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Despite recent experiments exhibiting an impressive enhancement in radiative heat flux between parallel planar silica surfaces with gap sizes of about 10 nm, the exploration of sub-nanometric gap distances remains unexplored. In this work, by employing non-equilibrium molecular dynamics (NEMD) simulations, we study the heat transfer between two SiO2 plates in both their amorphous and crystalline forms. When the gap size is 2 nm, we find that the heat transfer coefficient experiences a substantial ∼30-fold increase compared to the experimental value at the gap size of 10 nm confirming the dependence on the distance inversely quadratic as predicted by the fluctuational electrodynamics (FE) theory. Comparative analysis between NEMD and FE reveals a generally good agreement, particularly for amorphous silica. Spectral heat transfer analysis demonstrates the profound influence of gap size on heat transfer, with peaks corresponding to the resonances of dielectric function. Deviations from the fluctuational electrodynamics theory at smaller gap sizes are interpreted in the context of acoustic phonon tunneling and the effects of a gradient of permittivity close to the surfaces. [ABSTRACT FROM AUTHOR]

This study investigates the impact of arrangement of two cylinders on their flow-induced vibrations (FIV) and heat transfer behavior at a Reynolds number of 100. Both cylinders were allowed to vibrate in two degrees of freedom (2DOF), encompassing streamwise and transverse directions. The arrangement of identical circular cylinders was varied across tandem (α = 0°), staggered (α = 30°, 45°, 60°), and side-by-side (α = 90°) configurations, at a constant center-to-center distance of 6D. The cylinders were heated at a fixed temperature to observe the forced convection heat transfer behavior under the influence of 2DOF FIV. To observe the FIV, the reduced velocity was varied from Ur = 0 (stationary cylinders) to 14. Results unveiled cylinder response sensitivity, encompassing vibration and heat transfer, with respect to reduced velocities and arrangements. Tandem arrangement exhibited the greatest vibrations for both cylinders. While lower drag was experienced in tandem for cylinder 2 (C-2), it escalated in staggered positioning. Both cylinders experienced lock-in between Ur = 6 and 8 for all arrangements, involving significant transverse vibration amplitudes. Maximum streamwise vibration reached 6.07% of the maximum transverse vibration for C-2 and 2.34% for C-1. Distinct slender "figure-8" and "oval-shaped" cylinder trajectories emerged, accompanied by diverse vorticity patterns in cylinder wakes across arrangements. For α = 60°, C-2 experienced 75.3% lower transverse vibration and 9.4% higher average Nusselt number compared to tandem setup. Overall, a pronounced correlation emerged between cylinder hydrodynamic behavior and heat transfer characteristics, evident through cylinder vibration, vortex shedding, average Nusselt number, and temperature distribution results. [ABSTRACT FROM AUTHOR]

Concentric tube heat exchangers are vital in various industrial applications, including chemical, process, energy, mechanical, and aeronautical engineering. Advancements in heat transfer efficiency present a significant challenge in contemporary research and development. This study concerns optimizing flow and heat transfer in concentric tube heat exchangers by morphing the tube's walls. The adjoint shape optimization approach is implemented in a fully turbulent flow regime. The effect of inner tube deformation on flow physics and heat transfer is examined. The results show that morphing can lead to a 54% increase in the heat transfer rate and a 47% improvement in the overall heat transfer coefficient compared to straight concentric tube designs. Moreover, the thermal-hydraulic performance factor is calculated to account for the relative increase in heat transfer when the optimal and initial designs are operated under the same pumping power. A thermal-hydraulic performance factor of 1.2 is obtained for the new design, showing that the heat transfer enhancement caused by morphing the tube's walls outweighs the increase in pumping power. The physics of a radial flow, resulting from an adverse pressure gradient in an annular region caused by the successive inner tube deformation, significantly augments heat transfer. This study shows morphing can lead to higher thermal efficiencies, and numerical optimization can assist in achieving this goal. [ABSTRACT FROM AUTHOR]

