Thermal Diffusivity Research Articles

The donor/acceptor (D/A) interfaces in bulk heterojunction (BHJ) organic solar cells (OSCs) critically govern exciton dissociation and molecular diffusion, determining both efficiency and stability. Herein, we design a double-cable conjugated polymer, SC-1F, to insert into a physically-blended D/A system to optimize the interface. We have found that SC-1F spontaneously segregates to the interface through favorable miscibility and heterogeneous nucleation with the acceptor. Its long-lived charge-transfer (CT) state with a lifetime of >3ns enhances charge generation efficiency in the PM6:BTP-eC9 blend, boosting the power conversion efficiency (PCE) from 19.00% to 20.12%. More importantly, the double-cable nature of SC-1F enables it to be simultaneously miscible with donor and acceptor so as to act as the interfacial lock to prevent their self-aggregation under thermal treatment. Therefore, the PM6:BTP-eC9:SC-1F-based solar cells provided a high T80 of 2175 h compared to a T80 of 530 h based on PM6:BTP-eC9 under 65 °C treatment. Notably, SC-1F-based device demonstrates exceptional storage and thermal stability, with a T80 lifetime exceeding 10000 h. These results demonstrate the superior advantage of double-cable conjugated polymers as the third component to achieve efficient and stable OSCs.

The Boltzmann kinetic equation is considered to compute the transport coefficients associated with the mass flux of intruders in a granular gas. Intruders and granular gas are immersed in a gas of elastic hard spheres (molecular gas). We assume that the granular particles are sufficiently rarefied so that the state of the molecular gas is not affected by the presence of the granular gas. Thus, the gas of elastic hard spheres can be considered as a thermostat (or bath) at a fixed temperature $T_g$ . In the absence of spatial gradients, the system achieves a steady state where the temperature of the granular gas $T$ differs from that of the intruders $T_0$ (energy non-equipartition). Approximate theoretical predictions for the temperature ratio $T_0/T_g$ and the kurtosis $c_0$ associated with the intruders compare very well with Monte Carlo simulations for conditions of practical interest. For states close to the steady homogeneous state, the Boltzmann equation for the intruders is solved by means of the Chapman–Enskog method to first order in the spatial gradients. As expected, the diffusion transport coefficients are given in terms of the solutions of a set of coupled linear integral equations which are approximately solved by considering the first Sonine approximation. In dimensionless form, the transport coefficients are nonlinear functions of the mass and diameter ratios, the coefficients of restitution and the (reduced) bath temperature. Interestingly, previous results derived from a suspension model based on an effective fluid–solid interaction force are recovered when $m/m_g\to \infty$ and $m_0/m_g\to \infty$ , where $m$ , $m_0$ and $m_g$ are the masses of the granular particles, intruders and molecular gas particles, respectively. Finally, as an application of our results, thermal diffusion segregation is exhaustively analysed.

High-voltage ceramic insulators are routinely exposed to short-duration overvoltages such as lightning impulses, switching surges, and partial discharges. These events occur on microsecond to millisecond timescales and can produce highly localized thermal spikes that are difficult to measure directly but may compromise long-term material integrity. This paper addresses the estimation of the internal temperature distribution immediately after a lightning impulse by solving a three-dimensional inverse heat conduction problem (IHCP). The forward problem is modeled by the transient heat diffusion equation with constant thermal diffusivity, discretized using the finite element method (FEM). Surface temperature measurements are assumed available from a 12 kV ceramic post insulator and are used to reconstruct the unknown initial condition. To address the ill-posedness of the IHCP, a spatio-temporal regularization framework is introduced and compared against spatial-only regularization. Numerical experiments investigate the effect of measurement time (T=60 s, 600 s, and 1800 s), mesh resolution (element sizes of 20 mm, 15 mm, and 10 mm), and measurement noise (σ=1 K and 5 K). The results show that spatio-temporal regularization significantly improves reconstruction accuracy and robustness to noise, particularly when early-time measurements are available. Moreover, it is observed that mesh refinement enhances accuracy but yields diminishing returns when measurements are delayed. These findings demonstrate the potential of spatio-temporal IHCP methods as a diagnostic tool for the condition monitoring of ceramic insulators subjected to transient electrical stresses.

