Radiative Thermal Conductivity Research Articles

Colossal Near-Field Radiative Heat Transfer Mediated by Coupled Polaritons with an Ultrahigh Dynamic Range.

Near-field radiative heat transfer (NFRHT) can exceed the blackbody limit by several orders of magnitude owing to the tunneling evanescent waves. Exploiting this near-field enhancement holds significant potential for emerging technologies. It has been suggested that coupled polaritons can give rise to orders of magnitude enhancement of NFRHT. However, a thorough experimental verification of this phenomenon is still missing. Here this work experimentally shows that NFRHT mediated by coupled polaritons in millimeter-size graphene/SiC/SiO2 composite devices in planar plate configuration can realize about 302.8 ± 35.2-fold enhancement with respect to the blackbody limit at a gap distance of 87 ± 0.8nm. The radiative thermal conductance and effective gap heat transfer coefficient can reach unprecedented values of 0.136 WK-1 and 5440 Wm-2K-1. Additionally, a scattering-type scanning near-field optical measurement, in conjunction with full-wave numerical simulations, provides further evidence for the coupled polaritonic characteristics of the devices. Notably, this work experimentally demonstrates dynamic regulation of NFRHT can be achieved by modulating the bias voltage, leading to an ultrahigh dynamic range of ≈4.115. This work ambiguously elucidates the important role of coupled polaritons in NFRHT, paving the way for the manipulation of nanoscale heat transport, energy conversion, and thermal computing via the strong coupling effect.

Elevating high-temperature insulation performance of silica aerogels enabled by innovative surface-structured opacifiers

Silica aerogel, recognized as an exceptional material for thermal insulation, has gained considerable attention in thermal protection. However, its inherent infrared transparency compromises its insulating performance at high temperatures. To address this limitation, incorporating micron-sized opacifier particles has emerged as a crucial strategy. This study introduces a novel opacifier particle, distinguished by surface protrusions inspired by the ’structural absorption’ mechanism, and assesses its extinction capabilities. Then, a thorough analysis was conducted to understand how the shape, volume, and numbers of these surface protrusions influence the radiative heat transfer properties of silica aerogels. The findings reveal that the presence of protrusions on the opacifier surface significantly enhances its extinction capacity, consequently reducing the radiative thermal conductivity of silica aerogels. Notably, cylindrical protrusions demonstrate the most effective extinction properties compared to spherical protrusions and rectangular protrusions. Additionally, for opacifier particles with cylindrical protrusions, there exists an optimal number of 12 protrusions that minimize the radiative thermal conductivity of the aerogel. At 1300 K, the radiative thermal conductivity of the silica aerogel doped with opacifiers featuring 12 protrusions is 22.6 % lower than that of the silica aerogel doped with opacifiers lacking protrusions. Moreover, it was observed that maintaining a constant diameter of cylindrical protrusions while increasing their height diminishes the radiative thermal conductivity of silica aerogel. However, the effect on the radiative thermal conductivity becomes less significant beyond a certain protrusion height. The outcomes of this study provide significant insights into the innovation of opacifiers.

Intelligent computing for the electro-osmotically modulated peristaltic pumping of blood-based nanofluid

The study delves into a novel application of artificial neural networks within the biomedical realm, specifically focusing on the peristaltic pumping of ionized blood-infused nanofluid using the Casson model. The investigation takes into account the impacts of electrokinetic forces, chemical reaction, thermal radiation and variable thermal conductivity. The endorsed nanofluid model encompasses both thermophoretic and Brownian diffusions. The Nernst-Planck and Poisson equations are used to characterize electroosmotic process. The mathematical model is then numerically solved using NDSolve in Mathematica. The variation in relevant hemodynamic characteristics concerning key flow parameters is explored through numerous graphical representations. Two distinct artificial neural networks have been developed to estimate values for rates of mass and heat transfer. The Levenberg-Marquardt algorithm is used as the training algorithm in network models with multi-layer perceptron architecture. Graphical inspection of the results demonstrates a decrease in blood flow with an elevated Helmholtz-Smoluchowski velocity. A lower pressure gradient is recorded with a higher electroosmotic parameter. Furthermore, an augmentation in the thermal conductivity parameter leads to a reduction in heat transfer rate at the wall. The concentration profile demonstrates an increase with a rise in the chemical reaction parameter. The results obtained from the neural network models exhibit an ideal harmony with the target values. The developed neural network models demonstrated the ability to predict rates of heat and mass transfer values with average deviations of −0.01% and 0.004%, respectively.

