Dissipative Effects Research Articles

Hydration and microstructure evolution of cement paste in low vacuum environments

Low vacuum is one of the most challenging service environments for cementitious materials, which would affect their hydration and microstructure, and thereby impair strength and durability. In this study, the hydration phases and microstructural evolution of pastes based on Portland cement (PC), sulphoaluminate cement (SAC), and tricalcium silicate (C3S, the clinker of PC) were investigated under low vacuum conditions. The results show that rapid mass loss could be observed at the initial stage of low vacuum treatment, which was mainly attributed to the dissipation of free water. After that, the mass loss rate was greatly slowed down and maintained at a relatively low level, which was primarily due to the loss of chemical bound water in hydration products. As a result, C3S samples, with the slowest early hydration procedure, exhibited the highest mass loss, which was followed by PC and SAC samples. The dissipation effect by low vacuum treatment resulted in the inhabitation of cement hydration, and correspondingly the contents of hydration products remained almost constant, or even decreased especially for ettringite (AFt). Moreover, the examination of the hydration product morphology demonstrates that under low vacuum conditions, the needle-like morphology of the hydration product C-S-H transferred gradually from divergence to convergence or underwent collapse, while the AFt crystals experienced degradation and then transformed into an amorphous state. This consequently led to the sample after low vacuum treatment exhibiting increased total volume of pores less than 100 nm and elevated percentage of pores with sizes from 50 nm to 100 nm. Overall, this research holds great scientific significance in guiding the engineering application of concrete in low vacuum environments.

Experimental study of air curtains blocking saltwater intrusion under estuary dynamic conditions

The saltwater intrusion seriously threatens the water supply security of estuaries, while the existing salty blocking measures (e.g., gates and dams) are rude and the dynamic mechanism is not fully considered. In order to investigate countermeasures to reduce the risk of the saltwater intrusion, as well as enrichment blocking methods, in this paper, the salt-inhibiting properties of air curtain under tidal action was investigated based on a long-distance physical flume with dual tidal-salinity control capability. Experimental results indicate that air curtains significantly diminish distance of saltwater into estuaries. The bubble plumes, on the one hand, promote vertical mixing, elevating high-salinity water from the depths to the surface, thereby disrupting the vertical circulation structure of salt wedge. On the other hand, the energy dissipation and barrier effect produced by bubble bursting can significantly reduce the momentum of the invading saltwater. Meanwhile, the research emphasizes that the salt intrusion length is negatively correlated with the airflow discharge, whereas the salty-blocking effect prefer better of the weakly-mixed estuary than the strongly-mixed. Most importantly, the air curtain mixing coefficient ka were proposed at the first time to quantify the salty blocking effect. The mixing coefficient ka is the function of airflow discharge Qa and tidal current ut, demonstrating a direct proportionality to Qa and ut−1. Moreover, a quantitative relationship between ka and Qa/ut was obtained from experimental results. The research results would help inform the flexible salt-inhibiting measures of estuarine air curtain.

Viscous dissipation effects on time-dependent MHD Casson nanofluid over stretching surface: A hybrid nanofluid study

The study of MHD Couple stress Casson flow of a hybrid nanofluid is paramount due to its potential applications in advanced engineering systems, particularly in enhancing thermal management and efficiency in various industrial processes. In this report, the time-dependent MHD Couple stress Casson flow of a hybrid nanofluid, considering the impact of viscous dissipation over a stretching surface is presented. The main objective of this work is to enhance the transformation heat ratio to meet the requirements of the engineering and manufacturing industries. After conducting a continuity check, the issue is analyzed by applying the principles of momentum and energy conservation. This modeling process generates nonlinear partial differential equations (PDEs), which are subsequently converted into nonlinear ordinary differential equations (ODEs) using similarity transformation and thermophysical characteristics. To solve these ODEs, the Approximate Analytical Method HAM is employed, which is specifically designed for nonlinear problems. Velocity decreases with increasing values and higher nanoparticle volume fraction further slows the velocity. Increasing the couple-stress parameter reduces velocity; increasing the Casson parameter slows the velocity profile. Increasing magnetic parameter enhances temperature profile; profile escalates with Eckert number magnitude. These findings contribute significantly to understanding the structure, interactions, and dynamics of such liquids, aligning with the focus on exploring the fundamental properties of simple, molecular, ionic, and complex liquids.

