Heat Flux Research Articles

Vegetation-climate feedbacks across scales.

Vegetation is often viewed as a consequence of long-term climate conditions. However, vegetation itself plays a fundamental role in shaping Earth's climate by regulating the energy, water, and biogeochemical cycles across terrestrial landscapes. It exerts influence by consuming water resources through transpiration and interception, lowering atmospheric CO2 concentration, altering surface roughness, and controlling net radiation and its partitioning into sensible and latent heat fluxes. This influence propagates through the atmosphere, from microclimate scales to the entire atmospheric boundary layer, subsequently impacting large-scale circulation and the global transport of heat and moisture. Understanding the feedbacks between vegetation and atmosphere across multiple scales is crucial for predicting the influence of land use and land cover changes, and for accurately representing these processes in climate models. This review discusses the biophysical and biogeochemical mechanisms through which vegetation modulates climate across spatial and temporal scales. Particularly, we evaluate the influence of vegetation on circulation patterns, precipitation, and temperature, considering both long-term trends and extreme events, such as droughts and heatwaves. Our goal is to highlight the state of science and review recent studies that may help advance our collective understanding of vegetation feedbacks and the role they play in climate.

Biophysical impact of forest age changes on land surface temperature in China.

Forest age structures have been substantially affected by natural disturbances and anthropogenic activities worldwide. Their changes can significantly influence local and nonlocal climate through both the biogeochemical and biophysical processes. However, numerous studies have focused on the biogeochemical effect of forest age changes whereas the biophysical effect has received far less attention. Here we investigated how forest age changes influence land surface temperature (LST) by comparing older forests and adjacent younger forests pixels and unraveled underlying biophysical mechanisms using satellite observations over China during 2003-2012. Our study showed that older forests had a substantial annual cooling benefit than adjacent medium-aged and young forests. Attribution analysis indicated that the cooling effect of latent heat flux counteracted the albedo-induced warming effect, leading to the net cooling effect of older evergreen needle-leaved forest or evergreen broadleaved forest. Furthermore, the cooling effect of sensible heat flux is greater than the albedo-driven warming effect, contributing to the net cooling effect of older deciduous broadleaved forest. Our work is a step forward to underscore the potential of preserving mature forests as a local climate adaptation strategy and provides important parameterization foundation for earth system models without incorporation of forest age modules.

Analytical Solution of Thermal Performance in Metal Foam Partially Filled Channel with Asymmetric Wall Heat Flux

Analytical Solution of Thermal Performance in Metal Foam Partially Filled Channel with Asymmetric Wall Heat Flux

Divertor heat flux challenge and mitigation in the EHL-2 spherical torus

Divertor heat flux challenge and mitigation in the EHL-2 spherical torus

Predicting thermal stress and failure risk in monoblock divertors using 2D finite difference modeling and gradient boosting regression for fusion energy applications

Abstract This study presents a combined approach using a 2D finite difference method and Gradient Boosting Regressor (GBR) to analyze thermal stress and identify potential failure points in monoblock divertors made of tungsten, copper, and CuCrZr alloy. The model simulates temperature and heat flux distributions under typical fusion reactor conditions, highlighting regions of high thermal gradients and stress accumulation. These stress concentrations, particularly at the interfaces between materials, are key areas for potential failure, such as thermal fatigue and microcracking. Using the GBR model, a predictive maintenance framework is developed to assess failure risk based on thermal stress data, allowing for early intervention. This approach provides insights into the thermomechanical behavior of divertors, contributing to the design and maintenance of more resilient fusion reactor components.

Spectral heat flux redistribution upon interfacial transmission

In nonmetallic crystals, heat is transported by phonons of different frequencies, each contributing differently to the overall heat flux spectrum. In this study, we demonstrate a significant redistribution of heat flux among phonon frequencies when phonons transmit across the interface between dissimilar solids. This redistribution arises from the natural tendency of phononic heat to re-establish the bulk distribution characteristic of the material through which it propagates. Remarkably, while the heat flux spectra of dissimilar solids are typically distinct in their bulk forms, they can become nearly identical in superlattices or sandwich structures where the layer thicknesses are smaller than the phonon mean free paths. This phenomenon reflects that the redistribution of heat among phonon frequencies to the bulk distribution does not occur instantaneously at the interface, rather it develops over a distance on the order of phonon mean-free-paths.

