Dynamic heat flux analysis in a high-pressure turbine

Plasticity of marine ecosystem dynamics as a condition for its stability: modeling seasonal and vertical dynamics of the Arctic shelf ecosystem.

A challenge in validating land-atmosphere (L-A) coupling in Earth system models is the limited availability of global observation-based datasets for estimating coupling metrics. This study generates global L-A coupling indices of Pearson correlation coefficient, terrestrial coupling index between soil moisture (SM) and surface heat fluxes, as well as SM memory, at resolutions of 0.1° and 0.25° (with temporal coverage depending on input datasets), employing observationally-based data. The metrics are designed to account for random errors in satellite SM measurements and include quantification of those errors. Multiple SM and flux data products are combined to produce coupling metrics - their spread and error characteristics are used to quantify uncertainty. The global patterns of SM regimes and SM breakpoints of wilting point and critical SM are also quantified through segmented regression analysis. The dataset's performance is validated through inter-product comparisons, documenting high consistency in spatial patterns across different combinations. These datasets are valuable for initialization and validation of weather forecasts, climate modeling, model calibration, and applications in ecology, hydrology, and soil sciences.

Abstract Atlantic Multidecadal Variability (AMV) is a well-known mode of climate variability with well
understood impacts on several aspects of Northern Hemisphere climate. Its impact on climate
variability has long been studied and documented. However, its impact on heatwaves, a type of
heat extremes that is increasingly affecting human societies, remains less well understood. The
influence of AMV on extratropical summer heatwaves in the Northern Hemisphere is analyzed
with a suite of coupled climate model experiments from the Decadal Climate Prediction Project.
Our analysis suggests that AMV exerts substantial influence on the frequency (HWF) and number
(HWN) of heatwaves over subtropics and midlatitudes in the Northern Hemisphere. Compared to
the widespread seasonal mean warming response, these heatwave hotspots are less expansive geo
graphically. The warm AMV phase (AMV+) as opposed to the cold phase (AMV-) drives a global
stationary wave anomaly that links hotspots of HWF and HWN increases over North America,
North Africa, central/western Asia, and parts of East Asia. Such dynamic impacts of AMV on
heatwaves are more significant than the thermodynamic impacts of a warmer ocean surface. Hence,
mean surface warming alone due to the warming effects of AMV+ versus AMV- does not necessarily
equate to increased heatwaves. Furthermore, precipitation and surface heat fluxes responses further
amplify the HWF increases. By further comparing the tropical and extratropical portions of AMV
imposed in model simulations, we emphasize that linear and nonlinear interactions of these features
strongly shape the impacts of AMV. We further note model-observations discrepancies and inter
model uncertainties in the influence of AMV on atmospheric circulation and summer heatwaves.
This highlights challenges in pinpointing the influence of AMV, and improved understanding of it
is necessary for more accurate climate predictions and projections.

Hydrophobic surfaces are well recognized to eliminate the waiting period between bubble departure and subsequent nucleation. Present work numerically investigates the growth process of an isolated bubble in nucleate pool boiling (NPB) from curved hydrophobic surfaces, specifically plane, concave, and convex surfaces. The commercial software ANSYS Fluent 2021 R1 has been employed, utilizing its integrated volume of fluid method. Water is chosen as the working fluid and the phase change process at the liquid-vapor interface has been modeled using the “saturated-interface-volume” phase change model. This was implemented using a user-defined function. The influence of surface concavity on NPB has been analyzed through extensive study of bubble growth parameters, such as bubble morphology, bubble growth period, bubble radius and bubble base radius. A comparative analysis has been performed to demonstrate the role of wettability on bubble growth and associated heat transfer with change in curvature of the surface. Temporal and spatial variations of surface heat flux have also been examined for different values of surface curvature. Moreover, the effect of wall superheat on bubble growth and heat transfer has been analyzed for different curved hydrophobic surfaces. It is observed that the growth period of the bubble decreases with change in surface curvature from concave to convex. In the early stage of bubble growth, the heat flux on convex surface is found to be lower than that on the concave surface.

Long-term forecasting of water quality and algal dynamics in riverine systems using advanced physicochemical-informed machine learning models.