Numerical solution of an unsteady nanofluid flow with magnetic, endothermic reaction, viscous dissipation, and solid volume fraction effects on the exponentially moving vertical plate

This study analyzes the unsteady nanofluid flow phenomenon adjacent to an accelerating vertical plate under the influence of magnetic fields, chemical reactions,viscous dissipation and solid volume fraction factors. The analysis motivates the understanding of the behavior of complex fluids to improve existing processes and develop new technologies. The finite difference technique, with the help of the boundary and initial conditions, was employed for the numerical result. The numerical solutions were graphically analyzed through MATLAB software. The results reveal intricate flow behaviors, including the influence of magnetic fields and solid volume fraction in reducing the velocity of the nanofluid. Interestingly, a magnetic field drops the temperature of the nanofluid, which can be observed in a particular case. The chemical reaction is found to absorb the heat, leading to a decline in the velocity and concentration due to temperature drop and solute destruction factors. The viscous dissipation raises the temperature of the nanofluid, but the heat sink affects the temperature oppositely. The Soret number essentially quantifies the phenomenon known as thermophoresis, where solutes concentrate more in cooler regions. This analysis provides valuable insights into the design and optimization of systems involving nanofluids subjected to external magnetic fields, with implications for various engineering applications such as thermal management systems and nanofluid-based heat exchangers.

Stratified numerical heat and mass transport mechanism in MHD Maxwell fluid flow with nonuniform heat source/sink

The present boundary layer flow of Maxwell fluid over a stretching sheet has good number of practical applications in metallurgy, drawing of plastics, polymer sheet extrusion including hot rolling extrusion, glass blowing, spinning of fibers, rubber and plastic sheets, crystal growing and many more. Due to these extensive applications of Maxwell fluid in engineering, medicine and manufacturing industries including the above-mentioned applications, authors have motived, inspired and investigated the present problem. However, in this research paper, the influences of Soret and Dufour effects on the steady-state Maxwell fluid flow past a stretching sheet with nonuniform heat source/sink are considered numerically. The thermal and concentration stratifications impacts are also incorporated. The viscous dissipation and magnetic field effects are also included in the respective governing equations. The main novelty and uniqueness of this numerical research is to generalize the earlier studies and describe the salient features of magneto-thermo visco-elastic dissipative Maxwell fluid motion about a stretching sheet with cross-diffusion effects under the influence of double stratification phenomena. To differentiate the non-Newtonian fluids from those of Newtonian fluids, a well-known Maxwell fluid flow model is used in the present study. The investigated physical problem results the highly nonlinear coupled partial differential equations (PDEs) and which are not amenable to any of the direct methods. Suitable similarity transformations are deployed to reduce the highly complex PDEs into the system of ordinary differential equations (ODEs). A robust BVP4C Matlab function is employed to solve the rendered dimensionless system of ODEs. The numerically generated computed data is plotted in terms of velocity, temperature and concentration profiles including engineering quantities of interest such as skin-friction, Nusselt and Sherwood numbers in the flow region. It is evident from the current analysis that, the amplified magnetic field decreases the velocity field and increases the thermal and concentration distribution fields. Accelerating Maxwell’s number diminished the flow velocity and increased the temperature field. Increasing Soret and Dufour numbers enhances the concentration and temperature fields, respectively. Amplifying Maxwell’s number raises the skin-friction coefficient and enlarging the thermal stratification parameter magnifies the thermal transport rate. The mass transport rate amplified with a raise in concentration stratification number in the flow region. Finally, it is provided that, the current results are excellently matching with earlier published results in the literature and it confirms the accuracy of the used numerical method and the produced similarity solutions.

