Effect Of Heat Conduction Research Articles

Some investigative studies on dissimilar metals by friction stir welding

The aim of the current work is to develop weldments and to investigate the microstructure and mechanical properties of the aluminium alloy 6061-T6 and magnesium alloy AE42 plates (120x100x3 mm) which are welded through FSW. H13 conical thread tool pin was selected to prepare the welded joints. Two plates that were co-ordinated vertically according to the welding directions were well joined. In this study, two parameters such as weld speed at 60,150 mm / min and tool rotation speed at 800, 1200 RPM are taken into account as defect free. By changing these parameters similar and dissimilar alloys are welded together. Tensile specimens (according to ASTM standards) were developed to estimate mechanical properties including tensile strength, % elongation, yield s trength and joint efficiency. It was found that an increase in the tool rotational speed or welding speed of the tool led to an increase in the tensile strength, which reached a maximum value and then decreased. (LOM) Light optical Microscopy research was accustomed examine and study the weld zone properties. Dynamic recrystallization was discovered within the weld region in addition as within the thermo-mechanical heat-affected zone (TMAZ). There’s a transparent reduction within the quantity of precipitate through the TMAZ and from the BM (Base Material) into the weld zone. Observed precipitates from similar and dissimilar welded joints -Mg2Si, Al2O3, SiC, Mg17Al12, Mg2Al3, Al11Ce3 and Al2Ce. Welds are without porosity. XRD with the EDS characterization was executed in the NZ (Nugget Zone) demonstrated the existence of SEM intermetallic phases and their weight in percent. Rapid phase structures of welded joints were detected using X-ray diffraction (XRD), however, the SEM fractograph indicated a flexible ductile fracture mechanism. Vickers micro-hardness test was performed on the thickness of the plate within the weld space to review and perceive the variation of hardness with thickness. An interrelationship between size of precipitate and micro hardness was ascertained. The corrosion behaviour of the base alloy and welded joints was measured in 3.5% NaCl solution using the salt spray test and by investigating the corrosion parameters (corrosion rate, exposure time and weight reduction). Corroded products were analysed and classified using optical microscopy and SEM. The corrosion rate decreases with increasing exposure time, but remains uniform as the corrosion time increases. Finally, a three-dimensional finite element phases was developed for temperature evolution in the friction-stir welded joint plunge depth, dwell, moving phases, and the heat conduction effect is arbitrary in the LAGARAGIAN-EULERIAN formulation in the ABAQUS / EXPLICIT, Johnson-Cook (JC) elastic-plastic model Will be used. The JC model defines the strength of the material as a function of three parameters, i.e. the strength of the material depends on the strain hardening effects, strain rate effects and temperature and verifies the s imulated results with the experimental results.

A magnetic reconnection model for hot explosions in the cool atmosphere of the Sun

Context. Ultraviolet (UV) bursts and Ellerman bombs (EBs) are transient brightenings observed in the low solar atmospheres of emerging flux regions. Magnetic reconnection is believed to be the main mechanism leading to formation of the two activities, which are usually formed far apart from each other. However, observations also led to the discovery of co-spatial and co-temporal EBs and UV bursts, and their formation mechanisms are still not clear. The multi-thermal components in these events, which span a large temperature range, challenge our understanding of magnetic reconnection and heating mechanisms in the partially ionized lower solar atmosphere. Aims. We studied magnetic reconnection between the emerging magnetic flux and back ground magnetic fields in the partially ionized and highly stratificated low solar atmosphere. We aim to explain the multi-thermal characteristics of UV bursts, and to find out whether EBs and UV bursts can be generated in the same reconnection process and how they are related with each other. We also aim to unearth the important small-scale physics in these events. Methods. We used the single-fluid magnetohydrodynamic (MHD) code NIRVANA to perform simulations. The background magnetic fields and emerging fields at the solar surface are reasonably strong. The initial plasma parameters are based on the C7 atmosphere model. We simulated cases with different resolutions, and included the effects of ambipolar diffusion, radiative cooling, and heat conduction. We analyzed the current density, plasma density, temperature, and velocity distributions in the main current sheet region, and synthesized the Si IV emission spectrum. Results. After the current sheet with dense photosphere plasma emerges and reaches 0.5 Mm above the solar surface, plasmoid instability appears. The plasmoids collide and coalesce with each other, which causes the plasmas with different densities and temperatures to be mixed up in the turbulent reconnection region. Therefore, the hot plasmas corresponding to the UV emissions and colder plasmas corresponding to the emissions from other wavelengths can move together and occur at about the same height. In the meantime, the hot turbulent structures concentrate above 0.4 Mm, whereas the cool plasmas extend to much lower heights to the bottom of the current sheet. These phenomena are consistent with published observations in which UV bursts have a tendency to be located at greater heights close to corresponding EBs and all the EBs have partial overlap with corresponding UV bursts in space. The synthesized Si IV line profiles are similar to that observed in UV bursts; the enhanced wing of the line profiles can extend to about 100 km s−1. The differences are significant among the numerical results with different resolutions, indicating that the realistic magnetic diffusivity is crucial to revealing the fine structures and realistic plasmas heating in these reconnection events. Our results also show that the reconnection heating contributed by ambipolar diffusion in the low chromosphere around the temperature minimum region is not efficient.

