Radiative Heat Flux Research Articles

Impacts of slip and activation energy on MHD hybrid nanofluid flow past a stretching radiated surface with heat generation/absorption

The influences of slip and activation energy on the magnetohydrodynamic (MHD) flow of hybrid nanofluid over a permeable stretching radiated surface in attendance of heat source/sink have been studied. Al2O3 and Cu nanoparticles are mixed up in water to produce a hybrid nanofluid which is very important in various industrial sectors as hybrid nanofluid has wider applications in enhancing thermal efficiency to provide efficient and reliable cooling. As no one has yet searched for the collective impacts of radiative heat flux, ‘heat generation/absorption’ and ‘Arrhenius activation energy’ on MHD flow of ‘hybrid nanofluid’ in presence of slip that we are exploring in this article, this identifies the novelty of our work. Using ‘similarity transformations’, the main equations which are partial in nature are transformed to ODEs (ordinary differential equations) which are numerically solved with the assistance of ‘shooting technique and Runge–Kutta method’ using MATHEMATICA software. The outcomes of this investigation have a noteworthy impact on the physical outlook for flow field, transfer of heat and mass. Fluid velocity diminishes due to the rise of magnetic parameter but increasing nature of concentration and temperature are observed. For the rising volume fraction of Al2O3 nanoparticles as well as for rising volume fraction of Cu nanoparticles, the heat transfer coefficient rises. Momentum ‘boundary layer thickness’ diminishes for rising velocity slip. 19.694% decrease in rate of surface heat transfer is observed when volume fraction of Al2O3 nanoparticles changes from 0.01 to 0.12 whereas 24.394% decrease is noted when volume fraction of Cu nanoparticles changes from 0.2 to 0.14. The consequences of this study can be applied to many thermal systems used in engineering and industrial developments that utilize hybrid nanofluid for heating and cooling purposes.

The Abrikosov vortex structure revealed through near-field radiative heat exchange

The Abrikosov lattice is a property of type II superconductors in which normal and superconducting carriers coexist and arrange in a regular pattern. Here, we address the question on whether vortex matter, particularly the Abrikosov lattice, influences the local thermal properties of high-temperature superconductors. We find that their optical properties are not only dictated by the order parameter, but also that the near-field radiative heat flux acquires a periodic spatial structure inherited from the Abrikosov lattice. Surprisingly, we predict a radial displacement of the heat flux maxima with respect to the vortexes cores, for temperatures well below the critical one.

Influence of solar thermal radiations and convective boundary on Al2O3/H2O transient model efficiency

Riga plate is a new, sophisticated magnetic field device that may be created by adjusting a group of permanent magnets and a different electrode over a plane surface. The heat transport and fluid movement in such physical setup are of paramount interest and have numerous engineering and industrial application particularly in submarines technologies. Due to the fixed magnetics the field produced which imperatively affect the model dynamics. Keeping in mind the influential applications of such physical setup, the purpose of this study is to introduce a new model based scrutinization of heat transport of stagnation point flow of Al2O3/water along vertically oriented convectively heated Riga surface. The conventional stagnation point flow model extended for nanofluid via radiative heat flux, dissipation effects and the first order thermal slip. The values of thermal conductivity values estimated via Corcione model and achieved the final nanoliquid model. For the results interpretation, the numerical scheme used and portrayed the results using different parametric ranges. The fluid motion is observed very slow due to stronger mixed convection and higher concentration of Al2O3 nanoparticles. The temperature is determined very high against the stronger convection effects and radiation number. However, the fluid layers in the vicinity of Riga surface have high heat transmission ability. Further, thermal slip and viscous dissipation effects also boost the temperature of Al2O3/water. Further, buoyancy number δ resists the fluid movement and thermal boundary region reduces in the presence of buoyancy factor.

Prediction of flashover time in a compartment fire by CNN-LSTM based deep neural network considering wearable data collection equipment

Real-time prediction of flashover in a compartment fire is of great significance for rescue. This paper investigated a CNN-LSTM neural network to predict the flashover based on the temperature and radiative heat flux in 24 compartment fire cases simulated with FDS. Multiple conditions affecting compartment fires have been taken into account, like room size, room height, fire source location, opening size, number of vents, and fire load. Radiative heat flux meters and thermocouples were positioned at specific heights, to simulate sensors worn by firefighters entering a fire scene. The proposed model consisted of a convolutional layer and three LSTM layers. After training, the deep learning model effectively identified the flashover in compartment fires, with an average relative error of 4.1 % for temperature prediction and 11.2 % for radiative heat flux prediction. In addition, the model was validated on other simulated fire cases and full-scale experimental data, and the results showed good performance. In this paper, the sensitivity of the model to lead time was analyzed, and the application range of the model was determined. The model performed well within the lead time of 25s. In view of the strong performance of the proposed deep learning model in predicting flashover based on wearable sensors (temperature and radiative heat flux), it is believed that this model holds potential for application in a broader range of fire scenarios. This demonstrates the feasibility of using deep learning artificial intelligence models to predict compartment fire development, providing scientific guidance for smart firefighting technology.

