Abstract This study investigates the effects of structural parameters, such as porosity and pores per inch (PPI), on single-phase convection heat transfer enhancement in metal foams (MFs) with integrated pin-fins, using de-ionized (DI) water as the working fluid. Nine different foams with three different porosities and PPI values were examined. All foams were scanned using computed tomography (CT) and geometrically characterized. Experimental investigations, both with and without pin-fins, were conducted to analyze heat transfer and pressure drop characteristics. Comparison of computational predictions and measurements over the range of Re from 300 to 900 demonstrated 3.1% or better agreement in the Nu, and 9.3% or better agreement in the friction coefficient. The results revealed that, within the given Re range, increasing the metal foam density enhances Nu, whereas a higher PPI increases the pressure drop. Overall, metal foams with high density and low PPI exhibited superior heat transfer performance, both with and without pin-fins. A more significant improvement in heat transfer performance with pin-fins was observed in low-density (LD) metal foams, particularly those with 20 PPI. An artificial intelligence (AI) model, based on random forest regression, was developed to predict Nu, achieving an R-squared value of 0.99.

Abstract As the demand for cloud-based computer storage systems has been growing rapidly, aeroacoustic noise emission from data center server fans used for air cooling often exceeds safe values for those working in such an environment. Although axial fan-generated airflow and acoustic studies, both computational as well as experimental, are widely reported in literature, there is very little published work on integrated flow and acoustics study in an actual data center server setup. The present work reports on an aeroacoustic model of a server using high-fidelity transient computational fluid dynamics (CFD) and computational aeroacoustics (CAA). The model is validated against experimental flow and acoustics measurements for a server in a data center environment. The simulations demonstrate reasonable agreement with the experimental results, showing less than 10% deviation in fan curve data and sound pressure level (SPL), thus helping establish the present aeroacoustic model as a useful predictive tool for complete server aeroacoustics studies. The second part of this work involves noise control in a server using acoustic insulation materials. The effects of two commercial acoustic insulation materials and their influence on server noise reduction are investigated. The efficacy of the two materials is analyzed experimentally and compared against the baseline measurements, which are conducted without any insulation material. Additionally, a steady state thermal assessment was conducted on the server, which observed only a 2°C temperature rise due to the acoustic insulation. Therefore, the aeroacoustic model can be used as a benchmark method for aeroacoustic analyses.

As power density demands in power electronics escalate, integrated power delivery with embedded fluidic cooling has gained interest to leverage the exceptional characteristics of wide bandgap semiconductor devices. However, application-specific constraints-such as dielectric coolants, fewer package layers, and lack of topsided access for fluid ports-significantly limit the potential of this technology, leading to excessive fluid heating and reduced cooling effectiveness. These challenges become even more pronounced with homogeneous heat transfer enhancement structures, which lack the ability to provide spatial control of flow patterns. To unlock the potential of integrated cooling and power delivery, we proposed a hybrid architecture combining triply periodic minimal surfaces (TPMS) with micropillars to target local hot spots and enhance flow mixing where most needed. The cold plates were additively fabricated using binder jetting technique, and computational models were experimentally validated to unveil underlying physics, examining the unique flow structures generated by the combination of TPMS and pillars under diagonal flow. The swirling motion through a network of high-curvature channels intensified local vorticity, leading to disrupted thermal boundary layers and enhanced convective heat transfer. Unlike conventional micropillar-based cooling, which suffers from a downstream decline in local Nusselt number (Nu), the hybrid design expands the effective heat removal area by sustaining a positive downstream Nu gradient in the hot spot region. Overall, the hybrid architecture achieves a 17.9-57.0% increase in the average Nu compared to the traditional solution, offering promising potential to meet increasing power density demands with reduced cooling power overhead.