Heat transfer between a silver nanoparticle and surrounding water has been studied using molecular dynamics (MD) simulations. The thermal conductance (Kapitza conductance) at the interface between a nanoparticle and surrounding water has been calculated using four different approaches: transient with/without temperature gradient (internal thermal resistance) in the nanoparticle, steady-state non-equilibrium, and finally equilibrium simulations. The results of steady-state non-equilibrium and equilibrium are in agreement but differ from the transient approach results. MD simulation results also reveal that in the quenching process of a hot silver nanoparticle, heat dissipates into the solvent over a length-scale of ∼2 nm and over a time scale of less than 5 ps. By introducing a continuum solid-like model and considering a heat conduction mechanism in water, it is observed that the results of the temperature distribution for water shells around the nanoparticle agree well with the MD results. It is also found that the local water thermal conductivity around the nanoparticle is greater by about 50% than that of bulk water. These results have important implications for understanding heat transfer mechanisms in nanofluid systems and also for cancer photothermal therapy, wherein an accurate local description of heat transfer in an aqueous environment is crucial. [ABSTRACT FROM AUTHOR]

The heat transfer and wake-induced vibrations of a cylinder of circular cross section in the wake of another identical cylinder are numerically studied in this work at a Reynolds number (Re) = 100. The reduced velocities (Ur) are varied in the range of 2–14. The downstream cylinder is allowed to oscillate in two degrees of freedom, i.e., in the transverse as well as in the streamwise direction. The mass ratio (m*) is taken as 10, while the structural damping is ignored to get the maximum amplitude of vibration. The spacing ratio (L/D) between the cylinders is varied from 1.5 to 6, covering the major regimes, i.e., single body, reattachment, and co-shedding. The coefficients of lift (CL) and drag (CD), vibrational amplitudes of the cylinder, the Nusselt number (Nu), the Strouhal number (St), and vortex shedding patterns are studied. The results are discussed with the help of lift-displacement phase plots, cylinder trajectory plots, and vorticity and temperature contours. The lock-in condition at Ur = 8 is observed for all values of L/D, whereas the lock-in zone is the widest for the co-shedding regime at L/D = 6. By increasing L/D from 1.5 to 2.5 at Ur = 8, the CL of the downstream cylinder increases by 43%, whereas the CL of the upstream cylinder decreases by 61%. The downstream cylinder experiences lower drag as compared to the upstream cylinder and stationary isolated cylinder. A maximum decrease in the average drag coefficient of 107%, as compared to the stationary isolated cylinder, was observed for the downstream cylinder at L/D = 1.5 and Ur = 2, leading to the negative drag. Mostly, the 2S and C(2S) vortex shedding pattern is observed, whereas a steady flow and chaotic pattern emerged in a few cases. The results reveal that with increasing L/D, the average Nu for both the upstream and downstream cylinders increases as the effect of each cylinder on the other diminishes. [ABSTRACT FROM AUTHOR]

Interfacial heat transfer across curved surfaces has not been understood sufficiently well. The present study reports a significant decrease in heat transfer at a convex fluid-solid interface. Effects of curvature on the Kapitza length and the thermal accommodation coefficient are investigated for both gas and liquid phases to understand the occurrence of large temperature jumps. The study also examines the penetration depth of non-equilibrium effects into gas from the convex surface theoretically and reveals the expansion of the Knudsen layer at convex surfaces. [ABSTRACT FROM AUTHOR]