Exposure of Sn-Wetted W CPS Targets to Simultaneous NBI Beam and High-Power CW Laser Pulses at the High-Heat Flux OLMAT Facility

First experiments are reported of the simultaneous exposure of a number of Sn-wetted W CPSs and a reference W CPS to 100 ms NBI pulses (divertor steady-state loading conditions) and 2 ms long high-energy laser pulses (divertor ELM like loading conditions) at the High-Heat Flux OLMAT facility. The use of a fast-frame imaging camera allows monitoring the onset of particle ejection from the targets during laser pulses and obtaining the corresponding laser heat fluxes as a measure of the resilience of these targets. Fast camera images are used also to determine ejected particle numbers and to estimate their maximum velocities as laser power is increased in order to compare the influence of W CPS structure on these parameters. In addition, the craters resulting from particle ejection are studied for each target with an optical microscope and a scanning electron microscope. Moreover, in-situ W and Sn particle ejection is followed using visible emission spectroscopy and post-exposure W melting after particle ejection is observed using the energy dispersive X-ray method EDX for all the studied targets. This shows that Sn is unable to protect the underlying W substrate from high-energy laser damage, albeit a subsequent refilling of the formed craters with Sn is visible during NBI-only pulses after laser damage. Thus, it is considered that optimization of surface refilling/replenishment with Sn is needed to improve the W substrate protection. From this work, it is also found that the W CPS reference material has a higher laser heat flux threshold for particle ejection than the Sn-wetted targets. Nevertheless, it is important to take into account that in these experiments with laser pulses, the possible beneficial effects of vapor shielding that can take place during particle irradiation at ELMs or disruptions are not present, thus these experiments represent a worst-case scenario.

Auto-Deposited Microparticle Composite Coating for Low-Cost and Efficient Daytime Radiative Cooling.

Radiative cooling is an excellent strategy for mitigating global warming, by enhancing heat fluxes away from the Earth, thus balancing the Earth's heat flow. However, for randomly particle-dispersed radiative cooling materials, the particle content as high as 94-96 wt % or 60 vol %, far exceeds the critical pigment percentage (40-50%) of traditional coatings, preventing its large-scale application. Here, inspired by particle deposition under gravity in solution, we demonstrate an auto-deposited SiO2 composite radiative cooling coating (ADRC) which reduces the amounts of particles required and lowers costs. This particle density gradient structure enhances the local volume fraction of particles, thereby the coating exhibits high solar reflectance (93%) and infrared emissivity (89%), contributing to a daytime subambient temperature drop of 12 °C. The cooling energy-saving potential of buildings in China utilizing the ADRC as roofs ranges from 6.42 to 13.52%. This low-cost and scalable radiative cooler is expected to reduce energy consumption and carbon emissions, addressing global warming issues.

Effect of stent struts angle on body vessel shear stress at different heat fluxes

Effect of stent struts angle on body vessel shear stress at different heat fluxes

Investigation of the thermal structure in the atmospheric boundary layer during evening transition and the impact of aerosols on radiative cooling

