gas Reynolds number is in the range of 1100–2700, nonuniform distribution of the gas side will cause air maldistribution, and a 10%–30% effectiveness deterioration rate. It is found that air maldistribution will not result in gas maldistribution when the inlet air Reynolds number is in the range of 6000–18 000, but increasing air nonuniformity. Will lead to increasing deterioration in heat exchanger effectiveness. In the presence of air and gas flow maldistribution, the pressure drops on the gas and air sides increase by 5% and less than 12.4%, respectively. This work provides a computational framework for optimization of cross-flow-corrugated plate heat exchangers to achieve desired thermo-hydraulic performance.

Heat transfer measurement near injection hole of supersonic nozzle with a sonic jet injection

Heat transfer measurements were conducted to investigate surface heat transfer characteristics resulting from the interaction between a sonic jet and supersonic nozzle crossflow. A sonic jet was injected into the nozzle where the average Mach number is 2.88. Experiments were carried out for three different momentum flux ratios (J=0.5, 1.0, 1.5). A half-nozzle was introduced to measure heat transfer on the inner walls of the nozzle using Infrared thermography. Pressure measurements using PSP and oil flow visualization were also conducted to understand the heat transfer. From the oil flow visualization and heat transfer results, it was found that the area around the hole influenced by recirculation vortexes exhibited high heat transfer coefficients, showing up to 5 times higher values compared to the freestream. Furthermore, as the momentum flux of the jet increased, both the heat transfer augmentation area and the heat transfer coefficient also increased. To analyze the heat transfer characteristics between the nozzle and flat surface, comparisons were made using dimensionless heat transfer coefficients. The nozzle exhibited higher heat transfer in a smaller interaction area compared to that of a flat surface, but the average heat transfer coefficient near the hole was lower. Accordingly, distinct thermal treatment strategies should be employed for nozzles and flat surfaces, especially near injection holes. These insights could be valuable for the thermal design of rockets and other supersonic/hypersonic mobility systems.

Mechanical and thermal property analysis and optimization design of hybrid lattice structure based on triply periodic minimal surfaces

Hybrid lattice structures have significant potential in engineering applications owing to their outstanding mechanical and thermal properties. In this paper, an innovative design strategy for hybrid lattice structures is proposed involving the integration of primitive surfaces with truss lattice configurations. This approach allows for the full exploitation of the mechanical and thermal properties inherent in each component, leading to the development of new hybrid lattice structures. Firstly, the quasi-static compression and fluid-solid coupling heat conduction analysis of the hybrid lattice structure is carried out by numerical simulation. Then the effects of surface wall thickness, and truss diameter on the mechanical and thermal properties of the lattice structure are discussed. Additionally, the mechanical performance of the array hybrid lattice structure is evaluated through quasi-static compression experiments. These experimental results are compared with those from the numerical simulations, validating the accuracy of the simulation model. Finally, a multi-objective optimization model targeting specific elastic modulus and heat dissipation performance (indicated by Nusselt number) is established, in response to the demand of aviation and aerospace industries for lightweight, load-bearing, and heat-dissipating multi-functional integrated lattice design. The non-dominated sorting genetic algorithm is utilized to solve the optimal model, and the distribution of feasible solutions and Pareto front are obtained. The results show that the interpenetrating hybrid lattice structure has a greater improvement in mechanical and thermal properties than the primitive surfaces. This research holds significant implications for the design of multi-performance hybrid lattice structures.