Nucleation and growth of condensing droplets on horizontal surfaces are investigated via a 2-D double distribution function thermal lattice Boltzmann method. First, condensation on completely uniform surface is investigated and different mechanisms which cause dropwise and filmwise condensation are studied. The results reveal the presence of cooled vapor layer instability in the condensation on completely smooth surfaces. In the second step, condensation on chemically heterogeneous surfaces is investigated. Moreover, the effect of non-uniformity in the surface temperature is also studied. The results indicate that the vapor layer instability and the nucleation start from the heterogeneities. The effects of different numbers of heterogeneities, their distance, and hydrophobicity on the condensation are also inspected. It is shown that by increasing the hydrophobicity of the heterogeneities and considering an optimum space between the heterogeneities, maximum condensation performance can be achieved. Finally, condensation on wettability gradient surfaces is studied and the effects of the gradient form and contact angle of the core region on the condensation are studied. It is shown that hydrophobicity of the core region plays a key role in increasing the condensation performance. A heat transfer analysis and flow dynamics of dropwise condensation as a function of time is also presented and it is shown that the results are in good agreements with the previous theoretical and experimental results. [ABSTRACT FROM AUTHOR]

Understanding the behavior of viscoelastic (VE) fluids in confined geometries is crucial for applications in biologic systems, heat transfer devices, enhanced oil recovery, and many others. Here, we perform a systematic steady-state simulation of a VE fluid at low Reynolds numbers through a channel with successive smooth contractions and expansions. We analyze the hydrodynamic performance of the fluid with particular attention to vortex patterns that develop downstream of the contractions. We show that elastic vortices form at higher contraction ratios and that there are critical Weissenberg numbers (Wic) unique to each contraction ratio where the flow shifts from non-vortical to vortical. This Wic increases with an increasing contraction length. The coexistence of elongational-, shear-, and rotational-flow is essential for vortex development and evolution. We also analyzed the effect of the Deborah number (De) on the vortex pattern in a multiple contraction system and observed that the vortex area significantly depends on the distance between the contractions. We show that there are three distinctly different regions in De, in which the flow characteristics change in successive contractions. For high De, the flow in the downstream contraction is significantly affected by the upstream contraction. Our results have implications for the use of VE fluids with various VE properties in different types of porous media. [ABSTRACT FROM AUTHOR]

Present communication explores a novel application of the computational intelligence technique, namely, the Levenberg–Marquardt scheme under a Backpropagated Neural Network (LM-BNN) to solve the mathematical model for the magnetohydrodynamic peristaltic transport of Reiner–Philippoff (R–Ph) pseudoplastic fluid considering the influences of Ohmic heating, mixed convection, and viscous dissipation through a symmetric channel. The R–Ph fluid model is used in this investigation to elucidate the non-Newtonian behavior of the fluid under consideration. The Reiner–Philippoff fluid model delineates the intricate relationship between stress and deformation rate within the fluid. There are a few studies available on the peristaltic transport of the Reiner–Philippoff fluid that do not incorporate Joule heating, mixed convection, and magnetic field effects. Therefore, a novel mathematical model is developed to employ an artificial neural network technique with a different approach that has not been examined before. The governing equations of the problem are simplified using long wavelength and low Reynolds number approximations, and the resulting system is numerically solved using the BVP4c scheme in MATLAB based on the shooting algorithm. Furthermore, a dataset is constructed through the BVP4c technique for the proposed LM-BNN, considering eight scenarios of peristaltic motion of the Reiner–Philippoff fluid model by varying the Bingham number, the Brinkman number, the Grashof number, the R–Ph fluid parameter, and the Hartmann number. The numerical dataset is divided into 15 % for testing, 15 % for training, and 70 % for validation, which are utilized in LM-BNN to analyze the numerical solutions and Levenberg–Marquardt neural networks (LM-NNs) predicted results. The consistency and effectiveness of LM-BNN are validated through regression analysis, stresses at the wall, error histogram, correlation index, heat transfer, and mean squared error based fitness curves, which vary from 10 − 3 → 10 − 11 . Variations in several flow parameters affecting temperature and velocity profiles are explained physically through graphs. Additionally, an analysis of heat transfer and stresses at the wall, including absolute errors, is provided through tables. The outcomes reveal that the improving Grashof number and the Hartmann number tend to increase the temperature profile. Tabular results indicate that rates of heat transfer improve when assigning higher values to the Hartmann number, the Brinkman number, and the Grashof number, whereas stresses at the wall decrease for the Reiner–Philippoff fluid parameter and the Bingham number. The error analysis of numerical simulations is a valuable step in determining whether the data obtained are reliable and accurate. In terms of absolute error, the disagreement between numerical solutions and those predicted by LM-NNs is approximately 10 − 5 → 10 − 11 . It is clear from this error analysis that LM-NNs predicted results are consistent and reliable. [ABSTRACT FROM AUTHOR]

