Thermal Effects Research Articles

Numerical simulation of the temperature excursions of porous substrates during atomic layer deposition

Atomic layer deposition (ALD) processes are usually highly exothermic. For ALD on substrates with high specific surface area, the reaction heat per ALD cycle may lead to a substantial temperature rise of the substrates. The novelty of this study lies in quantifying the temperature excursions of porous substrates during ALD via numerical simulation and further addresses the issue of tuning this type of thermal effect. A comprehensive model has been developed and validated to investigate the ALD thermal effect with accounting for the roles of the precursor transport phenomena within the ALD reactor system, and the coupling among the precursor diffusion, heat transfer, film deposition, reaction heat generation within the porous substrates. The results show that the thermal effect of the sub-saturated ALD can change with different substrate thickness, precursor partial pressure profile, heat transfer coefficient, and kinetic parameters. In contrast, for saturated ALD with adiabatic condition, the maximum temperature rise of the substrate is a deterministic value, independent of the substrate thickness and precursor partial pressure profile. The thermal effect with the porous substrates can influence the ultimate deposit amount and its distribution for sub-saturated ALD and change the time required for attaining saturation for saturated ALD. The temperature rises of certain common substrates during typical half-ALD cycles have been simulated to demonstrate the capability of the present model in predicting the thermal effect of ALD.

Numerical investigation of turbulent wake thermal effects on surface ships

To investigate the evolutionary mechanism of the thermal wake of surface ships, this study has proposed a numerical method for the thermal effects of turbulent wake and computed the near-wake fields for three ship schemes. The study indicates that the thermal wake, formed by vortices produced by the ship's movement and the propeller's rotation, propagates in a fine, thread-like pattern, setting it apart from the characteristic V-shaped diffusion of the Kelvin wake. The diffusion of thermal wake is divided into three distinct stages: formation, growth, and maturity. The thermal wakes generated by ships with shaftless rim-driven systems exhibit significantly lower diffusion rates, extents, and intensities compared to those created by ships with propeller propulsion systems. In summer, the center of the thermal wake exhibits a cold peak that is significantly lower than the ambient temperature. A reduction in temperature of greater than 0.05 K was observed for the three design schemes. In contrast, a warm peak that is above the environmental temperature is present at the edge of the wake. As the speed of the ship increases, the duration of each stage of the thermal wake lengthens and the diffusion range expands. When the temperature gradient is larger, the thermal wake becomes more intense. The findings of this study have revealed the evolution mechanisms of thermal effects in the wake of surface ships, thereby contributing to the advancement of knowledge in the fields of hydrodynamics and thermodynamics.

Energy-Based Skin Rejuvenation: A Review of Mechanisms and Thermal Effects.

Energy-based photoelectric and ultrasonic devices are essential for skin rejuvenation and resurfacing in the field of plastic surgery and dermatology. Both functionality and appearance are impacted by factors that cause skin to age, and various energy types have variable skin penetration depths and modes of transmission. The objective is to advise safe and efficient antiaging treatment while precisely and sensitively controlling and assessing the extent of thermal damage to tissues caused by different kinds of energy-based devices. A literature search was conducted on PubMed to review the mechanisms of action and thermal effects of photoelectric and ultrasonic devices in skin remodeling applications. This paper reviews the thermal effects of energy-based devices in skin resurfacing applications, including the tissue level and molecular biochemical level. It seeks to summarize the distribution form, depth of action, and influencing factors of thermal effects in combination with the mechanisms of action of various types of devices. Accurate control of thermal damage is crucial for safe and effective skin remodeling treatments. Thorough investigation of molecular biochemical indicators and signaling pathways is needed for real-time monitoring and prevention of severe thermal injury. Ongoing research and technological advancements will improve the accuracy and control of thermal damage during treatments.

