Convection Radiation Research Articles

Thermal processes affected by carbon dioxide near ground surface

This study provides penetrative investigation of the effects of carbon dioxide concentration on time-dependent temperature and energy fluxes on the ground surface subject to solar irradiation. While global warming significantly impacts human life, the factors responsible remain controversial. This work considers unsteady one-dimensional heat conduction and radiative heat transfer, including collimated and diffuse components as functions of longitude, latitude, and altitude. Diffuse radiation depends on the different absorption bands of carbon dioxide and water vapor, as functions of wavelength, temperature, concentrations or pressure. The predicted results using COMSOL computer code show that the effects of carbon dioxide concentration on ground surface temperature are negligibly small, for example, over a 5-year period. Time-dependent ground surface temperature strongly depends on the absorption or dissipation of diffuse radiation and heat conduction. Diffuse radiation has a damping effect on temperature variation. Temperature changes due to solar irradiation absorption in the atmosphere are also negligibly small, despite solar irradiation being much greater than diffuse radiation and heat conduction. The absorption or dissipation of diffuse radiation depends on the dominant absorption bands centered at 4.3 and 15 μm of carbon dioxide at different times. This study, from the viewpoint of energy conservation, identifies diffuse radiation as a critical factor influencing the rate of temperature change at the ground surface, without assuming radiative or thermal equilibrium or modeling convection. Poor management of this radiation would hinder efforts to avoid droughts, water scarcity, severe fires, rising sea levels, flooding, catastrophic storms, and biodiversity loss.

Bioconvective magnetohydrodynamic flow of tangent hyperbolic nanofluid across a stretched surface, with Arrhenius activation and convective heat and slip conditions

The current study investigates mixed convective flow of an unsteady MHD tangent hyperbolic nanofluid due to a stretching surface with motile microorganisms via convective heat transfer and slip conditions. The flow analysis's governing equations were converted into a nondimensional relation by using the proper alteration. The pertinent similarity transformations are utilized in the main equations, and the solutions are obtained using the integrated bvp4c software. A good agreement with previously published data indicates the efficacy of the numerical technique. The following are the main findings: increasing the magnitude of the radiation and mixed convection parameters improves the velocity profile, whereas the Weissenberg number and magnetic field demonstrate the opposite influence; improvements in heat transfer occur due to the thermal radiation parameter, Brownian movement, and thermophoretic effects; activation energy improves concentration profile, whereas Lewis number shows opposite effect; bioconvection Lewis number and Peclet number declines the Motile microorganism density. Additionally, a tabular analysis of the skin friction, motile microorganism density, Nusselt number, and Sherwood number is also provided.

Tetrahybrid nanoparticles through squeezed channel with inclined Lorentz forces

Heat exchangers, nuclear power plants, and other engineering and manufacturing operations all involve high temperatures. These systems have a very big temperature gradient, which has a substantial impact on the fluid's transport characteristics. Under such circumstances, using the linear Boussinesq approximation and taking into account the constant thermophysical parameters for the ambient liquid become meaningless. Thus, under the impact on the angled magnetic field and joule heating, the radiative convection flow of the blood-based tetrahybrid nanoliquid in a squeezing channel is examined in this work. The base fluid that contains the distributed alumina, gold, silver, and titania nanoparticles is blood. Through suitable transformations, the partial governing equations were decreased into nonlinear ordinary differential equation's, which are then resolved mathematically applying the fourth-order accurate BVP4C technique. The increase in the viscous dissipation parameter corresponds toward the notable elevation on the blood temperature profile. The rate of heat transfer 57.4519% improved in Au-Ag-Al2O3-TiO2/blood than that of pure blood.