Design and performance assessment of a solar photovoltaic panel integrated with heat pipes and bio-based phase change material: A hybrid passive cooling strategy

This study investigates the effectiveness of an indirect passive cooling solution for photovoltaic (PV) panels using flattened heat pipes (FHPs) and phase change material (PCM). An innovative passive cooling design is proposed to cool a PV panel using multiple FHPs with a thin graphite sheet between the PV panel and the FHPs. Five experimental cases are examined under varying heat flux loads. Case O serves as the baseline with no cooling system, while Cases 1 to 4 feature different configurations of FHPs and aluminum sheets, with PCM heat sinks added in Cases 2 and 4. The investigation focuses on temperature profiles, temperature reductions, and final temperatures of the PV panel, especially at the end of a 4-hour experimental period when the PCM is fully melted. The results show significant temperature reductions in Case 1 compared to the baseline, with further improvement in Case 2 due to the PCM heat sink. Temperature reductions in Cases 2 and 4 are consistently higher than in Cases 1 and 3, demonstrating the enhanced cooling potential of PCM. Case 4 achieves the highest temperature reduction of 37.0 °C, followed by Case 2 with 34.9 °C under a radiative heat flux of 1000 W/m2. Using 4 FHPs (Cases 1 and 2) is economically justified, offering comparable cooling performance to 8 FHPs (Cases 3 and 4), thus ensuring cost-effectiveness and reducing material usage by over 50 %. A maximum enhancement in PV electrical efficiency of 17.3 % is achieved in Case 2 during PCM phase change with a radiative heat flux of 1000 W/m2.

Burning and flame extinction patterns of PMMA under external heating and oxygen deficiency

The paper presents an experimental study investigating the impact of under-oxygenated conditions on the burning characteristics and flame extinction of horizontal transparent poly(methyl-methacrylate) (PMMA) slabs subjected to external heating. Small-sized solids are exposed to various constant levels of radiant heat flux in a nitrogen-diluted environment at ambient pressure. The study aims to understand the multivariable dependence of PMMA combustion on oxygen and heating levels. The analysis goes beyond the study of global and local variables to provide an understanding of the mechanisms involved, revealing a notable effect on burning characteristics and flame extinction mechanisms by blow-off. The results provide a detailed assessment of the surface energy balance and flame bulk properties. The results demonstrate good repeatability up to a certain oxygen limit, beyond which the flame combustion regime exhibits stochastic behaviour. The study of heat transfer mechanisms has revealed that flame radiation and external heating play a predominant role in the heating of horizontal solid fuels, In contrast, within the flame, convection is the main contributor to solid heating, rather than flame radiation. Solid characteristics show linear trends proportional to oxygen depletion, while gas phase characteristics show monotonic trends strongly influenced by the changing combustion regime. The surface temperature of the solid is highly sensitive to the test conditions that affect the energy balance. Dimensionless parameters are developed and data are correlated with existing literature. The analysis demonstrates that the linear or monotonic trends are maintained regardless of external heating. Finally, models are proposed and validated to predict both the extinction limit and the burning rate independently of irradiance and oxygen levels.

Detailed radiation modeling of two flames relevant to fire simulation using Photon Monte Carlo — Line by Line radiation model

