Thermal Relaxation Time Research Articles

A comparative analysis of the time-dependent magnetized blood-based nanofluids flows over a stretching cylinder

This article explores the analysis of magnetized blood-based nanofluids flows over an extending cylinder. The nanofluid contains copper, copper oxide and iron oxide nanoparticles which are mixed with blood. The mathematical model has been built-up in partial differential equations (PDEs) form and then changed into ordinary different equations by mean of suitable similarity variables and then has been evaluated by homotopy analysis method (HAM). The convergence of the applied technique is presented in graphical form. During the solution process, the influences of physical parameters like magnetic parameter, unsteadiness parameter, curvature parameter and thermal relaxation time parameter on the flow profiles have been investigated and depicted in Figures and Tables. The correctness of the present model has also been presented in tabular form. The results show that the greater curvature factor reduces the radius of cylinder due to which thickness of layer becomes thin at the boundaries and therefore the velocity distribution declines, while the greater curvature parameter has the increasing impact on the temperature distribution for constant wall temperature (CWT) case and decreases the temperature distribution for prescribed surface temperature (PST) case.

Experimental study on the effect of impurity concentration on phonon and electronic transport properties of single-crystal silicon

Investigation of the impurity concentration dependence of phonon and electronic transports is essential for semiconductor devices requiring thermal management. However, the experimental study of phonon transport properties is limited compared to theoretical studies. Therefore, in this work, n-type single-crystal silicon with different impurity concentrations was prepared to measure group velocity and thermal conductivity using nanoindentation and spot periodic heating with infrared radiation thermometry, respectively. Phonon mean free path (MFP) was evaluated by analyzing the measured group velocity and thermal conductivity. Electron MFP was determined from thermal velocity and relaxation time based on mobility. The impurity concentration dependences of electron and phonon MFPs differed significantly. Electron MFP decreased from 53 to 4.6 nm when the impurity concentration was increased from 2.3 × 1014 to 7.0 × 1018 cm−3. In contrast, phonon MFP exhibited a constant value of approximately 36 nm for an impurity concentration ranging from 2.3 × 1014 to 1.6 × 1017 cm−3. However, upon a further increase in the impurity concentration to 7.0 × 1018 cm−3, the phonon MFP decreased to 30 nm. These findings are especially beneficial for the fabrication of high-performance nanostructured thermoelectric materials.

Significance of Cattaneo-Christov heat flux model and heat generation/absorption with chemical reaction in Walters’ B fluid via a porous medium in the presence of Newtonian heating

ABSTRACT This study investigates the Walters’ B fluid in two-dimensional boundary layer flow through a porous medium of an exponentially stretching sheet. In the face of Newtonian heating, the Cattaneo-Christov heat flux model which expresses the thermal relaxation time is examined together with heat generation/absorption for the heat equation. The resulting equations of the model are resolved into non-dimensional forms, which are further performed by the Homotopy Analysis Method. The key findings along with the result obtained demonstrated that the Cattaneo-Christov heat flux which depicts the thermal relaxation time makes low the temperature field, indicating that the neighbouring particles crave for more time for the heat to fall deeper, while heat generation/absorption, as well as Newtonian heating, permit the quick infiltration of thermal sequel to the quiescent fluid which in turn aids the dryness of the materials. Meanwhile, the variation in local Weissenberg number triggers viscoelasticity whose application is crucial for the processing of the polymer in industries and other related disciplines.

Cattaneo-Christov double diffusion based heat transport analysis for nanofluid flows induced by a moving plate