Scaling Law of Flow and Heat Transfer Characteristics in Turbulent Radiative Rayleigh-Bénard Convection of Optically Thick Media

Radiative natural convection is of vital importance in the process of energy storage, power generation, and thermal storage technology. As the attenuation coefficients of many heat transfer media in these fields are high enough to be considered as optically thick media, like nanofluids or molten salts in concentrated solar power or phase change thermal storage, Rosseland approximation is commonly used. In this paper, we delve into the impact of thermal radiation on the Rayleigh-Bénard (RB) convection. Theoretical analysis has been conducted by modifying the Grossmann-Lohse (GL) model. Based on turbulent dissipation theory, the corresponding scaling laws in four main regimes are proposed. Direct numerical simulation (DNS) was also performed, revealing that radiation exerts a notable influence on both flow and heat transfer, particularly on the formation of large-scale circulation. By comparing with DNS results, it is found that due to the presence of radiation, the modified Nu scaling law in small Pr range of the GL model is more suitable for predicting the transport characteristics of optical thick media with large Pr. The maximum deviation between the results of DNS and prediction model is about 10%, suggesting the summarized scaling law can effectively predict the Nu of radiative RB convection.

Integrated neural network based simulation of thermo solutal radiative double-diffusive convection of ternary hybrid nanofluid flow in an inclined annulus with thermophoretic particle deposition

Numerical simulation of magnetohydrodynamic radiative double-diffusive convective heat and mass transfer of a ternary hybrid nanofluid with thermophoretic particle deposition in an inclined annulus is studied. Both sides of cylinders are preserved at uniform temperatures, while the remaining sides are thermally insulated. The coupled nonlinear partial differential equations are solved using a finite difference approach. The detailed computational results of heat and mass transfer rate, temperature, concentration and flow fields are presented and discussed for a distinct range of significant physical parameters. The results demonstrated that increasing the angle of the inclination factor increases fluid flow. In light of buoyancy, when the annular cavity is set downward, the enhanced shear velocity is transported upwards, where it reaches its optimal temperature. The higher temperature difference leads to augmented dynamic fluid motion, particularly in the radial direction, as the system seeks to balance the thermal energy through convective transfer. The Brownian motion parameter has abrupt mobility of nanoparticles in liquid, which promotes particle collisions with liquid molecules, yielding kinetic energy. Increased values of thermophoretic parameters augment the thermophoresis force. Thermophoretic particle deposition increases the concentration of nanoparticles in an annulus due to the migration of particles from hot to cold regions under the influence of temperature gradient. The heat and mass transfer characteristics of ternary hybrid nanofluid are forecasted through an artificial neural network-based Levenberg–Marquardt backpropagated algorithm. The built model shows the heat and mass transfer rate root mean squared values through the Levenberg–Marquardt algorithm as one and mean squared error values as 1e-07 and 1e-08 respectively.

Non-uniform variation characteristics of temperature field and corresponding thermal effect of longitudinal continuous slab ballastless track structure

The longitudinal continuous slab ballastless track structure (LCSBTS) easily suffers from interface and joint damage when subjected to extremely high-temperature loads, significantly affecting the running smoothness and safety of high-speed trains. This paper establishes a numerical model of the LCSBTS using the heat transfer principle and real-time shadow technology to replicate the time-varying evolution and spatial distribution of the temperature field. The corresponding thermal effect is obtained based on the sequential thermal-mechanical coupling method. The results show that the temperature variation and the corresponding thermal effect exhibit strong temporal-spatial non-uniformity on the horizontal and vertical planes of the LCSBTS. Solar radiation and heat convection are the dominant factors for the temperature field of the LCSBTS in the daytime and night, respectively, resulting in a higher temperature and greater thermal deformation on the sunny side than on the shady one. The temperature and vertical thermal deformation along the longitudinal direction vary periodically with a specific wavelength between the two adjacent rail support concrete blocks. The thermal deformation increments under the studied non-uniform temperature loads cause an interface damage increment. Finally, the consideration of a non-uniform temperature load produces remarkably different thermal effects from those given by the design temperature load.