AbstractThe evening transition is crucial in various phenomena, including boundary‐layer stability, temperature inversion, radiation fog, vertical mixing, and pollution dispersion. We have explored this transition using data from 80 days of observations across two fog seasons at the Kempegowda International Airport, Bengaluru (KIAB). Through field experiments and simulations integrating aerosol interaction in a radiation–conduction model, we elucidate the impact of aerosols on longwave cooling of the atmospheric boundary layer (ABL). Field observations indicate that, under calm and clear‐sky conditions, the evening transition typically results in a distinct vertical thermal structure called the lifted temperature minimum (LTM). We observe that the prevailing profile near the surface, post‐sunset is the LTM profile. Additionally, the occurrence of LTM is observed to increase with decreases in downward and upward longwave flux, soil sensible heat flux, wind speed, and turbulent kinetic energy measured at 2 m above ground level (AGL). In such scenarios, the intensity of LTM profiles is governed primarily by the aerosol‐induced longwave heating rate (LHR) within the surface layer. Furthermore, the presence of dense clouds leads to increased downward flux, causing the disappearance of LTM, whereas shallow fog can enhance LTM intensity, as observed in both field observations and simulations. Usually, prevailing radiation models underestimate aerosol‐induced LHR by an order of magnitude compared with actual field observations. We attribute this difference to aerosol‐induced radiation divergence. We show that the impact of aerosol‐induced LHR extends hundreds of meters into the inversion layer, affecting temperature profiles and potentially influencing processes such as fog formation. As the fog layer develops, LHR strengthens at its upper boundary. However, we highlight the difficulty in detecting this cooling using remote instruments such as microwave radiometers.

Effects of Wall Temperature on Scalar and Turbulence Statistics During Premixed Flame–Wall Interaction Within Turbulent Boundary Layers

Abstract Direct numerical simulations (DNS) have been utilised to investigate the impact of different thermal wall boundary conditions on premixed V-flames interacting with walls in a turbulent channel flow configuration. Two boundary conditions are considered: isothermal walls, where the wall temperature is set either equal to the unburned mixture temperature or an elevated temperature, and adiabatic walls. An increase in wall temperature has been found to decrease the minimum flame quenching distance and increase the maximum wall heat flux magnitude. The analysis reveals notable differences in mean behaviours of the progress variable and non-dimensional temperature in response to thermal boundary conditions. At the upstream of the flame–wall interaction location, higher mean friction velocity values are observed for the case with elevated wall temperature compared to the other cases. However, during flame–wall interaction, friction velocity values decrease for isothermal walls but initially rise before decreasing for adiabatic walls, persisting at levels surpassing isothermal conditions. For all thermal wall boundary conditions, the mean scalar dissipation rates of the progress variable and non-dimensional temperature exhibit a decreasing trend towards the wall. Notably, in the case of isothermal wall boundary condition, a higher scalar dissipation rate for the non-dimensional temperature is observed in comparison to the scalar dissipation rate for the progress variable. Thermal boundary condition also has a significant impact on Reynolds stress components, turbulent kinetic energy, and dissipation rates, showing the highest magnitudes with isothermal case with elevated wall temperature and the lowest magnitude for the isothermal wall with unburned gas temperature. The findings of the current analysis suggest that thermal boundary conditions can potentially significantly affect trubulence closures in the context of Reynolds averaged Navier–Stokes simulations of premixed flame–wall interaction.

Linking Radiative‐Advective Equilibrium Regime Transition to Arctic Amplification

AbstractEmission of anthropogenic greenhouse gases has resulted in greater Arctic warming compared to global warming, known as Arctic amplification (AA). From an energy‐balance perspective, the current Arctic climate is in radiative‐advective equilibrium (RAE) regime, in which radiative cooling is balanced by advective heat flux convergence. Exploiting a suite of climate model simulations with varying carbon dioxide () concentrations, we link the northern high‐latitude regime variation and transition to AA. The dominance of RAE regime in northern high‐latitudes under reduction relates to stronger AA, whereas the RAE regime transition to non‐RAE regime under increase corresponds to a weaker AA. Examinations on the spatial and seasonal structures reveal that lapse‐rate and sea‐ice processes are crucial mechanisms. Our findings suggest that if concentration continues to rise, the Arctic could transition into a non‐RAE regime accompanied with a weaker AA.