Heat transport in insulator/ferromagnetic-insulator/insulator heterogeneous nanostructures at low temperatures

A kinetic approach to the heat transport by phonons and magnons through a ferromagnetic insulator (FI) layer located between two massive insulators $({I}_{1}$ and ${I}_{2})$ is analytically considered. The effective transverse heat conductivity of such a layered system with an arbitrary thickness of the FI layer is calculated, and the thickness at which the size effect is manifested in the thermal conductivity is found.

Real-time measurement method for the skin temperature of the human arm via large lateral shearing interferometry.

This paper presents a real-time measurement method for the skin temperature of the human arm. In this method, the air temperature close to the arm skin is measured via large lateral shearing interferometry, thus avoiding the possible influences of the different physical characteristics of different people, while maintaining the advantages of optical measurement, including its noncontact, noninvasive, and rapid features. The method captures the real-time fringe patterns generated using a parallel-sided plate when a collimated laser light beam transfers through the air surrounding the arm to be measured. Additionally, the phase difference distribution caused by the temperature difference is calculated in combination with the background fringe patterns. The phase difference in the light close to the arm skin is then estimated via a linear fitting method. Accordingly, based on the size parameters of the arm cross section and the ambient temperature monitored in real time, the air temperature close to the arm skin, which is considered equal to the arm skin temperature, is determined while considering the heat conduction effect. Experimental measurements of the temperature of human arm skin were conducted using the proposed method, and the axillary temperatures of the same person before and after the experiments were also measured using an electronic thermometer and a mercury thermometer. Good agreements were found, verifying the reliability of the proposed method. Moreover, based on this method, the possibility for the construction of a real-time body temperature measurement system is also discussed.

Numerical study on the low frequency sensitivity variation of the microphone in laser-pistonphone based primary calibrations

The low frequency sensitivity of microphone is crucial for monitoring large-scale natural and artificial activities, but is acoustically controlled by the disturbing pressure leakage and heat conduction effects in its back-chamber. This issue has been partly studied by theoretical and experimental means, and is further studied here through numerical simulations on the laser-pistonphone based primary calibration of the microphone. Firstly, the frequency response of the calibrating sound-field, affected by the disturbing pressure leakage and heat conduction effects, is studied. Independent and coupling correction values for two effects are obtained based on the proposed model comparison method. Then, joint simulations on the primary calibration process are proposed for both the vent located in the calibrating sound-field and out. Simulation results verified previous studies, and more details about the parameter adjustment of both the pistonphone and microphone affecting the diaphragm deformation and sensitivity output of the microphone are elaborated here.

Homogenization of heat transfer in fibrous composite with stochastic interface defects

The main aim of this work is verification how the interface defects appearing frequently in-between the fibres and the matrix affect the effective heat conductivity of fibrous composites. This analysis is provided assuming uncertainty in these defects geometry and frequency, which quite naturally induces randomness in homogenized characteristics of such a composite. Homogenization of this composite is mathematically formulated and numerically implemented using the Finite Element Method (FEM) and also using a combination of triangular and quadrilateral finite elements of the system ABAQUS© with linear approximating functions. Polynomial response functions relating effective conductivity with these defects parameters have been recovered using specific series of the FEM experiments and of traditional formulation of the Least Squares Method. Three different numerical techniques have been employed to determine the basic probabilistic characteristics of the effective heat conductivity – Monte-Carlo simulation, semi-analytical method and also iterative generalized stochastic perturbation technique. Numerical experiments completed assuming Gaussian uncertainties in the interface defects prove their remarkable influence on the homogenized composite. Composite computational model prepared in the system ABAQUS could be next extended towards anisotropic distribution of the fibres within the Representative Volume Element (RVE).