Effect of solar radiation on human thermal sensation and physiological parameters in a convection–radiation air conditioning environment

Effect of solar radiation on human thermal sensation and physiological parameters in a convection–radiation air conditioning environment

Accurate modeling of thermal-optical performance for a lightweight SiC mirror

The SiC mirror has excellent structural rigidity and thermal stability, making it widely applicable in high-power optical systems. This manuscript aims to establish a coupled analysis model of thermal-optical performance for a lightweight SiC reflector under high-power laser irradiation. First, based on the Fourier principle, the transient temperature rise of the mirror is analyzed using the finite element method, considering boundary conditions such as heat source and convective radiation. A transient thermal response model for the mirror is established. Then, the reflective surface deformation is solved based on the mirror temperature field. By processing the data of node deformation, the decrease in the mirror surface shape accuracy (RMS) value is obtained. Finally, the experimental platform is built to measure the transient temperature rise and wavefront aberration change of the mirror after high-power laser excitation. Based on the deviation between the calculated data of the analysis model and the measured data, thermodynamic parameters in the analysis model are adjusted according to the principle of minimum residual. The research findings of this manuscript can be utilized for accurately predicting the temperature rise and optical degradation of SiC mirrors under high-power laser irradiation and provide a theoretical basis for the subsequent design of actively compensating methods for thermal-induced distortions.

Magnetic dissipation on radiative free convection of a conducting hybrid nanofluid within a rotating cone and circular disc

A significant attention is gained on the thermophysical properties corresponding to hybrid nanofluid flow within a rotating cone and circular disc in this present investigation due to its several applications. The enhanced thermal conductivity of the nanofluid is particularly useful in cooling systems, reducing energy consumption in systems, preventing overheating, and improving the overall performance of electronic gadgets, etc. In the present investigation, the free convective flow of conducting fluid for the interaction of magnetic field and thermal radiation encases their greater impact on the flow phenomena. Further, the assumption of dissipative heat i.e. mutual effects of viscous and Joule, energies the flow properties. The complex nonlinear form of the constitutive equations presented in the dimensional form is renovated into the nonlinear ordinary system with a non-dimensional form by introducing suitable similarity rules. The computation of the profiles is obtained numerically with the help of the built-in function bvp4c in MATLAB and depicted graphically. Finally, it is observed that the volume fraction of both the nanoparticles favors enhancing the heat transport phenomena due to the augmented thermal conductivity whereas a dual characteristic is revealed at both the surfaces of the circular disc and the cone.

Radiative double-diffusive mixed convection flow in a non-Newtonian hybrid nanofluid over a vertical deformable sheet with thermophoretic particle deposition effects

Radiative double-diffusive mixed convection flow in a non-Newtonian hybrid nanofluid over a vertical deformable sheet with thermophoretic particle deposition effects

Analytical Investigation of Thermal Radiation Effects on Electroosmotic Propulsion of Electrically Conducting Ionic Nanofluid with Single-Walled Carbon Nanotube Interaction in Ciliated Channels

This study examines the behavior of single-walled carbon nanotubes (SWCNTs) suspended in a water-based ionic solution, driven by the combined mechanisms of electroosmosis and peristalsis through ciliated media. The inclusion of nanoparticles in ionic fluid expands the range of potential applications and allows for the tailoring of properties to suit specific needs. This interaction between ionic fluids and nanomaterials results in advancements in various fields, including energy storage, electronics, biomedical engineering, and environmental remediation. The analysis investigates the influence of a transverse magnetic field, thermal radiation, and mixed convection acting on the channel walls. The novel physical outcomes include enhanced propulsion efficiency due to SWCNTs, understanding the influence of thermal radiation on fluid behavior and heat exchange, elucidation of the interactions between SWCNTs and the nanofluid, and recognizing implications for microfluidics and biomedical engineering. The Poisson–Boltzmann ionic distribution is linearized using the modified Debye–Hückel approximation. By employing real-world approximations, the governing equations are simplified using long-wavelength and low-Reynolds-number approximation. Conducting sensitivity analyses or exploring the impact of higher-order corrections on the model’s predictions in recent literature might alter the results significantly. This acknowledges the complexities of the modeling process and sets the groundwork for further enhancement and investigation. The resulting nonlinear system of equations is solved through regular perturbation techniques, and graphical representations showcase the variation in significant physical parameters. This study also discusses pumping and trapping phenomena in the context of relevant parameters.