Hybrid nanofluids have gained much attention due to their better stability, enhanced thermal conductivity, and physical strength. This manuscript investigates nanofluid flow, induced due to an infinite plate, which is moving (at a constant velocity) toward/receding from normal stagnation point flow. The surface of the plate is suspended and immersed with water as a base fluid and nanoparticles, namely Copper and Alumina. The flow is governed by Reynolds number (Re), which is proportional to the constant velocity of the moving plate and is an exact reduction of the Navier–Stokes equations. Moreover, Hiemenz’s planar and Homann’s axisymmetric flows normal to the stagnation point are considered. Heat transport analysis is carried out by using Cattaneo–Christov theory with Ohmic heating and heat source/sink effects. The governing equations are solved by bvp4c in MATLAB. The behavior of skin friction, flow, and energy distribution is perceived by variation of pertinent parameters. The numerical and asymptotic solutions are computed for the wall shear stress parameter. It is seen that the numerical solution matches its asymptotic behaviors over an intermediate range of small and large valued Reynolds number. The asymptotic values (small-Re) of wall stress reduces for plate advancing toward the stagnation-point flow and receding from the stagnation-point flow for Hiemenz and Homann flow. The increment in magnetic parameter reduced the fluid flow by generating a resistive force against it; however, the energy of the system is enhanced because of it. The augmentation of nanofluid volume fraction initiates the random motion among the nanoparticles which raises the temperature field. Thermal relaxation time parameter causes the particles to require supplementary time for the conduction of heat toward the adjacent particles, which declines the thermal transport. In general, the thermal transport is enhanced for the hybrid nanofluids rather than mono nanofluids.

Magnetic-field-dependent electric-charge transport in hadronic medium at finite temperature

Electric charge transport of hadronic matter at finite temperature and magnetic field is studied within the linear sigma model. Anisotropic transport coefficients associated with the charge transport are estimated both in the weak and strong regimes of the magnetic field using the transport theory approach. In a weakly magnetized medium, the magnetic field effects are incorporated through the Lorentz force term in the Boltzmann equation. Strong magnetic field puts further constraints on the motion of charged particles through Landau quantization. Magnetic field-dependent thermal relaxation time is obtained from interaction rates of hadrons with the S-matrix approach by considering the Landau level kinematics of the charged hadrons. Mean-field effects are embedded in the analysis through the temperature-dependent hadron masses. Further, the hadronic medium response to a time-varying external electric field is studied in weak and strong magnetic field regimes. It is seen that electromagnetic responses of the hadronic matter have a strong dependence on the mean-field effects, sigma mass, the strength of the external fields, and its evolution in the medium.

Theoretical study on bio-convection of micropolar fluid with an exploration of Cattaneo–Christov heat flux theory

This research explores the heat transfer rate for micropolar fluid in a channel flow. In spite of formal Fourier’s law, the Cattaneo–Christov heat flux design is implemented in energy system. Using appropriate dimensionless parameters, the guiding coupled partial differential equations that represent the fluid flow are modified into ordinary differential equations. By executing Runge–Kutta integration procedure and the shooting method, the numerical results are achieved. The impacts of thermal relaxation time and bio-convection flow of micropolar fluid are examined in this assessment. Graphical analyses are used to assess the effects of physical factors for the momentum, micro-rotation, concentration, density of micro-organisms and temperature gradient. The skin friction values, motile density number, heat and mass transfer rate are the fascinating physical quantities whose numerical data are computed and validated against different parametric values. The variational iteration method (VIM) and Adomian decomposition method are the analytical modules which have been incorporated here for solving the nonlinear systems for showing better approximity. It is found from the study that larger the thermal relaxation time values, the more likely they are to increase heat transfer, hence lowering the fluid temperature. Moreover, both Fourier and Cattaneo–Christov heat conduction module exhibit qualitatively similar influence on embedded parameters also the temperature profile diminishes for larger values of [Formula: see text]. The culminations evidently disclose that the bio-convection Peclet number and the motile microbes parameter enhance the density of motile micro-organisms. From a computational perspective, the VIM is more effective, practical and ease of use. The numerical and analytical results are compared well with the existing articles. The optimum parameter level for maximum heat transfer is considered to be [Formula: see text]. Taguchi approach was successfully used to determine the optimum design parameters for maximum heat transfer is 1.724012 for the parameters A-5:B-5:C-0.5:D-0.5:E-0.7.