Effect of heat treatment on the microstructure evolution and mechanical behaviour of a selective laser melted Inconel 718 alloy

This study aims to address the fact that after the selective laser melting (SLM) of an Inconel 718 alloy, the microstructures at each fabrication position are anisotropic due to the coupling effect of multi-dimensional heat conduction caused by the forming mode, and combined with the formation laws of each phase in the Inconel 718 alloy, the microstructure evolution mechanism and corresponding mechanical behaviour laws at each fabrication position under different heat treatment regimes (including precipitation ageing (DA), δ ageing + precipitation ageing (SA) and high-temperature microstructure homogenization + ageing + precipitation ageing (HSA)) were studied. It is found that with increasing heat treatment temperature (DA→SA→HSA), the microstructure of each fabrication position gradually changes from anisotropic to isotropic, including the weakening and disappearance of the primary fabricated characteristic microstructure (“perlage” molten pools and long strip molten channels) and the primary crystal structure, and the corresponding recrystallization degree significantly increases. Among them, the nucleation and growth of recrystallized grains occurs through the process of high temperature polygonization recovery and the grain boundary migration mode, and the orientation of the recrystallized grains is determined by the direction of the grain boundary migration during recrystallization. Additionally, with the continuous dissolution of a large number of intergranular Laves phases precipitates in the primary fabricated microstructure (AB) and the further uniform diffusion of solute from intergranular to intragranular, the number of second-phase strengthening particles (γ″ phase and γʹ phase) precipitated in the crystal increases and the distribution uniformity is improved significantly. Furthermore, the intergranular δ phase precipitation will gradually change from intergranular to intragranular, and when the heat treatment temperature is close to the melting temperature of the δ phase, its shape changes from a primary short rod-like shape and needle-like shape to a bulk shape. Thus, under the influence of the precipitation-dissolution coupling between the strengthening phase in the crystal and the intragranular brittle phase, the comprehensive mechanical strength of the samples after heat treatment shows the trend of SA ＞ HSA ＞ DA ＞ AB, while the elongation shows the opposite trend (AB ＞ DA ＞ HSA ＞ SA) with the precipitation content of the δ phase, and the mechanical behaviours are all superior to those of the mechanical standards of forging and casting of Inconel 718 alloy.

Effective heat conductivity of Honeycomb (porous) composite panel

PurposeThe purpose of this paper is to validate an assumption of what to use as an effective (steady state) heat transfer coefficient of thermal conductivity for the honeycomb core sandwiched by Fiberglass face sheets composite. A one-dimensional model based on Fourier law is developed. The results are validated experimentally.Design/methodology/approachThe results were obtained from the one-dimensional mathematical model of an overall or effective heat conductivity of the Honeycomb composite panel. These results were validated experimentally by applying heat flux on the specimen under controlled environment. The surface temperatures at different voltages were recorded and analysed. The skin of the sandwich composite material used in the investigation was Fiberglass sheet with a thickness of 0.5 mm at the bottom and 1.0 mm at the top surface. Both skins have a stacking sequence of zero degrees. Due to the presence of air cells in the core (Honeycomb), the model considers the conduction, convection and radiation heat transfer, across the thickness of the panel, combined as an effective conduction mode, whose value may be predicted by using the coefficient of thermal conductivity of the air based on the average temperature difference between the two skins. The experimental results for the heat transfer through the thickness of the panel provide validation of this assumption/prediction. Both infrared thermography and conventional temperature measurement techniques (thermocouples) were used to collect the data.FindingsThe heat transfer experiment and mathematical modeling were conducted. The data obtained were analyzed, and it was found that the effective thermal conductivity was temperature-dependent as expected. The effective thermal conductivity of the honeycomb panel was close to that of air, and its value could be predicted if the panel surface temperatures were known. It was also found that as temperature raised the variation between experimental and predicted effective air conduction raised up. This is because there was an increase in molecular diffusion and vibration. Therefore, the convection heat transfer increased at high temperatures and the air became an insulator.Originality/valueHoneycomb composite panels have excellent physical and thermal properties that influence their performance. This study provides an appropriate method in determining thermal conductivity, which is one of the critical thermal properties of porous composite material. This paper also gives useful and practical data to industries that use or manufacture honeycomb composite panels.