Abstract The shallow water masses of the South China Sea (SCS) play a critical role in regulating regional climate and sustaining marine ecosystems. Using Argo float observations, we examine SCS water mass properties and eddy structures on isopycnal surfaces. By analyzing data in density space, we separate true water mass changes from vertical displacement of isopycnals. This approach helps reveal previously undocumented interannual variability in temperature and salinity together. We find that during the study period (2005–23), the shallow waters of the SCS, including within eddies, are strongly linked to El Niño–Southern Oscillation (ENSO) variability. During El Niño events, SCS waters become warmer and saltier, and during La Niña, they become colder and fresher. We show that the water mass variability can be explained by anomalies in local surface fluxes—with enhanced heating and reduced precipitation during El Niño and weaker heating with increased precipitation during La Niña. The water mass response is observed throughout the SCS but appears amplified within cyclonic eddies, likely due to their shallower mixed layer and greater sensitivity to surface fluxes. Our results demonstrate the sensitivity of SCS water masses to large-scale climate variability and provide new insight into the sensitivity of the SCS to ENSO. Significance Statement Using Argo data analyzed on isopycnal surfaces, we identify coherent temperature–salinity changes in South China Sea water masses that are not evident on fixed depth levels. The upper ocean becomes warmer and saltier during El Niño and cooler and fresher during La Niña in response to anomalous surface heat and freshwater fluxes associated with large-scale ENSO-related variability. Analyses on depth levels conflate true water mass changes with vertical isopycnal heave, masking this coupled signal.

Inversion of surface heat flux in high-enthalpy plasma flows via thermocouple measurements and back propagation neural networks

This study develops a semi-analytical transient thermoelastic formulation for thin circular disks subjected to a radially shifted Gaussian surface heat flux, a profile highly representative of helical undulator conditions in synchrotron radiation, semiconductor processing, and laser systems. The axisymmetric transient temperature field is obtained through a Bessel eigenfunction expansion, while the in-plane stresses are evaluated under a quasi-static plane-stress assumption. In addition to characterizing transient fields with high fidelity, this formulation elucidates a physical mechanism inaccessible through local-temperature heuristics: in-plane stresses are fundamentally governed by the geometrically weighted spatial accumulation of thermal contributions. Consequently, stress extrema are systematically non-coincident with the temperature maximum and migrate inward as transient diffusion progresses. These results establish a universal and precise framework for optimizing the mechanical integrity of high-heat components in extreme thermal environments.

This study investigates the thermal performance of n‐octadecane, a phase change material (PCM), in a Li‐ion battery cell through novel “N” shape fin configuration and the incorporation of Multi‐Walled Carbon Nanotubes (MWCNTs). The thermal management efficiency was assessed based on temperature variations, liquid fraction, energy storage, entropy, and heat generation. Adding 1% v/v. MWCNTs lowered the peak temperature to 301.9 K, indicating improved thermal conductivity. Energy storage results showed that the energy accumulation process centers on PCM melting: as the battery temperature rises, heat transfers to the PCM, which absorbs it until it melts and then dissipates it via natural convection. Enhancing PCM with MWCNTs improves thermal performance, allowing for greater energy absorption and faster battery cooling. Heat generation was highest at 53,347 W/m 3 for pure n‐octadecane but reduced to 21,996 W/m 3 in the eight‐fin configuration, and surface heat flux improved from −10.75 to −18.67 W/m 2 . These findings demonstrate that structural modifications and advanced materials substantially enhance thermal management performance, optimizing battery efficiency and longevity in energy storage applications. The proposed battery thermal management system (BTMS) shows significant promise for applications such as electric cars and renewable energy storage systems that require rapid charging and discharging.