Pulsating magnetohydrodynamic flow of Fe[formula omitted]O[formula omitted]-blood based micropolar nanofluid between two vertical porous walls with Cattaneo–Christov heat flux and entropy generation

The present article is aimed to investigate the impact of entropy generation on pulsating hydromagnetic flow of a micropolar nanofluid between two vertical porous walls using the Cattaneo–Christov heat flux model. Here Fe3O4(magnetite) is taken as a nanoparticle and blood as micropolar fluid (base fluid). The significance of viscous dissipation, Ohmic heating, and thermal radiation are considered. This model is noteworthy in the field of magnetic bioseparation, pressure surges, magnetofection agent, biomedical engineering, cancer therapeutic, artificial kidney, brain tumors, and nano-drug delivery in the arteries. The governing partial differential equations are transformed into the system of ordinary differential equations by deploying the perturbation process and then solved numerically by employing the fourth-order Runge–Kutta scheme with the support of the shooting technique. The flow variables like velocity, microrotation, temperature, entropy generation, and Bejan number are depicted graphically and discussed in detail. The heat transfer rate is displayed through a table. The results depict that the velocity is diminishing with the enhancement of coupling parameter, Hartmann number, and nanoparticle volume fraction. The temperature of micropolar nanofluid is increasing with an increment of viscous dissipation, thermal radiation, and heat source while it is reducing with the enhancement of magnetic field, thermal relaxation time, and heat sink parameter. The entropy generation is diminished by increasing the values of Hartmann number, thermal relaxation, and coupling parameter. Further, the Bejan number is enhanced by varying thermal radiation and nanoparticle volume fraction.

Insights into 3D flow of Casson fluid on exponential stretchable surface in rotating frame through porous medium

The magnetohydrodynamics boundary layer flow of a Casson fluid in rotating frame through porous medium caused by exponentially stretching surface is studied numerically in this piece of research. To investigate the transport properties of thermal and solutal energy, the phenomenon of relaxation time for thermal waves with chemical reaction effects is incorporated. Additionally, the bio-convection and process of stratification is also supposed in energy transport mechanism. The numerical outcomes of the problem presented graphically are obtained against the variation in physical constraints. The resistance to fluid motion improves as the Casson parameter is increased in its magnitude, therefore, the flow field is reduced. The higher values of thermal relaxation time slow down the heat waves propagation.

NUMERICAL SIMULATION OF THE INTERACTION OF HETEROGENEOUS DETONATION WITH THE POROUS INSERT OF DIFFERENT GEOMETRY

Numerical simulation of interaction of heterogeneous detonation with a porous insert was carried out. The mathematical model for porous inserts assumed that the porous zone was a continuous medium in the form of a grid of stationary cylinders. Main regimes and critical conditions of detonation attenuation in porous zones were obtained for micron-sized aluminum particles. Main features of the flow field in the channel were described. It was found that for micron particles in the empty space, a planar detonation wave formed. Main patterns for micron-sized combustible particles and inert porous zone were found. The critical height of the empty space without porous inserts was determined. The critical height of the empty space did not depend on the amount of open areas in the porous zone. The critical height did not depend on the width of the channel. For micron-sized particles, a physical explanation for the existence of planar detonation based on the values of thermal relaxation times is proposed.

Statistical Amplification of the Effects of Weak Magnetic Fields in Cellular Translation.

We assume that the enzymatic processes of recognition of amino acids and their addition to the synthesized molecule in cellular translation include the formation of intermediate pairs of radicals with spin-correlated electrons. The mathematical model presented describes the changes in the probability of incorrectly synthesized molecules in response to a change in the external weak magnetic field. A relatively high chance of errors has been shown to arise from the statistical enhancement of the low probability of local incorporation errors. This statistical mechanism does not require a long thermal relaxation time of electron spins of about 1 μs-a conjecture often used to match theoretical models of magnetoreception with experiments. The statistical mechanism allows for experimental verification by testing the usual Radical Pair Mechanism properties. In addition, this mechanism localizes the site where magnetic effects originate, the ribosome, which makes it possible to verify it by biochemical methods. This mechanism predicts a random nature of the nonspecific effects caused by weak and hypomagnetic fields and agrees with the diversity of biological responses to a weak magnetic field.