This work reports benchmark data sets for radiative heat transfer in two distinct fire configurations obtained from the Measurement and Computation of Fire Phenomena (MaCFP) working group database. The cases include a 19.2 kW non-sooting turbulent methanol pool fire and a 15 kW sooting ethylene flame (referred to as the FM burner). The base configurations were simulated with large eddy simulation (LES) approaches using two different codes, namely FireFOAM and Fire Dynamics Simulator, respectively. Multiple frozen snapshots from these LES runs were radiatively evaluated using a photon Monte Carlo radiation solver and a line-by-line spectral model. The results were presented at three levels: Firstly, the radiative fields, including radiative emission, reabsorption, and heat flux contours, were shown. Secondly, the global radiative contributions from molecular gas species, soot, and wall boundaries were compared. Thirdly, a detailed spectral analysis of radiative fields for different components within five distinct spectral bands was presented. In the case of the non-sooting methanol pool fire, the radiative emission from CO2 predominates. However, for the radiation reaching the boundaries, both CO2 and H2O contribute almost equally. Conversely, for the sooty FM burner configuration, radiative emission from soot, CO2, and H2O all contribute similarly. In terms of radiation reaching the boundary, soot is the primary contributor in FM Burner. In the methanol pool fire, the pool surface receives a comparable contribution from CO2, H2O, and burner rim radiation, whereas, for the FM burner, the burner inlet surface primarily receives radiation from soot.

Forecasting the flame geometry and ground received radiative heat fluxes of two parallel adjacent fires of hydrocarbon fuel with crosswinds

Radiative heat transfer in fires is a critical parameter and a key aspect of gas storage and fire prevention design. In this study, the flame geometric scale characteristics and ground-received radiative heat fluxes from two parallel adjacent hydrocarbon fuel fires with crosswinds were examined. The separation distance between the two parallel flames, crosswind speed, and heat release rates were considered. The experimental results indicated that the flame tilt angle of the two parallel flames increased with increasing crosswinds. The horizontal flame length scale of the two adjacent parallel flames first increased with the crosswind until a critical point was reached, followed by a fluctuation with a further increase in the wind speed. To further quantify this flame phenomenon, a physical model of the flame interaction between two parallel fires under the effects of crosswinds was proposed. The model analyzed major factors affecting the geometrical parameters of the flame, including the inertial force caused by the crosswind, thermal buoyancy from flame combustion, and the interaction and separation distance between the two fires. Additionally, correlations between the flame tilt angle and the horizontal flame length scale of the two adjacent flames were proposed. It was also demonstrated that the ground-received downstream radiative heat fluxes were the dominant parameters determining flame spread. Based on the assumption of the flame geometry of two adjacent parallel fires, the viewing factor was revised, and the relationship between the position of the radiant point and the horizontal length of the flame was considered in the flame model. Furthermore, based on the updated viewing factor of two parallel adjacent flames, a prediction model of ground-received radiative heat fluxes was proposed, which successfully estimated the variation of ground-received downstream radiative heat flux profiles along the centerline of the two parallel flames under crosswind conditions. This estimation is crucial for future fire research, particularly cross-wind-related experiments.

Experimental study on the diffusion and burning characteristics of continuous liquid fuel spillage on sloped ground in open space

When liquid fuel spills on sloped ground and an ignition source is nearby, it could lead to a continuous spill fire. To investigate the diffusion and burning characteristics of continuous liquid fuel spillage on sloped ground in open space, a series of experiments were conducted, considering different discharge rates (60–140 ml/min) and ground slopes (2°, 4°, 6°, 8°). Characteristic parameters were measured, including fuel diffusion rate, flame temperature, and burning rate. A model for the diffusion velocity was established. Results indicate that under non-ignited conditions, the diffusion velocity of the liquid fuel gradually decreases with time, eventually converging toward an asymptotic velocity. Under ignited conditions, the burning process of the spill fire in open space could be categorized into three distinct stages. Moreover, compared to our former study on tunnel spill fires, the mass burning rate per unit area of the spill fires in open space is obviously lower than that of spill fires in confined space in the range of experimental conditions in this study. This is mainly because the flame of a spill fire in open space is not constrained by a ceiling, which prevents the formation of a ceiling flame extension phenomenon. In contrast, the tunnel spill fire could form a ceiling flame expansion. This will intensify the radiation heat flux from the flame to the liquid fuel, thereby increasing the mass burning rate per unit area. This work is expected to provide a reference for predicting the diffusion process of a spill fire in open space.

A dataset of solar radiation and soil heat fluxes for agro-ecosystems in the hilly area of Central Sichuan Province (2005–2021)

A dataset of solar radiation and soil heat fluxes for agro-ecosystems in the hilly area of Central Sichuan Province (2005–2021)

An Increase in Autumn Marine Heatwaves Caused by the Indian Ocean Dipole in the Bay of Bengal