Thermal design of a non-isothermal microfluidic channel for measuring thermophoresis

Thermophoresis describes mass transport in a non-isothermal temperature field and thus provides a fundamental understanding of the behavior of colloidal particles. Various methods have been proposed for measuring the Soret coefficient, a representative value of thermophoresis. In particular, microscopic channels are an emerging method as they shorten the equilibrium time and allow direct observation of the particles. However, little emphasis has been placed on the simultaneous consideration of fluid dynamics, heat transfer, and mass transfer characteristics within the microfluidic channel, despite the simultaneous presence of natural convection and thermodiffusion phenomena. In this study, we present a novel approach to address this gap by introducing a figure of merit, which incorporates essential parameters to accurately characterize a specific cell configuration. This figure of merit allows for the identification of a reliable measurement range in a microfluidic channel with a temperature gradient, while accounting for fluid dynamics, heat transfer, and mass transfer characteristics. The proposed approach is validated through rigorous simulations and experiments, enabling an evaluation of the impact of figure of merit-derived parameters on the measurement channel. The findings from our study demonstrate that the figure of merit serves as a representative measure for stable thermophoretic measurements in a microfluidic channel. Moreover, we propose a threshold value that signifies the transition from a diffusion-dominant to a convection-dominant field.

Heat Load Development and Heat Map Sensitivity Analysis for Civil Aero-Engines

The design complexity of the new generation of civil aero-engines results in higher demands on engines’ components, higher component temperatures, higher heat generation, and, finally, critical thermal management issues. This paper will propose a methodological approach to creating physics-based models for heat loads developed by sources, as well as a systematic sensitivity analysis to identify the effects of design parameters on the thermal behavior of civil aero-engines. The ranges and levels of heat loads generated by heat sources (e.g., accessory gearbox, bearing, pumps, etc.) and the heat absorption capacity of heat sinks (e.g., engine fuel, oil, and air) are discussed systematically. The practical research challenges for thermal management system design and development for the new and next generation of turbofan engines will then be addressed through a sensitivity analysis of the heat load values as well as the heat sink flow rates. The potential solutions for thermal performance enhancements of propulsion systems will be proposed and discussed accordingly.

Introduction to thermal control design process for CubeSats in Mexico

Abstract CubeSats are a popular type of spacecraft categorized as nanosatellites. In 1999, Professors first developed these devices at California Polytechnic State University and Stanford University to offer an affordable and accessible experience to students. Data information updated up to May 31st, 2023, shows that 2286 Nanosats have been launched, where 2105 were CubeSats. Moreover, 82 countries have nanosats, whereas Latin America has 44 CubeSat. The fact that Mexico just 5 launched 5 CubeSats is a consequence of the complicated space sector ecosystem in the nation that combines lack of funding and, more importantly, the absence of ¨know-how¨ design space missions from scratch. This manuscript reviews the system engineering methodology used to develop space missions, according to NASA discussing a particular methodology for CubeSat Missions. Next, a CubeSat data trend is shown, followed by a general description of its subsystems. Afterward, the design process activities of the Thermal Control Subsystem (TCS) based on the “NASA Systems Engineering Processes and Requirements” and “Thermal analysis handbook is described. The TCS is often underestimated and confused to implement. For this reason, a design methodology for the TCS accepted to Mexico context is proposed. Finally, the conclusions are presented.

Research on PCB layout optimization of vehicle controller based on electrothermal hybrid simulation

Abstract With the rapid development of the electronic industry, electronic equipment is more and more widely used in automobiles. The integration of electronic components on the Printed Circuit board (PCB) is getting higher and higher, the size is getting smaller and smaller, and the power is getting larger and larger, which leads to a sharp increase in the heat flow density of the whole PCB. The surface temperature of the chip is too high when it is working, which leads to a series of thermal failure problems. In order to improve the thermal characteristics between PCB and electronic components and improve the heat dissipation capability and reliability of PCB, this paper designed a vehicle controller PCB. PowerDC was used to conduct an electrothermal hybrid simulation analysis, and the temperature distribution of the whole board was obtained. Meanwhile, the structural layout of the PCB was optimized by increasing the heat dissipation hole, floor copper foil, and wiring width. Thus, the temperature of PCB and electronic components is reduced, which provides a vital reference for the thermal design of PCB.