ABSTRACT This study presents an in‐depth analysis of the flow and thermodynamic behavior of Casson couple‐stress fluid in a vertical microchannel under the combined influence of Hall current, uniform heat source/sink, variable thermal conductivity, Brownian motion, thermophoresis, and pollutant discharge, subject to convective boundary conditions. The governing equations are transformed using similarity variables and solved numerically via the shooting technique coupled with the Runge–Kutta–Fehlberg (4,5th) scheme. The originality of this study lies in the simultaneous consideration of non‐Newtonian rheology, electromagnetic effects, variable transport properties, and pollutant dynamics, a combination rarely addressed in microfluidic studies. The thermal field demonstrates a direct sensitivity to heat generation, where the temperature rises with increasing heat source strength, while it declines when variable thermal conductivity is allowed to vary, owing to enhanced thermal diffusion. The concentration within the medium is elevated by Brownian motion and external pollutant source effects, both of which promote particle dispersion and accumulation, whereas thermophoretic forces act in the opposite manner by driving particles away from hotter regions, thereby suppressing concentration. Entropy generation responds dually to Brownian motion, thermophoresis, Casson parameter, and variable thermal conductivity, indicating the sensitive interplay of flow, mass, and thermal transport mechanisms. The Bejan number profile illustrates spatial variations in the relative contributions of heat transfer and fluid friction irreversibilities under the impact of heat source, variable thermal conductivity, Brownian motion, and thermophoresis parameters. These results provide a valuable approach to the design and optimization of microchannel systems in biomedical, chemical, and energy applications, in settings where precise heat control, mass, and pollutant transport are critical.

Implantable interstitial fluid (ISF) collection components have emerged as promising platforms for continuous health monitoring and diagnostic applications. Nonetheless, cellular contaminants and tissue ingrowth remain significant challenges for implantable ISF devices. Herein, a vapor-based porous coating technology is proposed, capable of producing a mechanically durable and homogeneous porous layer within the internal lumen of a nitinol tube. Biochemically, the coating prevents the ingrowth of cells or tissues into the porous structure while simultaneously ensuring the desired filtration performance of the ISF. The porous coating layers are thoroughly examined with respect to their ability to transport molecules. A variety of model probing molecules are loaded/encapsulated within the layered configuration to understand the molecular diffusion kinetics and transport phenomenon in the proposed porous coatings. Furthermore, in vitro and in vivo assessments of the interstitial fluids are used to validate the transport of biomolecules within the porous coatings. Moreover, when the perforated nitinol tube is incorporated, the filtration efficiency is > 80% for particles larger than 500nm, and more than 98% of the particles larger than 1000nm are retained during the filtration of these coatings.

Comprehensive investigation on dynamic energy performances of pipe-embedded enclosure structures with thermal anisotropic injection and diffusion features

3D-1D modelling of cranial mesh heating induced by low or medium frequency magnetic fields.

CFD simulation of mass transfer in adsorption column: Numerical analysis of molecular diffusion and convection

Modeling of gravity drainage and molecular diffusion mechanisms during miscible gas injection in naturally fractured reservoirs

ABSTRACT The integration of immiscible Cu and FeNi systems poses significant challenges in achieving defect-free interfaces and thermomechanical compatibility due to significant thermal mismatch stress. In this work, we propose a continuous gradient alloy micro laser powder bed fusion (CGA-μLPBF) strategy with material gradients in different degrees of freedom to address interfacial stress concentration and elemental distribution. Based on high-throughput experimental results and thermodynamic calculations, we have achieved theoretically-predicted optimal precipitation strengthening without the formation of cracks and intermetallic compounds and realised a continuous variation in the Coefficient of Thermal Expansion (CTE). The CTE of the as-printed CGA samples varies continuously from 1.4 × 10−6/K to 11 × 10−6/K at 100℃, resulting in difference in thermal strains of more than tenfold between the two ends without any cracking. It simultaneously exhibits continuously thermal expansion and thermal diffusion performances within the same component. The compositional continuous gradient alloys exhibit remarkable potential for applications in precision instruments and thermal management applications, offering a unique combination of thermomechanical performance and design flexibility. These findings highlight the unique capabilities of CGA-μLPBF in producing advanced materials for next-generation electronic devices.