Abstract This study investigates the interannual variability of marine heatwaves (MHWs) in the Bay of Bengal (BOB) associated with the Indian Ocean dipole (IOD) from 1982 to 2021. The results revealed a significant positive correlation at the 95% confidence level between the IOD and MHW days in the central bay at the peak of the IOD in autumn. During positive IOD (pIOD) events, the central bay experienced more MHW days in autumn, with an average increase of 7.4 days. The increased MHW days in the central bay could be primarily attributed to the enhanced net heat flux (TQ), which is 9.7 times the contribution of ocean dynamic processes (horizontal advection + entrainment). The reduced latent heat flux loss and enhanced shortwave radiation due to the anomalous atmospheric low-level high pressure associated with the pIOD account for 63% and 50%, respectively, of the anomalous enhanced TQ, while the longwave radiation and sensible heat flux make smaller contributions of −20% and 7%. In addition, thermocline deepening in the southwestern bay, caused by this anomalous high pressure and associated anticyclonic wind anomalies, favors the occurrence and persistence of MHWs by reducing the mixed-layer cooling rate. In addition to the influence of the IOD, El Niño–Southern Oscillation mainly affects MHWs from winter to the following summer, which confirms the result of a previous study.

A preliminary observational study on the characteristics of surface turbulent fluxes over the South China Sea Islands

AbstractIn recent years, there has been a rise in human activities in oceanic areas, making the land–atmosphere interactions over islands a major scientific concern on a global scale. Examining the observation data from offshore areas enables a more comprehensive understanding of the turbulent fluxes in offshore atmospheric environments, patterns of momentum, energy and material exchange between the atmosphere and underlying surface in an oceanic boundary layer, and development of a heterogeneous atmospheric boundary layer. The related findings will assist in developing theoretical models and parameterization schemes to simulate the influence of heterogeneous surfaces on land–atmosphere interactions on the South China Sea Islands. Existing studies on the turbulent fluxes over the South China Sea Islands were mainly conducted on the Nansha Islands, whereas studies on the waters of the South China Sea are scarce. In this study, we used 10 Hz high‐frequency turbulence measurements to calculate the latent and sensible heat fluxes over the South China Sea Islands using the eddy correlation method. These findings were then compared with data from the Dunhuang Gobi, Ordos desert, and Xilingol grassland regions in inland China, along with the observed net radiation and surface heat fluxes. The findings indicate that the energy fluxes over the South China Sea in summer exhibit prominent diurnal variations. The magnitude of either latent or soil heat flux is low, and the net radiation is predominantly transformed into sensible heat flux, which warms the atmosphere. Furthermore, the daily variation curves of sensible and latent heat fluxes are influenced by intermittent turbulence on the islands and reefs, resulting in a less smooth pattern compared with soil heat flux. Although the South China Sea Islands have small land areas and are surrounded by the sea, the land–atmosphere interactions over the underlying surface of this region are similar to those over the underlying surface of grasslands in inland China during summer. The daily mean sensible heat flux on the islands is higher than that in an inland area, and the time lag in its response to sunrise is longer than that in inland areas by approximately 1 h. The overall energy balance ratio is approximately 0.75, c which is in line with the average level, but an energy balance residual of approximately 25% still exists. Furthermore, extreme weather conditions, such as typhoons, can disrupt the diurnal variations of sensible and latent heat fluxes, and the cyclical patterns are subsequently restored.

Experimental Study of Near-field Radiative Heat Transfer Between Large-Area Polar Dielectric Films

Utilizing polar dielectric films can improve the performance of near-field thermophotovoltaic system. To confirm the enhancement of near-field radiative heat transfer (NFRHT) achieved by large-area polar dielectric films, we built an experimental setup and observe NFRHT between two 250 nm-thick SiO2 films on intrinsic Si substrate with an area 5 × 5 mm2. The two films are supported by SiO2 nano-spacers with a height of 302 nm. Temperature difference between the two films varies from 13 K to 42 K at room temperature. The observed near-field radiative heat flux closely matches the theoretical values, which surpasses substrate-only system by up to 9.87 times and could reach up to 7.45 times that of blackbody radiation due to excitation of the surface photon polaritons modes. These results demonstrate the effectiveness of polar dielectric films in enhancing NFRHT.

A repetitive pulsed electrothermal plasma jet ignition system based on capillary discharge.

