Macroscopic Temperature Research Articles

A lattice Boltzmann model for the conjugate heat transfer

Conjugate heat transfer problems are of great importance in many applications, while the available lattice Boltzmann (LB) models have some limitations in the study of such problems with the heterogeneous media. In this paper, we develop a new LB model for the conjugate heat transfer problems where the evolution equation with a modified equilibrium distribution function and a source term is considered. Through the Chapman–Enksog analysis, the macroscopic temperature equation can be recovered correctly. In order to test the accuracy, efficiency and stability of this LB model, some simple but nontrivial benchmark problems, including the planar thermal Poiseuille flow with two immiscible fluids, the conjugate heat transfer between a stratified heterogeneous medium with variable thermophysical properties, the steady and unsteady-state planer thermal flows with the two immiscible fluids, the steady-state conjugate heat transfer problem with a vertical interface, and the natural convection in a square cavity filled with circular and square rods, are studied. It is found that the results obtained from the present LB model are in good agreement with the analytic solutions or some previous works. In addition, it is also demonstrated that the developed LB model has a second-order convergence rate in space, and is more stable than some previous LB models. Finally, it should be noted that in our work, there is no special treatment to the interface, and the continuity conditions at the interface can be satisfied automatically.

Two-scale thermomechanical damage model for dynamic shear failure in brittle solids

A coupled thermomechanical damage approach for dynamic shear failure in brittle solids is proposed in the present contribution. The model is constructed by asymptotic homogenization from microstructures with dynamically evolving microcracks, in mode II, with unilateral contact and friction conditions on their lips. Crack-tip and frictional heating effects assumed at the small scale give rise to distributed heat sources in the macroscopic temperature equation and specific dissipation terms in the upscaled damage law. The analysis of the effective thermomechanical response of the model reveals strain rate and size effects and the influence of friction and growth of microcracks on the macroscopic thermal evolutions.

Development of empirical relationships for surface accommodation coefficients through investigation of nano-poiseuille flows using molecular dynamics method

In this work, we have studied the effects of macroscopic (temperature of gas and wall atoms; velocity of gas near the wall) and microscopic properties (energy well-depth parameter, $$\epsilon$$ , used in Lennard–Jones potential to describe gas–surface interaction strength) on both energy accommodation coefficients (EAC) and tangential momentum accommodation coefficient (TMAC) using molecular dynamics approach. The effect of aforementioned properties is studied through classical force-driven nano-Poiseuille flow using argon gas and platinum walls. Parameters like temperature of wall, external force acting on gas atoms, and energy well depth ( $$\epsilon$$ ) between gas and surface are varied systematically to study the effects of these parameters on accommodation coefficients. Empirical relationship between the accommodation coefficients (TMAC and EAC) and the above-mentioned properties is obtained by performing non-linear regression analysis.

Experimental investigation on the effects of thermal treatment on the physical and mechanical properties of shale

Shale is affected by high temperature and loads in deep mining, shale gas extraction, underground disposal of nuclear waste, and other shale projects. This paper aims to investigate the effects of thermal treatment on the physical and mechanical properties of shale. The uniaxial compression test and acoustic emission (AE) monitoring were conducted on shale specimens with different bedding plane inclinations (0°, 30°, 45°, 60°, and 90°) after thermal treatment of different temperatures. The results show that the P-wave velocity decreases with the increase in bedding plane inclination at each thermal treatment temperature showing anisotropy. A thermal explosion occurs when the specimen reaches the macroscopic thermal damage threshold temperature, and the threshold temperature and intensity of the thermal explosion are linked to the bedding plane inclination. The peak stress of specimens with the bedding plane inclinations of 0°, 45°, and 90° increases with the rise in thermal treatment temperature. After thermal treatment, the relationship curve between the cumulative AE counts of specimens with different bedding plane inclinations and time presents a step-jump trend. The thermal treatment has no significant effect on the failure modes of specimens with bedding plane inclinations of 30°, 60°, and 90°, while specimens with bedding plane inclinations of 0° and 45° begin to splitting failure with a rise in the thermal treatment temperature. The rockburst failure occurs in the shale specimens, and the main phenomena are spalling, particle ejection, and block collapse. The thermal treatment has a significant influence on the rockburst intensity of specimens with different bedding plane inclinations.

In Vitro Intracellular Hyperthermia of Iron Oxide Magnetic Nanoparticles, Synthesized at High Temperature by a Polyol Process.