Heat flow and thermal regime in the Guaymas Basin, Gulf of California: Estimates of conductive and advective heat transport

AbstractHeat flow is estimated at eight sites drilled int the Guaymas Basin, Gulf of California, during the International Ocean Discovery Program Expedition 385. The expedition sought to understand the thermal regime of the basin and heat transfer between off‐axis sills intruding the organic‐rich sediments of the Guaymas Basin, and the basin floor. The distinct sedimentation rates, active tectonics, and magmatism make the basin interesting for scientific discoveries. Results show that sedimentation corrected heat flow values range 119–221 mW/m2 in the basin and 257–1003 mW/m2 at the site of a young sill intrusion, denominated Ringvent. Thermal analysis shows that heat in the Guaymas Basin is being dissipated by conduction for plate ages >0.2 Ma, whereas younger plate ages are in a state of transient cooling by both conduction and advection. Drilling sites show that Ringvent is an active sill being cooled down slowly by circulating fluids with discharge velocities of 10–200 mm/yr. Possible recharge sites are located ca. 1 km away from the sill's border. Modelling of the heat output at Ringvent indicates a sill thickness of ca. 240 m. A simple order‐of‐magnitude model predicts that relatively small amounts of magma are needed to account for the elevated heat flow in non‐volcanic, sediment‐filled rifts like the central and northern Gulf of California in which heating of the upper crust is achieved via advection by sill emplacement and hydrothermal circulation. Multiple timescales of cooling control the crustal, chemical and biological evolution of the Guaymas Basin. Here, we recognize at least four timescales: the time interval between intrusions (ca. 103 yr), the thermal relaxation time of sills (ca. 104 yr), the characteristic cooling time of the sediments (ca. 105 yr), and the cooling of the entire crust at geologic timescales.

Nonlinear Rayleigh wave propagation in a layered half-space in dual-phase-lag

We investigate nonlinear Rayleigh wave propagation in a layered thermoelastic medium composed of a slab rigidly bonded to the surface of a half-space under prescribed external thermal boundary conditions within the dual-phase-lag theory. The heat conduction coefficient for both the slab and the matrix have a linear dependence on temperature. Our aim is to assess the effect of temperature dependence of the heat conductivity, as well as the thermal relaxation times, on the process of wave propagation in the layered medium. Poincaré expansion of the solution in a small parameter and the generation of higher harmonics allow to evaluate the coefficient of this nonlinear coupling in the slab through heat wave propagation measurement. For the used numerical values, the results show that some characteristics of the problem, e.g. the temperature, heat flux and one stress component suffer jumps at the interface, while the other stress components are continuous there. The jump in the heat flux is noticeable only in the first order of nonlinearity. The existence of jumps at the interface may be of interest for measurements. Comparison with the case of the half-space showed that the presence of the slab contributes to faster damping of the solution with depth in the half-space.

Energy‐based devices for melasma and postinflammatory hyperpigmentation

AbstractIntroductionMelasma and postinflammatory hyperpigmentation (PIH) are conditions commonly encountered by dermatologists, and they are often distressing to patients. While PIH can improve with time once the inflammatory process is controlled, melasma is a condition that often requires prolonged treatment and maintenance. There are numerous treatment options, ranging from UV protection and topical therapies (such as hydroquinone), to more procedural‐based options (chemical peels, micro‐needling, and energy‐based devices).ObjectiveThis review will focus on the treatment of melasma and PIH with various energy‐based therapies, including laser devices, intense pulsed light (IPL), high‐frequency ultrasound, and radiofrequency devices.MethodsReferences were collected by using Pubmed with search terms of “laser”, “melasma”, “post‐inflammatory hyperpigmentation”, and “energy‐based devices.”FindingsLasers and IPL target pigment in the epidermis and dermis by using the appropriate wavelengths and principles such as thermal relaxation time and photoacoustic damage. Other lasers, such as pulsed‐dye laser (PDL), target the vascular component of melasma. Used alone or in combination with topical treatments, these devices provide improvement in melasma and PIH. In addition, some authors have studied the use of these devices, such as fractionated lasers, in device‐assisted drug delivery of topical therapies.ConclusionWhile there is a benefit to the use of these devices, this change is usually temporary and balanced against the side effects of dyspigmentation and scarring. Therefore, these treatments are best used in combination, with a maintenance program that employs both topical therapies, procedures, and energy‐based devices.