Characterization and kinetics of whey protein isolate amyloid fibril aggregates under moderate electric fields

Food proteins solutions enable the controlled flow of electrical current when subjected to a Moderate electric field (MEF). This application results in internal heat generation, known as ohmic heating, accompanied by electrochemical reactions. These effects play a significant role in influencing the formation of protein amyloid fibril aggregates (AFA), which have broad applications in food and biomedical fields, ranging from improving food texture to biomedical applications such as drug delivery and disease treatment. This study focused on investigating the formation of β-Lactoglobulin (β-lg) AFA under MEF conditions using WPI as protein source and various characterization techniques (e.g., Thioflavin T fluorescence, circular dichroism, and electron microscopy). The results indicated that MEF prolonged the lag phase of AFA formation. Furthermore, nucleation and fibril growth showed higher activation coefficients and cooperativity level (n > 2) compared to conventional heating method. MEF treatment resulted in unique fibril clustering and the presence of unexpected higher-order AFA networks confirmed by electron microscopy. These findings highlight the significant role of MEF in influencing the aggregation kinetics of β-lg AFA. Exploring further into the electrochemical and thermal effects during protein aggregation processes holds the key to unlocking deeper insights fibril formation process.

Effects of freeze-thaw cycles and heat treatment on the odor-binding properties of myofibrillar protein to key fishy compounds

This study investigated the effects of different freeze-thaw (F-T) cycles and subsequent heat treatment on the odor-binding properties of myofibrillar protein (MP) in grass carp to four key fishy substances. The odor-binding ability of MP significantly decreased as freeze-thaw (F-T) cycles increased (p < 0.05). After heating, the odor-binding ability of MP further decreased. Freeze-thaw treatment induced the oxidative denaturation, decreased total sulfhydryl content and unfolded the α-helix in MP, which modified and re-buried the exposed odor-binding sites, reducing odor-binding ability. After heating, the oxidative damage and aggregation of MP induced by freeze-thaw cycles, along with thermal effects, synergistically accelerated the oxidative denaturation and formation of disordered structures of heated MP. Enhanced hydrophobic interactions led to a dominant aggregation effect, which reduced the binding sites and further decreased the odor-binding ability of heated MP, resulting in more release of odors.

Multiple-beam output, high-peak power passively Q-switched Nd:YAG/Cr4+:YAG laser for ignition application - Modeling of laser pulse characteristics and thermal behavior

In this work we report on the characteristics of a passively Q-switched Nd:YAG/Cr4+:YAG laser with four beams, developed for studies on the laser ignition of different combustible mixtures. The compact laser contains a Nd:YAG/Cr4+:YAG ceramic composite medium, with a monolithic optical resonator. A configuration in which each beam contains laser pulses with an energy of 3.1 mJ and a duration of 0.9 ns (i.e. with a peak power of 3.4 MW) is discussed; operation can be performed in pulse-burst mode, with up to five pulses per pumping pulse. The characteristics of the laser pulses are described by a model based on the rate equations for the photon flux and population inversions in the Nd:YAG gain medium and in the Cr4+:YAG medium with saturable absorption. In addition, the thermal effects are simulated for the operation up to 100 Hz repetition rate, considering the Nd:YAG/Cr4+:YAG laser medium with two geometries, the first of the rod type and the second of the annular type (i.e. cylinder with a central hole) for a good management of thermal effects. This work is an important advancement towards developing a compact laser device with multiple beams, featuring laser pulses and structural properties suitable for igniting combustible mixtures in real engines.

Electro-osmotic flow and heat transfer in Jeffery fluid: A multi-membrane microchannel model

Microscale heat transfer is vital for the performance of smart thermal devices like heat sinks, thermosyphons, and microheat pipes. This study introduces a biothermal pumping flow model based on a multi-membrane pumping mechanism that leverages microscale heat transfer. The model describes rhythmic contraction and relaxation of membranes, combined with electro-osmosis in Jeffery fluid flow within a vertical microchannel of finite length. Two membranes on the microchannel walls, with varying amplitudes, diameters, and phase lags, generate pressure that moves fluid in both directions through contraction and expansion cycles. The model is based on the conservation of mass and momentum, using a low Reynolds number approximation to capture microscale transport phenomena at biomedical scales. Dimensionless conservation equations are analytically solved under no-slip boundary conditions, with results computed in MATLAB for clarity. Axial velocity results are simulated and verified using the optimal homotopy analysis method. The model explores the influence of key parameters (UHS, me, λ, Gr, β) on pressure gradient, velocity distribution, volumetric flow rates, skin friction, Nusselt number, and stream function. The findings demonstrate that pressure from membrane motion is significantly affected by thermal effects and buoyancy forces, and flow and pumping characteristics are largely determined by the fluid's rheological qualities and the geometrical features of the membrane. This study provides novel ideas for enhancing the functionality and design of smart thermal devices while also advancing microscale heat transfer technology.