We report the synthesis of magnetite nanoparticles (IOMNPs) using the polyol method performed at elevated temperature (300 °C) and high pressure. The ferromagnetic polyhedral IOMNPs exhibited high saturation magnetizations at room temperature (83 emu/g) and a maximum specific absorption rate (SAR) of 2400 W/gFe in water. The uniform dispersion of IOMNPs in solid matrix led to a monotonous increase of SAR maximum (3600 W/gFe) as the concentration decreased. Cytotoxicity studies on two cell lines (cancer and normal) using Alamar Blues and Neutral Red assays revealed insignificant toxicity of the IOMNPs on the cells up to a concentration of 1000 μg/mL. The cells internalized the IOMNPs inside lysosomes in a dose-dependent manner, with higher amounts of IOMNPs in cancer cells. Intracellular hyperthermia experiments revealed a significant increase in the macroscopic temperatures of the IOMNPs loaded cell suspensions, which depend on the amount of internalized IOMNPs and the alternating magnetic field amplitude. The cancer cells were found to be more sensitive to the intracellular hyperthermia compared to the normal ones. For both cell lines, cells heated at the same macroscopic temperature presented lower viability at higher amplitudes of the alternating magnetic field, indicating the occurrence of mechanical or nanoscale heating effects.

Micro-macro heat conduction model for the prediction of local, transient temperature in composite media

Heat flow in heterogeneous media with complex microstructure follows tortuous path and therefore the determination of local temperature distribution is a challenging task. The paper presents a micro-macro heat conduction model for the prediction of this distribution. The proposed solution is based on the prior determination of the macroscopic temperature in a quasi-homogeneous medium characterized by effective properties and then on using the relations between the macroscopic and microscopic temperatures. The Ensemble Averaging Method (EAM) was applied to derive the macroscopic transport equations while the combination of the EAM with the Green's Function Theory (GFT) was used to obtain relations between microscopic and macroscopic temperature fields. The expansion of these relations versus powers of the ratio of the micro to macro dimensions was then used to obtain a two-scale approximation of the mentioned relations. The model is applicable wherever the characteristic dimensions of the microstructure, i.e., distance between inclusions, are smaller than macro-dimension associated with time and spatial variation of macroscopic temperature distribution. The latter can be found from the respective expansion of the macroscopic temperature distribution into the Fourier series. The verification of the proposed model was carried out for 2D transient heat conduction in a periodic composite with the fixed microstructure by comparing direct numerical solution of the energy equation with the results of the approximate micro-macroscopic modelling. The model will be further extended to the prediction of temperature distribution in the case when the thermal contact resistance between constituents, species concentration in heterogeneous media, phase change phenomena and formation of a medium microstructure are present.

Preparation of dual-emission polyurethane/carbon dots thermoresponsive composite films for colorimetric temperature sensing

Luminescent films have received great interest for chemo-/bio-sensing applications owing to their distinct advantages over solution-based probes, including their good stability; ease of storage, transport, and recycling; tunable shape and size; and non-invasive nature. In this study, mechanically stable polyurethane/carbon dot (PU/CDs) composite films with dual-emission for ratiometric temperature sensing were prepared. The films exhibited good light transmissivity, flexibility, and ductility. The obtained PU/CDs hybrid films with dual emission exhibited temperature response and reversible properties from 10 °C to 90 °C. At the appropriate reactive ratio of CDs to PU, the fluorescent color of the films shifted over a relatively large range from blue to green to yellow over a large temperature range. These findings indicate that the stretchable hybrid PU/CDs composite films could potentially be applied for colorimetric detection over a large temperature range (10 °C–90 °C). These materials thus have high application value for macroscopic dual-light temperature detection as well as further development of polymer composite modification.

Hydrophilicity Improvement of Quartz Glass Surface by a Large-Area Atmospheric Pressure Plasma Generator

In this article, experimental study of a device combining the advantages of dielectric barrier discharge (DBD) and atmospheric pressure plasma jet (APPJ) has been presented. This device with a total length of 500 mm was capable of generating stable uniform atmospheric pressure plasma (APP) with a length of 400 mm, which was operated using a 12-kV HV supply and the air flow rate of 20–30 L/min. The plasma spectra were obtained by optical emission spectroscopy (OES), in which N2(C-B) and N2+ can be observed, and the rotational temperature was calculated to be 360 K. The macroscopic temperature was measured by an infrared camera. The result showed that the central temperature was room temperature. In addition, quartz glass substrates were treated by this device. The surface properties of quartz glass were investigated by water contact angle (WCA), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS). The results revealed that hydrophilicity and surface roughness of the quartz substrates were gradually increased with increasing treatment time. However, the results of XPS indicated that the content of hydrophilic groups at the surface had a slight change. Therefore, hydrophilicity of quartz glass improved effectively after APP treatment, which was due to the change in surface morphology and the increase in roughness.