Research on the impact of land use and land cover changes on local meteorological conditions and surface ozone in the north China plain from 2001 to 2020

Land use and land cover changes (LULCC) alter local surface attributes, thereby modifying energy balance and material exchanges, ultimately impacting meteorological parameters and air quality. The North China Plain (NCP) has undergone rapid urbanization in recent decades, leading to dramatic changes in land use and land cover. This study utilizes the 2020 land use and land cover data obtained from the MODIS satellite to replace the default 2001 data in the Weather Research and Forecasting-Community Multiscale Air Quality (WRF-CMAQ) model. It simulates and analyzes the direct impact of LULCC on meteorological parameters and the indirect impact on surface ozone (O3) concentration through physical and chemical processes in the North China Plain during July in the summer. Six rapidly urbanizing cities were selected to represent the North China Plain. The results show that LULCC significantly increased sensible heat flux and 2-m temperature in rapidly urbanizing areas throughout the diurnal cycle, with more pronounced effects during the daytime, ranging from 6.49 to 23.46 W/m2 and 0.20–0.59 °C, respectively. The 10-m wind speed decreased at night and increased during the day, with changes ranging from − 0.43 to 0.27 m/s at night and − 0.16 to 0.15 m/s during the day. The planetary boundary layer height generally increased, with a larger rise during the daytime, ranging from 23.63 to 84.74 m. Simultaneously, surface O3 concentrations increased during both daytime and nighttime. The daytime increase ranged from 2.89 to 9.82 μg/m3, while the nighttime increase ranged from 1.76 to 7.77 μg/m3. LULCC enhanced meteorological and chemical processes as well as vertical transport, leading to an increase in O3. At the same time, it reduced the increase in O3 through horizontal transport and dry deposition processes. These changes are related to the meteorological variations. The impact on O3 concentrations was not limited to the surface but extended to the top of the planetary boundary layer (approximately 1500 m). Below 500 m, vertical transport increased O3 concentrations, while horizontal transport decreased O3 concentrations. Additionally, the meteorological and chemical processes induced by LULCC showed enhanced effects above the surface, whereas the dry deposition process had a smaller impact on O3 concentrations above the surface. This study reveals the significant impact of urban expansion on regional meteorological parameters and air quality. It optimizes the model’s simulation of regional air quality and provides new insights into understanding the effects of urbanization on meteorological conditions and air quality.

Atlantic overturning inferred from air-sea heat fluxes indicates no decline since the 1960s

The Atlantic Meridional Overturning Circulation (AMOC) is crucial for global ocean carbon and heat uptake, and controls the climate around the North Atlantic. Despite its importance, quantifying the AMOC’s past changes and assessing its vulnerability to climate change remains highly uncertain. Understanding past AMOC changes has relied on proxies, most notably sea surface temperature anomalies over the subpolar North Atlantic. Here, we use 24 Earth System Models from the Coupled Model Intercomparison Project Phase 6 (CMIP6) to demonstrate that these temperature anomalies cannot robustly reconstruct the AMOC. Instead, we find that air-sea heat flux anomalies north of any given latitude in the North Atlantic between 26.5°N and 50°N are tightly linked to the AMOC anomaly at that latitude on decadal and centennial timescales. On these timescales, air-sea heat flux anomalies are strongly linked to AMOC-driven northward heat flux anomalies through the conservation of energy. On annual timescales, however, air-sea heat flux anomalies are mostly altered by atmospheric variability and less by AMOC anomalies. Based on the here identified relationship and observation-based estimates of the past air-sea heat flux in the North Atlantic from reanalysis products, the decadal averaged AMOC at 26.5°N has not weakened from 1963 to 2017 although substantial variability exists at all latitudes.

Experimental research on heat transfer characteristics of a two-layer corium pool based on a three-dimensional ellipsoidal lower plenum