This study investigates flow boiling in pin-fin heat sinks, aiming to bridge the gap in the literature between microscale and macroscale geometries. The focus is on hydraulic diameters ranging from 880 mu m to 4.25 mm. Experiments were conducted on seven distinct pin-fin coldplate configurations, covering a wide range of mass fluxes from 70 kg/m2s to 2500 kg/m2s. The dielectric fluid HFE-7200 was used, with uniform heat fluxes applied up to 185 W/cm2, corresponding to a total heat dissipation of 1.85 kW. The thermal-hydraulic performance of the coldplates was characterized, and high-speed flow visualization was employed to identify flow regimes and elucidate the mechanisms underlying critical heat flux (CHF). Over 540 data points and 840 flow visualization videos were analyzed. The results led to the development of new empirical correlations for two-phase pressure drop, heat transfer coefficients, and CHF specific to dielectric flow boiling in meso-scale pin-fin coldplates.

Recent advances in the computational fluid dynamics and heat transfer (CFD/HT) modeling of flow boiling have enabled a more detailed analysis and understanding of thermal management in relatively complex microsystems. Most advanced modeling approaches allow the transient analysis of two-phase flow and phase-change processes, providing the capability to post-process in detail the temperature, phase and pressure distributions in microscale applications with the use of moderate computational resources. Although these models have significantly evolved in recent years, there are still several idealizations and assumptions that have yet to be improved or better justified, the boiling incipience treatment being a commonly questioned topic. In the present investigation, a boiling incipience model is incorporated into an existing CFD/HT model for the analysis of flow boiling mechanisms, where the superheat temperature is derived from fundamental thermodynamic relations and compared to the original CFD/HT model that does not account for such effects. Results are compared using a non-trivial case of a silicon micro-cooling layer with variable density of pin fins that has been demonstrated to be an efficient thermal control device in high-power applications. The dielectric fluid HFE-7200 is used as the coolant in flow boiling conditions. The two-phase flow regimes and heat transfer results for both models are compared.

Cooling presents a significant challenge for high-performance three-dimensional integrated circuits (3D ICs). To this end, this research explores through-silicon via (TSV)-compatible micropin-fin heat sink (MPFHS) for high-power 3D chip stacks. Copper TSVs with a diameter of 5.2 mu m and a high aspect ratio of 29:1 are developed. An extensive experimental and computational investigation of the MPFHS under varying flow rates and power conditions was conducted, showing that the MPFHS maintains an average chip temperature below 72 degrees C, even with a total power dissipation of 500 W and a power density of 312 W/cm (2) at a flow rate of 117 mL/min. The minimum total thermal resistance achieved was 0.286 degrees Ccm (2) /W.

Effective cooling strategy is critical to achieve improved performance and efficiency in electric-drive vehicle motors. Among approaches, direct winding heat exchangers (DWHXs), positioned inside the motor component slots, have demonstrated superior potential for cooling compared to conventional methods such as forced convection air cooling and liquid jacket cooling. In this work, an in-slot heat exchanger (HEx) based on the DWHX concept is developed for an outer-rotor motor with a 100 kW peak and 55 kW continuous power output, and 50 $\mathrm{kW} / \mathrm{L}$ power density. Initial work developed a baseline additively manufactured aluminum oxide heat exchanger to cool concentrated stator windings in an 18 -slot, 16 -pole outer-rotor motor; however, it lacked performance in cooling stator endwindings. A new design was envisioned to address this issue. The present study introduces a novel in-slot HEx design, which also incorporates a cooling solution for end-windings at both sides of the motor. The thermal performance of this new design is assessed and compared with the baseline concept. The results from the new design indicate an over 50% reduction in thermal resistance and more than 30% reduction in hot-spot temperature. The new design reduces end-winding temperature while maintaining improved thermal uniformity across the winding. The increase in pressure drop in the new design adds only 0.013 W to the pumping power. Furthermore, the results indicate that a potting material used as an interface material - with a thermal conductivity of 3$4 \mathrm{~W} / \mathrm{m} \cdot \mathrm{K}$ - to attach these heat exchangers to motor components is found optimal to ensure effective thermal performance. The achieved performance is realized without altering critical electromagnetic parameters, facilitating seamless integration with the current motor design. These results underscore the potential of ceramic-based in-slot HExs in improving the thermal performance and efficiency of modern electric-drive vehicle motors, representing a substantial advancement in the development of high-power-density electric motors.