A theoretical investigation on heat transfer of nanofluid transport in a ciliated channel is presented. A mathematical model for cilia oriented nanofluid transport through the human male reproductive tract is exhibited. Considering the structure of tubules, the Reynolds number is considered very small. The concept of a long wavelength approximation is incorporated to model the nanofluid flow problem. The exact analytical expressions for the x-component of velocity, temperature, nanoparticle concentration, stream function, volume flow rate, and pressure gradient are calculated. The solution for the transverse component of velocity, pressure rise per wavelength, and friction force on the wall of the channel is explored numerically, while variations in crucial flow parameters are examined graphically. [ABSTRACT FROM AUTHOR]

Mixed convective peristaltic flow of incompressible viscoplastic fluid is investigated in a two-dimensional symmetric channel. The rheology of viscoplastic material is characterized by the constitutive equation for Bingham plastic model. The coupling between momentum and energy equations is achieved through Boussinesq approximation. The coupled nonlinear partial differential equations are transformed in wave frame using Galilean transformation and then simplified under realistic assumptions of long wavelength and low Reynolds number. Approximate solution is obtained using regular perturbation method which is restricted to the smaller values of Grashof and Bingham numbers. The validity of approximate solution is established by comparing it with the numerical solution obtained via Matlab built-in routine bvp4c. Based on the numerical solution an extensive analysis is performed in order to analyze the effects of various parameters of interest on flow characteristics, pumping and trapping phenomena. It is found that velocity decreases at the center by increasing Bingham number showing a boundary layer character for large values. However, it increases by increasing Brinkman and Grashof numbers. Moreover, pressure rise per wavelength increases with Bingham number, Brinkman number and Grashof number, in the pumping region. The result further indicate that larger values of Bingham number circumvent bolus growth. [ABSTRACT FROM AUTHOR]

A novel theoretical model for unsteady, non-isothermal flow with temperature variant viscosity for the Newtonian fluid in the presence of transverse magnetic field is studied in the ductus efferentes of human male reproductive tract. Importance of cilia for the fluid transport through ductus efferente is elaborated in this study. To investigate the flow, we considered a channel and constant temperature difference is imposed between the wall of channel. A mathematical model is developed and analytical solution is achieved with the help of Adomian decomposition method (ADM) for MHD heat and fluid flow with temperature dependent viscosity. Flow is modeled by considering assumptions that Reynolds number is small, so that inertial forces are insignificant and wavelength to diameter ratio is maximum, so that pressure can be assumed uniform in the channel. Solutions are presented for the exponential dependent viscosity on temperature. Effect of different flow parameters on the axial and transverse component of velocity are analyzed graphically. Pumping characteristic due to ciliary beat from one row of cilia to another are investigated. Lastly variation of different flow parameters on the trapped bolus and pressure are examined graphically. [ABSTRACT FROM AUTHOR]