This study investigates the unsteady electroosmotic pumping flow of a Carreau-based ternary hybrid nanofluid (Al 2 O 3 –MoS 2 –Cu/blood) under the combined influence of an inclined magnetic field, thermal radiation, and cilia-modulated slip conditions. The system models a biologically inspired microchannel actuated by an externally applied axial electric field. The governing nonlinear partial differential equations are solved using the Chebyshev Collocation Spectral Method (CCSM), implemented in MATHEMATICA, offering superior spectral accuracy and computational efficiency. Numerical results reveal that the THNF achieves up to 11.3% higher thermal conductivity and 9.7% faster heat transport rate compared to hybrid nanofluid counterparts, and up to 18.6% improvement over mono-nanofluids. The electroosmotic parameter is shown to enhance temperature and axial velocity significantly, with a 12% rise in core temperature and a 15% increase in flow rate as the parameter increases from 0.5 to 2.0. Furthermore, the synergistic interaction of Ohmic heating and inclined magnetic field strengthens the thermal field, leading to a 19% boost in surface heat flux.

Abstract The emergence of an observed distinctive, meridionally confined surface cooling trend in the tropical Pacific cold tongue over recent decades contrasts sharply with the rapid warming simulated by most climate models, representing a key unresolved feature of climate change. Ocean-only simulations, even when forced with observed atmospheric conditions, likewise fail to reproduce the observed long-term absence of surface layer warming over the eastern Pacific cold tongue. Here we examine the long-term heat budget of the surface layer in the equatorial Pacific using atmospheric and oceanic reanalysis data, quantifying contributions from surface heat fluxes, ocean advection, and vertical diffusion inferred through Richardson number-based diffusivity estimates. In the Ocean ReAnalysis System 5 (ORAS5), the observed cold tongue cooling cannot be reproduced by the model’s intrinsic dynamics alone; instead, it depends on a surface heat flux adjustment imposed during data assimilation. A reduction in the warming effect associated with this adjustment in the eastern Pacific cold tongue over time emerges as the dominant contributor to the long-term cooling in the reanalysis data, a deus ex machina obscuring the actual physical drivers of change in the real ocean. We discuss potential origins of this deus ex machina cooling effect, including the influence of analysis increments, uncertainties in surface forcing and possible problems in the representation of oceanic processes, particularly subsurface turbulent heat flux induced by oceanic mixing processes. This work emphasizes that reanalysis-based assessments remain subject to inherent biases from the ocean models they are built upon. Resolving the discrepancy between observed and simulated Pacific trends will require confronting the structural limitations of models.

Abstract The convective velocity scale is commonly used to describe the vertical‐velocity variance in the convective boundary layer driven by surface heating, and is valid when the surface heat flux varies slowly compared to the eddy turnover time. This quasi‐equilibrium assumption typically holds from late morning to early afternoon, but breaks down in the late afternoon. Recent idealized large‐eddy simulations (LES) of free convection reported departure from the classical convective scaling due to quasi‐equilibrium breakdown, and identified the relevant parameters to describe the vertical‐velocity variance during the late afternoon transition. In this study, we evaluate these scaling predictions using extensive field observations spanning 264 days. Despite substantial day‐to‐day variability, averaging across multiple days reveals a good agreement between observations and the LES‐derived scaling, supporting its validity for describing vertical‐velocity variance in this regime.

Abstract Marine heat waves (MHWs) are extreme events characterized by prolonged periods of unusually high sea surface temperatures. The North Pacific has been a focus of MHW research due to the severe ecosystem impacts of several events in the 2010s. These events are influenced by global warming and climate variability patterns like El Niño–Southern Oscillation (ENSO) and the Pacific decadal oscillation (PDO). We identify MHWs in the Community Earth System Model, version 2, large ensemble using an object-based tracking algorithm (Ocetrac) and classify them via hierarchical clustering, focusing on five dominant midlatitude types. All types are initiated by reduced wind stress, which results in suppressed ocean cooling. This initial warming is then amplified by a cloud–shortwave feedback making net surface heat flux anomalies the largest contributor to peak intensity. While this two-phase atmospheric forcing is consistent, the dominant heat flux component and large-scale precursors vary regionally. Enhanced shortwave radiation drives peak warming in the subarctic northwest Pacific (favored during negative ENSO/PDO) and northeast Pacific (favored during positive ENSO/PDO). The three other types are driven primarily by weaker cooling via reduction in evaporation. The subtropical northeast Pacific and central Pacific types are associated with positive PDO conditions, while northwest Pacific types are associated with negative phases of the PDO/ENSO. Significance Statement Marine heat waves (MHWs), prolonged periods of anomalously high sea surface temperatures, have been associated with biodiversity loss, species mortality, altered community structures, and changes in marine species’ geographical ranges. Analyzing MHWs in a large climate model dataset enables a robust characterization of different types of MHW events in the North Pacific and allows characterization of local atmospheric drivers and linkages to large-scale climate variability modes such as the Pacific decadal oscillation and El Niño–Southern Oscillation.