Dynamics for wave equations connected in parallel with nonlinear localized damping

Abstract This study investigates the properties of solutions about one-dimensional wave equations connected in parallel under the effect of two nonlinear localized frictional damping mechanisms. First, under various growth conditions about the nonlinear dissipative effect, we try to establish the decay rate estimates by imposing minimal amount of support on the damping and provide some examples of exponential decay and polynomial decay. To achieve this, a proper observability inequality has been proposed and constructed based on some refined microlocal analysis. Then, the existence of a global attractor is proved when the damping terms are linearly bounded at infinity, a special weighting function has been used in this part, which eliminates undesirable terms of the higher order while contributing lower-order terms. Finally, we establish that the long-time behavior of solutions of the nonlinear system is completely determined by the dynamics of large finite number of functionals.

A novel composite bionic leaf vein and honeycomb microchannel heat sink applied for thermal management of electronic components

Based on the bionic concept and fractal theory, a composite bionic microchannel radiator based on veins and honeycombs is designed in this work to address the problem of heat dissipation in electronic components. The convective heat transfer within the novel microchannel structure is numerically investigated, and the effects of the coolant (Fe3O4-water nanofluids) and the surface bump structure on the overall performance of the microchannel are explored. Compared to the traditional ordinary leaf vein-shaped fractal microchannels, the proposed microchannel heat sink in this work demonstrated a significant heat dissipation effect, with an optimal increase in the Nusselt number of 64.5%. The best microchannel heat dissipation was achieved using Fe3O4-water nanofluids with a mass fraction of 0.5%. Additionally, changing the height and arrangement of the bump structure allows for improving heat transfer by a maximum of 8% compared to microchannels without the bump structure. Furthermore, the novel bionic microchannel heat sinks are evaluated, and the resulting optimized microchannel structure has a comprehensive performance index of 1.11. Overall, the study results provide useful information and serve as a reference for designing new bionic heat sinks for the thermal management of electronic components.

Comparative analysis of viscous dissipation effects on Prandtl fluid including contraction and relaxation phenomena

AbstractThis paper investigates the effects of magnetohydrodynamics and heat transfer on the peristaltic transport of Prandtl fluid in a vertical endoscopic tube. The reduction of the complexity of the equations governing the flow of Prandtl fluid entails the use of long wavelength and low Reynolds number approximations. These complex equations for the pressure gradient and velocity profile are handled analytically using the perturbation technique with convective boundary conditions, and the temperature and concentration profiles are carefully solved for the exact solution. The frictional forces and pressure rise are also simulated with numerical integration. The resulting formulas for velocity, temperature, concentration, pressure rise, and pressure gradient are graphed using the MATLAB and MATHMATICA software, and the effects of all the different physical parameters are investigated and assessed. The streamlines with five distinct wave types are sketched at the conclusion to show the phenomenon of trapping. It is investigated that the velocity profile rises due to buoyancy forces and falls due to the influence of magnetic forces.

Experimental and numerical analysis of heat sink using various patterns of cylindrical pin-fins

The increasing heat generated by electronic devices requires effective dissipation methods. This research proposes a unique pin-fin (PF) design inspired by cylindrical pin-fins, including three patterns: cross-pin-fins (CPFs), parallel-pin-fins (PPFs) and double-cross-pin-fins (DCPFs). The study examines the hydrothermal performance of these designs within Reynolds numbers of 4500 to 18,000 and heat fluxes of 445 W/m² to 2281 W/m². The PF design aims to maximise performance by increasing surface area and airflow turbulence. Experimental data confirmed the computational results for the PF and CPF heat sinks, exhibiting significant agreement. A numerical study evaluated the hydrothermal performance, revealing that DCPFs deliver a superior performance. As the diameter expands, the Nusselt number (Nu) rises significantly across each design, with increases of 100 %, 162 % and 328 % for the PPFs, CPFs and DCPFs, respectively. Each configuration achieved a Heat Transfer Performance Factor (HTPF) exceeding 1, indicating improved heat transfer efficiency over the friction factor. The heat sink comprising the DCPFs achieved a high HTPF of approximately 2, irrespective of the Reynolds numbers and heat fluxes, demonstrating its effectiveness in heat dissipation compared to other designs.