Thermal conductivity test and model modification of SiO2 aerogel composites based on heat flow meter method

In the composition of thermal protection system, lightweight and efficient super thermal insulation materials-aerogel and its composites have been paid more and more attention and applied in recent years. The heat transfer of aerogel composites is more complicated due to the influence of micro-scale additives, fiber distribution and coupling heat transfer of various heat transfer modes, so it is urgent to calculate the effective thermal conductivity (ETC) accurately. According to the variation law of gas, solid, gas–solid coupling and radiation thermal conductivity with temperature and pressure, the thermal conductivity test is conducted based on the heat flow meter method, so as to the mathematical models of thermal conductivity are modified. The modified models take into account the influence of various micro-scale additives, which can accurately and quickly calculate the ETC of aerogel composites under different working conditions. The questions that different aerogel composites need to reconstruct structural models and the existing theoretical formulas are inaccurate in calculating ETC are solved. This paper is of great theoretical value to accurately predict the thermal insulation performance of aerogel composites.

Impact of solar radiation in the presence of temperature-dependent thermal conductivity of non-Newtonian Casson flow on natural convection heat transfer in plume generated due to the combined effects of heat source and aligned magnetic field

Understanding the non-Newtonian Casson fluid is crucial for addressing various challenges in industrial, biological, and environmental applications. In this novel research, Casson fluid with temperature-dependent variable thermal conductivity is analyzed by a natural convective plume generated by horizontal line heat source. The plume system is under the influence of solar radiation and an aligned magnetic field. The momentum equation is transmuted for Casson fluid, while energy equation transmuted for solar radiation and variable thermal conductivity. The coupled partial differential equations changed into ordinary differential equation by employing stream function formulation. For computational evaluation, bvp4c built-in tool of MATLAB is employed in combination with Shooting technique in order to analyze both missing and specified boundary conditions. The upshots of Casson parameter β 1 , thermal conductivity variable γ 1 , radiation parameter Rd , magnetic force parameter S , Prandtl number Pr and magnetic Prandtl number γ on specified and missing conditions are highlighted in the graphical illustrations. The computed outcomes for missing conditions depicts that for Casson parameter β 1 velocity f ′ and temperature θ drops while current density increased with increment in β 1 . Whereas, for specified boundary conditions, the skin friction f ″ and magnetic flux ϕ ′ decreases while heat transfer rate θ ′ enhances for increasing β 1 . For missing conditions, the increasing thermal conductivity variable γ 1 causes velocity f ′ , current density ϕ ″ , and temperature θ to drop. While for specified conditions, the skin friction f ″ , magnetic flux ϕ ′ increases but heat transfer rate θ ′ exhibits reverse trend with enhancing γ 1 . Additionally, a validation analysis has been performed by comparing the values of f ′ ( 0 ) for various values of Pr with prior work, while excluding the other parameters to check its limitations at the boundary layer.

Greatly Enhanced Radiative Transfer Enabled by Hyperbolic Phonon Polaritons in α‐MoO3

AbstractOrthorhombic molybdenum trioxide (α‐MoO3) is a highly anisotropic hyperbolic material in nature. Within its wide Reststrahlen bands, α‐MoO3 has hyperboloidal dispersion that supports bulk propagation of high‐k phonon polariton modes. These modes can serve as energy transport channels to greatly enhance radiative heat transfer inside the material. In this work, large radiative transfer enabled by phonon polaritons in α‐MoO3 is demonstrated. The study first determines the temperature‐dependent permittivity of α‐MoO3 from polarized Fourier‐Transform Infrared (FTIR) spectroscopy measurements and then uses a many‐body radiative heat transfer model to predict the equivalent radiative thermal conductivity of hyperbolic phonon polariton. Contribution of radiative transfer to the total thermal transport is experimentally determined from the Time‐Domain Thermoreflectance (TDTR) measurements in a temperature range from −100 to 300 °C. It is found that radiative transfer can account for ≈60% of the total thermal transport at a temperature of 300 °C. That is, conductive thermal transport is enhanced by >100% by radiative transfer, or radiation inside α‐MoO3 is greater than that of conduction. These additional energy pathways will have important implications in thermal management in new materials and devices.