Investigation of the temperature field of the ice sheet in a prefabricated curling ice rink: Experiment and finite element simulation

Ice temperature is crucial for the quality of artificial ice rinks and ice sports. This study aims to investigate the temperature field of the ice sheet in the prefabricated curling rink for the Beijing Winter Olympics through a combination of experiments and simulations. Through the analysis of heat exchange in the ice sheet, three numerical models of the temperature field of the ice sheet were developed using the finite element software ABAQUS. An environmental temperature model and a comprehensive ambient temperature were proposed to consider thermal radiation and heat convection. Moreover, the simulation results at varying positions were validated through on-site observations of ice temperature, the comparison of three temperature field modeling methods was conducted, and the distribution characteristics of the temperature field were analyzed. In addition, the impact of various parameters on the ice temperature was investigated, and a parameter of the response efficiency of the ice temperature was proposed to conduct sensitivity analysis. Results show that the simplified finite element model of the ice sheet could provide a practical approach to obtain the ice temperature fields. The horizontal and vertical distribution characteristics of the ice temperature can be mathematically described using a sine function with variable amplitude and a cubic polynomial, respectively. A sensitivity analysis indicates that the response efficiency of the ice surface temperature corresponding to cooling medium, ceiling, and air is 90%, 10%, and 10%, respectively. And the ice surface is effectively regulated by the temperature of the cooling medium. The current study would help in the design, operation, and maintenance of ice sheets.

Carbon Nanotube Films with Fewer Impurities and Higher Conductivity from Aqueously Mono-Dispersed Solution via Two-Step Filtration for Electric Heating.

With the intensification of global climate problems, electric heating has recently attracted much attention as a clean and low-carbon heating method. Carbon nanotubes (CNTs) are an ideal medium for electric heating applications due to their excellent mechanical, electrical, and thermal properties. The preparation of electrothermal films based on an aqueous CNT dispersion as a raw material is environmentally friendly. However, in the traditional one-step filtration method, the residual excess dispersant and the small aspect ratio of the CNTs in the preparation process limit the performance of electrothermal CNT films. In this paper, we report a two-step filtration method that removes the free dispersant and small CNTs in the first filtration step and obtains denser CNT films by controlling the pores of the filter membrane in the second filtration step. The results suggest that, compared to the CNT1 film obtained from one-step filtration, the CNT1-0.22 film, obtained from two-step filtration using 1 and 0.22 μm membranes, has a smoother and flatter surface, and the surface resistance is 80.0 Ω sq-1, which is 29.4% lower. The convective radiation conversion efficiency of the CNT1-0.22 film is 3.36 mW/°C, which is 36.1% lower. We anticipate that such CNT films could be widely applied in building thermal insulation and underfloor heating.

An innovative simplified approach for conductive heat flux in pavement structures

Understanding the conductive heat flux at pavement surfaces and interior layers is crucial for reducing pavement distress, developing cooler pavements, and mitigating urban heat island (UHI) effects. Existing methods often rely on calculating the conductive heat flux as the residual heat flux from net radiation and heat convection, leading to significant measurement uncertainties in practice. This study overcomes this issue by introducing a novel model based on Maclaurin polynomial temperature profiles to more accurately determine the conductive heat flux across pavement surfaces and depths. Validated against designed experiments and existing literature, our model shows that both cubic and quadratic Maclaurin polynomials can approximate pavement temperature profiles properly. Our model facilitates the determination of conductive heat flux at various pavement depths, including the surface. By correlating the temperature gradient with measured conductive heat flux at specific depths, we accurately determine the thermal conductivity of the pavement. The proposed method more accurately estimates conductive heat flux compared to the traditional residual methods. The model proves useful in quantifying conductive heat flux, convection, and convection coefficients at various pavement locations, offering enhanced monitoring of conductive heat flux across urban streets.