High power density electric motor is essential to improve the overall performance of electric vehicle (EV) powertrain. However, the electromagnetic losses and winding temperature of the electric motor gradually increase with electrical load, which eventually limits the peak power density. Slot-embedded cooling solutions can be deployed to extract heat generated from the electromagnetic losses in the motor windings by establishing direct heat exchange between the winding and the coolant, and hence, winding temperature can be maintained below the thermal limit, even at high current densities. However, to accommodate the cooling architecture inside the motor slot, winding configuration may need to be modified, which can adversely affect the electromagnetic performance of the motor and can outweigh the thermal benefits of the embedded cooling technique. As such, the overall effectiveness of the slot-embedded cooling techniques strongly depends on slot size and winding configuration. This work studies the slot size effect on the overall effectiveness of three slot-embedded cooling techniques, namely, slot liner confined capillary flow-assisted evaporative cooling (EC), direct winding heat exchanger (DWHX), and evaporative cooling from the side and middle liner (EC-SML) and benchmarked their performance with the conventional jacket cooling (JC) technique. Two different permanent magnet motor topologies, a 125 kW BMW i3 motor with a small slot size of 91.65 mm(2)/slot and a 25 kW motor with a large slot size of 827.5 mm(2)/slot, have been considered to assess the slot size effect on the electro-thermal performance of all the cooling techniques. A two-way coupled electro-thermal modeling framework has been developed and after validating with experiments, used to quantify the performance of all the cooling techniques. Results show that in the case of 125 kW motor with small slot size, EC provides the best electro-thermal performance, whereas in the case of 25 kW motor with large slot size, EC-SML outperforms all other cooling techniques.

Outdoor digital displays deployed in harsh environments must withstand wide-ranging stresses driven by internal heat generation and fluctuating ambient conditions. The transient internal and external thermal conditions in the environment of a deployed display cause internal pressure and temperature fluctuations (termed "heartbeats"). This paper presents a transient computational fluid dynamics/heat transfer(CFD/HT) framework for simulating these fluctuations of pressure and temperature in gasketed outdoor digital displays and electronics enclosures. Using a pressure-based solver with the k-omega SST turbulence model and ideal-gas density, a new leakage model (based on experimental decay curves) is used to represent air losses from gasket and seams by using pressure and temperature driven source terms. Variable electronic heat loads and fan PWM duty cycles are imposed through user-defined named expressions. The developed framework is validated against experimental data from a production testing protocol designed to determine the quality of a gasket seal in an outdoor digital display prior to deployment, while under controlled ambient conditions. The MRI BoldVu Gen15 55 '' double-sided outdoor digital display was used for all experimental testing. The results reveal that gasket leakage dominates pressure decay during cooling, while the air thermal expansion drives the pressure increase during heating phase. This validated model offers insights into design optimization of enclosure sealing and thermal management strategies.

This study experimentally and computationally investigates the convection heat transfer performance of metal foams (MFs) having the same pores per inch (PPI) but different porosities attached to a uniformly heated surface using three different thermal interface materials (TIMs). Of the three TIMs considered, flexible graphite showed the best heat transfer performance by around 10%-25% compared to the reference case, where no TIM was used, due to its high in-plane thermal conductivity. In contrast, thermal epoxy was the worst, with a decrease in heat transfer by around 10%-30%, relative to the reference case. A comparable performance to the reference case was exhibited by the thermal gap pad. The MF hydraulic modeling parameters were extracted from the pressure drop data, and pore and filament diameters were obtained from micro-CT ( mu CT) scans and used in the numerical simulations. Thermal contact resistances (TCRs) are assessed from the numerical simulations. The results showed that total TCR tends to increase with increasing filament diameter and decreasing porosity. Moreover, the steady-state thermal analyses showed that the flexible graphite effectively spreads the heat in the TIM and reduces the overall TCR. Detailed temperature contours on the heated surface of the thermal gap pad and flexible graphite TIMs used with different porosity MFs are presented to support these findings.