Enhanced Far-Field Thermal Radiation through a Polaritonic Waveguide.

We experimentally demonstrate the enhancement of the far-field thermal radiation between two nonabsorbent Si microplates coated with energy-absorbent silicon dioxide (SiO_{2}) nanolayers supporting the propagation of surface phonon polaritons. By measuring the radiative thermal conductance between two coated Si plates, we find that its values are twice those obtained without the SiO_{2} coating. This twofold increase results from the hybridization of polaritons with guided modes inside Si and is well predicted by fluctuational electrodynamics and an analytical model based on a two-dimensional density of polariton states. These findings could be applied to thermal management in microelectronics, silicon photonics, energy conversion, atmospheric sciences, and astrophysics.

High-temperature resistance performance of silica aerogel composites through fiber reinforcement

Aiming to meet the fireproof requirements for bridges, three fiber/silica aerogel composites were fabricated using basalt fiber, a composite of basalt fiber and high silica glass fiber, and high silica glass fiber as the matrix. The dimensional, structural, mechanical, and thermal insulation stability of these composites under high-temperature heating ranging from 800 °C to 1000 °C were systematically studied. Upon high-temperature heating, the fracture and deformation basalt fiber occurred, leading to the breakage of the fiber skeleton and the aerogel integrity. This resulted in significant densification and a consequent decrease in porosity in the heated basalt fiber/aerogel composite and basalt fiber-high silica glass fiber/silica aerogel composite. Crystallization of basalt fiber began after heating to 800 °C and fully completed at 1000 °C. Besides, part of the high silica glass fiber in the basalt fiber-high silica glass fiber/silica aerogel composite crystallized at 900 °C and 1000 °C. These variations in micro-macro structures and phase compositions led to a substantial degradation of mechanical property and thermal insulation performance in the composites containing basalt fiber. In sharp contrast, the fiber skeleton and aerogel integrity remained relatively stable under high-temperature heating, enabling a synergistic thermal insulation effect of fiber and aerogel. The integrated fiber skeleton reduced the radiative thermal conductivity of the aerogel, while the unbroken aerogel protected the fiber from crystallization. Consequently, the mechanical property and thermal insulation performance of the high silica glass fiber/silica aerogel composite remained stable after high-temperature heating. The ultimate tensile strength and thermal conductivity of the pristine and 1000 °C-heated high silica glass fiber/silica aerogel composite were 0.74 MPa and 0.53 MPa, 0.0213 W/(m·K), and 0.0279 W/(m·K), respectively. This novel composite, exhibiting low thermal conductivity, high strength, excellent thermal stability, is expected to be a desirable candidate for bridge fireproof applications.

Overlapping Grid-Based Spectral Collocation Technique for Bioconvective Flow of MHD Williamson Nanofluid over a Radiative Circular Cylindrical Body with Activation Energy

The amalgamation of motile microbes in nanofluid (NF) is important in upsurging the thermal conductivity of various systems, including micro-fluid devices, chip-shaped micro-devices, and enzyme biosensors. The current scrutiny focuses on the bioconvective flow of magneto-Williamson NFs containing motile microbes through a horizontal circular cylinder placed in a porous medium with nonlinear mixed convection and thermal radiation, heat sink/source, variable fluid properties, activation energy with chemical and microbial reactions, and Brownian motion for both nanoparticles and microbes. The flow analysis has also been considered subject to velocity slips, suction/injection, and heat convective and zero mass flux constraints at the boundary. The governing equations have been converted to a non-dimensional form using similarity variables, and the overlapping grid-based spectral collocation technique has been executed to procure solutions numerically. The graphical interpretation of various pertinent variables in the flow profiles and physical quantities of engineering attentiveness is provided and discussed. The results reveal that NF flow is accelerated by nonlinear thermal convection, velocity slip, magnetic fields, and variable viscosity parameters but decelerated by the Williamson fluid and suction parameters. The inclusion of nonlinear thermal radiation and variable thermal conductivity helps to enhance the fluid temperature and heat transfer rate. The concentration of both nanoparticles and motile microbes is promoted by the incorporation of activation energy in the flow system. The contribution of microbial Brownian motion along with microbial reactions on flow quantities justifies the importance of these features in the dynamics of motile microbes.