Plasma ignition and combustion enhancement is a promising technology in applications of engines, industrial burners, pollutant emissions controls, etc. A new repetitive electrothermal plasma jet ignition system based on ablated capillary discharge under atmospheric pressure is presented in this paper. It consists of a capillary discharge module, a pulse current circuit, a pulse voltage circuit, a current release unit, an LC series resonant circuit, and a control system. The effects of the energy storage capacitor's voltage and resistance in the current release unit on the electrical parameters are investigated. Increasing the capacitor voltage helps to shorten the discharge delay and increase the energy deposition efficiency in the main discharge process. The increase of the resistance in the current release unit leads to a longer discharge delay and higher energy deposition efficiency in the main discharge process. Balanced parameters between the delay of discharge in 66 µs and the energy deposition efficiency in 84% are achieved through optimization, with a peak radiative heat flux of 23MWm-2 and a maximum jet length of 17cm. Repetitive capillary discharge at 20Hz under atmospheric pressure is achieved with the dispersion of energy storage capacitor charging voltage and energy deposition efficiency of 0.3% and 9.6%, respectively. Simplified circuit topology and control logic contribute to the miniaturization of the ignition system.

PERFORMANCE OF WATER COOLING FOR RADIATION HEAT FLUX FUEL STORAGE TANK

Full-surface fire on fuel storage tank emits high radiation heat transfer. As a fire protection strategy, the water curtain cooling system is activated to reduce the temperature on the adjacent tank surface. Therefore, the present work predicts and analyses the radiation heat flux and the maximum flame temperature of different types of fuels. Further, this analyses the effect of fuel total mass on radiation heat flux and maximum flame temperature and observes the effect of distance between two tanks on radiation heat flux distribution. The relationship between water cooling flow rate and outlet water temperature that absorbed radiation heat flux has been studied. The study has been conducted by using the Consequence modeling software trial version. The modeling setup of the tank is 17 m in height with 65 m inner diameter, and the meteorological data used are 5.4 m/s wind speed with north wind direction at atmospheric pressure in order to imitate the worst-case fire scenario. The results reveal that the gasoline fuel emitted the highest heat flux value of 11.03 kW/m2 and the raw gasoline sample emits the lowest heat flux value of 9.14 kW/m2. Furthermore, the total mass of the fuel shows no effect on the maximum flame temperature of 958.51°C. According to the findings, the critical tank distancing is 36 m and thus the appropriate tank distancing of 40 m is highly recommended by the standard. The result shows that the water cooling rate of 4.1 lpm/m2 is an excellent practice of water cooling to cool down the temperature of the fuel tank which is exposed to radiation heat flux.

Ignition limits of pine wood building material under the coupling effects of thermal radiation and cross winds

The ignition of timber buildings in the context of wildland-urban interface (WUI) fires has emerged as a significant challenge amidst the backdrop of global climate change. However, to the best knowledge of the authors, little attention was paid to the ignition conditions of wood building materials in WUI fires especially in thermal-fluid coupling environments. This study experimentally investigated the smoldering and flaming ignition characteristics of wood under the coupling effects of thermal radiation and cross winds. Surface temperature, internal temperature, mass loss rates, and time to ignition of wood samples were measured to study their variation with the above factors and the threshold between smoldering and flaming ignition phenomena. The results showed that wood exhibited reduced susceptibility to flaming ignition under low radiant heat flux conditions, and the introduction of cross winds posed more challenges for flaming ignition. In addition, both the critical surface temperature and mass loss rate varied with radiant heat flux and cross-wind speeds, so it was not feasible to determine the occurrence of flaming ignition by any of the two factors directly. This is because the coupling effects of thermal radiation and cross winds would result in a competition between radiant heating and convective cooling on wood surfaces. In light of this fact, two dimensionless quantities, namely Damköhler number and heat transfer ratio, were introduced to distinguish between smoldering and flaming ignitions. Damköhler number was used as an indicator of the potential for gas-phase flaming ignition, while the heat transfer ratio, namely the ratio of convective heat loss to radiant heat flux, was used to measure the net thermal energy received by wood surfaces. It has been demonstrated that the two quantities were effective to distinguish between smoldering and flaming ignitions from the perspectives of gas and solid phases with 20–40 kW/m2 in radiant heat flux and 0–1.0 m/s in cross-wind speed. The data and theories disclosed in this study could help predict the ignition behaviors of timber buildings under thermal-fluid coupling conditions, thus providing useful guidance for WUI fire mitigation and control.