Two-degree-of-freedom vortex-induced vibration (VIV) of a finned cylinder with heat transfer is studied numerically at the Reynolds number Re = 150. The governing equations in the Arbitrary Lagrangian-Eulerian frame are solved by the finite volume method. The dynamics of the oscillating cylinder (with or without fins) in the fluid flow was approximated as a mass-spring system. The effects of the number and arrangement of the fins (14 different cases) on the vortex shedding pattern, vibration amplitude, and frequency and heat transfer of the cylinder are investigated and discussed. The results indicate that in comparison with the stationary state, the effects of the number and arrangement of the fins on the wake pattern and the heat transfer enhancement in the VIV state are significant. Different vortex shedding pattern like 2S, P, 2P, S + P and combination of them with stable or unstable interactions between vortices and cylinders are observed in an oscillating cylinder. In the vibration state of finned cylinders, the heat transfer enhances up to 50.4% with respect to the stationary state and increases up to 64% with respect to the stationary smooth cylinder. [ABSTRACT FROM AUTHOR]

In this paper, the researchers explore heat transfer and magneto-hydrodynamic flow of hybrid nanofluid in a rotating system among two surfaces. The upper and lower plates of the system are assumed penetrable and stretchable, respectively. The thermal radiation and Joule heating impacts are considered. A similarity technic is applied to alter governing energy and momentum equations into non-linear ordinary differential ones that contain the convenient boundary conditions and used the Duan-Rach Approach (DRA) to solve them. Influences of assorted parameters including rotation parameter, suction/blowing parameter, radiation parameter, Reynolds number, hybrid nanofluid volume fraction, and magnetic parameter on temperature and velocity profiles are examined. Also, a correlation for the Nusselt number has been developed in terms of the acting parameters of the present study. The outcomes indicate that Nusselt number acts as an ascending function of injection and radiation parameters, as well as volume fraction of nanofluid. [ABSTRACT FROM AUTHOR]

Photothermal deflection (PTD) techniques have been used to monitor various laser-heating processes, including melt, vaporization, and ablation of solids. To interpret the complex signal response resulting from transient phase changes at a surface, the temporal profile of the PTD signal response must be considered. In doing so, the case of the linear heating of a target without phase change is first studied here. Numerical and experimental work is presented to show the effect on the shape, magnitude, and phase of a PTD signal due to changes in (1) the thermophysical properties of the target material and deflecting medium, (2) the dimensions and boundary conditions of the target, (3) the distance of the probe beam from the surface of the target, and (4) the modulation frequency of the heating source. Copper and lead target materials heated in air are used in the experimental work. The PTD signals show qualitative agreement with the temperature gradient normal to the surface calculated using. a numerical finite-difference two-dimensional thermal-diffusion model. The results also show that an unusual phenomenon occurs when heating with a laser or other finite-sized heating source. When the thermal diffusivity of the target and deflecting medium are different and the probe beam is close to the surface, a local maximum is observed in the time-response profile of the PTD signal during the heating cycle. The maximum occurs as a result of asymmetric changes in the temperature field over time. The shape of the PTD signal, therefore, can provide information about the laser-heating process at a surface in real time. [ABSTRACT FROM AUTHOR]

Graphene and several other two-dimensional (2D) carbon-based structures, including C3N, C3B, C2N, C3N4 (s-triazine), and C3N4 (tri-triazine), have attracted considerable attention due to their excellent thermal, mechanical, and electrical properties. In this study, the correlations between the interfacial thermal conductance (ITC) across these 2D nanostructures and the lattice-dynamical properties of the system, including (i) the phonon density of state (DOS) overlap between the sides of the interface and (ii) the percentage of different classes of vibrational modes for each heterostructure, are investigated. The results show that the percentage of localized interfacial modes is a strong descriptor for predicting ITC—even more effective than the widely accepted phonon DOS overlap. Moreover, the ITC between all combinations of these six carbon-based materials, its dependence on the length of the heterostructure, and the thermal rectification effect present in each interface structure is studied using non-equilibrium molecular dynamics simulations. The results show that the maximum and minimum ITC for infinite length systems belong to graphene/C3N and C2N/C3N4 (tri-triazine) heterostructures with values of 35.81 and 2.21 GW m−2 K−1, respectively. Comparing the thermal resistances at the interface and in the bulk of these heterostructures show that thermal transport in carbon-based 2D materials is influenced by the thermal resistance across their interfaces. These results not only contribute to our fundamental understanding of interfacial heat transfer, but can also serve as the basis for the design of nanoelectronic devices based on 2D materials, where the device level performance will indeed be influenced by interfacial phenomena. [ABSTRACT FROM AUTHOR]