Dominant mechanisms of thermo-mechanical properties of weberite-type RE3TaO7 (RE=La, Pr, Nd, Eu, Gd, Dy) tantalates toward multifunctional thermal/environmental barrier coating applications

Weberite-type RE3TaO7 (RE=La, Pr, Nd, Eu, Gd, Dy) tantalates have been studied as multifunctional thermal/environmental barrier coating materials with working temperatures above 1500 K. This study proposes the dominant mechanisms of their thermo-mechanical properties. The relative ionicity of the RE-O bonds increased with increasing RE+3 ionic radius, which weakened the bond strength and led to decreases in Young's modulus and hardness. A model was proposed to derive the high-temperature thermal conductivity based on the relationship between the phonon thermal conductivity and temperature, and the thermal radiative conductivity was estimated. RE3TaO7 exhibited a lower thermal conductivity than other fluorite-related oxides because its weak bond strength could slow down the phonon speed and enhance the an-harmonic vibrations of the lattices. At low temperatures, the RE atomic weight was a better descriptor of the thermal conductivity than the RE+3 ionic radius, and which could aid in further regulating the thermal conductivity. The thermal expansion coefficients of the different axes were affected by both RE-O and Ta-O bonds when weak RE-O bonds dominated the linear thermal expansion. The low oxygen ion conductivity derived from the strong covalent Ta-O bonds, which increased the activation energy for oxygen hopping in lattices of RE3TaO7. This study elucidates the dominant mechanisms of properties from the characteristics of crystals and chemical bonds, which are significant for high-temperature applications of tantalates.

High-entropy strategy for high-temperature broadband infrared radiation and low thermal conductivity

Developing high-performance infrared radiation ceramic materials with desired broadband emissivity while reducing thermal conductivity to prevent heat transfer is highly desirable for emerging industrial and aerospace applications. Nevertheless, it remains a grand challenge to simultaneously meet these requirements in existing infrared radiation ceramic materials. Herein, a high-entropy strategy is employed to enhance the high-temperature infrared radiation property with a high emissivity above 0.9 at room temperature and 0.68 at 1200 °C across the entire range of wavelength (1–14 μm), and integrate a low thermal conductivity (<0.88 W m−1 K−1 at 1000 °C) and remarkable mechanical properties. High-entropy rare earth (RE) disilicates ((Y0.4Yb0.4Tm0.1Lu0.05Ho0.05)2Si2O7) ceramic coating with high lattice entropy has a more complex electronic structure, inducing lattice distortion and extra multi-mode vibrations, which boosts the emissivity in mid-infrared range (3–14 μm). Meanwhile, the high-entropy strategy prompts the formation of impurity energy levels as gap states, achieving optical absorption at low photon energies, and thus enhancing the emissivity in near-infrared range (1–3 μm). Simultaneously, (Y0.4Yb0.4Tm0.1Lu0.05Ho0.05)2Si2O7) ceramic coating owns diffusion-mediated thermal transport properties with strong phonon scattering, assisted further by the lamellar porous structure, thereby enabling a low thermal conductivity. The excellent mechanical properties ensure the reliability of the coating in extreme environments. All these merits render the high-entropy ceramic coating competitive for the development of high-temperature broadband high-emissivity thermal radiation materials.