The Effect of Viscous Dissipation and Joule Heating on Poiseuille Flow of Hyperbolic Tangent Fluid

In this paper, we showed the computer solutions for the Flow of Poiseuille of (MHD) hyperbolic tangent impossible-to-compress fluid Amid a pair of parallel slabs that are sloped at an angle utilizing a uniformly porous medium. Heat transfer attempts and slip boundary conditions are taken into account. In the energy equation, radiation, joule heating, and viscous dissipation are also accounted for. It is presented in a cartesian coordinate system that supplies the model of the governing equations of the hyperbolic tangent fluid flow. The equations of velocity and Temperature are solved numerically by using "ND solver built". The effects of different factors such that Hartmann number, Darcy number, slip parameter, Grashof number, Brinkman number, radiation parameter and others on velocity and temperature profiles are explored and presented in the Mathematica program. It is noticed that the profiles of velocity and Temperature are an increasing function of Darcy number, slip parameter, Grashof number, inclination angle, pressure gradient, Brinkman number, radiation parameter, and index-power parameter while they are a decreasing function of Hartmann and Weissenberg numbers. The research intends to improve our understanding of the thermal behavior of hyperbolic tangent fluids in practical applications by studying the combined effects of viscous dissipation and Joule heating on the Poiseuille flow. The potential ramifications of this phenomenon extend to multiple domains, encompassing engineering, materials science, and fluid dynamics.

Transition from decaying to decayless kink oscillations of solar coronal loops

ABSTRACT The transition of an impulsively excited kink oscillation of a solar coronal loop to an oscillation with a stationary amplitude, i.e. the damping pattern, is determined using the low-dimensional self-oscillation model. In the model, the decayless kink oscillations are sustained by the interaction of the oscillating loop with an external quasi-steady flow. The analytical solution is based on the assumption that the combined effect of the effective dissipation, for example, by resonant absorption, and interaction with an external flow, is weak. The effect is characterized by a dimensionless coupling parameter. The damping pattern is found to depend upon the initial amplitude and the coupling parameter. The approximate expression shows a good agreement with a numerical solution of the self-oscillation equation. The plausibility of the established damping pattern is demonstrated by an observational example. Notably, the damping pattern is not exponential, and the characteristic decay time is different from the time determined by the traditionally used exponential damping fit. Implications of this finding for seismology of the solar coronal plasmas are discussed. In particular, it is suggested that a very rapid, in less than the oscillation period, decay of the oscillation to the stationary level, achieved for larger values of the coupling parameter, can explain the relative rareness of the kink oscillation events.

Sphaleron damping and effects on vector and axial charge transport in high-temperature QCD plasmas

We modify the anomalous hydrodynamic equations of motion to account for dissipative effects due to quantum chromodynamic (QCD) sphaleron transitions. By investigating the linearized hydrodynamic equations, we show that sphaleron transitions lead to nontrivial effects on vector and axial charge transport phenomena in the presence of a magnetic field. Due to the dissipative effects of sphaleron transitions, a wave number threshold kCMW emerges characterizing the onset of chiral magnetic waves. Sphaleron damping also significantly impacts the time evolution of both axial and vector charge perturbations in a QCD plasma in the presence of a magnetic field. Based on our analysis of the linearized hydrodynamic equations, we also investigate the dependence of the vector charge separation on the sphaleron transition rate, which may have implications for the experimental search for the chiral magnetic effect in heavy ion collisions. Published by the American Physical Society 2024

Peristaltic flow under the effects of tilted magnetic field: enhancing heat transfer using graphene nanoparticles

ABSTRACT This study investigates the consequences of inclined magnetic field and thermal radiation on peristaltic transportation of nanofluid through a porous media. The nanoliquid is composed of graphene nanoparticles and water. Viscous dissipation, mixed convection, thermal radiation, Joule heating and gravity effects are also considered. Mathematical modeling is carried out under small Reynolds number and large wavelength approximations. Resulting system of equations is numerically solved through built-in command NDSolve through Mathematica. The purpose of this research is to investigate the impact of volume fraction of nanoparticles, phase difference, inclination angle of the applied magnetic field, geometry parameters, Hartmann, Darcy and Brinkman numbers on axial velocity, temperature profile, heat transfer rates at the boundaries, pressure gradient, and pressure rise per wavelength. Outcomes of this study reveal that the addition of graphene nanoparticles enhances heat transfer performance. Velocity profile reduces and temperature increases for greater Hartmann number. Moreover, higher values of Hartmann number enhance heat transfer performance and peristaltic pumping. The enhancement of Darcy number increases velocity, temperature, and pressure while decreasing the peristaltic pumping. Variation in thermal radiation parameter reduces the temperature profile. The rate of pumping and pressure gradient decreases on increasing Froude number.