To better understand the application of IVR (In-Vessel Retention), extensive experiments have been conducted on the heat transfer characteristics of molten pool. However, most research mainly focuses on hemispherical lower heads, and the research on ellipsoidal lower head suitable for small pressurized water reactors is relatively lacking. In order to provide some reference for the implementation of IVR with ellipsoidal lower head, this paper conducted the experimental study on the heat transfer characteristics of a three-dimensional double-layer molten pool based on the design of a small pressurized water reactor. The test section consists of two parts: ellipsoidal and cylindrical, with a span of 1150 mm and a total height of 700 mm. The molten material is simulated by nitrate mixture (20mol%NaNO3-80mol%KNO3), and electric heating wire is chosen to simulate the oxide layer decay heat. The effects of heating power, oxide layer height and layered partition thickness on heat transfer characteristics of two-layer molten pool under static conditions were studied. The results show that the thermal stratification phenomenon mainly occurs in the lower and middle regions of the oxide layer, with a smaller dimensionless temperature gradient in the upper region; with the similar volumetric power densities, the height of the oxide layer has little effect on the wall heat flux density; the layered partition increases the thermal resistance between the two layers and reduces the upward heat transfer to the ceramic pool. In addition, the heat transfer relationships in the oxide layer, both downward and upward, are fitted for the internal Rayleigh number range of 3.43 × 1012 to 1.54 × 1013.

Revisiting the Inconsistent Influence of El Niño–Southern Oscillation on the Equatorial Atlantic

Abstract The impact of El Niño–Southern Oscillation (ENSO) on the equatorial Atlantic zonal mode (AZM) is investigated using two atmospheric reanalysis products and 44 models from phase 6 of the Coupled Model Intercomparison Project (CMIP6). While the impact of ENSO on equatorial Atlantic SST is inconsistent, as previously reported, there is a very robust influence of decaying ENSO events in boreal spring on the contemporaneous surface zonal winds over the equatorial Atlantic, with El Niño events associated with anomalous easterlies that cool the equatorial Atlantic. This dynamic impact is counteracted by a thermodynamic impact, in which El Niño events cause changes in surface heat fluxes that lead to warming over the tropical Atlantic. The thermodynamic influence is active throughout the life cycle of the ENSO event, but the dynamic influence is highly seasonal with a pronounced peak in boreal spring. Thus, a quickly decaying El Niño event will lead to warming, while a slowly decaying event will lead to cooling in the equatorial Atlantic. The ENSO–AZM relation is further complicated by partially independent Atlantic variability, in particular that associated with the South Atlantic subtropical dipole (SASD). Prediction experiments with a simple linear regression model support the role of the SASD as an AZM precursor. Many CMIP6 models show skillful predictions of the June–August AZM based on SST indices in the preceding December–February, with correlations above 0.5. When predictions are restricted to ENSO years, even more models exceed this threshold, but skill in the reanalyses remains relatively low, possibly due to insufficient training data. Significance Statement El Niño is the strongest climate signal on interannual time scales. Its influence on the equatorial Atlantic, however, is surprisingly inconsistent. Here, we show, using an ensemble of climate models and observation-based data, that El Niño has a very robust influence on equatorial Atlantic surface winds, but only in boreal spring. This leads to a large difference in how El Niño events influence the equatorial Atlantic, based on how quickly they decay in boreal spring. We also find that variability in the South Atlantic, which is partly independent of El Niño, has a strong influence on the equatorial Atlantic, supporting the result of previous studies. These findings suggest that the predictability of equatorial Atlantic temperature anomalies may be higher than previously thought.

Scrutinization of linear and nonlinear radiative heat flux on MHD Darcy–Forchheimer Casson ternary hybrid nanofluid flow through a porous microchannel

Scrutinization of linear and nonlinear radiative heat flux on MHD Darcy–Forchheimer Casson ternary hybrid nanofluid flow through a porous microchannel

Heat Enhancement of Ethylene Glycol/Water Mixture in the Presence of Gyroid TPMS Structure: Experimental and Numerical Comparison