Malaria parasites infect red blood cells where they digest host hemoglobin and release free heme inside a lysosome-like organelle called the food vacuole. To detoxify excess heme, parasites form hemozoin crystals that rapidly tumble inside this compartment. Hemozoin formation is critical for parasite survival and central to antimalarial drug activity. Although the static structural properties of hemozoin have been extensively investigated, crystal motion and its underlying mechanism have remained puzzling. We used quantitative image analysis to determine the timescale of motion, which requires the intact vacuole but does not require the parasite itself. Using single particle tracking and Brownian dynamics simulations with experimentally derived interaction potentials, we found that hemozoin motion exhibits unexpectedly tight confinement but is much faster than thermal diffusion. Hydrogen peroxide, which is generated at high levels in the food vacuole, has been shown to stimulate the motion of synthetic metallic nanoparticles via surface-catalyzed peroxide decomposition that generates propulsive kinetic energy. We observed that peroxide stimulated the motion of isolated crystals in solution and that conditions that suppress peroxide formation slowed hemozoin motion inside parasites. These data suggest that surface-exposed metals on hemozoin catalyze peroxide decomposition to drive crystal motion. This work reveals hemozoin motion in malaria parasites as a biological example of an endogenous self-propelled nanoparticle. This mechanism of propulsion likely serves a physiological role to reduce oxidative stress to parasites from hydrogen peroxide produced by large-scale hemoglobin digestion during blood-stage infection.

Understanding the mechanism of Li-ion transport is essential to the development of fast-charging Li-ion batteries. This study uses operando electron energy loss spectroscopy (EELS) to visualize the 1D movement of Li ions inside a LiMn2O4 nanowire cathode with one end immersed in an ionic liquid electrolyte during charge-discharge cycles. A series of maps is obtained quantifying the Li distribution near the interface between the nanowire cathode and electrolyte, which shows that changes in the Li concentration near the interface lag behind changes in the cell current. During delithiation, the Li concentration in the nanowire cathode decreases at locations away from the interface. Based on these observations, a model is developed that explains lithium-ion transport in 1D cathodes as drifting according to the electrochemical potential gradient rather than through simple diffusion.

Laser powder bed fusion (LPBF) is an advanced additive manufacturing method, but its productivity is relatively low, which limits its application. Performance can be increased without hardware modifications by enlarging the powder-layer thickness. However, this approach requires deeper investigation because the probability of defects (keyhole porosity, lack of fusion) rises substantially, and experiments become costly since each thickness value requires a separate LPBF run. High-fidelity simulation under such conditions can reduce the experimental workload. Reliable predictions, however, require numerous thermophysical parameters; reported values are often inconsistent or unavailable, and few studies have quantified their influence on simulation outcomes. A Lattice Boltzmann-based model is adopted to simulate the keyhole melting mode of AlSi10Mg. The effects of laser spot diameter, laser absorptivity, and the temperature dependence of thermal diffusivity and surface tension on the results are investigated. Predicted melt-pool morphologies are compared with cross-sections of experimental single tracks.

Abstract We propose a variation of the classic Cartesian diver experiment in which the diver moves within a fluid which is density stratified rather than uniform. At variance with the traditional setup, the diver reaches a stable equilibrium at a depth where its density matches that of the surrounding fluid under a given external pressure. By modifying the applied pressure, the diver's density changes, causing it to shift to a new equilibrium depth. When exposed to a sudden pressure pulse, its density fluctuates, leading to oscillations driven by a restoring force, with the oscillation frequency determined by the density gradient. We show that if the experiment is prepared by putting in contact two miscible liquids with different density and the diver is put at the interface of the liquids, the device can be used to monitor the variation of the density gradient along the diffusion process. Experimental data can be compared with those theoretically predicted by the diffusion equation.

We present the spatial regime conversion method (SRCM), a novel hybrid modelling framework for simulating reaction–diffusion systems that adaptively combines stochastic discrete and deterministic continuum representations. Extending the regime conversion method (RCM) to spatial settings, the SRCM employs a discrete reaction–diffusion master equation (RDME) representation in regions of low concentration and continuum partial differential equations (PDEs) where concentrations are high, dynamically switching based on local thresholds. This is an advancement over the existing methods in the literature, requiring no fixed spatial interfaces, enabling efficient and accurate simulation of systems in which stochasticity plays a key role but is not required uniformly across the domain. We specify the full mathematical formulation of the SRCM, including conversion reactions, hybrid kinetic rules, and consistent numerical updates. The method is validated across several one-dimensional test systems, including simple diffusion from a region of high concentration, the formation of a morphogen gradient, and the propagation of FKPP travelling waves. The results show that the SRCM captures key stochastic features while offering substantial gains in computational efficiency over fully stochastic models.

Mechanistic insights into band broadening in MOF-based liquid chromatography: Role of sub-nanopore diffusion and packing heterogeneity.