Semi-analytical and numerical investigation of a fully wet porous moving longitudinal fin exposed to a magnetic field with radiation and temperature-dependent thermal conductivity

ABSTRACT This article focuses on the thermal analysis of a fractional-order moving fin subjected to a magnetic field, specifically investigating natural convection and radiation effects. This research introduces a novel approach that combines the domains of both Homotopy perturbation and Sumudu transform techniques to tackle a previously uninvestigated issue related to a moving fin with thermal conductivity dependent on temperature. While previous research papers have utilised the Homotopy Perturbation Sumudu Transform Method (HPSTM) to derive analytical solutions for fins with temperature-dependent thermal conductivity, our current study employs the HPSTM to address a fractional-order problem associated with a moving fin. Through a comparison with numerical results, the present study has validated the dependability of its findings. The dimensionless temperature profile has been investigated by studying its relationship with several parameters. We found that as the value of the wet porous parameter raises by 400%, there is an 11.794% decrease in temperature of the fin and as the value of Hartman number increases by 400%, temperature of the fin has decreased by 14.196%. Furthermore, the efficiency of the fin by analysing graphical representations across various parameters. This study encourages the application of the Homotopy perturbation Sumudu transform technique in more complex fin problems.

Significance of quadratic radiation and variable thermal conductivity on heat transfer of hybrid nanofluid using Xue model: A Legendre wavelet approach

Carbon nanotubes have a broad spectrum of applications in thermal management, enhanced cooling, lubricants, sensors and detections, environmental remediation, biomedical, and drug delivery. Motivated by its industrial applications, this work analyses the effects of nonuniform heat source/sink and quadratic thermal radiation on the thermal characteristics of hybrid nanofluid flow over a curved stretching sheet using the Legendre wavelet collocation technique (LWCT). The base fluid is found to be composed of ethylene glycol and water in the ratio of 30:70, and the nanoparticles are taken as single-wall carbon nanotube (SWCNT) and multi-wall carbon nanotube (MWCNT) in the ratio of 2% each. The thermal conductivity models, namely Xue, modified Maxwell and Hamilton-Crosser, are compared for heat transfer enhancement. From the results up to 5% volume fraction, the Xue model shows the maximum rate of heat transfer enhancement, while the above 5% Hamilton-Crosser model shows the maximum rate of heat transfer enhancement. The temperature profiles of existing hybrid nanofluid are increased with a heat source, radiation and variable thermal conductivity. Moreover, the graphs describing the local Nusselt number display the heat transfer rate depreciation with an increase in variable thermal conductivity and radiation parameters.

Study on the effect of semi-transparency on thermal insulation performance of silica aerogel composites

This paper centralizes its focus on elucidating the distinctive thermal insulation performance of silica aerogel composites, emphasizing their semitransparent attributes under diverse heating methodologies. Firstly, the theoretical prediction of conductive thermal conductivity is undertaken utilizing the spherical hollow cube model and Davies model. Subsequently, the radiative thermal conductivity is numerically derived employing the two-flux approximation model, integrating experimental measurements of optical radiation characteristic parameters. The prediction results under high-temperature are validated by the measured data via a Hot Disk instrument, utilizing the transient plane source method. Finally, the influence of semitransparent properties of the aerogel composites on thermal insulation performance is exhaustively investigated. This is conducted through a meticulous examination of temperature responses resulting from distinct heating modalities, namely contact heating, quartz lamp heating, and arc heated wind tunnel heating. The findings discernibly illustrate that these diverse heating mechanisms significantly impact the thermal insulation performance of aerogel composites endowed with semitransparent characteristics.