Comparison of turbine blade film cooling efficiency between PSP and TLC techniques in a stationary wind tunnel

In general, pressure sensitive paint (PSP) and thermochromic liquid crystal (TLC) are used to indicate film cooling efficiency. However, due to the mechanisms of PSP and TLC being different, their results are not consistent in some cases. Thus, analyzing the divergence between these two measurement methods is essential. In this paper, a comparison of measured film cooling efficiency distribution between PSP and TLC has been made on the same wind tunnel; the effect of heat conduction on film cooling was analyzed qualitatively and quantitatively. Sixteen cases were analyzed in which the mainstream Reynolds number was 35 000, 45 000, and 57 000; the blowing ratio was 0.5, 1.0, 1.5, and 2.0; and the density ratio was 0.91 and 1.44. We found that both PSP and TLC results exihibit an optimum blowing ratio under the condition of small and medium mainstream Reynolds numbers, but the measured film cooling efficiency is slightly different. Differences between PSP and TLC results were caused by the heat conduction of the substantial region. At the same time, a high mainstream Reynolds number and a high blowing ratio would boost heat conduction. Furthermore, in cases of high mainstream Reynolds number and low blowing ratio, the effect of heat conduction decreased obviously. When the blowing ratio is small as 0.5 and N2 acts as a coolant, PSP and TLC results match well, showing that in cases of low blowing ratio and low density ratio, the effect of heat conduction can be ignored.

Flavor and texture characteristics of microwave-cooked Kung Pao Chicken by different heat conduction effects and further aroma improvement with moderate enzymatic hydrolyzed chicken fat.

Ceramic dish cooking method (CDCM) and microwave absorption dish cooking method (MADCM) were used to obtain one-step microwave-cooked Kung Pao Chicken. Processing the optimization of recipes, steaming time and microwave time was conducted for microwave cooking methods. CDCM showed higher taste scores, better umami and sweet attributes, and better color and aroma than MADCM. The NMR and FITC fluorescence analysis results indicated that free water in chicken cooked by CDCM was lost more and tends to shift to immobilized water during the microwave heating as compared with MADCM. However, the aroma intensity by CDCM was weaker than the traditional cooking method (TCM). Electronic nose analysis also showed difference in the flavor profile from CDCM and TCM. According to the GC-MS analysis, aldehydes, the oxidation products of fats, were higher from TCM than from other cooking methods. Therefore, enzymatic hydrolyzed chicken fat at 5 g per 150 g chicken with a degree of enzymatic hydrolysis of 17.00% was used in CDCM to produce ideal fatty and meaty flavor. Both fatty and meaty flavor have increased by 52% and 60% respectively, with less off-flavor, thus, obtaining a similarity of 92% compared to TCM and with appropriate contents of volatiles such as hexanal, heptanal, (E)-2-octenal, (E)-2-decenal, (E)-2-nonenal and 2,4-decadienal.

The Effect of Heat Conduction for Driving Chain Stitching of Dual-Type Hybrid Organosilica-Derived Membranes

The Effect of Heat Conduction for Driving Chain Stitching of Dual-Type Hybrid Organosilica-Derived Membranes

Existence of Transonic Solutions in the Stellar Wind Problem with Viscosity and Heat Conduction

The one-fluid stellar wind problem for steady, radial outflow is considered, including effects of heat conduction and viscosity. The associated nondimensionalized equations of conservation of mass,...