Cooling small components is becoming an attractive topic for researchers. In this paper, an attempt is made to use an ethylene glycol/water mixture as a cooling liquid. This liquid is a helpful application for when the fluid is in a harsh environment and should not freeze. The experiment uses an ethylene glycol/water mixture circulating through a triply periodic minimal surface structure (TPMS) made of aluminum and silver. A constant heat flux equal to 38,000 W/m2 is applied, and three different flow rates, 11.8 cm3/s, 15.5 cm3/s, and 19.6 cm3/s, are studied. The experimental setup is complemented with numerical modelling by solving the Navier–Stokes equation and the energy equation using the finite element technique. The flow is Newtonian, and a laminar regime is implemented. Results reveal that the performance of the ethylene glycol/water mixture did not enhance heat removal when compared to water. The average Nusselt number is similar regardless of the concentration of ethylene glycol in the mixture. This average Nusselt number, Nuaverage, in the presence of aluminum TPMS ranges between 60 and 80 (60 < Nuaverage < 80) and between 65 and 85 (65 < Nuaverage < 85) using silver TPMS. The increase in the mixture’s viscosity due to ethylene glycol increased the pressure drop. The performance evaluation criteria reach the maximum value of 90 when the mixture is composed of 5%vol ethylene glycol in water with aluminum TPMS. In the presence of silver TPMS, the maximum performance evaluation criterion is around 95 with a 5% ethylene glycol/water mixture. Finally, it is proven experimentally and confirmed numerically that the TPMS structure secures uniform heat extraction from the hot surface.

Full-Scale Fire Testing to Assess the Risk of Battery Electric Vehicle Fires in Underground Car Parks

Abstract Battery-only electric vehicle (BEV) fires have recently emerged as a significant safety concern in modern society, particularly when they occur in car parking spaces, where the consequences can be severe. While relatively few fatalities and injuries are reported, the associated economic losses are substantial. Car park structures present several challenges from a fire safety perspective, including high energy content, confined geometry, and difficulties in detecting and accessing to the fire’s origin due to smoke accumulation in spaces with limited ventilation and exits. This study investigates this fire hazard by conducting a full-scale fire test on a modern BEV in an instrumented test rig that simulates a segment of an underground car park. The data obtained were compared with standard fire curves to assess the hazard’s characteristics and with the data from a companion study to identify differences between BEV fires in underground and surface car parks. The primary difference observed was deflagration venting, which occurred shortly after the initial ignition of combustible gases accumulated beneath the ceiling, lasting until 13 min and 5 s. This phenomenon led to a rapid initial growth of the BEV fire, which burned more intensely for a shorter duration in the semi-enclosed configuration comparted to the open configuration. The enclosed fire recorded an average ceiling-jet temperature of approximately 1100°C and a peak incident heat flux exceeding 225 kW/m2. Additionally, thermal runaway within the lithium-ion battery cells was analysed to understand the adverse effects of the enclosed environment on thermal runaway propagation. This fire testing provides critical insights for developing firefighting strategies including the proper preparation of equipment and the design of fire protection systems. The principal findings could inform tactics for mitigating unforeseen fire risks and contribute to revisions of fire safety regulations.

Effect of Northeast Pacific Wind on the Improvement of El Niño Prediction in a Climate Model

Abstract The role of the northeast Pacific wind in the dynamics of El Niño has been proposed in previous theoretical studies. However, the actual effect of northeast Pacific wind on improving El Niño prediction remains unclear, and the mechanisms through which northeast Pacific improves El Niño predictions are not fully understood. In this study, we investigate the role of northeast Pacific wind in improving El Niño prediction. By utilizing CESM that assimilates the northeast Pacific wind, the model improves prediction skills of ENSO indices at a lead time of 6–12 months, with a correlation three times higher than the predictions without nudged northeast Pacific wind. Nudging northeast Pacific wind in the model enhances the prediction of central Pacific (CP) El Niño, thus leading to approximately 30% increase in the hit ratio of correct prediction of El Niño. However, the model overestimates CP El Niño predictions when the nudged northeast Pacific wind is incorporated. The mechanisms for the improvement of northeast Pacific wind in El Niño predictions are investigated. In spring, El Niño development is attributed to the wind–evaporation–SST (WES) feedback and oceanic downwelling induced by subtropical westerly wind stress. In contrast, during summer, El Niño development is dominated by the summer deep convection (SDC) response. During subsequent summer–autumn, anomalous surface latent heat flux related to wind speed and net shortwave radiation associated with the low cloud–SST feedback contribute to El Niño development. These processes are more favorable for CP El Niño development. This study implies that accurately simulating air–sea coupling associated with northeast Pacific wind may be an effective approach in improving El Niño prediction.