Thermal protection characteristics of non-enclosed thermal cloak

The aerodynamic heat of hypersonic vehicle nose cone can reach tens of MW/m&lt;sup&gt;2&lt;/sup&gt; during flight, which could be transferred to the interior of hypersonic vehicle in the form of conduction and radiation. High efficient thermal insulation technology is of significance in keeping internal electronic components working safely. Thermal metamaterials can regulate the macroscopic heat flow path, and they are developing rapidly and have a wide application prospect in the field of thermal protection. In this work, a non-enclosed point transformation thermal cloak is designed to guide heat flow around hypersonic vehicle nose cone by using the transformation multithermotics, which can control thermal conduction and radiation simultaneously. A multi-layer structure is designed as cloak’s simplified approximation due to the anisotropic parameters. Based on the software COMSOL, the thermal protection characteristics and heat transfer mechanism of the point transformation cloak and multi-layer structure are studied numerically. The results show that heat can flow around the object in the form of conduction and radiation in both point transformation thermal cloak and multi-layer structure, so the heat transferred to the inner area decreases. Comparing with the thermal insulation material, the heating rate of the protected area slows down, and the temperature in the front of the hypersonic vehicle nose cone is significantly reduced. However, the improvement of the thermal protection performance of point transformation cloak and multi-layer structures requires that the solid thermal conductivity and radiative thermal conductivity of the material are lower than those of the original thermal insulation material. To solve this problem, a non-enclosed region transformation thermal cloak is further proposed. The solid thermal conductivity and radiative thermal conductivity of region transformation thermal cloak are non-singular, which could be higher than those of the original thermal insulation material. Numerical simulation results show that the region transformation thermal cloak can guide heat flow around object, so the thermal protection capability is improved significantly. Comparing with the thermal insulation materials, the temperature of the front of the hypersonic vehicle nose cone is reduced by 100 K, and the temperature of the inner central zone of the hypersonic vehicle nose cone is reduced by 10 K. The non-enclosed region transformation thermal cloak provides a new approach to realizing thermal protection and is suitable for complex target areas, showing great application potential in thermal protection.

Numerical treatment of the radiated and dissipative power-law nanofluid flow past a nonlinear stretched sheet with non-uniform heat generation

The main aim of this paper is to investigate the effect of non-uniform heat generation and viscous dissipation on the boundary layer flow of a power-law nanofluid over a nonlinear stretching sheet. Within the thermal domain, the analysis considers both thermal radiation and variable thermal conductivity. Through the use of similarity transformations, the governing boundary layer equations are transformed into a system of ODEs. The spectral collocation method (SCM) with shifted Vieta-Lucas polynomials (VLPs) is implemented to give an approximate expression for the derivatives and then use it to numerically solve the proposed system of equations. By employing this technique, the system of ODEs is converted into a system of nonlinear algebraic equations. The dimensionless temperature, concentration, and velocity are graphically presented and analyzed for various values of the relevant governing parameters. Through the presented graphical solutions, we can see that the main outcomes indicate that an increase in the power law index, thermal conductivity parameter, and radiation parameter leads to a noticeable decrease in the local Nusselt number, with reductions of around 0.05 percent, 0.23 percent, and 0.11 percent, respectively. In contrast, the Prandtl parameter demonstrates an opposing effect, elevating the local Nusselt number by about 0.1 percent. We validated the accuracy of the numerical solutions by comparing them in some special cases with existing literature.

Darcy resistant of Soret and Dufour impact of radiative induced magnetic field sutterby fluid flow over stretching cylinder

The incompressible two-dimensional steady flow of Sutterby fluid over a stretching cylinder is taken into account. The magnetic Reynolds number is not deliberated low in the present analysis. Radiation and variable thermal conductivity are considered to debate the impact on the cylindrical surface. The Dufour and Soret impacts are considered on the cylinder. The mathematical model is settled by employing boundary layer approximations in the form of differential equations. The system of differential equations becomes dimensionless using suitable transformations. The dimensionless nonlinear differential equations are solved through a numerical scheme(bvp4c technique). The flow parameters of physical effects on the velocity, temperature, heat transfer rate, and friction between surface and liquid are presented in tabular as well as graphical form. The velocity function declined by improving the values of the Sponginess parameter. The fluid temperature is reduced by increment in curvature parameter.