Design analysis and experimental verification of insulation blankets for civil aircraft nacelle and pylon

Abstract The nacelle and pylon structures of civil aircraft, due to their proximity to the engine, are significantly affected by the high-temperature components of the engine. To reduce the impact of high temperatures on the nacelle and pylon structures and their internal systems, insulation blankets are typically arranged on the inner side of the nacelle fan cowl, the inner side of the core cowl, and the bottom area of the pylon to decrease the thermal transfer effect from the high-temperature components of the engine and the hot air inside the core compartment to the nacelle and pylon structure. This paper mainly describes the structural design method and requirements for the nacelle pylon insulation blanket, and through thermal analysis theoretical calculations, the temperature changes on the cold side of the insulation blanket at different hot sides are derived. The results are compared with the insulation test results of the insulation blanket test pieces, further verifying the insulating performance of the blanket. In addition, environmental qualification tests were conducted on the insulation blanket test pieces, and insulation tests were re-performed on the test pieces after environmental testing, demonstrating the reliability of the nacelle and pylon insulation blanket design.

Experimental investigation on fracture propagation in shale fractured by high-temperature carbon dioxide

The productivity of shale reservoirs was significantly enhanced by the high-temperature CO2 fracturing technique. The injection of high-temperature CO2 into the formation induced rock fracture propagation, creating advantageous pathways for fluid flow. In this research, a self-developed in situ high-temperature convective heat simulation experimental apparatus was employed to systematically conduct simulated experiments on high-temperature CO2 fractured shale under different influencing factors. The experimental results demonstrated that the permeability of CO2 increased as the injection temperature increased. The rock fracture pressure was effectively reduced by high-temperature CO2 fractured shale. Higher complexity was observed in fracture propagation, accompanied by a substantial increase in microcracks and branching fractures. The shale fracture pressure increased with increasing triaxial stress and CO2 injection rate. The confining pressure restricted the further propagation of fractures under relatively high stress conditions, thereby reducing the width and density of fractures, lowering the fracture complexity. Nevertheless, the thermal shock effect of the fluid was exacerbated as the injection rate of high-temperature CO2 increased. The initiation of microcracks was facilitated by the intensification of local thermal stress in shale, inducing multiple curved fractures and forming a more complex fracture network. Compared to horizontal bedding shale, the fracture pressure of vertical bedding shale was relatively higher during high-temperature CO2 fracturing. In addition, the geometric morphology of fracture propagation was more complex, characterized by rougher fracture surfaces, leading to a greater improvement in reservoir reconstruction volume. This research contributed to the optimization of CO2 resource utilization, provided experimental evidence for the application of high-temperature convection fracturing technology in in situ shale conversion projects.

Integrated all-fiber-optic sensor based on FPI and MZI composite structures for temperature and strain measurement

In this paper, a temperature and strain sensor based on fiber-optic Mach-Zehnder interferometer (MZI) cascaded with Fabry-Perot interferometer (FPI) is designed and fabricated. The integrated sensor structure consists of no-core fiber (NCF) sandwiched by two sections of multi-mode fiber (MMF), hollow-core fiber (HCF), and two single-mode fibers (SMF) which are cascaded at the ends of the MMF and the HCF. Due to the thermal expansion effect, thermo-optic and elasto-optic effects of fiber material, the increase of the temperature and strain will make the change of the transmission mode, which will cause the spectral fringes wavelength shifting with strain, and the intensity of the spectral fringes varying with temperature but not strain variations in multiple temperature ranges. The series experiments valid show that the sensor with integrated structure realizes the strain and temperature measurements in multiple temperature ranges, and the minimum and maximum temperature sensitivities are -0.278dBm/°C and -0.670dBm/°C in the temperature range of 68-86 °C and 123-141 °C, respectively. The strain sensitivity is 2.17pm/με all over the measured range. The integrated sensor structure has the advantages of high sensitivity, multiple measuring ranges, simple manufacturing, and low cost, which has the potential to be applied in the field of the internal strain and temperature measurements of different structures.