This article reviews and summarizes research conducted during and related to ASHRAE RP-1675, Guidance for Data Center CFD. The ultimate objective is to provide users and vendors of computational fluid dynamics (CFD) tools with best-practice modeling advice to support greater adoption of the technology to design and operate reliable and sustainable facilities. RP-1675 identified and developed good CFD modeling practices by benchmarking CFD simulations against experimental measurements for a "laboratory data center," considering past and concurrent research, and performing additional sensitivity studies in CFD. This article provides a detailed review of the experimental and CFD work conducted during RP-1675, which focused on the modeling of computer room air handler units (CRAHs) with vertical-axis blowers located in the raised-floor plenum, and modeling perforated floor tiles, and raised-floor stanchions. This article ultimately summarizes current guidance for data-center CFD.

As the capacity of electric vehicle (EV) battery packs increases and recharging times are reduced, effective battery thermal management becomes a key challenge. When exposed to elevated temperatures and non-uniform thermal conditions, insufficient heat dissipation within the battery module can detrimentally impact both its operational lifespan and performance, posing a potential risk of thermal runaway. Therefore, by reducing maximum temperatures and enhancing temperature uniformity through the batteries in order to improve lifespan and performance. Furthermore, depending on the specific battery cell technologies employed in EVs, battery swelling also emerges as a significant challenge as it can increase heat generation and drops in battery life. Thus, this paper develops a two-phase flexible battery thermal management system, enhanced with a copper microstructure, using a dielectric coolant (HFE-7000) to mitigate battery surface temperatures. The heat transfer performances were experimentally studied in a mass flow rate range of 4.5 g.s(-1) to 11 g.s(-1) with representitive heat dissipation values between 10 W.m(-2) and 1.4 W.m(-2) and shows the ability of the system to maintain average surface temperatures in a the battery optimal operational range between 25 degrees C and 35 degrees C.

The next generation of integrated power electronics packages will implement wide-bandgap devices with ultrahigh device heat fluxes. Although jet impingement has received attention for power electronics thermal management, it is not used in commercial electric vehicles (EVs) because of the associated pressure drop and reliability concerns. In this paper, we present a modular thermal management system designed for automotive power electronics. The system achieves superior thermal performance to benchmarked EVs while adhering to reliability standards and with low pumping power. The system utilizes a low-cost and lightweight plastic manifold to generate jets over an optimized heat sink, which is embedded in the direct-bonded-copper (DBC) substrate. The embedded heat sink concept leverages additive manufacturing to add elliptical pin fins to the DBC substrate. The heat sink geometry is optimized for submerged jet impingement using a unit-cell model and an exhaustive search algorithm. The model predictions are validated using unit-cell experiments. A full-scale power module model is then used to compare the DBC-embedded heat sink against direct DBC cooling and baseplate-integrated heat sinks for single-sided (SS) and double-sided (DS) cooling concepts. Using the SS and DS DBC-embedded cooling concepts, the models predict a thermal resistance that represents a reduction of 75% and 85% compared to the 2015 BMW i3, respectively, for the same water-ethylene glycol inverter flowrate. We have shown that an inverter with a 100-kilo-Watt-per-liter power density is achievable with the proposed design.