Numerical simulation and theoretical study on the impact of wind-sand flow of high-speed trains in long tunnel space

When high-speed trains (HST) run in enclosed spaces such as long tunnels, the thermal accumulation of their suspension devices is continuous and cannot be effectively dissipated. In addition, previous experiments or simulations for the heat dissipation of HST in tunnel spaces did not consider the impact of sand. To clarify the impact of HWS-LT on the heat accumulation of HST equipment cabin, this study used the CFD method to numerically simulate the impact of different wind-sand flow concentrations or no-sand wind on the cooling of equipment in the long tunnel space. Firstly, the sand particles in the wind-sand flow gather at the tunnel entrance and enter the equipment cabin with the train as it enters the tunnel. This boundary condition is more in line with actual engineering situations. Secondly, both flows show asymmetric intrusion into the cabin due to the asymmetrical tunnel arrangement, but the sand particles in the wind-sand flow are affected by the vortices and tunnel walls, resulting in more asymmetric flow and some particles being trapped in the grids or filters, leading to outflow ρQ < inflow ρQ. Under the wind-sand flow condition, the temperature of some equipment surfaces shows more significant increases than under the no-sand wind. Finally, contrary to popular perception, the wind-sand flow carrying sand particles can dissipate heat more effectively than no-sand wind, and the higher the volume fraction φ within a certain concentration range, the better the heat dissipation effect. This is because the wind-sand flow has a higher specific heat capacity, which can remove some heat from the contact point between the sand particles and the equipment wall upon contact. The higher sand particle concentration increases the contact frequency and contact area between the sand particles and the equipment wall, and the heat transfer pathway and heat dissipation efficiency are improved.

Optimized generation of entanglement based on the f-STIRAP technique

We consider generating maximally entangled states (Bell states) between two qubits coupled to a common bosonic mode, based on f-STIRAP. Utilizing the systematic approach developed by Wang et al (2017 New J. Phys. 19 093016), we quantify the effects of non-adiabatic leakage and system dissipation on the entanglement generation, and optimize the entanglement by balancing non-adiabatic leakage and system dissipation. We find the analytical expressions of the optimal coupling profile, the operation time, and the maximal entanglement. Our findings have broad applications in quantum state engineering, especially in solid-state devices where dissipative effects cannot be neglected.

Design comparison and effects of a chamber structure on wave dissipation

ABSTRACT Among all the ocean energy sources that have been widely studied, chamber structures such as oscillating water column (OWC) technologies are effective and low-cost methods to develop hundreds of wave power generation devices as the disadvantage is its lack of efficiency. Even if the OWC system does not perform any power generation operations, it is a wave-absorbing structure. A large part of the wave energy may be blocked by the structure’s acting chamber or could be dissipated during the interaction of the waves in the air chamber, which affects the actual power generation benefit evaluation. Nevertheless, a better wave attenuation structure may present a relatively poor design of the OWC generator chamber. A series of experiments were conducted with regular and irregular wave conditions to study the effects of energy dissipation caused by a chamber structure under varied barrier and orifice designs.