This study explores the unique advantages of hybrid nanofluids, known for their exceptional ability to boost heat transfer efficiency, making them ideal for advanced thermal applications. The objective is to assess the impact of slip and magnetic field on the velocity and temperature profiles over an exponentially elongated/contracted surface. Through the application of an appropriate similarity transformation, the governing equations for energy, momentum, and mass are converted into ordinary differential equations. These resulting equations are subsequently solved numerically via the bvp4c function in MATLAB. Results imply that magnetic fields decelerate the fluid while thickening the thermal boundary layer due to the Lorentz force. Increased viscous dissipation elevates temperature levels, while surface elongation promotes convective heat transfer. In contrast, surface contraction and velocity slip suppresses thermal transport by limiting momentum exchange. Thermal slip further reduces surface heat flux These findings underscore both the novelty and practical potential of Ag–Fe₃O₄ hybrid nanofluids in enhancing performance across thermal regulation systems, such as energy-efficient cooling devices, biomedical heat exchangers, and industrial applications.

Radiant floor heating systems (RFHS) are among the modern heating solutions that provide high energy efficiency and thermal comfort due to their low-temperature operating principle. However, in systems using flooring materials such as wood and laminate flooring, numerous design and operational parameters can influence surface temperature and heat flux. This makes system design a complex optimization problem. In this study, an integrated optimization approach has been developed to increase the energy efficiency of RFHS with parquet flooring, minimizing surface heat flux while also meeting thermal comfort and material safety constraints. First, ANSYS-based thermal analyses were conducted for various water temperatures, ambient temperatures, pipe spacing, parquet thickness, and material thermal conductivity values, resulting in a comprehensive dataset. Using the numerical data obtained, Random Forest (RF) based predictive models capable of accurately estimating surface temperature and surface heat flux were developed. The trained RF models were integrated with a Genetic Algorithm (GA) to solve a highly constrained optimization problem. The results obtained showed that the flooring material has a decisive effect on system performance. Furthermore, considering that theoretically optimal solutions providing very low heat flux could lead to slow heating problems in practice, a scenario analysis was conducted based on the water temperature-ambient temperature difference. The scenario analysis results revealed that this temperature difference is a critical balancing parameter between the system's heating response and energy consumption. Thus, the study offers a comprehensive decision support framework that evaluates not only theoretical optimums but also practical operating conditions. The developed Random Forest-based surrogate model demonstrated high predictive accuracy with an R 2 value of 0.992 and a Mean Absolute Percentage Error (MAPE) value of 4.21%. Furthermore, the model’s robustness was validated against unseen literature data, yielding a high R 2 value of 0.985. Scenario-based optimization results indicated that, under defined constraints, heat flux values varied between approximately 1 W/m 2 and 110 W/m 2 depending on the temperature difference between the heating water and the ambient environment. Multi-run robustness analysis confirmed 100% feasibility and stable convergence of the RF-GA framework, while comparison with Random Search highlighted substantial gains in computational efficiency and constraint satisfaction. Consequently, this study combines ANSYS-based numerical analyses, machine learning-supported predictive models, and evolutionary optimization techniques to propose a rapid, reliable, and energy-focused design approach for parquet-covered radiant heating systems.