Stretching/shrinking impact on the transient heat transfer in a radial moving porous fin of a longitudinal trapezoidal structure

The prime goal of the current pagination is to scrutinize the transient thermal response in a radial porous moving fin of a longitudinal trapezoidal structure. The solution of the constructed problem is heeded by a pdepe solver in Matlab, which works on the centered-finite difference technique. Darcy’s model is utilized to investigate porous nature. A stretching/shrinking mechanism has been incorporated to improve the fin efficiency. Stretching reduces efficiency, whereas shrinking improves fin efficiency indicating major benefits of fin design consideration. The relevant temperature results are shown visually and discussed quantitatively in detail to evaluate the competence of the suggested fin. With a rise in the Peclet number, temperature distribution decreases. A similar nature is noted with respect to the power index of convective heat transfer coefficient, convection and radiation parameters, porous parameter, stretching/shrinking parameter, and thermal conductivity gradient with temperature. The graphical outcomes also show that the fin temperature amplifies with the ambient temperature parameter. Also, it is noticed that thermal distribution is a decreasing function of the power index of the convective heat transfer coefficient such that there is a decrease of 1.64% in temperature distribution as the power index increases. To support the validity of the solutions, a comparison was made with notable results from the existing literature for the specific case of this study. The novelty of the work is to study highly nonlinear boundary value problems and such nonlinearities are more relevant in the system that describes the thermal processing of materials. It is also noted that initial transient heat transfer vanishes quickly under steady-state conditions when the material is exposed to the ambient temperature.

High-pressure drop rates in solid-state batch one-step scCO2 foaming of acrylic polymers: A way to stabilize the structure of micro-nano foams

One-step solid-state batch scCO2 foaming is used with the target of achieving acrylic polymer micro-nano foams. Foaming is triggered by an average pressure drop (APDR), covering two decades, from 0.3 to 30 MPa.s−1. This study principally addresses the combined beneficial effects of block copolymer addition (BCP, here denoted as MAM) and high APDR. Numerous subtle kinetic parameters actually interplay and compete in the production of the final foams. In particular, the material effective temperature, the effective glass transition temperature of the plasticized system and the instantaneous PDR are physical quantities each having their own kinetics during foaming. The resulting foam morphologies are quantified by SEM microscopy and image analysis. A high APDR and the presence of BCP are shown to play a key role in the final structure of the foams. Over the scrutinized range of saturation temperature (40 °C to 60 °C i.e. rather ‘low’ temperatures in the CO2 supercritical state), the APDR is the main factor for significantly reducing cell size and increasing nuclei density in foams from neat PMMA. In the block copolymer approach, increasing the APDR is of secondary importance as the targeted reduction of the porosity dimensions and augmentation of nuclei density are mostly the consequence of MAM presence. In this latter case, increasing the APDR still promotes the ‘efficiency’ of the BCP nucleants. A real efficient nucleation activity of MAM additive is observed at a very high APDR (30 MPa.s−1), leading to monomodal homogeneous distribution of tiny pores in nearly nanosized foams. At lower APDR, an interesting reproducible double porosity (foams containing intra-wall and inter-wall pores) is detected in PMMA/MAM systems. In such double porosity foams, benefits from the Knudsen effect achieved within well expanded local domains (showing micron-sized pores) may remain meaningful thanks to a locally poorly expanded nanoporous thick solid skeleton encapsulating these local domains. Thereby, the radiative thermal conduction can be minimized and does not override the conductive component at the sample scale. This work provides further insight on acrylic polymer BCP foams influenced by different kinetics.

Analysis of radiative MHD Carreau nanofluid flow with melting heat transfer and variable thermal conductivity

AbstractIn this work, we present the impacts of melting heat transfer phenomena on the steady, laminar, incompressible, two‐dimensional magnetohydrodynamic (MHD) Carreau nanofluid flow towards the stretching sheet. Additionally, in energy equation thermal radiation and variable thermal conductivity effects are also taken into consideration. By using similarity variables, governing non‐linear partial differential equations (PDEs) of the Carreau nanofluid flow model are transformed into dimensionless non‐linear ordinary differential equations (ODEs). Numerical solutions are then investigated and the results are illustrated through graphs and tables showing parameters effect on velocity, temperature, and concentration profiles of the fluid and on physical quantities including skin friction coefficient, Nusselt and Sherwood numbers, respectively. From the analysis, it is found that boosting melting heat transfer parameter leads to increasing behavior in velocity and concentration distributions, while the opposite trend is noticed for temperature distribution. Numerical results are found in close agreement and are accurate by carrying out its comparison with previous results for skin friction coefficient with different magnetic parameters while keeping other parameter values constant.