Hydrodynamics and Heat Transfer Characteristics of a Double Gradient Microchannel Porous Model: Fixed Gradients and Variable Gradients Structures

AbstractHydrogen production from fluid fuel catalytic reaction is currently a hot research topic and catalyst carriers are the core of the hydrogen production process. The relationship between variable gradient structure and fixed gradient structure is still unclear. The hydrodynamics and heat transfer characteristics of double gradient and fixed gradient microchannel porous models are investigated. A strategy of using a uniform interpolation method to investigate the laws of a continuity equation is developed. There are three major findings. First, the internal fluid velocity of the variable gradient model is greater than the internal fluid velocity of the fixed gradient model. Second, the overall temperature change of the variable gradient structure is greater than the temperature change of the control group. Third, the formula of the macroscopic average temperature change of the area‐based fluid is found to be theoretically reliable. These findings may contribute to improving the catalytic efficiency of microchannel porous catalytic supports.

Multi-Physics Finite Element Model of Relay Contact Resistance and Temperature Rise Considering Multi-Scale and 3D Fractal Surface

Contact resistance of the main circuit is an important parameter for measuring the performance and reliability of relay products. The contact resistance value interacts with the stress and temperature of the contact surface during the relay's operation, and it will change with the ambient temperature and load current. Therefore, it is difficult to calculate the contact resistance when the relay is in the working environment. However, the finite element model used to predict contact resistance in previous studies does not consider the effect of current and temperature on the contact surface stress at the microscopic level. In this paper, based on the fractal theory, we established three-dimensional electrical contact finite element models in micrometer-scale and nano-scale to solve the contradiction between the computational efficiency and accuracy of the finite element model containing fractal surfaces. In the microscopic electrical contact model, the multi-physics coupling process of electric-temperature-stress at the conductive spot is analyzed, to improve the accuracy of the calculation of the local contact resistance at the conductive spot. Through the data transfer between the macroscopic finite element temperature rise model of the relay and the microscopic electrical contact model, the temperature rise and contact resistance of the relay under different load currents are calculated more accurately. The feasibility of the simulation method is proved by comparison with experimental measurement results.

Comprehensive understanding of magnetic hyperthermia for improving antitumor therapeutic efficacy.

Magnetic hyperthermia (MH) has been introduced clinically as an alternative approach for the focal treatment of tumors. MH utilizes the heat generated by the magnetic nanoparticles (MNPs) when subjected to an alternating magnetic field (AMF). It has become an important topic in the nanomedical field due to their multitudes of advantages towards effective antitumor therapy such as high biosafety, deep tissue penetration, and targeted selective tumor killing. However, in order for MH to progress and to realize its paramount potential as an alternative choice for cancer treatment, tremendous challenges have to be overcome. Thus, the efficiency of MH therapy needs enhancement. In its recent 60-year of history, the field of MH has focused primarily on heating using MNPs for therapeutic applications. Increasing the thermal conversion efficiency of MNPs is the fundamental strategy for improving therapeutic efficacy. Recently, emerging experimental evidence indicates that MNPs-MH produces nano-scale heat effects without macroscopic temperature rise. A deep understanding of the effect of this localized induction heat for the destruction of subcellular/cellular structures further supports the efficacy of MH in improving therapeutic therapy. In this review, the currently available strategies for improving the antitumor therapeutic efficacy of MNPs-MH will be discussed. Firstly, the recent advancements in engineering MNP size, composition, shape, and surface to significantly improve their energy dissipation rates will be explored. Secondly, the latest studies depicting the effect of local induction heat for selectively disrupting cells/intracellular structures will be examined. Thirdly, strategies to enhance the therapeutics by combining MH therapy with chemotherapy, radiotherapy, immunotherapy, photothermal/photodynamic therapy (PDT), and gene therapy will be reviewed. Lastly, the prospect and significant challenges in MH-based antitumor therapy will be discussed. This review is to provide a comprehensive understanding of MH for improving antitumor therapeutic efficacy, which would be of utmost benefit towards guiding the users and for the future development of MNPs-MH towards successful application in medicine.