Numerical modeling of bamboo fences with various infill porosities deployed for mangrove restoration

As part of mangrove restoration initiatives eco-friendly fence has been implemented in eroded coastal areas in recent years. These fences provide the capacity to mitigate incoming wave energy and facilitate sediment deposition, thereby promoting the establishment and maintenance of mangrove habitats. Nevertheless, it is crucial to investigate the influence of the infill porosity on the wave dissipation performance of these fences, as the infill porosity can vary considerably across different restoration projects. The aim of this research is to explore the relationship between the infill porosity and wave dissipation effectiveness to identify more efficient designs for these eco-friendly restoration measures. The experiments involving wave interactions with fence models were conducted in a wave flume measuring 0.8 m in width and 25 m in length. Four wooden fences with distinct infill porosities ranging from 0.60 to 0.90 were strategically positioned to assess wave transmission, reflection, and dissipation phenomena under 18 distinct wave conditions. Additionally, the simulating waves till shore (SWASH)model was employed to calibrate critical bulk drag coefficient parameters and simulate the flow velocity distribution surrounding the fences under the experimental wave conditions. The findings indicated that a fence with a reduced infill porosity exhibits a higher wave transmission coefficient. However, this is accompanied by a higher reflection coefficient and lower wave energy dissipation within the fence. Both the infill porosity and incident wave conditions influence the flow velocity distribution characteristics in the vicinity of the fences. The area where the interaction between waves and fences is the most prominent is concentrated in the upper water layer immediately adjacent to the frontal section of the fences. Understanding the velocity distribution and hydrodynamic characteristics of the fence area aids in better determining the suitable porosity of fill materials for engineering applications.

Strain-induced fast domain wall motion in hybrid piezoelectric-magnetostrictive structures with Rashba and nonlinear dissipative effects

Strain-induced fast domain wall motion in hybrid piezoelectric-magnetostrictive structures with Rashba and nonlinear dissipative effects

Entangled multiplets, asymmetry, and quantum Mpemba effect in dissipative systems

Recently, the entanglement asymmetry emerged as an informative tool to understand dynamical symmetry restoration in out-of-equilibrium quantum many-body systems after a quantum quench. For integrable systems the asymmetry can be understood in the space-time scaling limit via the quasiparticle picture, as it was pointed out in Ares et al (2023 Nat. Commun. 14 2036) . However, a quasiparticle picture for quantum quenches from generic initial states was still lacking. Here we conjecture a full-fledged quasiparticle picture for the charged moments of the reduced density matrix, which are the main ingredients to construct the asymmetry. Our formula works for quenches producing entangled multiplets of an arbitrary number of excitations. We benchmark our results in the XX spin chain. First, by using an elementary approach based on the multidimensional stationary phase approximation we provide an ab initio rigorous derivation of the dynamics of the charged moments for the quench treated in Ares et al (2023 SciPost Phys. 15 089). Then, we show that the same results can be straightforwardly obtained within our quasiparticle picture. As a byproduct of our analysis, we obtain a general criterion ensuring a vanishing entanglement asymmetry at long times. Next, by using the Lindblad master equation, we study the effect of gain and loss dissipation on the entanglement asymmetry. Specifically, we investigate the fate of the so-called quantum Mpemba effect (QME) in the presence of dissipation. We show that dissipation can induce QME even if unitary dynamics does not show it, and we provide a quasiparticle-based interpretation of the condition for the QME.

Theoretical Analysis of Drilling Unloading and Pile-Side Soil Pressure Recovery of Nonsqueezing Pipe Piles Installed in K0-Consolidated Soils

Drilling with prestressed concrete (DPC) pipe pile is a nonsqueezing pile sinking technology, employing drilling, simultaneous pile sinking, a pipe pile protection wall, and pile side grouting. The unloading induced by drilling, the pipe pile supporting effect, and the dissipation of the negative excess pore-water pressure after pile sinking, all of which have significant effects on the recovery of soil pressure on the pile side, are the main concerns of this study, which aim to establish a method to reasonably evaluate the timing selection of pile side grouting. The theoretical solutions for characterizing the unloading and dissipation of the negative excess pore-water pressure are presented based on the cylindrical cavity contraction model and the separated variable method. By inverse-analyzing the measured initial pore pressure change data from borehole unloading, initial soil pressures on the pile side of each soil layer are determined using the presented theoretical solutions. Then, the presented theoretical solutions were verified through a comparative analysis with the corresponding measured results. Moreover, by introducing time-dependent coefficients αt1 and αt2 to characterize the pore pressure dissipation and rheology effects, the effects of the negative excess pore-water pressure dissipation on the pile-side soil pressure recovery are discussed in detail.