As power densities increase in heterogeneously integrated systems, with the introduction of new 3D architectures and the increasing number of transistors on chips, there exists a continued bottleneck for thermal management. High temperatures have a drastic impact on memory performances and refresh cycles. Moreover, thermal coupling between neighboring chiplets on a package is increasing as the types of chips on a heterogeneously integrated package diversify, and this, in turn, creates different heat flux densities within a heterogeneously integrated package. Thus, there arises a need for the implementation of efficient thermal design and solutions that cater to high heat fluxes within a package as well as different heights for different chip stacks within a package. In this paper, we present a parametric thermal design of heterogeneously integrated packages for high-performance computing. We focus on a 2.5D packaging structure, which includes components including artificial intelligence (AI) accelerators and high bandwidth memory (HBM) on a silicon interposer. Analytically and numerically, we investigate the thermal challenges stemming from high power density in stacked dies, variations in die heights, and cooling limitations at the package surface. To mitigate temperature gradients within the package, we propose a thermal-aware package structure, emphasizing the inside architecture. Also, the thermal coupling effect is studied for multiple cooling technologies on the outer surface using a thermal violation region graph. This research has shown that not only the internal structure of the package but also its ability to transfer heat to the outer surface has a significant impact on the thermal coupling effect. Using our approach, we can design package architecture systematically considering the external cooling environment in the early design stage.

Cities account for over 66% of global energy use and with over 68% of the population expected to live in urbanized areas by 2050, anthropogenic urban heat release is likely to become one of the most significant contributors to the creation of urban microclimates. In the present work, an open-source framework for one-way upstream coupled multiscale urban thermal environment simulations is examined and validated and can provide valuable insights about the flow behavior and energy transport between spatial scales. In this study, a city-wide multiscale model with over 500,000 building, road, and tree canopy data points parameterizing Atlanta, GA as a digital twin is developed and validated with a spatial scale of 5 m. The validated model is used to perform a parametric study on the implications bulk surface albedo (SA) has on the city's anthropogenic heat (AH) release in terms of heat flux. The study demonstrates that anthropogenic heat flux for building waste energy accounts for a small part of the total surface heat flux, and a detailed understanding of the components of urban heat (particularly with respect to total surface heat flux) is required to predict and simulate an urban thermal environment.

The unique properties of metal foams make them potential candidates for a range of applications, including microsystem thermal management. Using additive manufacturing to create foam-type structures can improve upon prior thermal solutions by eliminating thermal interface materials and allowing for customization/local control of parameters. In the present investigation, flow boiling in additive-manufactured metal foams is investigated both experimentally and numerically. Two test samples, one with uniform structure and the other with pathways for vapor removal, are compared both experimentally and numerically. A conjugate computational fluid dynamics and heat transfer (CFD-HT) model utilizing a three-dimensional volume of fluid (VOF) model with accompanying evaporation/condensation model provided in-depth visualization of the boiling flow phenomena. The experiments generated the thermohydraulic performance over a range of heat fluxes, demonstrating that the sample incorporating dedicated vapor pathways performed better in both pressure and heat transfer performance metrics compared to the uniform foam. Additionally, negative system-level effects (i.e., hydraulic oscillations) were shown to be abated using the vapor removal structures. The numerical model yielded further insight into the factors contributing to the improved performance. Results indicated the pathways functioned as vapor removal channels, allowing the generated vapor to vent from the foam structure into the lanes. Further computational investigations demonstrated changes in flow regimes, where the addition of vapor channels caused the flow to change from churn to annular. Bubble behavior unique to the vapor pathway structure was studied, showing stagnant regions that eject vapor into the channel.

This paper presents a 20,000 rpm 72-slot/12-pole heavy rare-earth-free interior permanent magnet synchronous motor (IPMSM) design integrated with novel in-slot evaporative cooling and single-phase shaft cooling techniques. The in-slot cooling design replaces traditional slot-liner paper with a micropin fin-enhanced liner to facilitate coolant flow between the active winding and slot-liner paper, allowing for direct heat extraction from the winding via thin-film evaporation. Additionally, single-phase shaft cooling has been implemented to regulate magnet temperatures below the threshold limit at high speeds. The motor topology has been systematically optimized to enhance power density and prevent premature demagnetization of heavy rare- earth-free magnets. An extensive electro-thermal analysis was conducted to evaluate the performance of the optimized motor configuration. Results showed that the proposed motor design can provide a 10 sec. peak power density of ~86.59 kW/L and a continuous power of ~78 kW without demagnetization, which are ~73% and 41.82% higher than the Department of Energy’s 2025 target for electric motor for electric vehicle (EV) applications.