Energy efficiency and thermal comfort characteristics of convection–radiation combined cooling system in office buildings

Energy efficiency and thermal comfort characteristics of convection–radiation combined cooling system in office buildings

The Influence of the Heat Transfer Mode on the Stability of Foam Extinguishing Agents

The mass loss mechanisms of an aqueous film-forming foam (AF foam), an AR/AFFF water-soluble film-forming foam extinguishing agent (AR foam), and a Class A foam extinguishing agent (A foam) at different levels of thermal radiation, thermal convection, and heat conduction intensity were studied. At a relatively low thermal radiation intensity, the liquid separation rate of the AF, AR, and A foams is related to the properties of the foam itself, such as viscosity and surface/interface tension, which are relatively independent of the external radiation heat flux of the foam. At low radiation intensity (15 kW/m2 and 25 kW/m2), the liquid separation rate of the AF and A foams is relatively stable. When the heat flux intensity is 35 kW/m2, the liquid separation rate of the AF and A foams increases notably, which may be mainly due to the rapid decrease in foam viscosity. And the mass loss behavior is dominated by liquid separation in the AF, AR, and A foams under the influence of thermal radiation and thermal convection. Under the same experimental conditions, the liquid separation rate of AF is the fastest. There is no significant difference in the evaporation rates of the three kinds of foam in the same heat conduction condition. In addition, the AR and A foams usually have a 25% longer liquid separation time (t) under thermal radiation and thermal convection, and the thermal stability is better than AF foam. The temperature reached by the AF foam layer under thermal convection was lower than that of the AR and A foams, and the time for the foam layer to reach the highest temperature under heat conduction was longer than that of the AR and A foams.

Mitigation of shady-sunny slopes effect on subgrade by photovoltaic sheltered boards in permafrost regions

With the great demand of global carbon reduction, a novel method, such as photovoltaic shelter board (PSB), is proposed to mitigate the shady-sunny slope effects in permafrost. The idea of PSB is an extension of traditional shelter board, which can potentially eliminate the shady-sunny slope effect in theory. However, its quantitative performance is still unclear due to limited application and research. To overcome this gap and explore the application possibilities of PSB in cold regions, this paper introduces a novel photovoltaic sheltered board subgrade and numerically investigates its effectiveness in mitigating the shady-sunny slope effect. Initially, a heat transfer model incorporating solar radiation and air convection was developed and validated with field-monitored ground temperature data. Analyses based on this model compare the thermal imbalance effects on exposed subgrade, traditional insulation boards subgrade, and the novel photovoltaic sheltered board subgrade. Results indicate that the photovoltaic sheltered board exhibits superior mitigation effects to traditional insulation boards, primarily due to enhanced heat dissipation by air convection in the suspension region. In the study area, the photovoltaic sheltered board significantly lowers sunny slope temperatures by over 3 ℃ on average and thaw depth by more than 1m compared to exposed subgrade. The photovoltaic sheltered board’s suspension height should not be less than 5.3cm to mitigate the sunny-shady slope effect effectively in this region. In summary, this study provides a reference for mitigating the shady-sunny slope effects and reducing carbon release in permafrost subgrade engineering.