Study of thermal and humidity environment and prediction model in impinging jet ventilation rooms based on thermal and moisture coupling

Variations of indoor humidity have significant influence on thermal comfort, calculation accuracy of air-conditioning load and selection of design parameters. As one of the most promising advanced ventilation strategies, impinging jet ventilation (IJV) has received much attention. However, few study concerned its coupled indoor thermal and humidity environment and there is also no complete mathematical model for the IJV to synchronously predict its indoor temperature and humidity distributions. Therefore, this study first simulated the thermal and humidity environment in IJV rooms with considering the coupled thermal and moisture transfer effect. The results demonstrate a significant correlation between temperature and humidity distributions in IJV, with a correlation coefficient of approximately 0.4. Then, a simplified theoretical model for predicting temperature and humidity distributions in the IJV was established based on the theory of nodal model, and the key parameters within the model that are influenced by indoor airflow pattern were also identified. Next, the model results were compared with the simulation ones and showed that the proposed model is with a mean absolute error of 0.4°C for the prediction of temperature distribution and of 0.21g/kg for the prediction of humidity distribution. These discrepancies are sufficiently minor to validate the accuracy of the proposed model. Last, the potential application value of the proposed model was discussed. Overall, the current study contributes to extend the application of the existing coupled thermal and humidity models to IJV scenarios, and provides a robust theoretical foundation for the more rational design and practical application of the IJV.

Adiabatic Shear Localization in Metallic Materials: Review.

In advanced engineering applications, there has been an increasing demand for the service performance of materials under high-strain-rate conditions where a key phenomenon of adiabatic shear instability is inevitably involved. The presence of adiabatic shear instability is typically associated with large shear strains, high strain rates, and elevated temperatures. Significant plastic deformation that concentrates within a adiabatic shear band (ASB) often results in catastrophic failure, and it is necessary to avoid the occurrence of such a phenomenon in most areas. However, in certain areas, such as high-speed machining and self-sharpening projectile penetration, this phenomenon can be exploited. The thermal softening effect and microstructural softening effect are widely recognized as the foundational theories for the formation of ASB. Thus, elucidating various complex deformation mechanisms under thermomechanical coupling along with changes in temperatures in the shear instability process has become a focal point of research. This review highlights these two important aspects and examines the development of relevant theories and experimental results, identifying key challenges faced in this field of study. Furthermore, advancements in modern experimental characterization and computational technologies, which lead to a deeper understanding of the adiabatic shear instability phenomenon, have also been summarized.

High-temperature behaviour of geopolymer composites containing carbon fibre and nano-silica: Mechanical, microstructure, and air-void characteristics

The fly ash–ground granulated blast-furnace slag-based geopolymer (FSG) represents a groundbreaking material, offering a sustainable and environmentally friendly alternative to conventional construction materials. This paper presents a systematic experimental study on FSG reinforced with carbon fibre (CF, 0%–1.0%) and nano-silica (NS, 1%–3%) at high temperatures (20, 200, 400, 600, 800, and 900 °C). Various tests concerning appearance, residual strength, uniaxial tension, XRD, FTIR, TGA, SEM, and air-void characteristics were conducted to analyse thermal effects. The findings show that as temperature increases, the colour of the geopolymer transitions from dark grey to yellow grey. Enhanced geopolymerisation during thermal solidification from 20 to 400 °C significantly increases the compressive, flexural, and tensile strengths of the geopolymer. The addition of CF and NS improves the residual strength of geopolymers at high temperatures, with optimal concentrations found to be 0.6% for CF and 2% for NS. CF maintains its bridging effect at high temperatures, enhancing fibre–matrix bonding, while NS promotes the formation of additional hydration products on CF surfaces, thereby strengthening the material further. After exposure to 800 °C, despite a weakening of the fibre–matrix interface, the modified geopolymers (FSGC0.6 and FSGC0.6N2) exhibit finer air bubble chord lengths and superior air-void characteristics than the control group. This supports the theory that the synergistic action of CF and NS not only enhances geopolymerisation but also fills pores, thus limiting crack propagation and densifying the pore structure.