Longitudinal Thermocapillary Flow over a Dense Bubble Mattress

A common form of superhydrophobic surface is made out of a periodically grooved solid substrate, wherein cylindrical bubbles are trapped in a Cassie state. When a macroscopic temperature gradient i...

Multiple-relaxation-time lattice Boltzmann model for convection heat transfer in porous media under local thermal non-equilibrium condition

In this work, a thermal multiple-relaxation-time (MRT) lattice Boltzmann (LB) model is proposed for simulating convection heat transfer in porous media under local thermal non-equilibrium (LTNE) condition. In the present model, the thermal non-equilibrium effects are incorporated into the model by adding source terms into the temperature-based MRT-LB equations. The discrete effects of the source terms are eliminated, and the temperatures of the fluid and solid phases are obtained through algebraic operations. Moreover, the error term which exists in the macroscopic temperature equation of the fluid phase is eliminated via a way that is consistent with the philosophy of the LB method. Numerical simulations show that thermal non-equilibrium natural convection problems can be well simulated.

Localization simulation of a representative volume element with prescribed displacement boundary for investigating the thermal residual stresses of composite forming

In this research, a methodology of localization simulation that not only discriminately described fiber and resin but also considered the global influence like external temperature loading was introduced. The newly proposed representative volume element with a prescribed displacement boundary that was deduced from a generalized viscoelastic shear lag model can link the macro and micro models if the edge effect was ignored. After the material models and software platform were demonstrated through a composite warpage experiment, the proposed localization simulation was investigated by comparing to a large-scale fully microscale benchmark model in an ideal cooling phase. The results show that the temperature and residual stresses evaluated from the new technique not only presented details fine to the scale of the representative volume element but also included the macroscopic temperature gradient, indicating a promising way to understand the composite forming process in a comprehensive format.

Prediction of Thermal Residual Stress and Microstructure in Direct Laser Metal Deposition via a Coupled Finite Element and Multiphase Field Framework

Direct laser metal deposition (DLMD) is a modern powder-fed additive manufacturing process, which builds up complex objects layer by layer, providing a potential capacity to produce key structural components specifically for the aerospace industry. The printing process is of a multidisciplinary nature, and has gained increasing attention in the areas of engineering mechanics, material science, control engineering and many other related fields. The quality control of the printed part depends on a large number of process parameters. The aim of this work, therefore, is to develop a coupled finite element and multiphase field framework, that provides an effective way to understand the quantitative relationship between the process parameters, temperature history, thermally-induced residual stresses and microstructures in the DLMD process. More specifically, the established multiscale framework is able to sequentially couple the heat transfer, metal melting/solidification, and stress analysis to simulate the macroscopic temperature distribution, thermal residual stresses and dendrite growth and solute segregation in a thin wall structure made of a binary nickel-copper alloy. The latest simulation technologies are used to model the process of progressive material deposition as well as the movement of the laser beam. It has been found that the high intensity laser introduced in DLMD can produce a complex thermal history and a significant level of thermal residual stresses and distortion. Microstructure predictions demonstrate the location-dependent morphology evolution, e.g., the dendrite spacing and the degree of solute segregation, attributed to the spatially variant temperature history.

Macroscopic and mesoscopic numerical model of melt filling process in complex mold cavity

In this paper an improved simple coupled level-set and volume-of-fluid (S-CLSVOF) method is proposed and applied to trace the melt front in complex mold filling process. Meanwhile, it is simulated the evolution of molecular orientation represented by oriented ellipses. Firstly, the shape level-set (LS) function is used to represent the complex mold cavity with R-function. The benchmark problems are carried out to verify the ability of S-CLSVOF method to capture the moving interface, and the flow past a cylinder is simulated to verify the FENE-P(Finitely extensible nonlinear elastic dumbbell with the Peterlin closure) constitutive equation model. Then, the non-isothermal filling process of the viscoelastic fluid based on the FENE-P model in the complex mold cavity (a simplified cellphone mold) is simulated, and the macroscopic temperature, stress and the behavior of mesoscopic molecular orientation are shown and analyzed in detail during the mold filling process. In order to better show the process of interface evolution, the location of the weldline is also displayed at the end of filling process. Numerical results show that the higher the melt or mold temperature is, the thinner the solidified layer is, and fixing the proper position of melt injection, as well as raising the melt and the mold temperatures will decrease or eliminate the weld lines in melt filling process.