The current investigation is based on the impact of the nanoparticle shape on the micropolar hybrid nanofluid flow in a vertical plate. Furthermore, the aim of this investigation is to optimize the skin friction as well as the Nusselt number using a statistical approach known as "Response Surface Methodology" (RSM). The micropolar hybrid nanofluid is considered due to its enhanced thermal properties likely the Hamilton–Crosser thermal conductivity, Gharesim model viscosity, etc. A suitable similarity rule is adopted for the transformation of the designed model into ordinary and then solved numerically utilizing the shooting-based Runge–Kutta fourth-order technique. The simulated results of diversified parameters are presented through graphs. Furthermore, RSM is employed to design and develop a mathematical model to get an optimized hear transfer rate along with the rate of shear stress. The required components are carefully selected, and the corresponding responses are recorded. The collected data is subsequently employed in constructing a response surface through regression analysis. This process allows for the determination of optimal conditions to enhance heat transfer, which is then confirmed through analysis of variance testing. However, the major outcomes of the study are; for the case of suction with increasing particle concentrations, the shear rate, hear transfer rate, and couple stress coefficients are enhanced significantly. Furthermore, the non-Newtonian parameter and the magnetic parameter also favor in enhancing the rate coefficients. [ABSTRACT FROM AUTHOR]

Flow and heat transfer problems in non-Newtonian fluids are considerably more complicated compared to Newtonian fluids due to their non-linear behavior and complex properties. This paper numerically studied the flow and heat transfer of a viscoelastic fluid around a hot rotating cylinder in a square enclosure. The Phan-Thien–Tanner (PTT) model, one of the most accurate models available to describe the behavior of viscoelastic fluids, was used to obtain the constitutive equations of the viscoelastic fluid, which were then solved by using the finite-volume method with the Rheoheatfoam solver of the OpenFOAM software. The log-conformation approach was employed to avoid the divergence problem at high Weissenberg numbers. Simulations were conducted to investigate the effects of the Weissenberg number, Brinkman number, Reynolds number, and the ratio of the polymeric viscosity to total viscosity on the behavior of fluid flow and heat transfer. The results showed that increasing the Weissenberg number led to a higher shear thinning effect, which decreased the fluid's effective viscosity and viscous dissipation near the cylinder. As a result, heat transfer from the cylinder increased, and the frictional torque applied to the cylinder decreased. However, the shear thinning effect was negligible when the Weissenberg number exceeded 100. Furthermore, the tangential normal stress significantly increased as the Weissenberg number increased up to one. However, with further increases in the Weissenberg number, the tangential normal stress reduced, eventually reaching close to zero at high Weissenberg numbers. [ABSTRACT FROM AUTHOR]

Van der Waals heterostructures have exhibited interesting physical properties. In this paper, heat transfer in hybrid coplanar bilayer/monolayer (BL-ML) graphene, as a model layered van der Waals heterostructure, was studied using non-equilibrium molecular dynamics (MD) simulations. The temperature profile and inter- and intra-layer heat fluxes of the BL-ML graphene indicated that, there is no fully developed thermal equilibrium between layers and the drop in the average temperature profile at the step-like BL-ML interface is not attributable to the effect of Kapitza resistance. By increasing the length of the system up to 1 μm in the studied MD simulations, the thermally non-equilibrium region was reduced to a small area near the step-like interface. All MD results were compared to a continuum model and a good match was observed between the two approaches. Our results provide a useful understanding of heat transfer in nano- and micro-scale layered materials and van der Waals heterostructures. [ABSTRACT FROM AUTHOR]