Land surface processes response to warming and wetting trend in Northwest China

Abstract The climate in Northwest China (NWC) has undergone a warming and wetting trend (WWT) since the 1980s, which has attracted considerable attention from the scientific and policy communities. However, the majority of previous studies have focused on overall effects of WWT, and very few have examined how land surface system responds to climate warming or wetting trend, respectively. For this purpose, this study uses the Community Land Model (CLM5) driven by the Chinese Meteorological Forcing Dataset (CMFD) to conduct four modelling experiments: a control experiment (CTRL) and three sensitivity experiments, in which the annual trend of air temperature (NonWarm), precipitation (NonWet), and both (NonWWT) are removed from the CMFD from 1979 to 2018. Compared to CTRL, the land hydrological variables (i.e., soil moisture, runoff and evapotranspiration) show a visible reduction in magnitude, interannual variability, as well as annual trend in NonWet, while they are enhanced in NonWarm. In both NonWarm and NonWet, the magnitude and trend of both net radiation and sensible heat fluxes increase, with a more pronounced change in NonWWT. Further analysis indicates that the land surface processes are more sensitive to wetting trend than to warming trend. Among all land surface hydrological variables and energy variables, runoff and snow cover fraction are the most susceptible to climate change. Overall, the effects of climate change in Ta and Pr on surface hydrological variables are non-linearly offsetting, while the effects on surface energy budgets are non-linearly superimposed. Compared to warming trend, wetting trend plays a larger impact in the variability of land surface processes in NWC.

Experimental study on condensation-free radiant cooling panel with low-temperature for local cooling in vehicles - Part 1: Design process and feasibility evaluation with performance test

Although radiant cooling has significant advantages (high efficiency and thermal comfort), insufficient cooling capacity and condensation risk limit the practical application. In this study, a novel condensation-free radiant cooling panel (RCP) with high cooling capacity is proposed. The performance of proposed RCP was experimentally evaluated at different operating conditions. The transparent cover and surface-painting spray materials of the RCP were examined using Fourier-transform infrared spectroscopy to analyze their transmittance and absorptivity. The total cooling heat flux of the proposed RCP ranged between 2019.5 and 3824.5 W m–2, which are significantly higher than those of previous studies (70–1457 W m–2), owing to low surface temperatures. The radiant heat flux decreased by 13.5% when the distance between the cooling surface and the heater increased from 10 cm to 20 cm, and decreased by 52% when evaporating temperature increased from –40 °C to –20 °C. However, the heater and ambient temperatures showed insignificant effect. The results of this study report feasibility of the proposed RCP and parameters that influence performance. The target application of the proposed RCP is local cooling systems in vehicles to enhance thermal comfort, which is given in succeeding research, Part 2: Demonstration with passengers for thermal comfort analysis.

Comparative analysis of varied thermal conductivity and viscosity models in a hybrid nanofluid flow - a non-similar solution

ABSTRACT We aim to investigate the flow of an ethylene glycol-based hybrid nanofluid over a horizontal surface with a free stream velocity. To assess the viscosity and thermal conductivity of nanoparticles with various shapes, we employed the Brinkman, Timofeeva, and Yamada Ota unit cell models. The study explores heat transfer in the flow system considering the effects of viscous and ohmic dissipations, linear radiative heat flux, and heat generation under convective boundary conditions. A non-similar system is developed using appropriate non-similarity transformations up to the third-level truncation and numerically solved using the bvp4c algorithm. The novelty of the proposed model lies in obtaining the non-similar solution and incorporating the Brinkman, Timofeeva, and Yamada Ota unit cell models. The results indicated that the Brinkman viscosity model resulted in an increase in the wall heat transfer rate with a rise in particle volume fraction. It is also inferred that platelet-shaped nanoparticles exhibit a significantly higher heat transfer rate compared to spherical-shaped nanoparticles.

Oceanic response to tropical cyclone in the northern South China Sea observed by underwater gliders during 2018 and 2020

In this study, we mainly used in-situ observations from underwater gliders to analyze the ocean response in the northern South China Sea affected by Son-tinh (2018), Mandal et al. (2018) Mangkhut (2018)and Noul (2020). The results showed that these TCs caused 0.6 °C, 1.1 °C and 1.7 °C maximum sea surface temperature cooling respectively, which were weaker than general conditions because of long distance, weak intensity and fast movement speed. Net solar radiation, precipitation, 10-m wind and sea surface heat flux also made contribution in changes of SST. The mixed layer depth (MLD) became shallower after Son-Tinh and Noul passed through, while during Mangkhut it did not change significantly. After TCs passed through, the stratification around MLD became more obvious, with a banded distribution and stronger high-value areas of buoyancy frequency. Within 1 week after the shortest distance, the temperature and salinity responses in the upper ocean were stronger than those at the sea surface, and the gradients of temperature and salinity and their anomalies were more evident in the subsurface layer. The results of this study show that underwater glider observations are important for understanding oceanic responses to tropical cyclones and are useful for studying tropical cyclone activities.