Investigation on microstructural patterns and hot crack in the molten pool via integrated finite-element and phase-field modeling

A multi-scale model combing phase-field model and finite-element model is applied to study microstructural patterns and susceptibility of hot crack in the molten pool. Firstly, the macroscopic temperature field during welding is calculated by finite-element model, and the geometry, thermal gradient G and solidification rate R are obtained. Then these macroscopic calculation results are employed as inputs to phase-field model. Finally, morphologies of microstructural patterns and susceptibility of hot crack at different locations in the molten pool are studied. Predicted and experimental morphologies of microstructural patterns are dendritic. Predicted primary dendrite arm spacing decreases from the bottom to the top surface in the molten pool, which agrees well with experimental measurements. The formation of hot crack is related to dendritic growth and micro-segregation between dendrites. Predicted susceptibility of hot crack decreases from the bottom to the top surface in the molten pool.

Nanoindentation-Induced Plasticity in Cubic Zirconia Up to 500ºC

Orientation-dependent crystal plasticity in cubic zirconia ceramics (8 mol% yttria-stabilized zirconia) was investigated from 25oC to 500oC, which is below the macroscopic brittle-ductile transition temperature. Nanoindentation experiments and subsequent electron microscope analysis revealed that dislocation activities on {001} planes predominantly governed small-scale plasticity at the grain interior for each crystal orientation in this temperature range. The maximum shear stress at yielding, τmax, necessary for plastic yielding, was comparable to the theoretical shear strength, τth, estimated from the measured elastic modulus at low temperatures, while their ratio, τmax/τth, almost monotonically decreased at elevated temperatures. This suggests that plastic yielding was predominantly mediated by atomistic shear processes at low temperatures and increasingly affected by thermally assisted processes at elevated temperatures. The orientation-dependent behavior switched in the vicinity of ~ 25o from impression axes. In the near-[001] axis, plastic yielding occurred more smoothly at lower stresses, which can be attributed for the surface nucleation and forest-cutting interaction of dislocations on multiple {001} slip planes along and across the impression axes. In near-[101] and [111] axes, on the other hand, yielding was more burst-like and typically accompanied by pop-in events at higher stresses, which could result from the homogeneous dislocation nucleation and free-gliding motion of dislocations on {001} planes with considerable Schmid factors for the impression axes.

LOW-TEMPERATURE PLASMA -A PROMISING METHOD OF REHABILITATION

Low-temperature plasma is a partially ionized gas obtained at atmospheric pressure and having a macroscopic temperature close to the ambient temperature. The composition of the torch of low-temperature plasma includes charged particles, neutral active particles, including free radicals and particles in metastable states, as well as ultraviolet radiation. The biological effects of plasma are associated with the synergistic effect of the listed factors, each of which has a subliminal concentration that does not cause changes in the biological object. Intensive research on the use of low-temperature plasma in medicine began about 10 years ago, although some pioneering work appeared much earlier, mainly in Russia. Since the mid-2000s. in the world began to actively develop sources of gas plasma, in which the temperature of the plasma torch is reduced to the temperature of the human body. The use of such structures makes it possible to subject the treated surface to direct plasma action and to use the entire spectrum of active plasma components, including photons, electrons, ions, free radicals, and molecules in an excited state. Low-temperature plasma has a number of fundamental advantages, which include high non-specific bactericidal activity, low probability of occurrence of stable forms, the absence of ionizing radiation and highly toxic substances. The described advantages together with a comfortable temperature, relative simplicity and low cost methods, the lack of specific requirements for the treated surface make low-temperature plasma a promising method for the treatment of various pathological conditions.

Atomic-scale thermal manipulation with adsorbed atoms on a solid surface at a liquid-solid interface

Modulating thermal transport through interfaces is one of the central issues in nanoscience and nanotechnology. This study examined thermal transport between atoms adsorbed on a solid surface and a liquid phase based on non-equilibrium molecular dynamics. The heat flux was detected at sub-atomic spatial resolution, yielding a two-dimensional map of local heat flux in the vicinity of the adsorbed atoms on the surface. Based on the detected heat flux, the possibility of atomic-scale thermal manipulation with the adsorbed atoms was examined by varying the interaction strengths between the liquid molecules and atoms adsorbed on the surface. The results of the local heat flux at the single-atom scale clearly showed effects of the adsorbed atoms on the thermal transport through the liquid-solid interface; they can significantly enhance the heat flux at the single-atom scale using degrees of freedom normal to the macroscopic temperature gradient. The effect was especially evident for a low wettability surface, which provides key information on local enhancement at the single-atom scale of the thermal transport through a liquid-solid interface.