Free convection flow of some water based fractional nanofluids over a moving infinite vertical plate with uniform heat flux and heat source is analytically and graphically studied. Exact solutions for dimensionless temperature and velocity fields, Nusselt numbers, and skin friction coefficients are established in integral form in terms of modified Bessel functions of the first kind. These solutions satisfy all imposed initial and boundary conditions and reduce to the similar solutions for ordinary nanofluids when the fractional parameters tend to one. Furthermore, they reduce to the knownsolutions from the literature when the plate is fixed and the heat source is absent. The influence of fractional parameters on heat transfer and fluid motion is graphically underlined and discussed. The enhancement of heat transfer in such flows is higher for fractional nanofluids in comparison with ordinary nanofluids. Moreover, the use of fractional models allows us to choose the fractional parameters in order to get a very good agreement between experimental and theoretical results. [ABSTRACT FROM AUTHOR]

With the emergence of phase change memory, where the devices experience extreme thermal gradients (∼100 K/nm) during transitions between low and high resistive states, the study of thermoelectric effects at small scales becomes particularly relevant. We had earlier observed asymmetric melting of self-heated nano-crystalline silicon micro-wires, where current densities of ∼107 A/cm2 were forced through the wires by 1 μs, ∼30 V pulses. The extreme asymmetry can be explained by the generation of considerable amount of minority carriers, transport under the electric field, and recombination downstream, a heat transfer process we termed as generation–transport–recombination, which is in opposite direction of the electronic-convective heat carried by the majority carriers. Here, we present a full semiconductor physics treatment of this carrier-lattice heat transport mechanism and the contribution of the minority carriers on the evolution of the melt–solid interface, which can be applied to various high-temperature electronic devices. [ABSTRACT FROM AUTHOR]

Whether it is glass, ceramics, cement, or concrete, minimizing thermal conduction through disordered materials is a determining factor when it comes to reducing the energy consumption of cities. In this work, we explore underlying physical processes involved in thermal conduction through the disordered glue of cement, calcium-silicate-hydrates (CSH). We find that at 300 K, phonon-like propagating modes in accordance with the Boltzmann transport theory, propagons, account for more than 30% of the total thermal conductivity, while diffusons, described via the Allen-Feldman theory, contribute to the remainder. The cumulative thermal conductivity proves to be close to both equilibrium molecular dynamics calculations and experimental values. These findings help us establish different strategies, such as localization schemes (to weaken diffusons) and scattering mechanisms (to constrain propagons), for reduction of thermal conductivity of CSH without sacrificing its mechanical properties. [ABSTRACT FROM AUTHOR]

For a nanostructure sitting on top of an AlGaN:Er3+ thin film, a new thermal imaging technique is presented where dual cameras collect bandpass filtered videos from the H and S bands of Er3+ emission. We combine this thermal imaging technique with our newly developed time-resolved temperature measurement technique which relies on luminescence thermometry using Er3+ emission. This technique collects time-resolved traces from the H and S bands of Er3+ emission. The H and S signal traces are then used to reconstruct the time-resolved temperature transient when a nanostructure is illuminated with a pulsed 532 nm light. Two different types of samples are interrogated with these techniques (drop-casted gold nanosphere cluster and lithographically prepared gold nanodot) on the AlGaN:Er3+ film. Steady-state and time-resolved temperature data are collected when the samples are immersed in air and water. The results of time-resolved temperature-jump measurements from a cluster of gold nanospheres show extremely slow heat transfer when the cluster is immersed in water and nearly 200-fold increase when immersed in air. The low thermal diffusivity for the cluster in water suggests poor thermal contact between the cluster and the thermal bath. The lithographically prepared nanodot has much better adhesion to the AlGaN film, resulting in much higher thermal diffusivity in both air and water. This proof-of-concept demonstration opens a new way to measure the dynamics of the local heat generation and dissipation at the nanoparticle-media interface. [ABSTRACT FROM AUTHOR]