Effect of nonlocality in the vibration of a microscale ribbon due to laser pulse

ABSTRACT The vibration analysis of elastic medium is very important along with the miniaturization of the device and wide application of ultra-fast lasers, where size effect on heat conduction and elastic deformation increase and classical theory of thermoelastic coupling does not hold any more. Due to these, size-dependent thermoelastic model have been introduced for higher order simple material to adopt both the size effect of heat conduction and elasticity with the aids of extended irreversible thermodynamics and generalized free energy. Keeping this in mind, the present analysis reports the effect of ultra-short-pulsed laser heating in coupled thermoelastic vibration of a microscale ribbon resonator. The heat transport law of the current problem is defined by incorporating the three-phase-lag heat transport law in the context of Caputo–Fabrizio (CF) derivative. Finite sinusoidal Fourier and Laplace transform techniques have been employed to determine the lateral vibration of the ribbon and the temperature increment within the microscale ribbon. The result provides the direction how the nonlocality and size-dependence can control the vibration analysis and some excellent predictive capability have been demonstrated due to the presence of energy absorption depth and the order of CF derivative also.

Effect of non-locality in the vibration of a micro-scale beam under two-temperature memory responses

ABSTRACT The vibration of elastic micro-beam is of major significance due to wide applications of ultra-fast lasers, where size effect on heat conduction and elastic deformation increase and classical theory of thermoelastic coupling does not hold any more. Accordingly, the size-dependent thermoelastic model has been developed to deal with higher-order simple material to adopt both size effect of heat conduction and elasticity with the aids of extended irreversible thermodynamics and generalized free-energy. This survey demonstrates the effect of ultra-short-pulsed laser heating in the problem of coupled thermoelastic vibration of a microscale resonator, in which, the non-local heat transport equation is drafted in an integral form of a common derivative on a slipping interval by incorporating the three-phase-lag memory-dependent heat transfer in the context of two-temperature theory. Laplace transform and finite sinusoidal Fourier transform techniques have been employed to determine the lateral vibration of the beam and the scaled thermal moment within the beam. According to the graphical representations corresponding to the numerical results, conclusions about the new theory is constructed. Specific attention is paid to study the effect of thermal non-local parameter, energy absorption depth, memory-dependent derivative, the two-temperature parameter and delay time also.

Effect of peripheral heat conduction in salt-gradient solar ponds

In this work, a detailed investigation on the effect of heat dissipation from side walls of a salt gradient solar pond on its various thermal aspects has been carried out. Both time-dependent and steady solutions have been reported. Finding the optimum thickness of side insulation is a challenge when it comes to setting up a solar pond system, as it requires a significant expenditure in the beginning. Here, the effects of side wall insulation on variable size of different zones and area of cross sections are studied using validated analytical and finite difference-based numerical approaches. Present study indicates that the heat extraction efficiency of a solar pond varies asymptotically with respect to the insulation thickness installed on the side walls, and the role of heat conduction within the middle layer is more than the radiative intensity reaching a given layer. It is highlighted that for a given insulation, there is always a unique value of non-convective zone where the pond's performance under a given operating condition becomes maximum. But, such optimal size does not exist for upper and lower convective zones, and beyond a certain value, further change in these zones is not useful. For a given insulation and other operating parameters, a circular cross section should always be selected for designing vertical-walled solar ponds. The impact of insulation is also found to depend on the radiative intensity and temperature profiles of a given location. The present work proposes cardinal guidelines regarding the suitability and the unsuitability of insulations along with appropriate selection of solar pond's design.

Effects of skin heat conduction on aircraft icing process

During the aircraft icing process caused by super-cooled droplet impingement, the surface temperature and heat flux distributions of the skin would vary due to the solid substrate heat conduction. An unsteady thermodynamic model of the phase transition was established with a time-implicit solution algorithm, in which the solid heat conduction and the water freezing were analyzed simultaneously. The icing process on a rectangular skin segment was numerically simulated, and the variations of skin temperature distribution, thicknesses of ice layer and water film were obtained. Results show that the presented model could predict the icing process more accurately, and is not sensitive to the selection of time step. The latent heat released by water freezing affects the skin temperature, which in turn changes the icing characteristics. The skin temperature distribution would be affected notably by the boundary condition of the inner skin surface, the lateral heat conduction and thermal property of the skin. It was found that the ice accretion rate of the case that the inner surface boundary is in natural convection at ambient temperature is much smaller than that with constant ambient temperature there; due to the skin lateral heat conduction, the outer skin surface temperature increases first and then decreases with uneven distribution, leading to an unsteady ice accretion rate and uneven ice thickness distribution; a smaller heat conductivity would lead to a more uneven temperature distribution and a lower ice accretion rate in most regions, but the maximum ice thickness could be larger than that of higher heat conductivity skin. Therefore, in order to predict the aircraft icing phenomenon more accurately, it is necessary to consider the solid heat conduction and the boundary conditions of the skin substrate, instead of applying a simple boundary condition of adiabatic or a fixed temperature for the outer skin surface.