Pressure Dependent Elastic and Thermo-Physical Properties of U Ternaries with ZrNiAl Structure Compounds

bstract: The Thermophysical and ultrasonic aspects of U- ternaries are examined theoretically under high pressure. In order to determine the second- and third-order elastic constants of U- ternaries (URhAl and ThRhAl) compounds under pressure conditions (0-45GPa), the potential model technique has been used. The assessed second-order elastic constants are used along with the pressure-dependent ultrasonic velocities, thermal relaxation time, and other significant and important thermophysical data to determine the orientation. It is observed that thermal relaxation time and mechanical & thermal properties exhibit an increasing trend with increasing pressure for U-ternaries URhAl and ThRhAl compounds. The effect of increasing pressure on the URhAl and ThRhAl compounds shows up as an increase in elastic constants, ultrasonic velocities, ultrasonic attenuation, and Debye temperature. The ratio B/G increases with pressure which indicates that the materials are ductile in nature. We have used the approximate values of SOECs, density, and lattice properties in calculating the melting point, ultrasonic velocity, and thermal conductivity.

Thiacalixarene Appended Azo-based Supramolecular Systems: Self-assembly and Photo Tuning Reversible Liquid Crystalline Properties.

Four new azo-based supramolecular materials containing thiacalixarene core substituted by variable alkoxy groups (TFA1 -TFA4 ) have been designed and synthesized for the mesomorphic and photoswitching properties. The liquid crystalline behavior were accomplished by using DSC, POM, and XRD studies. All azo-based thiacalixarene based materials with short and higher chain length display columnar hexagonal mesophase with broad temperature range. The thermal behavior of all the materials was investigated by DSC and TGA study. The structural and conformational study of the lower rim functionalized materials was confirmed by using different techniques. These thiacalixarene moulded liquid crystalline compounds shows columnar self-assembly type behavior and higher thermal stability. The introduction of bi-substituted azo-ester network towards the lower rim of thiacalixarene core has impact on the electron delocalization and liquid crystalline properties. The photoswitching properties suggested cis and trans azo-isomerization under radiation of UV light and higher thermal back relaxation time. The mesogenic behaviour of compound TFA2 and TFA4 were demolished by the influence of cis and trans isomerization. The structure-property correlation is studied to understand the variation in mesogenic properties with the substitution of variable alkoxy side chain.

Thermal oscillation in the hybrid Si3N4 - TiO2 microring.

The hybrid microcavity composed of different materials shows unique thermal-optical properties such as resonance frequency shift and small thermal noise fluctuations with the temperature variation. Here, we have fabricated the hybrid Si3N4 - TiO2 microring, which decreases the effective thermo-optical coefficients (TOC) from 23.2pm/K to 11.05pm/K due to the opposite TOC of these two materials. In this hybrid microring, we experimentally study the thermal dynamic with different input powers and scanning speeds. The distorted transmission and thermal oscillation are observed, which results from the non-uniform scanning speed and the different thermal relaxation times of the Si3N4 and the TiO2. We calibrate the distorted transmission spectrum for the resonance measurement at the reverse scanning direction and explain the thermal oscillation with a thermal-optical coupled model. Finally, we analyse the thermal oscillation condition and give the diagram about the oscillation region, which has significant guidance for the occurrence and avoidance of the thermal oscillation in practical applications.