The Importance of Ambipolar Heating in the Standard Thin Accretion Disk with Outflows

This study examines the importance of the thermal effects of ambipolar diffusion (AD), by analyzing the governing properties in the middle and outer regions of a standard thin accretion disk with outflows. To accomplish this, we derive the nonideal magnetohydrodynamic equations, considering both the dynamical and thermal impacts of AD in these regions of the disk. In a stationary state, we utilize the self-similar technique to analyze the vertical structure of a disk with outflows and express the ambipolar diffusivity in terms of the Alfvén velocity and the Elsässer number. Our main focus is on the vertical temperature profile at large radii of the disk when the values of the Elsässer number are small. While the findings indicate that AD heating has minimal effects within the disk, it does play a critical role near the disk surface. When the Elsässer number is low, there is a notable rate of outflows and disk evaporation, resulting in angular momentum transport in these regions. This issue becomes important when we decrease the value of turbulent viscosity, as it leads to highlighting the AD heating effect. This allows the surface regions to become hotter and results in an increase in the drive of the outflows. The results of this research may be important for studying disk coronae and disk dispersal in the middle and outer regions of the thin accretion disk.

The effects of ventilation layout on cough droplet dynamics relating to seasonal influenza

The primary aim of this paper is to investigate airborne virus transmission in a typical meeting room relating to the heating, ventilation, and air conditioning (A.C.) systems. While the installation of 4-way cassette A.C. systems in offices and meeting rooms has become increasingly common, their efficiency in mitigating short-range airborne virus spread remains poorly understood. Addressing this gap is critical in the post-pandemic era, where understanding the limitations of various ventilation systems is paramount for public health. We systematically compare the performance of the 4-way cassette A.C., various configurations of mixing and displacement ventilation systems, and natural ventilation in controlling the spread of respiratory viruses. Our research uniquely integrates evaporation models to accurately simulate cough clouds' multiphase behavior under both quiescent and thermally influenced conditions. The study benchmarks these systems against two widely recognized ventilation standards (i.e., 5 air changes per hour and 10 l/s per person), offering evidence-based insights applicable across diverse indoor settings. Our findings reveal significant thermal effects in the quiescent case, resulting in 32.3%, 54.3%, and 8.0% changes in the axial, vertical, and lateral spread of the virus-laden droplets, respectively. Notably, the 0.5 m/s 4-way cassette A.C. system demonstrated superior performance, reducing the axial spread by 29.6% compared to other mechanical ventilation configurations. Furthermore, the role of exhaust outlets or doors was found to be critical in shaping the spread pattern in natural ventilation scenarios. This work can offer practical guidance to office workers, engineers, and public health officials on enhancing indoor airborne infection control.

Theoretical model and verification of the laser thermal effect on the temperature measurement sensitivity of rare earth

The fluorescence temperature measurement based on rare earth ions has been studied widely. It is quite puzzling that the same thermal coupling energy levels present different relative sensitivities of temperature measurement in reports. Different relative sensitivities indicate that the level spacing of the same thermal coupling energy levels calculated by Boltzmann's formula is different. To solve this problem, a physical model is proposed to explain the influence of the laser thermal effect on the fluorescence temperature measurement. The results show that the additional temperature of the sample imposed by the laser thermal effect has an impact on the relative sensitivity, which is the higher the additional temperature, the lower the relative sensitivity. Furthermore, the source of heat generation from laser irradiation of rare earth is discussed. For Er3+ ions, the laser converted into heat mainly generated by the multiphonon transitions between 2H11/2 and 4S3/2 levels. The results show that the theoretical curve fitted well with the experimental data. It is instructive for the design of new temperature sensors.