The emergence of homochirality in the absence of external chiral influences remains a fundamental challenge in studies of abiogenesis and asymmetric materials synthesis. Here it is shownthat both the conglomerate polymorph of the supramolecular salt (BTBA)FeCl4 (BTBA = benzyl(tributyl)ammonium) (1, a racemic mixture of 1-P31 and 1-P32), and its achiral polymorph (2, P21/c) exclusively convert into 100% 1-P31 or 100% 1-P32 upon melt crystallization at a cooling rate of 3600Kh-1. Differential scanning calorimetry (DSC) reveals that, prior to this transformation, racemic mixtures of 1 convert into 3 (P21/c), an achiral polymorph distinct from both 1 and 2, whereas 2 crystallizes directly without intermediates. Nucleation experiments conducted at varying degrees of supercooling show that deeper supercooling effectively impedes molecular reorganization into stable crystal nuclei and, in particular, suppresses secondary nucleation by restricting molecular diffusion, thereby enabling a single chiral nucleus to dominate crystal growth. These results establish melt supercooling as a solvent- and template-free strategy for accessing homochiral materials and reveal how the balance between thermodynamic and kinetic factors governs spontaneous mirror-symmetry breaking (SMSB).

The rapid advancement of micro-electromechanical systems (MEMS) and the extensive utilization of ultra-short time heating technology in the precision machining of these devices have underscored the critical importance of studying the interplay between thermodiffusion and mechanical deformation. At the microscale, the size-dependent effect in elastic deformation and the memory-dependent effect in thermal transport processes become increasingly significant and must be taken into account. Meanwhile, many experimental and theoretical investigations suggest that, in practical analyses, thermal conductivity and diffusivity in materials should not be considered as a constant value. This paper addresses the thermoelastic diffusion response of a spherical microshell subjected to sinusoidal thermal and concentration loading including the simultaneous effects of the fractional-order parameter, the nonlocal parameter, and the variable thermal conductivity and diffusivity. Taking into account the variable thermal conductivity and diffusivity, the nonlinear governing equations are derived by the Laplace and Kirchhoff transformations. The results show that the nonlinear thermoelastic diffusion response of the spherical microshell can be adjusted by the suitably modified parameters, which strongly depend on the size-dependent effect, memory-dependent effect, and the variable thermal conductivity. It is hoped that the obtained results would be helpful in designing the microstructures induced by an ultra-short time heating.

This study aimed to evaluate the effects of cooking method and meat cut on the physical and thermal characteristics of camel (Camelus dromedarius) meat. Thirty-two samples from shoulder and round cuts of eight male Majaheem breed animals were prepared using three cooking methods: sous vide, electric oven, and pressure cooker. Cooking method (COM) significantly influenced pH, water activity, cooking loss, density, and all color parameters (L*, a*, b*, chroma, hue). Meat cut (MTC) significantly affected pH, water activity, cooking loss, and lightness (L*). Both factors significantly impacted specific heat capacity, thermal conductivity, and thermal diffusivity, while thermal resistance was unaffected by MTC. Significant interaction effects (COM × MTC) occurred for pH, thermal diffusivity, and all color parameters except chroma. Sous vide cooking demonstrated superior tenderness and moisture retention compared to electric oven and pressure cooker methods. It effectively preserved natural color attributes, resulting in enhanced lightness (L*), redness (a*), and chroma due to its uniform heating process. This controlled heat distribution minimized moisture loss and improved the meat's ability to absorb heat, as indicated by elevated specific heat values. These properties contributed to enhanced texture preservation and overall meat quality. The findings suggest that adopting sous vide could optimize the cooking of camel meat, enhancing its visual appeal and consumer satisfaction.

It has been shown experimentally that lead–silicate glass of various compositions itself becomes electrically conductive due to the diffusion of Ru atoms during the firing process. Using energy‐dispersive spectroscopy and profiling of the spreading resistance R S and thermoEMF S on beveled samples, a close correlation between the ruthenium concentration and the distribution of specific resistance and thermoEMF has been shown. Changes of the Ru atoms concentration and the spreading resistance R S , as well as the thermopower S through the diffusion layer, obey a simple diffusion law (complementary error function), when the diffusion coefficient does not depend on the concentration of diffusing atoms. At a very low concentration of Ru atoms (near the glass‐diffusion layer boundary), the thermopower S reaches 5–7 mV K −1 , while at the glass–RuO 2 boundary (high concentration of Ru atoms) it is several μV K −1 . The calculated diffusion length under normal annealing conditions of thick‐film resistors (10 min at 1123 K) exceeds 100 μm, which is many times greater than the average distance (0.5–2 μm) between RuO 2 particles and confirms that the glass matrix becomes uniformly doped and conductive.