Dynamics of heat transport in flow of non‐linear Oldroyd‐B fluid subject to non‐Fourier's theory

AbstractTo study non‐Fourier heat and mass transport in the stagnation point flow of magnetized Oldroyd‐B fluid due to stretching cylinder, the Cattaneo–Christov heat flux model is used in this investigation. Further, as the controlling agents for thermal and solutal transport in the fluid flow, the heat generation/absorption source and chemical reaction are also considered. The formulations of a such physical phenomenon are going to form the PDEs. Through appropriate similarity variables, these governing partial differential equations for flow and energy transport are converted into the ordinary differential. The analytical series solutions are obtained through the use of a homotopic approach. The graphical upshots are conducted for velocity fields, temperature, and concentration distributions. In addition, energy transport analysis is performed for two kinds of surface heating mechanisms, namely the prescribed surface temperature (PST) and constant wall temperature (CWT). The outcomes of the current investigation revealed that a higher rate of heat transfer is observed in the case of CWT as compared to PST. Moreover, the increasing values of thermal and solutal relaxation time parameters reduce the heat and mass transport in the fluid flow, respectively.

Novel Non-Fourier Ice Heat Conduction Model Considering Latent Heat Via Specific Heat Capacity Functionalization and Its Potential Application

Abstract Proton exchange membrane fuel cells are widely used in the automotive and aviation fields due to their high efficiency and environmental friendliness. However, the long starting time of fuel cell vehicles at low temperatures restricts large-scale commercialization. In this work, for the problem of rapid ice melting during a cold start, it is found that when Fourier’s law is adopted, the error is as much as three times higher compared with the non-Fourier heat conduction law, and for ice, the influence of latent heat cannot be ignored, so a novel non-Fourier ice heat conduction model considering latent heat via specific heat capacity functionalization is established. The results demonstrate that the temperature curve first remains unchanged with time and then changes suddenly after the arrival of the heat wave. When the temperature rises to the phase change range, the temperature hardly changes before the completion of the phase change, and then finally rises slowly. Changing the thermal relaxation time may significantly affect the temperature response. The research conclusions of this paper have scientific guiding significance for the materials and structures working in extreme thermal environments such as low temperatures and ultra-high temperature change rates, as well as the design of fuel cell vehicles.

Jeffreys heat conduction in coupled semispaces subjected to interfacial heating

A Jeffreys heat conduction problem for coupled semispaces subjected to the action of an interfacial heat source was defined. An analytical solution of the problem was derived for a polynomial specific power of the heat source using the Laplace transform approach. The asymptotic and parametric analysis was performed for different ratios of thermal conductivities K1,2, thermal diffusivities k1,2, thermal relaxation times τ1,2 and coefficients α1,2 indicating the relative contribution of Fourier heat conduction. It was found that Jeffreys heat conduction results in continuous variation of the contact temperature, whilst its particular case — Cattaneo heat conduction — is accompanied by a step change of the contact temperature at the initial time. Another finding is that the initial heat partition occurs due to the ratio of K1α1/k1 and K2α2/k2 under Jeffreys heat conduction and due to the different ratio of K1/k1τ1 and K2/k2τ2 under Cattaneo heat conduction. The solution applicability was demonstrated on the simulation example of ultrashort laser pulse welding. The type of heat conduction was revealed to have qualitative and quantitative impacts on the contact temperature and heat fluxes.

Investigation of variable thermal relaxation time in non-Fourier heat transfer flow with nonlinear thermal stratification

Energy utilization is a significant aspect of the manufacturing industrial processes, and inefficient transferring of heat is one of the disadvantages which can affect the quality measures of end product. Therefore, by controlling the heat transferring rate, the efficiency of manufacturing processes can be improved. Thus, the variable thermal relaxation time factor in the theory of Cattaneo-Christov is main concern of this analysis. The non-isothermal flow by means of a porous medium is modeled and analyzed for a viscous fluid. The fluid deformation is discussed under stretching mechanism. A study is also executed to interrogate the heat transfer features under the heat flux model of Cattaneo-Christov. Thermal relaxation time is also considered which is determined by temperature. The aspect of thermal stratification is also implemented to see the modifications in temperature. The flow and energy equations are reduced by appropriate variables. The reduced constitutive flow equations are then computed using an analytical convergent technique. The significant impacts of the numerous parameters on the flow field and heat transport features are evaluated in detail through various plots. Skin friction coefficient is evaluated mathematically. Results found that the temperature significantly decreases with increased stratification effects. For larger thermal relaxation time parameter, the temperature function shows increasing behavior.