Extreme heat loads during flight constrain the design of hypersonic vehicles. Further, certain missions necessitate the use of sharp leading edges, which enhance aerodynamic performance. Sharp leading edges decrease the shock standoff distance, which increases temperature gradient and thus surface heat flux. Additionally, reduced standoff distance introduces non-equilibrium phenomena into the near-surface gas mixture, which may result in high catalytic heating. Transpiration cooling is a method for reducing surface heat loads, preventing oxidative damage, and maintaining leading-edge geometry during flight, while also providing reusability. This paper investigates the application of transpiration cooling to stagnation points in hypersonic flight, across a wide parameter space. Results are generated from a stagnation line solver, applying Park two-temperature nonequilibrium thermochemistry and rigorous multicomponent evaluations for transport properties. This study explores a range of freestream altitudes and velocities, leading-edge radii, injectants, and surface properties. Correlations for both heat and mass Stanton numbers are presented and compared to existing correlations. Injectants similar to the shock-layer gas align with correlations established with equilibrium assumptions and mixture definitions for transport properties. However, wall catalycity, wall temperature, and dissimilar injectants modify the cooling behavior. These effects are due to alterations in near-wall mixing that can only be captured with nonequilibrium thermochemistry and multicomponent transport properties.

Ice crystal icing of turbofan engines occurs when an aircraft encounters atmospheric ice crystals in flight. The crystals permeate the compressor core, creating runback, which eventually refreezes, blocking airflow and leading to rollback, shedding, or flameout. The Ice crystal environment modular axial compressor rig (ICE-MACR) is a purpose-built compressor rig for investigating the physics of in-flight ice crystal icing of turbofan aircraft engines. Observations of heat flux and temperature transients of the ICE-MACR surfaces under ice crystal ingestion are presented and discussed. It was found that, when accretion occurs, heat flux transients can be modeled as Ae−kt, where A was found to be primarily a function of temperature and k a function of both total water content and temperature. In cases where accretion did not occur, heat flux transients were found not to fit any simple mathematical model. Analysis of both heat flux and metal temperature at the point of transition to steady accretion growth indicates that transition typically occurs when heat flux from the metal casing to the impinging mixed-phase drops below a threshold value.

Transpiration cooling is an active methodology in reducing surface heat flux for hypersonic vehicles, which offers the possibility of reducing nose bluntness and, therefore, increasing aerodynamic performance. This paper presents a numerical analysis of transpiration-cooled sharp leading edges made from ultra-high-temperature ceramics. The structural integrity of a 10 mm radius wedge leading edge is investigated numerically with regard to different coolant plenum geometries and pressurization magnitudes. It is found that the close spacing of individual plenum chambers reduces the stress in the material significantly and provides the maximum possible coolant mass flux. An optimization procedure of plenum pressure distribution is carried out using an analytical description of the porous flow in the leading edge. It is found that there exists an optimum plenum pressure that minimizes the probability of failure of the leading-edge model. Nitrogen coolant requires less pressure than helium to reach this criterion and, furthermore, requires less pressure to displace the air freestream and thus protect the leading edge from oxidation.

Abstract Oceanic meridional heat transport (MHT), a key component of Earth's energy flow, fundamentally shapes climate variability by redistributing heat between hemispheres and across latitudes, thereby regulating surface energy exchange, atmospheric circulation, and hydrological patterns. However, accurate quantification of the global MHT remains challenging. Here, we use the energy budget approach to derive MHT from 1985 to 2023 based on sea surface heat fluxes (Fs), ocean heat content tendency (OHCT), and heat changes related to sea ice melt/formation (Q ice ), with objective adjustment applied to these components under an ocean energy budget constraint. This approach enables an improved estimate of the MHT climatology, variability, and trend for the global, Indo-Pacific and Atlantic oceans. With good agreement with RAPID and OSNAP mooring array observation time series, our estimates indicate realistic northward MHT at all latitudes in the North Atlantic with a peak of 1.22 ± 0.07 PW at 24.5°N. In contrast, the Indo-Pacific MHT is poleward with a peak of −1.67 ± 0.06 PW at 13.5°S. Regional energy budgets reveal that Fs dominates the mean state of MHT, while OHCT controls its interannual variability. After 2000, when the data quality of both OHC and Fs improved a lot, the Indo-Pacific Ocean exhibited a statistically significant increase in MHT, whereas the Atlantic Ocean showed a basin-wide weakening of MHT, particularly between 25°S and 18°N. The derived ocean MHT data in this study provide a basis to evaluate model and reanalysis data, and support a better understanding of the Earth’s energy flow.