Improve the thermal performance of precooler by enhancing the utilization of chemical heat sink: Refined design method and characteristic analysis

The chemical heat sink of the coolant plays a crucial role in enhancing the performance of the precooler, which affects the overall performance of the air-breathing precooled engines. The conventional thermal design method for precoolers cannot accurately evaluate the chemical heat sink of coolants. To address this crucial issue, this paper proposes a refined model that considers the chemical reaction processes of n-Decane, based on a two-dimensional discretization unit model and the plug flow reactor model incorporating molecular-level chemical reaction mechanisms. The validation of this model is conducted by comparing it with publicly accessible data and computational fluid dynamics simulations, thereby demonstrating its excellent accuracy. Subsequently, an analysis is conducted on the factors influencing the chemical heat sink release of the coolant within the precooler, and enhanced design criteria for optimizing chemical heat sink utilization are proposed. Building upon these considerations, the performance of a precooler with a design point of Mach number 5 under off-design conditions was analyzed. The findings indicate that employing rational design methods can enhance the chemical heat sink efficiency of endothermic fuels by 8.0%, along with a concurrent 10.3% increase in the total heat sink. This underscores the significance of considering the impact of the chemical heat sink of endothermic fuels in the design of precoolers. In the case presented in this paper, the contribution of the chemical heat sink to the total heat sink within the n-Decane precooler could reach 35.3%.

Australian East-West Radio Relay System Revisited: Thermal Design of Repeater Shelters

The Journal revisits two historic papers from 1971 covering the thermal design and environmental controls in repeater shelters of the Australian East-West radio relay system from Northam in Western Australia to Port Pirie in South Australia.

Integrated manifold microchannels and near-junction cooling for enhanced thermal management in 3D heterogeneous packaging technology

The rapid advancement in electronic chip technology is driving the evolution of highly integrated and high-power configurations, which in turn imposes greater demands on thermal management. This study presents a novel approach to address the thermal management challenges associated with high-density integrated chips. By incorporating the near-junction cooling method into silicon-based chips, the thermal resistance during heat conduction is effectively reduced. To further enhance heat dissipation efficiency, we integrate manifold microchannels and near-junction cooling into an aluminum nitride ceramic substrate, creating a heterogeneous three-dimensional integrated chip. To verify the effectiveness of our approach, a thermal test chip and an aluminum nitride substrate with a manifold structure are meticulously prepared and packaged for experimental testing. Remarkably, the experimental results demonstrate that the heterogeneous integrated chip, featuring manifold microchannels, achieves an impressive heat dissipation capacity of 700 W/cm2 under normal operating temperature conditions. Additionally, sensitivity analysis and multi-objective optimization approach were employed, utilizing the Response Surface-Genetic Algorithm П(NSGAП), to optimize the manifold microchannels in the heterogeneous integrated chip. The optimization process yields significant improvements, reducing the total thermal resistance of the chip by 13.6 % and the maximum pressure drop by 68.5 %. These findings provide valuable theoretical insights and guidance for the thermal design of high heat flux integrated chips, and contribute to advance the design and development of high-performance integrated circuit systems.

Electro-thermal co-design of a variable pole toroidal induction motor

The United States Department of Energy targets an 88 % reduction in motor and power electronics volume by the year 2025 while minimizing or eliminating magnet usage. Induction machines are a magnet-free alternative with advantages such as low cost, high reliability, and capability of withstanding high short-term overload. To meet these societal goals, we develop an induction machine that uses an electro-thermal co-designed converter-integrated thermal management approach. The machine utilizes toroidal windings in the stator, and an 18-phase power converter to achieve 40 kW/L power density. An optimized jacket design was developed to enable the effective thermal management of the stator and integrated power electronics. The toroidal winding configuration provides advantages for thermal performance over conventional distributed windings due to an increased winding copper surface area without reducing slot-fill factor, thereby allowing for a higher stator density. The improved thermal performance of the toroidal winding design was verified using three-dimensional conjugate computational fluid dynamic simulations. A reduced-order transient model was then developed to generate torque-speed-temperature plots at various load conditions. The transient thermal analysis was extended to verify safe operation of the motor during a typical drive cycle for the desired application. The thermal design models developed in this work are robust and scalable to other motor sizes providing a framework for co-designing and developing thermal management systems for electric motors.