Heat conduction in two-dimensional momentum-conserving and -nonconserving gases.

Compared to that for two-dimensional (2D) lattices, our understanding of heat conduction in 2D gases is still limited. Here we study heat conduction behavior of 2D gas systems with momentum-conserving and -nonconserving interparticle interactions by using the nonequilibrium and equilibrium molecular dynamics methods. For the momentum-conserving system, we find that when the dimensionality of the system is changed from 2D to quasi-one-dimensional (quasi-1D), the heat conductivity κ diverges with the system size L as κ∼lnL (the theoretical prediction for 2D systems) for a short L and shows, in the thermodynamic limit, a tendency to κ∼L^{1/3} like that predicted in 1D fluids. This suggests that the dimensional-crossover effect of heat conduction exists in 2D systems with conserved momentum. In contrast, for the momentum-nonconserving system, as L increases, finite heat conductivity independent of L is observed. These findings are in agreement with the predictions given by hydrodynamic theory and thus further confirm the validity of the theory in 2D gases.

GASEOUS SLIP FLOW FORCED CONVECTION IN A MICROPIPE AND PARALLEL-PLATE MICROCHANNEL WITH A PIECEWISE UNIFORM WALL HEAT FLUX AND AXIAL HEAT CONDUCTION

A forced convective heat transfer problem inside a micropipe as well as inside a microchannel with parallel walls in the laminar gaseous slip flow regime, a with finite heating region and a prescribed wall heat flux, including the axial heat conduction effect, is analytically investigated. The temperature field and Nusselt number are derived under the assumption that the flow is hydrodynamically fully developed in the finite-length heating region. The solution is found by applying the functional analysis method, by decomposing the energy equation into a pair of first-order partial differential equations. The first-order slip boundary conditions are imposed at the gas–wall interface. The analytical solution is compared with available calculations. The results show that the thermal characteristics in the heating region are significantly affected by the axial heat conduction, rarefaction effects, and finite length of the heating region.

Contributory effect of diffusive heat conduction and Brownian motion on thermal conductivity enhancement of nanofluids

The effect of diffusive heat conduction and Brownian motion on the enhancement of thermal conductivity in nanofluids is presented here. $${\hbox {Al}}_{2} {\hbox {O}}_{3}$$ and $${\hbox {TiO}}_{2}$$ nanofluids were prepared at four different wt. fractions of 1%, 0.5%, 0.1% and 0.05% and their thermal conductivity values were measured over temperatures ranging from 25 to $$55^{\circ }\hbox {C}$$ for every $$10 ^{\circ }\hbox {C}$$ interval. The thermal conductivity of nanofluids increased with the increase in concentration and temperature. Diffusive thermal conduction and Brownian motion contribute to thermal conductivity enhancement. However, diffusive heat conduction has major contribution to thermal conductivity enhancement in nanofluids. The thermal boundary resistance was found to be increasing with wt. fraction and decreasing with temperature elevation. Finally, a correlation is presented using group method of data handling (GMDH) neural network to predict the thermal conductivity of nanofluids.

Improved Cauer thermal network considering thermal coupling effects of multi‐chip modules

The Cauer thermal network has made a realistic physical representation of thermal behaviour of a multi-chip module (MCM) theoretically possible. However, the traditional method assumes the heat conduction is critical, with an approximate one-dimensional heat conduction path for calculation and fixed heat spreading angle to make up for the compensation brought by the approximation. It will limit the accuracy and cause a significant error in estimating the junction temperature of MCM. In this study, the heat spreading angle in the area of two adjacent chips is studied by using a cross-section to change the problem to a two-dimensional heat transfer question. Based on the heat flow got from the results of calculation by using Fourier's law, an expression for heat spreading angle as a function of boundary conditions is given, which is capable of estimating the junction temperature by adjusting effective heat conduction area of an MCM whose thermal behaviour is seriously coupled among neighbour chips. The accuracy of the proposed method and expression is validated by both the finite-element method and experimental results and they both show a good agreement with the calculation.