Spatial Dispersion and Statistical Description of Organized Cumulus Cloud Ensembles in Radiative Convective Equilibrium

AbstractDescriptions of cloud ensembles in radiative convective equilibrium (RCE) rely mostly on the assumption that clouds are randomly distributed in space, a hypothesis that obviously fails in presence of strong organization. In this work, idealized RCE simulations at horizontal grid spacings ranging from 2 km to 125 m are analyzed, displaying a transition between complete randomness at coarse resolution to a high degree of cold pool driven organization at high resolution. The objective is then twofold: (a) characterizing the spatial cloud patterns focusing on correlation scales and association with covariates; (b) providing a statistical description of organized cloud ensembles to generalize existing theories based on complete randomness. It is demonstrated that organized cloud ensembles may be treated as heterogeneous point processes where individual clouds do not interact substantially with their neighbors. In other words, clouds may be considered as randomly distributed if we restrict the space to regions of high cloud density. In addition, it is shown that in highly organized situations local cloud counts may be modeled using negative binomial distributions, while cloud mass fluxes follow lognormal distributions. The total mass flux within regions of varying sizes can then be predicted by compounding the two aforementioned distributions. The total mass flux variability at scales ≲5 km is dominated by the heavy‐tails of the mass flux distributions, whereas at scales ≳5 km, it is entirely controlled by the spatial cloud count variability (the spatial cloud pattern). These results have important implications for the parameterization of organized convection in quasi‐equilibrium.

A comprehensive heat transfer prediction model for tubular moving bed heat exchangers using CFD-DEM: Validation and sensitivity analysis

This study established a complete heat transfer prediction model that integrates four heat transfer sub-models, including contact heat conduction, gas film heat conduction, heat radiation, and heat convection, along with an artificial softening correction based on combined approach of computational fluid dynamics and discrete element method (CFD-DEM). The model’s precision was confirmed by experimental results with relative errors below 5 %. The discussion on the heat flux contributions of the above four heat transfer mechanisms shows that with an initial particle temperature of 200℃, tube wall temperature of 30℃, and particle descent velocity of 1.3 mm/s, gas film conduction heat flux is the primary contributor to the total tube wall heat flux at 60.5 %, followed by radiation heat flux (19.5 %), contact conduction heat flux (12.1 %), and convection heat flux (7.9 %). Besides, the presentation of physical fields related to particles and the fluid showcases the model’s capability in elucidating the heat and mass transfer characteristics of the particle–fluid-wall system within tubular MBHEs. Furthermore, a local nominal range sensitivity analysis, along with a study of factors’ influence rules, was performed to quantify the effects of the 8 key model parameters on heat transfer results. The analysis indicates that fluid thermal conductivity is the predominant factor with its nondimensionalized first-order sensitivity coefficient of 54.9 %, succeeded by particle-to-wall angle factor (15.4 %), wall emissivity (14.4 %), gas film thickness (9.6 %), wall thermal conductivity (2.3 %), wall roughness (-1.6 %), particle Young’s modulus (-1.4 %), and particle specific heat capacity (0.4 %). Finally, their impacts on the heat prediction results were presented in detail.

Thermal Marangoni convection in two-phase quadratic convective flow of dusty MHD trihybrid nanofluid with non-linear heat source

The current study examines the effect of heat generation on thermal Marangoni convective boundary layer flow of dusty trihybrid nanofluid across a flat surface with thermal radiation and non-linear mixed convection. We consider, two phase dusty liquid model with non-linear heat generation. The fluctuation of surface tension gradients leads to the discovery of Marangoni convection. It can be used for growing crystals, drying silicon wafers, stabilising soap films, and wielding. The main objective of this study is to ascertain the trihybrid nanofluid thermal mobility. A trihybrid nanofluid consisting of magnesium oxide (Mgo), titanium oxide (TiO2), silver (Ag) and water as the base fluid is used. This model can improve the efficiency and dependability of thermal systems in a variety of applications by helping to optimize heat transfer processes in materials processing, electronics cooling, and the creation of cutting-edge cooling technologies in energy systems. The existing PDEs are converted into nonlinear ODEs via similarity variables. The nonlinear ODEs are then solved numerically using shooting technique (RKF-45th approach). When the Marangoni convection parameter rises, higher surface tension gradients lead to stronger induced flows and more efficient heat transfer inside the liquid. As the temperature profiles of the dust and fluid phases drop, the distribution of these characteristics in the liquid becomes more homogeneous.