Synergistic antimicrobial effects of ammonium persulfate, ultrasound, and mild heat on Staphylococcus aureus under varied conditions

This study elucidated the antimicrobial effect of ammonium persulfate (PS), ultrasound (US), and 40–60 °C mild heat on Staphylococcus aureus ATCC 27213 under various growth conditions, including non-adaptation, pH-adaptation, and aridity-adaptation, in buffered peptone water (BPW) and on orange peel surfaces. For non-adapted, pH-adapted, and aridity-adapted S. aureus, the combined treatment of PS, US, and mild heat showed a synergistic effect, with log reductions of 2.05, 6.44, and 1.11 log CFU/mL in BPW after 6 min, respectively. Mechanistic experiments showed that pH-adapted S. aureus had increased SOD activity due to oxidative stress from the acidic environment, but the introduction of PS further elevated this stress, leading to greater cell death primarily through membrane damage, as confirmed by TEM, with leakage of nucleic acids and proteins. This technique was applied to an orange peel washing system, effectively inactivating aridity-adapted S. aureus, resulting in 3.51 log CFU/cm2 and 3.20 log CFU/mL reductions on orange peel and in BPW washing water, respectively, after a 6-min treatment, without any quality changes, including color and texture attributes. The enhanced inactivation on orange peel may be attributed to the presence of compounds such as ascorbic acid and limonene, which further activate persulfate and exhibit antimicrobial properties, thereby contributing to the increased efficacy of the treatment. The combined PS, US, and mild heat treatment provides an effective strategy for controlling resilient bacterial strains in the food industry, enhancing food safety through oxidative stress and mild thermal effects.

Dielectric material processing with ultrashort pulses

AbstractFemtosecond lasers have become essential tools in material processing. Thanks to their ultrashort pulse duration, these lasers can process a wide range of materials without causing significant thermal effects, leading to superior quality. Dielectric materials, especially glass and ceramics, are among those that benefit the most from femtosecond laser technology. Traditional processing methods often struggle with these materials, but femtosecond lasers provide a solution with high precision and quality.

Numerical simulation of magnetically driven nanomaterial rotating flow configured by convective-radiative cone with chemical reaction

Indeed, nanoliquids have acquired substantial consideration in heat transference field because of their inimitable thermal attributes and favorable application likelihoods. In contrast to orthodox liquids, the haphazard movement of nanoparticles within nanoliquid strengthens fluid turbulence, accomplishes superior thermal effectiveness and declines thermal resistance. Nanoliquids have ample utilization, for illustration, solar energy, electronic chips, automotive radiators and heat exchangers etc. This communication reports chemically reactive electro-magnetized nanomaterial dissipative flow confined by rotating cone. Flow expressions include thermo-solutal buoyancy, varying viscosity and magneto-hydrodynamics. Radiative heat, thermophoresis, viscous dissipation, Brownian diffusion, thermal source and first order chemical reaction are pondered to model transport expressions. Relevant variables are introduced to transfigure partial differential mathematical expressions to mathematical ordinary ones. Numerical outcomes for non-dimensional mathematical expressions are reported via bvp4c algorithm in MATLAB. The comprehensive results featuring dimensionless quantities are explored through graphs and arithmetic representations. It is evaluated that escalating values of variable viscosity, Prandtl number and unsteady parameter decline temperature but temperature is improved as a consequence of progressive variation in radiation parameter, Eckert number, thermophoresis parameter, heat generating and Brownian diffusive variables. The study is relevant to cooling industry, electroconductive, thermal collector and nano-materials processing.

Cascaded Fabry-Perot cavity and fiber Bragg grating on sapphire fibers for high-temperature strain sensing

High-temperature strain sensors are key elements for several applications. Key issues of the existing devices include the difficulties of sensor operating above 1000°C as well as the very strong thermal effect under high temperatures introducing significant bias on the strain measurement. Here we developed a cascaded Fabry-Perot cavity and fiber Bragg grating strain sensor fully integrated on sapphire fibers, permitting a sufficient temperature compensation and strain measurement up to 1150°C temperature. A three-point adhesive bonding process is proposed to greatly improve the adhesion performance, and hence the robustness of the device at high temperatures. Experimental results show that the fabricated strain sensor can achieve a measurement range of ±1000 με at temperature up to 1150°C. The experimental results show that the measurement accuracy is not more than 5% at room temperature. the measurement accuracy is significantly decreased at high temperature, and the maximum strain measurement error is 14% at 1150°C.